Since a blog is usually some way for the author to try and educate readers about some topic, let’s start the New Year with busting some widely held misconceptions about heat treating in general, and flame hardening in particular.
Very often larger companies have inhouse staff engineers responsible for figuring out the machinery needed to process parts throughout the production line. These P.E.’s usually have good mechanical and spatial skills, but invariably lack the specialized knowledge of heat treating. We have heard more than once, after being called in to redesign a process that couldn’t be salvaged, the engineers didn’t think the heat treating process was that complicated. “You’re just throwing some heat at it,” we’ve heard again and again.
Jorgensen Forge, a Tukwila, WA, open-die forger and ring-rolling operation, has emerged from Chapter 11 bankruptcy as one of three companies now owned by CE Star Holdings LLC, a company formed to buy the assets from Constellation Enterprises, which filed for creditor protection in May.
The Seattle-area plant forges low alloy and stainless grades of steel, aluminum alloys, titanium alloys, and nickel-based alloys. Production equipment includes four open-die presses and two ring-rolling mills. It also offers heat-treating and machining, and it has special capabilities for “marine shafting” as well as full testing and inspection services. Its customers are manufacturers supplying aerospace, energy, defense, and general industrial markets.
Effective furnace scheduling requires the inclusion of several key elements.
“Customer” Demands: Manufacturers with in-house heat treat departments have internal customers who, like customers the world over have one thing in common, they want to provide parts to you tomorrow and have them processed and ready yesterday. These internal customers cause frustration and angst but their work is what pays the bills.
Product & Process Variables: There are numerous product and furnace process variables all of which must be considered when scheduling. Common variables include:
Material grade and chemistry
Atmosphere carbon potential
Hardening and tempering furnace temperatures
Ammonia addition for carbonitriding and the purge time required when finished
Belt speeds
Cycle times
Variable quench programs
Process changes are necessary but minimizing the degree of variation between consecutive product runs is the goal. The more significant the change, the longer the gap time required to allow the furnace to stabilize with the new furnace parameters. Gap time is an unrecoverable cost – wasted time and money.
Sample Furnace Scheduling Sheet
Sample Furnace Scheduling Sheet
Quality issues can also be caused by not allowing sufficient time between significant process parameter changes. If the proper gap time is not provided, the end of one lot or the beginning of the next may experience quality issues.
Each heat treat department must determine the balance of efficiency and customer service that works best for their operation.
Developing a close working partnership with your internal customers is beneficial for both parties. Heat treating is typically at or near the end of the manufacturing cycle and all the lead time has been utilized by the previous steps. Teach them the basics of your operation and explain the ways they can help you provide better service and delivery. By providing as much information as possible about their delivery requirements, you can schedule to meet their demands.
Rush jobs are the nature of the business and will always be with us. They are inevitable but they can be reduced. I know of one customer who provided parts at 3:00 PM and asked for impossible results for the next morning. After numerous conversations with the heat treat department, the part supplier finally understood the heat treat process and now allows one, two, or even 3 days for results. Encourage part suppliers to give you next week’s Hot List at the end of the current week.
Heat treat scheduling is never easy but it can be improved to help your operation.
About Young Metallurgical Consulting
Young Metallurgical Consulting works with in-house heat treat departments to teach the day-to-day processes necessary to manage and improve their area of operation. In-house heat treaters will learn the aspects of heat treating that are not taught in a classroom and can only be gained through direct, hands-on experience. Contact John Young at john@youngmetallurgicalconsulting.com.
Dr. Arvind Thekdi, an Energy Expert for the U.S. Department of Energy, routinely conducts energy assessments to improve energy efficiency of process heating systems at industrial plants. During the assessments, he often encounters questions that indicate confusion about how process heating systems operate. In this article, Dr. Thekdi provides some basic information about process heating systems, and offers solutions for reducing heat losses to increase efficiency.
“While some heat treatments are used to soften the material or improve its machinability, most are processed to obtain strengthened or hardened properties. The majority of heat treatments apply to metallic materials and, typically, the techniques include annealing, normalizing, quenching, tempering, precipitation strengthening, surface hardening, and case hardening. Heat treatment is so critically important that we can safely say a part undergoing extensive manufacturing processes such as melting, rolling, forging, and other related machining is of little or no value without the necessary and appropriate heat treatment.”
