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Abstract: Electron BackScattered Diffraction (EBSD) maps are used to characterize quantitatively the graded microstructure formed by Surface Mechanical Attrition Treatment (SMAT) and applied here to the 316L stainless steel. In particular, the analysis of GNDs – coupled with relevant and reliable criteria – was used to depict the thickness of each zone identified in the SMAT-affected layers: (i) the “ultrafine grain” (UFG) zone present at the extreme top surface, (ii), the “transition zone” where grains were fragmented under the heavy plastic deformation and, finally, (iii) the “deformed zone” where initial grains are simply deformed. The interest of this procedure is illustrated through the comparative analysis of the effect of some SMAT processing parameters (amplitude of vibration and treatment duration). The UFG and transition zones are more significantly modified than the overall affected thickness under our tested conditions. [Copyright &y& Elsevier]

Abstract: The texture changes occurring by phase transformations, induced by 10% plastic deformation of a 304 stainless steel sheet at T =−60°C have been analysed. The inherited α′ texture is obtained from the austenitic γ texture with variant selection involving the intermediate HCP ɛ phase. The local orientation analysis of the different phases suggested that the applied stress first promotes the ɛ variants in a γ grain. At this stage, a strong variant selection often occurs due to the influence of the external applied stress. Then, the selected ɛ variants transform into α′ variants. The selection of these consecutive α′ variants is more complex because of the superposition of the applied stress and the internal stresses due to the formation of the ɛ variants themselves. We analysed these transformations in austenitic grains at the light of the γ–ɛ and ɛ–α′ transformation mechanisms. The selected variants, calculated according to these mechanisms are in fair agreement with the experimental ones. [Copyright &y& Elsevier]

Abstract: Different tensile tests are performed at −60°C, on a 304 AISI stainless steel, to produce strain induced α′ martensite. Using EBSD analysis and X-ray diffraction methods, the corresponding texture and microstructure evolutions is studied, as well as the γ→α′ transformation mechanism. It is shown that α′ martensite is associated with {111}γ faulted bands, partially ε bands, as often reported in the literature for low SFE stainless steels. As a consequence, these deformation bands play a key role in the nucleation and growth of α′ martensite. A micromechanical model is applied to simulate the deformation behavior of the stainless steel as well as the corresponding transformation kinetic and γ texture evolution. Different simulations are proposed, using various assumptions for the γ→α′ transformation mechanism. The simulation data are in better agreement with the experimental ones, when the γ→α′ transformation strain is derived from the Bowles–MacKenzie theory using the (111)γ[−12−1]γ stacking fault shear system as lattice invariant shear. [Copyright &y& Elsevier]