Dynamic Strain-Aging in Fe-30%Cr Alloys
Mtohiko KOUSHIMA and Sei MIURA
Abstract:Many types of ferrite stainless alloys have deformation that is accompanied by serration. However, in many such cases, the actual cause of the serration still remains uncertain. Observations on Fe-30%Cr alloys revealed that 0.2%-proof stress increases at two different ranges of the deformation temperature. When the 0.2%-proof stress increased at the lower temperature range, two different types of serration could be observed. The strain hardening coefficient was calculated from the stress-strain curves. The strain hardening coefficient increased in the low temperature range but did not so in the high temperature range. The critical conditions for serration were determined by measuring the changes in the temperature and strain rate. When the critical conditions are determined, then the migration activation energy of moving solute atoms can be calculated. The solute atom that plays a role in causing the serration was determined from the activation energy of the solute atoms. Calculated activation energies were found to be 79.1kJ/mol and 216kJ/mol, respectively. Based on these results, we consider the cause of the serration observed in the low temperature range to be associated with the interaction of carbon and moving dislocations, while the serration evident in the higher temperature range is regarded as being due to the interaction between chromium and interstitial solute atom pairs with moving dislocations. Similar analyses were made for the pre-strain required to cause serration. The required pre-strain was observed for serration both in the low temperature range and that in the high temperature range. We also discuss the pre-strain required for causing serration. Key Words:Fe-Cr alloy, Dynamic strain aging, P-L effect, Ferrite steel, Solute atom, Solid solution hardening