| With the rapid development of modern industry, the level of mold manufacturing technique becomes an important symbol of the national product manufacturing horizon, which leads to the requirement of the performance of the molds becoming higher and higher. In addition, the life question is prominent day by day. It is necessary to strengthen the surfaces of the molds, because the damage of molds mostly started from their surfaces. Therefore, it has an important significance to study and apply the advanced surface modification technology for improving the mold life, saving costs, increasing productivity. Currently, the TD (Thermal Diffusion) salt-bath chromizing technique, which is considered as one of the ideal surface modification techniques in various kinds of developed surface strengthening technologies, with the merits of simple equipments, easy operation, higher productivity, lower costs, flexible cooling-down methods for work pieces etc.The author carried out a preliminary study on TD salt bath chromizing of cold working dies. Firstly, it obtained an ideal salt bath formula by comparing with a variety of formulas, and then obtained the influence rule of coating thickness based on studying of some process parameters. The microstructure morphologies and phase structures of the TD chromizing coating have been investigated by X-ray diffraction (XRD), energy spectrum analysis and other modern analysis methods. Meanwhile, it carried out a system of testing and analysis of coating, such as hardness, wear resistance, etc. The valuable conclusions are followed here based on the experimental study and comprehensive analysis.1. T10 steel can be achieved chromizing at a lower temperature by using salt bath formula ((68.4BaCl2+7.6NaCl)+10Cr2O3+10NaF+4Al) when considering the thickness of coating,the volatility and fluidity of salt bath and other parameters. The coating, with a uniform thickness, is mainly composed of Cr7C3 phase and a small amount of (Cr, Fe) 7C3 phase. The coating and matrix are in the state of metallurgical bonding.2. It is founded that the thickness of coating is directly proportional to the carbon content of matrix after "balance carbon" being removed. The growth rate of coating is hindered by strong carbide forming elements of matrix. Under the same process conditions, the thickness of coating thickened and the rate of chormizing rate increased along with temperature increment and the treatment time increasing.3. The testing results of surface hardness of coating by Victor hardness tester indicated that the surfaces hardness are all above 2000HV0.05 after TD chromizing. In addition, the surface hardness increased along with the hardness matrix increased and the processing times extended. The testing results of cross-sectional microhardness showed that the hardness between coating and matrix was gently transitional.4. The coating can significantly improve the performance in wear resistance in particle abrasion. And the wear morphology showed that the TD sample with shallower, fine, smaller grinding cracks compared with the other materials. There were partly shedding in the worn coatings, which showed a good metallurgical bonding state between TD coating and matrix. Vickers indentation with microhardness of coating analysis showed that there is proportional between matrix hardness supporting effect and the coating, the states of integrity, and the amount of cracks by indentation. It is also showed that there is a positive role to improve and enhance the performances of compressive resistance and anti-stripping by means of strengthening and toughening treatment to matrix after TD chromizing.5. Coating has a good high-temperature oxidation resistance. The coating still has 2017HV0.050 microhardness even after heat treated at 800℃.6. Coating has an excellent corrosion resistance in hydrochloride solution. The corrosion morphology showed that the surface of TD sample was with a shallower and less corrosion pits than that of the matrix, and showed a good corrosion resistance.
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