Microstructures of the heat-affected zone around a cold crack in weldments

Abstract

This paper presents a numerical and experimental study of three subregions within the heat-affected zone (HAZ) in the vicinity of a cold crack. The welding process of a T-joint assembly, including the tack welding process, was modelled in the finite element method utilising a transient heat-transfer analysis to capture the complete temperature history in the HAZ subregions. Temperature–time curves derived from the welding model, corresponding to the position of these subregions, were subsequently adopted as thermal loadings on physical coupon specimens using a Gleeble 3800 apparatus. The following subregions of the HAZ were experimentally simulated: intercritical HAZ, fine-grained HAZ, and coarse-grained HAZ. The results showed that the microstructures of the experimentally simulated HAZ subregions corresponded well with those found in the actual HAZ subregions near a cold crack in a sample taken from a bridge. Finally, the cooling rates from the tack welding process, in the absence of preheating, may lead to a microstructure that is sensitive to cold cracking in S355J2+N.