Precipitation behaviour and control of TiN inclusions in rail steels

Abstract

This paper studied the precipitation behaviour and the control of TiN inclusions in rail steels by thermodynamic calculation and industrial experiments. The results showed that TiN inclusions could not precipitate in molten steel at present condition owing to low [Ti] and [N] content in rail steels; but when solid fraction exceeded 0.87 in mushy zone during solidification process, TiN inclusions could precipitate because of the separation–crystallisation of [Ti] and [N], and even long strip inclusions were formed around grain boundaries. Two types of TiN inclusions, including long strip type with size ranging 20–30 μm and block type with size below 10 μm, could be found in rail steels. The formation of TiN inclusions could be affected by the content of [Ti] and [N], the superheat of liquid steel, secondary cooling intensity and the intensity of strand electromagnetic stirring. The metallurgical process III was conducive to the control of TiN inclusions precipitated and grown up. The results of thermodynamic analysis were consistent with those of the metallurgical process tests.

Keywords:

• TiN inclusions
• Precipitation of inclusions
• Rail steels
• Thermodynamic calculation

Acknowledgements

This work was supported by National 863 Project of China by grant no. 2015AA034302.