Štore, Slovenia
Štore, Slovenia

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Vrbek K.,Store Steel | Lamut J.,University of Ljubljana | Marolt M.,Store Steel | Knap M.,University of Ljubljana
Archives of Metallurgy and Materials | Year: 2015

Štore Steel produces steel grades for spring, forging and engineering industry applications. Steelmaking technology consists of scrap melting in Electric Arc Furnace (EAF), secondary metallurgy in Ladle Furnace (LF) and continuous casting of billets (CC). Hydrogen content during steelmaking of various steel grades and steelmaking technologies was measured. Samples of steel melt from EAF, LF and CC were collected and investigated. Sampling from Electric Arc Furnace and Ladle Furnace was carried out using vacuum pin tubes. Regular measurements of hydrogen content in steel melt were made using Hydris device. Hydrogen content results measured in tundish by Hydris device were compared with results from pin tube samples. Based on the measurement results it was established that hydrogen content during steelmaking increases. The highest values were determined in tundish during casting. Factors that influence the hydrogen content in liquid steel the most were steelmaking technology and alloying elements.

Drofelnik N.,Store Steel | Marolt M.,Store Steel
Archives of Metallurgy and Materials | Year: 2015

In Štore Steel steelworks steel is casted on a three strand continuous casting machine. Lining of tundish is mainly made from a magnesia based material. Tundish cover powder is based on alumina and silica. It also contains aluminum and carbon. During casting, the composition of cover slag is constantly changing. When steel in casted in sequences the change in cover slag composition depends on the amount of CaO rich ladle slag. The composition of tundish cover slag at the end of the casting sequence lies in the area of gehlenite (2CaO·Al2O3·SiO2) in ternary phase diagram CaO·Al2O3·SiO2. The result of the reaction between melted steel, refractory material and tundish cover slag are enstatite (MgO·SiO2) and monticellite (CaO·MgO·SiO2). Merwinite (3CaO·MgO·SiO2) is formed in the end of the casting sequence because of high basicity of the gehlenite based tundish cover slag. Clogging on the inner side of submerged entry nozzles (SEN) are made of calcium aluminates (CaO·2Al2O3) and spinel (MgO, MnO)·Al2O3. Only when steel is casted in sequence composition changes in tundish cover slag and clogging occurs.

Krajnc L.,Store Steel | Mrvar P.,University of Ljubljana | Medved J.,University of Ljubljana
Materiali in Tehnologije | Year: 2014

Non-metallic inclusion engineering is one of the most important aspects in steelmaking today. There are several thermodynamic and kinetic tools available that help to form non-metallic inclusions of the desired size, distribution and composition in steel. The goal of this work was to study the thermodynamic conditions responsible for the formation of multiphase inclusions in re-sulphurised steel grades that are produced for the automotive industry. Nozzle clogging on the continuous casting machine and surface defects on rolled rods are problems typically attributed to non-metallic inclusions. Samples of the 30MnVS6 steel grade were taken at five different stages of ladle treatment. The samples were prepared for metallography and images of inclusions were taken using a SEM. Thermodynamic calculations were made using the Thermo-calc software for each sample and for multiple inclusions in order to determine which phases are the most stable at a given stage of the ladle treatment. It was found that high-melting-point calcium sulphide (CaS) and spinel (MgO·Al2O3) inclusions and low-melting-point calcium aluminate (12CaO·7Al2O3) or calcium alumosilicate (2CaO·Al2O3·SiO2) inclusions are the most stable phases in current steelmaking practice.

Kovacic M.,Store Steel | Jager R.,University of Nova Gorica
Materiali in Tehnologije | Year: 2015

