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<p>The refinement of the as-cast grain structure in austenitic heat-resistant stainless steel depends on the formation of active solid nuclei during solidification. Titanium (Ti) additions successfully induced the formation of Ti-containing inclusions, enhancing heterogeneous nucleation and promoting equiaxed dendritic growth in 347H stainless steel. Thermal simulation experiments indicated that the equiaxed crystal ratios increased notably with Ti content; samples with 0.06, 0.12, and 0.36 wt.% Ti exhibited equiaxed ratios of 18%, 24%, and 41%, respectively. Three primary inclusion types—TiN, Al<sub>2</sub>O<sub>3</sub>–TiN, and TiO<sub><i>x</i></sub>–TiN—were identified at the cores of equiaxed dendrites, with nucleation core sizes predominantly ranging from 0.5 to 8 μm. Among the tested samples, the 0.36 wt.% Ti addition produced the highest nucleation core density. Increasing Ti content significantly elevated dendrite tip undercooling from 2.6 K (0.06 wt.% Ti) to 10.8 K (0.36 wt.% Ti), accelerating solidification front instability and thus enhancing heterogeneous nucleation. Additionally, higher Ti content increased the divergence angle between adjacent columnar dendrites, further promoting the columnar-to-equiaxed transition (CET).</p>

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Impact of titanium on solidification behavior and macrostructure of 347H stainless steel

  • 期刊论文

  • 发表日期：

    2025年12月23日

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  • Shang-Yan Jiang,
  • Yu-Xin Zhou,
  • Hui-Gai Li,
  • Jian-Ping Liang,
  • Jie Li,
  • Qi-Jie Zhai

摘要

The refinement of the as-cast grain structure in austenitic heat-resistant stainless steel depends on the formation of active solid nuclei during solidification. Titanium (Ti) additions successfully induced the formation of Ti-containing inclusions, enhancing heterogeneous nucleation and promoting equiaxed dendritic growth in 347H stainless steel. Thermal simulation experiments indicated that the equiaxed crystal ratios increased notably with Ti content; samples with 0.06, 0.12, and 0.36 wt.% Ti exhibited equiaxed ratios of 18%, 24%, and 41%, respectively. Three primary inclusion types—TiN, Al2O3–TiN, and TiOx–TiN—were identified at the cores of equiaxed dendrites, with nucleation core sizes predominantly ranging from 0.5 to 8 μm. Among the tested samples, the 0.36 wt.% Ti addition produced the highest nucleation core density. Increasing Ti content significantly elevated dendrite tip undercooling from 2.6 K (0.06 wt.% Ti) to 10.8 K (0.36 wt.% Ti), accelerating solidification front instability and thus enhancing heterogeneous nucleation. Additionally, higher Ti content increased the divergence angle between adjacent columnar dendrites, further promoting the columnar-to-equiaxed transition (CET).