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Journal of Materials Science

, Volume 41, Issue 18, pp 5994–6000 | Cite as

Effects of nitrogen content and weld cooling time on the simulated heat-affected zone toughness in a Ti-containing steel

  • Kook-soo Bang
  • Chan Park
  • Stephen Liu
Article

Abstract

An increase of nitrogen content in a 0.02 wt% Ti-containing carbon-manganese steel resulted in a low coarsening rate of TiN particles in the heat-affected zone (HAZ), which led to an accelerated ferrite transformation instead of ferrite side plates during weld cooling cycle. The mixed microstructure of ferrite side plate, acicular ferrite and grain boundary polygonal ferrite in the simulated HAZ produced higher toughness. However, the increase of nitrogen content gradually increased the free nitrogen content in the HAZ and deteriorated HAZ toughness. Impact energy of the simulated HAZ (with Δt8/5 ∼60 s) at –20 °C deteriorated by about 97 J per 0.001 wt% free nitrogen, in the free nitrogen range from 0.0009 wt% to 0.0034 wt%, even though the HAZ has the tough mixed microstructure. Cooling time after welding influenced the HAZ microstructure and toughness as well, and maximum toughness was obtained when cooling produced the tough mixed microstructure. Therefore, for a high HAZ toughness, both nitrogen content and cooling time should be controlled to obtain the tough mixed microstructure and to keep the free nitrogen content low. The optimal nitrogen content and cooling time from 800 °C to 500 °C were 0.006 wt% and between 60 s and 100 s, respectively, in this experiment.

Keywords

Ferrite Impact Toughness Acicular Ferrite Continuous Cool Transformation Diagram Free Nitrogen 

Notes

Acknowledgements

One of the authors (K.-s. Bang) wishes to acknowledge the financial support from POSCO, Pohang, Korea and would also like to thank B.-c. Kim for his contributions to this research.

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Copyright information

© Springer Science+Business Media, LLC 2006

Authors and Affiliations

  1. 1.Division of Advanced Materials Science and EngineeringPukyong National UniversityPusanKorea
  2. 2.Center for Welding, Joining and Coatings ResearchColorado School of MinesGoldenUSA

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