| H13 steel is the most widely used and representative hot-working die steel.With its excellent properties,it is widely used in hot upsetting,hot extrusion and die-casting die.Thermal fatigue and wear are the main failure modes of hot working dies,and 80% of the failure comes from the functional surface.Therefore,improving the thermal fatigue resistance and wear resistance of H13 steel functional surface has important practical significance for prolonging its service life.This paper combines laser cladding technology with bionic coupling theory,and Nickel-based alloy-based functional surface is prepared on H13 steel surface to improve the wear resistance and thermal fatigue resistance of H13 steel.In order to further improve the service life of the die,the research is carried out from the aspects of technology and material.The main research work is as follows.(1)A lot of experiments of cladding Ni60 powder on H13 steel surface were carried out.The influence curves between process parameters and microhardness of Ni60 laser cladding were obtained,and the effect of undercooling on microhardness was analyzed.Microstructure and grain size can be significantly changed by adjusting undercooling.The ratio of nucleation rate to crystal growth rate is affected by too much or too little undercooling.High undercooling can inhibit the precipitation of impurities,and it is good for crack suppression.(2)Laser cladding experiments were carried out by mixing 25% WC with Ni60 powder in order to improve microhardness and reduce cracks.It is found that the cracks in the cladding layer decrease with the decrease of the voltage ratio of WC to Ni60 powder feeding.When the voltage ratio of WC to Ni60 powder feeding is changed to 2:3,the cracks in the cladding layer begin to disappear.It just can’t eliminate the bubbles in the cladding layer.The cladding layer with good performance can be obtained by adjusting the ratio of powder feeding voltage to scanning speed and the ratio of laser power to scanning speed.When the ratio of powder feeding voltage to scanning speed is between 3 and 7 Vs/mm and the ratio of laser power to scanning speed is between 100 and 200 Ws/mm,there are no bubbles and cracks in the cladding layer,and its microhardness is greater than 900 HV.(3)Within the above data range,the height of the cladding layer and melting depth of matrix were studied.When the ratio of laser power to scanning speed is constant,the height of cladding layer increases firstly,then decreases with the increase of the ratio of powder feeding voltage to scanning speed,even it becomes zero.The melting depth of matrix decreases gradually with the increase of the ratio of powder feeding voltage to scanning speed,and the greater the ratio of laser power to scanning speed under the same ratio of powder feeding voltage to scanning speed,the greater the melting depth of matrix.When the ratio of laser power to scanning speed and cladding spacing are fixed,the surface will gradually steepen with the increase of the ratio of powder feeding voltage to scanning speed in multi-channel laser cladding.When the ratio of powder feeding voltage to scanning speed is 3Vs/mm,the cladding layer is flat.When it is 5Vs/mm,the cladding layer is wavy,and finally the cladding layer becomes a slope when it is 7Vs/mm.(4)Based on the above experimental data,bionic structure formed on H13 steel surface by laser cladding,and the thermal fatigue and wear resistance were tested.Thermal fatigue tests show that triangles have the best thermal fatigue resistance among the three bionic structures with the same spacing.The thermal fatigue resistance of quadrilateral bionic structure is higher than that of strip bionic structure,and the plane of die steel without bionic structure is the worst.Wear resistance test shows that the wear resistance of bionic structure begins to decrease obviously when the spacing is more than 5 mm.The triangular bionic structure has the best wear resistance. |
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