Fluorine-free mould slags for slab casting : utilisation of the hot thermocouple technique to build TTT diagrams

Abstract

The elimination of fluorine from slags is necessary because F-bearing materials pollute the environment and cause machinery corrosion at steelworks. Regarding the development of F-free mould slags for slab casting, the main problem is how to control the heat transfer between steel shell and mould. In commercial products the heat transfer control is obtained through the crystallisation of cuspidine (3CaO.2SiO2 .CaF2 ) from mould slag. Thus, the fluorine-free slag which would be used as the substitute must show similar crystallisation behaviour. This paper shows results of a cooperation work between Technische Universität Bergakademie Freiberg and Universidade Federal do Rio Grande do Sul. Ti-bearing slags were studied through the Single Hot Thermocouple Technique, building time-temperature-transformation (TTT) diagrams. The results indicate that the system CaO-SiO2 -TiO2 -Na2 O can be used as substitute for F-bearing slags, regarding crystallisation behaviour, since the incubation times at TTT diagram can be similar to commercial products. This is possible because addition of Na2 O shorten intensely the incubation times from the CaO-SiO2 -TiO2 slag system.