SOME OBSERVATIONS ON TIME-HARDENING AND STRAIN-HARDENING RULES FOR CREEP IN ZIRCALOY-2

The role of accurate creep prediction in zirconium alloys, and the Zircaloys in particular, has become increasingly important in light water reactor core component design and behavior analyses. A study was made of the applicability of time-hardening and strain-hardening rules to describe creep deformation in Zircaloy-2 under variable stress and temperature conditions. Variable stress and variable temperature creep data were compared to isotonic (iso-stress) and isothermal data in the stress regime 69 to 172 MPa and the temperature regime 325 to 400 degree C. It was observed that creep deformation under these variable conditions does not follow a time-hardening rule. This paper formulates strain-hardening rule, which describes well the variable temperature creep deformation at temperatures up to 375 degree C. At 400 degree C, however, the strain-hardening rule broke down because of a nonnegligible recovery rate.