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.
Highlights
Oil pipe steel is widely used to produce petroleum pipe in oil exploration, exploitation, and transportation [1]
The shrinkage porosity and spot segregation defects in round bloom are difficult to eliminate through hot rolling and heat treatment, which will cause the formation of inhomogeneity structure in the final oil pipe product, resulting in the early failure due to sulfide stress corrosion (SSC) [3]
This thermal-mechanical model has been verified by a soft reduction (SR) process in the Ø690 mm round bloom continuous casting
Summary
Oil pipe steel is widely used to produce petroleum pipe in oil exploration, exploitation, and transportation [1]. It is extremely important to effectively control the shrinkage porosity and spot segregation in the continuously cast round bloom of oil pipe steel. Shrinkage porosity occurs at the last stage of solidification in continuous casting, where the contraction of the central matrix cannot be fed completely by upstream molten steel due to high solid fraction [4]. Ø800 mm round bloom with newly designed three-roll-segment in vertical continuous casting, and the central quality was improved remarkably. The proper reduction zone, the reduction amount and ovality of round bloom, the deformation of central porosity zone, and the suitable reduction force distribution were calculated and discussed Based on these simulation results, a multi-unit soft reduction was carried out on a Ø195 mm round bloom of oil pipe steel, the central shrinkage porosity and spot segregation defects were effectively controlled
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