Research On The Technology Of Fe-based Powder Compact Sintering-Solid Boronizing

Material is the foundation of people's substantial life and development of human civilization. New material is the foundation stone of modern society and the leader of development of new technology. Corrosion, fracture and wear are three main failure modes of metal product. In recent years, China has imported mechanical devices which worth almost 100 billion dollars from other countries, it needs almost 1 billion dollars to maintain the equipments every year because of wear. It makes damages of 10-20 billion RMB every year by corrosion of metal, furthermore, it leads lots of indirect damages because of accidents by wear and corrosion of metal and maintenance of equipments. Boronizing technology can significantly improve the abrasion resistance, the corrosion resistance, the red hardness and the resistance of high-temperature oxidation of metai surface. But traditional boronizing technology had some disadvantages, for example, high temperature and long time is required when boronizing, which limits its application in industry. Boronizing layer has many disfigurements which makes the drop of mechanical Properties, furthermore, it affects the abrasion resistance and the corrosion resistance. We take Fe-2Cu-0.4C powder compact as matrix to boronizing, in order to realize boronizing process with short time and low temperature by taking advantage of low density, diffusion and disfigurements in Fe-2Cu-0.4C matrix.In the paper, we study the difference of boronizing layer between Fe-2Cu-0.4C power compact and the Q235 steel. Microstructure shows that the boronizing layer of Fe-2Cu-0.4C is deeper than steel's, it almost reaches 100-200 micron. The boronizing layer of Fe-2Cu-0.4C is low density and brittle under some parameters, but we can obtain deep, compact and continuous boronizing layer by optimizing testing parameters. It makes a lot of sense for increasing the properties of boronizing layer.We design orthogonal test which makes the depth of boronizing layer as standard, it confirms the exact parameters which can obtain the deepest layer. We find that it can obtain deeper layer with lower density, shorter time and longer time. In the experiment, we have obtained deepest boronizing layer with the parameters of compact density 6.4g/cm3, heaing temperature 11500C and holding time 4 hours.The depth of boronizing layer is not the only standard of boronizing. In the properties test and microstructure observation, we find the microstructure of boronizing layer is direct factor determining abrasion resistance and corrosion resistance.The abrasion resistance of surface increases obviously after boronizing. We use different parameters to boronizing, and find that abrasion resistance is better with more compact and more continuous layer according to the researches of wear rate and wear coefficient. The results shows abrasion resistance is the best with the parameters of compact density 7.0g/cm3, heaing temperature 11500C and holding time 4 hours.We put the samples which have been treated into NaCl solution, and measure Polarization Curve. We find that the corrosion resistance don't have obviously difference between matrix and surface, because pitting phenomenon is serious in surface. The compactness and continuity of boronizing layer determine corrosion resistance of surface which is better with more compact and more continuous layer. The experiment shows that the surface with parameters of compact density 7.0g/cm3, heaing temperature 11500C and holding time 4 hours can obtain the best corrosion resistance.The factors determine the hardness are phase composition of layer and microstrcture of layer. The hardness of FeB phase is high, but it is brittle. The largest hardness appears 100 micron from surface, it is up to 2000HV. The higher density, the larger hardness. Three-point bending test shows that bending property ie better when boronizing layer is above, especially after quenching treatment.In the last chapter of the paper, we use Q235,Fe-0.5Mn-0.2C as matrix to boronizing, the experiment shows that the layer is deeper with longer time. In the same temperature, the layer depth of Q235 is deeper than Fe-0.5Mn-0.2C's. According to the calculation of kinetics, the diffusion activation energy of Fe-0.5Mn-0.2C is 132.51KJ/mol, the Q235's is 192.35KJ/mol. It shows that powder compact is easier to boronizing than Q235 in the same conditions. We must consider that the properties of boronizing layer is better with more compact and more continuous layer, but if the content of FeB is high,the brittleness will increase, and the layer will detach easily. In the production, we hope to obtain the compact and continuous boronizing layer, which is mainly made up of Fe2B phase.