Solar Panels (photo source: InterestingEngineering.com)
Sometimes our editors find items that are not exactly "heat treat" but do deal with interesting developments in one of our key markets: aerospace, automotive, medical, energy, or general manufacturing. To celebrate getting to the "fringe" of the weekend, Heat Treat Today presents today's Heat Treat Fringe Friday Best of the Web article on efficient alloy-based solar panels. These solar panels are free of toxic metals and can be implemented in producing electronic devices, buildings, and vehicles.
Check out how scientists from Daegu Gyeongbuk Institute of Science and Technology in South Korea were able to overcome issues of underperformance in this article by Interesting Engineering: "Efficient Alloy-Based Solar Panels Created Free of Toxic Metals."
An excerpt: "'Thin-film solar cells using bronze (Cu-Sn) and brass (Cu-Zn) as base materials are composed of non-toxic earth-abundant materials, and have been studied worldwide because of their low cost, high durability, and sustainability,' said Kang[...] While theoretically they are said to perform as well as top market products, in reality, they severely underperform[...] The scientists looked for a way to bypass these flaws and produce the best quality CZTSSe (copper, zinc, tin, sulfur, and selenium) thin films. They came up with the ingenious solution..."
A Chicago-area automotive part supplier encountered frequent cracking of variable valve timing plates that were sent to a third party for heat treatment. The problem resulted in the company spending lots of time and money on part testing as well as wasting lots of steel. After a thorough examination of the manufacture and heat treatment of the parts, Paulo metallurgists identified the cause of the cracking and recommended a custom solution to keep it from happening in the future. The following is a case study on the part failure investigation and resolution by Rob Simons.
Case study of a part failure investigation and resolution
Being an integral part of customers’ success means more than just regularly receiving parts and treating them according to spec.
Sometimes a customer approaches a heat treater in search of answers to a problem they can’t quite grasp.
In this case, a Chicago-area supplier of automotive components needed to know why parts it sent off for heat treating kept coming back cracked. They were spending too much time and resources on tests and throwing out too many failed parts.
Persistent cracks in variable timing plates
Our customer produces variable valve timing plates for domestic automobile models. Variable valve timing (VVT) plates are part of a system designed to optimize engine performance by changing the lift, duration, and timing of valve lift events.
Variable Valve Timing Plates (Photo credit: Underhood Service http://www.underhoodservice.com/variable-valve-timing/)
In this case, the life cycle of these parts began in a steel mill, where coils of AISI 1045 carbon steel were produced. The parts were then annealed in preparation for fine blanking at our customer’s facility. Then, the parts would be through hardened and sent to the automotive manufacturer.
But our customer noticed that many of the parts came back cracked. This was the source of two big problems:
The customer had to perform inspections on every part that was returned from the heat treater, which came at significant expense of time and resources.
To satisfy the terms of its contract with the automotive manufacturer, our customer had to make far more parts than it would have ordinarily needed to on the assumption that many of the parts would not be acceptable. It cost too much money, and too much steel was wasted.
The customer approached metallurgists at Paulo to figure out what was wrong and what could be done to make it right.
Forensic heat treatment analysis
Our first task was to figure out what the customer’s heat treater was doing to the parts.
Upon our inspection, we noticed the parts were quite brittle. A closer look at the microstructure of the parts’ surfaces revealed they had been carbonitrided.
Meanwhile, we consulted with personnel at the mill and steel processor where the steel originated. We learned that the coils of 1045 steel were annealed in a nitrogen environment. Annealing is an important process that spheroidizes carbides in the steel which aids in fine blanking. In the case of our customer, the VVT plates could not be formed to the specified tolerance if they weren’t first annealed.
But the nitrogen present in the anneal was a problem. 1045 steel includes aluminum as a grain refining element. When aluminum and nitrogen combine during annealing, aluminum nitrides form. Aluminum nitrides create a much finer grain on the part surface, which prevents the full hardening of the material. We suspected our customer’s heat treater attempted to overcome the defect by carbonitriding. But instead of hardening, the parts just got brittle. That’s because 1045 steel lacks the hardenability that would be required to overcome the fine grain size that resulted from the presence of aluminum nitrides.
To confirm our suspicion, we ordered the same material from the customer’s mill and then carbonitrided the parts as we believed the previous heat treater had. Our post-treatment analysis of the parts shows the successful recreation of the failure mode.
