Control of Shrinkage Porosity and Spot Segregation in Ø195 mm Continuously Cast Round Bloom of Oil Pipe Steel by Soft Reduction

Abstract

Based on the Ø195 mm round bloom continuous casting of oil pipe steel, a two dimensional thermal-mechanical coupled model has been developed to investigate the deformation behavior of round bloom during soft reduction (SR) in the reduction force mode. Good agreement was achieved in surface temperature, shell thickness and contact zone width from modeling and measurement. Under the same reduction force, the reduction amount of round bloom at the front unit is much larger than back unit. Moreover, due to its higher temperature and lower center solid fraction, the deformation penetration before solidification is much stronger than that after solidification. Considering the limitation of the round bloom ovality, the maximum allowable force in reduction unit is calculated. According to the simulation results, a multi-unit soft reduction plan was proposed and carried out on the Ø195 mm round bloom. After the reduction process of No.1 to No.3 withdrawal units, the shrinkage porosity in the center of the round bloom was almost vanished, while the number and size of spot segregation were significantly reduced. Moreover, the oil pipe produced by the round bloom with SR got a better resistance to sulfide stress corrosion (SSC). It indicates that SR is an effective technology for the round bloom to control the shrinkage porosity and spot segregation in the continuous casting.