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<p>Ferrite–pearlite steels commonly develop banded microstructures that cause mechanical heterogeneity and potential safety risks. This study employs optical microscopy, scanning electron microscopy, electron probe microanalysis, Vickers hardness testing, and annealing, quenching, and interrupted-quenching treatments at different austenitizing temperatures to investigate how austenite grain size affects banded-structure formation in S355NL steel. Increasing the austenitizing temperature promotes austenite grain coarsening and reduces the tendency for banding, which fundamentally arises from solute segregation bands. When the austenite grain size exceeds about 0.8-1.2 times the width of the solute-enriched zone—the critical size—banded structures are effectively suppressed. The nucleation and morphology of proeutectoid ferrite strongly depend on grain size. With grains smaller than the critical size, ferrite nucleates and grows equiaxed, with much higher nucleation rates in solute-depleted regions, thereby promoting banding. When grains exceed the critical size, the nucleation rate decreases, and ferrite develops a network-like morphology that partitions the matrix more uniformly, suppressing banded features. Although high-temperature austenitizing improves carbon homogenization, it only weakly affects alloying-element segregation such as Mn. Because Mn segregation persists, banded structures may reappear during subsequent low-temperature austenitizing even after prior high-temperature treatment. This work clarifies the inherent link between austenite grain size and banded-structure development from the perspectives of proeutectoid ferrite nucleation and morphological evolution, offering theoretical insight and processing guidance for controlling banding in ferrite–pearlite steels.</p>

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The Effect of Austenite Grain Size on the Banded Structure of S355NL Steel

  • 期刊论文

  • 发表日期：

    2026年4月12日

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  • Dongsheng Liu,
  • Mingzhi Tan,
  • Huiping Qi,
  • Wen Yang,
  • Zhibing Chu,
  • Zhenjiang Li,
  • Zhonghua Jiang,
  • Baisong Cheng

摘要

Ferrite–pearlite steels commonly develop banded microstructures that cause mechanical heterogeneity and potential safety risks. This study employs optical microscopy, scanning electron microscopy, electron probe microanalysis, Vickers hardness testing, and annealing, quenching, and interrupted-quenching treatments at different austenitizing temperatures to investigate how austenite grain size affects banded-structure formation in S355NL steel. Increasing the austenitizing temperature promotes austenite grain coarsening and reduces the tendency for banding, which fundamentally arises from solute segregation bands. When the austenite grain size exceeds about 0.8-1.2 times the width of the solute-enriched zone—the critical size—banded structures are effectively suppressed. The nucleation and morphology of proeutectoid ferrite strongly depend on grain size. With grains smaller than the critical size, ferrite nucleates and grows equiaxed, with much higher nucleation rates in solute-depleted regions, thereby promoting banding. When grains exceed the critical size, the nucleation rate decreases, and ferrite develops a network-like morphology that partitions the matrix more uniformly, suppressing banded features. Although high-temperature austenitizing improves carbon homogenization, it only weakly affects alloying-element segregation such as Mn. Because Mn segregation persists, banded structures may reappear during subsequent low-temperature austenitizing even after prior high-temperature treatment. This work clarifies the inherent link between austenite grain size and banded-structure development from the perspectives of proeutectoid ferrite nucleation and morphological evolution, offering theoretical insight and processing guidance for controlling banding in ferrite–pearlite steels.