Effects Of Shape Coupling Factor And Temperature On Thermal Fatigue Property Of H13Steel

In this paper, the thermal fatigue property of H13hot working tool steel was studied.Based on the study of natural biological coupling phenomena and bionics, bioniccoupling conception of H13steel’s surface was proposed. This method could improve thethermal fatigue performance and extend the service life of H13steel. There are manyfactors which affect the thermal fatigue property of bionic coupling sample, such asbionic coupling unit’s size and distribution, but the unit sectional morphology and shapecoupling factor were not studied. Therefore, the objective of this study was to investigatethe effect of different unit sectional morphology (including ‘prolate’,‘U’ and ‘V’morphology) on the thermal fatigue property of H13hot-work tool steel, in order to fndout the optimum unit sectional morphology to effectively enhance the thermal fatigueproperty. The mechanism of different unit sectional morphology effect on thermal fatigueproperties was explored. There are three kinds of unit shape couping factor: spot-shape,striation-shape and reticulation-shape. The thermal fatigue properties of bionic sampleswith three kinds of shapes of bionic coupling unit and untreated samples wereinvestigated during different thermal fatigue temperature, at600℃,650℃,700℃and750℃, to explore the effects of shape coupling factor and thermal fatigue temperature onthermal fatigue property of H13steel. Then, the thermal fatigue mechanism was studied.Moreover, based on different thermal fatigue temperature, the evolution of microstructureand the variation of hardness of bionic coupling unit and matrix were studied andcompared.The results showed that the thermal fatigue property of hot-work tool steel processedby a laser bionic coupling process got a remarkable improvement compared to untreatedsample. Among three different bionic coupling unit sectional morphologies, the results showed that the ‘U’ morphology unit had the optimum thermal fatigue property, then the‘V’ morphology unit which was better than the ‘prolate’ morphology unit, because thedepth of ‘U’ morphology unit and ‘V’ morphology unit were greater than ‘prolate’morphology unit’s, the width on the depth direction of ‘U’ morphology unit was greaterthan ‘V’ morphology unit’s. As thermal cycle temperature increased, the number andlength of thermal fatigue cracks of H13hot-work tool steel both increased the thermalfatigue property of H13hot-work tool steel declined. After the thermal fatigue test, amongthree kinds of the bionic coupling samples, the number of thermal fatigue cracks ofreticulation-shape sample was the least, the thermal fatigue property of reticulation-shapesample was the best, striation-shape sample’s thermal fatigue property was better thanspot-shape sample’s. When the thermal fatigue temperature increased, the thermalstability of bionic coupling units and matrix got worse than before. As the thermal fatiguetemperature and the cycles of thermal fatigue both increased, the microhardness of bioniccoupling unit and matrix declined. The microstructure observation indicated that, withthermal cycle temperature increasing, the coarsening degrees of microstructures of bioniccoupling units increased and the martensite in matrix decomposed. The bionic couplingunit can not only inhibit the initiation of crack, but also restrain the expansion of the crack.Because of the individual reinforcement effect of bionic coupling unit, the sample couldinhibit the initiation of crack by stress counteraction mechanism and double mix strongmechanism. When the thermal fatigue cracks extended to the bionic coupling unit,thermal fatigue cracks were impeded, dulled, bifurcated, deflected, even terminated. Thepropagation speed of the thermal fatigue cracks declined, the bionic coupling unitinhibited the expansion of cracks effectively.