Study On Microstructure And Properties Of Surface Modified Laser Cladding Coatings On 2Cr13 Steel

The turbine blades of blast furnace top gas recovery turbine unit（TRT）are the main part of the rotor system.During service,the blades fail in a short time due to the comprehensive effects of erosion and corrosion of blast furnace gas and wear of furnace dust on the blade surface.Take advantage of laser cladding technology to modify the surface of TRT blades to meet the requirements of operating conditions,not only can it lay a theoretical foundation for improving the corrosion resistance and wear resistance of TRT blades,but also have certain practical significance for improving the service life of the blades.Here,the TRT blade material 2Cr13 steel was selected as the substrate.Two sets of coatings,FeCoCrNiAlMo_x（x=0,0.25,0.5,0.75,1,mol ratio）and Inconel 625+xWC（x=10%,15%,20%,mass fraction）,were prepared on substrate surface by means of a single-pass and multi-layer superposition cladding method under wide beam mode.OM,SEM,EDS,XRD,EPMA,microhardness tester and electrochemical workstation were used to test and analyze the microstructure,phase composition,cross-sectional alloy element distribution,microhardness and electrochemical performance of cladding layers in 0.5 mol/L HCl solution.The effects of different Mo addition and WC addition on the microstructure and properties of the two coatings were also studied.The results show that the two sets of coatings prepared by laser cladding technology are of good quality and have no obvious defects such as cracks,pores and oxide inclusions.The coatings have a good metallurgical bonding with the substrate,and the microstructure of the coatings is compact,which has the typical characteristics of laser rapid solidification,and there is no overlapping interface between the layers.For FeCoCrNiAlMo_x alloy coatings,due to the dilution of the substrate,the actual composition of each coating deviates from the designed composition to varying degrees.The main component phases of coatings are body-centered cubic solid solutions（BCC）.With the change of Mo content,the main composition phase of the coatings does not change,but the microstructure is not the case.Mo₀,Mo_0.75.75 and Mo_1.0.0 coatings are mainly composed of columnar crystal and Cr-rich needle-like precipitates.Needle-like precipitates（α-Cr phase）are dispersed in the coatings and have a precipitation strengthening effect,which makes the microhardness of Mo₀,Mo_0.75.75 and Mo_1.0.0 coatings significantly improved.Mo_0.25.25 and Mo_0.5.5 coatings have typical dendritic structure,there is no significant difference in composition between dendrites and interdendrites,and their microhardness are similar.The average hardness（excluding transition zone）of Mo₀,Mo_0.25,Mo_0.5,Mo_0.75.75 and Mo_1.0.0 coatings is 478.6 HV₁,410.7 HV₁,369.26 HV₁,539.8 HV₁,540.5 HV₁,respectively,which is much higher than that of 2Cr13 steel（202HV₁）.In addition,all coatings can ameliorate corrosion resistance of the substrate.With the best corrosion resistance,a stable passive region appeared on the polarization curve of Mo_1.0.0 coating,and its surface corrosion morphology is a small amount of etch pits and granular oxides,which indicates that the addition of an appropriate amount of Mo is beneficial to improve the corrosion resistance of the coatings.For Inconel 625+xWC composite coatings,the main constituent phases areγ-（Ni,Fe）matrix and different kinds of secondary carbides(MC,M₂₃C₆),and numerous block-like M₆C carbide especially appears in 20%WC coating.The WC content has a significant effect on the microstructure of the composite coatings.When the WC content is 10%and 15%,the coatings have a developed columnar dendritic structure,while the20%WC coating is mainly composed of cellular and columnar dendrites.After analysis,theγ-（Ni,Fe）phase is present in the dendrites of several coatings,while the lamellar eutectic structure is composed ofγ-（Ni,Fe）+carbide between dendrites.With the increase of WC content,the average hardness of the composite coatings increases gradually.The hardness of the 20%WC coating is the highest（536.98 HV₁）,which is2.64 times of that of the 2Cr13 steel substrate.As the WC content increases,the corrosion resistance of the coatings gradually decreases.The 10%WC coating has the best corrosion resistance.Its self-corrosion potential is 790 mV higher than that of the substrate,and the self-corrosion current is only 0.86%of the substrate,which has a significant protection effect on the substrate.By comparison,it can be seen that among all the coatings,Mo_1.0.0 coating has the highest microhardness and better corrosion resistance,while 10%WC coating has the best corrosion resistance.