Microstructure And Properties Of In-situ Graphite Self-lubricating Iron-based Alloy By Arc Hardfacing Of Metal Powder Core

In today's rapidly developing engineering field,friction and wear is one of the main reasons for the failure of engineering equipment.Lubrication is the most common way to reduce the wear between two friction pairs.In addition to the common lubricant lubrication,the use of metal-based solid self-lubricating materials with antifriction characteristics is also one of the hot research.In this paper,a metal powder cored wire with SiC decomposable in-situ self-lubricating graphite phase is designed.The feasibility of chemical reaction in-situ self-lubricating graphite phase of SiC under surfacing environment is studied.The burning and oxidation of graphite under surfacing environment is solved,and the iron-based graphite self-lubricating wear-resistant surfacing alloy layer is prepared.Through high-speed camera,the droplet transition and spatter form of welding wire were observed;the morphology,size,distribution,microstructure and composition of SiC decomposed in-situ graphite in hardfacing layer of metal powder cored wire were analyzed by metallographic microscope,SEM,EDS and XRD;the HRC hardness,abrasive wear and friction coefficient of hardfacing layer of metal powder cored wire were measured,and the hardness and friction wear performance of hardfacing layer of metal powder cored wire were analyzed.The results show that SiC can decompose itself to produce graphite under the arc of surfacing and react with molten iron to produce graphite in high temperature molten pool.The spherical graphite can be formed in the hardfacing layer by adding 25wt.%SiC to the metal powder cored wire.The distribution is uniform,the size is about 8-15?m,and the maximum volume fraction is about 8%.The matrix structure of the hardfacing layer is pearlite,the relative wear resistance is 1.4 times of Q235 steel.The wear mechanism is the combination of micro chip plough and multiple plastic deformation plough.The friction coefficient of Q235 steel is0.36 under the same parameter experiment.The self-produced graphite is helpful to improve the friction and wear performance of the hardfacing layer.When Cr and Ni are transferred to the hardfacing layer at the same time,the amount of autogenous graphite is reduced,the volume fraction is reduced from 8%to 6%,and the size is 7-12?m.The joint action of Cr and Ni affects the formation of graphite,but increases the hardness of the hardfacing layer from 40 HRC to 51HRC.When the SiC content is 35wt%,the number of spherical graphite phase is the most,the size is 15-20?m,the volume fraction is 20%,the relative wear resistance is 2.8 times of Q235steel,and the friction coefficient is 0.15.This content of SiC is the most favorable for the precipitation of graphite phase,with the best wear resistance and friction coefficient.N₂protected surfacing can reduce the spatter of welding,and part of nitrogen transits to the molten pool to form nitride as the heterogeneous nucleation core of graphite and promote the formation of spherical graphite phase.With the increase of welding electric parameters,the transition type changes from short circuit transition to droplet rejection transition.The type of spatter changes from short-circuit explosion spatter to arc force spatter,and CO₂ gas protection will cause gas escaping spatter.When the welding current is 200A,the welding voltage is 20-22V,the welding speed is 1.5mm/s,and the width of single-layer weld bead is 20mm,the surfacing process is stable,the weld formation is good,the spatter is small,and the graphite phase precipitation is most favorable.The graphite particles are squeezed to the surface of the hardfacing layer to form a self-lubricating layer and improve the wear resistance of the hardfacing layer.