Different Test Parameters Under 3cr2w8v Steel Thermal Fatigue Performance Study

3Cr2W8V, which is one kind of hot work tool steels, has been used for a long time in our country. Thermal fatigue crack is the main form of its failure, but the experimental parameters of thermal fatigue property test method have not been standard yet. By changing the maximum temperature and the heating rate in the thermal cycles, this work use Uddeholm self-controlled fatigue experimental method to test the thermal fatigue property of 3Cr2W8V, which has been pre-treated with different heat treatment methods. The influences of different experimental parameters to the thermal fatigue property of 3Cr2W8V are studied, by using the OM, SEM and other modern technologies. The results show like that:In the thermal cycles, the pressure strain occurs while 3Cr2W8V is heated and the tensile strain occurs while it is cooled. The maximum temperature in the thermal cycles has the main influence on the initiation and expansion of thermal fatigue crack of 3Cr2W8V steel. When the heating temperature rises, the initiation life of thermal fatigue crack shortens, and the expansion rate of thermal fatigue crack accelerates. The expansion path of the thermal fatigue crack is along the boundary. While 3Cr2W8V is heated at a high temperature in thermal cycles which beyond the tempering temperature in heat treatment, the life of 3Cr2W8V decreases obviously. By analyzing the stress in the sample and observing the morphology of the thermal fatigue crack, the results show that: the thermal stress of the specimen increases with the heating temperature increases; thermal fatigue cracks formed along the axis on the surface of the sample, and then they extend with the thermal cycle times increase. In the end, they form net thermal fatigue crack.The failure mechanism of thermal fatigue is determined by the heating rate in thermal cycles. When the sample is heated at a high heating rate, it is out of use in the form of thermal fatigue crack, which is caused by thermal stress; while the specimen is heated at a very low heating rate, the surface of it is dominated by oxidation. As a result, the failure mechanism of it is oxidation and corrosion. When the heating rate is between the two mentioned before, thermal fatigue crack and oxidation form on the suface of the sample, which lead the sample to failure. The thermal fatigue crack and the oxidation are caused by the effect of thermal stress and oxygenation, which have mutual influence on each other. The thermal stress increases and the oxidation become serious with the heating temperature increases, when the specimen is heated at a very high heating rate. Both of them can accelerate the expansion rate of thermal fatigue crack, whick can also shorten the life of 3Cr2W8V steel. At this time, the failure mechanism of it is thermal fatigue crack.The heating rate can influence the thermal stress of 3Cr2W8V in heating cycles and the extending rate of thermal fatigue crack, which also has an obvious impact on the test result of its thermal fatigue property. The extending rate of thermal fatigue crack decreases when the heating rate decreases, while the width-increase value becomes larger and the oxidation degree become serious. All these reduce the lifetime of 3Cr2W8V.The thermal fatigue property of 3Cr2W8V is determined by the final heat treatment method. Because different heat treatment methods due to different microstructures.When 3Cr2W8V steel is tested under the same experimental parameter, the sample which is quenched at a high temperature and tempered at a high temperature too, has a good resistance of thermal fatigue.