Mechanical Behavior And Fatigue Performance Of Carburized Steel Parts

Carburization of steel parts is a classical manufacturing step for mechanical parts,such as gears,to improve the fatigue performance.How to characterize the influence the mechanical behavior of carburized layer and transition zone,quantify the fatigue performance of different parts are still issues that have not solved.In this work,three different carburization specemens,i.e.completely carburized,case-carburized and heat treated(core material),are invested.Experimental test are carried on these materials to obtain their stress-strain curve,elastic modulus,yield stress and fracture stress.Micro hardness and elastic modulus distributions are determined by nanoidentation experiment.The influence of carbon content on hardness will be further determined.Residual stress is measured by focused ion beam(FIB).The S-N curves of three different materials are constructed.Experimental results show that carburization process will not change elastic modulus,but will increase yield stress and hardness accompanying decrease in fracture strain.Fatigue performance of completely carburized steel is slightly lower than core material.Case-carburized material's fatigue performance is greater increased,fatigue limit increases from 300 MPa to 550 MPa.Fatigue performance increament mainly caused by compressive residual stress in carburization layer.Fatigue limit of case carburized steel can be predictied by correction of residual stress.With the applied load increasing,the influence of residual stress become insignificant and the fatigue performance is not increasing very much.In low cycle area,fatigue performance of carburized steel may be even worse than core material.