Semi-solid Hypereutectic High Chromium Cast Iron Reheating And Thixotropic Squeeze The Filling Study

Semi-solid slurries of hypereutectic high chromium cast iron were prepared by inclined cooling plate method, followed by the reheating at the range of the solidus and the liquidus temperature. Based on the investigation of the influence of reheating temperature and holding time to the micro-structural evolution of primary carbides, the moulds were designed and filling processes of thixoforming were made. Furthermore, comparison was successfully made between the as-cast and semi-solid-thixoforming samples to study the macroscopic quality, microstructure and mechanical properties. Those are of great importance for extending the utilization of hypereutectic high chromium cast iron in industry.Studying the rules of microstructure evolution of primary carbides in hypereutectic high-chromium cast iron during reheating is very important to the thixotropic forming research. In this assay, the semi-solid and cast billets were reheated at different temperature and respectively in different time for holding. The results indicate that primary carbides have experienced three stages: refining or spheroidzing, growing and dissolving in the process of tests. At the end of the first stage, a fine, uniform, round primary carbides can be created with the effect smallest equivalent diameter, the largest shape factor, relative high solid fraction and the highest practical count. Compared to the semi-solid billet, the primary carbides of the cast have merely experienced two stages: refining or spheroidzing, dissolving when the reheating and holding temperature is 1290℃or 1300℃. Only when they have been reheated at temperature 1320℃or 1340℃,are the changes of their microstructure similar to the semi-solid ones. Comparison of the reheating samples in liquid quenching and cooling at room temperature has been made to observe the changes of the microstructure.The fact that agglutinating and melted corrosion has become such a serious problem is related to the high-temperature of reheating billets and strong thermal shock when the moulds are thixoformed, which results in difficulty of opening the moulds to sampling and short service life of the moulds. In order to solve those problems, the new moulds were designed as combination partition of taper. Good results can be achieved.According to process parameters of reheating, the semi-solid and as-cast billets were molded by thixoforming and then the forming samples were analyzed to investigate the macroscopic quality, microstructure and mechanical properties respectively. The results indicate that, though the hardness of semi-solid forming sample is a little lower than the as-cast one, its impact toughness and wear resistance are improved remarkably.