Effect of slag composition on the cleanliness of drill rod steel

ABSTRACT

In order to obtain the 55SiMnMo drill rod steel with a high cleanliness, the slag refining has been simulated by laboratory experiments. More desired spherical-shaped complex inclusions with an average diameter of about 2.7 μm, total oxygen of 4 ppm and Mg of 10 ppm after refining were obtained with initial slag basicity of 2.1 and Al₂O₃ 15 wt-%. The relationship between the slag composition and the melting temperature and viscosities of slag was achieved based on a calculation by Factsage Software and Einstein–Roscoe Equation. The refractory–slag–metal–inclusion multiphase reactions were investigated from the viewpoint of thermodynamics and kinetics by the estimation of viscosities, MgO solubility, Al₂O₃ activity in slag and sulphur capacity of slags. It is experimentally confirmed that the corrosion of MgO crucible by slag was affected by the MgO solubility and viscosity of slag. The factors facilitating to obtain low oxygen and control sulphur content were also analysed. Finally, the composition transformation of inclusions during slag refining and cooling process was discussed based on thermodynamic calculation.

KEYWORDS:

• Slag refining
• cleanliness
• inclusion
• viscosity of slag

Disclosure statement

No potential conflict of interest was reported by the authors.

Conflicts of interest

The authors declare no conflict of interest.

Additional information

Funding

This project is financially supported by the National Science Foundation of China with the grant No. 51704085, 51574190 and 51704083. Also, this project is supported by Program Foundation for Talents of Guizhou University with the grant No. 2017(05) and is supported by the technology planning project of Guizhou Province with grant No. Qian Ke He [2017]5788. The National Natural Science Foundation of Guizhou Province with grant No. [2018]1060 is gratefully acknowledged.