Effect of multilayer welding conditions on the resistance of Kh15N5D2T and Kh16N4B-steels to cold crack initiation

The results are presented of investigations into the causes of cracking in multilayer argon-arc welding with a tungsten electrode of thermally resistant stainless steels Kh15N5D2T and Kh16N4B. It has been established experimentally that cold cracks appear in specimens of steel Kh15N5D2T and Kh16N4B of thickness 16-20 mm, welded with continuous superposition of layers. In specimens welded intermittently (with cooling to room temperature after superposition of each layer) no cold cracks have been found. Using the vacuum melting method, the authors established that the hydrogen content increases in cold cracks formation zone, but they failed to observe any substantial difference in the macrocontent of hydrogen in the metal of welds obtained by the welding techniques investigated. Metallographic analysis has showed that cold cracks are formed at bounderies of austenite grains, and also at the sigma-ferrite-martensite interface. It is supposed that cold cracking in multilayer welding of the steels investigated is mainly due to the intensified precipitation of carbides at the indicated boundaries in continuous welding