| AISI H13?4Cr5MoSiV1?die steel is one of the most widely used die steels because of its high toughness,high red hardness and high resistance to cold and thermal fatigue.However,due to its poor hardness and wear resistance,there will generate some serious results,such as oxidation,adhesion and wear when it was used as die-casting aluminium die and penetrating plug of seamless steel tube bearing high temperature and pressure,which greatly reduces production efficiency and increases cost.This severe situation can be improved by plasma surface heat treatment process.The tribological properties of H13 steel were improved by plasma nitriding,plasma nitrocarburizing and plasma sulfurizing.The first two process improved the wear resistance of the material by forming a layer mainly consisting of?and??phases on the surface,while plasma sulfurizing can reduce wear by producing a layer mainly composed of FeS at lower temperature and shorter holding time.The microstructure and tribological properties of the treated materials were studied by XRD,SEM and friction and wear tests.The main research contents and conclusions are as follows:?1?Plasma nitriding of H13 steel was carried out at a constant pressure of 100 Pa.The tribological properties of H13 steel at different temperatures,nitrogen and hydrogen ratios and different times were studied.Firstly,in the atmosphere of N2/H2=1/2,the plasma nitriding was conducted for 6 hours at 480,500,and 520?,respectively.The results showed that with the increase of temperature,the compound layer became thicker gradually,while the thickness of the nitriding layer showing changeless with a value of 140 um.The samples treated at 500?owned excellent tribological properties.Secondly,under the conditions of N2/H2=1/2,1/1 and 2/1,the experiment was carried out in 500?with a duration of 6 h.The results showed that with the increase of nitrogen ratio in mixed atmosphere,it tended to form?-Fe2-3N phase in the compound layer,and the wear resistance of the material increases gradually.When N2/H2=2/1,the wear resistance was superior.Finally,the holding time was extended to 8 hours at 500?with the N2/H2 being 2/1.To some extent,it was found that the thickness of compound layer and diffusion layer increased,and the nitriding layer was 20?m thicker than that at 6 h.Besides,wear resistance increased by 1/3 compared with that at 6 h,about 15 times higher than that of non-nitrided samples,showing superior tribological properties.?2?A small amount of methane was introduced into N2/H2=2/1 nitriding atmosphere as carbon source for plasma nitrocarburizing at different temperatures for 6 hours.The results showed that the compound layer of nitrocarburizing layer was mainly composed of?-Fe2-3?C,N?,??-Fe4N and CrN.The surface hardness was lower,the surface morphology smoother,and the thickness of the nitrocarburizing layer smaller than that of the nitriding layer.However,the wear resistance of the nitrocarburizing layer was superior,and the samples treated at 500?possessed better wear resistance than nitriding layer.?3?H13 steel was treated by plasma sulphurizing at different temperatures for 2 hours.The results showed that the thickness of sulphurized layer increases with the increase of temperature.The friction coefficients of the samples without sulphurization treatment,sulphurization at 150 and sulphurization at 170 were 0.75,0.72 and 0.65,respectively.The friction coefficients of the sulphurized samples decreased gradually with the increase of sulphurization temperature,which was attributed to the formation of FeS compound with dense hexagonal crystal structure in the sulphurized layer,liable to slide along the dense row plane when subjected to stress,so the shear strength was low and owned excellent anti-abrasion performance and anti-abrasion effect,as a result,the wear rate was more than four times lower than that of the sample without sulphurizing treatment. |
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