| Owing to the heavy load development of railway transportation,the service environment of frog and heavily loaded rail is becoming more and more severe,which leads to wearing failure,spalling and even crushing deformation of the frog and the rail.This has significantly shortened the service life of the high manganese steel frog and the rail,and seriously threatened the safety of running the train.Laser cladding technology is widely used in repairing broken workpieces and surface modification of metal materials due to its advantages such as metallurgical combination of cladding layer and substrate material,small thermal deformation and easy automation.In this paper,three iron base alloy powders(brand DJ101,DJ106 and DJ108 respectively)and a nickel base alloy powder(brand Ni625)were selected as cladding material system with high manganese steel(ZGMnl3)and rail steel(U20Mn2SiCrNiMo)as the substrate for laser cladding experiments.Metallographic microscope,scanning electron microscope(SEM),transmission electron microscope(TEM)and X-ray diffraction(XRD)were used to characterize the formability,microstructure and phase composition of iron-based and nickel-based laser cladding layers.The hardness,abrasion resistance,stretching and bending properties of the laser cladding layer were analyzed by means of microhardness tester,wear tester,tensile testing machine and other instruments,so as to provide ideas for repairing damaged frog and rail by means of laser cladding technology.The main experimental results are shown as following:(1)A solid metallurgical bond is formed between the iron base cladding layer DJ101,DJ108 and the frog foundation of high manganese steel,as well as the iron base cladding layer DJI01,DJ106,DJ108 and the nickel base cladding layer Ni625 and the rail steel substrate,with no crack defects existing in the cladding layers of all systems.From fusion line to surface layer,the solidified microstructure of Fe-based and Ni-based cladding layer is plane crystal,cellular crystal,dendrite/cellular dendrite,and equiaxed crystal/equiaxed dendrite,exhibiting obvious rapid and directional solidification microstructure.(2)Iron chromium solid solution,iron nickel solid solution,as well as(Cr,Fe)7C3 and Cr3C2 hard phases are found in iron and nickel based cladding layers.Resulting from solid solution strengthening and second phase strengthening effects,the hardness of cladding layer is significantly higher than that of steel substrate.The microhardness of iron base cladding layer DJ101 is 2.3 times and 1.8 times that of rail steel substrate respectively.The hardness of iron base cladding layer DJ108 is 2.2 times and 1.7 times that of high manganese steel frog and rail steel respectively.The hardness of iron base cladding layer DJ106 is 1.1 times that of rail steel.The Ni-based Ni625 cladding layer is 1.8 times that of rail steel.(3)The wear resistance of the iron and nickel based cladding layer is higher than that of the substrate.When the wear time is 60 minutes,the weight loss of the high manganese steel frog substrate is 2.6 times and 2.3 times of the iron based cladding layer DJI01 and DJ108 respectively.The weight loss of rail steel substrate is 1.8 times,1.3 times,1.6 times and 1.8 times of DJI01,DJ106,DJ108 and Ni625 respectively.Solid solution strengthening and second phase strengthening of iron base and nickel base cladding layer contribute to their abrasive wear and adhesive wear mechanism,whereas high manganese frog steel and rail steel demonstrate adhesion wear mechanism.(4)The bending fracture results of DJ106 cladding layer on rail steel show that the substrate of rail steel is cleavage fracture,and DJ106 cladding layer contains ductile fracture,quasi-cleavage fracture and cleavage fracture. |
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