Steel is primarily iron with up to 1% carbon, plus other alloying additions (generally totalling less than 5%).
A steel composition can be thought of as a recipe; different amounts of each ingredient make up your final product. In steel these ingredients are known as alloying additions and can affect the steel in different ways. We can affect the:
Properties of steels.
strength
hardness
toughness
ductility
fatigue
formability
machinability
weldability, and
corrosion resistance.
The addition of carbon to iron is probably the most important addition in steels which makes ‘The Iron Carbon Equilibrium Diagram’ very useful. Equilibrium means that enough time has been allowed on heating and cooling for any reactions to fully complete.
Typical Iron Carbon Diagram
In a steel <723°C, different structures are present and depending on the carbon content we can have at <0.8% Carbon – ferrite and pearlite, at 0.8% carbon – pearlite and >0.8% carbon – pearlite and cementite.
While the iron carbon diagram describes the structures of steel under equilibrium conditions, two further diagrams can be used when faster cooling rates are used; these are the CCT (continuous cooling transformation) diagram and the TTT (time temperature transformation) diagram. Both of these diagrams are helpful in selecting the optimum steel and process parameters.
When we cool a steel at faster cooling rates we can achieve additional structures, these can be bainite and martensite. CCT and TTT help determine the structures achieved.
In metallurgy the hardenability of a steel is a key parameter and when we talk about hardenability in steels we are often describing how deep into the steel we can achieve hardening. If a steel is described as having a low hardenability this will mean that the steel will produce a shallower depth of hardness. Hardenability is not to be mistaken for hardness; when describing the hardness we are often looking at the microstructure achieved during cooling. For a given steel it can be assumed that the quicker the cooling rate the greater the chance of achieving a harder structure and if that steel has a high hardenability this hard structure will be present deeper into the thickness.
In metals there are atomic defects called dislocations, these dislocations reduce the strength of the metal. The principle of strengthening mechanisms is to reduce the ability of these dislocations to move through the metal, this can be achieved by:
Atomic dislocations within the metal potentially reduce the metal’s strength.
Grain Size; the grains can interact with the dislocations preventing further movement. If we reduce the grain size we can increase the number of grains interacting with the dislocations, preventing movement and thus strengthening the metal.
Cold work introduces a large amount of strain into the metal; this strain interacts with the dislocations strain field, impeding the movement of the dislocations.
Solid solution strengthening is applied when we add other chemical elements to a metal. Addition of these elements can either be called interstitial or substitutional solid solution strengthening and will cause distortion in the atomic structure, restricting the dislocation movement and strengthening the steel.
Dispersion or precipitation strengthening is highly related to the structure of the metal and takes place when a phase is finely precipitated through a softer matrix. This precipitate acts as a barrier to dislocation movement.
The next in the series will be Steel Making and Casting.
WATERLOO, IA—Advanced Heat Treat Corp. (AHT) recently announced that it has received a Federal Firearms License (FFL) issued by the U.S. Department of Justice, Bureau of Alcohol, Tobacco, Firearms and Explosives at their facility in Monroe, Michigan. AHT now has licenses at all four of the company’s locations in Iowa, Alabama and most recently, Michigan. All licenses are available to view or download on the Quality section of their website: www.ahtcorp.com under the “About” section.
“While we are no stranger to processing firearms, the addition of this license will allow us to better serve those customers whose parts require an FFL,” stated Gary Sharp, President and CEO. “Our firearm customers have recently experienced better lubricity and corrosion resistance with one of our trademarked processes, UltraOx®, so we wanted to be better equipped to handle all of their parts for aesthetics and consistency. We are excited to now be able to expand that offering to our Michigan customers.”
The London-based metals trading and manufacturing company Liberty House Group (LHG) has launched a metal recycling business called Liberty Metal Recycling (LMR), which it says is a step toward it achieving its Greensteel vision to create a competitive and sustainable steel sector in the United Kingdom.
Source: Flame Treating Systems
“Customer” Demands: Manufacturers with in-house heat treat departments have internal customers who, like customers the world over have one thing in common, they want to provide parts to you tomorrow and have them processed and ready yesterday. These internal customers cause frustration and angst but their work is what pays the bills.
