In Situ Preparation And Abrasive Wear Resistance Research On Chromium Carbide Particles Reinforced Iron Matrix Composites

With the properties of high strength rate, high modulus rate, heat resistance, andabrasive wear resistance, carbide particles reinforced iron matrix composites arebecoming the focus of material research in recent years. In a wide range of carbideparticles, chromium carbides are suitable for reinforcing steel and iron matrixcomposites due to their high micro-hardness, good wear resistance, corrosion resistance,high temperature stability, oxidation resistance, and good compatibility with steel oriron.This thesis focuses on Fe-Cr-C ternary alloy system, combing casting and in situreaction to invent the composite casting with in situ reaction technology, which uses thematerial of chromium alloy wire, pure chromium wire, pure chromium grating and grayiron, white cast iron, to make Chromium carbide particles reinforced iron matrixcomposites and surface composites in different chromium-carbon ratio. Themicrostructure, phase composition and micro elements were observed by the scanningelectron microscope (SEM), X-ray diffraction (XRD), and differential thermal analyzer(DSC), respectively. The hardness and abrasive wear resistance of the composites weretested by Rockwell hardness tester, micro hardness tester, abrasive wear testingmachine. The results show that:(1) In Fe-Cr-C ternary alloy system, all the chromium carbide such as Cr4C, Cr7C3,Cr23C6, and Cr3C2can be stable at the reaction temperature (1160℃), and thestablilization from strong to weak are Cr23C6, Cr3C2, Cr7C3, and Cr4C. The differentialthermal analysis results show that the phase transition from-Fe to γ-Fe was occurred at821.08℃, and both of the reactions C+γ-Feâ†'M3C+L and γ-Fe+M3Câ†'M7C3+Lwere occurred at1156℃. The main reason and driving force of the reactions were the carbon and chromium atoms diffusion in the iron matrix.(2) Under the condition of low Cr/C ratio, the carbide transforms from M7C3toM3C with the time extension of heat preservation. The mechanism is the in situ eutecticreaction between C and the austenite γ-Fe+M3Câ†'M7C3+L, where the M7C3wasmanufactured. Far away from the alloy wire region, the eutectic reaction C+γ-Feâ†'M3C+L was occurred, and M3C was manufactured. In the composite, themicro-hardness of the compound region is higher than that of the matrix, which is about4-5times. And the highest value reaches1339HV.(3) Under the condition of high Cr/C ratio, with the time extension of heatpreservation, the micro-structure transforms from eutectic to hypoeutectic highchromium cast iron. The formation process of composite materials is diffusion andreaction of Cr, C, and Fe layer by layer, until the wire used up. The macro-hardness ofthe composites reaches55HRC. Under the condition of the soft abrasive wear, the peakrelative wear resistance of composite is38.1times to that of white cast iron, andmicro-ploughing is the major wear mechanism.(4) In the surface gradient chromium carbide reinforced iron matrix composites,Cr7C3ceramic area, granule (Fe,Cr)7C3area, plate strip (Fe,Cr)7C3area, and non-graphitephase matrix area were observed. The formation mechanism of the surface compositematerial is spreading and reaction layer by layer. The hardness of Cr7C3ceramic area isabout1484HV0.1, which is the highest. And in wear experiment, the relative wearresistance of dense ceramic layer is6.96. The main wear mechanism were micro-cracksand a small amount of micro-cutting, and the micro-crack extension direction wasvertical to the wear direction.