INDUCTION HEATING TECHNICAL CONTENT

How 3D-Printed Copper Inductors Improve Heat Treat Performance

/ INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH

Inductor design plays a critical role in heating efficiency, temperature uniformity, and process stability, but conventional manufacturing methods can limit what coil geometries are possible. In this Technical Tuesday installment, Max Wissing, technology manager at PROTIQ, explores how 3D-printed copper inductors expand design freedom, allowing heat treaters to more closely tailor electromagnetic fields, cooling, and overall coil performance to demanding applications.

This informative piece was first released in Heat Treat Today’s October 2026 Ferrous & Nonferrous Heat Treatments/Mill Processing print edition.

Why Inductor Design Matters More Than Ever

Induction heating remains one of the most established and widely used technologies in modern heat treating. It enables precise, contactless energy transfer and offers a high degree of repeatability, making it particularly suitable for demanding applications, such as surface hardening, partial hardening, and localized treatment of highly stressed components.

At the same time, requirements in industrial heat treatment continue to increase. Manufacturers are expected to improve energy efficiency, reduce cycle times, and maintain consistent process quality. These demands are further intensified by the growing complexity of component geometries, which require more precise control of electromagnetic fields and temperature distribution than ever before.

Within this context, the inductor itself becomes a decisive factor, as its design directly influences heating behavior, efficiency, and process stability. However, many conventional inductors are still constrained by the limitations of their manufacturing methods. These constraints often force compromises between manufacturability and functional performance, meaning that coil geometries are not always ideally adapted to the component or the specific heat treat application. In more complex cases, this can lead to reduced energy efficiency or non-uniform temperature distributions, ultimately affecting process consistency.

In response, recent developments have increasingly focused on application-driven coil design and improved engineering approaches. Industrial 3D printing introduces a fundamentally different paradigm by enabling inductors to be designed according to functional requirements rather than production constraints. This shift opens up new possibilities for optimizing electromagnetic field distribution, improving energy transfer, and enhancing overall process performance in induction heat treating.

Where Conventional Coil Design Reaches Its Limits

Traditional induction coils are typically manufactured by bending and assembling copper tubes or machined elements. These methods are well established and widely used, but they impose inherent restrictions that can limit further optimization.

Geometric flexibility, for example, is constrained by bending radii and available tube profiles. As a result, the coil design often represents a compromise between what is theoretically optimal and what can be manufactured. In more complex applications, this can lead to non-uniform heating or less efficient energy coupling.

In addition, conventional manufacturing involves a considerable degree of manual work, which can introduce variability. Small deviations in geometry may affect electromagnetic behavior and, consequently, process consistency. The presence of joints — created through soldering or welding — further introduces potential weak points that can impact durability under thermal and mechanical stress.

Taken together, these factors not only influence manufacturing efficiency but also define the performance limits of the entire induction heating process.

3D Printing as a Design Enabler

Industrial metal 3D printer | Image Credit: PROTIQ

Additive manufacturing, often referred to as industrial 3D printing, is a production technology that creates metal components directly from digital design data. In processes like laser powder bed fusion (LPBF, often called SLM), a high-power laser selectively melts thin layers of metal powder. By repeating this process layer by layer, complex metal parts can be produced without the need for molds, tooling, or many of the manufacturing steps associated with conventional production methods.

This manufacturing approach offers a fundamentally different level of design freedom. Traditional manufacturing processes often require designers to adapt component geometries to machining, forming, or joining constraints. With additive manufacturing, many of these restrictions can be reduced or eliminated, allowing engineers to focus more directly on the functional requirements of the heat treatment application.

For induction heating, this means that the geometry of the inductor can be tailored more closely to the desired electromagnetic field distribution and heating characteristics. As a result, component design, process requirements, and performance objectives can be aligned more effectively.

Another important advantage is the ability to manufacture inductors as monolithic components. Instead of assembling multiple individual parts, the inductor can be produced in a single piece. This eliminates joints that may act as potential mechanical weak points while also enabling the integration of internal features, such as cooling channels. These channels can follow complex three-dimensional paths that would be difficult or impossible to realize with conventional manufacturing methods, enabling more targeted and efficient thermal management.

Impact on Induction Heating Performance

The increased design freedom enabled by additive manufacturing translates directly into improved process performance. When the geometry of the inductor is closely matched to the component, the electromagnetic field can be shaped more precisely. This allows for a more uniform temperature distribution, which is essential for achieving consistent material properties in heat treated parts.

Inductor with spray cooling | Image Credit: PROTIQ

Optimized geometries also improve the coupling of energy into the workpiece. In practical terms, this means that the required heating energy can be delivered more efficiently, often resulting in shorter cycle times. At the same time, improved cooling concepts help stabilize the process by keeping the inductor within its operating limits, even under demanding conditions.

Because additive manufacturing allows components to be reproduced with high accuracy, it also supports consistent process results. Compared to manually fabricated coils, this reproducibility reduces variability and contributes to overall process stability. The absence of soldered or welded joints can further increase service life, as common failure mechanisms are eliminated by design.

Copper in Additive Manufacturing: From Challenge to Application

Copper is the preferred material for induction coils due to its high electrical conductivity. However, its processing in laser-based additive manufacturing systems has long been considered challenging. The high reflectivity of copper and its thermal conductivity make it difficult to achieve stable and efficient melting during the build process.

In recent years, these challenges have been addressed through advances in machine technology, laser systems, and material development. Today, it is possible to manufacture copper components with properties suitable for demanding industrial applications, including conductivity levels comparable to conventional materials.

Despite this progress, successful implementation still requires a detailed understanding of both material behavior and process conditions. The interaction between geometry, material properties, and manufacturing parameters must be carefully considered to ensure that the final component meets both functional and mechanical requirements.

Companies such as PROTIQ have developed extensive experience in processing pure copper by additive manufacturing. This knowledge helps ensure stable production processes and application-oriented solutions for demanding industrial components like inductors.

Bridging Design and Reality Through Simulation and Experience

Simulation tools are an important element in the development of modern inductors. They provide insights into electromagnetic field distribution and thermal behavior, allowing engineers to evaluate and optimize designs before manufacturing.

Inductor simulation optimization | Image Credit: PROTIQ

However, simulation alone cannot fully predict how a component will perform under real operating conditions. Factors, such as material characteristics, surface quality, and manufacturing tolerances, can influence actual results. For this reason, experience in both additive manufacturing and induction applications remains essential.

In practice, effective inductor development is based on a combination of simulation, engineering expertise, and manufacturing know-how. This integrated approach helps ensure that theoretical designs can be translated into reliable solutions for industrial use.

Typical Applications in Heat Treating

The advantages of additively manufactured inductors become particularly evident in applications where conventional designs reach their limits. This is often the case in the heat treatment of components with complex geometries or varying cross-sections, where uniform heating is difficult to achieve.

In surface hardening processes, for example, tailored coil geometries can improve the consistency of hardness profiles across critical areas. Similarly, localized hardening applications benefit from the ability to precisely confine the electromagnetic field to specific regions of the component.

Custom 3D-printed inductors | Image Credit: PROTIQ

Another important field of application involves components with limited accessibility or intricate features. Here, additive manufacturing allows the realization of coil designs that can be adapted closely to the part geometry, enabling effective heating in areas that are difficult to reach with conventional inductors.

These application scenarios illustrate how additive manufacturing expands the solution space in induction heating, particularly for tasks that require a high degree of customization.

From Technology to Industrial Practice

While additive manufacturing offers significant opportunities, its successful use in induction heating depends on several factors. Material selection, manufacturability, and process stability must all be considered from the outset. Not every theoretically optimal design can be produced reliably, and design decisions must account for the specifics of the additive process.

Equally important is a deep understanding of the application itself. The requirements of the heat treat process, the properties of the component, and the desired outcomes must all be reflected in the inductor design.

In practice, additive manufacturing is not always the only or best solution. Depending on the application, a combination of conventionally manufactured and additively produced features can provide the most effective balance between performance, manufacturability, and cost.

This is where manufacturing expertise becomes critical. Companies like PROTIQ support clients in evaluating which parts of an inductor benefit from additive manufacturing and which may be better suited to conventional production methods. By combining process knowledge, material expertise, and industrial manufacturing capabilities, innovative designs can be translated into reliable and economically viable components.

Application-Driven Inductor Design

Additive manufacturing represents a shift in how induction coils are conceived and realized. By removing many of the constraints associated with conventional manufacturing, it enables a more direct alignment between design and function.

For heat treat operations, this opens up new possibilities for improving efficiency, quality, and reliability. Instead of adapting processes to the limitations of available coil geometries, inductors can be tailored to the specific requirements of the application.

As the technology continues to mature, additively manufactured inductors are likely to become an increasingly important element in advanced heat treat processes. Their successful application, however, depends not only on access to manufacturing technology but also on a comprehensive understanding of materials, processes, and application context.

About The Author:

Max Wissing
Technology Manager
PROTIQ

Max Wissing is the technology manager for 3D printing at PROTIQ with nearly a decade of industry experience. He holds a degree in mechanical engineering, specializing in the optimization of 3D-printed induction coils.

For more information: Contact Max Wissing at mwissing@protiq.com.

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Reliable Induction for Heat Treating Automotive Components

/ AUTOMOTIVE HEAT TREAT TECHNICAL CONTENT, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT

Reliable induction heat treating depends on more than metallurgy — it requires precise, repeatable performance from every part of the induction system. In this Technical Tuesday installment, Aaron Goodwin, business development engineer for Inductoheat, explores how induction coils, power supplies, quench systems, and real-time process monitoring work together to consistently achieve the hardness, case depth, and microstructure demanded by today’s automotive components. Learn how equipment reliability, preventive maintenance, and process control help manufacturers reduce variability, improve quality, and keep production running efficiently.

This informative piece was first released in Heat Treat Today’s August 2026 Annual Automotive Heat Treating print edition.

If you have any comments or queries, on this article, let us know at editor@heattreattoday.com.

Para leer el artículo en español, haga clic aquí.

There is a critical partnership between an automotive component’s design and its heat treat requirement. In modern vehicle manufacturing — whether trucks, SUVs, or crossovers — the margin for error is very small. Components like axles, gears, shafts, and other engine/drivetrain elements are subjected to demanding loads, high torque, and complex operating conditions. These vehicles must balance durability, efficiency, quiet operation, and performance. They also need to successfully handle a wide range of driving scenarios, from stop-and-go urban traffic to towing, off-road use, and long-distance travel.

Across these vehicle platforms, one reality remains constant. While material selection and engineering design are critical, consistency and reliability of the heat treating process determine whether components perform as intended in real-world conditions. Induction heating for case hardening of automotive components is a common choice among design engineers, and reliable induction heating equipment is key.

From the induction coil to the power supply and the quench system, each must operate with precision and repeatability for every cycle. Induction case hardening depends on tightly controlled variables working in harmony. When performance is stable, quality heat treated components follow. When it is not, variability is introduced and with it risk.

