Effect of Zr addition on toughness and microstructure of coarse grained heat affected zone in Al deoxidised low carbon steel

Abstract

The effect of Zr addition on the toughness and microstructure of coarse grained heat affected zone (CGHAZ) in Al deoxidised low carbon steel was investigated. In this present work, the specimens (Zr free and Zr added) were subjected to weld thermal cycle with heat input of 54, 80 and 100 kJ cm^− 1 at 1350°C peak temperature using thermal simulator. The typical inclusions were characterised by scanning electron microscopy, and the chemical composition of the inclusions was determined by energy dispersive spectroscopy. The nanoscale precipitates were analysed by transmission electron microscopy and energy dispersive spectroscopy. It was verified that the occurrence of Zr in steel mostly exists in the form of oxide inclusions, but a few in the form of solid solution state and Zr containing precipitates when the concentration of Zr is 0.015%. The improvement of CGHAZ toughness is obtained when the heat input is 80–100 kJ cm^− 1. The possible reasons about the effects of Zr on the toughness of CGHAZ, including Zr containing inclusions, precipitates and microstructure characteristics, were also discussed.

Keywords:

• Al deoxidised low carbon steel
• Zirconium
• Precipitate
• Coarse grained heat affected zone (CGHAZ)
• Intragranular ferrite

Acknowledgements

We wish to thank the National Natural Science Foundation of China for providing financial support during this study (project nos. 51374059 and 51374060). We also appreciate Professor Lijun Wang (Northeastern University) and Professor Deyong Wang (Schoow University) for the discussion about the study.