Effect of Ca on the evolution of inclusions and the formation of acicular ferrite in Ti–Mg killed EH36 steel

ABSTRACT

The characteristics of inclusions and the formation of acicular ferrite (AF) in Ti–Mg-Ca killed EH36 steel were researched. Typical inclusions in the Ca-free samples were MgO·Al₂O₃ + MnS and pure MgO·Al₂O₃. With the addition of Ca, MgO·Al₂O₃ was modified into Mg–Ca–Al–O , which promoted MnS precipitating on those inclusions. Mg–Ca–Al–O+MnS/MnS–CaS was the nucleus of AF. While pure MgO·Al₂O₃ was inert for nucleation of AF. Therefore, the percentage of AF increased to 21% in the steel with 0.0017% Ca. However, 0.0051% Ca led to a rise of CaS content in the inclusions. Probability of AF nucleation on the inclusions was reduced due to high lattice mismatch between CaS and α-Fe. Area fraction of AF in the steel with 0.0051% Ca decreased while that of ferrite side plates increased. It is appropriate when the content of Ca is 0.0017% in this study.

KEYWORDS:

• Ca content
• Size
• Composition
• Evolution
• inclusion
• acicular ferrite
• Microstructure
• EH36 steel

Conflict of interest

The authors declare no conflict of interest.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (NSFC): [Grant Numbers 51774024 and 52074025].