Large Inclusions in Plain-carbon Steel Ingots Cast by Bottom Teeming

Abstract

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...

Nucleation, Growth, Transport, and Entrapment of Inclusions During Steel Casting

“…Solid inclusions can agglomerate on any surface with favorable surface tension effects, including refractory walls. 22 Clogs forming on the surface of the nozzle wall can change the flow pattern or dislodge, 22 causing defects such as TiN clusters in continuous cast Ti-stabilized stainless steel (Fig. 3d 23 ).…”

State of the art in the control of inclusions during steel ingot casting

“…[73] These inclusions are normally small (,10 mm), [47] but may form large clusters. [74] An example of sulfide inclusions (MnS) in an ingot is shown in Figure 10.…”

“…[30] Zhang et al estimated the threedimensional size distribution of both indigenous and exogenous inclusions by converting the two-dimensional microscope observations at many different locations into three dimensions. [74] This converting method assumes that the diameter of inclusions under the two-dimensional microscope observation is the same as that of the real threedimensional inclusions, and the number of inclusions observed by the two-dimensional microscope is the same number of inclusions in a volume of sample section area multiplied by the inclusion diameter as thickness. The difference between these measurements was partially due to the different bin size used.…”

“…Only a few size distributions of inclusions in steel ingots were reported, and these data are summarized in Figure 13. [74,30,77] Inclusions in this figure include both indigenous and exogenous inclusions. [7] Fig.…”

Simulation of fluid flow and solididification in the funnel type crystalizer of thin slab continuous cast

“…On the other hand, increasing the submergence depth and contact of the fluid from lower nozzle port to the lower part of the solidified shell can cause the breakout. In contrary, at the top surface the flow field is weaker and meniscus is more likely to solidify, giving a chance for the formation of defects like blisters and oscillation mark on the surface of the slabs and rolling products [21][22][23][24]. The steel jets traverse the liquid pool to impinge against the narrow faces, splitting into two flows along the narrow face.…”