Microstructure-toughness relationship in the simulated CGHAZ of V-N microalloyed X80 pipeline steel

Abstract

The microstructure evolution, hardness and impact toughness in the simulated coarse-grained heat-affected zone (CGHAZ) of a V-N microalloyed X80 pipeline steel were studied. The results indicated that the microstructure mainly consisted of bainitic ferrite, acicular ferrite and granular bainite. The area fraction and size of M/A constituents were increased with increasing heat input. As heat input increased from 15 to 60 kJ cm⁻¹, the hardness gradually decreased from 301 to 243 HV, and impact energy decreased from 284 to 33 J. Hardness in the CGHAZ was not sensitive to heat input. When the heat input exceeded 30 kJ cm⁻¹, the formation of coarse granular bainite and large-sized blocky M/A constituents resulted in the deterioration of impact toughness.

KEYWORDS:

• V-N microalloying
• coarse-grained heat-affected zone
• pipeline steel
• acicular ferrite
• M/A constituents
• crack propagation
• impact toughness
• hardness

Acknowledgements

The authors at NEU are extremely grateful to R. D. K. Misra for his willingness to collaborate and meaningful discussion.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This study is financially supported by the National High Technology Research and Development Program of China (863 Program) [grant number 2015AA03A501].