Ladislav Lazić

METALLURGY ON THE TERRITORY OF REPUBLIC CROATIA

Prof. dr. sc. Ladislav Lazić, Faculty of Metallurgy, University of Zagreb, Sisak, Croatia,

A BRIEF HISTORICAL OVERVIEW OF THE DEVELOPMENT OF METALLURGY

Metallurgy in the territory of today's Sisak and Banovina, as a region of Sisak-Moslavina County, was developed from Vučedol as well as Celtic and Roman culture. The manufacturing of basic metals and metal products has a long tradition in Sisak. Since Halstatt period onwards today's Sisak has continually been settled and, in all historic periods, has been closely connected with the production of iron and iron products as its most important industrial branch.Solid traces of an Illyrian settlement, dating from the Halstatt period, can be found in Sisak on the position called Pogorelec, on the right-bank of the Kupa (around 800 BC). In the Mt. Trgovi area the numerous craters and slag heaps witness about intensive mining activity in search of iron and silver-bearing lead ores already in Illyrian times.

On the position of the former Halstatt settlement on the right bank of the Kupa, the Celts founded Segestica, the most important settlement of that time in the southern Pannonia. This center is actually the continuation of the already established relations with the mines and iron production from the previous period.

Large geological formations of iron ore are located in this region, more precisely on the Mount Trgovi (Trgovska gora), the western spur of the Mount Zrinj (Zrinska gora), both in Croatia, and south of the river Una on the Mountain Majdan (Majdanska planina; majdan, the Arabic word for mine) in northwestern Bosnia (Fig. 1). Apart from the iron ore, mainly limonite, there are deposits of silver-bearing lead ore, as well as copper ore.

Figure 1. Position of Trgovska gora

The Roman conquest of Pannonia began from the year 35 BC. Oktavian August destroyed the Celtic settlement Segestica and very soon a new settlement Siscia was established on the left-bank of the river Kupa, more precisely between the flows of the Kupa and the Sava.

When, the Romans took over the already established Celtic exploitation and manufacture of iron at Mt. Trgovi, some forty kilometers to the south of former Segestica, they also, whence defeated and Maezeans, integrated the iron mines located on the Maezean territory, some twenty kilometers southward at Mountain Majdan. Roman mines, slag accumulations and settlements in the northeastern Bosnia, concentrated around the Mountain Majdan (covering an area of 1200 km2) confirm that. The quantities of the Roman age slag found in Blagaj and Maslovare near the river Japra amount to 2 million tons containing 50% of iron.

In Roman times, Sisak (Siscia) and its wider surroundings become one of the largest metallurgical centres of the whole empire with metallurgical workshops for making arms and tools, and mints. There were established the water and road communications for delivery of pig iron in the form of forged pieces as well as dispatch of finished products.

The greatest part of the processed iron ore ended up or at least passed through Siscia in the form of forged pieces. Part of it travelled by diagonal land routes, from Japra to Sisak via Osječenica (about 60 km), but the greatest part was transported by rivers: the Sana, Japra and Una downstream and the Sava and the Kupa (4 kilometers) upstream - totally 220 kilometers. Blacksmith workshops for the production of iron products were distributed all along this route, which can best be supported by a find of 97 forged pieces, in the form of semi-finished products (Fig. 2), 4 kilometres downstream of Hrvatska Dubica. They were found in 1880 and 28 of them are kept today in the Archaeological Museum in Zagreb.

Figure 2. Iron forged pieces found out in the area of Hrvatska Dubica

After the fall of the Roman Empire the metallurgical activity dies out to be renewed at the end of 10th century upon arrival of the Saxons. In the Middle Ages, together with opening the mines of iron, silver-bearing lead ore and copper ore, the first coin foundry and mint were establish by the Count Petar Zrinski on the territory of Banovina. With penetration of the Turks these mining and metallurgical activities die out to revive again in 18th century with building up the copper foundries and the stone-blast furnaces for production of pig iron.

Stone blast furnace in Bešlinac

Stone blast furnace in Vranovina

After the Second World War in the area of the Mt. Zrinj and Mt. Trgovi the metal ore mining and metallurgical production ceased.

