WC/steel Composites Preparation And Their Performance Optimization

Economic and social development puts forward higher and higher requirements for the material,WC/steel matrix composites which combine high strength and high hardness of reinforcing phase with toughness of steel matrix have a series of advantages such as be conductive processing,heat treatment strengthening,wear-resisting.The cost of composites is much lower than the WC-Co carbide,and it has a wide range of applications in mould,wear parts,roll and so on.In this paper,WC/steel matrix composites are designed which matrix is a kind of super high strength steel.With powder metallurgic method,WC/steel matrix composites are made by seeking the optimum formulation and processing conditions(pressing pressure,sintering temperature and heat treatment process,etc.).The materials have good hardness,toughness and abrasive resistance.With electroslag melting and casting method and centrifugal casting method,two kinds of WC/steel matrix composites are made,and whole heat treatment and chemical heat treatment are applied on two kinds of WC/steel matrix composites.The comprehensive performance of materials is optimized.Main achievements are shown as follow:1)A new WC/steel matrix composites are designed which binder is a kind of super high strength steel 45CrNi2Mo2.The best pressing force(300Mpa)and sintering temperature(1220?)about powder metallurgy method are determined by the optimization of process.The results showed that the samples under 300MPa have the highest hardness,the least pore,and the uniform distribution.The performance of the sintered samples is best at 1220 ?,and meanwhile the samples with 40wt%WC have 33.68%volume shrinkage rate and micro hardness 404.7(HV0.3).2)The paper explores the effect of the WC content on the mechanical properties and microstructure of the steel matrix composites which prepared by powder metallurgy.The results showed that the addition of WC improves micro hardness of composite material.40wt%WC and 45wt%WC have little difference on performance.Both of them have dense tissue and minimum porosity,meanwhile they get higher performance than the others formula.The maximum micro hardness of 40wt%WC reaches 404.7HV and Rockwell hardness reaches 67HRC at 1200?.At this moment,comprehensive performance reaches the maximum.The organization of 40wt%WC distribute well.Fe3W3C?Fe3C?FeW3C are produced when WC and matrix phase solute each other.From the point of economy,40wt%WC is the best formula in this paper.3)The effects of different heat treatment systems on the structure and mechanical properties of WC/steel matrix composite materials by centrifugal casting are studied.The results showed that the defects reduce after annealing,the hardness decrease,while bending performance increase.Samples have more uniform tissue and more regular network after quenching-tempering,meanwhile martensite inside increase.The structure is the most uniform and regular at the quenching temperature of 980?.At the moment,Rockwell hardness is 81.7HRA,Vickers hardness is 595HV10 and bending performance is 1263MPa.When centrifugal casting sample bornding at 965?which is the best process,both Vickers hardness(876HV10)and Rockwell hardness(71.6HRA)reach the maximum,and bending strength is 1078MPa.Boriding at 965? ensure the sample has certain toughness and high hardness.4)The influence of different heat treatment systems on the structure and performance of steel matrix composite materials by the electroslag melting and casting method is analyzed.The results showed that the hardness of DGJW20 is slightly lower after the annealing and the hardness of Rockwell is greatly improved.With the increase of quenching temperature,hardness of the sample rises.It reaches the maximum of 84.4HRA,873HV10 at 980?.At this moment,bending strength is 811MPa.When the quenching temperature rises over 980 ?,the hardness decreases.Optimum heat treatment system is quenching at 980 ? and tempering at 200 ?.When electric melting and casting sample boriding at 965 ?,and then keep it warm for 7h works best,Vickers hardness(1120HV10)doubled than original sample.At this moment,Rockwell hardness reaches 77HRA,and bending strength reaches 695MPa.After boriding,FeB?Fe2B?CoB ? Ni3B are appeared on surface.5)The effect of different overall heat treatment and chemical boriding system on the 40wt%WC composite materials prepared by powder metallurgy is studied.Results show that the hardness of samples decrease after the annealing,however it increases obviously after quenching-tempering.For sample of powder metallurgy method,the performance reaches the best when quenching at 970 ? and low tempering at 200 ?,meanwhile the Vickers hardness reaches the maximum of 1107.7HV0.2.Main phase in quenching sample are Fe3W3C?Fe3W3C-Fe4W2C.When using boriding medium formula(5%B4C?5%KBF4?85%SiC?5%charcoal powder)for powder metallurgy method samples,hardness reaches at the maximum when boriding at 975 ?,meanwhile decay resistance are the best as well.For new formula(B4C,KBF4,SiC,Ce(NO3)3,activated carbon),with the addition of 5%Ce(N03)3 in boriding medium,sample after borinding have excellent performance when boriding at 980?.