Effect of Grain Size on Dynamic Recrystallization and Hot-Ductility Behaviors in High-Nitrogen CrMn Austenitic Stainless
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TRODUCTION
HIGH-NITROGEN CrMn austenitic stainless steel (HNAS) has an interesting combination of mechanical, chemical, and physical properties: high strength and toughness, good corrosion resistance, and low magnetic susceptibility.[1] It has been widely used in the energy industries. However, surface cracks and coarse-grained and mixed-grain structures occur easily during the hotworking process of HNAS, leading to high production costs and low efficiency.[2,3] Dynamic recrystallization (DRX) is a characteristic phenomenon of medium- and low-stacking-fault energy metallic materials during the hot-forming process and is of importance for two main reasons. The first is to soften and restore material ductility. The second is to control the grain structure by replacing initial coarse grains with small DRX grains.[4] Therefore, a study of ZHENHUA WANG, Associate Professor, is with the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, P.R. China, and also with the Key Laboratory of Advanced Forging & Stamping Technology and Science, Yanshan University, Ministry of Education of China. SHUHUA SUN and WANTANG FU, Professors, and BO WANG and RONGHUA ZHANG, Students, are with the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University. Contact e-mail: [email protected]; [email protected] ZHONGPING SHI, Student, is with the Key Laboratory of Advanced Forging & Stamping Technology and Science, Yanshan University, Ministry of Education of China. Manuscript submitted January 4, 2014. Article published online April 5, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
factors affecting DRX in HNAS can promote the use of it to a large extent. Wang et al.,[2] Lang et al.,[5] and Hong et al.[6] investigated the effect of deformation parameters on the DRX behaviors of HNASs. Grain size as well as deformation parameters also influences the DRX behaviors.[7–13] However, limited information exists in the published literatures related to the grain size effect on the DRX and hot ductility behaviors in HNAS. In fact, the effect of grain size on DRX in metallic materials is still being debated. In terms of DRX mechanism, Manshadi and Hodgson[8] found an interesting transition from ordinary to continuous DRX with a decrease in the initial grain size. However, Jafari and Najafizadeh[14] summarized that fine-grained initial structure favors ordinary DRX. In terms of DRX grain size, for high-purity[7] and ordinary[8,9] 304 austenitic stainless steels, the DRX grains evolved in fine-grained specimens are much smaller than those in the coarsegrained specimens. However, there is no major difference in DRX grain size between the two initial grain sizes in ultrahigh-purity 304 austenitic stainless steel.[7] This phenomenon also exists in some ordinary 304 austenitic stainless steels[10,11] and in Mg alloy.[12] In contrast, the initial coarse-grained material results in a finer DRX grain size than material with a finer starting microstructure in pure Ni.[13] In this study, the depe
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