Spot weldability of TRIP assisted steels with high carbon and aluminium contents

Abstract

We examine here the spot welding characteristics of transformation induced plasticity assisted steels, which contain delta-ferrite as a consequence of their aluminium concentrations of 3.5 or 5.6 wt-% and which also have high carbon contents of 0.3 or 0.4 wt-% when compared with conventional automotive steels. The resistance spot welds are tested in both shear and cross-tensile tests in order to determine the so called ductility ratio, which is a parameter associated with the fitness of such welds for automotive applications. With an increase in the delta-ferrite fraction from 0.19 to 0.5, the hardness variation across the weld and heat affected zone is decreased approximately from 400 to 150 HV. It seems that the presence of stable delta-ferrite is helpful in reducing hardness variations and in achieving a significant ductility ratio of 0.39.