Reaearch On The Technology And Microstructure And Properties Of Stellite 6/WC Gradient Composite Coatings By Laser Cladding On The Surface Of 45 Steel

In the cold rolling process of steel,rolls are used as key components of rolling steel plates.The work conditions are relatively harsh.During the service,they are easily impacted and worn by the steel plate.The surface is often turned due to bumps and wear.Because the amount of machining is too large,the size is out of tolerance,causing the failure to scrap.In this paper,the high hardness wear-resistant hard coatings was prepared on cold rolling rollers regular materials 45 steel surfaces by coaxial powder-feeding laser cladding technology.In order to increase the service life of the rolls and save production costs.In order to reduce the sensitivity of the cladding layer cracking,while ensuring its hardness and wear resistance.In this paper,the gradient composite cladding layer of metal-based ceramic materials was adopted.Spherical WC with different mass fractions（10%,20%,30%,40%）were added to Stellite 6 powder as a surface reinforcement layer.Stellite 6 powder was used as an intermediate transition layer.The tediousness of multi-layer gradient coatings was reduced.The Stellite 6/WC gradient composite cladding layers were prepared.The effects of spherical WC addition on surface forming,phase composition,microstructure,microhardness and wear resistance of Stellite 6/WC gradient composite cladding layer were explored.Thus the optimal WC addition amount was derived.On this basis,the optimal amount of irregular WC was added to Stellite 6 powder as a surface strengthening layer.The differences in WC melting methods of different morphographies under the same gradient were studied.And the effects of WC morphology on surface forming,phase composition,microstructure,microhardness and wear resistance of Stellite 6/WC gradient composite cladding layer were studied.Firstly,the orthogonal test was adopted.The laser power,scanning speed,powder feeding speed were used as the main parameters.The height and microhardness of the cladding layer were used as evaluation indicators.The best single-pass process parameters were determined by range analysis:laser power 1400 W,scanning speed 5mm/s,powder feeding speed 12 r/min,powder feeding gas flow rate 6 L/min,protective gas flow 6.5 L/min,defocus amount 16 mm.The well-formed double-layer Stellite 6cladding layer was prepared with optimized process parameters as well as a 50%lap rates.The results show that the element content at the fusion site did not change much.The microstructure of the Stellite 6 cladding layer was mainly composed of intracrystallineγ-Co and M₂₃C₆ carbides distributed along the grain boundaries.The surface layer was similar to the middle layer in hardness,about 514.2 HV₁.It had excellent wear resistance,and the wear rate was 1.69×10^-5 mm³·N^-1·m^-1.The gradient composite cladding layer could effectively solve the cracking problem of the cladding layer caused by excessive WC addition.The W element content and the number of un-melted WC particles were gradient transitions from the middle layer to the surface layer.After the addition of spherical WC,the microstructure of the cladding layer was still composed of dendrite and intergranular carbide,and the M₇C₃ phase was added.As the amount of WC additions increases,the Co₆W₆C,WC,W₂C phases were found in the composite cladding layer.The degree of melting of individual WC particles was weakened.The area occupied by intergranular carbides was increased.The un-melted WC particles were distributed more evenly,and the solidification method of the area around the un-melted WC particles would be change.The microhardness was increased in a gradient from the intermediate to the surface layer.At 30%spherical WC addition,the gradient composite cladding layer had the best molding quality,microhardness and wear resistance.The 30%was the optimal amount to add,and the gradient composite cladding layers with spherical and irregular WC were prepared.Comparison analysis found that the combined effect of edge melting and internal crushing was the spherical WC melting method with rough surfaces and loose structures.The melting method of irregular WC was only edge melting.Its interior was relatively intact,and the bond between WC particles and the cladding layer could be enhanced through the transition reaction zone formed at the edge.During solidification,un-melted WC particles could be used as nucleation points.Micro-zone directed cooling was formed.The intergranular carbide area in the spherical WC cladding layer was accounted for a larger proportion.When irregular WC was added,the microhardness of the surface layer was reduced by about 16.6%compared with the spherical WC cladding layer.However,its wear resistance was better.The analysis concluded that un-melted irregular WC particles had a complete interior.It was not easily broken during the wear process.It could be used as a support point to hinder the development of furrows.The ploughing of the grinding ball to the cladding layer was reduced.