Hot top design and its influence on feeder channel segregates in 100-ton steel ingots

Abstract The influence of hot top design on feeder channel segregates (F-CS) and centerline shrinkage porosities (C-SP) were investigated both experimentally and numerically. Two 100-ton 30Cr2Ni4MoV steel ingots with different insulating hot tops were longitudinally sectioned. The experimental results showed few channel segregates but severe shrinkage porosities appeared in the ingot with poorly insulated hot top, while it was the opposite case after the improved hot topping practice. By employing the finite element numerical simulation, the critical condition for the formation of F-CS in 30Cr2Ni4MoV steel was verified to be R 2.1 G  ≤ 1.0 × 10 − 5  °C mm 1.1  s − 2.1 . Through coupling with the published C-SP criterion ( GR − 0.5  ≤ 2.5 °C mm − 1.5  s 0.5 ), it was found out that the increase of hot-top height and preheating temperature would aggravate F-CS while alleviate C-SP contrarily. Hence, to comprehensively control those two defects, the optimum hot-top height and preheating temperature for 100-ton ingot were suggested to be 700 mm and 600 °C, respectively. Ultimately, the ratio of the solidification time for the whole ingot to the ingot body ( t f / t b ) was proposed as a novel criterion for hot top design. This practical criterion has been successfully utilized to optimize the hot top of a 5-ton steel ingot.