The Formation and Distribution of Ti(C,N) to Prevent Blast Furnace Refractory Wear

The charging of titanium-bearing ore in blast furnaces has long been known to prevent blast furnace (BF) hearth wear and to extend the campaign life of the BF.1–3 Despite being “operationally effective” in protecting the furnace, much is still unknown about the exact mechanism of prevention. Narita et al. were the first to find Ti(C,N) crystals in the wall of a blown-out blast furnace with a chamotte brick hearth.2 Since then, Bergsma and Fruehan hypothesized that Ti(C,N) forms scaffolds in locations with less thermal resistance, i.e., where the refractory is thinner, and these scaffolds protect the walls by restricting flow to the hot face.4 In essence, this is a higher-temperature variation on solidifying an iron skull. Wen et al. reported that the apparent solidus temperature increased with Ti content.5 This is an argument of fluidity with the flow of metal decreasing as the solid fraction increases.6 Typical operational additions of titanium-bearing ore to obtain 0.07–0.15 wt.% Ti in hot metal agrees with thermodynamic data on the conditions to form Ti(C,N), in support of this mechanism.7–9 However, the literature lacks an experiment directly proving this mechanism. Zhao has proposed an alternative mechanism premised on an effect of Ti on the viscosity of molten iron;8 dissolved Ti is proposed to increase the hot metal viscosity strongly. While there is no clear fundamental basis for this proposed mechanism, it does appear to be supported by rotating rod experiments of Deng et al.;10 though those experiments were performed under conditions unstable for TiC, the erosion rates decreased with higher Ti additions.