抄録
It is known that the crystal structure within the molten pool affects the initiation and propagation of solidification cracking. Cracking can occur where crystals meet or where crystals are adjacent to each other. To evaluate cracking behavior more precisely, analysis that takes into account the crystal structure associated with melting and solidification is required.
In this study, a simple method was developed to visualize the growth direction of columnar crystals during the solidification process of weld metal from the temperature distribution, temperature gradient and their histories in FEM heat conduction analysis. In addition, by determining the location of the liquid phase in the weld transient and reflecting it in FEM thermal-elastic-plastic analysis, a solidification cracking analysis that takes into account the crystal structure and the existence of the liquid phase between crystals was proposed.
As a result, it was confirmed that the distribution of columnar crystals growing in the molten pool and the strain behavior acting on the liquid phase region between crystals during welding can be well visualized. The proposed method was applied to a two-dimensional analysis to investigate the effect of crystal size on the existence of liquid phase and the amount of strain generated in the liquid phase region, and it was confirmed that the plastic strain increment in BTR generated in the liquid phase region was larger under conditions with larger columnar crystal diameter. The effect of welding speed on crystal growth and strain behavior in the molten zone were investigated by three-dimensional analysis, and it was confirmed that the growth of columnar crystals similar to the actual phenomenon could be well represented by varying the welding speed. The strain behavior acting on the liquid phase region during welding transient was examined, and it was confirmed that large strain occurred at the low temperature side and expanded to the high temperature side.
