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Solar Atmospheres Inc.
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New Medical Heat Treat Process Developed for Bright Stainless Steel
SOUDERTON, Pa.—Using advanced gas cooling technology, Solar Atmospheres has developed a unique three-step heat treat process to austenite condition, in situ cool, and bright-age harden 17-7 precipitation hardenable (PH) stainless steel in a vacuum furnace without breaking vacuum. Company representatives say that this is a highly desirable development because it is difficult to keep 17-7 bright during the PH treatment after breaking vacuum and exposing parts to the ambient atmosphere required for adequate cooling, where it can discolor due to oxidation.
Solar Atmospheres worked with the medical industry to develop a new in situ process where desirable mechanical properties could be consistently obtained. With this new process, a new medical device design could be based on the established set of mechanical properties, and the medical company would reap the benefit of reduced costs owing to reduced pricing associated with the new in situ, three-step process.
The 17-7 PH stainless steel is classified as a semi-austenitic stainless steel that has expansive use in aerospace and growing new applications in the medical industry. The reason for this is 17-7 PH's attractive combination of properties, including very high, spring-like strength, good ductility, and excellent corrosion resistance due to its high alloy content. In order to obtain these properties, however, 17-7 must be heat treated in a more controlled manner than many other alloys.
Even within these controlled parameters, flexibility exists to obtain attractive properties other than those classified as standard PH conditions. Solar Atmospheres performed a recent study that showed its vacuum heat treatment technology offers a unique processing advantage to achieving these highly desirable properties. As a baseline, the new set of mechanical properties and microstructure characteristics were compared to standard Condition TH 1050, the most common condition specified in industry for 17-7 PH.
A three-step austenite conditioning, in situ cooling and precipitation hardening process resulted in a new condition of 17-7 that Solar Atmospheres has coined SH 950. Compared to 17-7 Condition TH 1050, Condition SH 950 showed comparable yield strength, higher tensile strength, and, on average, twice the ductility. These tensile properties were obtained with two different heats of steel with three tensile specimens tested for both heats and conditions, resulting in 12 separate tensile test results. The findings are both consistent and inspiring, according to company representatives. The microstructure of SH 950 also appeared superior with respect to lower delta ferrite stringers being present.
The positive results associated with Solar Atmosphere's Condition SH 950 for 17-7 stainless steel indicate that a new medical device design could be based on the newly established range of mechanical properties. This new vacuum heat treatment technology offers a unique processing advantage for achieving desirable properties while cost effectively producing bright, non-discolored parts, company representatives say.
Solar Atmospheres (www.solaratm.com), a major provider of commercial vacuum heat treating services, offers thermal processing that is said to produce bright, scale-free parts with minimal distortion. The company has an in-house R&D team of metallurgists and scientists who work to develop innovative, custom process solutions. Solar Atmospheres serves more than 18 markets, offering services that include vacuum brazing, carburizing, nitriding, and advanced processing of raw materials, such as titanium, tantalum, and nano powders. The company also operates plants in Hermitage, Pa., near Pittsburgh, and in Fontana, Calif., near Los Angeles.
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