Trial Addition of Inoculants to the Steel Stream during Bottom-Pouring

Abstract

Out-of-furnace treatment methods are successfully being used to perform several operations involved in the finishing of steel ‐ finalizing its chemical composition, reducing the content of harmful impurities, and alleviating the contamination of the steel by nonmetallic inclusions. However, secondary oxidation can significantly reduce the effectiveness of these measures when they are performed in the ladle and the steel is then bottom-poured into ingot molds. According to theoretical and practical findings [1‐3], inoculation and microalloying should be performed on steel that has been desulfurized as much as possible and has been thoroughly deoxidized with conventional deoxidizers (manganese, silicon, aluminum). The readily oxidized elements (magnesium, calcium, rare-earth elements) that are used as complex master alloys for inoculation should be added as late as possible due to their oxidation by the covering slag and atmospheric air. Work on introducing additives to steel during its casting was begun as far back as the 1960s by Chelyabinsk Metallurgical Combine in concert with the Scientific Research Institute of Metallurgy (NIIM). This collaboration led to the development of a technology for obtaining lead-bearing steel for the Volga Automobile Factory [1]. We developed the Modinar technology (inoculation of steel for casting) [4], which provides for the introduction of master alloys based on readily oxidized elements (calcium, magnesium, barium, rare-earth elements, aluminum) to the stream during casting. This significantly improved the effectiveness of the additives because they were introduced immediately before the steel solidifies. Such a treatment not only realized more extensive “chemical” action (the nonmetallic inclusions had the more desirable globular form) but also a greater “physical” effect, which was related to changes in the conditions of solidification of the ingot. For example, the solid metallic particles of the modifier that are introduced into the liquid melt have an inoculating effect on the steel. The pipe in the inoculated ingots was formed compactly, without underlying cavities or axial porosity. This made it possible to increase useable output from the deformation of the ingot. Batchers can be used to organize work on the basis of the Modinar method [5, 6]. An apparatus that we developed to feed inoculants is easy to build and use. The dimensions of the unit depend on the capacity of the discharge hopper and the size of the heat being cast ‐ (400‐500) 〈 (400‐600) 〈 (1200‐1500) mm. The batcher is either suspended on a ladle, mounted on a hot-steel car, or moved along the pouring platform on a monorail. A feed pipe secured to the batcher is moved to the location where the steel stream leaves the ladle. No system of conduits (to deliver electric power or compressed air) is needed for the inoculation process, and the operation itself is easily managed by service personnel. Steel was treated with the use of finely crushed (1‐20 mm fraction) materials or “chips” ‐ (5‐20) 〈 (5‐20) mm disks 2‐3 mm thick obtained on a special unit by quenching a liquid melt. The composition of the inoculating alloy was 0.8‐1.2 kg/ton steel. Alloying and inoculating steel with highly active and readily volatilized elements during ingot-mold filling was tried out in the production of different steels. Structural Steels 20 and 45. This work was done at NOSTA together with NIIM. 1 A liquid melt of steel 20 containing 0.024‐0.026% S was obtained in a 100-ton electric furnace and bottom-poured into square 6.2‐ton ingots. Samples