Study on Hot Cracking Susceptibility in Multipass Weld Metal of Ni-Base Super-Alloys

Research Project

Project/Area Number	01550561
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	溶接工学
Research Institution	Osaka University
Principal Investigator	SHINOZAKI Kenji Osaka University, Faculty of Engineering, Research Associate, 工学部, 助手 (70154218)
Co-Investigator(Kenkyū-buntansha)	NAKAO Yoshikuni Osaka University, Faculty of Engineering, Professor, 工学部, 教授 (20029086) SAIDA Kazuyuki Osaka University, Faculty of Engineering, Research Associate, 工学部, 助手 (30178470)
Project Period (FY)	1989 – 1990
Project Status	Completed (Fiscal Year 1990)
Budget Amount *help	¥2,800,000 (Direct Cost: ¥2,800,000) Fiscal Year 1990: ¥1,600,000 (Direct Cost: ¥1,600,000) Fiscal Year 1989: ¥1,200,000 (Direct Cost: ¥1,200,000)
Keywords	Ni-base superalloy / Solidification crack / Liquation crack / Multipass weld metal / Microsegregation / Ductility-dip crack / Reheated weld metal
Research Abstract	This paper was carried out in order to make clear the cracking mechanism of microfissure in multipass weld metal of Ni-base super-alloys. Metallographic and fractographic examinations were performed to the fracture surface of microfissure. Moreover, the effects of P, Si and S on hot cracking susceptibilities in reheated weld metal of 70%Ni-Cr-Fe ternary alloys were evaluated in order to make clear the effects of these impurity elements on hot cracking susceptibilities in multipass weld metal of Ni-base welding rods. Main results obtained are as follows. (1) A detail fractographic examination has made clear that microfissure in multipass weld metal was liquation crack or ductility-dip crack occurring at reheated weld metal. (2) The liquation cracking susceptibilities in reheated weld metal of 70%Ni-Cr-Fe ternary alloys were too low and they increased with an increase in impurity elements. Ductility-dip cracking susceptibilities of materials containing S were much higher than those containing P and Si. Especially cracking susceptibilities of 0%Cr and 20%Cr alloys containing 0.007%S were higher than those of 5%Cr and 10%Cr alloys. (3) There was the suitable Cr content for reducing the ductility-dip cracking susceptibility because of contrary effects due to grain boundary carbide, hardness and grain boundary segregation of S.