Sectioned and etched case-hardened shaft with large splines | Image Credit: Inductoheat

Heat treated components are evaluated based on hardness, case depth, and microstructure of the steel after processing. Each component has a heat treat specification that defines these metrics. Some components require shallow case depths while others have very deep case. Shallow case is needed for surface wear resistance, while deep case is specified for strength under high torsional loads, and there are scenarios in between.

Induction heat treatment equipment reliably executes several tightly controlled variables to produce the required metallurgical properties. Key variables include power output and frequency, heating time, coil geometry and position, quench timing, and flow rates.

Each variable plays a critical role: even small deviations can significantly alter results. A slight fluctuation in power delivery, for example, may reduce case depth or create uneven hardness profiles. In truck components, this could result in reduced fatigue life under high loads. In a crossover or SUV, it may show up as premature wear or component failure. Reliable equipment ensures that these variables remain tightly controlled cycle after cycle, part after part. It transforms heat treating from a “variable process” into a repeatable, engineered system.

The Role of Induction Coil

The induction coil is where the energy meets the automotive component. Its design and condition directly influence heating and resulting hardness case patterns. A well-designed and properly maintained coil provides consistent electromagnetic coupling, uniform heat distribution along the surface, and sufficient penetration sub-surface for creating required case depths and hardness profiles.

When energized, the induction coil produces a magnetic field. From this, the automotive component begins to experience Joule heating from induced current, known as eddy currents. Heat times vary but are often only a few seconds in duration to reach the temperature required for the formation of austenite (range of 750–850°C [1382–1562°F], depending on chemical composition of steel).

Induction scan coil with integrated spray quench for case hardening | Image Credit: Inductoheat

Induction coils are perishable tooling components. Over time, thermal cycling, surface oxidation, and degradation, along with mechanical fatigue can reduce performance. Minor changes in coil geometry, alignment, or surface conditions can alter the electromagnetic field and introduce variability. What makes this especially challenging is that these changes are often gradual and not immediately visible. A coil may continue operating while quietly affecting heat distribution. Routine inspection, cleaning, and scheduled replacement are essential. In high-volume automotive manufacturing, proactive coil management is critical to maintaining process stability and reliably heat treated components.

Power Supply Stability

The induction power supply governs how energy is delivered to the coil and thus the component being heat treated. A stable output of power is critical for repeatable heating and consistent metallurgical results. Selection of the proper output frequency is important to balance the required depth of heating and the surface temperature of the component. For case hardening, the most common frequencies utilized fall in the range of 1,000 Hz up to 200 kHz. While a single power supply cannot cover this entire frequency range, most will provide some range of frequency flexibility.

Power supplies have precise and programable energy delivery at a stable frequency. They provide rapid response to variations in load as the temperature of the automotive component increases, passes through the curie point, and reaches the target temperature. This power supply gives reliable performance across long production runs. This is important when thousands of components must meet specifications in a narrow margin of variability. If a power supply introduces fluctuations, these will affect the heating rates and final hardened properties. For manufacturers, this leads to scrap parts and reduced profitability.

Power supply analog meter, % power–kilotwatts | Image Credit: Inductoheat

These work horses need scheduled maintenance. After all, reliable power delivery directly supports both quality and productivity. Personnel must:

  • Periodically check the power supply for tight electrical connections on bus work and wire terminals.
  • Check all cooling water hosing connections for tightness as the hoses age.
  • Verify that all protection switches are working.
  • Ensure that the cooling system’s water is clean and check its conductivity monthly.
  • Refer to the manufacturer’s manual for more information.

Quenching: Completing the Process

Heating is only half of the equation. The quenching process is initiated after the component has reached its austenitizing temperature at the desired depth. Quench fluid is sprayed uniformly onto the surface of the component, which removes heat in a rapid and controlled manner. This produces the formation of martensite giving the automotive component a case-hardened surface layer. All of this is done within proper limit set points to produce repeatable heat treated components.

Quench fluid is typically water with polymer additive. It needs to be maintained at the appropriate temperature and with the required percentage of polymer quench additive. The quench system delivers it with precise timing relative to heating. The pump and valves must provide consistent flow rates and pressures. The heat exchanger in the quench system will remove excess heat from the quench fluid. Otherwise, the temperature of the fluid will continue rising after each cycle.

Quench concentration monitor (left) and quench plumbing valves (right) | Image Credit: Inductoheat

Over time, quench water evaporates raising the concentration of polymer quench. It also becomes contaminated with oily residue, metal chips, and more. Quench system bag filters become full, and the many orifices of quench spray devices get clogged with scale and debris. The quench system needs to be maintained to ensure that cooling is controlled and repeatable. This completes the heat treating process with consistency and reliability.

Data-Driven Reliability

Induction equipment must function with precision to achieve the required heat treatment. When this equipment includes real-time monitoring and data collection during the process, further confidence is provided. Signature monitoring measures the many aspects of induction heat treatment for every cycle. This “signature” can record electrical parameters like inverter power, current, voltage, and frequency over the process time. It can also include quench fluid temperature, flow, and pressure, along with machine scan speed and spindle rotation speed. Each of these is given a percentage of permitted variation, graphed over time. Any deviation outside of these boundaries during the cycle, and the machine will initiate a process fault.

Inductoheat QAS process signature with high/low boundaries; graphing interverter KVA scan speed, quench flow-left spindle, quench slow-right spindle | Image Credit: Inductoheat

This can be an important part of a quality assurance system (QAS) and ensure confidence during each production shift. For automotive components with barcodes or other unique markings, traceability becomes possible, saving the process signature from the machine and assigning it to the heat treated component. This step can provide critical data to isolate a batch of parts should the need arise, avoiding the tendency to quarantine more pieces than necessary.

Reliable Equipment. Better Parts. Stronger Vehicles.

Across the full spectrum of vehicle manufacturing, from heavy-duty trucks to everyday SUVs and crossovers, performance is built layer by layer. As vehicle platforms continue to evolve, heat treating processes must keep pace with increasingly complex component designs and performance requirements. Reliable induction equipment is essential to meet these challenges. Each aspect must operate with precision and consistency. Routine maintenance, including the replacement of wear items such as induction coils, helps ensure process stability, consistent results, and dependable production.

For many manufacturers, maintaining reliability also means modernizing existing equipment. Aging induction systems can often be rebuilt with updated controls, power supplies, and critical components, extending service life while improving performance and uptime. They can also be re-tooled for new heat treat programs.

By investing in induction equipment, manufacturers can continue producing high-quality components that support the demands of today’s vehicles.

About The Author:

Aaron Goodwin
Business Development Engineer
Inductoheat

Aaron Goodwin has over 32 years of experience in the induction heating industry, having held a variety of technical positions with Inductoheat in Madison Heights, Michigan. In his current role as business development engineer, Aaron provides technical support to both sales and engineering, with responsibilities that include leading the finite element analysis (FEA) simulation team for coil and process design. Aaron also collaborates with global sister companies throughout the Inductotherm Group, supporting technology development, knowledge sharing, and customer-focused solutions worldwide.

For more information: Contact Aaron Goodwin at agoodwin@inductoheat.com.

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Tratamiento térmico por inducción confiable para componentes automotrices

/ AUTOMOTIVE HEAT TREAT TECHNICAL CONTENT, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT

Un tratamiento térmico por inducción fiable depende de algo más que la metalurgia: requiere un desempeño preciso y repetible de cada parte del sistema de inducción. En este artículo, Heat Treat Today Aaron Goodwin, ingeniero de desarrollo de negocios de Inductoheat, explora cómo las bobinas de inducción, las fuentes de alimentación, los sistemas de temple y el monitoreo del proceso en tiempo real trabajan en conjunto para lograr de manera consistente la dureza, la profundidad de capa y la microestructura que demandan los componentes automotrices actuales. Conozca cómo la confiabilidad del equipo, el mantenimiento preventivo y el control del proceso ayudan a los fabricantes a reducir la variabilidad, mejorar la calidad y mantener la producción funcionando eficientemente.

Este artículo informativo se publicó por primera vez en Heat Treat Today’s August 2026 Annual Automotive Heat Treating print edition.

Si tiene comentarios o preguntas sobre este artículo, háganoslo saber en: editor@heattreattoday.com.

To read this article in English, click here.

Existe una relación fundamental entre el diseño de un componente automotriz y los requisitos de su tratamiento térmico. En la fabricación moderna de vehículos ya sean camiones, SUVs o crossovers, el margen de error es extremadamente reducido. Componentes como ejes, engranes, flechas de transmisión y otros elementos del motor y del tren motriz, están sometidos a elevadas cargas, altos niveles de torque y condiciones de operación cada vez más exigentes. Estos vehículos deben ofrecer un equilibrio entre durabilidad, eficiencia, operación silenciosa y desempeño. Además, deben responder de manera confiable a una amplia variedad de escenarios de conducción, desde el tráfico urbano con constantes arranques y paradas, hasta el remolque de cargas, la conducción todoterreno y los recorridos de larga distancia.

Independientemente del tipo de vehículo, existe una constante. Si bien la selección del material y el diseño de ingeniería son fundamentales, la consistencia y confiabilidad del tratamiento térmico son las que determinan si un componente cumplirá con el desempeño esperado en condiciones reales de servicio. El calentamiento por inducción para el endurecimiento superficial de componentes automotrices es una de las tecnologías preferidas por los ingenieros de diseño, y contar con equipos fiables de calentamiento por inducción es fundamental.

Desde la bobina de inducción hasta la fuente de potencia y el sistema de temple, cada elemento debe operar con precisión y repetibilidad en cada ciclo de producción. El endurecimiento superficial por inducción depende de un conjunto de variables estrictamente controladas que deben trabajar de manera sincronizada. Cuando el proceso permanece estable, se obtienen componentes tratados térmicamente de calidad; cuando esto no ocurre, surge la variabilidad y, con ella el riesgo.

La Relación entre el Equipo de Inducción y la Metalurgia

Los componentes tratados térmicamente se evalúan principalmente por tres características: la dureza, la profundidad de capa endurecida y la microestructura del acero después del procesamiento. Cada componente cuenta con una especificación de tratamiento térmico que define estos parámetros. Algunos componentes requieren capas endurecidas poco profundas para maximizar la resistencia al desgaste superficial, mientras que otras demandan capas mucho más profundas para soportar elevadas cargas de torsión; también existen situaciones intermedias.

Eje cementado, seccionado y atacado químicamente, mostrando estrías de gran tamaño | Crédito de la imagen: Inductoheat

Los equipos de tratamiento térmico por inducción controlan de manera confiable diversos parámetros críticos para producir las propiedades metalúrgicas requeridas. Entre las más importantes se encuentran, la potencia suministrada y la frecuencia, el tiempo de calentamiento, la geometría y posición de bobina de inducción, sincronización, y el caudal del sistema de enfriamiento.

