Abstract
The effect of cold-working, grain size and heat-treatment on the creep rupture properties of AISI 321 stainless steel has been investigated. 650°C creep rupture tests up to about 3,000 hrs have been carried out with the forged materials under 9 different conditions. The results were as follows: (1) The creep rupture strength of 40% cold-worked material is large at the beginning, but it decreases considerably with time and became smaller than that of annealed material. With 20% cold-worked material, a large creep rupture strength is maintained for a long time, but the elongation at rupture is small. (2) The grain size has only a slight bearing upon the creep rupture strength. (3) The creep rupture strength is affected greatly by the heat-treatment after working. The creep rupture strength is small when the material is subjected to low-temperature heat-treatment, and large when subjected to high-temperature heat-treatment. The rupture elongation is decreased by higher-temperature solution-treatment. But, even though the material has been solution-treated at 1,200°C, it has the rather high elongation of 15%. (4) If the solution-treatment temperature before cold working is high, the decrease in the creep rupture strength due to cold-working is much retarded.
