Microstructure And Wear-resistance Of Open-arc Hardfacing High Boron Alloys

High boron alloy has self-fluxing nature, that is its self-deoxy nature and melt fluidity is very good, the shaped weld beads is beautiful. As the boron resources is abundant, replacing W, Mo, Nb and Cr with boron to reduce the powder core material cost of flux-cored wire. Boron alloy contents Fe2 B main abrasion phase which has good thermal stability and micro-hardness up to 1400~1500HV0.1, its grinding abrasion resistance is excellent. In view of the above advantages, high boron alloy was prepared by optimizing alloy system on the basis of Fe-Cr-B-C.Firstly, the effects of current on Cr12B4 SiMn high boron open arc welding alloys were studied, under the scanning electron microscopy, we can see that M2 B is formed in the middle of lumps M23(C,B)6.With the increasing of current, the number of embed block-like M2 B increases significantly and it’s micro-hardness increases gradually; γ-Fe disappears;the number of martensite and M23(C,B)6 reduces;. The bulk hardness of hardfacing alloy firstly increases, then decreases and the abrasion resistance gets down firstly, then fluctuates in a narrow zone. The abrasion resistance is improved greatly mainly for the increasing of M2 B volume fraction as well as its micro-hardness and the dominating wear mechanism is micro-spalling.Keeping the welding parameters unchanged, respectively it investigate the effect of Fe-B, B4 C, Mn and Si on the microstructure and mechanical properties of high boron hardfacing alloy by the single variable method. Experiments show that the change of boron component has big influence on weld forming and residue. The number of primary M2 B and primary M23(C,B)6 is growing with increasing Fe-B components, meanwhile alloy hardness became higher and crack tendency increased. Rising B4 C components, organization became finer, then primary M23(C,B)6 phase grow coarsely. Hard phase chunks falled off in abrasive wear test which results abrasion resistance decreased. Mn/Si is often used in combined deoxygenation, but Si is narrow austenite phase element, which can improve the fluidity of the weld pool and reduce splatter, when the Si content increases, the hardness of high boron alloy increases, mainly because the Si dissolves in γ-Fe and α-Fe, which can promote carbide aggregate that results boron-carbide aggregated distribution, while shape, size and number of the primary M23(C,B)6 has significant effects on metal hardness. Mn is an austenitic strengthening elemens, it can reduce the Ms point, moderate amount of Mn can increase austenite and is beneficial to alloy toughness. The experiment proved that Mn has little impact on hardness, but the impact on the wear resistance is the more obvious.As additional strengthening phase, WC/W2 C has a great influence on processing properties and mechanical properties of welding alloys. when WC/W2 C amount is appropriate, during welding spatter become smaller and less,particle transition become faster, surfacing layer surface has a good forming and is little short of no residue, holes,slag and other defects. In high-boron alloy, WC/W2 C promote the formation of M7C3. Tungsten have solid solution strengthening effect,results that austenite increases and martensite reduces, organization has targeted growth tendency. Ti has strong affinity for carbon atoms,will generate small particles of TiC phase(the microstructure hardness of 3200~3800HV0.1),which scattered in the organization; its forming consumes carbon, reduced the boron content in M23(C,B)6 thus its toughness is improved; As TiC is the core of heterogeneous nucleation, tissue is refined,the wear resistance improves. When the pool has excess Ti, reducing atmosphere will be too strong and play an inhibitory effect on carbide synthesis reactions, abrasion resistance of the alloy brings down, so should not add too much.