| Automotive mould is an important part in the car production, the surfacestrengthening and repairing are the most effective methods of improving its wearresistance. Laser cladding Fe-Cr-B alloy coating was fabricated on the surface ofCr12MoV automotive mold steel by using6kW fiber laser. The effects of laser power,scanning velocity, powder feeding rate on the formability, size, dilution rate andmicrostructure and microhardness of cladding layer had been researched by means ofmetallographic, microscope, and microhardness tester. The results show that themicrostructure of the cladding layer is composed mainly of plane crystal, dendritesand equiaxial grains. The rational laser cladding parameters are as follows: P (laserpower)=2000W, V1(scanning speed)=4mm/s, V2(powder feed rate)=15g/min,powder feed rate is15g/min.Under this laser cladding parameters, the gains arerefined, the dilution rate is9.8%and the highest microhardness of the cladding layerreached to900HV.A Fe-based composite coating reinforced by in situ synthesized TiC particleswas fabricated on Cr12MoV by using6kW fiber laser cladding. A serials ofexperiments have been carried out with different laser power, scanning speed, andpowder feed rate, from which TiC could be in situ synthesized only in certain realmslaser cladding paraterms. The coating is mainly composed of α-Fe, TiC and Fe3C. TheTiC particles are commonly precipitated in three kinds of morphologies, such asquadrangle, cluster, and flower-like shape. The gains are refined, there is no cracksand few stomas. Dense and defect-free coating with metallurgical joint to thesubstrate was obtained. TiC distributed more concentratively in the upper layers thanthe middle and bottom layers. From the surface of cladding layer0.8mm the highestmicrohardness is up to HV930, obviously higher than that of the substrate. In situsynthesized NbC particles was fabricated by laser cladding Nb-Fe, high-carbonferrochrome and iron-based alloy powder on Cr12MoV. The designed of NbC contentwas5%,10%,20%and30%. The coating is mainly composed of γ-Fe, NbC, Fe3C,Iron solid solution and martensite. With the content of NbC increased, themorphology of NbC from quadrangle, cluster to flower-like shape. And on this basis, in situ laser cladded Fe-NbC composite coatings with CeO2addition were prepared toimprove the mechanical properties of mould steel surface. CeO2play an importantrole in suppressing defect, refining grain, improving NbC precipitation and reducingdilution ratio, which improve the microhardness of coatings. The addition of CeO2canreduce the porosities and make the surface of coatings more smooth. CeO2refines thegrain size, improves the increase of amount of NbC particles and the solid solubilityof matrix. In addition, dilution ratio of coatings is decreased when the content CeO2ofis4%. The effects of CeO2above mentioned improve the hardness of coatings.In comparison with the Cr12MoV steel, the laser cladding NbC coating onM-200ring-on-block tester.exhibits good wear resistance, samples with10%NbCadded4%CeO2have the best wear resistance. The wear coefficient of the coatingrange from0.2to0.3. Wear mechanism of specimens with laser cladding NbC coatingare abrasive wear and oxidation wear. The wear mechanism of specimens withoutlaser cladding NbC coating are adhesion wear and oxidation wear. Laser cladding TiCcoating on the MLS-225wet sand rubber wheel testing machine also have good wearresistance,Under the condition of this experiment, samples with15%TiC have thebest wear resistance, and its wear mass loss is1/3of that of Cr12MoV steel. |
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