2024 Volume 2024 Issue 69 Pages 1-7
The permanent strengths of cold-rolled austenitic stainless steel sheets for springs and subsequent annealing are systematically investigated. The athermal, time-independent permanent strength corresponds to the basic ability to withstand stresses induced by external forces. Stress relaxation tests of sufficiently long duration (24 hours) were performed and the experimental stress-relaxation time relationship was extrapolated to estimate the permanent strength remaining after an infinite time. Permanent strength was dominant at 0.2% proof stress at the general strain rate (έ = 1×10-2/s). The percentage of temporal strength was not always high in existing cold- worked structural materials. Also, the 0.2% proof stress and the permanent strength were generally equal so that no problems occurred during design without considering the permanent strength. The proportion of permanent strength included in the 0.2% proof stress at the general strain rate (έ = 1×10-2/s) was about 85% for the delivered material and about 90% for the annealed material, while the increase in permanent strength was about 200 MPa. It was suggested that low-temperature annealing in the specimen not only increased the permanent strength but also increased its residual stress ratio.