Cada una de estas variables desempeña un papel fundamental; incluso pequeñas desviaciones pueden modificar significativamente los resultados obtenidos. Por ejemplo, una ligera fluctuación en la potencia suministrada puede disminuir la profundidad de capa endurecida o generar perfiles de dureza no uniformes. En componentes para camiones, esto puede traducirse en una menor vida útil a fatiga bajo cargas elevadas. En vehículos tipo SUV o crossover, puede manifestarse como desgaste prematuro o incluso la falla del componente. Los equipos confiables garantizan que todas estas variables permanezcan estrictamente controladas ciclo tras ciclo y pieza tras pieza. De esta manera, el tratamiento térmico deja de ser un proceso susceptible a variaciones y se convierte en un proceso de manufactura repetible y controlado.

El Rol de la Bobina de Inducción

La bobina de inducción es el punto donde la energía interactúa directamente con el componente automotriz. Su diseño y estado de conservación influyen de manera directa en el calentamiento y, en consecuencia, en el patrón de endurecimiento obtenido. Una bobina correctamente diseñada y con un mantenimiento adecuado proporciona un acoplamiento electromagnético uniforme, una distribución uniforme del calor sobre la superficie y una penetración subsuperficial suficiente, permitiendo alcanzar la profundidad de capa endurecida y el perfil de dureza especificados.

Al recibir energía, la bobina de inducción genera un campo magnético. Esto provoca que el componente automotriz experimente un calentamiento por efecto Joule debido a la corriente inducida, fenómeno conocido como corrientes de Eddy. Los tiempos de calentamiento varían, generalmente basta unos pocos segundos para alcanzar la temperatura necesaria para la formación de austenita (rango de 750 a 850°C [1382–1562°F] dependiendo de la composición del acero).

Bobina de inducción con sistema de enfriamiento por rociado integrado para el endurecimiento superficial | Crédito de la imagen: Inductoheat

Las bobinas de inducción son componentes de herramiental sujetos a desgaste. Con el tiempo, los ciclos térmicos repetitivos, la oxidación superficial, el desgaste y la fatiga mecánica reducen gradualmente su desempeño. Pequeñas modificaciones en la geometría de la bobina, su alineación o sus condiciones superficiales pueden alterar el campo electromagnético e introducir variabilidad. Lo más complejo es que estos cambios suelen producirse de forma gradual y no resultan visibles de inmediato. Una bobina puede continuar funcionando mientras afecta la distribución del calor sin que el problema sea evidente. Inspecciones periódicas, la limpieza y el reemplazo programado de las bobinas son fundamentales. En la manufactura automotriz de alto volumen, una gestión proactiva de las bobinas es esencial para mantener la estabilidad del proceso y garantizar la fiabilidad de los componentes tratados térmicamente.

Estabilidad de la Fuente de Alimentación

La fuente de alimentación del sistema de inducción controla la forma en que la energía se suministra a la bobina y, por lo tanto, al componente que será tratado térmicamente. Una salida de potencia estable es fundamental para lograr un calentamiento repetible y resultados metalúrgicos consistentes. La selección de la frecuencia de salida adecuada es esencial para equilibrar la profundidad de calentamiento requerida y la temperatura superficial del componente. En procesos de endurecimiento superficial, las frecuencias más utilizadas se encuentran en un rango de aproximadamente 1,000 Hz hasta 200 kHz. Aunque una sola fuente de alimentación no puede cubrir todo ese rango de frecuencias, la mayoría ofrece cierto grado de flexibilidad en cuanto a la frecuencia.

Las fuentes de alimentación proporcionan un suministro de energía preciso y programable a una frecuencia estable. Además, proporcionan una respuesta rápida ante las variaciones de carga a medida que la temperatura del componente automotriz aumenta, atraviesa el punto de Curie y alcanza la temperatura objetivo. Esta fuente de alimentación ofrece un rendimiento fiable durante ciclos de producción prolongados. Esto es fundamental cuando miles de componentes deben cumplir con especificaciones muy estrictas y con una variabilidad mínima. Si la fuente de alimentación presenta fluctuaciones, estas afectarán la velocidad de calentamiento y las propiedades finales de endurecimiento. Para los fabricantes, esto se traduce en piezas rechazadas y disminución de la rentabilidad.

Estos equipos requieren un programa de mantenimiento preventivo. Después de todo, un suministro confiable contribuye directamente tanto a la calidad como a la productividad. El personal debe:

Medidor analógico de la Fuente de alimentación, % potencia–kilovatios | Crédito de la imagen: Inductoheat
  • Verificar periódicamente que las conexiones eléctricas de las barras conductoras y de las terminales de cableado estén firmes.
  • Revisar que todas las conexiones de las mangueras del sistema de enfriamiento estén firmes, especialmente a medida que las mangueras envejecen.
  • Verificar que todos los interruptores de protección funcionen correctamente.
  • Asegurarse de que el agua del sistema de enfriamiento esté limpia y comprobar su conductividad mensualmente.
  • Consultar el manual del fabricante para obtener más información.

El Temple: Finalización del Proceso

El calentamiento representa solo la mitad del proceso. El temple comienza una vez que el componente ha alcanzado la temperatura de austenización a la profundidad deseada. El medio de enfriamiento se rocía uniformemente sobre la superficie de la pieza, extrayendo el calor de forma rápida y controlada. Este enfriamiento permite la formación de martensita, proporcionando al componente automotriz una capa superficial endurecida. Todo el proceso se lleva a cabo dentro de límites de operación previamente establecidos para garantizar la repetibilidad del tratamiento térmico.

El fluido de temple suele ser agua con aditivo polimérico. Es fundamental mantenerlo a la temperatura adecuada y con la concentración especificada de polímero. El sistema de temple suministra este fluido con una sincronización precisa respecto al ciclo de calentamiento. Asimismo, la bomba y las válvulas deben garantizar caudales y presiones constantes. El intercambiador de calor del sistema elimina el exceso de calor del fluido de temple; de lo contrario, su temperatura aumentaría progresivamente después de cada ciclo.

Monitor de concentración (izquierda) y válvulas de la tubería del sistema de temple (derecha) | Crédito de la imagen: Inductoheat

Con el paso del tiempo, parte del agua del fluido de temple se evapora, incrementando la concentración del polímero. Además, el fluido se contamina con residuos de aceite, virutas metálicas y otras impurezas. Los filtros tipo bolsa del sistema se saturan y los múltiples orificios de las boquillas de aspersión pueden obstruirse debido a la acumulación de incrustaciones y partículas. Por ello, el sistema de temple debe recibir mantenimiento periódico para garantizar un enfriamiento controlado y repetible. Solo así el proceso de tratamiento térmico puede completarse de manera consistente y confiable.

Confiabilidad basada en datos

Los equipos de inducción deben operar con un alto nivel de precisión para lograr el tratamiento térmico especificado. Cuando estos sistemas incorporan monitoreo en tiempo real y adquisición de datos durante el proceso, se incrementa aún más la confianza en los resultados obtenidos. El monitoreo mediante “firmas” de proceso mide las múltiples variables del tratamiento térmico por inducción en cada ciclo. Esta “firma” puede incluir parámetros eléctricos como la potencia del inversor, la corriente, el voltaje y la frecuencia a lo largo del proceso. Asimismo, puede registrar la temperatura del medio de enfriamiento, el flujo y la presión del fluido de temple, así como la velocidad de escaneo de la máquina y la velocidad de rotación del husillo. Para cada una de estas variables se establece un rango de variación permitido, el cual se representa gráficamente en función del tiempo. Cualquier desviación fuera de estos límites durante el ciclo, hará que la máquina genere un fallo de proceso.

Firma de proceso del sistema QAS de Inductoheat, mostrando los límites superior e inferior permitidos y el registro de variables como la potencia del inversor (kVA), la velocidad de escaneo y el caudal de temple de los husillos izquierdo y derecho | Crédito de la imagen: Inductoheat

Esta funcionalidad constituye un elemento fundamental dentro de un sistema de aseguramiento de la calidad (QAS por sus siglas en inglés), ya que garantiza la confianza durante cada turno de producción. En el caso de componentes automotrices identificados mediante códigos de barras u otros marcadores únicos, también permite garantizar la trazabilidad de los componentes tratados térmicamente, almacenando la firma del proceso y asociándola a cada componente tratado térmicamente. Este paso permite obtener datos clave para aislar un lote de piezas si fuera necesario, evitando la necesidad de poner en cuarentena más unidades de las estrictamente necesarias.

Equipos Confiables. Mejores Componentes. Vehículos más Resistentes.

En toda la industria automotriz, desde camiones de servicio pesado hasta los SUVs y crossovers de uso cotidiano, el desempeño de un vehículo se construye capa por capa. A medida que las plataformas vehiculares continúan evolucionando, los procesos de tratamiento térmico deben avanzar al mismo ritmo de diseños de componentes cada vez más complejos. Contar con equipos de inducción confiables es fundamental para afrontar estos desafíos. Cada elemento del sistema debe operar con precisión y consistencia. El mantenimiento preventivo, incluido el reemplazo periódico de componentes sujetos a desgaste, como las bobinas de inducción, contribuye a mantener la estabilidad del proceso, obtener resultados consistentes y garantizar una producción confiable.

Para muchos fabricantes, preservar la confiabilidad también implica modernizar sus equipos existentes. Con frecuencia, los sistemas de inducción de mayor antigüedad pueden reacondicionarse mediante la incorporación de controles modernizados, nuevas fuentes de alimentación y componentes críticos actualizados, lo que permite prolongar su vida útil al tiempo que mejora el rendimiento y el tiempo de actividad. Asimismo, estos equipos pueden reacondicionarse para adaptarse a nuevos programas de tratamiento térmico.

Al invertir en tecnología de inducción confiable, los fabricantes pueden seguir produciendo componentes de alta calidad capaces de satisfacer las exigencias de los vehículos actuales.

Acerca del autor:

Aaron Goodwin
Ingeniero de Desarrollo de Negocios
Inductoheat

Aaron Goodwin cuenta con más de 32 años de experiencia en la industria del calentamiento por inducción, durante los cuales ha desempeñado diversos cargos técnicos en Inductoheat, ubicada en Madison Heights, Michigan. Actualmente se desempeña como Ingeniero de Desarrollo de Negocios, brindando soporte técnico tanto al equipo de ventas como de ingeniería. Entre sus principales responsabilidades se encuentra la dirección del equipo de simulación mediante análisis por elementos finitos (FEA) para el diseño de bobinas y procesos de calentamiento por inducción.

Además, Aaron colabora con las empresas hermanas del grupo Inductotherm alrededor del mundo, impulsando el desarrollo tecnológico, el intercambio de conocimientos y la implementación de soluciones enfocadas en las necesidades de los clientes.

Para más información: Contacte con Aaron Goodwin en agoodwin@inductoheat.com.