"Sisak Ironworks"Prominent pre war metallurgist ing. Milivoj Tomac also worked in Bešlinac for two years. He was meritorious for building the first modern blast furnace in Croatia. In fact, in the late thirties of the last century the production of steel in Europe was rapidly increased, primarily because of intensive preparation of fascist forces for war. This is partly reflected in Croatia, which facilitated the achievement of ing. Miroslav Tomac’s long time idea - the construction of blast furnaces under his own design. Ing. Tomac could not independently achieve this idea because of financial reasons. Therefore, on his incentive was established the Mining Association - Melting Plant Caprag. Chosen location was based on four essential factors: nearness of the ore deposits, convenient possibility of coke delivery as well as dispatch of finished product and available workforce. Building-up of the melting plant began in the mid-1938 and the blast furnace was celebratory started-up on 20th August 1939. Particularly it should be emphasized that the blast furnace, although of a low capacity, was originally designed and built with welded shell, which provoked interest and foreign experts. Afterwards the same technique was applied in other countries. Initial production of the melting plant was about 40 tons a day. Blast furnace in Caprag in 1939 can be considered as the first metallurgical plants on the territory of today’s Croatia, in the industrial sense of the word.

In 1950 Željezara Sisak/ Sisak Ironworks commenced the production of seamless steel tubes and castings. In the period until 1990 "Sisak Ironworks" was the only manufacturer of seamless pipes among 34 countries in the world, with an annual production of about 150.000 t, an important manufacturer of welded pipes of over 200.000 t per year and cold processing pipes (drawing, pilgering) of about 10.000 t per year. Steel production with 2 Siemens-Martin furnaces and 1 electric arc furnace together with 2 blast furnace of 150 m3 was about 360.000 t per year. Up to 850.000 t coke per year was produced in Coke Plant Bakar.

Production development has been accompanied by the establishment of the institution of higher education. Namely, in 1960, the Faculty of Metallurgy was founded in Sisak.

During the Croatian War of Independence (1991-1995) the production was drastically falling. Thus, e.g. in 1994 the production of welded pipes was about 28.000 t/year, seamless pipes below 70.000 t/year and cold processing pipes about 2.000 t/year. Afterwards the Coke Plant Bakar, both blast furnaces with agglomeration, both SM furnaces as well as the strip and billet rolling mill with 2 pusher type reheating furnaces were dismantled.

After two unsuccessful privatization process (Truboimpeks, Mechel) the basic metals industry in "Sisak Ironworks" was owned by CMC SISAK d.o.o., Sisak. Annual steel production was at the level of about 18.500 t seamless pipes, 16.000 t welded pipes and 2.000 t cold processed pipes.

Today's owner of steelmaking in Sisak is Italian company A.B.S. Sisak d.o.o. They have electric steelmaking technology with continuous casting of round products from 210 mm to 410 mm and billets 160x160 and 170x170 mm. The furnace has capacity of 75 t of steel scrap.

Željezara Split (Steelworks Split) was specialized in production of rolled reinforcing steel. On two electric furnaces the steel production was up to 120,000 t per year. Up to 80.000 tons of steel per year was processed in the hot rolling mill and to almost 30.000 t in the cold rolling mill. The steel plant was reconstructed in the following way: one electric furnace with the ladle furnace of capacity up to 190.000 t per year and the rolling mill with equal capacity. However, production has been suspended for a long period.

A.B.S. Sisak d.o.o. has the contemporary process route: primary steelmaking in the electric arc furnace, after that, removal of oxygen as well as subsequent adjustment of composition and temperature in a vessel (ladle furnace) beyond the primary steelmaking furnace (so-called the secondary metallurgy or ladle metallurgy steelmaking), and vacuum process for degassing operations, i.e. removing dissolved gasses from the melt.

The operations of secondary metallurgy, carried out in a vessel beyond the primary steelmaking furnace, increase the economics and maximize the productivity of steelmaking. Composition and cleanliness control invariable follow primary steelmaking owing to the increased demand of a diverse range of high-quality steels. Downstream continuous casting process operations demand stringent control of composition, cleanliness, and temperature. The total duration of secondary steelmaking (i.e. deoxidation, alloying, heating, degassing, etc.) operations is long and often exceeds that of primary steelmaking.

Despite being a modern plant for the production of high quality steel, there are many opportunities to improve existing technological processes that could be achieved with scientific research projects in cooperation of scientific educational institutions and the steelmakers.

Modeling in steelmaking process analysis, design, optimization, and control

Higher productivity and superior product quality are interlinked with efficient process control. Because of that, the development of an adequate measuring devices and an increasing of process models for effective control and automation technology in steelmaking have special importance.

