| The preparing for slag-free hardfacing alloys with the method metal powder-cored wireself-shielded open arc welding has such advantages as continuous operating without removingresidual slag, high efficiency, energy and material saving, etc. The prepared hardfacing alloywith high hardness and good wear resistance has been used in surface wear-resisting layerssuch as cement conveyer pipe, coal grinding roll. At present, due to the challenge fordeveloping self-shielded open arc slag-free flux-cored wire is more severe than those withslag or gas protection, so most of available self-shielded open arc slag-free flux-cored wiresare imported or produced by wholly foreign enterprise with high price. Moreover, theperformances of those flux-cored wires are still unsatisfactory and hard to meet the practicalrequirements, such as crack resistance and welding spatter. Based on the above facts andanalysis, a Fe-Cr-C-B-Si metal-powder self-shielded open arc hardfacing slag-free flux-coredwire was studied after a large number of tests, and the wire is good to meet the practicalrequirements with the advantages of stable welding process, lower spatter and nearly slag-freehardfacing alloys.Firstly, for the welding processing properties of the flux-cored wire, the effects of SiC,Fe-Si, B4C, Fe-B and graphite on its self-shielded performance were studied, and the residualslag was analyzed by XRD. The results show that the slag was mainly composed of Al2O3andFeBO3, and these components contained in the flux-cored wire have significant but differentimpacts. For example, gases produced by the oxidization and decomposition of carboncontaining components such as graphite, B4C played a dominant self-shielded role on moltenmetal. Si, B atoms provided by silicon and boron containing components promote theformation of lower melting eutectic to improve the shape of weld beads as well asself-deoxidation. Slag-free hardfacing alloys can be obtained with optimized allocating ofboron, silicon and carbon containing components in flux-cored wire. The amount of remainedslag was changed with the added mode of these components for different atom activity atelevated temperature.Secondly, the effects of SiC, Fe-Si, B4C, Fe-B and graphite on the microstructure andproperties of open arc self-shielded hardfacing alloys were investigated by optical microscopy(OM), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and attached energyspectrometer (EDS). The experiment results showed that with the continuous increasing ofcarbon and boron containing components, the microstructure of hardfacing alloy changedfrom the hypoeutectic to eutectic, and then to hypereutectic. The morphology of the microstructure varied with the added form of these components. Among them, the grains wereremarkably refined by the addition of SiC and B4C, and Si atoms can intensify theaggregation tendency of carbon atoms. Proper amount of SiC and B4C can promote theformation of hard phases such as M23C6, but excessive Si atoms provided by thedecomposition of SiC can intensify the graphitization tendency, which inhibited the formationof carbide phases, and it resulted in the decreased toughness and wear resistance of hardfacingalloys. In addition, the experimental results also showed that hard phases such as M23C6hadchanged from intermediate phase M6C with rich chromium, and it showed that Mn canpromote the transition of intermediate phase to hard phases.Finally, the abrasion resistance of open arc slag-free hardfacing alloys was analyzed bywet sand rubber abrasion test machine as well as the abrasion mechanism of alloy with wearmorphology. The results show that the open arc hardfacing alloy has excellent wear resistance.The wear resistance is related with the number, the size and the distribution of hard phases.The abrasion mechanism of hardfacing alloy includes micro-cutting and micro-spalling for theappearance of such brittle phase as Fe4N, Fe2N. |
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