Research On The Microstructure And Abrasion Resistance Of High-chromium Hardfacing Alloys Deposited With Composite Powder Particles And H08A Solid Wire

The conventional hardfacing materials include such welding consumable as coated electrode,solid wire,flux-cored wire,powder addition,etc.The transition amounts of alloying elements from solid wire to deposited metal were extremely limited and thus only low alloy hardfacing layers can be acquired.Although coated electrode and flux-cored wire can transit high content alloying elements into hardfacing alloys and their composition can be adjusted conveniently,their developed procedure appears time consuming and their production processes seems excessively complex.Powder used by such additive manufacturing technology as laser,was delivered to weld beads by coaxial airflow,which need spherical shape or nearly spherical one.It results in fussy manufacturing technology of raw powder and expensive price.All above materials cannot meet those development requirements of welding consumable,such as economy,efficiently supply and so on.In view of the situation and based on a number of experiments results,a new type welding consumable named as composite powder particle?CPP?was proposed in this paper by the leader of our research group and its manufacturing processes were also introduced,which included such process as dry mixing of weighing components,binding admixture adding,rotary pelleting,sintering and screen sizing.During welding process,composite powder particles were preset on the base metal surface along the weld path and H08A solid welding wire was used as arc carrier.It mixed the melts of composite powder particles and the molten drops together into weld pools.Then they were cooled to room temperature and wear resistant alloys deposited on base metals came into beding.The researched contents of this paper are as follows:?1?The effects of the preparation process of composite powder particles on the hardfacing alloy properties,?2?Effects of the composition of composite powder particles on the properties of surfacing alloy,?3?The influence of welding parameters on the properties of hardfacing high chromium alloys.The properties of high chromium alloys deposited by the method of self-shielded arc hardfacing with composite powder particles and solid wire were investigated by optical microscopy?OM?,X-ray diffractometer?XRD?,scanning electron microscopy?SEM?,energy spectrometer?EDS?as well as macro-and micro-sclerometer.Firstly,the powder addition ratios of composite powders particles on open-arc high chromium hardfacing alloys were studied.With the increase of powder addition ratio,the dilution degree on hardfacing layers imposed by base metals decreases down and alloying content of deposited layers correspondingly rises up.The hard phases of hardfacing alloys include M₇C₃ and?Ti,V?C,in which M represents Fe,Cr,V,etc.The morphology of such primary abrasive phase as M₇C₃ changes from net-like shape to block-like one.The baume degree of sodium silicate used as binder significantly affects the grain size of composite powder particles.With the increase of baume degree of sodium silicate,the microstructure of hardfacing alloys transform from hypoeutectic to eutectic at first and then to hypereutectic,The volume fraction of M₇C₃ carbide gradually increases accordingly.The main wear mechanism changes from micro-cutting to micro-spalling.It shows that the increasing baume degree of the water glass obviously reduces the dilution effects induced by base metals on the alloy layers.It also advances the volume fraction of the carbide in high chromium alloys,which improves the wear resistance of hardfacing layers.Secondly,the effects of alloying component such as V,Si,C and B on the microstructure and abrasion resistance of high chromium alloys were investigated.The results shows that,with the increase of ferro-vanadium content in composite powder particles,the microstructure of hardfacing alloy is refined and the volume fraction of the carbides also rises up,which leads to the improvement of the toughness of hardfacing alloy correspondingly.When the Si containing components are added into the composite powder particles,it reduces the size of the M₇C₃ carbides in hardfacing alloy at first,and then advances it.As carbon content of hardfacing alloys increases,the size of M₇C₃ phase in the alloy gets coarser significantly,and the volume fraction of hard and brittle phase of Fe₃C also increases,so the wear resistance of hardfacing alloys decreases down.Boron atoms in high chromium composite powder particles hardfacing alloy can solid saluting into M₇C₃ phase and then complex carbon-borides such as M₇?C,B?₃ are generated,which advances the volume fraction of hard phases and thereby improves the wear resistance of the hardfacing alloy.However,the wear resistance decreases down when the size of wear-resisting phase are too large.Finally,the effects of welding speed and welding current on the composite powder particles hardfacing alloys indicated that,with the increase of travel speed,it can significantly reduce the dilution of the base metal and make the M₇C₃ carbide changing from mesh-like to block-like shape.When welding speed was 30cm/min,the hardness and wear resistance of the hardfacing alloy were obviously improved,which due to the precipitation of a large number of carbides.The welding current would enhance the influence of arc power on the CPPs and base metal as well as the melting amount of the base material in alloy layers.The matrix changed from?-Fe into cell-like?-Fe.Those mesh-like M₇C₃ phases distributed along the grain boundary of cell-like cannot effectively hinder the micro-cutting movement of abrasive particles and their main wear mechanism was the micro cutting of abrasive particles.Compared with coated electrode and flux-cored wire,all above results shows that,composite powder particles composite powder particles used as a new type of welding consumable,exhibit many advantages,such as the easy adjustment of alloying composition conveniently,the easier and faster preparation process with high economy,the availability application on automatic and continuous welding processes,as well as long-range developing prospects in the future.It also shows a positive significance for a large number of small and medium-size domestic industrial enterprises.Furthermore,it can also be used as a material of laser additive manufacture and adapts to rapid development,widely application of the production and the manufacture.It shows significant advantages and researching values.