| The method of flux cored open arc welding has been widely used to manufacture and remanufature wear resistant hardfacing layers of advanced mechanical parts because of its economy, conveniene and reliability. Flux-cored wire or solid wire open arc welding with alloying powders presetting on welds beads is one method with the characteristics such as low dilution rate, high deposition efficiency, energy saving, low consuming, which effectively compensates for the limited powder of flux-cored wire and the limited alloy element addition of solid wire. In this paper, with the optimizing of some components contained in flux-cored wire or powder components presetting on weld beads, the effects of hardfacing process and alloying element content on the microstructure and the properties of hardfacing alloy were systematically discussed by optical microscopy(OM), X-ray diffractometer(XRD), scanning electron microscopy(SEM) and attached energy dispersive spectrometer(EDS).Firstly, Fe-17Cr-4C-2V-Mn-Si-Ti complex alloying system wear resistant alloys were deposited by the method of flux-cored wire self-shielded open arc welding on Q235 A plates to investigate the effect of silicon on the microstructure and abrasion resistance of the alloy. The results showed that, with the continuous addition of silicon-contained component, the size of primary M7C3 carbides gradually reduced and transited from rod-like shape to hexagonal block-like shape in dispersion distributing state,M represent Fe, Cr, V, Mn alloying element. γ-Fe phases, which adjacent to those rod-like primary M7C3 grains, gradually surrounded those phases, but their volume fraction progressively decreased until disappeared. The wear test results showed that proper amount of silicon can improve the abrasion resistance of open arc hardfacing alloys, but excess addition was detrimental. The analysis on the surface worn morphologies indicates that the micro-cutting and micro-spalling wearing mechanisms coexist. The abrasion resistance of the alloys is not only related to the microhardness, their distribution and the shape of primary M7C3 phases, but also with the surrounding microstructure, such as proper amount of γ-Fe phases, which surrounds the primary M7C3 phases, can enhance the toughness and improve the abrasion resistance.Then, in order to increase the alloy content in the hardfacing layers and reduce the dilution rate of Q235 A, the effect of welding current and presetting alloying components on the microstructure and wear resistance were investigated. The results showed that, with the increasing of welding current, the dilution rate of Q235 A increased,M7C3、Fe3C、M2B、Fe2N and those M2 B phase precipitated from the melts of Fe-B particles, the size of primary hard phase and its volume fraction also increased, but the hardness of the alloy changed in a narrow range, the wear mass loss changed firstly a little by a little, the wear-resistance of the alloy was the best at 430 A due to the appearance of γ-Fe phase surrounding those primary M7C3 phases.With the increasing addition of presetting Fe-B powders, M7(C,B)3、M2B and some other hard phase precipitated from the melts, primary M7(C,B)3 changed from long strip to granular in shape. The shape was firstly in bulk shape, then refined as the number increased. The interface microstructure changed from hypoeutectic、eutectic to hypereutectic. With the increasing of high carbon ferrochrome in the presetting powders, hexagon M7C3 grains which precipitated from the melts have much more time to grow large at 4mm near fusion line, where those primary M7C3 grains is the most hard and then decrease when it approaching the surface. With the increasing of presetting Fe-Si powder, the volume fraction of Fe3 C reduced, austenite decreased, the shape of primary M7C3 transited from rod-like shape to granular one, then with bigger size in dispersion distributing state,the volume fraction of the total M7C3 increased, the primary M7C3 fluctuates smoothly in some range, the hardness of the surface layer of the alloy changed a little by a little, ΔM dramatically reduced firstly, then reduced.Their abrasion resistance was markly improlved by the addition of Fe-Si powders. With the increassing of medium carbon ferromanganese presetting powders, primary M7C3 get shortened from rod-like shape, then the size become large with uniform shape, the hardness changed in a narrow range, ΔM increased at first, then reduced and finally increased again. The dominating abrasion form was micro-spalling and Micro-cutting.Finally, hardfacing alloy was deposited by the method of solid wire open arc hardfacing with presetting alloying powders on weld beads, the effects of presetting Fe-Si, Fe-B content on the microstructure and abrasion resistance were investigated. The results showed that, with the increassing of Fe-Si powders, the matrix structure changed from cellular ferrite the composite of ferrite and martensite, the amount of ferrite increased while the content of presetting Fe-Si alloying powder increased, as with cellular(Fe,Cr)23C6 along the grain boundary. The hardness of the hardfacing alloye layers changed a little at the same time,then it increased sharply while ΔM increased a little at first and then it increased sharply. With the increassing of the presetting Fe-B powders, the size of cell α-Fe increased, the content of carbonboride along the grain boundary increased too. The hardness of the alloy increased while ΔM changed a little when the content of Fe-B rised up. The dominating abrasion form was microspalling. |
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