Feasibility studies have been performed on ingots with reduced hot-top heights for the cost-effective hot forging of heavy ingots. The quality of the heavy ingots is generally affected by internal voids, which have been known to be accompanied by inclusions and segregation. To guarantee the expected mechanical performance of the forged products, these voids should be closed and eliminated during the hot open die forging process. Hence, to effectively control the internal voids, the optimum hot-top height and forging schedules need to be determined. In order to improve the utilization ratio of ingots, the ingot hot-top height needs to be minimized. To investigate the effect of the reduced hot-top height on the forged products, shaft and bar products have been manufactured via hot forging of ingots having various hot-top heights. From the operational results, the present work suggests effective forging processes to produce acceptable shaft and bar products using ingots having reduced hot tops. The mechanical properties of shop-floor products manufactured from ingots with reduced hot tops have also been measured and compared with those of conventional ingot products.
Keywords: bar; forging; heavy ingot; hot top; main shaft; shrinkage porosity.