Tratamiento térmico por inducción confiable para componentes automotrices Read More »

Decarburized Steel Critical for Induction Hardening Rotary Blades

/ ANNEALING TECHNICAL CONTENT, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH

For in-house heat treat operations, the number one goal is to produce a reliable product with consistent in-service performance. Yet supply chain and specialized processes can cause consistency stressors. In this article, Heat Treat Today underlines the importance of consistent feedstock for in-house induction heat treater, National Steel Rule, and how the essential mill process of controlled decarburization can be actualized.

This informative piece was first released in Heat Treat Today’s April 2026 Annual Induction Heating & Melting print edition.

If you have any comments or queries, on this article, let us know at editor@heattreattoday.com.

Para leer el artículo en español, haga clic aquí.

Introduction: Steel Rule that Bends

National Steel Rule manufactures rotary cutting rule for the corrugated box industry. Located in Linden, New Jersey, the company supplies products to the die making and die cutting industries globally. They have established a high standard of sourcing, researching, and testing material for their rule, in addition to a complete testing laboratory with both rotary and flat die cutting equipment.

Their steel rule is purchased from a mill that performs a controlled decarburization on the entire feedstock. When National receives the steel feedstock, they work the steel to create teeth, employing induction hardening as part of the process. The finished cutting rule is then sold to steel rule die makers who mount these blades and an ejection rubber on laser cut wooden boards. The manufacturer must ensure their rule blades are sound, as even microscopic cracks will open during the die cutting process.

Figure 1. Small diameter bent rule | Image Credit: National Steel Rule

National’s rotary blades and other products rely on purchasing decarburized steel. “Flexibility and formability are paramount,” states Ed Mucci, president of the company, and Alexander Heucke, chief engineer. Cutting rule must be bent to form a circular blade; in service, that blade rotates to cut into the corrugated material. The curve geometry can be extreme, often bending up to a 7-inch interior diameter. As such, the purchase of decarburized steel is critical for the manufacturer’s business. At present, National sources the material internationally. Mucci explains, “Manufacturers aren’t using large quantities of decarburized steel, making it challenging to source, at least domestically.”

Rotary rule feedstock typically involves C36 (SAE 1036) to C50 (SAE 1050) carbon steel with a hardness range of 32–34 HRC. Mucci and Heucke note that their steel of choice has a total decarburization layer to a depth of 0.0005” depth, with partial decarburization of at least another 0.0005–0.00075”. This ensures that when the rule is bent, the surface stretches versus cracks. Bending the rule is itself a test of whether it has been properly decarburized, with metallurgical testing serving as a quality control verification that suppliers are producing the appropriate decarburization levels.

Precise Induction Hardening Teeth

While bending is essential to forming the appropriate curve, the teeth must be resistant to wear and breakage. National’s rotary cutting rule has performance expectations of at least 750,000 impressions on paper, itself a highly abrasive material. To do this, their in-house heat treat operations induction harden the edge of the rule to ensure a long die life.

There are two methods used to harden the teeth. The primary method is to shave a profile into the strip steel and then induction harden this edge. Serrated teeth are then ground in. “This gives us better control of hardening depth,” according to Mucci and Heuke. The second method is to induction harden after the serrated teeth are ground in. “We have to make sure we don’t harden the teeth too deeply, or we can affect the bendability.”

Induction hardening involves short cycles, and as such requires careful process control to guarantee consistent results; temperature-indicating crayons that melt at a specific temperature are used as one of the process control methods. Hardness testing is performed as well.

Screenshot

Decarburization Revisited

“Usually, one tries to prevent decarburization or even add carbon,” states Mark Hemsath, executive consultant at WINGENS CONSULTANTS and longtime expert and innovator in the thermal processing industry. “Decarb often occurs by accident in poorly designed annealing systems, especially in continuous-type furnaces.”

Figure 3. Ellingham Diagram depicting that hydrogen-to-water vapor relationship, the key to a successful, controlled decarburization.
Figure 4. Typical bell-annealing furnace | Image Credit: RAD-CON

Oxygen, in the form of air or water vapor, is key to the decarburizing process. Less carbon on the surface means a softer, more malleable steel, and while the art of a controlled decarburization process is well known, it can be challenging. Decarburization is a process usually performed below 1500°F. “The preferred method is to use water vapor or steam as a source of the oxygen,” notes Hemsath, pointing to the stability of hydrogen-to-water vapor (H₂/H₂O ratio) derived from the Ellingham diagram. These H₂/H₂O ratios indicate the non-oxidizing qualities of the gaseous mixture, which will allow it to be the carbon reducing agent in the atmosphere. Most furnace companies can provide the necessary equipment and customize size specifications to make it suitable for this special process, and these furnaces are typically retort-based bell or pit type.

Two Methods to Control the Decarb

There are two ways that a decarburization process can be intentionally completed. The first is decarburizing the entire product. In this method, even decarburization is applied to the entire coil sheet surface. “This cold rolled steel, typically with lower carbon, is used for appliances that need enamel adhesion,” Hemsath explained, noting U.S. Steel and AK Steel, now a part of Cleveland-Cliffs, have used this form of controlled decarburization.

Another form of decarburization is selective surface decarburization. Hemsath shared, “If selective decarburizing is required only on the edges, then you could keep the coils tightly wound and the decarburization would affect mainly the coil edges. There would be ingress of carbon loss, reducing towards the center of the wound coil surfaces.”

Conclusion

“Decarburized steel just isn’t in high demand,” according to Mucci, as “most industries are looking to harden and temper the steels they use.” In fact, preventative steel decarburization is more typical and often emphasized in trade shows, technical presentations, and in thermal processing publications. Yet there are products that rely on intentional decarburization to be successful.

Controlled decarburization at the mill brings challenges, in part because successful, consistent decarburization is not often cost effective for the North American thermal processing market. These challenges encompass regional access issues, niche market access, equipment selection needs, and technical process execution.

National’s experience underlines the challenges North American mills face in providing local, in-house heat treaters with reliably, well-controlled decarburized steel that will maintain service life.

Acknowledgements: Heat Treat Todayextends thanks to Dan Herring, The Heat Treat Doctor® at The HERRING GROUP, Inc., who was instrumental in the development of this article.

For more information: Contact Heat Treat Today’s Editorial Team at editor@heattreattoday.com.

Main image: RP8 rotary rule edge hardened | Image Credit: National Steel Rule

Decarburized Steel Critical for Induction Hardening Rotary Blades Read More »

Acero Descarburizado: Crítico para el Endurecimiento por inducción de Cuchillas Rotativas

/ ANNEALING TECHNICAL CONTENT, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH

Para las operaciones de tratamiento térmico internas (in house), el objetivo principal es producir un producto confiable con un desempeño consistente en servicio. Sin embargo, la cadena de suministro y los procesos especializados pueden generar factores que comprometen la consistencia. En este artículo, Heat Treat Today destaca la importancia de contar con material base consistente para el tratamiento térmico por inducción interno de National Steel Rule, y cómo se puede implementar el proceso esencial de descarburización controlada en la planta proveedora de acero.

Este artículo informativo se publicó por primera vez en Heat Treat Today’s April 2026 Annual Induction Heating & Melting print edition. Traducido por Ana Laura Hernández Sustaita.

Si tiene comentarios o preguntas sobre este artículo, háganoslo saber en: editor@heattreattoday.com.

To read this article in English, click here.

Introducción: Regla de Acero que se Dobla

La empresa National Steel Rule produce reglas de corte rotativas para la industria del cartón corrugado. Ubicada en Linden, Nueva Jersey, la empresa suministra productos a las industrias de troquelado a nivel mundial. La compañía ha establecido altos estándares de abastecimiento, investigación y pruebas de material para sus reglas de corte, además de contar con un completo laboratorio con equipos de troquelado rotativo y plano.

Su regla de acero se adquiere de una planta proveedora de acero que realiza una descarburización controlada en todo el material. Cuando National recibe el material, procesa el acero para generar los dientes, empleando endurecimiento por inducción como parte del proceso (ver la imagen principal al inicio de este artículo). La regla de corte terminada se vende posteriormente a fabricantes de troqueles de regla de acero, quienes montan estas cuchillas junto con una goma de expulsión sobre tableros de madera cortados con láser. El fabricante debe asegurarse de que las cuchillas de las reglas estén libres de defectos, ya que incluso grietas microscópicas se abrirán durante el troquelado.


Figura 1. Regla de acero doblada de diámetro pequeño | Crédito de la imagen: National Steel Rule

Las cuchillas rotativas y otros productos de National dependen de la compra de acero descarburizado. “La flexibilidad y la conformabilidad son fundamentales”, afirma Ed Mucci, presidente de la empresa, y Alexander Heucke, ingeniero en jefe. La regla de corte debe doblarse para formar una cuchilla circular; durante el servicio, la cuchilla rota para cortar el material corrugado. La geometría de la curvatura puede ser extrema, llegando a doblarse hasta un diámetro interior de 7 pulgadas. Por lo tanto, la compra de acero descarburizado es crítica para el negocio del fabricante. Actualmente, National obtiene el material a nivel internacional. Mucci explica: “Los fabricantes no utilizan grandes cantidades de acero descarburizado, lo que dificulta su abastecimiento, al menos a nivel nacional”.

El material para las reglas rotativas suele ser acero al carbono C36 (SAE 1036) a C50 (SAE 1050) con un rango de dureza de 32–34 HRC. Mucci y Heucke señalan que el acero que utilizan presenta una capa de descarburización total de 0.0005” de profundidad, con una descarburización parcial adicional de al menos 0.0005”–0.00075”. Esto garantiza que cuando una regla se dobla, la superficie se elongue en lugar de agrietarse. Doblar la regla es, en sí mismo, una prueba para comprobar si se ha descarburado correctamente, y las pruebas metalúrgicas sirven como verificación de control de calidad para garantizar que los proveedores estén produciendo los niveles adecuados de descarburización.

Endurecimiento Preciso por Inducción de los Dientes

Si bien el doblado es esencial para formar la curvatura apropiada, los dientes deben ser resistentes al desgaste y la rotura. La regla de corte rotativa de National tiene una expectativa de desempeño de al menos 750,000 impresiones en papel, que es en sí mismo un material altamente abrasivo. Para lograrlo, las operaciones de tratamiento térmico internas endurecen por inducción el borde de la regla, garantizando una larga vida útil del troquel.

Existen dos métodos usados para endurecer los dientes. El método principal es maquinar el perfil de la tira de acero y posteriormente endurecer por inducción el borde. Posteriormente los dientes son rectificados. “Esto nos da un mejor control sobre la profundidad de endurecimiento”, comenta Mucci y Heuke. El segundo método consiste en endurecer por inducción después de rectificar los dientes. “Debemos asegurarnos de que el endurecimiento de los dientes no sea muy profundo, ya que esto puede afectar la capacidad de doblado”. El endurecimiento por inducción implica ciclos muy cortos, y por lo tanto requiere un control minucioso del proceso para garantizar resultados consistentes. Entre los métodos de control del proceso se utilizan crayones indicadores de temperatura, que se funden a una temperatura específica. También se realizan pruebas de dureza.


