Strain and temperature contributions to structural evolution in a Re-containing 10% Cr-3% Co-3% W steel during creep

Abstract

ABSTRACT A Re-containing 10% Cr-3% Co-3% W steel with low N and high B contents subjected to normalising at 1050°C and tempering at 770°C was crept at 650°C under the applied stresses ranging from 200 to 100 MPa with a step of 20 MPa. During creep both the temperature and the strain affect the tempered martensite lath structure that causes the thermal and strain-induced recoveries, respectively, and degradation of structure. Both these recoveries lead to premature failure. The microstructure in the gauge and grip portions of the crept samples were investigated separately to estimate the contributions of temperature and strain during creep to the evolution of tempered martensite lath structure of the Re-containing 10% Cr-3% Co-3% W steel. The W depletion from the solid solution was accelerated by creep strain during short-term creep. The lath width and particle sizes were stable during long-term ageing at temperature of 650°C in the grip portions of the crept samples. The width of martensitic laths was 350 nm after 13,600 h of long-term ageing. The creep strain facilitates the recovery of the structure causing the subgrain formation with a mean size of subgrains of 1.1 μm and particle coarsening in the gauge and neck sections. The precipitation of W-rich Laves phase particles was observed in both grip and gauge portions. The constant coarsening rate of M23C6 carbides was significantly lower during long-term ageing than that during creep, whereas the constant coarsening rates of Laves phase particles were comparable in both grip and gauge sections of the crept samples.