Statistical analysis of influential factors on the stability of retained austenite in low alloy TRIP steel

Abstract

The factors representing the stability of retained austenite (gamma(R)) in low-alloy TRIP steel at a plastic strain of up to 0.04 were statistically analyzed by evaluating the size, strain level, crystal orientation, morphology, and precipitation site of a large number of gamma(R) grains (>1000). The ratio (R-area) of the area of gamma R after deformation to that before deformation was adopted as a representative parameter for the stability of gamma(R). The frequency of low R-area in fine gamma(R) was significantly high, indicating that they were unstable. Moreover, it was indicated that gamma(R) in the high-strain regions tended to be unstable, whereas gamma(R) in the bainite region was stable. The crystal orientation and aspect ratio did not correlate with R-area in TRIP steel. The strain level and precipitation sites in coarse gamma(R) were uncorrelated with R-area, indicating that the size of the y R has a greater effect on its stability. The stability of gamma(R) was not dominated by the carbon concentration but was affected by other factors. The size of gamma(R) may represent the stress conditions at the gamma(R) /ferrite or bainite boundaries, which is why this factor represents the stability of gamma(R) in the TRIP steel at a plastic strain of up to 0.04.