Study On Microstructures And Properties Of Bimetal Composites By The Addition Of Particles

In this paper, only one furnace was used to get the molten iron for a bimetal composite roll by the addition of high carbon ferrochrome particles, centrifugal casting and gravity casting. The size of the bimetal composite roll isΦ180mm×500mm. The material of the surface working layer of the roll is high chromium cast iron and the core is ductile cast iron. The mechanical properties of samples in different heat treatments were measured using HR-150D Rockwell hardness tester and JB-300B pendulum impact testing machine. The microhardness nearby the interface between high-chromium iron and ductile iron was measured using MH-3 digital micro hardness tester. The microstructure was observed and investigated by optical microscope, German Brook D8 X-Ray diffractomer and JSM-5610LV scanning electron microscope with EDAX energy spectrometer. The high-speed tribological properties of samples in different heat treatments were researched by MMS-1G high speed pin-disc friction wear test machine and the main wearing mechanisms were researched by scanning electron microscope.The experimental results show that:1. The mechanical properties of the surface working layer of the bimetal composite roll reach: impact toughness 5.2⁶.6J/cm², hardness HRC56.7⁶4.8. And the mechanical properties in different heat treatments are different. With the increasing of austenitizing temperature(900¹000℃), the macrohardness of the surface working layer of the bimetal composite roll first increases and later decreases, but the impact toughness reduces slightly. The optimal integrated mechanical properties can be achieved when the austenitizing temperature is about 950℃.2. The as-cast microstructure of the surface working layer of the roll consists of alloy-carbide, pearlite, and retained austenite. After heat treatment, the microstructure consists of martensite, Cr₇C₃, residual austenite and a modicum of Cr₂₃C₆ and Cr₃C. The eutectic carbides are streaky, blocky or chrysanthemum-like. Many granulated tempering carbides are precipitated in the matrix of tempered martensite. Energy spectrum analysis shows they are composite carbides containing Fe, C and Cr.3. The bonding interface between high-Cr iron and ductile iron is clear without any casting defect, such as pore, inclusion, crack, void, etc. The two metals interweave with one another indentedly. From the side of ductile iron to the side of high-chromium iron, the number of graphite is getting smaller, and their sizes are getting shorter. From the side of high-chromium to the side of ductile, the number of carbides is becoming smaller, and their sizes are getting shorter. Nearby the interface, the microhardness of the side of high-Cr iron is about 800HV, and the side of the ductile iron is about 350HV. Although the difference is great, but the microhardness in the interface changes slowly. We may reasonably conclude that elemental diffusion occurs between the two metals and the bonding between them is good.4. The high-speed friction and wear experimental results show that, all the austenitizing temperature, additional load and friction speed significantly affect the friction and wear properties of the wear-resistant layer of the two-metal composite roll. The wearing capacity of material varies with increasing of the austenitizing temperature and reaches its minimum when the austenitizing temperature is about 950℃. On condition that the friction speed is constant, with the increasing of additional load, the wear rate increases gradually and the friction coefficient decreases gradually. On condition that the additional load is constant, with the increasing of friction speed, the wear rate increases gradually and the friction coefficient decreases gradually. According to analysis, the main wearing mechanisms are abrasive wear, oxidative wear and adhesive wear. Under the same test condition, the wear capacity, wear rate and friction coefficient of the surface wear-resistant layer material of the two-metal composite roll are less than that of high-alloy anti-wear steel, it suggests that the high-speed dry sliding friction and wear characteristics of the material of surface wear-resistant layer of the two-metal composite roll is better than high-alloy anti-wear steel.