New Medical Heat Treat Process for Bright 17-7 PH Stainless Steel Souderton, PA. August 22, 2014 – Using advanced gas cooling technology and out-of-the-box thinking, Solar Atmospheres has developed a unique three-step process to austenite condition, transform, and bright age harden 17-7 precipitation hardenable (PH) stainless steel without removing the material from the furnace for transformation. 17-7 PH 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. Interestingly, even within these controlled parameters, flexibility exists to obtain attractive properties other than those classified as the standard RH and TH conditions. By adjusting the austenite conditioning temperature to raise the martensite finish (Mf) temperature to its highest theoretical point, in situ cooling to fully transform the material is now possible using Solar’s advanced technology. As a baseline, the new set of mechanical properties and microstructure characteristics were compared to standard Condition TH1050, likely the most common condition specified in industry for 17-7 PH. Solar Atmospheres has coined the new condition “SH950.” Compared to 17-7 PH Condition TH1050, Condition SH950 shows comparable yield strength, higher tensile strength, and on average twice the ductility. The 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. The microstructure of SH950 also appeared superior with respect to lower delta ferrite stringers being present. There are two reasons why the continuous process is desirable. First, in order for 17-7 PH heat treated to the TH condition to fully transform from the austenite conditioning temperature one must cool to below 60°F (Mf) which is not practical inside a vacuum furnace. Therefore the product must be removed from the furnace and cooled (sometimes artificially in a freezer or cooler) to obtain transformation. This takes time and requires additional equipment. Solar’s SH condition eliminates the removal requirement due to the Mf being higher than 60°F. The second reason Solar’s continuous process is desirable is that by removing the parts from the furnace the risk of discoloration is increased as water vapor is reintroduced into the vacuum furnace upon unloading and reloading. Solar’s continuous process reduces this risk. The positive results associated with Solar’s Condition SH950 for 17-7 PH indicate that a new medical device design could be based on the newly established range of mechanical properties while reducing both the risk of discoloration and the cost of heat treating. For more information on this new process contact Don Jordan, Corporate Metallurgist at don@solaratm or 215-721-1502 x1206. ABOUT SOLAR ATMOSPHERES Solar Atmospheres is one of the world’s largest providers of commercial vacuum heat treating services. Through unmatched technical expertise, equipment, and quality assurance, Solars thermal processing produces bright, scale-free parts with minimal distortion. For clients requiring an out-of-the ordinary application, an in-house R&D team of metallurgists and scientists develop innovative, custom process solutions. Serving over 18 markets, Solars state-of-the art services include vacuum brazing, carburizing, nitriding and advanced processing of raw materials such as titanium, tantalum, niobium and tungsten. With over 50 furnaces ranging from laboratory furnaces to the world’s largest commercial vacuum furnaces, Solar can efficiently handle any size job. Headquartered in Souderton, near Philadelphia, Solar also operates plants in Hermitage, near Pittsburgh, and in Fontana, California, near Los Angeles. Please visit solaratm for more information. ###
Posted on: Mon, 25 Aug 2014 18:09:20 +0000
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