Analysis of internal cracks in high carbon casting bloom induced by soft reduction process and its improvement using numerical simulations and industrial experiments

To comprehensively investigate and improve the internal cracks in high carbon casting bloom induced by the soft reduction process, a three-dimensional mechanical model was developed to calculate the cracking zone, centre solid fraction and the strain states in as-cast bloom. In the present work, the specific relationship between cracking zone area, centre solid fraction and maximum equivalent strain in cracking zone has been established under a number of withdrawal machines. A two-stage sequential soft reduction method was carried out for high carbon bearing steel, which aims to provide theoretical basis for improving the internal quality and effectively decrease the risk of internal cracks. According to the experimental results, the internal cracks were effectively alleviated and center shrinkage cavities were nearly eliminated by optimum designed experiments. Along the bloom central part, the proportion of length where the segregation rate is between 0.95 and 1 has been increased from 16.7% to 91%, and the fluctuation of carbon distribution in the center line of as-cast bloom was decreased to obtain the high homogeneity of the internal structure. In addition, grade of banded carbide in the hot-rolled wire decreased accordingly from 2.5 to 1.67.