Scandinavian Journal of Metallurgy 2001; 30: 127–135 Copyright C Munksgaard 2001 Printed in Denmark. All rights reserved SCANDINAVIAN JOURNAL OF METALLURGY ISSN 0371-0459 The influence of different calcium-based additions on desulphurisation and inclusion characteristics Margareta Andersson 1 , Dean Berlin 2 , Pär Jönsson 1 and Martin Löwnertz 1 1 Division of Metallurgy, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden; 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA The size, distribution, and composition of inclusions during the desulphurisation and deoxidation steps were studied in labora- tory experiments. 3 different calcium-based desulphurisation mixtures were used. The number of inclusions and composition of inclusions were then determined using optical microscopy and scanning electron microscopy, respectively. The results show that 2 of the 3 proposed desulphurisation mixtures managed to render lower and roughly equivalent inclusion counts. The results also show that the composition of the inclusions in all 3 samples varied from the beginning to the end of the desulphurisation pro- In the modern integrated steel plant, the demand for efficient production of high-quality steel is high. To- day, the conventional practise is to desulphurise the pig iron before blowing in the Basic Oxygen Furnace (BOF). If the desulphurisation operation is partly con- ducted during ladle treatment, after the BOF treat- ment, the flexibility of the total process is increased. However, desulphurisation by injection of wire or powder into the ladle will also affect the formation or modification of non-metallic inclusions. In many cases the amount of dissolved oxygen in the molten steel is determined by the aluminium deoxidation, resulting in the formation of alumina inclusions. The degree to which alumina inclusions later are modified by cal- cium treatment is simply a question of competition between sulphur and oxygen for calcium in the melt [1]. The work presented in this paper was a laboratory- scale study of the influence of different calcium-based desulphurisation mixtures on the desulphurisation and inclusion characteristics of aluminium deoxidised steel. CaSi was included in the desulphurisation mix- tures for modification of inclusions. CaCO 3 was in- cluded because its decomposition reaction produces carbon dioxide, which is useful in stirring the melt. The effect of the simultaneous use of Al and the dif- ferent CaO/CaCO 3 /CaSi mixtures on inclusion 127 cess. A desulphurisation mixture consisting of Al, CaO, CaCO 3 and CaSi produced the overall best results with respect to desul- phurisation and inclusion characteristics. Key words: desulphurisation, inclusions, calcium modification, size distribution, inclusion composition. c Munksgaard, 2001 Accepted for publication 8 August 2000 characteristics was evaluated using optical and scan- ning electron microscopy. This research project represents the second phase of a larger three-part project initiated by Partek Nord- kalk AB. The aim of the overall project is to explore the possibility of using Ca-based compound additions for desulphurisation and inclusion reduction and con- trol during ladle treatment. In the 1st phase of the pro- ject, experiments were conducted to investigate the extent to which and rate at which the three different desulphurisation mixtures managed to reduce the sul- Fig. 1. Schematic overview of the experimental set-up.