Effect of stress-relief annealing on isothermal fatigue life of a new hot stamping die steel 4Cr2Mo2V

Abstract For 4Cr2Mo2V hot stamping die steel, the isothermal fatigue test was suspended at different cycles, and the stress-relief annealing was carried out in situ . After annealing, the fatigue tests were continued. The stress-relief annealing was carried out at 30%, 50% and 70% of the cycle life when the total strain amplitude was 0.5%, and the fatigue life was increased by 30.27%, 23.84% and 10.24% respectively. On the basis of Basquin-Coffin-Manson life prediction model, by adding the influence of stress-relief annealing on life, obtained the stress-relief annealing life prediction model. The dislocation density, microstructure and pole figure were analyzed by TEM and XRD to explore the mechanism of stress-relief annealing on prolonging fatigue life. After stress-relief annealing, the full width at half maximum (FWHM) decreased, and the dislocations originally piled up at the grain boundary moved into the grain, delayed the time of dislocation cell or wall formation. At the same time, it could also eliminate the trend of consistent orientation of most grains in the fatigue process. This is the main reason why stress-relief annealing prolongs fatigue life.