OAO NLMK Research Articles

Benefits and Risks of High-Intensity Blast-Furnace Operation

More intense blast-furnace operation at OAO NLMK has been made possible by improvement in quality of the coke and the iron-ore products, increase in pressure below the charge hole, and oxygen enrichment of the blast. That increases the rate of indirect wustite reduction and decreases the heat losses to the cooling water. However, high intensity also significantly increases the risks of accidents in batch admission. Besides change in quality of the batch components, the disruptions in batch descent may be due to change in the ore distribution over the furnace radius. A new diagnostic method has been developed to identify the factors responsible for such disruptions. Simulation permits analysis of the influence of change in the ore load and the size of the iron-ore products on the temperature change of the peripheral gases and the utilization of the carbon monoxide. The method is based on analysis of the total change in gas temperature and the utilization of the carbon monoxide in the peripheral region. On that basis, the factors responsible for the change in the pressure difference over the furnace height may be identified. Analysis of the dynamics of the pressure differences over the furnace height permits judgments regarding the probability of disruptions in batch delivery. The possibility of decreasing the pressure difference by redistribution of the ore over the furnace radius and decreasing the quantity of gas is assessed. Various methods of decreasing the quantity of gas are accompanied by changes in the coke consumption and furnace productivity. A mathematical model has been developed for the selection of the best combination of blast adjustments for specific conditions.

Production of new isotropic electrical steels at OAO NLMK

Specialists at OAO NLMK, in close collaboration with research institutes, have developed new grades of isotropic electrical steels and practical principles for their mass production, especially for use in high-efficiency magnetic cores. These include steels with low magnetic losses, high magnetic induction, and high magnetic permeability (high-permeability steel); semiprocessed rolled products from several alloying groups; and steel for high-speed stamping. The proposed technologies have no counterparts anywhere in the world and permit complete import substitution.

Pulverized-coal injection at a blast furnace with a conical charging system

The initial experience with pulverized-coal injection in two blast furnaces at OAO NLMK is analyzed. Factors affecting the pulverized-coal combustion in the tuyere are identified. The operational efficiency of the blast furnace with different pulverized-coal flow rates is discussed. Stable pulverized-coal consumption no lower than 135 kg/t has been attained at a blast furnace with a conical charging system; the corresponding furnace productivity is 70–75 t/m2 per day.

Converter production of low-alloy steel with low impurity content at OAO NLMK

The production of low-alloy steel with low impurity content at OAO NLMK is described. Means of limiting the impurity content—to 0.001% S, 0.01% P, and 0.0002% H—are discussed.

Formation of dual-phase structure during cooling on the exit conveyer of the 2000 broad-strip rolling mill at OAO NLMK

The step-by-step development in the production of HDT580X hot-rolled dual-phase steel (according to the EN 10338 standard) by means of the 2000 broad-strip hot-rolling mill at OAO Novolipetskii Metallurgicheskii Kombinat is considered. The analysis is based on theoretical and experimental results regarding topics such as the influence of alloying elements and the cooling parameters on structural and phase transformations in dual-phase steel for the auto industry. Physical modeling of the deformational parameters and the rolling and cooling temperatures and speeds on the broad-strip mill also proves helpful. Rolling and cooling rates are proposed for the 140 FGA semicontinuous hot-rolling mill.

Blast-furnace smelting with the production of low-silicon hot metal

Blast-furnace smelting today is organized so as to produce low-silicon hot metal, with subsequent desulfurization. In that case, economical furnace operation is facilitated by the use of low-ash coke characterized by hot strength and low adhesion to the slag melt, as well as stable chemical composition, minimum softening temperature range, and increased melting point of the iron. The production of low-silicon hot metal with <0.5% Si at OAO NLMK is considered.

Improving air-tuyere operation in blast furnaces by means of coatings and sealant

To extend the life of air tuyeres and reduce heat losses through their surfaces, boron-carbide sealant is applied to tuyeres with a sprayed aluminum coating after heat treatment. The influence of the B4C-based sealant on the heat losses is theoretically assessed. The efficiency of the sealant is confirmed by industrial trials at OAO NLMK and by metallographic investigation of samples from used tuyeres.

Improving the batch distribution at OAO NLMK blast furnace 6

The charging programs for a blast furnace with a nonconical charging system are investigated. On that basis, rational charging conditions are developed and tested. Experimental experience indicates more economical furnace operation, on account of the improved batch distribution over the charge hole and the reduced heat losses through the cooling systems.

Improving blast-furnace smelting at OAO NLMK

Smelting of hot metal with reduced silicon content is considered. The use of higher-basicity sinter with increased pellet content in the batch is of interest. Other options considered include the use of a gasoxygen mixer and optimization of product discharge at OAO NLMK.

Resource-control system based on the SAP ERP system

The regeneration and stabilization of Russian manufacturing companies may be judged from the growing interest in enterprise resource planning (ERP). Today, the need to make sound management decisions imposes new requirements on data processing and storage systems. Automation of production at OAO NLMK is based on SAP ERP R/3 software, which integrates all the group’s economic processes. Important characteristics of the SAP ERP system are integration of applications, modular structures, shared data storage, open access, international acceptance, and applicability for any branch of industry.

