Research Of Thermal Fatigue Recover Of Hot Work Die Steel Treated By Current Pulse

The costs of mould possess a high proportion in industrial production process because of the high properties of mould materials, complicated cavity, long processing time and the expensive cost. Due to the high temperature operational environment of hot working mould steel, a fatigue phenomenon can occur on the surface of mould steel, which caused by high temperature, pressure, corrosion and abrasion, etc. The principal failure form of hot working mould steel is fatigue failure. The present developing tendency of industries are energy saving and nonpollution. Therefore, the research of extending fatigue failure cycle is very important significance in science and engineering fields.Organism self-restoration function can be imitated on mould steel fatigue restoration by inputting transient high energy utilizing high-density current pulse during the pulse treated process, which can extend the inoculation period of fatigue crack, depressing the expand velocity. Thus, the service life of mould is extended, and accordingly reduces fabrication cost and energy consumption. About 40-50 thousand of hot work die steel are consumed every year in our country, which worth several billion Yuan. Therefore, there is great national economic significance to enhance the thermal fatigue performance of hot work die steel.This paper mainly studies the effect of the thermal fatigue performance of newhot work die steel which is made in Jilin University treated by current pulse with different parameter including pressure, treating time, current density. And it also discusses the mechanism of current pulse treating, by analyzing the experimental results and the changing of parameter of pulsing current, the following conclusion can be made.(1) After the tired samples was treated by current pulse (parameter of the current pulse: 7V, 8.9×104A /m2, 100 ms, 1 time), its grain size decrease, with obvious refined martensite structure and the recrystallization behavior is the main causation. However, the microstructure of un-tired sample was not refined after treated by the same current pulse parameter.(2) It is found that a lot of bigger fatigue cracks in the un-treated fatigued sample during the heat cycle process, and there are much of chromic compound in the interior of cracks. After treated by current pulse, the size of crack is very minor, and there are small quantities of vanadium and carbide compound in the interior of cracks instead of chromium compound.(3) The hardness of precrack tip zone increased after treated by current pulse (parameter of the current pulse: 7V, 8.9×104A /m2, 100 ms, 1 time), while the hardness decreased at other zone, and the hardness value is similar with the untreated samples. The microstructure becomes homogeneous and fine at precrack tip zone, and the microhardness at that zone is higher than the same area of the untreated sample.(4) Based on the contrast of different current pulse parameter, the following parameter is the best, voltage, 7V, current density, 8.9×104A/m2, treated time, 100ms. Namely, the fatigue crack inoculation period extend 166.7%, with expanding velocity reducing 60.7% in comparison with untreated sample. And the effect is worse while the current pulse parameter is unsuitable, even it couldaccelerate the crack propagating rate of sample if the parameter of current pulse was too excessive.