Carbon steel C45 with an increased content of carbon is used for tempering in the automotive industry for highly stressed parts (axles, shafts), machine parts, screws, drills for wood, axes, knives, hammers and similar. In the present work an attempt of analyzing the influences of different steelmaking parameters is presented. On the basis of the monitored data about the casting-temperature changes, the total oxygen, the number of added aluminum rods, the chemical analyses before and after steelmaking, the added lime, the aluminum-cored wire, the calcium-silicon-cored wire, the sulphur-cored wire, the rolling dimensions, the casting speed, the opening of the ladle nozzle with oxygen and surface defects (scrap fraction) on rolled bars, a mathematical model was obtained with the help of the genetic programming method. The results show that the most influential parameters for the surface-defect occurrence on the C45 steel are the opening of the ladle nozzle with oxygen and aluminum. On the basis of the results, the steelmaking technology was changed. Instead of the aluminium-killed steelmaking technology the aluminium-calcium-free (ACF) steelmaking technology was used. The batches from an aluminium-calcium-free steelmaking period statistically have a significantly lower level of surface defects (scrap fraction). The scrap fraction was reduced from the average of 68.45 % to 1.92 % - by more than 35 times.

Mramor K.,COBIK | Vertnik R.,Store Steel | Vertnik R.,University of Nova Gorica | Sarler B.,COBIK | And 2 more authors.
Computers, Materials and Continua | Year: 2013

This paper explores the application of Local Radial Basis Function Collocation Method (LRBFCM) [Šarler and Vertnik (2006)] for solution of Newtonian incompressible 2D fluid flow for a lid driven cavity problem [Ghia, Ghia, and Shin (1982)] in primitive variables. The involved velocity and pressure fields are represented on overlapping five-noded sub-domains through collocation by using Radial Basis Functions (RBF). The required first and second derivatives of the fields are calculated from the respective derivatives of the RBF's. The momentum equation is solved through explicit time stepping. The method is alternatively structured with multiquadrics and inverse multiquadrics RBF's. In addition, two different approaches are used for pressure velocity coupling (Fractional Step Method (FSM) [Chorin (1968)] and Artificial Compressibility Method (ACM) [Chorin (1967)] with Characteristic Based Split (CBS) [Zienkiewicz and Codina (1995); Zienkiewicz, Morgan, Sai, Codina and Vasquez (1995)]). The method is tested for several low and intermediate Reynolds numbers (100, 400, 1000 and 3200) and node arrangements (41x41, 81x81, 101x101, 129x129). The original contribution of the paper represents extension of the LRBFCM to Reynolds number beyond 400 and assessment of the method for two different types of RBFs and two different types of pressure-velocity couplings. The obtained numerical results, in terms of mid-plane velocities, are in a good agreement with the data calculated in several reference publications and by commercial code. Both RBF's used give approximately the same results. Both pressure-velocity coupling methods give approximately the same results, however the FSM turns out to be slightly more efficient. The advantages of the method are simplicity, accuracy and straightforward applicability in non-uniform node arrangements. Copyright © 2013 Tech Science Press.

Kovacic M.,Store Steel | Kovacic M.,University of Nova Gorica | Jurjovec B.,Store Steel | Krajnc L.,Store Steel
Materiali in Tehnologije | Year: 2014

Štore Steel Ltd. faces a huge problem with the ladle nozzle opening during the production of a wide variety of steel grades. After a ladle treatment the steel melt is poured from the ladle through the sliding gate and the nozzle into the tundish on the continuous casting machine. Due to frequent clogging the ladle nozzle must be opened with oxygen which can cause melt pollution. The purpose of this paper is to present an attempt to reduce ladle-nozzle openings. In this attempt the genetic-programming method was used. The experimental data on 115 consecutively cast heats was used. The steelmaking-technology number, the batch sequence number, the time spend for secondary metallurgy, the sustainability of the upper-nozzle brick, the sustainability of the nozzle seating block, the sustainability of the lower-nozzle brick, the ladle number, the sustainability of the ladle and of the foreman of secondary metallurgy and the melt chemical composition (Al, C, Mn and Si) were taken into account for the prediction of the ladle-nozzle opening. The best genetically developed model for the ladle-nozzle-opening prediction correctly predicts 107 out of 115 situations of opening the ladle. The results of the genetic-programming-based modeling have been used in practice to change several steelmaking technologies.

