In the article there are presented the results of studies to improve the quality of blast furnace cast iron. It was established that using fire clay suspension for increasing the mould covering heat conductivity improves significantly pig iron salable condition and filtration refining method decreases iron contamination by nonmetallic inclusions by 50 – 70 %

A. Z. Akashev

A. Z. Issagulov

B. D. Issin

B. M. Kimanov

D. K. Issin

T. K. Balgabekov

Zh. D. Zholdubayeva

English

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556  METALURGIJA 53 (2014) 4, 556-558Т. К. BALGABEKOV, D. K. ISSIN, B. M. KIMANOV, A. Z. ISSAGULOV, ZH. D. ZHOLDUBAYEVA, А. Z. AKASHEV, B. D. ISSINSTUDYING AND IMPROVING BLAST FURNACE CAST IRON QUALITYReceived – Prispjelo: 2013-11-09Accepted – Prihvaćeno: 2014-04-30Preliminary Note – Prethodno priopćenjeISSN 0543-5846METABK 53(4) 556-558 (2014)UDC – UDK 669.162.2:669.1:669.13=111Т. K. Balgabekov, D. K. Issin, A. Z. Issagulov, A. Z. Akashev, Zh. D. Zholdubayeva Karaganda State Technical University, Karaganda, Ka-zakhstanB. M. Kimanov, Zh. Abishev Chemical-Metallurgical Institute, Kara-ganda, KazakhstanB. D. Issin, Tomskij politehnicheskij university, Tomsk, RossiaIn the article there are presented the results of studies to improve the quality of blast furnace cast iron. It was estab-lished that using fire clay suspension for increasing the mould covering heat conductivity improves significantly pig iron salable condition and filtration refining method decreases iron contamination by nonmetallic inclusions by 50 – 70 %.Key words: blast furnace, cast iron, fire clay, filter, filtering elementsINTRODUCTIONWith the development of motor transport industry, machine-tool building and other machine building branches there increased the requirements to the quality of blast furnace cast iron. With the use in the cupola mixture of cast iron melted in large-volume furnaces with the melting progressive parameters, at machine building plants there became often defective castings with shrinkage defects, friability, cracks.To increase the quality of blast furnace cast iron there were carried out scientific-research works. Pig cast iron, under the condition of observing the melting parameters and pouring, was obtained with high carbon content, rough surface with graphite-and-slag clusters on it. In large-crystal bright fracture of pigs there were voids, blisters filled with graphite kish.To increase heat conductivity of mould coverings in the lime solution there were added carbon-containing additives: graphite, coal charge of coke-chemical pro-duction of 3 – 0 mm grade, coke breeze of 1 – 0 mm fraction, thin-milled coal powder of 0,2 – 0,00 mm grade after processing in the ball mill. The best results were obtained with the addition in the lime of graphite solution, but its deficit and high cost limit its use. How-ever, hydration water and underburning of lime lumps cannot be eliminated when preserving the lime cover-ing. For this purpose lime solution was completely re-placed by the suspension of unburnt fire clay.The fire clay suspension with density 1,13 – 1,15 g/сm3 waters moulds well, possesses sufficient refractori-ness and its protective layer on the mould does not prac-tically contain water after mould drying with coke gas. Therefore, pig iron salable condition improves signifi-cantly.Besides, the use of fire clay for mould coverings ex-cludes claps in dissolution and prevents the lime solu-tion corroding action when split on the open parts of the worker’s body, increases the culture of production and decreases labor intensity when making solution, as there is excluded the waste presence up to 30 – 40 % in the form of underburning with the use of lime. The weight clay rate is 1,5 – 1,7 decreased as compared with lime.Starting from the fact that with iron temperature de-creasing the carbon solubility reduces, there were car-ried out experiments for artificial decreasing liquid iron temperature in ladles by the way of smelting in them unlettered iron scrape. In the iron-transporting ladle of 100 t volume there were loaded 5 t of preliminarily heated scrape, then the ladle was filled with iron. At present alongside with the abovementioned meth-ods for the product quality improving there is more widely used the filtration method of refining alloys, mainly based on iron and aluminum. Its essence is in passing metallic melt through a special device (filter) where as a result of physical-chemical, adsorption, me-chanical phenomena there takes place the melt purifica-tion from harmful impurities, inter-metallic compounds, nonmetallic and gas inclusions.Filters used in metallurgy can be structurally divided into two groups: two-dimensional and depth filters. A two-dimensional filter is a grid (a plate) of ceram-ics or glass fiber. At present ceramic grids present a widely used type of filters and are manufactured in a wide range of shapes and sizes. Such filters with the openings diameter ≥ 2 mm purify the metal from large inclusions of exogenous character, but they do not per-mit to decrease the content of fine, thin-dispersed inclu-sions whose size is significantly smaller than the open-ings in the grid.557METALURGIJA 53 (2014) 4, 556-558T. K. BALGABEKOV et al.: STUDYING AND IMPROVING BLAST FURNACE CAST IRON QUALITYnificant increase of the pig density. However, due to the fact that in scrape melting in iron transporting ladles there takes place graphite additional emission, the sur-face of pig iron was respectively obtained more con-taminated with the graphite kish. More efficient and reliable are depth filters (Figure 1). The characteristic feature of such filters (grain, lump) is their large contact surface with metal in the course of filtering and presence of long and thin inter-grain channels of variable section, which causes remov-ing from the melt of both large and fine inclusions [1]. A depth filter presents a layer