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<p>An appropriate cooling rate of liquid steel will improve the solidification structure of steel and reduce the microsegregation degree of alloying elements and consequently enhance the quality of 25Cr-20Ni-Nb-N casting billet. The effect of the cooling rate of liquid steel on solidification characteristics, solidification structure, eutectic carbonitrides, and microsegregation degree of alloying elements in 25Cr-20Ni-Nb-N steel was studied via <i>in situ</i> observation and microstructure analysis. The initial solidification temperature increases first and then decreases, which is attributed to the fact that the number of potential heterogeneous nucleation sites increases initially and then decreases with increasing the cooling rate. The final solidification temperature decreases monotonously, whereas the solidification temperature interval increases monotonously with the increase in the cooling rate from 10&#xa0;°C/min to 100&#xa0;°C/min. The rate constant associated with the nucleation and growth exhibits an increasing trend with higher cooling rates, and the nucleation mechanism is the site saturation nucleation at different cooling rates. The value of the effective activation energy of solidification at various cooling rates is negative, which indicates an anti-Arrhenius behavior for liquid steel solidification and liquid steel solidification is mainly controlled by nucleation of austenite. The values of nucleation effective activation energy and growth effective activation energy for the steel are −&#xa0;8842.28 and −&#xa0;676.88&#xa0;kJ/mol, respectively. The secondary dendrite arm spacing decreases from 80.1 to 32.3&#xa0;μm with higher cooling rates. The volume fraction and size of eutectic Nb(C,N) decrease with higher cooling rates, whereas the number density increases. The microsegregation degree of the alloying elements C, N, and Nb alleviates with higher cooling rates, which is conducive to reducing the generation of eutectic Nb(C,N).</p>

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Solidification Characteristics and Eutectic Carbonitrides in 25Cr-20Ni-Nb-N Austenitic Heat-Resistant Stainless Steel

  • 期刊论文

  • 发表日期：

    2025年7月7日

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  • Peng Ren,
  • Chengbin Shi,
  • Linchen Li,
  • Lingyu Meng

摘要

An appropriate cooling rate of liquid steel will improve the solidification structure of steel and reduce the microsegregation degree of alloying elements and consequently enhance the quality of 25Cr-20Ni-Nb-N casting billet. The effect of the cooling rate of liquid steel on solidification characteristics, solidification structure, eutectic carbonitrides, and microsegregation degree of alloying elements in 25Cr-20Ni-Nb-N steel was studied via in situ observation and microstructure analysis. The initial solidification temperature increases first and then decreases, which is attributed to the fact that the number of potential heterogeneous nucleation sites increases initially and then decreases with increasing the cooling rate. The final solidification temperature decreases monotonously, whereas the solidification temperature interval increases monotonously with the increase in the cooling rate from 10 °C/min to 100 °C/min. The rate constant associated with the nucleation and growth exhibits an increasing trend with higher cooling rates, and the nucleation mechanism is the site saturation nucleation at different cooling rates. The value of the effective activation energy of solidification at various cooling rates is negative, which indicates an anti-Arrhenius behavior for liquid steel solidification and liquid steel solidification is mainly controlled by nucleation of austenite. The values of nucleation effective activation energy and growth effective activation energy for the steel are − 8842.28 and − 676.88 kJ/mol, respectively. The secondary dendrite arm spacing decreases from 80.1 to 32.3 μm with higher cooling rates. The volume fraction and size of eutectic Nb(C,N) decrease with higher cooling rates, whereas the number density increases. The microsegregation degree of the alloying elements C, N, and Nb alleviates with higher cooling rates, which is conducive to reducing the generation of eutectic Nb(C,N).