Microstructure And Mechanical Property Control And Wear Mechanism Study For New Air-Cooled Martensitic Wear-Resistant Steel

Martensitic wear-resistant steels are widely used in rail transportation,coal mining and construction machinery due to their high strength,high hardness and low cost.Conventional martensitic wear-resistant steels are often produced by off-line quenching and tempering processes after rolling to ensure strength and toughness,and adding large amounts of Cr,Ni and Mo elements to improve hardenability.However,the addition of high-priced metal elements,the need for fast cooling equipment and the long production process greatly increase the production cost of martensitic wear-resistant steels.Based on this,a new type of air-cooled martensitic wear-resistant steel using Mn instead of Cr and Ni to reduce material cost and air-cooling instead of quenching and tempering to reduce equipment cost and production process is designed in this paper.The low temperature hot rolling process,which is significantly lower than the common rolling temperature,is proposed.The effect of low-temperature rolling on austenite grain growth behavior during reheating is also elucidated.The effects of reheating process on the second phase particle precipitation behavior,austenite grain growth behavior,martensitic microstructure and its mechanical properties are investigated.The effects of rolling temperature and heat treatment process on the wear properties of air-cooled martensitic wear-resistant steel under different wear conditions were investigated.And the relationship between wear properties and strength,hardness and toughness was revealed.The main research results are as follows:The air-cooled martensitic wear-resistant steel has excellent hardenability,and a full martensitic organization can still be obtained at a cooling rate of 0.05°C/s.After low-temperature hot rolling,the multi-level structure of martensite is significantly refined,and the density of high-angle grain boundaries,low-angle grain boundaries,dislocation density and nanoscale V(C,N)precipitation increase,and stronger fine-grained strengthening,In addition,the refined microstructure effectively increases the toughness fracture region,extends the crack propagation path and significantly improves the impact toughness.Its tensile strength,yield strength,hardness and impact absorbing energy at-40°C are 1701 MPa,1174 MPa,482 HB and 38 J,respectively,fully meeting the performance requirements of NM450 grade wear-resistant steel.Austenite grain hyperfabrication was successfully achieved by combining low-temperature rolling with heat treatment.It was found that the flattened structure obtained by low-temperature rolling can effectively improve the austenite nucleation rate during reheating,and can promote the precipitation of nanoscale V(C,N)particles during reheating,pinning austenite grains and inhibiting austenite grain growth.When the reheating temperature was 820°C,the average austenite grain size of the experimental steel was only 3.79 μm.Compared with the hot-rolled state test steel,the test steel obtained higher fine-grain strengthening,dislocation strengthening and precipitation strengthening after 1h heat treatment with holding at 820°C.The optimum tensile strength,yield strength,hardness and impact absorbed work at-40°C were 1690 MPa,1244 MPa,496 HB and 50 J,respectively.The study on the wear resistance of the test steel under different working conditions found that: in the dry sliding wear test,the wear morphology of the test steel was dominated by grooves and the wear mechanism was microcutting mechanism.Compared with the commercial Hardox 450 steel,the hot-rolled air-cooled martensitic wear-resistant steel showed higher wear resistance,and the wear resistantce increased with the final rolling temperature decreased.In the three-body impact abrasive wear test,as the impact energy increased,the furrow area in the wear morphology decreased,and the fracture,delamination,fatigue wear and abrasive embedding area increased.The air-cooled martensitic wear-resistant steel after low-temperature rolling effectively improves the hardness and toughness of the matrix,resists abrasive embedding,inhibits crack sprouting and expansion,reduces wear weight loss,and improves wear resistance,and its wear performance reaches the same level as Hardox 450 steel.Meanwhile,the wear resistance of the low temperature hot-rolled test steel is further improved after heat treatment at 820 ℃,and the fracture and delamination area in the wear profile is significantly reduced,and the impact wear performance is further improved,which is significantly better than Hardox450 steel.