Optimization of Heavy Reduction Process on Continuous-Casting Bloom

Abstract

Heavy reduction (HR) is an effective technique to control V segregation in continuous casting bloom, but the effect of segregation improvement is limited by the parameters such as reduction position and reduction amounts. In order to improve the macrosegregation of bloom, numerical simulation and plant experiments are adopted in this research. A heat transfer model and a reduction model with comprehensive thermo-physical parameters were established. The two models were verified by comparing the measured surface temperature and the theoretical strain at the solidification front. It is determined that the position of the HR of the bearing steel bloom is 20.82 m~24.97 m from the meniscus, and the solid fraction in the center of the bloom is 0.6~1. The total reduction of the HR is set to 30 mm, and the reduction of each roller in the reduction range is set to 4 mm, 5 mm, 9 mm, 7 mm, and 5 mm, respectively, to prevent the formation of internal cracks. Plant trials were conducted to verify the effect of the optimized HR. The results show that the carbon segregation degree on the V channel and non-channel of the bloom decreases from 1.2 to 1.16 and increases from 0.93 to 0.95, respectively, and the central carbon segregation degree decreases from 1.17 to 1.15. Meanwhile, the internal crack was not found in the bloom.

Modelling of continuous casting processes parameters on the shrinkage cavity formation in bearing steel blooms

“…The specific physical parameters are shown in Ref. [37]. In this study, when the bloom temperature is higher than 1380.6°C…”

“…The specific physical parameters are shown in Ref. [37]. In this study, when the bloom temperature is higher than 1380.6°C, the thermal expansion coefficient of bearing steel is zero.…”

“…The effect of superheat on the solidification process of 380 mm × 450 mm (section A) bearing steel bloom has been discussed in the previous work. Previous studies have shown that for every 15°C change in superheat, the distance from the liquidus of the bearing steel bloom to the meniscus changes by 0.5 m and the solidification end point changes by 0.32 m [37]. Therefore, the change of superheat will change the centre and surface temperature of the bloom at the same position in the solidification process and finally change the centre thermal stress thus affecting the changes of nodes A, B, C and D. The displacement of A, B, C and D nodes in the X and Y directions in the area where shrinkage cavity may be formed under the condition of thermal stress during the solidification process of bloom with superheat of 19°C and 42°C was calculated, respectively.…”

“…As shown in Figure 2 [37], the research object of this paper is a bowed continuous casting machine. The main production bloom section specifications are 380 mm × 450 mm (section A) and 250 mm × 250 mm (section B).…”

“…As described in Ref. [37], the simulated and measured temperatures of a 380 mm × 450 mm bearing steel bloom were compared in previous work with a maximum error of 1.16%. The measured and simulated temperature results of 250 mm × 250 mm bloom are shown in Table 2.…”