Research On Microstructure And Properties Of Composite Coating By Laser Cladding On Alloy Steel Surface

As one of the most important components of the rolling mill, it’s surface possess oxidation and wear failure by synergetic effect of periodic thermal and mechanical force during rolling. These failures have serious impacts on steel rolling quality and production efficiency. In this paper, ceramic particles reinforced Fe-based composite coatings were produced on high chrome cast steels by laser cladding using ferrotitanium, ferrochromium, ferromolybdenum and graphite as raw powders. The microstructure and properties of base metal and composite coatings are investigated by means of optical microscopy (OM), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), microhardness tester and block-on-ring wear tester, resistance furnace and high temperature wear tester.Composite coating was prepared by laser melting the preplaced powders on high chrome cast steels. The influences of laser cladding parameters such as laser power, pre-placed powder thickness and overlapping rate on formation, shape coefficient and dilution of the clad layers were studied in this paper. Results show that when laser beam defocused 15 mm, laser power was 900W, scanning speed was 5 mm/s, thickness of pre-placed powder was about 1.2 mm, overlapping rate was 30%, the laser clad layers would have better appearance, proper shape coefficient and dilution and a good metallurgical bonding with the substrate.Constituents and contents of raw powders were key factors in influencing microstructure hardness and room temperature wear resistance of clad layer. Using ferrotitanium and graphite as raw materials, TiC reinforced Fe matrix composite coatings were prepared. Phase constituent of coating is α-Fe and TiC. The hardness and room wear resistance of these coatings are slightly improved than steel substrate. Adding ferromolybdenum or ferrochromium to ferrotitanium and graphite as raw powders separately, TiC-MoC and TiC+Cr7C3 ceramic particles were synthesized in the coating respectively, these carbides can effectively improve hardness and wear resistance of composite coatings. TiC\MoC and Cr7C3 carbides were synthesized in the clad layer by laser melting raw powders consist of ferromolybdenum, ferrochromium, ferrotitanium and graphite. As the content of ferromolybdenum and ferrochromium in raw materials were both 15wt.%, the hardness and wear resistance of clad layer is the best among all clad layers involved in this paper, they are 2 and 5 times than that of steel substrate respectively.Different content of ferromolybdenum or ferrochromium in precursor powders would affect the oxidation resistance and high temperature wear resistance of clad layers. Dense Cr2O3 will generate on surface of composite coating by reacting between Cr and O. Mo can improve the thermal stability of the clad layer and the bonding strength between oxide film and clad layer. Mo and Cr are both of effects to improving oxidation resistance and high temperature wear resistance of clad layer. In aspect of high temperature wear resistance, Mo has a certain impact on improving the property, but there is a few impact if adding Cr into raw powders separately. When 15wt.% ferromolybdenum and 15wt.% ferrochromium were added in precursor, oxidation mass gain and high temperature wear weightlessness of coating were only about 1/2 and 1/20 than that of the steel substrate.