Modelling is a well-established scientific technique with demonstrated capabilities and finds widespread application in engineering process analysis, design, control, and optimization.

Physical modelling - The key objective in physical modelling is to measure and visualize one or many characteristics of the real system, rather inexpensive and conveniently. Obtained results can be applied to validate a mathematical model.

Mathematical modelling

A mathematical model is a set of equations, algebraic or differential, which may be used to represent and predict certain phenomena. As the steelmaking is a complex process which involves multiphase turbulent flow, heat and mass transfer as well as chemical reactions among slag, metal, gas, and solid, numerical idealizations are applied to formulate reasonable realistic process models in steelmaking. Mathematical modelling offers many advantages: low cost, remarkable speed, simulation of real conditions, complete information, etc.

Various types of mathematical models are applied in steelmaking process analysis, design, optimization, and control:

• Computational fluid dynamics based models for simulation of reacting turbulent flows and transport• Artificial intelligence based models (neural network models) for process control and optimization • Thermodynamic models for equilibrium calculations• Reduced order models for automation and control, which are already applied in practice.

Process analysis and optimization involve mathematical modelling primarily in an off-line fashion. In contrast, process control requires modelling and prediction in real time. Models in category 1 are in general far too complex and therefore, not suited for real time applications in steelmaking process control. Online control requires simpler models and in such context, reduced order models have made in the practice.

Electric arc furnace

A.B.S. Sisak d.o.o. has the electric arc furnace with three supplemental burners mounted in the sidewalls. In addition to productivity improvements of 5% to 20%, the burners provide economical energy for melting scrap at low cost. An efficient oxy/fuel practice typically supplies 25% of the total energy required to melt the steel. This may be higher or lower, depending on the desired results and characteristics of the furnace and operation in question. The many opportunities exists in varying the power of electricity and burners during the melting process in order to reduce the overall fuel consumption (electricity and natural gas), melting time, and consumption of refractory and electrodes.

Ladle preheating

The ladle heating parameters significantly affect the metallurgical processes and there are four primary reasons for preheating ladles prior to pouring molten metal into them:

1.To minimize the cooling effect on the molten metal2.To minimize the thermal shock on the refractory3.To remove any moisture that may have accumulated in the vessel4.The benefits of ladle preheating include increased ladle lining life, lower refractory maintenance costs, and increased productivity and quality in casting due to more consistent melt temperatures.

The issue of proper conducting the process of drying and heating the ladle lining has received a special importance with the development of ladle metallurgy and the dissemination of continuous steel casting. Requirements of ladle drying and heating are different, but these processes have a major impact to its durability, reliability and the quality of the castings. The drying requires a very slow and uniform heating with controlled velocity and dependent on the lining and the capacity of the ladle. Usually a ladle lining is composed of two layers - insulation and operating. The appropriate temperature conditions have to be required depending on the type of lining.

Today’s refractories and steelmaking processes often require ladle preheated temperatures above 1100°C, which can be difficult to obtained with conventional air/fuel burners. There is a possibility to replace the existing system with advanced commercially available combustion technologies such as High Temperature Air Combustion (HiTAC) or Flameless Oxy-Fuel Combustion. This type of burner, equipped with full automation and flame detection, ensures safe operation and precise control of the temperature distribution during the heating process.

In comparison with the existing conventional air/fuel burners, the ladle preheating with one of the advanced combustion technologies, for example with automatic self-recuperative burner, has the following benefits:

• faster heating - depending only on the technology• reducing the natural gas consumption up to 35%• possibility of increasing the ladle heating temperature of around 250 - 400°C• uniform surface temperature distribution (differences between the measured points not exceed 10°C) • radical reduction in CO and NOx emissions • increasing the durability of the ladle linings

Environmental aspects

were and have been a serious challenge for steelmakers. Large volume of gasses and dust are generated during various stages of steelmaking. Efficient gas cleaning plants or dedusitng system are required to clean off-gases, to be practically free of dust and sulphur. Dust and slag, etc. are valuable by-products of the steel plants that can help conserve energy and natural resources in an effective manner and therefore require serious considerations. Similarly, human involvement in risk-prone area and hazardous environment should be as little as possible.

Apart from the producers of steel, Metallurgical faculty have cooperation with a number of metal processing companies in Croatia, providing them various technical and research services.