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<p>Increasing the hole expansion ratio is significant for developing high formability parts. Hole expansion tests were carried out on low carbon hot-rolled steel containing 0.11% Ti, 0.072% Ti–0.03% Nb and 0.097% Ti–0.059% Nb, respectively. The effects of microstructure, texture, crack propagation behavior and second phase precipitation behavior on hole expansion ratio were investigated. The precipitation behavior of TiC and (Ti, Nb)C in austenite and ferrite in three groups of steel samples was calculated theoretically. The results showed that the hole expansion ratios of 0.11Ti, 0.072Ti–0.03Nb and 0.097Ti–0.059Nb test steels were 51.73%, 51.17% and 66.24% following simulated coiling at 600 °C, respectively. The microstructure was mainly polygonal ferrite with a small amount of pearlite. The grain refinement of 0.097Ti–0.059Nb test steel and the low texture ratio of {110}//ND improved the hole expansion ratio. The low overall hole expansion ratio was due to the microstructure inhomogeneity. The microstructure uniformity was improved by the quenching and tempering treatment, and the hole expansion ratio of the three test steels was greatly increased. The fastest precipitation temperatures in the austenitic region of 0.11Ti, 0.072Ti–0.03Nb and 0.097Ti–0.059Nb test steels were 880, 860 and 830 °C, while those in the ferrite region were 680, 675 and 675 °C, respectively. The addition of Nb element increased the volume free energy, so that the critical core size of the nucleation on the dislocation line increased, resulting in the decrease in the fastest precipitation temperature.</p>

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Effect of Nb addition on hole expansion ratio and its precipitation behavior in Ti-microalloyed hot-rolled high-strength steel

  • 期刊论文

  • 发表日期：

    2025年1月21日

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  • Kang-feng Zhu,
  • Wen-jun Wang,
  • Bo Zhang,
  • Xin-jun Sun,
  • Cai-fu Yang

摘要

Increasing the hole expansion ratio is significant for developing high formability parts. Hole expansion tests were carried out on low carbon hot-rolled steel containing 0.11% Ti, 0.072% Ti–0.03% Nb and 0.097% Ti–0.059% Nb, respectively. The effects of microstructure, texture, crack propagation behavior and second phase precipitation behavior on hole expansion ratio were investigated. The precipitation behavior of TiC and (Ti, Nb)C in austenite and ferrite in three groups of steel samples was calculated theoretically. The results showed that the hole expansion ratios of 0.11Ti, 0.072Ti–0.03Nb and 0.097Ti–0.059Nb test steels were 51.73%, 51.17% and 66.24% following simulated coiling at 600 °C, respectively. The microstructure was mainly polygonal ferrite with a small amount of pearlite. The grain refinement of 0.097Ti–0.059Nb test steel and the low texture ratio of {110}//ND improved the hole expansion ratio. The low overall hole expansion ratio was due to the microstructure inhomogeneity. The microstructure uniformity was improved by the quenching and tempering treatment, and the hole expansion ratio of the three test steels was greatly increased. The fastest precipitation temperatures in the austenitic region of 0.11Ti, 0.072Ti–0.03Nb and 0.097Ti–0.059Nb test steels were 880, 860 and 830 °C, while those in the ferrite region were 680, 675 and 675 °C, respectively. The addition of Nb element increased the volume free energy, so that the critical core size of the nucleation on the dislocation line increased, resulting in the decrease in the fastest precipitation temperature.