Effects of nitrogen content and weld cooling time on the simulated heat-affected zone toughness in a Ti-containing steel
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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.
KeywordsFerrite Impact Toughness Acicular Ferrite Continuous Cool Transformation Diagram Free Nitrogen
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.
- 2.George T, Kennon N (1972) J Austral Inst Met 17:73Google Scholar
- 3.Maurickx T, Taillard R (1989) In: Proceedings of the Conference on High Nitrogen Steels, Lille, May 1989, J Foct, A Hendry (eds) Institute of Metals, p 327Google Scholar
- 4.Edwards R, Squires I, Barbaro F (1986) Austral Weld J Autumn 11Google Scholar
- 9.Hannerz N (1978) In: Proceedings of the Conference on Welding of HSLA (microalloyed) Structural Steels, Rome, November 1977, A Rothwell, J. Malcolm Gray (eds) ASM, p 365Google Scholar
- 10.Cuddy L, Raley J, Poter L (1984) In: Proceedings of the Conference on HSLA Steels Technology and Applications, Philadelphia, October 1983, M Korchynsky (eds) ASM, p 697Google Scholar
- 12.Zajac S, Siwecki T, Svensson L-E (1988) In: Proceedings of the Conference on HSLA Steels, Pittsburgh, November 1987, AJ DeArdo Jr (ed) TMS, p 511Google Scholar
- 13.Liao F, Liu S, Olson D (1994) In: Proceedings of International Conference OMAE 93, Gladgow, 1993, M Salama et al. (eds) ASME, p 231Google Scholar
- 15.Wagner C (1961) Z Electrochem 65:581Google Scholar
- 18.den Ouden G (1968) Brit Weld J September 436Google Scholar