Study On Semi-solid Squeeze Casting Technique And Microstructure Property Of Low Alloy Steel

With the development of railway transportation towards high speed and over loading, the service conditions of engine vehicle are becoming much worse. Common carbon steel castings have been unable to satisfy the higher requirements at present, which are replaced by low alloy steel parts gradually. When low alloy steel replaced carbon steel castings, a series of questions were uncovered in traditional sand casting process. In order to solve the questions uncovered, semisolid rheological squeeze casting technique used as the process for critical steel castings of engine vehicle was put forward firstly in this paper. In this study, C grade steel (ZG25MnCrNiMo) which is the common material for coupler knuckle of engine vehicle is used as the research material, axle box body steel cast and property sample obtained through semisolid rheological squeeze casting were used as examples. The technique was studied systemically through experiments and theories in the following aspects: preparation of the semisolid slurry, control of the quality, structure of the formed parts and their mechanical properties etc.Nondendritic-structure slurry that suitable for semisolid rheological squeeze casting was made by near liquid line insulation, and characteristic of the nondendritic-structure slurry was analyzed quantitatively by the average equal-area-circle diameter, then the suitable process parameters are obtained: holding temperature of 1508℃, holding time of 15min. Under these processing parameters, the average equal-area-circle diameter of the ZG25MnCrNiMo nondendritic-structure is 85.4μm. Qualities of the ZG25MnCrNiMo low alloy steel formed by semisolid rheological squeeze casting process were studied through the example of axle box body cast, and the study was done under the most suitable processing parameters mentioned above. The results revealed was as: the suitable processing parameters are the critical factor to obtain the advantages of semisolid rheological squeeze casting process. If improper processing parameters are chosen in semisolid rheological squeeze casting process, flow marks and cold laps are engendered easily on the surface of the formed parts, shrinkage void and gas hole are formed easily. When preheating temperature of the die is 400~425℃, stripping angle of the punch is 1°, the forming pressure is among 100~115MPa, and the holding time is 5~10s, favorable axle box body casts are formed with excellent inner and outer quality. The effect of processing parameters on structure of C grade steel and low-temperature impact property were studied by orthogonal...