Abstract
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.
Highlights
Following the rising demands of production efficiency and security, an increasing number of large forgings are applied in various fields including heavy industrial machinery
For method 1, which follows the conventional main shaft forging in this study
As the quality of heavy ingots is commonly affected by internal voids, extensive studies on optimum hot-top heights and forging schedules must be performed to efficiently and effectively control the number and size of any internal voids
Summary
Following the rising demands of production efficiency and security, an increasing number of large forgings are applied in various fields including heavy industrial machinery. Large forgings are often afflicted by process-induced internal void defects due to the inevitable non-uniform solidification of large ingots during casting. Internal voids in steel ingots significantly deteriorate the mechanical properties of the forged products and may nucleate a crack or become a source for defects during the subsequent forging steps [1,2,3,4,5]. During the forging operation, the voids present in cast ingots should be eliminated to guarantee the mechanical performance of the forged products. The algorithms based on the void closure in forged products provide reasonable reliability when applied in industrial environments. Lee et al [7] investigated internal void closure during the forging of large cast ingots using a simulation approach. Through the comparison of experimental results and numerical simulation, a criterion for void closure based on the Materials 2020, 13, 2916; doi:10.3390/ma13132916 www.mdpi.com/journal/materials
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