Reduced iron powder: Manufacturing problems and prospects

The range of raw materials that may be used in the production of reduced iron powder is severely constricted by the strict requirements on its chemical composition and properties. Industrial tests at OAOAvtoVAZ have shown that optimal performance is obtained for iron powder produced from granulated iron oxides supplied by OAO NLMK and also from rolled scale supplied by Il’ich Mariupol Metallurgical Works. Industrial production of reduced iron powder at OAO NLMK is proposed.

Heat-storing screens for broad-strip hot-rolling mills

Heat-trapping systems to moderate the cooling of components on the intermediate roller conveyer of broad-strip hot-rolling mills are considered. In terms of performance, Encomech panels are compared with Russian screens at the 2000 mills of OAO NLMK, OAO Severstal’, and OAO MMK, and also at the 1700 mill of PAO MMK im. Il’icha (Ukraine). Significant benefits of the Russian systems are noted.

Improvement of OAO BKO oxide-carbon refractories

Properties are provided for oxide-carbon refractories produced by OAO BKO, used for lining various zones of steel-pouring ladles and converters. The dynamics of lining life for a OAO NLMK 350-ton converter, executed with refractories produced by OAO BKO, are demonstrated.

Innovations in industrial technologies for producing iron and alloyed iron powder

Results are provided of a study for development of advanced technology and creation of new grades of iron and alloyed powders. It is shown that the production properties of atomized iron powder may be improved significantly and even advanced to a new level of quality using powder additions of iron oxide that is waste from rolled sheet production of OAO Severstal. The desired raw material for producing powder by carbothermal reduction in unmixed layers is OAO NLMK granulated oxide. A whole range of partly alloyed powders is manufactured that makes it possible to expand considerably the range of powder objects for structural and electrical engineering purposes.

Assessing the metallurgical coke produced at OAO NLMK

Up-to-date methods of assessing coal and coke quality have been introduced at OAO NLMK. Industrial coking tests using high-quality Russian and imported coal have been conducted to boost coke quality. Algorithms are proposed for predicting the postreactive strength (CSR) and reactivity (CRI) of coke as a function of the batch characteristics.

Centrifuge treatment of coal tar

New technology is required for the removal of water and heavy fractions from regular coal tar. Centrifuges offer the best option. Purification of coal tar by means of centrifuges at OAO NLMK permits the production of pitch coke or electrode pitch that complies with current standards.

Quality requirements on coke for blast furnaces operating with coal-dust fuel

Analysis of the CSR values of coke corresponding to specific consumption of coal-dust fuel—on the basis of operational data for furnaces in the United States, Canada, Belgium, Germany, France, Italy, Spain, and South Korea—permits the estimation of the mean CSR value of coke required when the coal-dust injection is 120, 130, 150, 180, and 200 kg/t of hot metal. This information is used in the construction of systems based on coal-dust fuel at OAO Severstal, OAO NLMK, OAO NTMK, and OAO ZSMK.

Rational configuration of finishing group and winding unit for a continuous broad-strip mill

7In hot rolling on a continuous broad-strip mill, the final structure and mechanical properties of the strip are mainly formed in the finishing group and the winding unit. A number of factors limit the development of new hot-rolling conditions for low-carbon steel strip on the basis of the austenite recrystallization diagram [1] and optimal metal structure [2]. The chosen conditions are often somewhat nonoptimal on account of the technological, energy, and configurational constraints of the mill. Thus, the equal intercell distances L int in the finishing group of the mill and the actual distance from the last cell of the finishing group to the first section of the sprayer unit L fg-su do not permit the required optimization. For example, for the 2000 mill at OAO NLMK, L int = 6 m and L fg-su = 28 m. Less severe reduction in the first cells of the finishing group (at high temperature and low speed of the strip) in optimizing thick-strip rolling only partially limits the collective growth of the austenite grains in the intervals between the cells, after the end of primary recrystallization. Increasing the reduction in the subsequent cells (at lower temperatures and higher rolling speeds) ensures complete primary recrystallization but there is an upper limit on the rolling force in the penultimate cell. Moreover, in establishing the relative reduction, its critical value must be taken into account ( e < e cr ). In the present work, we develop a rational configuration of the finishing group and winding system for a continuous broad-strip mill, by analysis of the conditions of structure formation in the rolled strip. The completeness of recrystallization of the austenitic structure in eU 3 OO low-carbon steel at the beginning of the next reduction in finishing-group cell ( i + 1) is described by the equation [1]

Operating experience of the working layer of a 350-ton converter in CW-2 of OAO Novolipetsk Metallurgical Combine

Periclase-carbon linings made from objects supplied by OAO Borovichi Refractory Combine have been tested under operating conditions of converter workshop No. 2 at OAO NLMK in 2007-2008. There is comparative analysis of linings and directions for improving refractory composition are determined.

Optimization of complex injection in converters at OAO NLMK

The use of complex injection in converters permits intensification of oxygen injection and steel output and also reduction in the injection time, the oxidation of the intermediate product, the carbon content in the metal after injection, and the total iron content in the slag. In addition, the consumption of reducing agents and ferroalloys is reduced for all steel and the range of steel with carbon and phosphorus content is expanded.