Abstract
The understanding of stress relaxation behavior is important to evaluate the safety and reliability of structural materials used in high temperature plants. In this study, the long-term stress relaxation behavior was investigated for SUS 316 stainless steel at 500°C to 750°C. The residual stress gradually increased in the stress relaxation test below 550°C. On the other hand, the residual stress rapidly decreased after testing for 1000 to 3000hr above 600°C. The increase of residual stress at 550°C was caused by thermal densification due to the drop of carbon content in matrix accompanying the precipitation of carbide. The rapid decrease of residual stress at 650°C was caused by lowering of creep resistance due to the drop of Mo content in matrix accompanying the precipitation of Laves phase.
