Effect Of Pulse Electric Current On The Thermal Fatigue Behavior Of Cast Hot Work Die Steel

As the shape of mould cavity is complex, the time of machining mould is long and the value of mould is expensive, so it has the name"black gold". In our country, a great number of mould will be consumed one year, which costs tens million RMB. As the mould works under the circumstance that the temperature changes all the time, which causes mould fatigue, craze and rupture easily. So it needs researchers to probe a method to prolong the thermal fatigue life of mould. Researchers find that the treatment of pulse electric current not only can prolong the thermal fatigue life of materials, but also avoid the whole microstructures be damaged in the process of electrifying to the fatigue materials, so the treatment of pulse electric current is a good method to prolong the fatigue life of materials, and it has high value to research.This paper mainly studies the effect of pulse electric current with different duration time, voltage and electrifying times on thermal fatigue behavior of cast hot work die steel made in Ji Lin University.(1) The treatment of pulse electric current (7.04V and electrifying once) can change the state of stress in thermal fatigue samples, samples containing crack, which means the treatment of pulse electric current can make drawing-stress change into press-stress, and can retard the initiation and propagation of crack in some excess. (2) Under the same voltage, the longer the duration time of pulse electric current is, from 0ms to 220ms, the thinner the microstructure ahead of prefab notch is; from 220ms to 420ms, the thinner the microstructure in the white- brightness zone ahead of prefab notch. Under the same duration time of pulse electric current (300ms), the larger the voltage (3.52V—7.04V)is, the thinner the microstructure ahead of prefab notch is. Under the same voltage (7.04V) and duration time of pulse electric current, electrifying continuously can the microstructures ahead of prefab notch in the thermal fatigue samples and samples containing crack thick.(3) The treatment of pulse electric current can change the hardness ahead of prefab notch in samples. Under the voltage is 7.04V, the duration time is from 0ms to 200ms, the hardness ahead of prefab notch in the thermal fatigue and containing crack samples by the treatment of pulse electric current takes on the drop trend; From 280ms to 380ms, the hardness ahead of prefab notch in the thermal fatigue and containing crack samples by the treatment of pulse electric current takes on the increased trend. Under the same voltage (7.04V) and duration time (200ms), electrifying continuously can make hardness ahead of prefab notch in thermal samples and samples containing crack drop; Electrifying discontinuously can increase hardness ahead of prefab notch in thermal samples and samples containing crack.(4) Under the same duration time of pulse electric current, the larger the voltage is, the better the effect on retarding crack initiation and propagation by the treatment of pulse electric current once. The white-brightness zone caused by the treatment of pulse electric current has the better effect on retarding crack initiation and propagation. The parameters of pulse electric current which are 7.04V and 220ms are best in making thermal fatigue recover. In the process of retarding crack propagation, the protruding zone ahead of prefab notch in thermal fatigue samples, samples containing crack caused by treatment of pulse electric current once has the best effect on retarding crack propagation.