The Remanufacturing Research On Repairing Waste Roller With Fe-Cr-B Alloy As Coating Layer

China has a developed metallurgical industry,and its steel output was ranking first in the world for more than ten consecutive years.As the main parts of steel forming,the annual consumption and scrap quantity of rolls are amazing.In the environment of low carbon,energy conservation and emission reduction advocated by the state,the repair and remanufacturing of waste rolls is in line with the national policy and has broad market potential value.Existing repair technologies,such as surfacing welding technology,laser cladding technology,etc.,are mostly suitable for small repair.Large repair technologies,such as eternal casting method and electrometallurgy method,are subject to complex equipment and process promotion.In view of the problems aboved,this research adopts independently developed liquid-solid composite equipment to restore the volume of waste rolls.The cladding adopts a new type wear resistant alloy of Fe-Cr-B to improve the performance of the working layer.Waste rolls have a wide variety of sources and low prices.After remanufacturing,the products cost greatly reduced,improved the performance,and strong,the market competitiveness which has great significance to enterprises and society.In this research,the composition of coating Fe-Cr-B alloy optimized by thermodynamic calculation.According to the calculation,the effect of chemical composition on the microstructure and mechanical properties studied experimentally.The wear mechanism discussed combination with the characteristics on microstructure of Fe-Cr-B alloy.The research providing theoretical basis and experimental data for the popularization and application of Fe-Cr-B alloy.The key process parameters of remanufacturing were tested,the process parameters suitable for industrial production were established,and the interface formation process and mechanism revealed.On this basis,completed the industrial production test successfully and the improved process further.First,the thermodynamic calculation carried out to design the composition of Fe-Cr-B alloy.The precipitated phase of the Fe-Cr-B alloy during the solidification mainly have?-Fe,M₂B(M=Fe,Cr,Mn),M₇(C,B)₃,M₂₃(C,B)₆,etc.B mainly affects the volume fraction of M₂B in the alloy.Cr change the structural and chemical components of M₂B,promote the transition of Fe₂B?(Fe,Cr)₂B?(Cr,Fe)₂B thus changing the mechanical properties.Mn promote the transformation from(Fe,Cr)₂B to(Cr,Fe)₂B.C increase the volume fraction of M₇(C,B)₃.The designed range of elements in alloy were B:0.5%?3%,Mn:0.5%?4%,Cr:5%?15%,C:0.5%?1%.Effects of B,Cr and Mn on the microstructure and mechanical properties of Fe-Cr-B alloy studied by experiments.The microstructure of Fe-Cr-B alloy casted by water-cooled metal mold composed of hard phase and matrix.The hard phase is composed of boron carbide(M₇(C,B)₃,Fe₃(C,B))and boride(M₂B).With the different content of alloy B,M₂B presents the morphology of coarse rod and eutectic grid shape.Increasing B significantly increase the volume percentage of M₂B in the alloy.Cr will make the grid shape distribution of boride more dispersed.Cr preferentially strengthen the M₂B,and then strengthen the matrix.The macro hardness of the alloy and the micro hardness of the matrix increased so as the impact toughness.With the increase of Mn,the edge of M₂B tends to be smooth,and the morphology changes to petal-like morphology.The residual austenite in the matrix changed from primary dendrite structure to the finer secondary and tertiary dendrite structure.The macro hardness of the alloy and the micro hardness of the matrix increased,but the impact toughness decreased.The first principle calculation based on Density Functional Theory(DFT),considering spin polarization,using super soft pseudopotential and Perdew-Burke-Ernzerhof(PBE),functional of Generalized Gradient Approximation(GGA),the models of Fe₂B,Fe₇Cr B₄,Fe₇Mn B₄,Cr₇Mn B₄ and Cr₂B were established and optimized geometrically.The elastic constants calculated by stress-strain method.Through the calculation of Pugh modulus ratio(G/B),the improvement of alloy element doping on the brittleness of M₂B phase was analysised.Cr mainly improves the toughness of M₂B,followed by the hardness.Mn greatly improves the hardness of M₂B and reduces the toughness.High Cr and low Mn doping can greatly improve the micro hardness of M₂B without sacrificing toughness.The wear resistance of Fe-Cr-B alloy was tested.Combined with fracture mechanism,wear surface morphology and roughness,the effects of hard phase and matrix on wear resistance analyzed and discussed the abrasive wear mechanism.The wear resistance is directly proportional to the macro hardness.Under high load,the wear resistance of Fe-Cr-B alloy is better than comparison sample(Km TBCr26).The wear mechanism includes micro cutting,low cycle fatigue and micro-fracture.The wear mechanism of matrix included micro cutting and low cycle fatigue while M₂B were mainly micro cutting and micro fracture.B element improves the wear resistance by increasing the volume fraction of M₂B while Cr and Mn by strengthening the M₂B.The influence of process parameters on Fe-Cr-B/45 steel composite roll interface studied through experiments.The diffusion process of elements and the formation mechanism of interface analyzed.When the liquid-solid ratio is low(1.78?1),the process parameters of formation metallurgical interface as follow:Holding time is greater than 15 mints and preheating temperature higher than 950°C.When the liquid-solid ratio is high(5.25?1),the process parameters of formation metallurgical interface as follow:Preheating temperature is higher than 900°C,holding time is longer than15min.The main factor affecting the formation of interface are heat conduction and the diffusion of elements.The alloying elements diffuse from Fe-Cr-B alloy to the interface.The interface microstructure is pearlite-like structure;the mico hardness is about HV260?380.The impact toughness of interface is greater than that of Fe-Cr-B alloy,and the impact fracture position is on the side of Fe-Cr-B alloy.Fe-Cr-B alloy side divided into quench layer,fine grain layer and coarse grain layer from the interface to outside.45steel side divided into carbon-poor layer,carbon-rich layer and 45steel layer from interface to the inside.According to the actual working conditions,the industrial test of the remanufactured roll carried out,and the equipment and technology improved.The over-steel amount for 10mm thread rebar steel of remanufactured Fe-Cr-B composite roller is 330 tons(Original high-nickel-chromium-nickel Cast iron roller is 160 tons).The single grinding volume from 8-10mm reduced to 4-5 mm.The comprehensive life span more than doubled.The interface remains intact after use.After heat treatment,the morphology and distribution of M₂B have little change,fine M₂₃(C,B)₆ precipitated in the matrix.The hardness from the interface to the coating surface maintained at HRC56?60.