Figura 2. Detalle de la capa descarburizada | Crédito de la imagen: National Steel Rule

Revisitando la Descarburización

“Generalmente se intenta prevenir la descarburización o incluso agregar carbono a la superficie”, comenta Mark Hemsath, consultor ejecutivo en WINGENS CONSULTANTS y reconocido experto e innovador en la industria del tratamiento térmico. “La descarburización a menudo ocurre accidentalmente en sistemas de recocido mal diseñados, especialmente en hornos de tratamiento continuo.”


Figura 3. Diagrama de Ellingham que muestra la relación hidrógeno-vapor de agua, clave para una descarburización controlada exitosa.

Figura 4. Horno típico de recocido tipo campana. | Crédito de la imagen: RAD-CON

El oxígeno en forma de aire o de vapor es la clave del proceso de descarburización. Menor porcentaje de carbono en la superficie indica un acero más blando y maleable, y si bien el arte de un proceso de descarburización controlada es bien conocido, puede resultar un desafío. El proceso de descarburización suele realizarse por debajo de 1500°F (815°C). “El método preferido es usar vapor de agua o vapor como fuente de oxígeno”, señala Hemsath. Esto se basa en la estabilidad de la relación hidrógeno-vapor de agua (H2/H2O) derivada del diagrama de Ellingham. Estas relaciones H2/H2O indican las propiedades no oxidantes de la mezcla gaseosa, lo que permite que actúe como agente reductor de carbono en la atmósfera del horno. La mayoría de las empresas fabricantes de hornos pueden proporcionar el equipo necesario y personalizar las dimensiones para hacerlos adecuados para este proceso especial. Estos hornos suelen ser de tipo campana o tipo foso con retorta.

Dos Métodos para Controlar la Descarburización

Existen dos formas de realizar intencionalmente un proceso de descarburización. La primera consiste en descarburar todo el producto. En este método, la descarburización se aplica de manera uniforme en toda la superficie de la lámina o bobina. “Este acero laminado en frío generalmente con menor contenido de carbono, se utiliza en electrodomésticos que requieren una buena adherencia del esmalte”, explica Hemsath. Empresas como U.S. Steel y AK Steel (ahora parte de Cleveland-Cliffs) han utilizado esta forma de descarburización controlada.

Otra forma es la descarburización selectiva en la superficie. Hemsath explica: “Si la descarburización solo se requiere en los bordes, se podrían mantener las bobinas enrolladas firmemente, por lo tanto, la descarburización afectaría principalmente a los bordes. Se produciría una pérdida de carbono que disminuiría hacia el centro de las superficies enrolladas”.

Conclusión

“El acero descarburizado tiene mucha demanda, ya que la mayoría de las industrias buscan endurecer y templar los aceros que utilizan”, indica Mucci. De hecho, la prevención de la descarburización del acero es más común y suele destacar en ferias industriales, presentaciones técnicas y publicaciones de procesamiento térmico. Sin embargo, existen productos que dependen de la descarburización intencional para funcionar correctamente.

La descarburización controlada en la planta proveedora de acero presenta desafíos, en parte porque lograr una descarburización exitosa y consistente no suele ser económicamente viable para el mercado norteamericano de tratamiento térmico. Estos desafíos abarcan problemas de acceso regional, acceso a nichos de mercado, necesidades de selección de equipos y ejecución de procesos técnicos.

La experiencia de National destaca los desafíos que enfrentan las plantas proveedoras de acero de América del Norte para proveer a las empresas de tratamiento térmico interno, acero descarburizado de forma fiable y bien controlada que mantenga su vida útil.


Agradecimientos: Heat Treat Today agradece a Dan Herring, The Heat Treat Doctor®, The HERRING GROUP, Inc., quien fue fundamental en el desarrollo de este artículo.


Para más información: Contacte con Heat Treat Today’s Editorial Team en editor@heattreattoday.com.

La imagen principal: Regla rotativa RP8 con borde endurecido | Crédito de la imagen: National Steel Rule

Acero Descarburizado: Crítico para el Endurecimiento por inducción de Cuchillas Rotativas Read More »

Ask The Heat Treat Doctor®: Why and How Do We Heat Treat Gears? Part Two

/ AEROSPACE HEAT TREAT TECHNICAL CONTENT, CARBURIZING TECHNICAL CONTENT, HARDENING TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, OP-ED, QUENCHING TECHNICAL CONTENT, VACUUM FURNACES TECHNICAL CONTENT

Ask The Heat Treat Doctor® has returned to bring sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues. In this installment, Dan Herring continues his discussion on gear heat treatment, exploring vacuum and induction hardening methods for gears — from low-pressure carburizing for advanced materials to single shot and tooth-by-tooth induction techniques — and how each can be matched to the specific demands of any gear application.

This informative piece was first released in Heat Treat Today’s March 2026 Annual Aerospace Heat Treating print edition.

In Part One of this discussion (Air & Atmospheres Heat Treating, February 2026), we discussed various gear types, materials, and how they can be atmosphere heat treated. This month, we are focusing on vacuum and induction heat treating methods. Let’s learn more.

Vacuum Heat Treatment Processing Methods

Table A. Advanced Materials Processed by LPC

Vacuum processing can be used for most of the atmosphere treatments mentioned in Part One including carburizing (Figure 1). Low pressure carburizing (LPC) is a proven technology and the choice for many advanced applications in aerospace, automotive, off-highway, and motorsports markets, as well as the development of carburizing cycles for high-performance materials (Table A).

Figure 1. Typical commercial heat treat load of gears for vacuum carburizing (Otto and Herring 2007) | Image Credit: Photo courtesy of Midwest Thermal-Vac
Figure 2. Pyrowear 675 – LPC – anneal – double normalize – harden – anneal – deep freeze – double temper | Image Credit: The HERRING GROUP, Inc.

The range of effective case depths for most of these grades can range up to 2.0–3.0 mm (0.080–0.120 inches) without significant sacrifice of microstructure (Figure 2). Furnace variables, such as temperature uniformity (± 3°C or ± 5°F), control of cycle parameters (boost/diffuse times, gas flow rate, pressure, hydrocarbon type) and surface carbon optimize the microstructure, producing case uniformities of ± 0.05 mm (± 0.002 inches). Where permitted, the range of carburizing temperatures now includes the use of high temperature (> 980°C, or 1800°F) techniques.

All these advanced materials required extensive development testing to produce custom designed recipes to optimize cycle parameters. Also, quenching methods (Otto and Herring 2002) have improved, allowing us to achieve desired core properties with quenching parameter selection (high-pressure gas or oil) for distortion-sensitive and distortion-prone part geometries (Otto and Herring 2005, 2008).

Induction Hardening Methods

Various methods of hardening via applied energy are used in manufacturing gears, including flame hardening, laser surface hardening, and induction hardening.

Of the various types of applied energy processing, induction hardening is the most common. Induction heating is a process that uses alternating electrical current that induces a magnetic field, causing the surface of the gear teeth to heat. The area is then quenched resulting in an increase in hardness within the heated area. This process is typically accomplished in a relatively short time. The final desired gear performance characteristics are determined not only by the hardness profile and stresses but also by the steel composition and prior microstructure. External spur and helical gears, bevel and worm gears, racks, and sprockets are commonly induction hardened. Typical gear steels include AISI/SAE grades 1050, 1060, 1144, 4140, 4150, 4350, 5150, and 8650.

Figure 3. Patterns produced by induction hardening (Rudnev 2000)

The hardness pattern produced by induction heating (Figure 3) is a function of the type and shape of inductor used, as well as the heating method. Quenching or rapidly cooling the workpiece can be accomplished by spray or submerged quench. The media typically used for the quench is a water-based polymer. The severity of this quenchant can be controlled by the polymer’s concentration. Cooling rates are usually somewhere in between what would be obtained from pure water and oil. In some unusual situations compressed air or nitrogen is used to quench the part.

The most common methods for hardening gears and sprockets are by single shot (Figure 4) or the tooth-by-tooth method (Figure 5). Single shot often requires large kW power supplies but results in short heat/quench times and higher production rates. This technique uses a circumferential copper inductor, which will harden the teeth from the tips downward.

Figure 4. Typical single shot induction hardening operation | Image Credit: Photo courtesy of Ajax-Tocco-Magnethermic
Figure 5. Tooth-by-tooth induction hardening of a helical gear | Image Credit: Photo courtesy of Ajax-Tocco-Magnethermic

The larger and heavier loaded gears (where pitting, spalling, tooth fatigue, and endurance are issues) need a hardness pattern that is more profiled like those produced by carburizing, which can be obtained by tooth-by-tooth hardening. This method is limited to gear tooth sizes with modulus 4.23–5.08 (6 or 5 DP) using frequencies from 2 to 10 kHz and about 2.54 (10 DP) using a range of 25 to 50 kHz.

The lower the frequency, the deeper the case depth. Tooth-by-tooth hardening is a slow process and usually reserved for gears and sprockets that are too large to single shot due to power constraints. The process involves heating the root area and side flanks simultaneously, while cooling each side of the adjacent tooth to prevent temper-back on the backside of each tooth. The induction system moves the coil at a pre-programmed rate along the length of the gear. The coil progressively heats the entire length of the gear segment while a quench follower immediately cools the previously heated area. The distance from the coil to the tooth is known as coupling or air gap. Any changes in this distance can yield variation in case depth, hardness, and tooth distortion. The gear is indexed after each tooth has been hardened, often skipping a tooth. This requires at least two full revolutions in the process to complete the hardening of all teeth. Straight, spur, and helical gears up to 5.5 m (210 inches) weighing 6,800 kg (15,000 lb) have been processed with this method. The entire process yields a repeatable soft tip of the tooth with hard root and flank. In other applications, the tip and both flanks can be hardened simultaneously and yield a soft root.

In Summary

Today’s design engineer has the good fortune of being able to choose from a number of heat treatment technologies for any given type of gear material and design. When selecting a gear hardening method, it is essential to specify not only the desired mechanical and metallurgical properties, but the critical dimensions that must be held and even the desired stress state of the gears themselves. The secret to success is understanding the advantages and limitations of each technology and taking these into consideration when determining the overall cost of gear manufacturing.

References

Herring, Daniel H. 2004a. “Gear Heat Treatment: The Influence of Materials and Geometry.” Gear Technology, March/April.

Herring, Daniel H. 2004b. “Reducing Distortion in Heat-Treated Gears.” Gear Solutions, June.

Herring, Daniel H. 2007a. “Oil Quenching Technologies for Gears.” With Steven D. Balme. Gear Solutions, July.

