Bonding Property Between Surfacing Alloys For Cement Squeeze Roller And The Base Metal Of 45 Steel

As the foundation of China's national economy,the cement industry has good prospects for development.Roller press is an important crushing equipment in the cement production process,and the core component of roller press is the squeeze roll.The squeezing roller works under high stress abrasive wear and fatigue for a long time,and it is prone to fatigue wear,resulting in failure of the sample.In order to improve the wear resistance of the roller surface,wear metal is often deposited on the surface of the extrusion roller.Although the wear-resistant layer can play a role in improving the wear resistance of the squeezing roller,due to the difference in composition and microstructure of the wear-resisting layer and the base metal,there is a difference in performance between the two,and the bonding performance between two materials is poor,resulting in failure of wear layer peeling due to fatigue and wear.Therefore,it is of great scientific significance and practical value to study how to improve the wear resistance and the combined strength of the wear-resisting layer and the base metal,which can extend the service life of the components,and reduce the maintenance time of the equipment.The surfacing materials used in this paper include:3 kinds of commercially available welding wires,6 kinds of self-made modified high-carbon ferrochromium additions surfacing welding wires,and 6 kinds of self-made modified graphite additions Fe-Cr-C-Nb surfacing welding wires,with 45 steel as the base metal.The surfacing alloy was prepared and the composition,microstructure,hardness,wear resistance and bonding properties of the surfacing alloy were studied.Based on the existing test methods for the combined properties of surfacing alloys and base metals,a new criss-cross push-off test method that can be used to test the bonding strength between surfacing alloys and base metals is proposed.The main test results are as follows:?1?Analyzed the microstructure of austenitic steel,niobium-alloyed steel and high chromium alloy cast iron surfacing welding on 45 steel base metal.The criss-cross push-off test method was used to test the bond strength between the commercially available surfacing alloy and the base metal.The bond strengths between this three commercially available surfacing alloys and the 45 steel base metal are 369,191,and 48 MPa,respectively.The criss-cross specimen was observed and analyzed the fracture location and fracture characteristics.?2?Micro-structures of surfacing alloys with different amounts of high-carbon ferrochrome were analyzed,and the effect laws of C and Cr contents towards the structure and property of surfacing alloys were also studied.The result showed that,micro-structures of a series of surfacing alloys with six different amounts of high-carbon ferrochrome mainly consisted of martensite,austenite and NbC carbide dispersed in the matrix.When the amount of high-carbon ferrochrome was 0%,matrix structure of the hard-facing alloy was composed of martensite,mixed with residual austenite;with the increase of the amount,C and Cr elements in the hard-facing alloy also increased,while the amount of martensite decreased and that of austenite increased,too;when the amount of high-carbon ferrochrome reached 7.5%,independent austenite started to appear,and with the continuous increase of C and Cr contents,independent austenites gradually combined with one another and formed flakes.In welding metallurgical reaction,Nb element first combined with C element and generated NbC;with the increase of C and Cr contents,more amount of NbC was precipitated,and the dimension also grew larger,with the dimension of maximal NbC increasing from 1?m to 4?m.The increase in both the number of NbC hard phases and the dimension remarkably improved the hardness and wear-resistance of surfacing alloys.When the amount of high-carbon ferrochrome was 5%,the hardness and wear-resistance of the hard-facing alloy reached the summit,with an average micro-hardness of 861HV_0.2.2 on the upper part of the hard-facing alloy and a wear-resistance about 6 times larger than that of 45 steel matrix.When the amount of high-carbon ferrochrome continued to raise,both hardness and wear-resistance dropped due to the augmentation of austenite in the matrix.?3?Influences of 6 different amounts of graphite on the micro-structure and property of the hard-facing alloy were studied.Micro-structures of a series of surfacing alloys made by flux-cored wires with different amounts of graphite were mainly composed of ferrite,martensite,austenite and NbC carbide dispersed in the matrix.When the amount of graphite was 0%,matrix structure of the hard-facing alloy was made up of ferrite,martensite and NbC;with the increase of the graphite amount,C elements in the hard-facing alloy also increased,while ferrite disappeared,together with the decrease of martensite and increase of austenite;both the amount and dimension of NbC increased,with the dimension of the maximal NbC raising from 1?m to 6?m.Hardness and matrix structure of the hard-facing alloy were related to the dimension of NbC particles,while the change of wear-resistance corresponded with that of surface hardness.When the amount of graphite reached 3%,there was a certain amount of martensite in the matrix,and the dimension of NbC was relatively large;hardness of the alloy was 61.8HRC and the wear-resistance also reached its summit,about 3 times higher than that of the base metal.?4?Bond strength of surfacing alloys with different amounts of high-carbon ferrochrome was tested with the help of cross push-off method.The bond strength performed best when the amount of high-carbon ferrochrome was 0%,reaching513MPa;with the increase of high-carbon ferrochrome,bond strength dropped since large NbC blocks split the matrix;it hit the bottom when the amount of high-carbon ferrochrome was 7.5%,reaching 147MPa.With the increase of high-carbon ferrochrome,amount of austenite increased in the hard-facing layer;plasticity and toughness were good,and bond strength was also improved.When the amount of high-carbon ferrochrome was 13%,bond strength reached 283MPa.Through the push-off test,it was discovered that the bond strength of hard-facing alloy with 45parent metal decreased at first,followed by an increase later,and was distributed in the U shape.?5?Bond strength of surfacing alloys and 45 steel base metal with different amounts of graphite was tested with cross push-off method.When the amount of graphite was 0%,the content of C in the surfacing alloy is 0.5%,and the bond strength performed well,reaching 355MPa;with the increase of graphite,bond strength dropped and it hit the bottom when the amount of graphite was 2%,reaching147MPa,the content of C in the surfacing alloy is 1.01%.With the increase of graphite,amount of austenite increased in the hard-facing layer;plasticity and toughness were good,and bond strength was also improved.When the amount was5%,the content of C in the surfacing alloy is 1.64%,bond strength performed best,reaching 460MPa.Bond strength was mainly influenced by the changes of components and structure.Through the push-off test,it was discovered that the bond strength of hard-facing alloy with 45 parent metal decreased at first,followed by an increase later,and was distributed in the V shape.When high-carbon ferrochrome and graphite flux-cored wire were adjusted to make surfacing alloys with similar structures,the changes of their respective bond strengths of the 45 steel base metal shared the same trend.