Korean Journal of Materials Research (한국재료학회지)

Materials Research Society of Korea (한국재료학회)
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Effects of TiN and B on Grain Refinement of HAZ Microstructure and Improvement of Mechanical Properties of High-strength Structural Steel Under High Heat Input Welding

고강도 구조용 철강소재의 대입열 용접 시 열영향부의 조직 미세화 및 기계적 특성 향상에 미치는 TiN 및 B의 효과

  • Park, Jin-seong (Department of Advanced Materials Engineering, Sunchon National University) ;
  • Hwang, Joong-Ki (School of Mechanical Engineering, Tongmyong University) ;
  • Cho, Jae Young (POSCO Technical Research Laboratories) ;
  • Han, Il Wook (POSCO Technical Research Laboratories) ;
  • Lee, Man Jae (Analysis and Assessment Group, Research Institute of Industrial Science and Technology (RIST)) ;
  • Kim, Sung Jin (Department of Advanced Materials Engineering, Sunchon National University)
  • Received : 2018.10.30
  • Accepted : 2018.12.24
  • Published : 2019.02.27
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Abstract

In the current steel structures of high-rise buildings, high heat input welding techniques are used to improve productivity in the construction industry. Under the high heat input welding, however, the microstructures of the weld metal (WM) and heat-affected zone (HAZ) coarsen, resulting in the deterioration of impact toughness. This study focuses mainly on the effects of fine TiN precipitates dispersed in steel plates and B addition in welding materials on grain refinement of the HAZ microstructure under submerged arc welding (SAW) with a high heat input of 200 kJ/cm. The study reveals that, different from that in conventional steel, the ${\gamma}$ grain coarsening is notably retarded in the coarse grain HAZ (CGHAZ) of a newly developed steel with TiN precipitates below 70 nm in size even under the high heat input welding, and the refinement of HAZ microstructure is confirmed to have improved impact toughness. Furthermore, energy dispersive spectroscopy (EDS) and secondary-ion mass spectrometry (SIMS) analyses demonstrate that B is was identified at the interface of TiN in CGHAZ. It is likely that B atoms in the WM are diffused to CGHAZ and are segregated at the outer part of undissolved TiN, which contributes partly to a further grain refinement, and consequently, improved mechanical properties are achieved.

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References

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