Research About Effects Of Surface Heat Treatment Processing On The Fatigue Life Of Coupler Knuckle

Reasonable surface heat treatment process is an important method to excavate the strength and toughness of alloy steel. In view of the new enhanced cast steel coupler knuckle designed by QI factory, I used the method of experiments and simulations to fully analyze the effect of surface quenching and its boundary on the fatigue properties of cast steel coupler knuckle, from the macro and micro structure of the material.It was found that the fatigue limit of cast steel was indeed affected by surface quenching but was not obvious; however, it can greatly improve the anti-fatigue performance and surface hardness of cast steel. Under the same conditions of surface quenching on the F51AE cast steel coupler knuckle, the fatigue life of surface S can be improved by 81.1%, and the fatigue life of bounce table can be increased by 145.7%, moreover the surface hardness of the cast steel can be improved by 53.2%. Certainly, the effect of quenching boundary cannot be ignored, although it can also improve the coupler knuckle’s fatigue life in a certain extent, it is far less than that of the surface. Its impact on the surface S of the coupler knuckle is only 86.7% of the quenching, the impact on bounce table is only 83.8%. Therefore, in the actual operation process of the coupler knuckle’s surface quenching, it must be sure that the quenching boundary does not appear on the coupler knuckle’s external surface, especially the fatigue weak parts, such as the upper and lower bounce table and surface S.Microstructure analysis results show that the micros reasons of these changes are that surface quenching makes the metal structure in the surface of cast steel hook tongue occur Sorbite transition, with micro globular cementite evenly distributing in the ferrite matrix, grain is very fine, grain boundary distance is shortened, the number of grain boundaries is relatively increased. So, under the external load, the grain dislocation motion is hindered. In this way, not only can it reduce the formation of the initial surface crack, but also reduce the velocity of crack extension, thereby eliminating the defects of cast steel surface, and improving the surface quality. Of course, to a certain extent, the cast steel anti-fatigue properties and surface hardness are improved.Accounting that the strengthen F51AE hook tongue is a new hook tongue type and is to be used in 35.5t axle load ore car exported to Australia, the strength of the hook tongue should be checked. As well, the line load conditions are very poor and severe, with those previous vehicle hook tongue occurring plastic deformation when damaged.Therefore, in this paper, I utilized the elastic-plastic mechanics and finite element simulation calculation method, according to the ARR standard and UF type coupler, to check the hook tongue’s structure strength.