| Particle reinforced iron matrix composites possessing the advantages of steel (oriron) matrix and ceramic particle reinforcements are the ideal choice for applicationsof wear resistant materials, refractory alloys and tool materials. The main advantage ofin situ technology is that the surface of reinforcements generated in situ tend to remainclean, i.e. free from gas absorption, oxidation or other detrimental surface reaction andthe matrix-reinforcements interface bond therefore tends to be stronger. So, in recentyears, there has been an increasing interest in the in situ formation of iron-basedcomposites with carbide reinforcements. Among these in situ techniques available,SHS and casting technologies are widely used. Few studies have been made on in situsintering to produce iron-based composites. Compared with other in situ technologies,the typical advantages of in situ sintering are: the surface quality and precision ofproducts are good; a high volume fraction of second-phase particles in an alloy can beobtained; the reduction of porosity is achieved during liquid phase sinteringtechnology; combined with braze coating technology the composite coating can beproduced.Both of Titanium carbide (TIC) and vanadium carbide (VC) having characteristic ofhigh hardness, thermodynamics stableness are frequently chosen for the reinforceparticles of iron matrix composites. Moreover, additions of vanadium into steel can be expected to minish matrix crystal grains, improve hardenability and resistance totempering or result in temper hardening. Hence, in this paper (Ti,V)C/Fe compositeswere produced by in situ sintering of mixed titanium powder, ferrovanadium powder,carbon powder, molybdenum-iron powder, errochromium powder and iron powder.The intention of the study is to bring into play the strongpoint of the production routeand that of TiC, VC metal ceramic to synthesize high performance and inexpensive(Ti,V)C/Fe composites.The aims of the study is to reveal the microstructure of the (Ti,V)C/Fe composites,assess the heat-treatability, investigate the influence of vanadium on the microstructure,heat treatment and mechanical properties.The study results are as follows:The optimal sintering temperature for TiC/Fe, (Ti,V)C/Fe composites is 1420℃,1400℃, respectively. The sintering time of TiC/Fe or (Ti,V)C/Fe composites is for 1hour. The complete reaction can be carried out in the course of sintering. There is noresidual carbon, titanium, vanadium and impurity phase such as TiFe, TiFe2 exist in theXRD patterns of final products. The reaction dynamic process of Fe-Ti-V-C system is:first, formation of VC at 765℃; second, formation of TiC at 1140.4℃, third, with theincrease of sintering temperature, (Ti,V)C solid solution formation. Finally, the TiC/(Ti,V)C particles continue to grow during liquid sintering by Gibbs-Thomsonmechanism.With the increase of V/Ti atomic ratio, the dissolvability of (Ti,V)C particles in Feincrease, and the interactions between (Ti,V)C and iron matrix become stronger. So,compared with TiC particles, the (Ti,V)C particles assume spherulitic morphology andtend to grow up. The interactions between (Ti,V)C and iron matrix cause an effects onthe components of matrix. Additionally, the matrix-reinforcements interface bondtends to be stronger because of the metallurgical bonding interface resulted from theinterface solution and inter-diffusion of Fe,V,Ti etc. elements.The matrix microstructure of (Ti,V)C/Fe (or TiC/Fe) composites after sintering iscomposed of pearlite and M3C plus M7C3 carbides. Under the proper quenchingtemperature conditions, the microstructure of the composites changes to the needle-type martensite and residual austenite plus (Ti,V)C (or TiC) carbides. Withincrease of V/Ti atomic ratio, the hardenability of (Ti,V)C/Fe composites afterquenching increase. In the process of proper quenching plus temper in the range of450-550℃, the Cr, C etc. alloying elements solid-dissolved in the supersaturatedaustenite precipitate as (Cr, Fe)7C3. Thereby the retained austenite transforms intomartensite in cooling p rocess, which results in secondary hardning. The interactionsbetween (Ti,V)C and iron matrix cause various effects on the tempering resistance anddifferent hardenability.The amount of vanadium plays an important role in affecting the morphology andvolume fraction of (Ti,V)C particles and the mechanical properties of the composites.With the increase of V/Ti atomic ratio, the volume fraction of (Ti,V)C particlesdecrease, the size of the particles become large. Thereby the bending strength and wearresistance of (Ti,V)C/Fe composites decrease. Although the volume fraction of hardphase is at the most, the bending strength and wear resistance of TiC/Fe composites donot reach the maximum because the morphology of the TiC particles is poor.The wear resistance of (Ti,V)C/Fe composites can be improved after proper heattreatment. The wear resistance after quenching at 1000℃plus temper at 500℃isapproximately equal to that after quenching at 1000℃plus temper at 250℃.
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