New Bainitic Steel Wear Loads Collaborative Preliminary Study Of The Fatigue Life

This study investigates and analyses the fatigue life of the low-carbon low-alloy GDL-1 steel under wear and fatigue load.Research the effect of wear condition on cycle lifetime of samples through wear device desigened by ourselves.Try to simulate the evolutionary process of the cumulative,expansion and failure of the micro-crack on surface and subsurface of the real components.Obain the preliminary law of variation of fatigue life under the wear condition through the above experiments,so that lay the foundation for strength design and forecast of fatigue life of components under wear condition.Through the observation of the fatigue of the spiral drill rod,under the severe wear and the erosion of high pressure stream current(or gas) and mine water,drill rod bears tensile stress,compression stress,flexure stress,torsional stress and high frequency impulse load.When drill shank is revoluting,the drill rod will wear with the rock,specially the surface of the screw chaser pontes will wear severely,which affect the fatigue life.All of this make us form a new acquaintanceship with the evolutionary process of the cumulative,expansion and failure of the micro-crack on surface.Birng forwars that the surface will form a thin distuibance layer(consist of wearing layer and deformation layer),when samples are under the interaction of several loads.The formation of the distuibance layer affects the nucleating and expending machanism severely.Competition mechanism between the formation speed rate of disturbance layer(V_m+V_x)(V_m stands for the wear rate,V_x stands for the forming speed of formation layer) and the expending rate da/dN of the main crack in micro-crack,which determines the fatigue life of the materail.This fatigue life is not the intrinsic fatigue Life(the fatigue life only under single fatigue load) but co-fatigue life.Co-fatigue life means:the fatigue life of materials or samples which are under the interaction of one or more loads.In this paper classify the co-fatigue life effect into two cases:positive co-fatigue life effect and negative co-fatigue life effect.Otherwise this paper also represents the relationship between the wear rate V_m and forming speed of formation layer V_x and the effect of the formation speed rate of the disturbance layer determined by them on the expending rate da/dN of the main crack in micro-crack,and discuss the relationship between the wear rate V_m and the formation speed rate of the disturbance layer V_x and co-fatigue strength.In addition,SEM observed the evolution of longitudinal plane of the micro-crack from nucleating and growing up,then,analyse all kinds of damages before samples are fail:from single micro-crack,multiple micro-crack,triangle intergranular morphometry of micro-crack,intergranular crack of single grain,intergranular crack of multiple grains,fatigue micro-crack of intracrystalline fluctuate,multi-line intracrystalline fatigue micro-crac etc.to destructive macro-crack.After analysing the effect of the transformation time and transformation style and the stress distribution of formation layer in disturbance layer, conclude that disturbance layer formed by wear loads has a severe effect on fatigue life. By controling the thickness of wear layer well(for example,GDL-1 steel tempered in air,when the thickness of the carburized layer is 0.6mm,wear layer is within 0.12mm, the thickness of formation layer is about 0.1mm),will make the strength of the components improve by 25MPa,so the fatigue life of the components is improved under the interaction of wear and other loads.This has the practice significance to extend the fatigue life when the components are under multiple loads and also provide a new way to solve premature failure during using drill rod.