A Stacking Fault Energy Perspective into the Uniaxial Tensile Deformation Behavior and Microstructure of a Cr-Mn Austeni
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THE low-cost 200 series of the Cr-Mn austenitic steels containing 5 to 9 pct Mn are based on the substitution of Ni in the 300 series with Mn and the interstitial elements C and N to stabilize the austenitic structure (fcc). The 200 series of steels typically have a low stacking fault energy (SFE) ~16 mJ/m2 at room temperature[1,2] and they are metastable, so that straininduced martensite formation occurs during deformation.[3] SFE is one of the most important parameters H. BARMAN, Graduate Student, and P. SAHU, Assistant Professor, are with the Department of Physics, Jadavpur University, Kolkata 700 032, India. Contact e-mail: [email protected], [email protected] A.S. HAMADA, Researcher, formerly with the Metallurgical and Materials Engineering Department, Faculty of Petroleum & Mining Engineering, Suez Canal University, Box 43721, Suez, Egypt, is now with the Centre for Advanced Steels Research, University of Oulu, Box 4200, 90014 Oulu, Finland. T. SAHU, Assistant Professor, is with the Department of Physics, Ramananda College, Bishnupur 722 122, West Bengal, India. B. MAHATO, Technical Officer, is with the Materials Science and Technology Division, National Metallurgical Laboratory, Jamshedpur 831 007, India. J. TALONEN, Director, Corporate R&D, is with the Outokumpu Oyj, P.O. Box 140, 02201 Espoo, Finland. S.K. SHEE, Assistant Professor, is with the Department of Physics, Midnapore College, Midnapore 721 101, West Bengal, India. D.A. PORTER, Professor and Head, and L.P. KARJALAINEN, Emeritus Professor, are with the Centre for Advanced Steels Research, University of Oulu. Manuscript submitted August 23, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
governing the transformation and deformation behavior in such metastable steels. Low SFE also promotes mechanical twinning which is an important deformation mechanism enhancing strain hardening by retarding dislocation glide. Consequently, there are two mechanisms affecting the0 strain hardening behavior of these Twinned (TWIP effect) and cfcc ! a0bcc steels, i.e., cfcc ! cfcc 0 or cfcc ! ehcp ! abcc martensitic transformation (TRIP effect). According to Allain et al.,[4] in high-Mn steels, SFE £ 18 mJ/m2 favors the TRIP effect,[5] while the TWIP effect is observed for: 12 mJ/m2 < SFE < 35 mJ/m2. Saeed-Akbari et al.[5] suggested that SFE of 20 mJ/m2 should be taken as the upper limit for the appearance of the TRIP effect. It is generally agreed that with increasing SFE of austenite, the deformation mode gradually changes from deformation-induced martensite transformation (DIMT) to deformation twinning and finally to dislocation slip.[6,7] It is well known that the test temperature influences the SFE significantly and thus can also be expected to be crucial in controlling the deformation mode of the alloys concerned. Compared to Cr-Ni steels, there is relatively little literature concerning the deformation behavior of 200 series steels.[3,8–10] Previously,[11] we have observed that at 193 K (80 C), the uniaxial tensile deformation of the type 201L austenitic steel a
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