Effects of Volume Fraction and Stability of Retained Austenite on Ductility of TRIP-aided Dual-phase Steels

Abstract

The effects of silicon and manganese contents on volume fraction and stability of retained austenite particles in 0.2C-(1.0-2.5)Si-(1,0-2.5)Mn (mass%) TRIP-aided dual-phase steels were investigated. In addition, the relationships between above retained austenite parameters and ductility at room and moderate temperatures were discussed through studies on strain-induced transformation behavior of retained austenite. As increasing the silicon and manganese contents except for 2.5 mass% manganese steel, the initial volume fraction of retained austenite increased with accompanied by reducing carbon concentration in retained austenite. It was found that the ductilities of these steels became maximum at a given temperature between 23 and 175°C, i.e., a peak temperature. The peak temperature was concluded to agree well with the temperature at which the strain-induced transformation of retained austenite was suppressed moderately for each steel. Moreover, the peak temperature Tp (°C) was related to estimated martensite-start temperature Ms (°C) of the retained austenite as Tp = 3.04Ms +187. Strength-ductility balance, i.e., the product of tensile strength and total elongation, at the peak temperature linearly increased with an increase in the initial volume fraction of retained austenite. © 1992, The Iron and Steel Institute of Japan. All rights reserved.