Development of TRIP-Aided Lean Duplex Stainless Steel by Twin-Roll Strip Casting and Its Deformation Mechanism
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DUPLEX stainless steels (DSS), which possess an excellent combination of corrosion resistance and mechanical properties, are widely applied to many industrial fields such as pollution control, oil and gas, petrochemical, and ocean engineering.[1–3] In order to further reduce the cost and increase strength, lean duplex stainless steels, in which nickel is partially or completely replaced by manganese and nitrogen, are being developed. Wang et al. validated the feasibility of replacing nickel with manganese and nitrogen and reported that Ni-free DSS (Fe-20Cr-10Mn-3Mo-N) had the tensile strength of at least 750 MPa and an ultimate elongation of about 40 pct.[4] In numerous modern applications including automobile industries, structural steels are required to possess ultra-high product of strength and elongation, together YAN ZHAO and WEINA ZHANG, Ph.D. Students, XIN LIU, Master Student, and ZHENYU LIU and GUODONG WANG, Professors, are with the State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, P.R. China Contact e-mail: [email protected] Manuscript submitted April 7, 2016. Article published online October 4, 2016 6292—VOLUME 47A, DECEMBER 2016
with low ratio between yielding strength and tensile strength for good formability.[5] Recently, new advanced high strength steels with high corrosion resistance are also highly demanded for the replacement of galvanized steel sheets in order for saving Zn resources in the world.[6] Therefore, design of new duplex stainless steels, which can fulfill the requirements of high strength, high corrosion resistance, and low cost, is becoming one of the most important topics in steel industries.[7,8] Much research attention has been paid to designing the compositions of lean duplex stainless steels (LDX) to control the stacking fault energy (SFE) and appropriate stability of austenite to generate transformation-induced plasticity (TRIP). Fujisawa et al.[9,10] optimized the alloying design of lean duplex stainless steels, whose strength and plasticity were significantly improved as compared to LDX2101. Choi et al.[11–13] studied the effect of nitrogen content on mechanical properties of DSSs (Fe-20Cr-5Mn-xN), which showed that the fractions of austenite and strain-induced martensite (SIM) increased with the content of nitrogen, and excellent mechanical properties could be obtained with high nitrogen contents. Herrera et al. developed a novel Mn-based duplex stainless steel, which contained relatively high carbon content, and had tensile strength of 1 GPa and total elongation of about 60 pct.[14] The METALLURGICAL AND MATERIALS TRANSACTIONS A
Table I.
Chemical Composition of the Present Mn-N Alloyed Lean DSSs (wt pct)
Steel 19Cr-DSS 21Cr-DSS 23Cr-DSS
C
Cr
Mn
Ni
N
0.016
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