Original Article

Effect of secondary cooling water distribution on internal cracks in P91 steel Φ600 mm large round blooms

School of Metallurgical Engineering, Xi'an University of Architecture and Technology, Xi'an, 710055 PR China

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Received: 30 August 2025
Accepted: 9 December 2025

Abstract

Secondary cooling control is a critical aspect in continuous casting production, significantly influencing the thermal state of cast blooms and directly affecting bloom quality. Focusing on the internal crack issues in P91 steel Φ600 mm large round bloom continuous casting, the influence of secondary cooling water distribution on bloom crack susceptibility is systematically studied through numerical simulation combined with high-temperature tensile tests. Results show that with the specific water rate increasing from 0.10 L/kg to 0.14 L/kg, the uniformity of cross-sectional temperature distribution is significantly improved. High-temperature tensile tests identify the high-temperature brittle range of P91 steel as 1410–1440 °C. Numerical simulation reveals that increasing the specific water rates from 0.10 L/kg to 0.14 L/kg advances the solidification end point by 0.41 m and reduces the width of the crack-prone zone by 1.10 mm. Based on crack index evaluation, the crack index at the maximum reheat point in the secondary cooling zone at 0.14 L/kg specific water rates is 12% lower than that under 0.10 L/kg, with temperature distribution more concentrated in low-risk regions. These findings provide theoretical references for optimizing secondary cooling water distribution in large bloom continuous casting and offer critical guidance for controlling internal crack defects in practical production.