Martensite transformation of a Cr-Ni type weld metal and its application to analysis of welded joints

We have investigated the martensite transformation phenomena of a Cr-Ni type weld metal, especially the effects of stress and plastic strain that exist before the martensite transformation start. Tensile specimens machined from the weld metal were firstly heated up to 800 °C to austenitize the specimens and then cooled down. During the cooling, we applied stress and plastic strain before the martensite transformation starts. The results show that the stress increases the Ms temperature, while the plastic strain decreases the Ms temperature. In addition, the transformation-induced plasticity was also investigated. Finite element method (FEM) analysis was conducted considering these effects, and the results show that these effects on the residual stress and the weld distortion are considerably large. The FEM analysis shows that the compressive residual stress in the weld metal is likely to be decreased by the transformation-induced plasticity. We also conducted hydrogen diffusion analysis for the case that the retained austenite exists in the weld metal by varying the Ms temperature in order to consider the appropriate time period to keep a cold cracking test specimen before the crack observation.