Research On The Process Of Surface Cast-infiltration With Thermite Reaction

Due to simple technical equipment and low cost, the cast-infiltration was widelyapplied and progress in application research was made. However, the disadvantage ofthis technology is that the quality of cast-infiltration layer is unstable, more susceptibleto the change of technological parameters.Considering the problem mentioned above, this paper took the thermalcompensation and purity of liquid metal as breakthrough point. The carbon steel（0.45%C） being selected as matrix, and high carbon ferrochrome powder as cast-penetrated agent, the steel-based surface composites were fabricated by conventionalcast-penetrating process. Reaction thermodynamics of the Al/Fe₂O₃system wereanalyzed. The influence of various processing parameters on formation of cast-infiltration layers were studied, including the content of aluminum, the pouringtemperature and the binder etc. XRD, SEM, EDS and other means were employed toanalyze the phase structure and microstructure of cast-infiltration layers with differentaluminum content. Hardness and wear resistance of cast-infiltration layers weremeasured. The influence of thermite reaction on cast-infiltration was further studiedcombining with the cast-infiltration dynamics. The results were as follows:1. In the differential thermal analysis experiment of the Al/Fe₂O₃system, themore the aluminum content in the mixed powder, the easier to react. The temperatureof molten steel is fully capable of ignition the thermite reaction in this experiment.2. When the content of aluminum is2%and adding no any binder, the density ofperform one is50%, the pouring temperature is1650℃and the performs areembedded in the lower part of the mold wall, the optimal surface quality of cast-infiltration layer can be obtained.3. The thickness of composite layer increases with the increase of aluminumcontent when the aluminum content is not greater than2%, the interfacial bonding ismetallurgical fusion between cast-infiltration layer and the matrix, the thickness of the cast-infiltration layer containing2%aluminum can reach to15mm. The cast-infiltration composites mainly consist of （Cr,Fe）₇C₃, Cr₇C₃and there is Al₂O₃in thecast-infiltration layer containing aluminum powder.4. The hardness is first increased and then decreased from matrix to cast-infiltration layer. The hardness of cast-infiltration layer containing2%aluminum isapproximately3times harder than that of matrix and the wear resistance isapproximately6.65times higher than that of the matrix. The wear resistance of cast-infiltration layer containing aluminum is higher than that of cast-infiltration layerwithout aluminum. The wear resistance of composite layer increase with the increaseof aluminum content when the aluminum content is not greater than2%.5. The thermite reaction during the process of cast-penetrated can realize thermalcompensation for liquid metal and improves the mobility of liquid steel by reducingoxidation film of liquid steel surface, the thickness and wear resistance of the cast-infiltration layer is improved. Formation of the cast-infiltration layers is the outcomeof mutual effect between thermodynamics and kinetics.