ＷＣ‐Ｃｏ系超硬合金と炭素鋼とのＴＩＧ溶接組織における複炭化物の形成

Abstract

The formation of complex carbides in the interface between hard metal and bead has been investigated in Tungsten Inert Gas welded joints of WC-Co hard metal and carbon steel. This welding process is expected to be a new bonding method of hard metals and steels. But, it is necessary to reveal the formation factor of complex carbides that decrease the strength of hard metal/steel joints. WC-30 mass%Co alloy as welding layer in functionally gradient hard metal and 0.48 mass%C steel were joined by TIG welding of direct current using a pure Ni and 57 mass%Ni-Fe alloy filler rod. These joints were also welded overlays in 1 and 4 times. In the case welded using pure Ni filler, the complex carbides are not formed. On the other hand, in the case welded using 57 mass%Ni-Fe alloy filler, the complex carbide particles, (M, W)6C; i.e., η carbide, are formed in the hard metal side of the interface between hard metal and bead. The thickness of region that the η carbide particles were formed in 1 and 4 overlays welding joints are approximately 50 and 150 μm in maximum value, respectively. In these regions, Fe concentration in hard metal becomes approximately 35 at% or more due to the diffusion from Ni-Fe bead to WC-Co hard metal during welding process. The amount of Fe atom diffusing from bead to hard metal side increase in accordance with the increase of Fe concentration of filler rod, melt-mixed steel and the number of overlay times, and the Fe atoms accelerate the formation of η carbide.