Study On Microstructure And Property Of Mig Welds Between Cemented Carbide And Steel

Cemented carbides are multiphase materials comprised of hard phase’s skeletonembedded in a metallic binder, with high hardness, good abrasion resistance, excellenttoughness and heat resistance, corrosion resistance and other properties. Especially thehigh temperature strength and corrosion resistance in liquid and chemically inert make itused widely in the industry. At present, research on welding of cemented carbide has beenput forward, many welding methods are used to weld cemented carbide and steel, however,most of the them are limited. During welding process, it is confirmed that hard and brittleη phases with carbon-poorare easily formed near interface between cemented carbide andwelds, which leads to cracks.In current research, welds of cemented carbide with low binder to304stainless steelwere fabricated by using robotic MIG (metal inert gas) welding withNi (nickle) fillermetal.First, robotic welding can improve welding production. Second, during thehard phase WC (tungsten carbide) dissolution occurs,, it is okay to substitute nickel atomsfor tungsten atoms followed by carbon-poor phenominon. And (W, Ni) C was formed.Consequently, the W-Ni-C ternary equilibrium system was formed at theregion nearinterface between cemented carbide and weld after W and C atoms diffused to the weldand the Ni atom diffused to the HAZ (Heat Affected Zone). It was obviousthat the areaof ηphase region occurred in W-Ni-C ternary equilibrium system was much smaller than that inW-Co-C or W-Fe-C ternary equilibrium system according to the phase diagram analysis.Therefore, the additive Ni can inhibit the formation of η phase. The welding parametersand the factors for weld formation and welding joint were researched and optimized.Besides, the weld defects were analysed. The microstructure and composition wereinvestigated by using SEM (Scanning Electron Microscope), EPMA (Electro-Probe Microanalyzer), XRD (X-Rays Diffraction) and hardness expeiment. The conclusions areas followed:1. In order to weld cemented carbide with low binder, the heat input should be strictlycontrolled to avoid cracks formationby using MIG method. Welds with well metallurgy,appearance and mechanical properties by optimized welding parameters without preheat,postheat or posweld heat treatment (PWHT).2. The heat transfer and diffusion behaviour were happened at the region nearinterface between cemented carbide and welds during the welding process. The W-Ni-Ti-Csystem was broken by the diffusion of W, C, Ti and Ni atoms from cemented carbide toweld. On the while, the Ni atom was diffused from weld to HAZ, which suppressed thevariation of the system and inhibited the η phase formation.3. The growth and dissolution of WC grain were observed in welds. It is easy for ηphase to form at the brim of the dissolved WC grains.4. In current research, welded joints with well metallurgy were obtained. The hardnessdistributed smooth near interface between cemented carbide (about1100HV) and weld(about220HV). which can meet the requirements of the mechanical properties.