Microstructure and Mechanical Properties of Ausformed Ultra High-Strength TRIP-Aided Steels

摘要

Ultra high-strength low-alloyed TRIP-aided steels possess high impact toughness, fatigue strength and hydrogen embrittlement performance, as well as good formability. So, it is expected that the TRIP-aided steels are applied to some automotive parts such as not only center pillar but also driving parts, spring and bolts. In the present study, the effects of ausforming conditions (temperature and strain) after austenitizing on tensile properties and toughness of TRIP-aided steels with bainitic ferrite matrix were investigated to develop a new type of ultra high-strength forging steel. TRIP-aided steel with chemical composition of 0.2%C, 0.5%Si, 1.5%Mn, 1.0%Al , 0.02%Nb and 0.1 %Mo achieved large total elongation and high impact toughness by ausforming to 0-50% strain at 600-900℃, followed by austempering at 400℃ for 500s. This was mainly caused by refined microstructure and stabilized retained austenite.