Investigation of the precipitation mechanism in HAZ of supermartensitic stainless steels. Two-pass weld simulation

Weld simulation is widely used for studying weldability of steels. Mostly HAZ of one pass welding is simulated and then specimens are mainly used for mechanical testing. Another way of using the simulation equipment is to find a simulation regime resulting in a certain microstructure observed in the HAZ of a real multipass weld, i.e. to find the temperature history leading to a certain type of microstructure. In the present work a two-pass weld simulation was used to investigate the precipitation mechanism of carbides in HAZ of two supermartensitic stainless steels. Previously a model of carbide precipitation was suggested [1]. According to this model a reheating of the HAZ in the martensitic stage is needed to provoke strong carbide formation. In this work the peak temperatures of the first and second heating pass and also the temperature of the interpass holding were varied together with holding time during the reheat (the second pass). The heating regime, most favorable for the carbide precipitation was found for both investigated steels. Also measurements of chromium content across prior austenite grain boundaries were done for one of the investigated steels. The thin foils were prepared from the specimens where the strongest carbide precipitation was observed.