POSITRON-ANNIHILATION STUDY ON THE THERMAL FATIGUE IN A DIE STEEL

Samples of 5Cr2NiMoVSi die steel which underwent thermal fatigue with different fatigue cycles have been studied by using microhardness and positron lifetime measurements. It is found that the microhardness and the positron lifetime parameters increase and decrease alternatively with increasing the number of the fatigue cycles. The experimental res ults reveal that the fatigue strain, the dynamical recovery, and recry stallization and the precipitation are main causes of variation of the defects in the process of thermal fatigue.