Study On The Microstructures And Mechanical Properties Of Backing Surfacing With Self-shielded Flux-cored Wire

Surfacing welding,as an economical and convenient technological method for surface modification of materials,is more and more widely used in the manufacturing and repairing of workpiece in various industrial sectors.A more reasonable welding process is a key to obtain high quality product,which should be combined with the characteristics of the hardfacing alloys and matrix.Moreover,larger binding capacity force between the surfacing layer and matrix can be gotten,which apply the merits of both materials.In this paper,the microstructures(which were collectively referred to as the surfacing microstructures in the text later)and related mechanical properties of the weld zone,fusion zone and overheated zone(of the welding joint)were taken as the research object,the effects of interpass temperature,preheat temperature and arc stability on the microstructures and mechanical properties of the surfacing fusion zone were mainly investigated.Finally,a relatively reasonable welding process was gotted,and the repetitive experiment were carried out partly again.The microstructures and linear thermal expansion coefficients at different cooling rates of hardfacing alloys(welded with self-shielded flux-cored wire)and 45 quenched and tempered steel used as matrix materials in our research were analyzed through OM and thermal simulator technology.The results showed that the microstructures of the both kinds of materials were extremely different.The linear expansion coefficients of hardfacing alloys was greater than that one,which means the welding process belonged to the dissimilar steel welding category.The surfacing microstructures were investigated by OM,SEM/EDS,and XRD analyser.The results showed that,compared to the control groups of preheating temperature of 50 ? or 150 ?,the distribution of surfacing microstructures obtained at the preheating temperature of 100 ? was relatively uniform and the grain size was moderate.Volume fractions of residual austenite the impurities or microcracks were relatively small,indicating a better transition.When the interpass temperature was150 ?,the grains were relatively fine and the content of martensite was relatively low.No microcracks were observed.And the microstructures transition wassignificantly better than those of interpass temperature of 100 ? and 200 ?.The residual stress in fusion zones were investigated by blind-hole method.The results showed that compared to the control groups,when the preheating temperature was 100 ?,the residual stress values at different positions were the smallest,and the residual stress value in the middle position was the lowest compared to two ends.When the interpass temperature was 150 ?,the residual stress values at different positions were smaller than those of the control groups,especially the ones in the middle position,which is more conducive to the stability of materials.The impact toughness and microhardness in fusion zone were studied through impact test at room temperature and vicker-hardness test.The results showed that at the middle of the fusion zone welded at preheating temperature of 100 ?,the average value of impact work was 35.1 J,and the microscopic fracture was a typical river pattern,belonging to the cleavage fracture.The micro-hardness fluctuations were relatively smaller and significantly better than those of control groups.When the interpass temperature was 150 ?,the average value of impact work at the middle of the fusion zone was 34.4 J,which belonged to the cleavage fracture as well.And the microhardness fluctuations were also minimal compared to those of control groups.In addition,compared to the two ends in fusion zone,at the middle position,the distribution of microstructures were more uniform,and the smaller welding residual stress,better impact toughness(higher impact work)as well as less microhardness fluctuations can be obtained.This means the better arc stability,the better the surfacing microstructures and related mechanical properties.In summary,the reasonable welding process was more conducive to ensuring surfacing quality.The optimum preheating temperature and interpass temperature were 100 ? and 150 ?,respectively.Under this condition,the better microstructures and related mechanical properties can be obtained.In addition,the microstructures and related mechanical properties in the middle of the test board were much better compared to two ends,which mean good arc stability would help the welding quality.