Study On The Fatigue Resistance Of The Surfacing Layer For Cement Squeeze Roller

In the process of cement production,the squeeze roller of the cement roller press is subjected to abrasive wear of high strength and cyclic compressive stress,which cause wear failure and fatigue break-down of resistant wear layers.Therefore,improving the wear resistance and fatigue resistance performance of surfacing layers is the key to extend the service life of the squeeze roller and improve production efficiency with low cost.In this paper,metal electrode arc surfacing process was used on 45 steel base metal with self-shielded flux-cored wires.The effect of wires with different additons of high carbon ferrochrome or graphite on the compositions,microstructures,hardness,wear resistance and fatigue resistance performance of the surfacing layers was studied.The experiment studies showed that,as the amounts of high carbon ferrochrome in the wires were increased from zero to 500 grams,chromium contents in the surfacing layers were increased from 0.08% to 6.65% and carbon contents were increased from 1.07% to 1.90%.While very little change was found on the contents of other elements such as Nb,Si,and Mn.Microstructure analysis found that,when the high carbon ferrochrome content is 0g,the microstructure of the surfacing layer consisted of ferrite +(martensite + retained austenite)+ NbC particles.With the high carbon ferrochrome content increase the microstructures were gradually changed into(martensite + retained austenite)+ NbC particles?(martensite + retained austenite)+ austenite + NbC particles ?austenite + NbC particles.With the increase of the amounts of high carbon ferrochrome,the macro hardness and relative wear resistance of the surfacing layers rose at first and then descended.Without the high carbon ferrochrome addition,the hardness of the surfacing layer was 45.2HRC.Then the hardness increased with the increase of the high carbon ferrochrome additions.when the amount of high carbon ferrochrome was added to 50 g,the surfacing layer had its highest hardness of 62.7HRC.As the additions of high carbon were ferrochrome continuously increased,the hardness decreased constantly,which reached the lowest value of 36.1HRC with the highest carbon ferrochrome addition of 500 g.The experimental results were found during study on the wear resistance of surfacing layers,with 0g ferrochrome addition,the relative wear resistance of the surfacing layer was only 1.5263 which was the lowest.When the ferrochrome addition was 150 g,the relative wear resistance was 4.1198,which was the highest.With the increase of the amounts of graphite,carbon contents in surfacing layers increased from 0.5% to 1.64%.And contents of elements such as Cr,Nb,Si,and Mn fluctuated slightly.when the graphite addition is 0g in the wire,the microstructure of the surfacing layer consisted of ferrite + NbC particles.With increase of the graphite additons,the microstructures gradually changed into(martensite + retained austenite)+ ferrite + NbC particles?(martensite + retained austenite)+ Nb C particles ?(martensite + retained austenite)+ austenite + NbC.As the additions of graphite increased,the macro hardness and the relative wear resistance of the surfacing layers rose at the beginning and declined afterwards.When graphite addition was 0g,the hardness was the lowest,which was 35.7HRC.And the relative wear resistance was the worst,which was 1.1143.Then the hardness and relative wear resistance increased with the increase of graphite additions.When the graphite addition reached to 60 g,the hardness reached its maximum,which was 61.1HRC.And the relative wear resistance was at its best,which was 3.9758.Continuously increasing the graphite additions resulted of lower hardness and relative wear resistance.The three-point bending fatigue performance of the surfacing layers was studied by a self-made fatigue testing machine.The a-N curves,fatigue crack initiation and fracture loading times of different fatigue test specimens of surfacing layers were analyzed.The fatigue experiment studies showed that,fatigue crack propagation could be divided into three stages: the slow propagation stage,the stable propagation stage and the unstable propagation stage.Changing tendency of the fatigue resistance performance of surfacing layers was opposite to that of their hardness.With the increase of high carbon ferrochrome and graphite additions,the fatigue resistance decreased first and then increased.When surfacing layers with large quantity of martensite,its high hardness caused poor fatigue resistance.The fatigue crack would initiate after short loading cycles under cyclic loading.When surfacing layers containing large quantity of austenite or ferrite,the hardness of surfacing layers was low but high fatigue resistance and long fatigue life were achived.The effect of high carbon ferrochrome and graphite addition in wires on the fatigue resistance performance of surfacing layers was investigated.When the addition of the ferrochrome was 50 g,the loading times for fatigue crack initiation were and the fatigue life was.When the ferrochrome addition reached to 500 g,they were and correspondingly.When the graphite addition was 0g,loading times of fatigue crack initiation was and the fatigue life was.While the graphite addition was 60 g,they decreased to and correspondingly.The fatigue resistance performance of the surfacing layers made by wires with high carbon ferrochrome addition was better.When the high carbon ferrochrome addition was 500 g,the fatigue resistance performance was the best.