Preparation And Properties Of Fe-C-V-Mo-Cr High Strength Wear Resistant Steel For High Pressure Grinding Roller

The strength and wear resistance of a high pressure roller surface will directly affect the service life of the high pressure roller,making it the main component of a high pressure grinding roller.Rolls with studded wear-resistant column nails,such as advanced high pressure roller surfaces,have a much higher service life than that of welded hardfacing rollers.However,the matrix material of rollers with studded wear-resistant column nails has insufficient abrasion resistance and strength during actual using process,which severely restricting its service life.In this study,a new type of high strength wear resistant steel roller surface material was prepared via centrifugal casting technology in accordance with operation conditions.The characteristics of multi-component alloy with the new type of high strength wear resistant steel lead to further improvement of the performance by rational heat treatment process.The application of high strength wear resistant steel has been achieved in high pressure grinding roll stud-lined roller.At the same time,usability and the serving life of high strength wear resistant steel can be further improved through deep cryogenic treatment and gas nitriding.The main achievements are listed as follows:According to the performance requirements of high pressure grinding roller surface material and the technological characteristics of centrifugal casting large roller sleeve,we first designed the chemical compositions of roller surface material for high pressure grinding roller.The large type Fe-C-V-Mo-Cr high strength wear resistant steel roller sleeve test samples prepared by centrifugal casting technology has uniform microstructure,steady performance and no macro-segregation.The as-cast microstructures consist of martensite,multi-component alloy carbides and retained austenite.The hardness of the cross section and surface of roller are about 55 HRC.Granular and short rod MC carbides are distributed in the center of grains,and are rich in V and Mo.Lamellar M2C carbides are formed along grain boundaries,and are rich in Mo and Cr.Fine granular M23C6 carbides are uniformly distributed in the matrix of as-cast high strength wear resistant steel,and are rich in Cr and Fe.In addition,Cr exists in M2C carbides and matrix in the form of solution.The microstructures of high strength wear resistant steel after heat treatment consist of a small amount of retained austenite,MC carbides,M2C carbides,M6C carbides and the precipitation of secondary carbides after tempering.The hardness of high strength wear resistant steel significant increased after heat treatment,when compared with as-cast sample.The secondary hardening peak of high strength wear resistant steel presented at 560 ℃ after tempering,hardness was more than 65 HRC.With the increase in the austenitizing time,the compressive strength of the high strength wear resistant steel tended to increase,the maximum compressive strength was 3800 MPa.Under the same quenching process conditions,prolonged tempering time led to decrease in compressive strength.The high strength wear resistant steel material exhibited excellent abrasive wear resistance.After 1080℃ × 120 min + 640 ℃ x 60 min(50 HRC)and 1080 ℃ x 120 min + 560 ℃ x 60 min(65 HRC)heat treatment,the wear resistance of the hardness with 50 HRC and 65 HRC of high strength wear resistant steel samples were 3 and 15 times higher than that of Crl6 under the same experimental conditions.There were four different zones on the wear scar of high strength wear resistant steel observed in our experiments:serious wear zone,transition zone,mild wear zone and exit zone.As sample hardness decreased,the mild wear zone reduced while the serious wear zone and transition zone of the wear scar enlarged.During the wear process,the movement of particles by rolling and sliding rather than only sliding was attributed to the skeleton structure of high hardness MC carbides which hindered particle motion in high strength wear resistant steel,thus reducing the wear of the sample.After deep cryogenic treatment,there was a large amount of dispersed carbides precipitation in the high strength wear resistant steel,secondary carbides ever increased due to the increased deep cryogenic processing time and number of cycles in this study.The deep cryogenic treatment decreased the hardness of the steel but increased its impact toughness and wear resistance compared to the conventional treatment.This is attributed to a large number of second phase carbide particles that can effectively resist abrasion matrix.The carbon content in the martensite decreased result from precipitation of carbides,led to decreased the strength of matrix,but increased the toughness.When second phase carbide particles fell off,it could be "rolling effect" during the wear process,and wear resistance of samples can be further improved.Initiation of microcracks around M2C carbides was reduced due to the improvement in toughness of martensitic matrix.The surface of the nitriding layer of the as-cast,quenched,quenched + tempered high strength wear resistant steel samples after gas nitriding mianly contained γ’-Fe4N,ε-Fe2-3N,Mo2N,VN,the original M2C and MC carbides,and the compound layer is about 10 μm.The diffusion layer contained the original M2C and MC carbides,high nitrogen matensite,M2(C,N)and VN,and the nitriding layer depth were more than 250 μm The hardness of high strength wear resistant steel samples after gas nitriding was above 1100 HV.The quenched sample after gas nitriding has higher hardness,and the as-cast sample after gas nitriding has higher wear resistance.