A custom-developed solution
We believed the most direct way to solve the problem was to eliminate the factors that caused it at the start. We again approached the mill, this time to see if they could anneal the steel in a different environment. They said they could not.
The next best thing would be to “spike” the 1045 steel with another alloying element that would add hardenability despite the fine grain sizes that result when nitrogen and aluminum interact during annealing. We pinpointed chromium as the ideal alloy, and after some trial and error, we identified a formula for the chromium spike that would result in fully-hardened parts without cracks after through hardening.
Today, the customer’s mill still produces the 1045 steel with our recommended chromium spike. And as of mid-2018, we’ve treated 25 million variable valve timing plates for this customer.
This case study illustrates the importance of a few key lessons suppliers should keep in mind. First, stay in touch with what’s going on further up the supply chain. You may be able to react to problems more quickly or stop them altogether.
Second, have a working knowledge of part materials and the chemistry at play during any manufacturing process. Armed with this knowledge, you can ask key questions as you vet potential heat treatment partners. It could end up saving you time and expense in the long run.
Finally, know where to get a second opinion, and have a backup heat treater ready in case your primary partner can’t do what you need them to do.
Rob Simons is a metallurgical engineer specializing in ferrous heat treatments with 35 years of experience in the industry. He earned a degree in metallurgical engineering from the University of Missouri – Rolla in 1982 and most recently was a featured presenter at the ASM Heat Treat 2017 conference. He has been at Paulo for over 30 years.
When steel needs to be softened to alter ductility, toughness, or properties, or to produce a specific microstructure, a heat treater can turn to any one or combination of processes to suit the material or the application.
Metlab Heat Treat’s primer series includes a short explanation of the options available, whether it is
annealing, which “removes the internal stresses, which build up as a result of cold working and other fabrication processes;”
protective atmosphere normalizing, which “refines the grain size and enhances the uniformity of the microstructure;” or
spheroidize annealing, which “is generally done on parts which have been work hardened, to allow them to be further worked, either rolled in the case of coils, or drawn for wire.”
1.) Load of torsion bars, manufactured from 4340 steel, normalized in the vertical position to maintain straightness. Parts measure approximately 3\” in diameter by 6\’ long.
2.) 26,000 pounds of low carbon steel flat wire being prepared for spheroidize annealing. Spheroidize annealing is an intermediate processing step to allow the wire to be further rolled to a smaller gage without cracking.
Heat treating more often than not includes the process of annealing in order to induce precise softness; to alter ductility, strength, or properties; or to produce a definite microstructure. Because of the wide variety of steels and metal alloys, it is important for heat treaters to match the correct annealing process with the steel grade and to the application of the parts being treated.
Machine Manufacturing has provided a summary of the annealing process and listed seven types of annealing, describing the process and the objectives for each. Included in the list are:
And to take the analysis into more specific types of annealing, over at Knergize.com, Dr. S.B. Sarkar discusses Spheroidized Annealing and its benefit to bearing manufacturers, describing the metallurgical science behind the process, noting the need to adhere to international standards and specifications, and addressing equipment management and quality control of the process.
Researchers at Toyohashi University of Technology have collaborated with their counterparts at Massachusetts Institute of Technology (MIT) to develop a new material capable of retaining high transmissivity after annealing at 850°C (1562°F). The results address the challenge manufacturers face when combining different materials that react differently to heat treatment at certain temperatures.
BILSTEIN CEE a.s, based in the Czech Republic, is part of the globally active BILSTEIN GROUP. The BILSTEIN GROUP produces various grades of high-quality cold rolled strip for a wide variety of applications.
Two years ago an order was placed with EBNER to supply a HICON/H2® bell annealer facility to heat treat steel strip coils, comprising four workbases.
Although this facility was commissioned successfully less than one year ago, BILSTEIN CEE a.s. awarded EBNER the contract for the expansion of this facility by a further three workbases.
The new workbases will be commissioned in 2017, increasing production by about 60%.
Direct-chill (DC) casting is currently the most common semi-continuous casting practice in non-ferrous metallurgy. The process is characterized by molten metal being fed through a bottomless water cooled mould where it is sufficiently solidified around the outer surface that it takes the shape of the mould and acquires sufficient mechanical strength to contain the molten core at the centre. As the ingot emerges from the mould, water impinges directly from the mould to the ingot surface (direct chill), falls over the cast surface and completes the solidification.
Source: Interesting Engineering
