Study On The Microstructure And Properties Of Laser Cladding Layer On 5CrNiMo Steel

In the service process,hot-work die is often affected by large high temperature impact and alternating load,causing wear and oxidation failure on the surface.This not only seriously influences the quality of the products and production efficiency,but also increase the cost of manufacturing enterprises.Therefore,it has important economic benefits to prepare a coating of wear resistance and high temperature resistance by surface modification technology on the die surface to prolong its service life.Ceramic particles reinforced Fe-based composite coating produced by laser cladding has excellent performance,making it get more and more attention in the field of die repairing.In this paper,on the basis of laser cladding ceramic particles reinforced Fe-based coating,we further optimize it from two directions:adding rare earth oxide and introducing external field.The phase composition and microstructure of the cladding layers were characterized by X-ray diffraction,scanning electron microscopy and energy dispersive spectroscopy.The room temperature and high temperature mechanical properties were investigated by means of microhardness tester,ring-block wear tester,box-type resistance furnace and high temperature wear testing machine.Using B4C powders and ferroalloy powders such as ferrotitanium,ferrochromium and ferromolybdenum to prepare the cladding layer by laser cladding on the surface of 5CrNiMo steel.The cladding layer has good metallurgical bonding with the substrate,and the distribution of hard phase particles in the cladding layer was uniform.After the addition of rare earth Y2O3 to the alloy powders,the microstructure of the cladding layer was refined,and the hard particles became fine and uniform.When the rare earth content of Y2O3 was 2wt.%,the cladding Iayer had no cracks,pores,or other defects.The influence of rare earth Y2O3 content on the mechanical properties of cladding layer was studied.The results showed that with the addition of rare earth Y2O3,the hardness of the cladding layer was gradually increased,and the abrasion resistance increased first and then decreased.When the content of rare earth Y2O3 was 2wt.%,the hardness and wear resistance were the best,and the wear mechanism was the surface scratch.Though the 600? high temperature oxidation test and high temperature wear test,the cumulative oxidation weight and the high temperature friction coefficient of the cladding layer adding Y2O3 was significantly smaller than that of the cladding layer without Y2O3,and the high temperature wear volume was about 0.36 of the cladding layer without rare earth Y2O3.In the rotating magnetic field assisted,the microstructure and mechanical properties of the cladding layer have changed greatly.The morphology of the hard particles in the cladding layer tended to be refined and homogeneous with the increase of the magnetic field strength,and the internal quality of the cladding layer was obviously improved.The mechanical properties of the Fe-based cladding layer before and after the application of the magnetic field were measured at room temperature and high temperature.It was found that the microhardness,room temperature and high temperature wear resistance and high temperature oxidation resistance of the cladding layer were greatly improved after applying the magnetic field.When the magnetic field strength was 40 mT,the average microhardness of cladding layer was 1353HV0.2,the room temperature wear weight loss was about 0.57 of which without magnetic field.After oxidation at 600? for 54h,the cumulative oxidation weight of the cladding layer was significantly smaller than that of the cladding layer without the magnetic field.Using SEM to observe the morphology of the cladding layers after oxidation,it could be seen that the oxide layer of the cladding layer was smooth and compact.After 20min high temperature wear,the friction coefficient of the cladding layer fluctuated around 0.3 and was quite stable.