α系,γ系異材継手の溶接ボンドに関する研究(第1報)

Abstract

In the welding of dissimilar metals such as α-steels (carbon steel, Cr-Mo steel, low alloying steel, etc.) to γ-steels and alloys (austenite stainless steel, Ni alloys, etc.), martensite-like structure at weld bound and macroscopic segregation in weld metal are observed by unsuitable welding procedures and its conditions, and these structures result in lower ductilities of the welds and lead to weld crackings.Taking notice of such metallurgical phenomena at weld bound and in weld metal, the authors investigated on the substance of martensite-like structure and the effects of chemical compositions of the electrodes and welding conditions on the formation of this structure. Some metallurgical considerations on the macroscopic segregation in weld metal were also discussed.The formation of martensite-like structure at weld bond in the welding of above dissimilar metals was reduced and the ductility of the welds was improved with increasing Ni content in the electrodes.Martensite-like structure at weld bond will be formed due to the diffusion of alloying elements such as Ni, Cr, Mo, C, etc. at a stagnation area where flow of the molten metal contacting with the fusion line does not occur. In lower range (less than 35%) of Ni content in weld metal, martensite-like structure at weld bond was formed in large quantity with pre-heating.Here, the weld bond in the bead-on-plate test specimen of above dissimilar metals, it is not merely as a fusion line, will be defined as a wide semi-melted zone of the base metal that was melted by the molten metal after arc travelling.Macroscopic segregation in weld metal was greatly observed with increasing welding speed and content of carbide formers as Cr, Mo, V etc. in α-steels, the segregation area was identified as martensite structure partially including carbide.