of filtering material grains of certain size and thickness located in a crucible or a funnel with openings in the bottom part, or a whole block of ceramics. Depending on the ratio of the densi-ties of the filtering material and the melt, the grain (lump) filter is either laid in the funnel [2] or located between two crucibles [3, 4], grids [5, 6] in the funnel for preventing their floating.EXPERIMENTAL STUDIES The results of the experiments for changing liquid iron temperature (Table 1) and its chemical composition (Table 2) are shown below (iron temperature was meas-ured with optical pyrometer). The keeping from the be-ginning of the ladle filling to the beginning of pouring was in the usual range of 40 – 50 minutes. Blast furnace cast iron filtering was carried out in the industrial conditions of JSC “ArcelorMittal Temirtau”. It was performed by the way of passing the melt through a filtering nozzle (Figure 2a) that was assembled in a stand-ard funnel (1) by means of fixing in it two ceramic grids (2 and 4), between which there were located filtering ad-sorbents (3) in the form of granules with diameter 14 – 16 mm. As the material for making granules there was used silica, magnesite and yttrium oxide. In one mould there were obtained two castings with mass of 12 kg for each variant of filtering (Figure 2b).RESULTS AND DISCUSSION The fracture of cooled iron by the way of scape ad-ditive does not differ from uncooled iron with an insig-Figure 1 Filtering section components appearance Table 1  Changing iron temperature when melting scrape in iron transporting ladlesMethod of carrying out experimentIron tem-perature at discharge / °СIron tempera-ture in pouring / °СIron tempera-ture changing / °СWith scrape melting1 430 1 302 128Without scrape melting1 415 1 322 93With scrape melting 1 400 1 230 160Without scrape melting1 400 1 330 70Table 2  Changing iron chemical composition when melting scrape in iron transporting ladles Method of carrying out experimentIron chemical composition / %C Si Mn P SWith scrape melting 4,05 2,71 0,46 0,16 0,03Without scrape melting 4,02 2,47 0,42 0,15 0,03With scrape melting 3,80 2,78 0,45 0,13 0,04Without scrape melting 3,94 2,85 0,45 0,16 0,03а)b)1 – moulding boxes; 2 – ceramic moulds; 3 – funnel with filter; 4 – feeder Figure 2 Diagram of assembled filter (а) and blast furnace iron filtering (b) 558  METALURGIJA 53 (2014) 4, 556-558T. K. BALGABEKOV et al.: STUDYING AND IMPROVING BLAST FURNACE CAST IRON QUALITYCONCLUSIONSAt the considered stages of the study there were im-proved the appearance of pig iron quality: the pigs were obtained with clean surface, there was liquidated the pockmark affection of the pigs bottom surface, the frac-ture on the pig thickened part was more compact.Thus, by implementing the considered measures it can be improved the salable condition of pig iron, to increase the product quality and the efficiency of its manufacturing.LITERATURE[1] Kurdjumov A. V., Inkin S. V., Chulkov V. S. i dr. Fljusova-ja obrabotka i fil’-trovanie aljuminievyh rasplavov. – M.: Metallurgija, 1980. – P. 196.[2]  V. А. Kudrin. Vnepechnaja obrabotka chuguna i stali. – М.: Мetallurgija, 1992. – P. 336.[3]  Kimanov B.M. Fil’tracionnoe rafinirovanie metallicheskih rasplavov. – Karaganda: CNTI. – 2007. – P. 39.[4]  B. M. Kimanov, V. A. Kim, Zh. D. Zholdubaeva. K vopro-su o rafinirovanii metallurgicheskogo kremnija ot primesej // Materialy mezhdunarodnoj nauchno-prakticheskoj kon-ferencii Metallurgicheskij kremnij-2012 »Fiziko-himiche-skie processy i tehnologii poluchenija metallurgicheskogo kremnija«. – Karaganda, HMI. – 2012. – P. 137-138.[5]  Fil’trovanie metalla v litejnoj forme (Sbornik materialov po fil’tram, jeffektivnosti primenenija, opytu ispol’zovani-ja v otechestvennoj i zarubezhnoj praktike). – M.: ITCM Metallurg. – 2005. – P. 221.[6]  Apelian D., Mitharagan R. Filtration f met refining method // Journal of Metals. – 32 (1980) 9, 14-19.Note: The translation of the N. М. Drag, Karaganda, KazakhstanThe most suitable there appeared the method of de-taining graphite, slag and other inclusions in the iron transporting ladle when pouring cast iron on the pour-ing machine. There was developed and introduced a structure of a siphon opening made of refractory brick in the pouring lip of the ladle. When pouring iron from the ladles there was de-tained the emitted graphite, for this a part of iron in the amount of 3 t was necessary to be left in the ladle, as at the full discharging with the last portions of iron there is discharged the arrested graphite.The working practice showed reliability of opera-tion of ladles with siphon devices. Besides, the intro-duction of ladles with such devices permitted to melt iron scrape from the pouring machines and casting bed chutes that usually contains foreign impurities and not to be afraid of graphite emission with increasing the time of keeping iron in the ladles.As a result of filtering refining of blast furnace cast iron the efficiency of filtering was evaluated by the changing of iron chemical composition, mechanical properties and content of nonmetallic inclusions. The results of the chemical analysis show that the extent of sulfur removal depends significantly on the filter mate-rial nature. For example, in iron filtered through silica granules the sulfur content does not practically change as the iron limit tensile strength, and Brinnel’s hardness increases by 20 – 30 %. When filtering the melt through the magnesite filter the sulfur content decreases by 10 – 25 %, hardness does not change. The filtered contam-ination with nonmetallic inclusions, according to the data of metallographic analysis, in all the variants de-creases by 50 – 70 %.

Studying and improving blast furnace cast iron quality

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Studying and improving blast furnace cast iron quality

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