| With the increasing environmental protection requirements of the country,the light weight of heavy-duty trucks has become an important issue for vehicle manufacturers.Therefore,heavy-duty trucks have attracted much attention for weight reduction,energy conservation,safety and environmental protection.High-grade wear-resistant steel plate can reach higher safety design requirements with thinner steel plate through its higher hardness and ultra-high wear resistance,and can effectively reduce the vehicle's own weight and meet the requirements of energy saving and environmental protection.However,the current production and supply of NM600 wear-resistant steel is mainly monopolized by foreign companies.Foreign companies mainly guarantee the performance of wear-resistant steel through advanced smelting process and heat treatment process.There are many difficulties in the production technology of NM600 wear-resistant steel in China,which need to be overcome.Therefore,researching and solving the key technology of NM600 wear-resistant steel production is of great significance for improving the quality of domestic wear-resistant steel,improving domestic wear-resisant steel varieties and enhancing the competitiveness of the international market.In this paper,the composition design,smelting and forging of NM600 wear-resistant steel were carried out under laboratory conditions.Multi-pass controlled rolling and controlled cooling were carried out on a two-roll hot rolling mill.After hot rolling,the hot-rolled raw materials for on-line quenching and air-cooling were studied.In the heat treatment process research,the NM600 wear-resistant steel was obtained by the optimized heat treatment process,and the microstructure was composed of lath martensite structure.Finally,the wear characteristics of wear-resistant steel were systematically studied and analyzed,and a new anti-wear mechanism was proposed.Firstly,the austenite grain coarsening law,hot deformation behavior and cooling phase transformation law of test steel were studied,which provided basic support for rolling process and heat treatment process.The austenite structure of test steel excluding niobium was significantly roughened after it was greater than 900?,and the austenite structure of test steel containing niobium was significantly roughened after it was greater than 1050?,and its degree of roughening was lower than that of test steel excluding niobium.The true stress-true strain curve of the test steel at different temperatures and different strain rates is shown by the high temperature thermal compression test.The dynamic recrystallization change of the test steel during hot deformation was obtained.Through the classical thermal deformation constitutive model,the constitutive model of the material is constructed with 95%confidence.Establishing a therma,l processing map based on dynamic material model theory.The microstructure evolution of the material at different deformation temperatures and strain rates is accurately analyzed,and the safety zone and danger zone during thermal deformation are obtained.In the study of phase transition law,it is found that when the cooling rate is greater than 10?/s,all of them are transformed into martensite structure,and the addition of trace(0.05%)microalloying element niobium had no significant effect on the transformation law.Secondly,the optimal on-line heat treatment and off-line heat treatment process parameters were determined,and NM600 wear-resistant steel with qualified performance was obtained.By studying the effect of tempering process parameters on the microstructure of test steel,combined with the influence of austenite grain growth and holding time under austenitizing temperature,an orthogonal test scheme of quenching and low temperature tempering was designed.The effects of different heat treatment process parameters on performance of the two test steels were investigated.The test steel containing niobium is heated at 900? for 60min and water quenched,then the material was tempered at 200? for 30min,obtain tempered lath martensite and a small amount of retained austenite structure.The hardness value is 592HBW,tensile strength is 2037.8MPa,yield strength is 1605.8MPa,elongation after fracture is 11.1%,and impact energy at-20? is 16.8J,which meets the standard requirements of NM600 low alloy high strength wear-resistant steel.At the same time,the impact wear properties of the test steel under different impact energy and impact wear time conditions were studied.The wear resistance of materials is an important index to evaluate the wear-resisting materials.The wear resistance of the qualified NM600 wear-resistant steel obtained through the optimal heat treatment process is studied,the weight loss of test steel containing niobium is low,indicating that the addition of niobium element is beneficial to the improvement of wear resistance.The niobium element mainly improves the wear resistance of the martensite structure by refining grain and precipitation.In view of the phenomenon that the wear weight loss rate decreases when the impact energy is higher,a new wear layer anti-wear mechanism is proposed,which mainly includes buffering effect,lubrication effect and protection effect of wear particles.Finally,the correlation between the test steel structure,impact energy and material wear characteristics was studied.The wear process of materials is a complex failure process with multi-factor coupling.Through the comparative analysis between different factors,the idea of improving the wear resistance of materials is proposed for the wear-related factors.When the impact energy of different energies acts on the surface of the material,the surface of the material exhibits different wear characteristics.When the impact energy is low(0.5J),the wear resistance is improved by increasing the surface hardness of the material.When the medium impact energy(2.5J),it is preferred to ensure that the material has good toughness and reduce the initiation of cracks during impact wear.In high impact energy(5J),it is necessary to ensure that the material has good toughness while having a high hardness. |
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