Hot cracking susceptibility in laser weld metal of high nitrogen stainless steels

Abstract

High nitrogen stainless steels are used as structural materials required to possess high strength and fracture toughness at low temperatures. The solidification mode in weld metals of stainless steels is generally designed to be the primary ferrite solidification mode to prevent hot cracking. The weld metals in some high nitrogen stainless steels, however, exhibit the primary austenite solidification mode because of an austenitizing effect of nitrogen, which enhances hot cracking susceptibility. In addition, laser welding provides the primary austenite solidification mode in weld metals of stainless steels due to the high solidification rate. Therefore, the laser weld metal of high nitrogen stainless steels likely occurs hot cracking.This study was conducted to make clear an effect of nitrogen and the solidification rate on hot cracking susceptibility in the laser weld metals of type 304 stainless steels varied with nitrogen content. The hot cracking susceptibility was examined by the preloading tensile strain (PLTS) cracking test. The PLTS test results showed that hot cracking susceptibility was remarkably increased with increase in the solidification rate and the nitrogen content. On the other hand, the solidification mode in the weld metal was changed from the primary ferrite to the primary austenite, as the solidification rate was raised. The primary austenite solidification mode was also observed in the weld metals with higher nitrogen content at lower solidification rate conditions. The experimental results indicated that the increase in hot cracking susceptibility is in agreement with the transition of solidification mode from the primary ferrite to the primary austenite in the weld metal. The transition of solidification mode in the weld metals of high nitrogen stainless steels could be predicted by the calculation using the modified Kurz–Giovanola–Trivedi model considering the effect of nitrogen.