Effect of Tempering on the Phase Composition and Texture of the α and γ Phases in VNS9-Sh TRIP Steel

X-ray diffraction quantitative and texture analyses are used to study the effect of tempering at 300–600°C on the structural, phase, and orientational changes in a VNS9-Sh TRIP steel ribbon 0.3 mm thick. Cold rolling is shown to lead to the formation of a heterogeneous structure of TRIP steel, which consists of the metastable γ phase undergoing the γ–α' transformation in a near-surface layer 5–10 μm thick; this transformation is accompanied by a positive volume affect and compressive stresses higher than 800 MPa. Tempering at 300°C for 2 h does not change the phase composition in the ribbon volume and increases the fraction of martensite at the surface from 60 to 71% as compared to that in the as-received state. An increase in the tempering temperature to 500°C leads to a decrease in the fraction of martensite in both the surface layer (to 54%) and the ribbon volume (to 16%). In the case of tempering at 600°C, the martensite content at the surface decreases to 45% and increases to 42% in the ribbon volume. A correlation between the metastable retained austenite content and the ultimate tensile strength of TRIP steel is found.