Influence of Bonding Conditions and Nitrogen Content on Diffusion Bonding of 316L-type Austenitic Steels: Diffusion Bonding for Low-temperature Dampers of Superconducting Generators

Keeping HIP treatment in mind, diffusion bonding conditions of 316L-type austenitic steels for a low-temperature damper were investigated. It was found that diffusion bonding of 316L with high-content nitrogen onto 316L with high-content nitrogen was difficult. It was tentatively concluded that the martensite formation near the bonding surface induced during the cooling process was most likely responsible for reducing the bonding strength at -196°C. Complete diffusion bonding properties at -196°C were attained by adopting a combination of 316L with high-content nitrogen and 316L with low-content nitrogen under the following bonding conditions: nitrogen content less than 0.017% in 316L with low-content nitrogen, bonding temperature above 1039°C, surface roughness below 0.07 μm, pressure above 130 MPa and pressing time above 4 h.