Cr12MoV模具钢渗氮层服役过程中不同磨损阶段的摩擦学特性

Tribological Properties of Nitriding Layer of Cr12MoV Die Steel in Different Wear Stages during Service

目的分析经渗氮处理后Cr12MoV模具钢的显微结构,以及不同取样厚度处渗氮层的摩擦学特性,了解渗氮处理对Cr12MoV模具钢耐磨性的影响,为服役过程中不同磨损阶段渗氮层的磨损行为提供理论依据。方法采用气体渗氮法对Cr12MoV模具钢进行恒温渗氮处理,研究渗氮处理对Cr12MoV模具钢显微结构的影响,以及不同取样厚度处渗氮层的磨损行为,并分析不同取样厚度处渗氮层的磨损机理。结果经渗氮处理后Cr12MoV模具钢的表面会形成一层厚度约为120μm的致密渗氮层,材料的表面硬度从3.65 GPa提高至12 GPa,磨痕深度从3.5μm降至0.35μm。随着取样厚度的增加,试样的磨损量会逐渐增加,但均远低于未渗氮试样,其中渗氮层的最大磨损量约为120μm^(3),为基体材料磨损量的1/10;渗氮影响层的最大磨损量约为330μm^(3),为基体材料的1/3,可见采用气体渗氮处理可显著增强Cr12MoV模具钢的耐磨性。此外,在磨损过程中Cr12MoV模具钢的表面磨损较严重,出现了大块撕裂损伤,主导磨损机理为疲劳磨损;经渗氮处理后试样表面的损伤较轻微,主导磨损机制为磨粒磨损。随着取样厚度的增加,试样表面的磨损现象逐渐加剧,磨损机制由磨粒磨损逐渐转变为疲劳磨损。结论渗氮处理可以在Cr12MoV模具钢的表面生成一层致密的渗氮层,渗氮层的磨损量会随着取样厚度的增加先减少后持续增加,说明在服役过程中渗氮层的耐磨性呈先增强后减弱的趋势。

Cr12MoV can be considered as one of the most widely used cold working die steel due to its excellent comprehensive performance,such as good hardness and toughness,and high compressive strength.However,the cold working die steel often withstand extremely high circulating pressure,cutting force and high impact force during industrial applications,resulting in the production of crack sources such as scratching and peeling on the surface,which ultimately leads to the failure of cold working die.Generally,nitriding treatment is one of the most economic methods to enhance the comprehensive performance of cold working die steel,but the present researches mainly focus on the effects of nitriding process parameters on the microstructure evolution,hardness and wear resistance of die steel,few studies are dedicated to the tribological properties and corresponding wear mechanism of die steel at different wear stages after nitriding treatment.In order to understand the effect of nitriding treatment on the wear resistance of Cr12MoV die steel and provide a theoretical basis for the wear behavior of nitriding layer in different wear stages during service,the microstructure of Cr12MoV die steel after nitriding treatment and the tribological characteristics of nitriding layer at different sampling thickness are analyzed.The Cr12MoV die steel is treated by gas nitriding at constant temperature,the effect of nitriding treatment on the microstructure of Cr12MoV die steel and the wear behavior and corresponding wear mechanism of nitriding layer at different sampling thickness are studied in detail.The results show that a compact layer with a thickness of about 120μm is formed on the surface of Cr12MoV die steel,resulting in the increased microhardness from 3.65 GPa to 12 GPa,while the depth of wear marks reduces from 3.5μm to 0.35μm.With the increase of the distance between the sampling position and the coating surface,the abrasion loss of the sample increases gradually,but it is still far lower than that of the substrate.Among them,the maximum wear of the nitriding layer is about 120μm^(3),which is approximately 1/10 of the base material.The maximum wear of nitriding affected area is about 330μm^(3),which is almost 1/3 of the matrix.Therefore,gas nitriding treatment can significantly enhance the wear resistance of Cr12MoV die steel.Moreover,the Cr12MoV die steel is seriously worn during the wear process,resulting in large tear damage,and the dominant wear mechanism is fatigue wear.After nitriding treatment,the surface damage of the nitriding layer is slight,and the dominant wear mechanism is abrasive wear.However,with the increasing distance between the sampling position and the coating,the wear phenomenon of the samples gradually intensifies,and the dominant wear mechanism changes from abrasive wear to fatigue wear.Thus,nitriding treatment can form a dense nitriding layer on the surface of Cr12MoV die steel,and the wear amount of nitriding layer will first decrease and then continue to increase with the increase of sampling thickness,indicating that the wear resistance of nitriding layer increases first and then decreases during service.Therefore,the nitriding treatment can significantly improve the wear resistance of cold-working die steel and the service life of the cold work die,which has vital practical significance in industrial applications.