Technology And Coating Performance Research Of Welding Wire Laser Cladding On High Speed Steel Surface

In order to achieve the aim of repairing high speed steel (HSS) tools by laser cladding with welding wire, the laser cladding experiments on the surface of M2 HSS base material with high hardness 966T welding wire by Nd:YAG pulse laser device have been done. This paper researched on the influences of laser processing parameters on geometrical morphology of cross-section and dilution rate, and optimized the processing parameters by orthogonal experiment. The performance of clad layer, such as chemical component, microstructures and morphology, microhardness, Rockwell hardness, red hardness, tribological properties, etc, were also studied and analyzed. The results verify the feasibility of acquiring the clad layer, which meets the requirement of industrial application, on the surface of HSS by laser cladding using high hardness welding wire and provided fundamental basis for HSS tools repairing by laser cladding.Single track cladding experiments show the processing parameters impact geometrical morphology through affecting the amount of heat input of laser. With the increase of laser current and pulse width, the thickness of clad layer decreases and the width and depth of melt pool increase. With the increase of scanning speed, the width and depth of melt pool have the trend of increasing. When the scanning speed is above 100 mm/min, the change of width of melt pool become stable and the depth decreases obviously because of the reduce of power density and large loss of heat. With the increase of defocusing amount, the width of melt pool increases and then decrease and the change of the thickness of clad layer is steady while the depth decreases significantly.The result of orthogonal experiment shows defocusing amount has the most significant impact on dilution rate and the significant level is α= 0.005, while the laser current and pulse width is on the level of α= 0.05. The impact of scanning speed is the least significant factor among all the experiment factors. It is still non-significant on the level of α= 0.1.Based on the criterion of minimum dilution rate, the processing parameters for laser cladding with welding wire are optimized. In the optimized combination the current values are 130 A or 135 A, the pulse width is 4.5 ms, the defocusing amount is 2 mm and the scanning speed is 195 mm/min.The observations of morphology of clad layer show the cross-sections are divided into 2 parts because of the laser pulses effect. The upper layers are the repeated fusion section and mainly consist of isometric crystals and dendrites crystal while the bottom layer consist of dendrites. The surface morphology of multi-track clad layer is like fish scale, and the melt pool boundary of pulse points are obvious.The analyses of hardness tests show 4 sections with different hardness value distribute in the cross-section along the direction of laser input. The highest hardness value is found near the fusion boundary while the lowest appears in the surface section. The range of heat affect zone along vertical direction is approximately among 150～200 μm. The values of Rockwell hardness and red hardness of clad layer are all lower than that of the base material, but they are still above HRC 60, which meets the requirement of hardness value of cutting tools for metal, and these results prove the feasibility of repairing cutting tools by laser cladding using high hardness welding wire.The results of friction-wear test shows when testing with GCr15 balls, which has a lower hardness than base material and clad layer, the friction state of clad layer is not as stable as base material, and both of the wear forms are adhesive wear. When testing with cemented carbide balls, whose hardness is higher than base material and clad layer, the wear form has the feather of both adhesive wear and abrasive wear because of the crisp trending in the surface of clad layer. The wear resistant ability of clad layer is evaluated by the amount of weight loss after the reciprocate friction-wear test. The result shows the wear resistant ability meets the requirement of repairing HSS cutting tools.