INVESTIGATION OF THE DEGREE DEFORMATION INFLUENCE DURING TENSILE TESTS ON THE TEXTURE, PHASE COMPOSITION AND RESIDUAL STRESSES IN THE α- AND ɣ-PHASES OF STEEL VNS9-SH

X-ray diffraction methods were used to study the influence of the degree of deformation during tensile testing on the phase composition, texture and stress state of the α- and ɣ-phases of the VNS9-SH alloy. It is shown that during testing to failure, the amount of the α-phase increases on the surface from 75 to 91% and from 45-50 to ~70% in the subsurface layers. To assess the susceptibility of two-phase steels to the trip effect, a parameter of austenite metastability is proposed in the form of the relative fraction of decomposed austenite at individual stages of tensile deformation. It has been established that in the initial steel strip 0.3 mm thick, as a result of the positive volumetric effect of the transformation ɣ => α, compressive stresses are formed in austenite, reaching a value of –1000 MPa on the surface, in contrast to tensile stresses in martensite. Their presence is associated with heating of the metal, the cooling of which leads to tensile stresses in martensite due to its significantly lower temperature coefficient of linear expansion value compared to austenite.