Study On Process Technology Of Laser Cladding Iron-based Alloy Powder For High-speed Trains Brake Disc

Disc braking is the most reliable braking method in the mechanical braking mode of high speed train,whose essence is to convert kinetic energy into thermal energy through the interaction between friction pairs.However,frictional wear and thermal fatigue often lead to wear and crack on the surface and near surface of brake disc,which results in failure of the disc brake device.By using the method of compound manufacturing,this study takes domestic cast steel as the matrix and prepares a laser cladding layer with a thickness of less than 5 mm on its surface.By studying and controlling the microstructure and properties of the wear-resistant layer,the purpose of improving the performance of the brake disc of high speed trains is achieved.Firstly,the laser cladding layer was prepared on the cast steel matrix with mechanical mixed iron base powder.The phase of the laser cladding layer is the?of the solid body centered cubic?bcc?structure strengthened by Fe-Cr,Ni-Cr-Fe and?Fe,Ni?.The burning loss of C element in the laser cladding layer is 80%.The microstructure of the laser cladding layer is mixed by martensite and ferrite,and the microhardness is similar to the hardness of the substrate,floating within the range of330³45 HV.The main defects of the laser cladding layer are inclusions,non fusion and pores.The tensile test of the laser cladding layer shows that there is no work hardening stage,the yield strength is 929 MPa,and the elongation is 11%.Secondly,the laser cladding layer was prepared on the cast steel matrix with alloyed iron base powder.The phase of the laser cladding layer is the?-Fe of the solid body centered cubic?bcc?structure strengthened by Fe-Cr,Ni-Cr-Fe and?Fe,Ni?.The burning loss of C element in the laser cladding layer is 25%.The microstructure of the laser cladding layer is martensite,and the microhardness is higher than that of the substrate,floating within the range of 360³80 HV.Compared with the laser cladding layer made by mechanical hybrid iron based powder,the number of defects in the laser cladding layer is significantly reduced.The tensile result shows that the laser cladding layer does not have a work hardening stage,the yield strength is 1190 MPa,and the elongation is 8.8%.The impact gap positions of the complex of laser cladding layer and cast steel are different,and both of the impact toughness is more than 40 J·cm^-2,and the impact toughness of the complex is about2.5 times higher than that of a single matrix material.Finally,the friction and wear test of the laser cladding layer of alloyed iron base powder is carried out.The titular brake pressure is 1 times higher than the actual brake pressure of the high speed train.The results show that the average wear of the laser cladding layer is 3.333 mg,the average friction coefficient is 0.702,the grinding mechanism is abrasive wear,the average wear of the matrix is 4.667 mg,the average friction factor is 0.797,and the grinding mechanism is abrasive wear.In addition,under the condition of 600?,the wear of the laser cladding layer is negative,and the average friction coefficient is 0.398.The wear mechanism is mainly adhesive wear,and abrasive wear and oxidation wear also exist.The results show that the microstructure,mechanical properties and friction and wear properties of the alloying Fe based powder laser cladding layer are better than those of cast steel substrate,which can provide a research idea or a research means for further improvement of the brake disc performance of high speed train.