Comparative study of the impact response and microstructure of 304L stainless steel with and without prestrain
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E 304L stainless steel is an attractive engineering material because of its outstanding properties such as corrosion resistance, weldability, high strength, and good formability. The basic properties of 304L stainless steel have been studied and can be found in the materials handbook.[1] Since the strain-rate effect plays an important role in plastic deformation of materials, several investigators have focused on the strain-rate effect for 304L stainless steel at low rates.[2,3] For example, Semiatin and Holbrook[2] presented the workability and isothermal plastic-flow behavior of 304L stainless steel under uniaxial compression and torsional loading under low-rate conditions. Venugopal et al.[3] studied the hot-working behavior and microstructure of 304L stainless steel subjected to low-rate loading at elevated temperatures. Over the past decades, many researchers[4] have indicated that the plastic deformation of materials under dynamic loading is very different from that under static loading. Dynamic plastic behavior is often found during the metal-forming process, vehicular accidents, and unexpected foreign impacts. Products made from 304L steel are not infrequently subjected to dynamic loading. Although some investigators[5–8] have studied the impact and shock-loading behavior of 304-series stainless steel, the data for the 304L steel’s dynamic plastic deformation, mechanical behavior, and associated microstructural evolution are still insufficient. WOEI-SHYAN LEE, Professor and Director of Machine Shop, and CHI-FENG LIN, Graduate Student, are with the Department of Mechanical Engineering, National Cheng Kung University, Tainan 70101, Taiwan, Republic of China. Contact e-mail:[email protected] Manuscript submitted November 1, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
On the other hand, many 304L parts are made by cold working. These processes vary not only the shape, but also the properties of the material. The effect of prestrain on material characteristics has interested many researchers,[9,10] who have indicated that properties such as yield stress, creep behavior, fracture toughness, and microstructure are strongly affected by prestrain. However, little work has been done to clarify the mechanical behavior and microstructure of prestrained 304L under dynamic loading and to analyze the difference between unprestrained and prestrained 304L stainless steel. From a structural design viewpoint, dynamic experimental results are often used to analyze or simulate high-rate deformation under various dynamic loading situations. A constitutive model which adequately describes plastic deformation as a function of strain rate and temperature is necessary. Both empirical and physically based constitutive equations have been proposed by several investigators.[11,12] The Johnson–Cook model and the Zerilli–Armstrong model are usually used in empirical and physically based models, respectively, and successfully describe the dynamic stressstrain behavior of many materials.[13,14] For purposes of computer simulation,
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