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TRODUCTION

DUPLEX stainless steel (DSS) containing austenite (c) and ferrite (d) in equal proportion is widely used in oil, gas, paper, desalination, and petrochemical industries as the economical alternative to austenitic stainless steel.[1] DSS shows high mechanical strength along with excellent resistance to corrosion and stress-corrosion cracking. Since the processing of DSS involves high-temperature deformation, such as hot rolling and hot forging, it is important to study the hot deformation behavior of this steel.[2–12] The changes in microstructure and crystallographic texture during hot deformation of DSS determine SUDIPTA PATRA, Doctoral Student, is with the Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India, and also with Jindal Stainless Limited, Hisar, Haryana 125005, India. Contact email: [email protected] ABHIJIT GHOSH, formerly Doctoral Student with the Indian Institute of Technology Kharagpur, is now Research Associate with the Indian Institute of Science, Bangalore, India. LOKESH KUMAR SINGHAL, Head, R&D, ARIJIT SAHA PODDER, GM, R&D, and JAGMOHAN SOOD, Head, Operation, are with Jindal Stainless Limited. VINOD KUMAR, DGM, is with the R&D Center for Iron and Steel, RDCIS, SAIL, Ranchi, Jharkhand 834002, India. DEBALAY CHAKRABARTI, Associate Professor, is with the Indian Institute of Technology Kharagpur. Manuscript submitted March 31, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A

(1) the resistance against deformation, i.e., load required for deformation; (2) the resistance to hot cracking during deformation; and (3) the final microstructure and mechanical properties of the steel. Now the hot-flow behavior of DSS depends on microstructural and textural changes taking place within individual phases and their mutual correspondence. Several studies have been carried out on the microstructural evolution during hot deformation of conventional (high-Ni) DSS.[2–11,13–17] The samples of DSS were deformed over a wide temperature range [Tdef = 1123 K to 1473 K (750 C to 1200 C)] and strain-rate range (_e = 0.01 to 10/s) using different techniques, such as hot-compression tests, hot-torsion tests, plane-strain compression tests, and laboratory scale hot forging and hot rolling. The general observations are as follows. (1) (2) (3) (4)

Decrease in Tdef and increase in e_ , i.e., the increase in the Zener–Holloman parameter, Z, increases the flow stress. Higher Tdef [>1273 K (1000 C)] and lower e_ ( 0.65. This behavior has not been reported in earlier studies on DSS[20,24] and can be justified by the following points. First, earlier studies hardly deformed the as-cast samples of lean DSS below ~1273 K (1000 C). Besides that, the increase in flow stress at higher strain levels could be attributed to the strain-induced precipitation of secondary austenite islands at lower deformation temperatures, as reported recently in another study.[21] The fine austenite islands can significantly hinder the plastic flow inside d-ferrite, resulting in the increase in flow stress. At lower deform