【作者】 陈磊；

【导师】 崔向红；

【作者基本信息】 江苏大学 ， 材料工程（专业学位）， 2020， 硕士

【摘要】 高温磨损是热作模具在严酷工作条件下的一种典型的失效形式,高温下热作模具钢的耐磨性的差异直接影响着热作模具的使用寿命。然而目前,针对热作模具钢高温磨损失效机理以及影响因素等尚不完善,特别对高温下摩擦层和钢基体对耐磨性的作用缺少深入分析。本文采用高温磨损实验机对H13、H21钢进行了销-盘式高温磨损实验,采用XRD、SEM、EDS和显微硬度等分析手段,对磨损表面及亚表面进行了系统的检测与分析,系统的研究了不同滑动条件下的摩擦层、基体与磨损行为及机制的对应关系,揭示了两种典型热作模具钢的高温磨损失效机理,具有重要的理论意义和工程应用价值。实验结果表明:在高温400-600℃、载荷50-150 N和转速50、100 r/min下,H13和H21钢表现出不同的磨损行为,磨损率随着滑动条件而变化的规律有很大差异。对于H13钢,转速对磨损率影响显著,在50 r/min下磨损率随载荷增加先升后降;而100 r/min下随载荷增加单调升高,尤其在600℃、150 N下,磨损率指数级快速增长,转变为严重磨损;100 r/min下磨损率均高于50 r/min下的;不论转速和载荷,500℃的磨损率最低,50 r/min下600℃次之,400℃最差,100 r/min下400℃次之,600℃最差。而对于H21钢,磨损率随载荷、温度增加单调升高;在400-500℃下,磨损率较低,转速影响不大;而在高温600℃下磨损率发生突变,转变为严重磨损,且转速影响显著,50r/min下的磨损率3-4倍于100 r/min下的。在400-500℃下,H13和H21钢具有高的耐磨性,且耐磨性相近,H13钢的略高于H21钢的;而在高温600℃下,H13钢在50 r/min、50-150 N和100 r/min、50-100 N下具有高的耐磨性,H21钢耐磨性极差,且50 r/min下耐磨性比100 r/min下耐磨性更差;而H13钢仅在100 r/min、150N下耐磨性与后者相近。通过对H13和H21钢的磨损特征的微观分析,发现H13钢在50 r/min、500℃下的磨损机制为氧化轻微磨损,而H13钢在100 r/min、600℃和150 N条件下发生了严重塑性挤出,其余情况下磨损机制为氧化磨损。H21钢在400-500℃下为氧化磨损,当温度升高至600℃,磨损加剧,转变为氧化严重磨损。高温磨损中,热作模具钢的耐磨性取决于磨面形成的摩擦氧化物层以及基体的热稳定性。高温下磨面逐渐形成摩擦氧化物层,当亚表面基体具有足够的承载能力时,摩擦氧化物层可以有效保护基体,此时为氧化轻微磨损。而当基体由于软化而承载能力降低而发生一定的塑性变形,导致摩擦层部分剥落,只能部分保护基体,发生氧化磨损,即氧化磨损的轻微-严重磨损转变;当亚表面基体由于软化发生塑性流变(H21钢在高温、高载、高转速下),摩擦氧化物层大量剥落而完全失去保护作用,发生塑性挤出磨损;而对于H13钢在高温下第二相碳化物发生粗化而变脆,在周期性摩擦力作用下,易发生沿着基体与第二相的界面开裂,使得、其上的摩擦氧化物层大量剥离,其保护作用部分失去(400-500℃)或完全失去(600℃),从而发生氧化磨损或氧化严重磨损。更多还原

【Abstract】 High temperature wear is a typical failure mode of hot-working die under severe working conditions.The difference in wear resistance of hot-working die steels at high temperatures directly affects the service life of hot-working die.However,at present,there is a lack of in-depth research on the failure mechanism and influencing factors of high-temperature wear of hot-working die steels.The effects of friction layers and steel substrates on wear resistance at high temperatures are not yet clear.In this paper,a high-temperature wear test machine was used to conduct pin-disc high-temperature wear experiments on H13 and H21 steels,and XRD,SEM,EDS,and microhardness were used to systematically detect and analyze the worn surface and subsurface,studied the corresponding relationship between tribo-layer,matrix and wear behavior and mechanism under different sliding conditions,and revealed the high temperature wear failure mechanism of two typical hot-working die steels,which has important theoretical significance and engineering application value.The experimental results shown that at high temperatures of 400-600 ℃,loads of 50-150 N and speeds of 50 and 100 r/min,H13 and H21 steels exhibited different wear behaviors,and the law of wear rate changed greatly with sliding conditions difference.For H13 steel,the speed had a significant effect on the wear rate.At 50 r/min,the wear rate rose first and then decreased as the load increased;at 100 r/min,it increased monotonically with the load increased,especially at 600 ℃ and 150 N.The rate increased exponentially and changed into severe wear;the wear rate at 100 r/min was higher than that at 50 r/min;regardless of the speed and load,the wear rate at 500 ℃ was the lowest,followed by 600 ℃ at 50 r/min,400 ℃ was the worst,followed by 400 ℃ at 100 r/min,and 600 ℃ was the worst.For H21 steel,the wear rate increased monotonously with the increase of load and temperature;at400-500 ℃,the wear rate was low,and the rotational speed had little effect;while at high temperature 600 ℃,the wear rate changed suddenly and changed into severe wear The speed had a significant effect.The wear rate at 50 r min was 3-4 times that at 100r/min.At400-500 ℃,H13 and H21 steel had high wear resistance,and the wear resistance was similar,H13 steel was slightly higher than H21 steel;and at high temperature of 600 ℃,H13 steel had high wear resistance at 50 r/min,50-150 N and 100 r/min,50-100 N,H21 steel wear resistance was extremely poor,and the wear resistance at 50 r/min was worse than the wear resistance at 100 r/min;The wear resistance of H13 steel was similar to the latter only at 100r/min and 150 N.Through microscopic analysis of the wear characteristics of H13 and H21 steels,it is found that the wear mechanism of H13 steel at 50 r/min and 500 ℃ was slight oxidation wear,while that of H13 steel at 100 r/min,600 ℃ and 150 N was severe plastic extrusion,the wear mechanism in the remaining cases is oxidative wear.H21 steel suffered from oxidative wear at 400-500 ℃.When the temperature rose to 600 ℃,the abrasion increased and it became oxidation severe wear.In high temperature wear,the wear resistance of hot work die steel depends on the oxidative tribo-layer formed on the worn surface and the thermal stability of the substrate.The oxidative tribo-layer is gradually formed on the worn surface at high temperature.When the sub-surface matrix has sufficient bearing capacity,the oxidative tribo-layer can effectively protect the matrix.At this time,it is slightly oxidized and worn.When the substrate is softened and the bearing capacity is reduced,a certain plastic deformation occurs,which causes the tribo-layer to partially peel off,which can only partially protect the substrate.Oxidative wear occurs,that is,a slight-severe wear transition of oxidative wear;When the sub surface matrix is softened,plastic flow occurs(H13 steel at high temperature,high load,high speed),a large amount of oxidative tribo-layer is peeled off and completely loses its protective effect,plastic extrusion wear occurs;for H21 steel,the second phase carbide coarsens and becomes brittle at high temperature,and under the periodic friction,it is easy to crack along the interface between the matrix and the second phase,resulting in a large number of peeling off of the oxidative tribo-layer,and the protective effect is partially lost(400-500 ℃)or completely lost(600 ℃),resulting in oxidative wear or severe oxidative wear.更多还原