Evolutions of Microstructure and Properties During Cold Rolling of 19Cr Duplex Stainless Steel
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TRODUCTION
DUPLEX stainless steels (DSSs) with dual-phase microstructure, ferrite (a) and austenite (c), have attracted great interest of the researchers because of their advantages due to the combination of both ferrite and austenite phases. They could exhibit excellent combination of mechanical properties and corrosion resistance, especially pitting resistance in chloride solution.[1–4] Therefore, these types of stainless steels are suitable for many applications, such as oil and gas, petrochemical,[5,6] pulp and paper, and pollution control industries.[7,8] Conventional DSSs usually contain high amounts of expensive alloying elements such as chromium, nickel, and molybdenum to meet the requirements in terms of microstructure and properties.[9] Meanwhile, excellent mechanical properties are also achieved by solid solution hardening of substitutional elements. However, many efforts have been made to develop novel DSSs with lower expensive alloying elements in the past several decades, especially nickel and molybdenum, which are called as lean DSSs. These alloys have QINGXUAN RAN, WANJIAN XU, and ZHAOYU WU, Ph.D. Candidates, JUN LI, Assistant Professor, and YULAI XU, Postdoctoral Student, are with the Laboratory for Microstructures, Institute of Materials, Shanghai University, Shanghai 200072, China. XUESHAN XIAO, Professor, is with the Institute of Materials, Shanghai University, and Shanghai University Xinghua Institute of Special Stainless Steels, Jiangsu 225721, China. Contact e-mail: [email protected] JINCHENG HU and LAIZHU JIANG, Senior Engineers, are with Baoshan Iron & Steel Co., Ltd., Shanghai, 200431, China. Manuscript submitted August 30, 2015. Article published online July 18, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
attracted much attention due to their lower price, higher strength, and better corrosion resistance compared to conventional AISI 304 austenitic stainless steel.[10–12] Therefore, these types of DSSs have enormous application potential, which underlines the need for much deeper research. Recently, researchers have already designed some lean DSSs which could exhibit better mechanical properties than conventional ones, especially in ductility. Herrera et al.[13] have reported a novel Mn-based lean DSS, which had an ultimate tensile strength of 1 GPa and an elongation of about 60 pct with a sequential martensite transformation of c fi e-martensite fi a¢-martensite during tensile deformation. Induced martensite nucleated not only at in-grain e-martensite band intersections but also at austenite grain boundaries and annealing twin boundaries. Choi et al.[14] found that lean DSSs with higher nitrogen content could exhibit higher strength and ductility because of transformation-induced plasticity (TRIP) effect in austenite phase and additional solid-solution strengthening of nitrogen. Transformation process of metastable austenite to martensite occurred in a wide region due to the improvement of austenite stability by increasing annealing temperature.[15] We have also reported a series of
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