Investigation on Precipitation Transition in CGHAZ for TRIP Steels Containing Vanadium and Titanium

Abstract

Two kinds of low-carbon low-silicon TRIP (Transformation Induced Plasticity) steels containing vanadium are designed using Thermo Cale software in the light of both thermodynamics and kinetics. TRIP heat treatment process of different steels is determined according to the calculation results respectively. Weld HAZ (Heat-Affected Zone) simulation tests indicate the weldability of TRIP steels is crucially sensitive to CE (carban equivelent) of the steel. However the impact toughness of CGHAZ (Coarse Grain Heat-Affected Zone) does not decrease drastically for TRIP steels microalloyed with Ti+V. The steel containing both of vanadium and titanium shows smaller grain size compared with that containing vanadium solely. This is because the precipitation of TiN carbonitride slows down the grain boundary motion speed and then retards the grain size coalescence in CGHAZ.