Research On Macrostructure And Properties Of Deposited In-situ NbC Alloy With High Resistance To Crack And Wear

Surfacing is a method of using alloys of certain properties deposited on the surface of material by means of heating, giving the base metal special performance or to restore the original shape and size of the parts. Using this method to repair or manufacturing components, we could use materials reasonablely, improve product design, improve product quality, and reduce cost, which all have important significance.This thesis studied the wear resistance of surfacing material, analyzed various alloying elements in the hardfacing layer, and designed the ideal alloy system, developed a kind of facing electrode suitable for serious abrasive wear conditions, which is used to solve the problems of wear under similar conditions.Using low carbon steel welding core, adding different types and quantities of alloying elements to the electrode clad, a kind of surfacing electrode has been developed for low stress abrasion with the method of the multi-alloy strengthening to meet the technical feasibility, economy and good use of surfacing electrode which has high hardness. Nb is suitable element to obtain ideal microstructure, which origin carbides dispersedly distributing on the strong and tough matrix, and Ti,V,W,Cr,Mo are not suitable elements in metallurgy or thermodynamics. The hardfacing ferrous based alloy finally developed belongs to middle carbon martensite alloy in the wear-resistant materials, which is of the Fe-Nb-Cr-Mo-Ti-C system.The direct reading spectrometer, optical microscope, SEM and ED AX spectrum analysis, microhardness meter, pin-disc abrasive wear tester have been used for analyzing composition, microstructure and properties of the hardfacing layer, the results show that the composition of the optimized niobium carbides electrode 842# hardfacing layer is C-1.30%,Nb-6.10%,Cr-3.33%,Mo-0.41%,Mn-1.28%,Si-1.68%,Ti-0.3%. The microstructures of deposited layer are mixtures of martensites and a small amount of residual austenite, and dispersed NbC particles. Ti precipitated in situ TiC first under high temperature in welding process, and provides core to form dispersed NbC particles.While the amount of high-carbon martensite and is similar to that of low-carbon martensite in the matrix, strong and tough matrix with mixture of martensites can link and support endogenous NbC enhancement particles, which play an anti-wear effect. Comparing the optimized niobium-carbide electrode to standard tungsten-carbide electrode D707, we found that although the amount of NbC is less than WC, but fine NbC particles make material performance undergone a fundamental change. The deposited metal has the performance of composite, which has higher crack resistance, high hardness, and higher wear resistance. The overlays have no crack observed with eye, which deposited on plates in the water. The average hardness of surfacing layer reached HRC57, which wear resistance is 3.3 times of D707, while the cost of raw materials is only half of D707. All of these make it will have high application value.