Yield Stress of 21-6-9 Stainless Steel Over Very Wide Ranges of Strain Rates and Temperatures

Abstract

The yield strength of solution-annealed 21-6-9 austenitic stainless steel was determined over a wider temperature range (−195 to 1100 °C) and strain rate (10−4 to 104 s−1) than has been previously reported. The most noteworthy characteristic of the variation of yield stress with temperature was the dramatic decrease in yield strength from −195 to 300 °C. The strain-rate sensitivity exponent, m, was determined using strain-rate change tests. m dramatically increases at about 850 °C with increasing temperature and m is approximately independent of strain (structure). Hopkinson split-bar tests from ambient temperature to 750 °C indicate that the strain-rate sensitivity of 21-6-9 is not strongly influenced by the over eight orders of magnitude change in strain rate. This suggests that the mechanism(s) of plastic flow at the higher rates is similar to that at lower rates. This contention was corroborated by transmission electron microscopy. The yield stress shows grain-size dependency.