ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Regular Article
Characterization and Control of Secondary Phase Precipitation of Nb–V–Ti Microalloyed Steel during Continuous Casting Process
Lei-lei ZouJiang-shan ZhangQing Liu Biao Tao
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2022 Volume 62 Issue 11 Pages 2286-2293

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Abstract

The strand surface and subsurface cracks could be prevented through the control of the strand surface microstructure, which correlates with the precipitation behavior of carbonitrides in the microalloyed steel. In this study, the carbonitride precipitation behavior was characterized in-situ with a high-temperature confocal laser scanning microscope, and the effects of cooling rate on the morphology and distribution of precipitates was investigated. The results show that the carbonitride precipitation process is usually accompanied by the formation of dark particles due to the volume expansion of the solute depletion region. The evolution of dark particles suggests that carbonitrides mainly precipitate between 910°C and 1085°C, and the “fast-growing region” ranges from 910°C to 960°C. As the cooling rate increases, the size and volume fraction of carbonitrides decrease. Meanwhile, the nucleation location changes from grain boundary to grain interior. To quantify the pinning capacity of the carbonitrides, the pinning force factor σ is defined according to the classical Gladman equation, which is a power function of the cooling rate, namely σ=0.43−0.1(1+2.76Vc3.48)−1. Combining the above research, a new secondary cooling method is proposed and has been applied on an actual caster, which improves the crack resistance of the bloom surface microstructures.

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© 2022 The Iron and Steel Institute of Japan.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs license.
https://creativecommons.org/licenses/by-nc-nd/4.0/
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