Microstructural development in the coarse-grained, heat-affected zone in titanium-vanadium microalloyed HSLA steels

Abstract

The development of the microstructure in the coarse-grained, heat-affected zone (CGHAZ) of two medium-strength Ti-V microalloyed steels was examined. Single-pass welding of 19mm-thick plates at 5.5kJ/mm resulted in a smaller austenite grain size and a correspondingly narrower CGHAZ in the low-Ti, high-V steel than in the high-Ti, low-V steel. The observed effect is correlated to the differing stability of microalloy precipitates, TiN/TiCN in the high-Ti, low-V steel and TiVN/TiVCN in the low-Ti, high-V steel, and their differing size distributions in the normalized starting materials. The formation of large TiN inclusions reduces the level of Ti and N available to form fine particle dispersions and may, in part, account for the observed austenite grain growth in the high-Ti, low-V steel.