Papers by Keyword: 304H Stainless Steel

Abstract: 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.

Abstract: Experiments were carried out in which the dependence of the fractional softening on temperature, time and strain rate was determined in a 304H stainless steel. Three prestrain ranges were identified pertaining to three different post-deformation softening behaviors: 1) prestraining to below the DRX critical strain: strongly strain dependent softening by SRX alone with softening kinetics controlled by growth rate of the nuclei; 2) prestraining to above the DRX critical strain: SRX + MDRX softening with weaker strain dependence of the kinetics but still controlled by grain growth; 3) at a prestrain of ε* and beyond: nucleation-controlled MDRX softening with the full inhibition of SRX. The transition prestrain ε* can exceed the peak strain if the DRX grain refinement ratio g = D0/DDRX > 4. The transition to MDRX-dominated softening can be attributed to a constant value of the normalized strain hardening rate independent of the preloading temperature and strain rate. The softening data from the compression tests show that at ε*, the time for half softening t50 exhibits a minimum. These data differ somewhat from observations obtained in the torsion testing of solid bars, in which no strain dependence of t50 was detected at ε* and beyond. Whether or not the strain dependence of t50 vanishes in the MDRX range is sensitive to the test method employed to study the post-deformation softening.