Herring, Daniel H. 2007b. “Heat Treating Heavy Duty Gears.” With Gerald D. Lindell. Gear Solutions, October.

Herring, Daniel H. 2012–2016. Vacuum Heat Treatment. Vols. 1–2. BNP Media Group.

Herring, Daniel H. 2014–2015. Atmosphere Heat Treatment. Vols. 1–2. BNP Media Group.

Herring, Daniel H., Gerald D. Lindell, D. J. Breuer, and B. Matlock. 2001. “Atmosphere vs. Vacuum Carburizing.” Heat Treating Progress, November.

Herring, Daniel H., Gerald D. Lindell, D. J. Breuer, and B. Matlock. 2002. “An Evaluation of Atmosphere and Vacuum Carburizing Methods for the Heat Treatment of Gears.” In Off-Highway Conference Proceedings. SAE International.

Otto, Frederick J., and Daniel H. Herring. 2002a. “Gear Heat Treatment: Today and Tomorrow, Part 1.” Heat Treating Progress, June.

Otto, Frederick J., and Daniel H. Herring. 2002b. “Gear Heat Treatment: Today and Tomorrow, Part 2.” Heat Treating Progress, July/August.

Otto, Frederick J., and Daniel H. Herring. 2005. “Vacuum Carburizing of Aerospace and Automotive Materials.” Heat Treating Progress, January/February.

Otto, Frederick J., and Daniel H. Herring. 2007. “Advancements in Precision Carburizing of Aerospace and Motorsports Materials.” Heat Treating Progress, May/June.

Otto, Frederick J., and Daniel H. Herring. 2008. “Improvements in Dimensional Control of Heat Treated Gears.” Gear Solutions, June.

Rudnev, V. 2000. “Gear Heat Treating by Induction.” Gear Technology, March/April.

About the Author

Dan Herring
“The Heat Treat Doctor”
The HERRING GROUP, Inc.

Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.

For more information: Contact Dan at dherring@heat-treat-doctor.com.

For more information about Dan’s books: see his page at the Heat Treat Store.

Ask The Heat Treat Doctor®: Why and How Do We Heat Treat Gears? Part Two Read More »

Hybrid Heating Systems Unlock Heat Process Decarbonization

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, FOUNDRY CASTING TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH

As pressure mounts to cut industrial CO2 emissions, hybrid heating systems are emerging as a compelling pathway to decarbonizing industrial process heat. In this Technical Tuesday installment, Dr.-Ing. Marco Rische and Dr. Martin Ennen of ABP Induction Systems GmbH explore how integrating induction technology at the front and end of traditional gas-fired furnace heat treating can reduce energy consumption, improve temperature control, lower operating costs, and offer a realistic bridge to full electrification.

This informative piece was first released in Heat Treat Today’s January 2025 Annual Technologies To Watch print edition.

The metalworking industry is undergoing a profound transformation, as the pressure to reduce emissions and replace fossil fuels continues to shape technological strategies across all areas of the value chain. In addition to melting technology, process heat is increasingly coming into focus — namely the heating, warming, and tempering of materials, which is required in virtually every production process.

With hybrid approaches that combine conventional gas furnaces with induction heating units, energy consumption, CO2 emissions, and costs can be reduced simultaneously. ABP Induction, a global provider of electric heating and melting technologies, has continued to refine and expand hybrid heating concepts over the past several years. Its strategy aims to help shape the path to CO2 neutrality as a partner to the metalworking industry through holistic solutions that balance technological advances and cost efficiency.

The Pressure to Act in the Industry

The starting point is both a challenge and an opportunity; the metalworking industry ranks among the largest industrial producers of CO2 emissions worldwide. The steel industry, in particular, is at the center of the decarbonization debate, accounting for roughly one quarter of global industrial emissions. Natural gas was the preferred fuel for many years: affordable, easy to control, and simple to transport. But with rising CO2 prices and increasing political pressure to decarbonize, the balance is shifting. While primary processes like pig iron production are increasingly shifting toward direct reduction using hydrogen, heat input in downstream processing steps, such as melting, heating, or rolling, still primarily relies on fossil energy sources.

At the same time, the economic landscape is shifting; rising CO2 prices, high energy costs, and the need for stable supply chains are driving a reassessment of conventional technologies and laying the foundation for induction-based burner substitutes to gain economic traction. The megatrends of digitalization, deglobalization, demographic change, and decarbonization are now shaping business decisions across the metalworking industry. After all, the energy policy framework is creating incentives to deploy electric solutions, especially where they can be powered by green electricity. This makes induction — contactless heating of metallic materials using electromagnetic fields — a key technology on the path to CO2 neutrality.

Induction Heating as a Foundational Technology

The physical principle of induction is well established. An alternating electromagnetic field transfers energy directly into the workpiece, heating it evenly and in a controlled manner. The advantages lie in high energy efficiency, dynamic controllability, and reliable process stability. While gas burners rely on convective and radiant heat, induction applies energy directly without intermediate losses — a decisive efficiency advantage that enables practical efficiencies of up to 90%.

For many applications, the technology is already widely adopted. In foundries, induction furnaces are increasingly replacing cupola furnace systems, while in forges and aluminum plants, induction systems are used for efficient preheating and heating. New application areas are emerging in the steel sector, particularly in the fields of reheating and heat treatment.

However, the limitations are equally clear; induction works optimally only where the material to be heated is electrically conductive and the electromagnetic field can be efficiently coupled. For large-volume or indirect heating processes, such as those involving gas flows or non-metallic materials, complementary concepts are required.

The Principle of Hybrid Heating

This is precisely where hybrid heating systems come into play. They combine proven induction technology with conventional furnace systems, typically gas-fired continuous or chamber furnaces. The goal is to leverage the strengths of both systems and compensate for their weaknesses.

A typical hybrid system integrates an induction section before or after the gas-fired furnace. When the induction unit is positioned upstream, it handles the rapid heating phase, bringing the workpiece to a defined temperature in a short time, which effectively reduces the load on the gas-fired furnace. It can then operate with reduced energy input. When the induction unit is positioned downstream, it ensures precise temperature control, homogenizes the temperature profile, or compensates for fluctuations in transport speed.

The benefits are multifaceted: gas consumption decreases, temperature distribution becomes more uniform, production speed can increase, and CO2 emissions are significantly reduced. Pilot projects have achieved savings of up to 60% in previous fossil energy consumption.

In addition, the hybrid solution enables a gradual transformation process. Existing furnace systems can continue to be used, keeping investments in new infrastructure to a minimum. This provides operators with an economically and technically viable path to decarbonization and allows them to stay close to the existing process without compromising production reliability.

Process Integration and Control

Hybrid heating systems are highly adaptable. The design of the induction section depends on material, geometry, throughput, and process objective. Modern control technology ensures precise coordination between induction and furnace operation.

Figure 1. Billet after induction heating process | Source: ABP Induction Systems GmbH

In the area of reheating slabs or billets in rolling mills, for example, an inductive preheating station can be installed in front of the furnace. Here, the induced power density is utilized to significantly shorten the heating time. At production rates of up to 200 tons per hour for long products and 1,000 tons per hour for flat products, induction systems achieve electrical efficiencies of 85% to 90%. Downstream of the furnace, a post-heating unit can help maintain a uniform temperature profile, a critical factor for product quality, dimensional accuracy, and potentially reduced wear on subsequent forming equipment. Process stability also benefits. Gas-fired furnaces are sluggish systems whose temperature responds slowly to process changes. Induction systems, on the other hand, can be controlled within fractions of a second, adding a dynamic component to the overall system. This allows temperature fluctuations to be compensated, which helps to prevent product defects.

A Tool for Transformation

The idea of replacing fossil fuel burners with induction systems is not new. Pioneers in the field considered this decades ago and developed alternative processes and methods, but it was never cost-effective. Fossil fuel usage remained cheaper and allowed existing processes to continue unchanged. Now the situation is different.

Figure 2. UHT Thermo Jet UHT200® — Induction heating concepts for fluids | Image Credit: TUBAF University of Freiberg

A key element in ABP Induction’s strategy for electrifying process heat is the Ultra-High-Temperature (UHT) Thermo Jet, a newly developed high-temperature hot gas technology that replaces conventional fossil fuel burners and electrifies industrial thermal processes. The innovation marks a decisive step toward fully electric process heat, demonstrating that even high-temperature applications are feasible without the combustion of fossil fuels.

The system is based on an inductively heated metallic susceptor located inside a high-temperature-resistant, thermally insulated channel. A process gas flows through it, typically air, though inert gases or exhaust gases can also be used. The induction coil generates an electromagnetic field (Figure 2) that heats the susceptor without physical contact. The susceptor then transfers the heat to the gas flowing past it. The result is a hot gas jet with temperatures well above 1000°C (1830°F), fully replicating the thermal characteristics of a natural gas flame. Industrial test series have already achieved stable temperatures of up to 1400°C (2550°F) with response dynamics that surpasses conventional burners.

The technology transfers energy in two stages: first, the susceptor is heated via induction; then, the heat is transferred to the gas stream. This decoupled structure enables precise control of temperature, gas flow, and power input. The key lies in synchronizing the electrical power control with the gas flow to ensure a consistent and reproducible hot gas quality. The system responds to load changes within seconds, offering a level of controllability for high-temperature applications that has never been achieved before.

Technologically, it operates with minimal losses, as no exhaust gases are produced and the heat is transferred almost entirely to the process. By using closed gas circuits, the residual thermal energy of the exhaust stream can be reused without generating pollutants or releasing combustion residues into the atmosphere. This not only reduces energy consumption but also improves the process atmosphere, for example, through low-oxygen conditions that enable high-quality heat treatment.

Another key feature is its ability to integrate into existing systems. The design enables direct replacement of gas burners in many industrial applications without requiring fundamental modifications to the furnace architecture. This provides a fast and cost-effective path to decarbonizing existing installations.

The concept was developed at the Foundry Institute of TU Freiberg. To bring the technology from the lab into real-world application, an alliance was formed: the university as the originator and development partner, Primetals as the system integrator, and ABP Induction for induction technology, contributing its insights in control systems, coil design, and power supply. Following successful lab trials with power levels between 10 and 35 kilowatts, an industrial demonstrator rated at 200 kilowatts is currently undergoing testing, serving as the foundation for market entry (Figure 3). The results demonstrate that the system is scalable — from compact applications to large-scale processes in the steel industry as well as glass, ceramics, and chemical.

Figure 3. UHT Thermo Jet UHT200® — test facility for 200kW heating power | Image Credit: TUBAF University of Freiberg

The UHT Thermo Jet transfers the principle of induction to indirect process heat. While previous systems exclusively heated metallic workpieces directly, the new technology now enables controlled generation of hot gas streams — a decisive step toward full electrification of industrial heat supply. By combining efficiency, responsiveness, and sustainability, this solution paves the way toward a CO2-neutral future while ensuring cost-effective operation.

