Tensile and fatigue properties of 17-4 PH stainless steel at high temperatures
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PRECIPITATION-HARDENING stainless steels have been widely used as structural components for various applications, such as nuclear, chemical, aircraft, and naval industries, due to their excellent mechanical properties, good fabrication characteristics, and excellent corrosion resistance. Of the former, 17-4 PH* stainless steel is currently *17-4 PH is a trademark of the Armco Steel Corporation, Pittsburgh, PA.
one of the most commonly used alloys in this type.[1] The alloy 17-4 PH is a typical martensitic precipitation-hardening stainless steel and is most often supplied from the mill in the solution-annealed condition (condition A), in which the microstructure is comprised of low-carbon equiaxed martensite and up to several volume percent of ␦ -ferrite stringers.[1,2,3] By applying suitable heat treatments in the temperature range of 482 ⬚C to 621 ⬚C (900 ⬚F to 1150 ⬚F), a wide range of mechanical properties can be obtained for this type of stainless steel.[1,3–7] The maximum strength and hardness values are obtained after aging at 450 ⬚C to 510 ⬚C, by which the precipitation of coherent copper-rich clusters occurs.[1,3,4] Aging at higher temperatures (above 540 ⬚C) would result in the precipitation of incoherent fcc copperrich precipitates, lower strength and hardness, and an enhancement in toughness.[1,3,4] Most of the previous investigations on 17-4 PH were concentrated on the analyses of the microstructural, mechanical, and fatigue properties at room temperature;[2,3,8–13] little work has been on the high-temperature mechanical and fatigue properties of this alloy. Although a few studies on the high-temperature characteristics of the 17-4 PH alloy have been reported,[8,14] the emphasis in those investigations
JUI-HUNG WU, Graduate Research Assistant, and CHIH-KUANG LIN, Professor, are with the Department of Mechanical Engineering, National Central University, Chung-Li 32054, Taiwan R.O.C. Contact e-mail: [email protected] Manuscript submitted August 7, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
was on the effect of embrittlement, caused by long-term aging at 300 ⬚C to 400 ⬚C, on the mechanical properties. As some applications of 17-4 PH stainless steels are subjected to long-term cyclic loading at high temperatures, it is important to characterize the high-temperature fatigue behavior and associated microstructural variation of this alloy in order to better predict the fatigue lifetime for components made from this material. The objective of this study is, macroscopically and microscopically, to characterize the effect of environmental temperature on the tensile and fatigue properties of variously heat-treated 17-4 PH stainless steels by systematic experiments. Tensile tests with different hold times at temperature and high-cycle fatigue tests were conducted at room temperature, 200 ⬚C, 300 ⬚C, and 400 ⬚C for 17-4 PH steels in the solution-annealed (condition A), peak-aged (condition H900), and overaged (condition H1150) conditions, in order to study the variation of tensile and fatigue strength wi
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