| The widely used hardfacing flux-cored wire on the market mainly contains elements like chromium, titanium, aluminum, vanadium, and niobium to combine with carbon to form hard particles in order to increase the hardness and resistance of alloys. However, the higher content of carbon and alloying elements would result in higher carbon equivalent of surfacing layer, so as to produce a significantly higher tendency to crack. What's more,the carbide in high carbon hardfacing alloy materials usually has a lathy morphology and gather along the grain boundaries, which result in an uneven distribution, leading to a lower plastic of the surfacing layer. As a result, high content of carbon and alloy elements make the surface easily worn, which goes against the original purpose.This paper aims to improve the disadvantage of traditional hardfacing alloys. Cr13 martensitic stainless steel was chosen as the object of the research and an appropriate amount of nitrogen was considered to be added in to replace part of carbon to get a nitrogen alloying modification. By this modification, we can obtain a sufficient number of dispersed carbonitride phase to increase the service life of mechanical parts.The study was conducted through the following steps: Using an optimized welding process specification, 5 welds were overlayed on Q235 steel(each weld has 4 layers).After that, a chemical composition analyzer was used to obtain the component of each alloy element in deposited metal, and the microstructure of the deposited metal during the heating and cooling process were observed by high temperature photographic instrument;Specimens cut from the layer were tempered in different temperatures from 450 ? to600 ? and then a series of tests and examinations were conducted on them including:hardness detection by Rockwell hardness tester, microstructure observation using a microscope, weight-loss measurement by abrasive wear testers(25 ? and 500 ?), and finally the observation of microstructure and wear morphology of the surfacing layer bySEM. Also, EDS points analysis at the second phase particles and debris were conducted.Though the steps above, we get the results as follows:(1) The microstructure of the overlayed hardfacing flux-cored we designed is mainly martensite and residual austenite with small carbon nitride(Nb, V, Cr)x(C, N)y evenly distributed in the base body and the grain boundary. Specifically, with the addition of the nitride-forming elements like vanadium, niobium, the organization of the hardfacing becomes refined. When strong nitride forming elements like vanadium, niobium is constant, the added amount of chromium has an upper-limited. Exceeding this upper-limit will form nitrogen holes in the surfacing layer.(2) When chromium nitride was added into flux cored without vanadium and niobium, the hardness hardly changes. In contrast, when we add vanadium and niobium in addition, the hardness increases along with the content of chromium nitride. As to the heat treatment, when the tempered temperature was below 450 ?, hardness almost has no change; when tempered from 480, the hardness decreased slightly; when the temperature continue to elevate, hardness rose again but then fell.(3) When 2% niobium iron, 2% vanadium iron and 5% chromium nitride were added into flux cored wire, the abrasive wear resistance was 30% higher than carbide alloyed layers. With an appropriate heat treatment program, the abrasive wear resistance of nitrogen alloyed layers could increased by 15% than before, which was 35% higher compared with carbide-alloyed layers.(4) The main failure by high- temperature wear includes peeling of the surface oxidation, friction were and abrasion. The addition of vanadium iron, niobium iron and chromium nitride can effectively improve the high-temperature resistance. When the wear takes place in a ambient-temperature of 500 ?, tempering from a proper temperature above 500? will make the scuffing resistance of nitrogen-alloy improve. |
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