Effect of Postweld Heat Treatment on HAZ Microstructure and Toughness of Microalloyed C-Mn Submerged-Arc Welds

TWI Industrial Member Report Summary 323/1986

By D J Sparkes

Background

There is disparity between the international codes of practice in stipulating postweld heat treatment (PWHT) cycles to be applied to C-Mn steel weldments. As part of a project with the overall aim of establishing a rational basis for specifying PWHT procedures, work has been undertaken to examine the effect of varying PWHT cycles on the as-welded HAZ microstructure and toughness of C-Mn steels. Bead-in-groove welds were produced by the submerged-arc process at an arc energy of 3.5kJ/mm in two steels, these being microalloyed with niobium, and niobium plus vanadium. Optical and electron microscopy were carried out, with toughness being assessed in terms of CTOD testing.