Effect of Tensile Deformation on the Texture, Phase Composition, and Residual Stresses of the α and γ Phases in VNS9-Sh Steel

Abstract

X-ray diffraction is used to investigate the effect of the tensile strain on the phase composition, texture, and stress state of the α and γ phases in VNS9-Sh alloy. The α phase content increases from 75 to 91% at the surface and from 45–50% to approximately 70% in the subsurface layers during testing until failure. The relative amount of decomposed austenite at different stages of tensile deformation, which reflects the metastability of austenite, is proposed as a parameter to measure the tendency of two-phase steels to the TRIP effect. Compressive stresses up to –1000 MPa form in austenite at the surface in a 0.3-mm-thick initial steel strip due to the positive volume effect of the γ → α transformation. In contrast, tensile stresses are observed in martensite. Heating the metal creates the compressive stresses, but the subsequent cooling causes tensile stresses in martensite because of its lower linear thermal expansion coefficient (LTEC) as compared to austenite.