Abstract
The mechanism of the grain refining observed in the zirconium containing ferritic stainless steel overlay weld metal has been investigated.
The grain size in the overlay weld metal manufactured with the filler metal containing chromium ranging from 19% to 30% with no addition of zirconium was almost same regardless of the chromium content.
The grain refining in the overlay weld was remarkably promoted by the increase of the zirconium content in 19Cr-2Mo steel filler metal.
Most intergranular and intragranular zirconium carbide in the overlay weld metal precipitated during cooling in welding thermal cycle. Increasing in zirconium content provided the increase of intergranular carbides and made the grain boundary jigzag manner, which suggested that the zirconium carbides act as the obstacle against the grain boundary migration.
On the basis of these results, it was suggested that the precipitation of intergranular zirconium carbide was a main factor of the grain refining.
The theoretical model has made clear that the grain refining in the overlay weld by the addition of zirconium was attributed to the retardation of grain growth during the weld thermal cycle, which was caused by pinning effect of zirconium carbide against the grain boundary movement.
