Microstructures And Mechanical Properties Of Friction Surfacing For Pipeline Steel

Friction surfacing(FS)is a variant of conventional friction welding technology,with a promising application in the repairing of worn parts and manufacturing of wear resisting and corrosion resisting layers.Up to now,there exist detailed reviews about FS.However,it didn’t cause wide attention from domestic researcher,and no specific industrial application report has been published.The superior advantages of FS in the local recovery and refabrication of various materials deserve deeply exploitation and application study.In this paper,X52 and X65 pipeline steel were chosen as the substrate and this two with 316 L austenite stainless steel were chosen as the consumable rod to carry out the FS experiment.The interactions between the process parameters and macro forming,interface bonding,microstructure evolution and mechanical properties(bending,wear and corrosion property)were studied.The experiment results provide an important basis for the application of FS in local repairing and property modification of pipeline steels.In the range of 39.8~99.5MPa & 3500~4500rpm & 150~250mm/min,macro-defect-free and continuous friction surfacing coatings were obtained of all consumable rods.Except individual stuck or surface cavitation occurred under lower or bigger parameters,all other coatings obtained a high surface forming quality.The effective bonding width of X52 and X65 steel FS coatings arrived 10.46 mm and 14.3mm,respectively.The FS interface microstructure showed great difference from FS coating and Heat Affected Zone(HAZ),and achieved a metallurgical bonding transition in a way of forming new grains or ferrite bands.Microvoids or weak bonding would form under a lower parameter,while a higher parameter would cause the forming of overheated microstructure.The FS joint of pipeline steel was made up of three zones,including FS coating,HAZ and Base Metal(BM).The FS coating of X52 steel showed fine lath bainites,and that of X65 steel was composed of coarse lath and granular bainites.Different zones suffered different thermal-dynamic conditions in a FS joint.The coating surface presents equiaxed fine ferrites characterization;the HAZ was composed of overheated zone and phase recrystallization zone,which showed bainites and fine ferrites microstructure,respectively;the BM of X52 and X65 steel was both composed of ferrites and pearlites,while the pearlites in X65 steel was much less and mainly distributed at the grain boundary of ferrites.The results showed that a higher parameter window would promote the microstructure homogeneity.The hardness of X52 steel FS coating reached a maximum of 465HV1,which was 232% of that of BM.The hardness of X65 steel FS coating was lower than that of X52 steel with a highest hardness of 309HV1.This can be attributed to the fine lath bainites in X52 steel FS coating.Microstructure inhomogeneity caused inhomogeneous hardness distribution in the horizontal direction of FS coating of both two pipeline steel materials.The difference between the highest and lowest hardness was about tens of HV1.Except the phase recrystallization zone,all the other zones achieved a higher hardness than the BM.The bending results indicate that a good metallurgical bonding has been achieved between the X52 steel FS coating and the substrate.All specimens reached a 180°bending angle and no lift up or delamination occurred in the bending process.The X65 steel FS coating showed better wear resistant property than the BM.The wear volume can be mostly reduced 33.3% compared to that of the BM.The wide area surfacing of 316 L stainless steel has been finished in the way of multi-layer and multi-pass FS.The electrochemical corrosion property of the 316 L FS coating was between that of the 316 L BM and the X65 BM,indicating that FS process has effectively improved the corrosion resistance of X65 substrate,further to justify a continuous and integral wide area coating has been obtained.