The Effects Of Cryogenic Treatment On Hardening Behavior And Abrasion Resistance Of High Chromium Cast Irons Subjected To Sub-critical Treatment

High-chromium cast irons have long been considered candidate materials for wear-resistance components in the mining and minerals industry. In the as-cast condition, the microstructure consists essentially of dendrites of austenite in a matrix of a eutectic mixture of austenite and M7C3 carbides embedded in a martensite matrix that contains retained austenite. The as-cast high-chromium cast irons have not well abrasion resistance and they must be properly heat-treated, and then has the finer wear resistance, commonly. The heat treatments used commonly are destabilization treatment and sub-critical treatment. Compared with destabilization heat treatment, adopting sub-critical treatment can avoid deforming and fissuring of casts, reduce cost, save on energy resource and improve working conditions of workers.Over the past few decades, interest has been paid in the effect of low-temperature treatment on the performance of steels. Cryogenic treatment is an inexpensive one time permanent treatment affecting the entire section of the component.In this paper we has investigated hardening behavior, mechanism and abrasion resistance of high-chromium cast irons subjected to sub-critical treatment followed by cryogenic treatment by X-ray diffraction, SEM, TEM, magnetic method,hardness test, and wear test.The results show that in the sub-critical treatment followed by air cooling, when the heating temperature (from 400℃ to 650℃) is increased, the hardness of the alloy increases until it reaches the maximum, and then the hardness begins to fall. For the deep cryogenic treatment, there is similar characteristic in hardening behavior. But its hardness is higher than that of air cooling. Cryogenic treatment makes the alloy present a more refined and homogeneous matrix. In the course of sub-critical treatment followed by cryogenic treatment, the amount of precipitated secondary carbide was more than that in air cooling. Cryogenic treatment can further reduce the austenite content but can not make retained austenite transform to martensite completely.The results of wear test indicate that the abrasion resistance of high-chromium cast irons relates with their hardness. With the increase of hardness, the abrasion resistance has been improved. Their microstructures contained still some retained austenite when the abrasion resistance reaches the maximum. Because the amount of retained austenite in the matrix can inactivate crack tip and inhibit crack developing for better microplasticity of retained austenite. Too less retained austenite is not favourable for improving the abrasion resistance.After cryogenic treatment, the hardness and abrasion resistance of high chromium cast irons can be improved obviously due to the precipitation of secondary carbides, the martensite transformation and a refined microstructure resulting from cryogenics treatment.