Comparison of hot cracking susceptibilities of various Ni-base, heat-resistant superalloys by u-type hot cracking test. study of laser weldability of Ni-base, heat-resistant superalloys (2nd report)

摘要

Laser welding is currently used for high-speed welding of relatively thin plates, such as Al alloys and stainless steels, though it is set to see strong demand in future for welding of a variety of materials, including Ni-base, heat-resistant superalloys. These materials are generally regarded as having a high hot cracking susceptibility, and the previously reported results obtained during bead-on-plate laser welding of Inconel 718 show that the penetration shape resembles a nail head, that liquation cracking readily occurs in the heat affected zone (HAZ) in the nail head necked part, and that the liquation crack occurrence frequency depends on the penetration shape. To compare the hot cracking susceptibilities with regard for various material-related factors and the welding parameters during laser welding, it is accordingly necessary to have available a test method for quantitative evaluation of the hot cracking susceptibility. Currently available as such hot cracking susceptibility test methods are the bar restraint test and the self-restraint cracking test, although both the latter are unsuitable for testing during laser welding of thin plates, and it is desirable to develop a new test method. The hot cracking test method used in the present study to evaluate the hot cracking susceptibilities of various Ni-base, heat-resistant superalloys is a modified version of the restraint/relaxation U-type hot cracking test developed by Matsuda et al. It has also been previously reported that the grain size affects the hot cracking susceptibility. The effect of the grain size on the hot cracking susceptibility is therefore examined in this study.