Inclusions in commercial low and medium carbon ferromanganese
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INTRODUCTION
FERROALLOYS are commonly used in the steel manufacturing industry to alloy or deoxidize the steel. Experience shows that the additions of ferroalloys influence the cleanliness of the steel, and hence the material properties of the end product.[1] To determine the influence of different alloys, controlled alloying experiments are necessary. Such experiments have been performed with ferrochromium[2] and ferrosilicon,[3] but are lacking for ferromanganese. Before establishing the influence of ferromanganese on steel cleanness, it is essential to obtain relevant information about the microstructure and, in particular, impurity elements and inclusions present in ferromanganese. In a study of carbide formation in commercial high carbon ferromanganese with typically maximum 6 wt pct C, Mihok et al.[4,5] showed that carbides mainly precipitate as small irregular particles at low cooling rates. Balbi et al.[6,7] investigated nonmetallic inclusions present in commercial ferromanganese containing up to 7.4 wt pct C, concluding that MnO and SiO2 inclusions are the most common ones. Furthermore, they state that SiO2 inclusions are in majority when the silicon content is above 1 wt pct. These investigations have concentrated on high carbon ferromanganese with high contents of silicon, rather than on low and medium carbon ferromanganese. The present investigation aims to extend the knowledge about the microstructure of commercial low carbon (maximum 0.5 wt pct C), denoted LC, and medium carbon (maximum 1.5 wt pct C), denoted MC, ferromanganese with emphasis on inclusions present. Therefore, the presented results include characterization and counting of inclusions present in six qualities of ferro-manganese.
¨ QVIST, Doctoral Student, and PA ¨ NSSON, Professor, ¨ R JO THOBIAS SJO are with the Department of Materials Science and Engineering, Division of Metallurgy, Royal Institute of Technology, SE-10044, Stockholm. ¨ YSTEIN GRONG, Professor, is with the Department of Materials TechO nology and Electrochemistry, Norwegian University of Science and Technology, N-7491 Trondheim, Norway. Manuscript submitted March 13, 2000.
METALLURGICAL AND MATERIALS TRANSACTIONS A
II. METHODS AND PREPARATIONS A. Sampling Considering that the aim of the study was to examine the quality of ferromanganese reaching the customers, sampling were made from cast ferromanganese after cooling. Sampling were made at Elkem’s production sites in Norway. All samples were collected in the form of solid pieces from cast material. B. Chemical Analysis From each sample, three pieces were taken. One was used for chemical analysis and the other two for microscopic examination. The chemical analyses were made on 50 g of each sample using two different methods. These samples were analyzed for C and S by combustion using a LECO* *LECO is a trademark of LECO Corporation, St. Joseph, Ml.
CS444 unit with a relative accuracy of ⫾1 and ⫾10 pct, respectively. A LECO TC136 unit was used to analyze O and N with a relative accuracy of about ⫾5 pct. The remaining p
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