Sencic B.,Store Steel | Leskovsek V.,Slovenian Institute of Metals And Technology
Materiali in Tehnologije | Year: 2011

In the work the possibilities of the vacuum heat treatment of spring steel grade 51CrV4 are presented. Charpy-V notch (CVN) impact-test values are widely used in toughness specifications for spring steels, even though the fracturing energy is not directly related to the spring design. The plain-strain stress-intensity factor (K Ic) at the onset of unstable crack growth can be related to the spring design; however, K Ic values are not used in the toughness specifications. This is surprising since to the designer K Ic values are more useful than CVN values, because the design calculations for springs from high-strength steels should also take into account the strength and the toughness of materials to prevent rapid and brittle fracture. An investigation was conducted to determine whether standardized fracture-toughness testing (ASTM E399-90), which is difficult to perform reliably for hard and low ductility materials, could be replaced with a non-standard testing method using circumferentially notched and fatigue-precracked tensile specimens. The results of this investigation have shown that using the proposed method it was possible to draw, for the normally used range of working hardness, combined tempering diagrams (Rockwell-C hardness -Fracture toughness K Ic - Tempering temperature) for the vacuum-heat-treated spring steel grade 51CrV4. Fractographic and metallographic analyses of the K Ic-test specimens used shows in steel the presence of positive and negative segregations. It was found that the width of the segregations bands and the distance between the positive and negative segregations influence significantly the fracture toughness due to the presence of bainite in the negative segregations.

Kovacic M.,STORE STEEL | Sarler B.,University of Nova Gorica
Materiali in Tehnologije | Year: 2012

Štore Steel Ltd faces a problem of producing a large number (approximately 1400) of different steel compositions in relatively small quantities (approximately 15 t). This production is performed in batches of predetermined quantities (50-53 t). The purpose of this paper is to present a methodology for optimizing the production of predetermined steel grades in predetermined quantities before the customers' deadline and in such a way as to reduce the non-planned and ordered quantities with the date before the deadline and minimize the number of batches. The particle-swarm method was used for the optimization. The results of the research have been used in practice since 2006. Since then the production of non-planned and ordered quantities were reduced from 17.17 % to 10.12 %.

Kovacic M.,STORE STEEL | Sencic S.,KOVA
Materiali in Tehnologije | Year: 2012

To implement sound air-quality policies, regulatory agencies require tools to evaluate the outcomes and costs associated with various emission-reduction strategies. However, the applicability of such tools can also remain uncertain. It is furthermore known that source-receptor models cannot be implemented through deterministic modeling. The article presents an attempt of PM10 emission modeling carried close to a steel production area with the genetic programming method. The daily PM10 concentrations, daily rolling mill and steel plant production, meteorological data (wind speed and direction - hourly average, air temperature - hourly average and rainfall - daily average), weekday and month number were used for modeling during a monitoring campaign of almost half a year (23. 6. 2010 to 12. 12. 2010). The genetic programming modeling results show good agreement with measured daily PM10 concentrations. In future we will carry out genetic programming based dispersion modeling according to the calculated wind field, air temperature, humidity and rainfall in a 3D Cartesian coordinate system. The prospects for arriving at a robust and faster alternative to the well-known Lagrangian and Gaussian dispersion models are optimistic.

Mramor K.,COBIK | Vertnik R.,Store Steel | Sarler B.,COBIK | Sarler B.,IMT Inc
CMES - Computer Modeling in Engineering and Sciences | Year: 2013

The purpose of the present paper is to extend and explore the application of a novel meshless Local Radial Basis Function Collocation Method (LRBFCM) in solution of a steady, laminar, natural convection flow, influenced by magnetic field. The problem is defined by coupled mass, momentum, energy and induction equations that are solved in two dimensions by using local collocation with multiquadrics radial basis functions on an overlapping five nodded subdomains and explicit time-stepping. The fractional step method is used to couple the pressure and velocity fields. The considered problem is calculated in a square cavity with two insulated horizontal and two differentially heated vertical walls with magnetic field applied in the horizontal direction. Numerical predictions are calculated for different Grashof numbers, ranging from 10 4 to 106, and Hartman numbers, ranging from 0 to 100, at Prandtl numbers 0.71 and 0.14. The results of the method are compared to predictions, obtained by other numerical methods, including FLUENT [Fluent (2003)]. Good agreement has been achieved. The LRBFCM has been used in this kind of problems for the first time. The main advantage of the method is its simple numerical implementation and no need for polygonisation. Copyright © 2013 Tech Science Press.

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