Thermomechanical processing and characterisation of multi-phase microstructures in a V-bearing medium carbon micro-alloyed steel

Abstract

Due to cost effective processing, micro-alloyed (MA) steels with ferrite–pearlite microstructures are increasingly used in automotive applications in place of quenched and tempered (Q&T) steels, but the toughness of MA steels is inferior to that of Q&T steels. To improve toughness, forging is followed by a two step cooling (TSC) and a subsequent annealing. In this exploratory investigation a vanadium-bearing medium carbon MA steel was subjected to the above processing but finish forged at two different temperatures. The resulting multi-phase microstructures and mechanical properties were evaluated by optical and transmission electron microscopy, hardness and tensile property measurements. A comparison of the properties corresponding to the new routes of processing with those of the same steel containing structures of ferrite–pearlite and tempered martensite (Q&T condition) is also made.