Abstract
304 stainless steel is one of the most common stainless steels due to its excellent corrosion resistance and mechanical properties. Typically, a good balance between ductility and strength derives from deformation-induced martensite transformation (DIMT), but this mechanism has not been fully explained. In this study, we conducted in situ neutron diffraction measurements during the tensile deformation of commercial 304 stainless steel (at room temperature) by means of a Time-Of-Flight type neutron diffractometer, iMATERIA (BL20), at J-PARC MLF (Japan Proton Accelerator Research Complex, Materials and Life Science Experimental Facility), Japan. The fractions of α′-(BCC) and ε-(HCP) martensite were quantitatively determined by Rietveld-texture analysis, as well as the anisotropic microstrains. The strain hardening behavior corresponded well to the microstrain development in the austenite phase. Hence, the authors concluded that the existence of martensite was not a direct cause of hardening, because the dominant austenite phase strengthened to equivalent values as in the martensite phase. Moreover, the transformation-induced plasticity (TRIP) mechanism in austenitic steels is different from that of low-alloy bainitic TRIP steels.
Highlights
Austenitic stainless steels are widely used in industries because they have both superior corrosion resistance and mechanical properties
The ε (HCP) martensite first appeared followed by α0 martensite formation at the true strain of 0.11
This strain corresponded to the transition of the strain hardening state without deformation-induced martensite transformation (DIMT)
Summary
Austenitic stainless steels are widely used in industries because they have both superior corrosion resistance and mechanical properties. The most commonly used grade is JIS-SUS304 (equivalent to AISI 304), which contains mainly 18 mass% Cr, 8 mass% Ni, and less than 0.08 mass% C In this steel, the FCC austenite (γ phase) is a metastable phase at room temperature. Nishiyama showed that the occurrence of ε martensite is strongly affected by chemical composition, microstructure, and temperature [3]. Such factors affect the route of DIMT, i.e., whether it will proceed as γ→ε→α0 or the simultaneous γ→α0 and γ→ε transformations occur [4,5]
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