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<p>Mn alloying is widespread in structural steels as it increases strength and toughness. However, the use of high amounts of Mn is challenged by the marked segregation during continuous casting, which increases the degree of banding after rolling, and the reduction of weldability of steels. In order to decrease the Mn contents in structural steels, steelmakers are seeking to partially replace it by other alloying elements, for example, Nb. This work evaluates the effect of Mn and Nb additions on the hardenability of a structural microalloyed steel by austenite decomposition dilatometry testing. Continuous cooling transformation diagrams of three different alloys and two prior austenite grain sizes of 10 and 50&#xa0;<i>µ</i>m were developed. It is shown that Nb microalloying has a strong effect on hardenability, lowering the austenite decomposition temperatures and obtaining finer microstructures with increased hardness. Both Mn and Nb additions have a greater effect on transformation temperatures for larger prior austenite grain size. The Nb micro addition evaluated has a similar effect on hardenability than the Mn addition.</p>

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Effects of Mn and Nb Alloying on Austenite Decomposition in High-Strength Low-Alloy (HSLA) Steels for Long Structural Applications

  • 期刊论文

  • 发表日期：

    2025年5月23日

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  • Nicolas E. Tenaglia,
  • John G. Speer,
  • Eliseo Hernandez Duran,
  • Emmanuel De Moor

摘要

Mn alloying is widespread in structural steels as it increases strength and toughness. However, the use of high amounts of Mn is challenged by the marked segregation during continuous casting, which increases the degree of banding after rolling, and the reduction of weldability of steels. In order to decrease the Mn contents in structural steels, steelmakers are seeking to partially replace it by other alloying elements, for example, Nb. This work evaluates the effect of Mn and Nb additions on the hardenability of a structural microalloyed steel by austenite decomposition dilatometry testing. Continuous cooling transformation diagrams of three different alloys and two prior austenite grain sizes of 10 and 50 µm were developed. It is shown that Nb microalloying has a strong effect on hardenability, lowering the austenite decomposition temperatures and obtaining finer microstructures with increased hardness. Both Mn and Nb additions have a greater effect on transformation temperatures for larger prior austenite grain size. The Nb micro addition evaluated has a similar effect on hardenability than the Mn addition.