Impact Response and Microstructural Evolution of 316L Stainless Steel under Ambient and Elevated Temperature Conditions
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316L stainless steel (SS) has many advantageous properties, including a high strength at elevated temperatures, excellent corrosion resistance, and an enhanced resistance to sensitization and intergranular cracking. As a result, it is widely used as a structural material in the chemical, petrochemical, power engineering, automobile, and aviation industries.[1] The mechanical properties, fatigue behavior, and corrosion characteristics of 316L SS under high temperatures and static or quasi-static loading conditions are well documented.[2–5] However, 316L SS components are commonly subjected to high strain rates and temperatures during their fabrication and/or service lives. Thus, to ensure the mechanical integrity of 316L SS components under realistic fabrication and service life conditions, it is necessary to investigate the impact properties and microstructure of 316L SS over a wide range of temperatures and strain rates. In most materials, the flow stress increases significantly with increasing strain rate or decreasing temperature.[6–8] Several mechanisms have been proposed to describe this high strain rate loading behavior.[9–12] WOEI-SHYAN LEE, Distinguished Professor, and WEN-ZHEN LUO, Graduate Student, are with the Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan, R.O.C. Contact e-mail: [email protected] TAO-HSING CHEN, Assistant Professor, is with the Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan, R.O.C. CHI-FENG LIN, Associate Researcher, is with the National Center for High-Performance Computing, Hsin-Shi Tainan County 744, Taiwan, R.O.C. Manuscript submitted June 18, 2011. Article published online May 30, 2012 3998—VOLUME 43A, NOVEMBER 2012
Microscopically, the deformed microstructure of 316L SS can be characterized by the distribution and density of the dislocations, the formation of twins, and the volume fraction of transformed martensite. The dislocations within the deformed microstructure may form loops, accumulate at the grain boundaries, or arrange themselves into different types of cells, thereby resulting in a strengthening effect.[13–16] In addition to dislocation slip, twinning is also an important deformation mechanism under high strain rate loading conditions, particularly in low stacking fault energy alloys such as 316L SS. Previous studies have shown that the formation of mechanical twins enhances the strength of metals.[17,18] Furthermore, the formation of deformation twins in alloys increases at high strain rates and/or low temperatures.[19–21] Because 316L SS contains thermodynamically metastable austenite, a¢ martensite is readily formed during plastic deformation. As a result, a significant strengthening effect occurs.[22,23] However, martensite transformation is suppressed at higher strain rates because of a deformation-induced adiabatic heating effect.[24] The impact response of 316L SS was examined in a recent study by the present group.[25] However, the correlation betwee
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