Study On The Compression Fatigue Resistance Of The Surfacing Layers For Squeeze Roller

In cement production,the wear-resistant surfacing layer of the squeeze roller of the cement roller press is susceptible to fatigue wear failure due to long-term cyclic compressive stress.Therefore,improving the anti-fatigue properties of surfacing layer is of great significance to improve the service life of the squeeze roller.In this paper,the self-made self-shielded flux-cored wire with different amount of graphite was used to surface on the 45 steel base metal.The composition,microstructure,hardness and compression fatigue resistance of the surfacing metal were studied.The main results are as follows:(1)With the addition of graphite in the wire changes from 0g to 100 g,the content of carbon in the surfacing layers increases from 0.51 wt.% to 1.65 wt.%,while the contents of Mn,Nb,Cr and other elements remain generally stable.The microstructure of the surfacing metals were analyzed,and the results showed that when the content of carbon in the surfacing layer is the lowest,the microstructure is mainly ferrite + granular NbC,and the hardness of the surfacing layer is at a lower level due to the lower hardness of ferrite matrix,the average hardness is 37.2 HRC.With the content of carbon in the surfacing layer increases,the content of ferrite and martensite in the microstructure of the surfacing layer decrease,while the content of NbC increases,and the size of NbC grew larger accordingly.When the content of carbon in the surfacing layer is 1.36 wt.%,the microstructure is mainly martensite + retained austenite + tetragonal NbC.The hardness of the martensitic matrix is high,therefore,the hardness of the surfacing layer reaches the maximum and the average hardness is 63.9HRC.With the content of carbon in surfacing layer increases continuously,the content of martensite in the microstructure of the surfacing layer decreases,while the content of independent austenite increases.Since the hardness of the austenite matrix is low,the hardness of the surfacing layer begins to decrease.When the content of carbon in the surfacing layer is 1.65 wt.%,the microstructure of the surfacing layer consists of austenite and granular NbC,and the average hardness of the surfacing layer reaches a minimum of 36.5 HRC.(2)In order to design the compression fatigue specimens reasonably,so that the specimens can both meet the test requirements of high-cycle fatigue and shorten the test period,reduce the number of cyclic loadings during the compression fatigue test,the finite element analysis was used to analysis the stress and strain of three kinds of compression fatigue specimens which contain non-notch,single-notch,dual-notch specimen during the loading process and the results were finally verified by actual test.The results show that fatigue crack initiation and propagation directions are similar for all three kinds of compression fatigue specimens,and all extend obliquely downward at an inclination to the vertical direction.The notch in the specimen can accelerate the initiation of crack and the rate of fatigue propagation,especially in the dual-notch compression fatigue specimen.Meanwhile,the fatigue cracks generally initiate and propagate at the end of the notchs,which is beneficial for observing the fatigue specimens.The a-N curves of the non-notch fatigue specimen and dual-notch fatigue specimen are similar to each other,both of them are linear.Meanwhile,the a-N curve of single-notch compression fatigue specimen can be divided into two obvious stages,rapid propagation stage and slow propagation stage,and is deviate from the non-notch specimen.Therefore,the dual-notch compression fatigue specimen is the most reasonable among all three kinds of fatigue specimens to be used in the compression fatigue test.(3)The self-designed compression fatigue testing machine and the dual-notch compression fatigue specimen were used to operate the compression fatigue test,and the influence of carbon content in the surfacing layer on the compression fatigue resistance of the surfacing layer was studied by comparing the cyclic loading times when the crack length reaches the critical length of 6 mm.The results show that when the content of surfacing layer carbon is the lowest,the fatigue cracks length of the specimen after 480,000 cyclic loadings reaches 6329 ?m,and the compression fatigue resistance of the surfacing layer is good.With the content of carbon in the surfacing layer gradually increases,the compression fatigue resistance gradually decreases.When the carbon content in the surfacing layer is 1.36 wt.%,the fatigue cracks length of the specimen after 50,000 cyclic loadings reaches 7303 ?m.With the content of carbon in the surfacing layer increases continuously,the compression fatigue resistance begins to increase.When the carbon content in the surfacing layer is 1.65 wt.%,the fatigue cracks length of the specimen after 540,000 cyclic loadings reaches 6728 ?m.The result reveals that as the carbon content in the surfacing layer gradually increases,the compressive fatigue resistance of the surfacing layer decreases firstly and then increases.This trend is negatively correlated with the hardness change trend,so that the specimen with lower hardness has a better anti-fatigue performance while the specimen with higher hardness has a worse anti-fatigue performance.