Research On Friction And Surface Damage Of Alloy Steel Brake Disc Materials

The brake disc is the basic brake element of the rail vehicle.In the course of service,the train can reduce the speed of the train or stop the brake by the strong friction with the pad.During the braking process,the brake disc surface undergoes hot and cold cycles and thermal-mechanical coupling,resulting in problems such as friction and wear,surface hot spots,crackles and cracks.Therefore,this study is maily focus on friction and surface damage of alloy steel brake discs,which shows great theoretical significance and engineering value on understanding the fatigue failure behavior of the brake disc deeply,the research and development of China's independent innovation alloy steel brake disc material and the guarantee of the train safety.In this paper,two kinds of alloy steel brake disc materials of 28CrMoV and 28CrNiMo are chosen to be the object,and a series of theoretical and experimental studies are conducted.The testing of tensile properties at high temperature,the study of friction properties and the study of surface damage have been carried out.The main contents and conclusions of this paper are as follows:(1)Based on the 1:1 brake test,the surface temperature of the brake disc was obtained.The changes of microstructure transformation and microhardness of two alloy steel brake disc materials of 28CrMoV and 28CrNiMo were observed by heat cycle treatment at different temperatures.Besides,the finite element thermal stress analysis of the brake disc is carried out.It is expounded that the existence of high stress area in the hot spot area will induce the initiation and expansion of the friction surface crack on the brake disc.(2)The tensile properties and micro structure evolution of two kinds of alloy steel brake discs at 25,400,600 and 800 degrees were compared,and the effects of vanadium on the tensile properties of 28CrMoV steel were analyzed.(3)According to the temperature change of the friction surface of the brake disc obtained by the emergency braking test on the 1:1 power platform,3 kinds of thermal cyclic tests were carried out of the brake disc material.The friction and wear properties and the formation and evolution mechanism of the third body in the hot spot and non hot spot regions of two alloy steel brake discs were studied.It is found that the failure modes of abrasion or wear transition are easily occurs in the hot spot area(4)We carried out cold and hot fatigue tests on the brake disc material at 35?400 ? and 40?600 ?.Through the study of the propagation of thermal fatigue cracks and the microstructures,the factors that affect the propagation of the brake disc material were analyzed.It shows that the anti cold and hot fatigue property of 28CrMoV material is better than that of 28CrNiMo material.