Inclusions in industrial-cast bottom-teemed ingots of plain carbon steel are investigated using ultrasonic detection, optical microscope observation, and SEM analysis. The composition, size distribution, entrapment locations, and sources of ingot inclusions were revealed by examining all the macro-inclusions (larger than 20 mm) that were observed in 35 000 mm 2 of sample surface area. Based on 78 non-sulfide inclusions observed, around 3.23ϫ10 7 macro-inclusions per m 3 steel exist in the ingot, with a size distribution increasing with decreasing size. Inclusions are distributed uniformly within a given horizontal section through the ingot, but with more found towards the bottom. The largest inclusions exceed 7 mm and originate from mold flux in the ingot. The largest inclusion source appears to be reoxidation, as evidenced by 59% of the ingot inclusions composed of pure alumina clusters and lumps. Eroded refractories from the ladle well block and ladle inner nozzle bricks accounted for 31% of the ingot inclusions.KEY WORDS: steel ingot; inclusions; mold flux; alumina; exogenous inclusions.portion, due to the mechanism of positive segregation.29) It should be noticed that most of these papers on inclusions in steel ingots were published before 1990s, and very few are published in recent 15 years.This current work is part of a larger project to investigate inclusions in bottom-teemed steel ingots by combining computational models and plant experiments conducted at member companies of the Ingot Metallurgy Forum. A survey with responses from six steel ingot producers in the US revealed that the total annual tonnage of bottom-poured ingots where cleanliness is a concern is at least 700 000 tons. Rejections at these companies due to inclusion defects range from 0.2-5 % with a cost of $900-3 600/tonne (depending on grade). This corresponds to $10 million per year (assuming a typical rejection rate of 1 % at $1 500/ ton). From the survey replies, 10-25 % of defects sources are estimated to be related to ladle sand/packing sand entrapment, 25-50 from mold flux entrainment, 0-5 % from runner erosion, and 0-35 % related to other exogenous inclusion sources. In addition to the above exogenous inclusion sources, the companies estimated that 0-15 % of their defects were from alumina inclusions (deoxidation products), 0-20 % from air absorption, 0-5 % from reoxidation reactions with slag and refractory, and 0-10 % from unknown sources. Clearly, exogenous defects are the greatest problem. The actual amount and nature of these inclusion sources is investigated in the present work, based on industrial trials conducted at Ellwood Quality Steels Co. Process Description and MethodologyThis work investigates large inclusions measured in a bottom-teemed ingot of 1022 carbon steel, with a composition (ladle analysis) shown in Table 1.The ingot production process of concern is shown Fig. 1 and is described as follows:Step 1: Scrap is loaded into clam-shell buckets and charged into an ultra high powered (UHP) eccentric bottom tapping (E...
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