Study On Preparation, Microstructure And Properties Of TiCN_p/20Cr Hypoeutectic High Chromium Cast Iron Composite

High chromium cast iron（HCCI）,as an outstanding wear-resistant alloy with high cost performance,is widely used in many industrial fields,such as power sectors,mining,cement and metallurgical industries.It’s hard for the alloy fabricated by casting to give full play to its excellent wear resistance because there are clusters of petal-shaped coarse carbides with sharp edges in its metal matrix,which would lead to serious stress concentration in the service process.Powder metallurgy（PM）HCCI has been developed in recent years,with doubled strength and impact toughness in comparison with cast alloy,because the carbides in its matrix become fine and rod-shaped,which will increase the alloy’s market share in the future.By the way,PM HCCI’s wear resistance is still unqualified due to its conventional hardness 57～66HRC at some very harsh abrasion conditions,but it can be used as a good candidate matrix on account of its high strength and toughness as well as high performance to price ratio in excellent wear resistant composite development.Therefore,a novel particle reinforced PM HCCI is systematically explored by the author to meet the growing demand for outstanding wear-resistant materials in industries and expand the alloy’s application range.Taking TiCN_pand 20Cr hypoeutectic high-chromium cast iron powder as raw materials,powder metallurgy technology and super solid line liquid phase sintering technology（SLPS）as the sinstering process,this paper successfully prepared high chromium cast iron composites containing 10wt.%～30wt.%TiCN_p.The effects of reinforcing phase content and sintering temperature on the densification behavior,microstructure,phase composition and mechanical properties of composites were systematically studied.On this basis,the effects of quenching and tempering processes on the microstructure and mechanical properties of TiCN_p/20Cr high-chromium cast iron composites were studied,and also the heat treatment process was optimized.Comparative experiments of sliding wear and impact abrasive wear under different loads were carried out on TiCN_p/20Cr high-chromium cast iron composite and TM-52 steel-bonded cemented carbide to analyze their wear resistance characteristics and reveal their wear mechanism.The main conclusions of the paper are as follows:（1）In this paper,fully dense high chromium cast iron composites of10wt.%～30wt.%TiCN_p/20Cr were successfully prepared by vacuum supersolidus liquid phase sintering.When the sintering temperature is gradually increased in the range of 1235℃～1260℃,the density of the composite material shows a typical densification behavior change law,which increase rapidly at first and then gentle and stable.And the phases of the high chromium cast iron composite are mainly composed of TiCN,Cr₇C₃carbide,martensite and a small amount of austenite composition.TiCN_pdistributes along the grain boundary,and gradually forms a relatively continuous network distribution structure with the increase of the reinforcement phase addition,while Cr₇C₃mainly precipitates in the form of short rods in the matrix of high-chromium cast iron.At the same time,the hardness of the composite material increases linearly,but its flexural strength and impact toughness decrease.When the sintering temperature is 1250℃,the high chromium cast iron composites of30wt.%TiCN_p/20Cr have the greatest property with hardness of 87.8HRA,flexural strength of 1304MPa,and impact toughness of 2.35J/cm²（using a 5×5×50mm unnotched sample）.（2）With the increase of the quenching temperature,the secondary carbides in the composites show the evolution behavior of gradual precipitation,growth and coarsening,and final dissolution,and the hardness firstly increase and then decrease.The subsequent tempering treatment makes the hardness of the composite material decrease to varying degrees.When the tempering temperature is 500°C,the precipitation of secondary carbides increases,and the strength and toughness gradually increase.The optimum heat treatment process of high chromium cast iron composite of 30wt.%TiCN_p/20Cr is:after quenching at 1040℃for two hours,air cooling is carried out without tempering treatment.Under this condition,the composite material have the mechanical property with a hardness of 89.2HRA,an impact toughness of 2.17J/cm²and a flexural strength of 1569MPa.（3）The main wear mechanisms of composites under static load sliding wear conditions are cutting wear and fatigue brittle spalling,and the fatigue brittle spalling mechanism is more obvious under the condition of a larger load.Compared with TM52 steel-bonded cemented carbide,the as-quenched composites exhibited better wear resistance under the load of both 50N and 80N.Under the load of 80N,the wear volume of the quenched high-chromium cast iron composite of 30wt.%TiCN_p/20Cr decreased by 59%,and compared to the sintered high-chromium cast iron composite of 25wt.%TiCN_p/20Cr,the wear volume of the quenchedcomposite of25wt.%TiCN_p/20Cr decreased by 23%.（4）The wear mechanisms of TiCN_p/20Cr high-chromium cast iron composites are mainly cutting wear and chisel spalling wear under the condition of impact abrasive wear.Compared with TM52 steel-bonded cemented carbide,the TiCN_p/20Cr high-chromium cast iron composites has a greater wear resistance advantage under the condition of low and medium impact energy with a stable wear behavior and lower wear volume.When the impact energy is 1J/cm²～3J/cm²,the volume wear amount can be decreased by 30%～44%respectively.