TWI Industrial Member Report Summary 402/1989
By A M Barnes
A major industrial problem in welding heavy section structural steels is the reliable attainment of high toughness in the heat affected zone (HAZ). In current steels, toughness may be lowest in that part of the HAZ which has been transformed, and is subsequently reheated by further weld runs. Previous work has indicated this to be a result of cleavage initiation taking place at grain boundary microphases, but there has been no study of the relative effects of such microstructural constituents and the intragranular transformation product.
In this work, a series of single and dual cycle thermal simulations were performed on a C-Mn-AI-Nb steel (Steel 1). The microstructural effects of intercritical reheating on the coarse grained HAZ were examined and related to fracture toughness and hardness. Comparative microstructural and toughness data were generated by the introduction of a second steel (Steel 2) of very similar chemical composition (0.17wt% higher Mn content).