Abstract
Numerical model to calculate the fraction of liquid phase which takes into account the formation of crystallized phase during welding solidification was proposed in order to predict the solidification cracking susceptibility of high Ni steel weld metals. For evaluating the validity of the proposed model, changes in the fraction of residual liquid phase on solidification process for Fe-36%Ni-0.02%C-1%Nb weld metal solidifying at nearly γ phase and Fe-36%Ni-0.2%C-1%Nb weld metal solidifying with niobium carbide during γ solidification were quantitatively investigated as follows. After each quenched solidification microstructure of these weld metals was made by liquid tin, the change in the fraction of residual liquid phase for Fe-36%Ni-0.02%C-1%Nb weld metal was quantitatively evaluated by analyzing the region corresponding to residual liquid phase in SEM (Scanning Electron Microscope) image of the quenched weld metal. Also, Fe-36%Ni-0.2%C-1%Nb weld metal was quantitatively evaluated by separating NbC from residual liquid phase by using the mapping data of Nb and C by EPMA (Electron Probe Micro Analyzer). These experimental data coincided with the fractions of liquid phase obtained by using the model for Fe-36%Ni-0.02%C-1%Nb and Fe-36%Ni-0.2%C-1%Nb weld metals and the morphology of niobium carbide predicted by the model also corresponded to TEM (Transmission Electron Microscope) observations. Furthermore, the effects of niobium and carbon contents on the solidification cracking susceptibility of Fe-36%Ni weld metal was able to be explained by using the model.
