Determination of the M_s~σ temperature of dispersed phase TRIP-aided steels

摘要

The stability of retained austenite is the most important parameter controlling the transformation plasticity effect in high strength multiphase low alloy TRIP (transformation induced plasticity) -aided steels. The thermodynamic stability of the retained austenite is characterized by the M_s~σ temperature, at which the stress necessary to initiate the martensitic transformation of the retained austenite equals the yield strength of the parent phase. The best mechanical properties are obtained at M_s~σ, i.e. the highest uniform elongations. In this paper the mechanical stability parameter of the retained austenite has been determined for seven different types of TRIP-aided steels. The single-specimen temperature-variable tension test (SS-TV-TT) technique was used, which allows to link the appearance of a yield point in the stress-strain curve with the mechanically-induced martensitic transformation of the retained austenite. The M_s~σ temperature was determined to be 10 +- 5℃. The results indicated that a certain amount of retained austenite is necessary to determine the M_s~σ temperature by the SS-TV-TT technique. For the steels containing volume fractions of less than 8 % retained austenite, it was not possible to determine the M_s~σ temperature.