3 Stages: Technical Application Development

The development of hybrid heating systems follows a clear technological logic:

  • In the short term, fossil-based systems are supplemented by complementary induction modules.
  • In the medium term, they are replaced by electric heat sources, such as the UHT Thermo Jet.
  • In the long term, they are fully electrified.

This evolution creates multiple advantages: first and foremost, a rapid entry into decarbonization through the retrofit of existing systems, resulting in lower operating costs due to reduced gas consumption and decreased maintenance requirements. This also leads to an increase in product quality thanks to precise temperature control. Companies also stand to benefit from the energy transition in the market, with long-term supply security, as electricity from renewable sources can be generated locally.

At the same time, new requirements are emerging for control and integration. Electric heating systems respond instantly to grid fluctuations and can be integrated into digital energy management systems. This makes it possible to optimize load profiles, adapt production processes flexibly to energy availability, and manage energy consumption with full transparency — a key milestone on the path to climate-neutral industrial production.

The ecological impact of hybrid heating systems is thus directly measurable. By partially replacing fossil burners, CO2 emissions can be reduced significantly. At the same time, nitrogen oxide and particulate emissions, which are typically generated during combustion, are reduced.

The economic picture is similar; while the investment costs for electric systems are higher, operating costs decrease due to lower gas consumption and improved energy efficiency. In addition, expenses for emission certificates, burner maintenance, and exhaust gas treatment are eliminated. In many cases, the investment pays off within a few years, especially when funding programs for the decarbonization of industrial processes are utilized.

In addition, the resilience of production systems improves. Electrically operated systems are less dependent on geopolitical energy imports and can potentially be powered directly by locally generated green electricity or by synthetically produced energy (via power-to-X processes) in the future. New energy storage concepts will also play a role here.

Practical Considerations

There are four key megatrends in industry: digitalization, deglobalization, demographic change, and decarbonization. Electrification of process heat is a key area of action, following the three-stage logical flow to implement fully electric, CO2-free process heat solutions. This approach reflects the reality in many industrial enterprises, which, due to their investment cycles, cannot implement an immediate transition. Hybrid solutions provide the essential bridge — both technologically and economically.

Despite these innovations, it is clear that the transformation of industrial process heat will not happen overnight. It requires time, investment, and a high degree of technical integration. Nevertheless, the electrification of thermal processes is considered an indispensable component of industrial decarbonization.

Hybrid heating systems represent a key enabling technology in this context. They enable the gradual replacement of fossil fuels, increase efficiency, and open up new degrees of freedom in production control. With innovations such as the UHT Thermo Jet, the range of applications expands significantly — reaching into areas like process gases and high-temperature applications that were previously considered the domain of fossil combustion.

Hybrid technology does not mark the end, but rather the beginning of a new generation of industrial heating systems — efficient, flexible, and climate-neutral.

About The Authors:

Dr.-Ing. Marco Rische
Chief Technical Officer and Director System Business
ABP Induction

Dr.-Ing. Marco Rische is a highly qualified professional in induction heating systems technology with over 26 years of experience as the vice president of service, chief technical officer (CTO) and director system business with ABP Induction. He has demonstrated a deep technical understanding as a leader, leveraging his management and engineering background to solve complex technical and organizational challenges.

Dr. Martin Ennen
Application and Development Engineer
ABP Induction

Dr. Martin Ennen has studied electrical engineering and obtained his PhD in the field of electrical process engineering, with a focus on inductive heating processes. He has been working for three years at ABP as an application and development engineer. He is responsible for research and development work that entails numerical process simulation leveraging state-of-the-art FEM methods.

For more information: Contact Dr.-Ing. Marco Rische at Marco.rische@abpinduction.com and Dr. Martin Ennen at Martin.ennen@abpinduction.com.

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Optimizing Your Induction Heating System

/ INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT

Whether you need insight on enhancing your energy utilization, managing induction systems (troubleshooting), or prolonging equipment longevity, today’s Technical Tuesday original content feature will keep you well-informed.

Heat Treat Today has coalesced technical information across articles from key experts, including tips to improve your energy efficiency, a walk-through guide for troubleshooting your induction system, and ten practical tips for improving your equipment longevity.

Induction and Sustainability Tips Part 2: Efficient Power

As energy efficiency becomes a driving force in modern heat treating, manufacturers are turning to smarter induction technologies to cut waste and lower costs. In this second installment of Heat Treat Today’s sustainability series, explore how AC-to-DC conversion, intelligent power feedback systems, and advanced diagnostics can transform your induction heating setup into a cleaner, more consistent, and cost-effective process.

“Furthermore, transformers operate at optimal efficiency when under a reduced load – i.e., less than 70% output in steady-state heating – rather than ramping up to the full operating temperature. Another advantage of the DC-type transformer is that its operating power factor is very close to 1.0, which lowers the utility company’s calculation of peak demand surcharges.”

Read the full article here: Induction and Sustainability Tips Part 2: Efficient Power

10 Steps To Troubleshoot Your Induction System

Facing erratic heating, poor consistency, or unexpected shutdowns in your induction system? This comprehensive guide walks heat‑treat operators through a ten‑step diagnostic framework for identifying and resolving common induction issues.

Figure 2. Induction system components
Source: Contour Hardening, Inc.

“The induction process involves many characteristics such as: position of the piece within the induction coil, load positions, cooling positions, cycle times, applied electric power, and others. It is important that the professional can identify the failure and the particular situation at the moment in which it is occurring.

On some occasions, the failures are not evident and therefore it is essential to analyze the part that has been treated. This analysis can be key to understanding situations such as poor depth due to electrical power or decrease in output frequency, among other possible scenarios.”

Read the full article here: 10 Steps To Troubleshoot Your Induction System

New and Improved Tips for Induction Equipment Longevity

Heat treaters are always looking for ways to extend the life of their induction tools, but what methods are proven maintenance strategies? Focusing on the durability of coils, bus bars, inductors, and quench components, this technical article will give you practical and reliable tips to promote longevity in your equipment.

Figure 2. Break-Away bolts designed to fail beneath the washer if over tightened

“More than coils — When working to optimize the life of induction equipment, don’t focus solely on the coils. Bus bars, inductors, and quenching equipment are also key to success. 

Austenitic stainless steel — Use austenitic stainless steel for fasteners, fittings, and hose clamps, and remember, non-ferrous is the way to go.  

CNC machining — Manufacturing with a 5-axis CNC machine ensures quality and consistency.  

“Break-Away” bolts — For fasteners, use “Break-Away” bolts on contact surfaces. These bolts are designed to fail beneath the washer if they are overtightened, a design that prevents damage to the threaded insert inside the copper contact.”

Read the full article here: New and Improved Tips for Induction Equipment Longevity

Find heat treating products and services when you search on Heat Treat Buyers Guide.com

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Induction Hardened Case Depth Measurement Using Ultrasonic Backscattering

/ INDUCTION HEATING TECHNICAL CONTENT

By Jose Miguel Equihua Toral, Head of the New Projects and Development, BOINSA Mexico and Manager, InTech NDT, USA.

Nondestructive testing (NDT) techniques have been used exclusively to detect defects in structures and components after they have been manufactured. To protect public safety and security, it is imperative to test parts efficiently and ensure their quality. Nondestructive evaluation, like ultrasonic backscattering, serves an important role in this area. 

This informative piece was first released in Heat Treat Today’s April 2025 Annual Induction Heating & Melting print edition.

Introduction

Figure 1a. Induction hardening (top)
Figure 1b. UT backscattering testing (bottom)

Induction hardening is a critical process in manufacturing automotive, agricultural, and aeronautical components, such as crankshafts, camshafts, constant velocity joints, and axle shafts (Figure 1a). The procedure for the evaluation of metallurgical characteristics is carried out in the laboratory and is destructive testing (Bernard, “Methods of Measuring Case Depth in Steels”). This means the component will be unusable. Additionally, this procedure is time-consuming, expensive, and cannot be integrated into the production line. Over time, the industry has sought faster and more efficient methods to evaluate metallurgical characteristics, such as eddy current testing, magnetic methods, and ultrasound. Having the capability of monitoring material properties after each key process can help minimize the cost of processing out-of-specification material. A combination of nondestructive testing methods can help to guarantee the quality of induction heat treatment operations (ASM Handbook, vol 4c).  

Ultrasonic methods, for example, can be used to determine microstructural differences in metals. For this, contact testing with pulse-echo technique is used. For inductive-hardened parts, the ultrasonic backscattering method works because the hardened layer (martensite) is almost transparent to ultrasonic waves (in range of 20 MHz), while bulk material (ferrite-pearlite) scatters ultrasonic waves very strongly.  

In this article, we will address the use of industrial ultrasound applying the backscattering technique, which offers a direct determination of the depth. This method is simple and does not require prior calibration to evaluate the components (Figure 1b). 

The Ultrasonic Backscattering Technique  

Figure 2a. Ultrasonic backscattering technique (top)
Figure 2b. Time-of-flight measurement (bottom)

Iron crystals exhibit notable acoustic anisotropy, meaning the acoustic velocity (c) varies depending on the direction of travel within the crystal. Grain boundaries represent transitions between crystal structures with varying orientations. The resulting variation in impedance causes the ultrasonic pulse to scatter at the grain boundaries. The ultrasonic technique for measuring hardness depths (SHD) utilizes this grain boundary scattering effect. This technique is known as the ultrasonic backscattering method (Kruger et al., “Broadband Ultrasonic Backscattering”).  

The ultrasonic backscattering method for hardness depth testing relies on finding the ultrasound frequency that does not scatter at the fine-grained hardened microstructure of the outer layer but at the coarse-grained core material (Figure 2a). The different scattering properties from the varied grain sizes of the hardened surface layer and the core material are seen in the backscattering measurement. The connection between scattering and the material’s grain size is utilized to produce a detectable backscattering echo when the ultrasound penetrates the core material.  

The depth (SHDUS) of the interface can be determined using the time (t) it takes for the sound pulse to reach the scattering interface, the angle of the shear wave (βT), and the velocity (c) of the shear wave in steel. Therefore, the following equation is relevant for a flat shape:  

SHDUS=1/2∙c∙t∙cos∙βT  

Based on this equation, the acoustically measured surface hardness depth (SHDUS) is always found before the sound exit point of the probe wedge. To guarantee an accurate measurement of this location during destructive testing, this distance (A) must be calculated. The next equation is used for a plane geometry:  

A=1/2∙c∙t∙sin∙βT  

The backscattered ultrasonic amplitude depends on the actual gradient of the microstructure. In the transition zone, grain boundaries, grain size, and second phases change the acoustic impedance value discontinuously, depending on the ultrasonic frequency. Different backscattering signals in the hardened and bulk material occur (Yanming Guo, “Effects of material”). Th ese amplitude characteristics can be used to evaluate the case depth by using simple time-of-flight measurements (Figure 2b). Contact testing is generally done by using portable equipment, using a contact wedge where the transducer is mounted to be inclined at a certain angle, and shear waves are emitted into the component. Ultrasonic backscatter takes place at the surface of the component due to surface roughness and results in the return of the energy to the transducer (first echo). Ultrasonic energy enters the hardened surface layer made of fine martensitic structure, and thus, no scatter of ultrasonic waves takes place in this region. However, when the shear waves reach the transition zone where martensitic structure is gradually converted into ferrite-pearlite structure, which has a larger grain size, once again energy is scattered at the grain boundaries, and the transition zone backscatter forms the second echo. The difference in time-of-flight of these two echoes is proportional to the case depth of the component. 

