Metallurgical and Materials Transactions A

, Volume 42, Issue 3, pp 717–728 | Cite as

Low-Temperature Toughening Mechanism in Thermomechanically Processed High-Strength Low-Alloy Steels

  • Byoungchul HwangEmail author
  • Chang Gil Lee
  • Sung-Joon Kim


High-strength low-alloy (HSLA) steels were fabricated by varying thermomechanical processing conditions such as rolling and cooling conditions in the intercritical region, and the low-temperature toughening mechanism was investigated in terms of microstructure and the associated grain boundary characteristics. The steels acceleratedly cooled to relatively higher temperature had lower tensile strength than those acceleratedly cooled to room temperature due to the increased volume fraction of granular bainite or polygonal ferrite (PF) irrespective of rolling in the intercritical region, while the yield strength was dependent on intercritical rolling, and start and finish cooling temperatures, which affected the formation of PF and low-temperature transformation phases. The steel rolled in the intercritical region and cooled to 673 K (400 °C) provided the best combination of high yield strength and excellent low-temperature toughness because of the presence of fine PF and appropriate mixture of various low-temperature transformation phases such as granular bainite, degenerate upper bainite (DUB), lower bainite (LB), and lath martensite (LM). Despite the high yield strength, the improvement of low-temperature toughness could be explained by the reduction of overall effective grain size based on the electron backscattered diffraction (EBSD) analysis data, leading to the decrease in ductile-to-brittle transition temperature (DBTT).


Acicular Ferrite Polygonal Ferrite Lower Bainite DBTT Granular Bainite 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



This study was financially supported by the Ministry of Knowledge Economy, Korea. The authors thank Professor Sunghak Lee, Dr. Sang Yong Shin, and Mr. Hyo Kyun Sung, Pohang University of Science and Technology, Korea, and Mr. Hong Dong Kim, Korea Institute of Materials Science, for their help with the tensile and Charpy impact tests.


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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2010

Authors and Affiliations

  • Byoungchul Hwang
    • 1
    Email author
  • Chang Gil Lee
    • 1
  • Sung-Joon Kim
    • 1
  1. 1.Korea Institute of Materials ScienceChangwonKorea

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