High Temperature Wear Behavior And Mechanism Of Hot-working Die Steels

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.