Effect Of Titanium On Microstructure And Wear Resistance Of Open Arc Hardfacing High-carbon Type High-boron Alloys

Boron alloys are widely used as wear-resistant materials due to their excellent abrasion resistance.Their main wear-resistant phases of Fe2 B are easily formed,they are more economic than high-chromium cast irons.Boron alloys deposited on low carbon steel are obtained by the method of welding and wear-resistant alloy layers with higher thickness are obtained for low constraint degree with longer working life of parts under severe conditions.However,high volume fraction of graphite needed to add into flux-cored wire for improving its processing and molding performance.It results into the formation of high carbon or medium carbon high-boron hardfacing alloys and large number of brittleness eutectic structure.Cracks so easily generate that the problem of insufficient toughness should be settled.In view of this,in this paper the principle of controlling carbon content to toughen is used by the precipitation of TiC particles with high melting point and high microhardness with the addition into flux-core of Ti-contained components.Thus,a large number of free carbon atoms are fixed to reduce the probability of their participation in the formation of brittle eutectic and improve the toughness of boron alloy.On the basis of the researched results of our project team,the addition of Cr,Si or other components into the core can change the morphology of primary boride M2 B and increase the toughness of the phase,A series of new boron wear resistant alloya with excellent abrasion resistance were prepared by means of flux cored wire additive manufacturing and made it meet the requirements of harsh working condition.Three layers Fe-C-Cr-Ti-B hardfaing alloys were cladded on low carbon steel surface by the method of flux-cored wire self-shielded open arc welding.The effects of titanium on the microstructure and wear resistance of the samples with different boron addition were studied by optical microscopy,X-ray diffractometer,scanning electron microscopy,attached energy dispersive spectrometer together with Rockwell hardmeter and micro-hardness tester.The effect of vanadium on the microstructure and practicability of the material was studied.Firstly,the effect of titanium on the microstructure and the properties of Fe-C-Cr-B high boron alloys with the addition of iron boron and boron carbide were studied.The results showed that the por-precipitated TiC phases can act as the nonuniform nucleation cores of the primary phases of M2 B and made them refin eand disperse.Those M₂₃?C,B?₆ phases that surrounding M2 B are early formed than the M3?C,B?in the melts is formed before the M3?C,B?.It consumes a large amount of free carbon and boron atoms in the melt and the remaining melt can not meet the component requirement of eutectic ?-Fe+Fe3?C,B?.So it effectively avoids the formation of brittle eutectic to improve the toughness.The precipitation of a large amount of TiC phase decreases the diffusion resistance of the boron atoms in the melt and increase the size of M2 B.Howerver,TiC phase contained in the grains of M2 B continuously absorbs those carbon atoms that emitted from the M2 B phase during the growth course and resulted in the crack of M2 B phases.With the increase of titanium content,the growth mode of high-boron surfacing melt crystal gradually changed from non faceted growth to faceted growth.Then,the effect of Ti on the microstructure and properties of high boron alloy only with one component B₄ C was investigated.When silver graphite is 1.3%,the XRD pattern shows that the appearance of FeO in the alloy indicated that insufficient self-protection performance of the wire.The results also show that Ti promotes the decomposition of boron carbide and makes it easier to precipitate the primary phase M2 B.However,when the amount of Ti component added exceeds 16.7%,the alloy structure changed significantly,and the primary main wear-resistant hard phase disappeared and the abrasion resistance was seriously affected.When the addition of Ti component exceeds 30%,the best wear resistance of boron alloy is obtained by surfacing method.When the amount of graphite is 3.3%,the primary M2 B phase does not appear only when the Ti-contained component increases to a certain amount.The appropriate Ti content promotes the formation of good toughness with appropriate microstructure sufficient toughness including the matrix and composite wear-resistant phase TiC,M2 B and M₂₃?C,B?₆.However,when graphite is excess,it strongly inhibits the decomposition of B₄ C as well as the formation of M2 B phase.Finally,the effect of Ti on the microstructure and properties of high boron alloy with FeB18 addition was investigated.When the graphite 1.3%,the primary M2 B phase largely precipitates from the melts,but no surroudding M₂₃?C,B?₆ phases appeared for insufficient supply of carbon atoms.With the increase of Ti,the samples changed from the hypereutectic to the hypoeutectic and the hardness and abrasion resistance of the samples decreased significantly,When graphite is 3.3%,titanium can change the precipitation form of M2 B and grain orientation.Ti content increases,the main wear-resistant phase of the alloy changed from the irregular group into a regular square,then into a long strip.Their size gradually reduced until completely disappeared.The microstructure changes from the hypereutectic to the eutectic.On the other hand,when Ti content increased,the microhardness of the primary wear-resistant phase increased.Under the condition of constant titanium content and increasing carbon content,the morphology of the primary phase changes from elongated and square to agglomerate,The primary phase changes from a single M2 B phase to a composite phase of M₂₃?C,B?₆ and M2 B.Altough the macro-hardness rapidly increasing,it became more brittle and the abrasion resistance reduced.