In this study, several methods were examined to evaluate the post-weld heat treatment (PWHT) cracking susceptibility of Ni-base heat resistant alloys. The results obtained in this study are as follows; 1) The PWHT cracking susceptibility of Ni-base heat resistant alloys can be estimated qualitatively by a PWHT cracking test apparatus using specimens with reinforcement. Quantitative evaluation of the PWHT cracking sucseptibility can be done using specimens with notch instead of specimens with reinforcement. 2) The PWHT cracking susceptibility of Ni-base heat resistant alloys can be esaily evaluated by the minimum value of critical crack opening displacement obtained by the elevated temperature tensile test.
An effect of heat treatment on the amount of the residual stress and its distribution in the explosively austenitic stainless clad steel was investigated. The stress was measured by X-ray method at both surfaces of clad and then at the interior of the cladding metal. Consequently, it was recognized that the stress considerably increased with the heating temperature at the surface and the interior of the cladding metal, and an existence of discontinuity in stress, that is, an abrupt change from a large tensile stress (in cladding metal) into a compressive stress (in base metal) was confirmed. As a result of theoretical calculation, it was concluded that such increase in stress due to the heat treatment depended on the difference of the expansion coefficients between the cladding metal and the base metal, and also the calculation values agreed with the measured values quantitatively.
The diffusion-welding characteristics of γ' precipitation-hardened nickel-iron alloy A286 and solid-solution-strengthened nickel-base alloy Hastelloy X have been studied by microscopy, electron probe microanalysis, tensile tests, and stress-rupture tests. In diffusion welding of A286 without any interlayer metals some titanium compounds were formed at the weld interface, which caused very poor joint properties. However, the formation of these compounds were fairly prevented by welding with a nickel foil interlayer at above the solvus temperature of γ' and η precipitates. The diffusion heat treatment to promote the joint homogenization remarkably improved the joint properties, and diffusion welds of A286 and Hastelloy X with nickel foil interlayers were made which exhibited 80-100 % joint efficiency in 815°C stress-rupture tests. An alloy interlayer having similar compositions to those of the base metal sometimes reduced the weldability.