The Strain-Independence of Interpass Softening during the Hot Compression of 304 H Stainless Steel

The kinetics of interpass softening and the strain (ε*) at which they become strain-independent were determined by means of double-hit hot compression tests. For this purpose, interrupted compression tests were conducted at strain rates of 0.01 and 0.1 s-1 to initial strains ranging from that corresponding to the initiation of DRX (εc) to the onset of steady state flow (εs.). Test temperatures between 1000 and 1100 °C (inclusive) were employed. Interpass times were varied from 0.3 to 1000 seconds. The fractional softening was determined using the 0.2% offset method. It is clear from the results that there is a transition strain (ε*) that separates the straindependent range of post-dynamic softening from the strain-independent range. The value of ε* obtained in this work was ε* = 4/3 εp. It was also found that the strain hardening rate was identical at all the critical strains (ε*) and took the value -22 MPa.