Study On Microstructure And Properties Of Hardfacing Alloy With Mo-Fe-B System

The Mo-Fe-B system surfacing alloy has excellent mechanical property,abrasion resistance and corrosion performance,which can be used to weld the surface of machine elements on the condition of high temperature,high pressure,heavy load,oxidation and corrosion.We designed and prepared alloy powder blocks of diverse Mo-Fe-B system,then fabricated surfacing alloy using argon arc welding process,studied the effect with the addition of Mo,B,as well as N on the microstructure and the properties of surfacing alloy through optical microscopy,scanning electron microscopy,X-ray diffraction,microhardness,Rockwell hardness and wear test.We also designed and prepared alloy powder blocks with different sources of B,and studied the microstructure and the properties of surfacing alloy.The surfacing alloy with 30%or 25%Mo contents consisted of Mo2FeB2 hard phase,Fe-based solid solution,and a small amount of Cr2B3 and MoB binary boride.When the Mo content was 30%in alloy power blocks,there were a lot of long strips of the hard phase in surfacing alloy.While the Mo content was 25%,not only the rate of hard phase reduced,but also the form of the hard phase became small square and irregular polygon.If the Mo content was less than 20%in alloy powder blocks,there was no hard phase obviously in the surfacing alloy.Hard phase and the matrix both contained Mo,Fe and Cr elements,the highest percentage of Mo in the hard phase,the highest content of Fe in the matrix and Cr hypodispersion in the surfacing alloy.When the Mo content was 25%,the surfacing alloy whose Microhardness and Rockwell hardness reached 1053HV0.5 and 58.6HRC respectively had the highest hardness.The hardness would be reduced whether the Mo content is increased or reduced.What’s more,the wear resistance reduced with the decreasing of Mo content.With the increasing of B content,the slag could be cleaned easier and the weld appearance would be better.When Mo content was 15%and the B content was 6%in alloy power blocks,hard phase appeared in surfacing alloy.The number of hard phase increased with the increasing of B content.Microhardness and Rockwell hardness of the surfacing alloy also increased with the increasing of B content.When the B content was 10%,the microhardness was 1266HV0.5 and the Rockwell hardness was 70.1HRC.With the addition of B,the wear resistance of surfacing alloy increased gradually.When the N content was 0%,1%,2%in alloy power blocks,the hard phase in the surfacing alloy formed square and long strips,small square shape,irregular shape,respectively.The surfacing alloy with no N content consisted of Mo2FeB2 hard phase,Fe-based solid solution,Cr2B3 and MoB binary boride.When the N content was mixed in alloy powder block,it mainly existed in the form of Cr2N.Microhardness and Rockwell hardness of the surfacing alloy decreased with the increasing of N content.With the addition of N,the wear resistance of surfacing alloy decreased gradually.We used BFe powder,B powder and MoFeB powder as the source of B and studied the effect of different sources of B on the microstructure and the properties of surfacing alloy.The following can be concluded.When BFe powder and MoFeB powder were used as the source of B,there were a lot of long strips of the hard phase in surfacing alloy.When BFe powder were used as the source of B,the surfacing alloy consisted of Mo2FeB2 hard phase,γ-FeCr and binary boride and they formed long strips and square.Microhardness and Rockwell hardness were 830HV0.5、54.5HRC respectively.When MoFeB powder were used as source of B,the hard phase in surfacing alloy formed square,and the number of the hard phase was big than the first group.Microhardness and Rockwell hardness were 1136HV0.5、56.8HRC.When B powder were used as source of B,the surfacing alloy consisted of Fe-Cr,σ-FeMoCr and a few Mo2FeB2 hard phase.The Microhardness and Rockwell hardness were 368HV0.5、37HRC respectively.