In this study, the torsion creep limits for the 1050°C solution heat-treated 18-8 type stainless steel bar well known as a high-temperature spring material containing 0.12%C, 16.79%Cr, 6.44%Ni, were measured at 400-720°C. In order to obtain the effect of cold work on the creep strength, the specimens were twisted in an amount of 0.064-0.256π/cm (5∅bar) at room temperature, and then subjected to creep testing.
At temperatures of 400°C, 450°C and 500°C, the torsion creep strength was greatly increased by torsional cold work, and especially, 0.192π/cm work was found to be most effective when testing was 450°C and 0.128π/cm when it was 500°C. At 600°C, however, only the cold work around 0.064π/cm gave a slight improvement, and at 720°C, cold work induced the deterioration of creep resistance. No change of hardness for the cold twisted specimens were observed at the temperatures below 500°C, but above 600°C the hardness was reduced remarkably.