| Nowadays,countries pay more attention to the recycling of resources and sustainable economic development,and our remanufacturing industry is becoming more and more important and has been included in the category of strategic emerging industries.As a big producer,our country faces great challenges in waste disposal and resource consumption.Train axle is a crucial component in rail transit.In the process of train running,the wheel bearing is subjected to alternating load,which will lead to the fretting of the mating surface between the train axle and the wheel,and then lead to the fretting wear of the contact edge area between the train axle and the wheel,thus affecting the service safety of the train axle.Therefore,the remanufacturing of the train axle has become an urgent topic to be solved.In this paper,the multi-factor,multi-level and multi-objective experimental design method is adopted,the plasma cladding and submerged arc surfacing process is used,the axle steel EA1N is used as the matrix material,the iron base alloy powder provided by the company is used as the powder material,the influence of the process parameters in the plasma cladding and submerged arc surfacing process on the porosity and hardness of the coating is explored and optimized.And the Muffle furnace equipment is used to temper the sample prepared by the optimized parameters of submerged arc surfacing.The microstructure and mechanical properties of the optimized coating were analyzed by means of ultra-depth of field optical microscope,X-ray diffractometer,scanning electron microscope,microhardness tester,friction and wear tester,etc.The remanufacturing process suitable for train axle（axle）is analyzed.By plasma cladding and submerged arc surfacing,wear-resistant coating suitable for train axle surface repair was successfully prepared on the surface of steel EA1N.The results show that:（1）The hardness and wear resistance of the coating optimized by plasma cladding process are higher than that of the substrate,and the porosity is lower than that of the substrate.The microstructure of the coating is ferrite,lamellar pearlite and austenite.Multi-factor,multi-level and multi-objective experiment design optimization process parameters range:voltage（V）=29-31;Scanning speed（mm/min）=72-73;Powder delivery rate（r/min）=8-9;Ionic gas flow（L/min）=3.9-4.1.A group of parameters were selected in this interval to carry out the actual verification test,and the sample voltage was measured at 30 V.Scanning speed 73 mm/min;Powder feeding rate 8.0 r/min;Under the process parameters of ion gas flow rate 4.0L/min,the coating has good microstructure density,porosity of 0.238%,68.1%lower than that of the substrate,hardness of 54.2 HRC(585 HV0.2),191.3%higher than that of the substrate,and wear resistance is significantly higher than that of the substrate.The existence of austenite is because the temperature drops too fast in the process of plasma cladding and the high temperature austenite is not completely transformed.（2）The hardness and wear resistance of the coating optimized by submerged arc surfacing process are higher than that of the substrate,and the porosity is lower than that of the substrate.The microstructure of the coating is pearlite,ferrite and austenite.Multi-factor,multi-level and multi-objective experiment design optimization process parameters range:current（A）=340-350;Voltage（V）=24.5-25.5;Surfacing speed（m/h）=8.5-9.0;Dry elongation of welding wire（mm）=8.5-9.0.A group of parameters were selected in the process parameter interval to carry out the actual verification test,the sample was measured at 345 A;Voltage 25 V;Surfacing speed 9.0 m/h;At the dry elongation of the welding wire 9.0mm,the coating porosity is 0.352%,which is 52.9%lower than that of the substrate,the coating hardness is 36.6 HRC(360 HV0.2),which is79.3%higher than that of the substrate,and the wear resistance is significantly improved than that of the substrate.The existence of austenite is due to the high temperature and fast cooling rate of submerged arc surfacing welding,which leads to the failure of some high temperature austenite to transition to normal temperature phase.（3）The optimized submerged arc surfacing coating was tempered,and the highest hardness was 258HV0.2at the tempering temperature of540℃held for 4 h,which was 28.5%higher than that of the substrate.The microstructure of the coating was observed to show that the austenite changed to normal temperature pearlite and the grain became larger.The hardness of the coating was reduced after tempering compared with that before.The wear resistance is higher than that of matrix.Because the heat input of submerged arc surfacing welding is large,the internal stress is significantly reduced after tempering,and the cracks are less than before.（4）Two remanufacturing processes were used to successfully develop a method suitable for the remanufacturing of train axle.The wear resistance of the prepared coating was improved compared with that of the substrate,and the overall performance was in line with the international standard of train axle EA1N,providing a practical basis for the practical application of remanufacturing process to repair train axle. |
