Effects Of Sliding Speeds On The Dry Sliding Wear Behavior Of Steels

The tribo-layers different from the matrix formed on worn surfaces of metallic alloys during dry sliding wear determine the wear behavior and mechanism.However,the studies about dry sliding tribo-layers were not systematic and comprehensive enough so that there is no consistent cognition about their formation and function mechanism,Therefore,it will possess great theoretical and engineering values to explore the mechanism of formation and function of tribo-layers.In this paper,the pin-disc dry sliding wear test on H13 steel and 45 steel with different microstructure was performed under various loads and sliding speeds,the wear characteristics of the worn surfaces and subsurface were were analyzed by means of XRD,SEM,EDS and microhardness tester,the effects of material properties and sliding conditions on the wear behavior and mechanism was systematically studied,and the correspondence between the tribo-layers evolution and the mechanism transition was discussed.It is found that the composition,morphology and stability of the tribo-layers of H13 steel and 45 steel changed with the variation of sliding conditions and tissue performance,which ultimately lead to the transition of wear mechanism.When the worn surfaces of two kinds of steels were covered by no-oxide tribo-layers,the wear behavior depends on their own property and nothing to do with the tribo-layers.When the worn surface of two kinds of steels were covered by oxidative tribo-layers,the wear behavior depended on the combined action of the oxidative tribo-layer and subsurface matrix.If the subsurface matrix has sufficient strength to resist the plastic shear,the oxidative tribo-layers can be stable on the worn surfaces,and the wear rate was low,the wear mechanism belonged to mild oxidative wear.Once the subsurface matrix softened seriously under the action of friction heat,oxidative tribo-layers were extruded out of the worn surfaces with the subsurface matrix that wear rate rose sharply,the mild-severe wear transition in oxidative wear occurred.However,the critical sliding conditions for the mild-severe wear transition of H13 steel and 45 steel with different hardness are various.In this paper,under the fixed load,the critical sliding speed when the subsurface matrix of some tissue soften severely that cannot resist plastic shear was called the softening critical speed of this tissue under this load.The value range of the softening critical speed of different tissues of the same steel was referred to as the softening interval of the steel under this load,and than a simple computational formula for softening critical speed was deduced based on the assumption that all the relation between the influence factors are linear,which further reveals the essential law of the transition of mild-severe wear of steels.In addition,the wear mechanism maps of H13 steel and 45 steel with hardness of 37 HRC and 50 HRC were plotted according to the experimental results,the existence of transition ofmild-severe wear in oxidative wear under low load was proved,at the same time,the problems existing in the wear mechanism map of steel proposed by Lim,Ashby and M.X Wei were also expounded,and further amendment was made.The results show that: under fixed load,with the increase of sliding speed,the mild-severe wear transition of the higher hardness tissues of H13 steel and 45 steel occurred in advance of the lower hardness tissues in most cases,and when the mild-severe wear transition of different tissues happened at the same sliding speed,the transition of the higher hardness tissues occurred more sharply than that of the lower hardness tissues;in addition,the mild-severe wear transition of two kinds of steels occurs earlier as the increasing of load.The wear resistance is proportional to the hardness in the left speed range of the softening interval;the wear resistance is inversely proportional to the hardness in the right speed range of the softening interval;in the softening interval,there is no clear uniform proportional relationship between the hardness and wear resistance.At the same time,with the increase of load,the softening interval of H13 steel and 45 steel is shifted to the left.A large number of Cr and Si significantly reduced the oxidation capacity of H13 steel and inhibited the generation of oxides,lead to the wear resistance of H13 steel is lower than 45 steel under the low load and speed,and under the same load,the mild-severe wear transition of H13 steel occurred earlier than 45 steel.At the same time,the existence of Cr and Si also greatly improved the thermal stability and thermal strength of H13 steel,so that under high load and speed,H13 steel is still in the stage of intermittent plastic extrusion wear while 45 steel occurred the continuous plastic extrusion wear,the wear resistance is significantly superior to 45 steel.