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ISSN : 1225-0562(Print)
ISSN : 2287-7258(Online)
Korean Journal of Materials Research Vol.29 No.2 pp.97-105

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

Jin-seong Park,Joong-Ki Hwang,Jae Young Cho,Il Wook Han,Man Jae Lee,Sung Jin Kim
1Department of Advanced Materials Engineering, Sunchon National University, Suncheon 57922, Republic of Korea
2School of Mechanical Engineering, Tongmyong University, Busan 48520, Republic of Korea
3POSCO Technical Research Laboratories, Pohang 37673, Republic of Korea 4Analysis and Assessment Group, Research Institute of Industrial Science and Technology (RIST), Pohang 37673, Republic of Korea
Corresponding author E-Mail : (S. J. Kim, Sunchon Nat’l Univ.)


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 γ 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.

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

1순천대학교 신소재공학과, 2동명대학교 기계공학부, 3포스코 기술연구원, 4포항산업과학연구원