The influence of Ti and Nb on solidification cracking of ferritic stainless steels, as determined using self-restrained samples

The susceptibility to solidification cracking of ferritic stainless steels was studied using the self-restrained method. The unstabilised steel was compared with mono and dual stabilised (Ti and/or Nb) steels. Autogenous gas tungsten arc welding at a speed of 6 mm/s, 3 mm/s, and 1 mm/s was done. All the specimens cracked at a welding speed of 6 mm/s. The weld metal of both the unstabilised and the stabilised steels contained a mixture of columnar and equiaxed grains. At a welding speed of 3 mm/s, all the specimens except the unstabilised grade cracked. The weld metal microstructures were mostly columnar, and the dual stabilised grades showed equiaxed grains. At a welding speed of 1 mm/s, the Nb stabilised and the dual stabilised steel containing Mo cracked whilst the other alloys did not crack. At a welding speed of 1 mm/s, the weld metal was dominated by columnar grains. The cracks were interdendritic. The crack surfaces were enriched in Nb, Ti, Mn, Si, Al, Mn, and Mo. The unstabilised ferritic stainless steel was resistant to solidification cracking whilst the stabilised steels were not. Low melting point eutectic phases associated with Ti and Nb might have contributed to solidification cracking.