| Steel is one of the most widely used materials in industry for its favorable properties of high strength, high toughness, good machining ability and low cost. But steel is vulnerable to wear, corrosion, erosion corrosion, strong shock and fracture, which limit its application in many fields and seriously affect the life of machine components. Preparation of coatings on steel for protection has been an effective method. In the field of surface modification, surface cladding technologies have been used to modify the surface of materials to improve their hardness, tribological properties and corrosion resistance. Several methods such as thermal diffusion, high velocity arc spraying, laser cladding, solid boriding process and electron beam boriding technology can be used to prepare alloy coating with high corrosion and wear resistance. Compared to the other technologies, the high frequency induction cladding is an excellent technology with advantages of high heating speeds, simple operation, clean environment and small thermal deformation. Meanwhile, the coating could obtain different tissues and micro structures by adjusting the proportion of coating powder.In the paper, the Fe-B alloy coating is melted on the surface of low carbon steel Q235 by high frequency induction cladding. The microstructure, elemental composition, the surface hardness and erosion wearing resistance of the coatings are analyzed to provide valuable references for the preparation of alloy coating with high frequency induction cladding. The main results and conclusions are shown as the following:(1) The results show that Fe2B phase with dendritical structure and FeB phase with wedge-shape are formed in the coating, which is attributed to the diffusion of B atoms on the substrate. The diffusion of B atoms toward substrate leads to the poor B around the coating near substrate and only Fe2B is formed near the substrate. While the B atoms far from the substrate cannot move quickly to the interface, therefore, enough B content can promote the formation of FeB phase. The amount of FeB phase with wedge-like shape increases with increasing of B content. The hardness and erosion wear results show that the coating can improve significantly the surface hardness and erosion wear resistance, which is attributed to the formation of FeB and Fe2B phase in the coating. The hardness of coating reaches to 64.77HRC, which is about 2 times higher than that of substrate. The erosion wear rate decreases to 1.02%, which is 1/3 of that of the substrate. That is attributed to the existence of FeB phase with wedge-like shape, it separates matrix sharply, leading to the decrease of erosion wear resistance of coating. The results indicate that the increasing long wedge-like shape of FeB promotes the increasing of the hardness, meanwhile decreases its wear erosion resistance.(2) From the observation of coating micro structure and the XRD testing on the powder and coating of Fe80P13C7 and FesoP11C9, it is found that a bright band appears in the interface between cladding coating and substrate, which means the good metallurgical bonding between the coating and the substrate. The inner coating was composed by Fe-C and Fe-P enhanced phase and intermetallic compounds. From the hardness and corrosion resistance testing of the induction cladding coating, it can be known that the average hardness of the two kinds of coatings are approximate to 44.02HRC and 49.47HRC, significantly higher than that of matrix (about 33.33HRC). The erosion wear rate of coating is up to 1.61%, and the corrosion rate decreases to-2.129mA/cm2, lower than that of matrix-1.192mA/cm2. The corrosion current density decreases to 0.0877mm/a, which is lower than that of matrix 0.2395mm/a. It can be concluded that the wear resistance and corrosion resistance of the substrate are enhanced by the formation of Fe-C and Fe-P intermetallic compounds.(3) XRD testing on the powder and coating of Fe71Nb6B23 which obtained from different milling times indicates that only the FeB phase is formed in the powder and Fe2B, NbB as well as Fe2Nb phase can be found in the coating, it is also found that the plane dendrite appears in the interface between cladding coating and substrate, which means the good metallurgical bond between coating and the substrate. The inner coating was composed by crystalline dendrites and packages. While the crystalline dendrites and packages are becoming smaller and smaller as the powders milling time goes on. It means that the increasing of milling time can refine the layers dendrite structure. The coating surface hardness is approximately in the range of 34-40HRC, slightly higher than the hardness of the matrix. And the different milling times correspond to different electrochemical corrosion density and corrosion rate are similar, which were smaller than that of the matrix. The influence of milling time on the coating surface hardness and corrosion resistance was not so obvious, and when the milling time reaches to 32h, the tissue distribution is more uniform, the coating hardness reaches to the maximum of 42.23 HRC, corrosion density reaches to-1.214mA/cm2, which shows best comprehensive properties. |
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