Effect of weld thermal cycle on behaviour of Ti–Nb carbonitrides in HSLA steel

Abstract

AbstractThe effect of weld thermal cycle on the stability of carbonitrides has been investigated for an HSLA steel containing Ti and Nb. The precipitates at various distances from the fusion line of a bead on plate weld were characterised using energy dispersive X-ray analysis and electron energy loss spectroscopy. The results showed that starlike precipitates originally present in the strand cast condition had survived the controlled rolling treatment, but weld thermal cycling caused dissolution of the ‘arms’ to a varying extent depending on the distance from the fusion line. It was also shown that larger ( ≥ 50 nm) Ti, Nb particles became richer in Ti on approaching the fusion line and displayed a compositional gradient from core to skin, the skin in all examples showing a greater enrichment in Ti than the core. Equilibrium thermodynamics can be used to make reasonable predictions of particle composition following processing; however, for low heat input welding it is necessary to take diffusional kineti...