Technical Papers and Discussions - Steelmaking - Oxygen in Basic Electric-furnace Baths (Metals Tech., June 1947, T. P. 2185, with discussion)

At the time this investigation was initiated variations were observed in the quality of different heats of basic electric-furnace steels, although they had been made under purportedly similar conditions. This indicated that these variations were related to normally unobserved variations in the character of the bath, especially during the "refining" period. Although the slags used for this operation are commonly referred to as "reducing" slags, and are regarded as having a "deoxidizing" action on the bath, no reliable measurements of this action were available. It was decided, therefore, to study the behavior of oxygen in the metal for ' large enough number of heats to learn its normal variations and to relate these variations to regularly observed conditions of operation. The most important general conclusion reached was that the time a heat is held under a reducing 'lag should be reduced to a minimum, which was about an hour and a half under the conditions studied. Beyond this time no observable beneficial effects are obtained from the reducing slags, insofar as oxygen and sulphur content of the bath are concerned. It is likely that added time may increase hydrogen content as well as heat costs. The oxygen content of the bath is never reduced below the amount in equilibrium with the carbon. Concurrently with this work, J. S. Marsh1 presented data that supplement and support many of the results of this paper. Procedure The work was done in two different electric-furnace shops of the same plant. The selection of heats was made primarily with regard to the convenience of heat schedules. companion slag and metal samples were taken just prior to slag-ofi and throughout the refining period for an initial set of 17 heats, and before slag-off and near tap for an additional I3 heats. slag Sampling presented no particular problem; a spoonful of slag was poured onto a metal plate and when sufficiently cool was sealed in an airtight container. Sampling the metal for oxygen presented a more complex problem. Because of the lack of previous experience in sampling electric-furnace baths, a number of methods were compared. Chilled Wedge Samples2 An unkilled metal sample is removed from the furnace in a well-slagged car-bometer spoon and poured immediately into a heavy copper mold designed to provide rapid freezing. Three different types of molds were used to determine the optimum for electric-furnace hats. The Big wedge Mold (a) was a 4 by 4 by 4-in. split copper mold, yielding a wedge-shaped casting I in. wide, 1 1/2 in. long, and 34 in. maximum thickness, and was finally adopted as the most satisfactory design.