Evolution of Ms Temperature as a Function of Composition and Grain Size

Abstract

Martensite transformation was studied in 16 steel compositions with various C, Mn, Si, Al, and Cr contents. Different annealing treatments were performed on the elaborated steels to obtain different prior austenite grain sizes (PAGSs) and M s temperatures. This permitted the concomitant evolution of M s temperature as a function of chemical composition and PAGS. The experimentally built database allowed the decorrelation of the effects of chemical composition and PAGS, and a new empirical equation to predict M s temperature was proposed. The obtained experimental results and equation are discussed, and some future improvements are proposed.

A New Systematic Approach Based on Dilatometric Analysis to Track Bainite Transformation Kinetics and the Influence of the Prior Austenite Grain Size

“…The martensite start temperature, Ms, was measured at all selected T conditions, and when possible, the prior austenite grain size (PAGS) was revealed and measured as well; the results thus obtained are presented in Figure 2. It is clear that the effect of the austenitisation heat treatment and thus, of the PAGS on the Ms of the steels, is very limited if not negligible, which agrees with recent reports that show that average austenite grain sizes above 15-20 µm have a negligible effect on the Ms temperature of steels [25][26][27].…”

Effects of Carbon Content and Austenite Grain Size on Retained Austenite Fraction in Stir Zone of Friction Stir Welded 6%Ni Carbon Steels

“…15(b) and 13, it was implied that the decrease in the average intercept length of the prior austenite grains from 2 to 1 μm stabilized the austenite, which corresponded to a reduction of 110°C in the apparent Ms temperature. However, the reduction in the Ms temperature was estimated to be approximately 30°C when extrapolating the decrease in the average intercept length from 2 to 1 μm in the model, 31) which is validated in the prior austenite grain diameter range greater than 6 μm. Therefore, it is suggested that the calculated ∆Ms incorporated the effects other than that of the prior austenite grain size, such as the density of the low-angle subgrain boundaries, 15) which increases concurrently with grain refinement.…”

Quench and Bainite (Q&B) Thermal Cycle as an Alternative to Standard Quench and Partitioning (Q&P) Annealing to Produce AHSS

“…To define the Tq, the method described in [4] was used but the formulas and criteria were modified as follows. Ms value was estimated using the formula reported in [9] and assuming the PAGS to be around 15µm:…”