Diffusion Welding Copper-Nickel Alloys to Carbon Steel

概要

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The effects of post weld heat treatment on the diffusion weld characteristics of copper-nickel alloy Monel metal (65Ni, 35Cu) and cupronickel (20Ni, 80Cu) to a carbon steel have been studied by microscopy, electron probe microanalysis, tensile tests, and microhardness tests. The diffusion behavior at the joint interface has been also examined by constructing diffusion paths on a copper-nickel-iron ternary phase diagram. Post weld heat treatment of the diffusion welds of cupronickel to the steel at temperatures above 900℃ for longer than 4 hours reduced the joint strength markedly. Electron probe microanalysis and microhardness tests revealed that uphill diffusion in nickel content at the joint area took place during the heat treatment, which accelerated the formation of a nickel reduced zone with lower harndess in cupronickel parent metal. The diffusion weld properties of Monel metal to the steel did not deteriorate by the heat treatment. These variations in mechanical properties of diffusion welds during heat treatment appeared to be predictable to some extent with close examination of the ternary diffusion paths.
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