| The methods of self-shielded flux-cored open arc welding are used for their characteristics such as economic,adaptability.However,their surfacing alloys were easily spalled as a result of the appearance of so many brittle eutectic phases and led to premature failure of hardfacing parts.It have a serious impact on the service efficiency of advanced machinery equipments,the improvement of the toughness of flux-cored open arc welding alloys were studied in the past few years and still to be a challenge to advance their service life.For such matrix as ferrite,martensite and austenite,austenite with excellent toughness is choosed to be the main matrix such as in the impact abrasion working condition due to the deformation-induced martensitic transformation to enhance its wear resistance.For these excellent characteristics of austenitic matrix,Cr-Mn-Nb-Ti-V-Si complex alloying system austenitic matrix wear-resistant alloys were deposited on mild steel base metals by the method of self-shielded flux cored open arc welding in this paper.Such strong carbon forming elements as Nb,Ti and V elements is added to strengthen the austenitic matrix as a result of the precipitation of those in-situ MC-type carbide particles.The effects of alloying elements on their microstructure and abrasion resistance were investigated by the method of optical microscopy(OM),X-ray diffractometer(XRD)and scanning electron microscopy(SEM),attached energy dispersive spectrometer(EDS)as well as the testing of the bulk-hardness,micro-hardness and wear resistance.Firstly,the effects of Si on the microstructure and abrasion resistance of austenite-matirx hardfacing alloy were studied.The results indicate that with the increase of silicon content,the grains of ?-Fe and(Nb,Ti,V)C together with M23C6(where M stands for Fe,Cr,Mn,V elements)phases distributing along ?-Fe grain boundary become thicker,so also their spacing distance.The shape of intergranular M23C6 carbide changes from skeleton to isolated sheet.When the excess of silicon content,(Nb,Ti,V)C particles are thickened,and the matrix is transformed from ?-Fe to ?-Fe.The results of wear testing show that proper silicon content can improve the abrasion resistance of the alloy,and excessive silicon contentwill reduce.The abrasion resistance of austenite-matrix hardfacing alloys is not only related to these in-situ precipitated(Nb,Ti,V)C particles,but also with the size of intergranular carbides,and the type of matrix as well as the grain size.Then,the effects of Nb,Ti and V alloying element on the microstructure and abrasion resistance of austenite-matrx alloys were investigated by the method of single variant.The results show that with Nb content increased,the number of(Nb,Ti,V)C particles gradually increase and their size get bigger,their shape changes from dispersively distribution into thickly aggregation.It improves the abrasion resistance of the hardfacing alloy.When niobium content is excessive,the strength of austenitic matrix is insufficien for the reason that those in-situ precipitated(Nb,Ti,V)C phase particles become coarser and their abrasion resistance get lower instead.The results of EDS show that only a small part of vanadium element involves in the formation(Nb,Ti,V)C particles and most of them are solid soluted in austenite or M23C6 carbides.These gradually size-thicker and volume-higher intragranular M23C6 carbides is a advantage for the increasing cutting resisting forces of abrasive particles,but they become more fragile to be easily break and reduce the abrasion resistance.Ti and C are formed at the style of TiC.The results of backscattered electron image show that those TiC particles can act as the nucleation cores of the(Nb,V)C phases and lead to massive precipitation of(Nb,V)C particles and dispersively strengthen of y-Fe matrix.However,excessive Nb,Ti and V alloying element content reduce the stability of ?-Fe matrix due to their carbon-poor effects,which is unfavorable to the hardfacing alloy toughness.Finally,the effects of Cr,Mn,C alloying elment on the microstructure and abrasion resistance of austenite-matrix hardfacing alloy were investigated.The results show that,with the increasing addition of Cr component,it lead to the increasing of the size and the volume fraction of intragranular carbides.Proper chromium content can improve the abrasion resistance of hardfacing alloys and excessive chromium content will increase the size and the volume fraction of intragranular M23C6 carbides and enlarge the rate of metal spalling.When manganese content is 1.9%,the matrix of hardfacing alloys transforms from ?-Fe to ?-Fe.As Mn continues to increase,the volume fraction of intragranular M23C6 carbide is higher and their size gets larger with the shape changing from dendritic to cluster.When carbon content increase,those M23C6-type carbides along the ?-Fe phase grain boundary are precipitated with high volume and large size.Their shape also change from isolated sheet into skeleton and the bulk-hardness of hardfacing alloy raises up,but the brittleness of hardfacing alloy also increases at the same time.At first,abrasion resistance of Cr-Mn-Nb-Ti-V-Si austenite-matrix alloys are mainly dependent on these in-situ precipitated(Nb,Ti,V)C particles.Secondly,it is related to intragranular carbides ofy-Fe.Their wear mechanism is mainly micro-cutting of abrasive particles.The developed hardfaing alloy with high toughness can be applied to impact load abrasive wear condition. |
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