Technical Requirements  

Technical requirements for testing hardness depth using the ultrasonic backscattering method will produce optimal results in the following conditions:  

  • The test parts should be induction-hardened.  
  • The test parts must be forged, not cast.  
  • There is minimal or no microstructure present between the hardened martensitic microstructure and the core material. 
  • The grain size of the core material is significantly larger than the grain size of the hardened microstructure, leading to considerable backscattering of shear waves at a frequency of 20 MHz. 
  • The minimum hardness depth that can be measured is 1.2 mm. Smaller hardness depths need special considerations, such as adjustments to the wedge design.  

Practical Correlation Between NDT and DT

Destructive hardness depth testing is a method to determine the thickness of the case depth of hardened parts. In the process, the parts are destroyed, or their surface is altered rendering each tested part unusable. Hardness depth profiles are usually determined by using the Vickers test to measure the hardness of a reference sample at different points in a line from the surface to the core.  

If you compare the acoustically measured surface hardness depth SHDUS with the surface hardness depth measured with destructive methods SHDDT, you will see a basic difference: Independent of the hardness limit and the minimum hardness, the acoustic testing always determines the depth of the core material that has not been affected by the hardening process. As a consequence, this value tends to be slightly higher than the surface hardness depth measured with destructive methods SHDDT. This difference can be compensated by means of a correction term ΔT (“Off set”):  

SHDUS = SHDDT – ΔT  

In the case of hardness curves with rapidly decreasing hardness values just above the interface, the transit time is measured at 20% of the height of the backscattering signal’s amplitude, and the results of the acoustic and the destructive hardness depth tests will match. The reason for this is the slightly shorter sound path in the marginal ray of the divergent sound field, which induces the backscattering echo.  

If cases occur regularly in which the hardness curve deviates significantly from the characteristics, reference tests must be conducted to determine the correction factor ΔT. Reasons for this could be material and/or process related. The calculated correction factor can then be integrated in the respective test task as a test parameter.  

Technical Description and Measurement Highlights  

The manual device includes a four-channel ultrasonic board managed by a software package for program settings, signal processing, reporting, and overall quality assurance requirements. The parts are put together in an industrial notebook meant for tough industrial settings. The probe systems allow testing of components with complex shapes. The wedge of the probe system is adjusted to fit the geometry of the specific test location. Testing can be done before or after machining.  

The primary cause of measurement error is the evaluation of surface position; the shape of the surface signal relies on proper coupling and the operator’s skill. Another source of error is the placement of the marker that indicates the time-of-flight when the pulse hits the interface. The sharper the signal rises, the less the error. Therefore, a shear wave angle as low as reasonable is employed, and scanning in the direction of decreasing SHD is advised. Achievable accuracy of better than ±0.1 mm is possible for standard parts with high-quality surfaces. Nevertheless, the operator must monitor the “good” shape of the A-scan during data collection. Accuracy based on microindentation hardness profiles compared to the backscatter method is slightly lower, estimated at ±0.2 mm on average, based on the material microstructure (Bogaerts et al., “Surface Hardness Depth Measurement”). We are able to test different geometries like crankshafts (Figure 3), camshaft s (Figure 4), tulips (Figure 5), and barshafts (Figure 6), to mention some components. 

Figure 3. Crankshaft
Figure 4. Camshaft
Figure 5. Tulip
Figure 6. Barshaft

Feasibility Testing

Situation: During induction hardening, an unanticipated variation on the case depth was detected on the shaft of an axle bar (Figure 7). We were requested to examine the case depth in this important area using a P3123 Hardness Depth Tester to find out if the case depth met specifications.  

Figure 7. Induction case-depth variation
Figure 8. Axle bar inspection

Results: During the testing, we noted the case depth was insufficient compared to the minimum required case depth of 5.5 mm. This meant all induction hardened parts made before the discovery had to be paused while a complete check of the case depth was performed. All axle bars hardened after the discovery were analyzed (Figure 8), starting with the most recently hardened parts. Case depth was also evaluated by making a microindentation hardness profile in the hardened area, showing a case depth consistent between ultrasound readings with the P3123 and the destructive testing measurements. In Figure 9, we can observe the measurement of the out of specification case depth, and in Figure 10, we have the measurement within specification case depth. 

Hardness depth testers are used for optimizing production parameters, reducing downtimes after inductor changes, fast production control, and quality management. The techniques discussed in this article offer the technical advantages to ensure quality assurance for both steel and induction hardened components. Feasibility testing is required, which can be performed with prompt review of the ultrasound behavior in components. 

Figure 10. Case depth within specification
Figure 9. Case depth out of specification

References  

ASM International. ASM Handbook Volume 4C: Induction Heating and Heat Treatment. 2014.  

Bernard, William J. “Methods of Measuring Case Depth in Steels.” Steel Heat Treating Fundamentals and Processes (2013): 405-416. https://doi.org/10.31399/asm.hb.v04a.a0005795. 

Bogaerts, Mike, Michael Kroening, Paul Kroening, and Tobias Mueller. “Surface Hardness Depth Measurement Using Ultrasound Backscattering.” AM&P Technical Articles 177, no. 8 (2019): 58-62. https://doi.org/10.31399/asm.amp.2019-08.p058. 

Guo, Yanming. “Eff ects of material microstructure and surface geometry on ultrasonic scattering and fl aw detection.” Dissertation, Iowa State University, 2003. 

Kruger, S.E., J.M.A. Rebello, and J. Charlier. “Broadband Ultrasonic Backscattering Applied to Nondestructive Characterization of Materials.” IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 51, no. 7 (2004): 832-838. https://doi.org/10.1109/tu c.2004.1320742.

About The Author:

Jose Miguel Equihua Toral
Head of New Projects and Development
BOINSA Mexico
Manager,
InTech NDT, USA

Jose Miguel Equihua Toral graduated as a mining engineer from Guanajuato University and obtained his Master’s Degree in Engineering from the National Technology Institute of Mexico. He currently works as head of the new projects and development department of BOINSA de Mexico, involved in technological and operational advances in the design, manufacture, and repair of induction coils, as well as advances in the application of non-destructive testing methods for the quality assurance of components for the automotive, agricultural, and energy industries. This experience has led to the formation of InTech NDT, to serve the U.S. market.  

For more information: Contact Jose Miguel Equihua Toral at miguel.equihua@intech-ndt.com. 

Find heat treating products and services when you search on Heat Treat Buyers Guide.Com

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New and Improved Tips for Induction Equipment Longevity

/ INDUCTION HEATING TECHNICAL CONTENT

What is missing from induction heat-treating maintenance? Learn seven methods for improving your induction tooling component performance in today’s article by David Lynch, Vice President of Engineering at Induction Tooling, Inc.

This informative piece was first released in Heat Treat Today’s April 2025 Annual Induction Heating & Melting print edition.

Figure 1. Solid-machined gear tooth scan inductor manufactured on 5-axis CNC machine 

The heat-treating industry is constantly evolving, whether it is due to the influx of AI or the introduction of new materials. The field of induction is not exempt from this constant change. Yet there remains a constant — induction tooling components need to be tough to resist harsh environments comprised of high frequencies, high power, heat, smoke, steam, dirt, oil, quench fluid and additives, and contaminants. It’s been almost four years since we visited the topic of induction tooling equipment longevity and maintenance (see the May 2021 print edition). Amidst the constant change, how do we protect against the same old toxic environment?  

Let’s explore some new methods of improving the performance and longevity of induction tooling components:  

Figure 2. Break-Away bolts designed to fail beneath the washer if over tightened
  1. More than coils — When working to optimize the life of induction equipment, don’t focus solely on the coils. Bus bars, inductors, and quenching equipment are also key to success. 
  2. Austenitic stainless steel — Use austenitic stainless steel for fasteners, fittings, and hose clamps, and remember, non-ferrous is the way to go.  
  3. CNC machining — Manufacturing with a 5-axis CNC machine ensures quality and consistency.  
  4. “Break-Away” bolts — For fasteners, use “Break-Away” bolts on contact surfaces. These bolts are designed to fail beneath the washer if they are overtightened, a design that prevents damage to the threaded insert inside the copper contact.  
  5. Cooling water — For cooling the inductor coil, bus bars, and adapters, reverse osmosis and distilled and deionized water are overkill. Stick with keeping the water below 70°F. This may require a separate cooling supply. Through laboratory experimentation and real-world production trials, it has been proven that lower cooling water temperatures can drastically increase the life of these components, especially in high-volume, high-power, and short cycle applications. In some hard water areas, this may not be possible. Typical cooling-conductivity for the inductor and bus bar is 200–800 microsiemens per centimeter (μS/cm). 
  6. Non-ferrous fittings — Use non-ferrous fittings on cooling and quenching water connections, as well as color-coded hoses.
  7. Cleaning — Design with cleaning in mind. Designing a quench with bolted removable quench plates ensures easy clean out. As the heat-treating industry continues to evolve, our practices and technologies for optimizing the performance and longevity of induction tooling equipment evolve with it. Whether it’s using a new method or revamping a tried-and-true practice, we can continue to produce strong induction tooling components to sustain these harsh environments.
Figure 3. 5-axis CNC machining of water-cooling passages to maximize water flow and minimize sharp transitions
Figure 4. CVJ inductor with non-ferrous fittings and color-coded hoses on cooling and quench water connections
Figure 5. Barrel style OD quench ring with bolted removable quench plates to allow easy clean out
Figure 6. Multi-turn OD scanning inductor with integrated quench featuring removable quench plate for easy clean out
Figure 7. Heavily used inductor

About The Author

David Lynch
Vice President of Engineering
Induction Tooling, Inc.

David Lynch is Vice President of Engineering at Induction Tooling, Inc. He has over 36 years of experience and is the deputy of the ISO quality system. He has created and developed the system and templates being used today for creating and tracking engineering drawings, job history, rate tracking, and job performance. David holds several design patents, has authored several published articles, and has often presented at technical sessions. He enjoys working closely with customers to develop valued solutions across a wide range of induction heating applications from initial design concepts to implementation, customer support, and troubleshooting.

For more information: Contact David Lynch at dlynch@inductiontooling.com.

Find heat treating products and services when you search on Heat Treat Buyers Guide.Com

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