Study On Fatigue Resistance Of Hardfacing Layer Metals Of Roller Press

Cement industry is the basic industry of the national economy, and the rollerpress is the most important equipment of ore crushing and grinding system in cementproduction. In real-working conditions, under the high recycle pressure and wearenvironments, there will exist the roll surface abrasion and frictional wearaccompanied by fatigue, while fatigue crack initiating and expanding lead to fatiguefailure and chunks falling off. So studying on fatigue resistance of hardfacing layersof roller press is very meaningful.In this paper, the three popular different flux-cored hardfacing layer and atransition layer wires were used by MIG self-protection welding method to hardfaceon45steel base metal and then analyze the microstructure characteristics of these foursurfacing layers. And six different fatigue specimens were prepared in which therewere three ones without and other three with transition layer. A self-designed fatiguetesting machine was applied to carry out fatigue experiment. The differences offatigue resistance of the three hardfacing layers without the transition layer werecompared to other three with transition layer to analyze the impact of transition layeron fatigue resistance and the mechanism. Finally, the fatigue fractographes offatigue specimen were analyzed.Three different flux-cored hardfacing layers were used and correspondinghardfacing metals are followings. The first one is niobium alloy steel. There are agreat deal of NbC particles dispersively distributing in hardfacing steel matrix inwhich microstructures are mainly combined by martensite plus some retainedaustenite. It’s harder and plasticity and toughness are relatively good. The second oneis niobium high chromium alloy cast iron. The hypoeutectic microstructures can befound at the bottom of the hardfacing layer.while in the middle part of the hardfacinglayer,the mainly microstructures are eutectic. And hypereutectic microstructures canbe found in the upper part. Actually, lots of NbC particles dispersively distributed in hardfacing layer as well. The hardness of the hardfacing layer is high but with poorplasticity and toughness. The last one is hypereutectic high chromium alloy cast iron.Hypereutectic microstructures can be found in the middle and upper parts of thehardfacing layer. But the main microstructures are eutectic at the bottom. Thus it hashigher hardness and worse plasticity and toughness. The transition layer was surfacedby flux-cored welding wire with high contents of chromium and manganese andcombined by austenite microstructure with better plasticity and toughness.It was found that the difference is less during fatigue crack initiation periodamong three different hardfacing layers without transition layer, but the apparentdifference took place during the crack propagation period. Conversely, the fatiguecrack initiation period for three different hardfacing layers with transition layer ismuch different, but the crack propagation period is nearly the same. The fatigueresistance performance of niobium alloy steel hardfacing layer is best. The fatiguecrack stopped propagation when meeting to the interface between transition andhardfacing layers. But with the cyclic stress loading increase, a new fatigue crackemerged at the interface and then propagated rapidly through the hardfacing layer.The next one is high-chromium alloy cast iron hardfacing layer with some niobiumcontents. And the worst is hypereutectic high chromium cast iron hardfacing layer. Inboth cases, the fatigue crack in base metal propagated directly through the transitionand hardfacing layers. Moreover, peeling cracks initiated at the fusion zone betweenhypereutectic high chromium alloy cast iron hardfacing and transition layers.The transition layer made the base metal and hardfacing layer bond well andeffectively prolonged the fatigue crack initiation stage because of its good plasticity.When fatigue crack in base metal propagated to the interface between the base metaland the transition layer, its propagation path changed from vertical to transversedirection, thereby improving the fatigue strength. It was found from the SEM analysisof fatigue fractographes that, in the crack propagation region, there were river-likefatigue striations with slightly arc and regular spaces. And they were perpendicular tothe fatigue crack propagation direction.