Recently, a new class of TRIP steels without Si or Al but containing 5-10 wt% Mn have been considered as potential third-generation automotive steels.This Mn-TRIP steel exhibits an excellent combination of tensile strength (1-1.5 Pa) and total elongation (30-44%) owing to the presence of 20-40% stable austenite in the matrix.The process that is critical for the production of Mn-TRIP steel is intercritical annealing (IA), which transforms part of the original martensite or ferrite to austenite that is retained at ambient temperatures.The austenitization kinetics during IA is then of great importance since it determines the chemical compositions and sizes of austenite grains formed.