Development of analysis method for hot cracking considering mechanical and metallurgical factors

Abstract

Since welding hot cracking is one of the most harmful defects which may largely reduce the strength of welded joints and structures, it is very important to study the prediction and prevention of its generation. Hot cracking is caused by both mechanical and metallurgical factors. In this research, authors proposed a new computational method for evaluating the occurrence of hot cracking through considering both mechanical and metallurgical behavior. As the metallurgical behavior, strain due to solidification shrinkage and mechanical resistance of molten metal were modelled using the solidification ratio as a parameter. The mechanical behavior, an index for generation of hot cracking using the increment of plastic strain is proposed. In addition, authors proposed a simplified prediction method using the temperature gradient for the direction of columnar crystal growth, which affects the location of hot cracking, and is used to evaluate the associate angle of the columnar crystals. The developed method was applied to butt welding. Through the computation using proposed method, it was found that the predicted direction of columnar crystal growth by the proposed method is in good agreement with the experimental results. In addition, the generation of hot cracking in the same butt welding was predicted using the proposed method and the obtained cracking positions agreed well with those observed by experiment. The Influence of the strain of solidification shrinkage on hot cracking was investigated in relation to the surrounding constraints, the temperature gradient and solidification mode, which are presumed to be highly related to the occurrence of hot cracking. From the above results, it can be concluded that the proposed method can analyze the effects of mechanical and metallurgical factors on hot cracking.

Keywords:

• Hot cracking
• Thermo-elastic-plastic analysis
• plastic strain increment in BTR
• crystal growth direction
• solidification shrinkage
• solidification latent heat
• brittleness temperature range

Acknowledgements

The original study was conducted with experimental data provided by Mr. Takeshi Miwa and Dr. Kei Yamazaki of Kobe Steel, Ltd. and Mr. Kensaku Nishihara and Dr. Hiroyuki Takeda of Kobelco Welding Techno Co. We hereby express our gratitude.