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 steel containing Fe-0.2C-2Mn-Si-Al was annealed using intercritical Q&P cycles. Quenching temperature and partitioning time at 440°C was varied. Analysis of microstructure evolution during such Q&P treatments was performed using different characterization tools: FEG-SEM, EBSD, dilatometer and saturation magnetization measurements. Especially, phenomena taking place during partitioning were investigated. The microstructure was analyzed at the end of soaking, before and after partitioning and at the end of the annealing cycle. It was found that bainite transformation happens during partitioning and has a significant effect on the final retained austenite fraction. Quenching temperature has an important effect on both martensitic transformation during cooling and subsequent bainite transformation during partitioning.