Study on Microstructure and Properties of Iron Base Hardfacing Alloy Strengthened by Borides
Four groups of Fe-B-Ti-C hardfacing alloys with different B mass fraction were prepared on Q235 steel substrate by plasma arc surfacing technology.The influence of different B content on the morphology,quantity of hard phases and properties of the alloy hardfacing layer was analyzed.The microstructure and hardness of each surfacing layer were tested by scanning electron microscopy(SEM),X-ray diffraction(XRD)and Vickers hardness tester.The results show that the microstructure of Fe-B-Ti-C hardfacing alloy is composed of austenite(γ),Martensite(M),Fe23(C,B)6,Ti(C,B)and Fe2B phases.With the increase of B content,the microstructure of the surfacing layer changes from hypoeutectic to eutectic and hypereutectic,the morphology of eutectic borides changes from honeycomb to lamellar and chrysanthemum,and the number of eutectic borides and Ti(C,B)carbides also increases gradually.When the boron content is 7.1％,a large number of blocky brittle Fe2B primary phases appears in the hypereutectic structure,which causes the internal cracks of the surfacing layer after welding.The hardness value of the surfacing layer surface increases with the increase of B mass fraction.When the B mass fraction is 4.7％,the average microhardness of top part of the alloy surfacing layer is the highest,reaching 991 HV0.2.
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