The Investigation of Strain-Induced Martensite Reverse Transformation in AISI 304 Austenitic Stainless Steel
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ion of martensite during deformation is a very common phenomenon in austenitic stainless steels which, if susceptible to such transformations, are called metastable. The transformation from FCC (FaceCentered Cubic, c) austenite to BCC (Body-Centered Cubic, a¢) martensite may happen in a direct manner (c fi a¢) which usually occurs on intersections of shear
_ G. CIOS, T. TOKARSKI, A. ZYWCZAK, M. STE˛PIEN´, and M. MARCISZKO are with the Academic Centre for Materials and Nanotechnology, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland. Contact e-mail: ciosu@ agh.edu.pl R. DZIURKA, B. PAWŁOWSKI, and K. WIECZERZAK are with the Faculty of Metals Engineering and Industrial Computer Science, al. A. Mickiewicza 30, 30-059 Krakow, Poland. Ł GONDEK is with the Faculty of Physics and Applied Computer Science, al. A. Mickiewicza 30, 30-059 Krakow, Poland. P. BAŁA is with the Academic Centre for Materials and Nanotechnology, AGH University of Science and Technology, and also with the Faculty of Metals Engineering and Industrial Computer Science. Manuscript submitted January 31, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
bands, twins, or via HCP (Hexagonal Close Packed, e) martensite (c fi e fi a¢).[1] However, e martensite fully transforms into a¢ when a higher strain is applied. The maximum volume fraction of e martensite is strongly dependent on the deformation temperature and usually takes place at strains lower than 0.15.[2,3] As reported by Tavares et al.,[4] it is possible to obtain a different transformation succession, i.e., c fi a¢ fi e when applying high pressure, for instance by HPT (High Pressure Torsion) processing at the highest possible pressure and deformation conditions. The influence of BCC martensite and/or its formation on the materials properties such as mechanical,[5,6] corrosion resistance,[7,8] formability,[9–12] hydrogen cracking susceptibility,[13–15] and fracture propagation[16] have been investigated. Mathematical models for strain-induced transformation in austenitic stainless steels have also been already developed.[17–19] BCC as well as HCP martensite undergoes a reverse transformation during the heating process. Previous dilatometric studies revealed e fi c reverse transformation between RT and 473 K (200 C) and a¢ fi c reverse transformation in the range of 773 K to 1073 K (500 C
to 800 C).[3,20] Both (e fi c, a¢ fi c) transformations are shifted to higher temperatures with the increase of heating rate (at the heating rate higher than 0.1 K/s).[21] Tomimura et al. described two types of possible reverse transformation (a¢ fi c) mechanisms: 1st diffusive by nucleation and growth of new austenite grains and 2nd diffusionless shear reversion.[22] The reverse transformation plays a significant role in grain refinement in metastable austenitic stainless steels. UFG (Ultrafine-grained) as well as NG (nano-grained) materials have been produced by reversion annealing of AISI 304, AISI 304L, and less stable AISI 301LN and AISI 201 metastable stainless steels, where the mat
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