Analysis of State and Possibilities for a Profitable Production of Steel in Croatia Analiza stanja in možnosti za dobičkonosno proizvodnjo jekla na Hrvatskem M. Kundak1, J. Črnko, Metalurški fakultet Sisak, Croatia Prejem rokopisa - received: 1996-10-04; sprejem za objavo - accepted for publication: 1997-01-17 The production and deveiopment of the integrated Sisak Ironvvorks since 1973 are presented. The ironworks participates with 80% in the totai roiling stock production in Croatia. The deveiopment of the world steel production is presented and compared to the circumstances in Croatia. The feasible manufacture level of rolled products in Croatia is shown and discussed considering the low priče steel manufacturing in electric are furnaces. A comparison between the production in electric are furnace and a feasible steel manufacture in existing blast furnaces and converters with enlarged share of steel serap is prepared with the aim to contribute to a better insight into the possibilities of a more profitable steel manufacturing in Croatia. Key words: steel production, state, possibility, Croatia Predstavljeni sta proizvodnja in razvoj integralne železarne Sisak od leta 1973. Železarna Sisak je proizvajala 80 % valjanih izdelkov na Hrvatskem. Razvoj svetovne proizvodnje jekla je primerjan z razmerami na Hrvatskem. Dosegljiva proizvodnja valjanih izdelkov je pripravljena in analizirana z upoštevanjem nizke cene v električnih obtočnih pečeh. Pripravljena je primerjava med proizvodnjo v elektro obtočnih pečeh in proizvodnjo, ki jo je mogoče doseči v obstoječih plavžih in konvertorjih s povečanim deležem jeklenih odpadkov z namenom boljše ocene možnosti za bolj dobičkonosno proizvodnjo jekla na Hrvatskem. Ključne besede: proizvodnja jekla, stanje, možnosti, Hrvatska 1 Introduction The basic deficiency of ferrous metallurgy in Croatia is the unprofitable low priced steels manufacture, which has also prevented the deveiopment of technology. About 20 years ago important improvements took plače in con-verter steel processing, from the inerease in volume of blast furnaces (BFs) and converters, which greatly re-duced the production prices to the recent inerease of the share of serap in converter charge from 25% to 60%. Thts has been achieved by preheating the charge and ad-dition of coke in converters. The basic reason for inereas-ing the share of serap is the cheaper processing in converters than in electric are furnaces (EAFs), particularly small ones. The inereased share of serap, always less ex-pensive than pig iron, permitted to stop small and out of date BFs. EAFs were earlier used for manufacturing of quality steels at acceptable prices. The inereased capacity of EAFs and the introduction of secondary steel processing enabled the manufacturing of low priced steel with acceptable profit because of the greatly inereased pro-ductivity. At present, EAFs melting takes less than one hour, while the further processing is made in ladles. 2 Projection of deveiopment of Sisak Ironworks since 1973 Until 1973 two BFs a with volume of 150 m3 each produced pig iron, which vvas mostly used in open hearth 1 Dne. dr. Mijo KUNDAK Metalurški fakultet Sisak Aleja narodnih heroja 3. 44000 Sisak, Croatia furnaces (OHFs) and less in EAF. After 1973, the volume of both BF was enlarged up to 202 m3 and the production inereased by about 16%. Steel was manufactured in two 145-ton OHFs charged with 50% of molten pig iron and 50% of serap, and in one 30-ton EAF. Parallelly, the processing was intensified by blovving of oxygen, which required the construction of an oxygen plant in 1973. In 1974 and 1975 oxygen blowing equipment vvas installed and the production of steel in OHFs inereased. In 1973 a continuous caster with a capacity of 500000 tpy was put in operation and the size of roiling billets was altered. In 1987 a new sinter plant with a capacity of 550000 tpy was put in operation as well. In the long term projection of steel production started in 1970 the construction of 1200 m3 BF at the seaside, economically correct but ecologically questionable, and one of the same size in Sisak were planned. The coke plant with the capacity of 850000 tpy vvas put in operation in 1978. Since the financial funds for the construction of BF were not disponible, in 1980 the manufacturing of steel in EAFs began to be considered. 3 Deveiopment of world-wide steel technology since 1970 The basic reason for the decrease of OHFs production after 1970 vvas the poor economy when compared to the steel production in converters and EAFs. The im-provement of converter processing vvas made possible because of BFs (up to 5500 m3) and converters giving much higher production and productivity, as shovvn in Figure 11. It has to be noticed that the productivity per 1950 1960 1970 1980 Years 1990 Year 1960 1965 1975 1980 1955 TZ "55" -i—i—i-1-1-r- 100% _ 630 kVVh/t EZZ22ZZZZZZZZZZZ2ZZZ22ZZ2ZZZZZ3 6 k9/( H-1- 567 kWh/t 148 min 5 kg/t H-1-1-1-1-f- 537 kWh/t 118 min L, kg/t -b—H 460 kWh/t 86 min 3,2 kg/t 400kWh/t 70 min 2;6 kg/t Figure 2: Decrease of the consumption of electric power, shortening melting tirne and decrease of consumption of electrodes vvith the development of high efficiency EAFs Slika 2: Zmanjšanje porabe električne energije, skrajšanje časa taljenja in zmanjšanje porabe elektrod z razvojem učinkovitih elektro obločnih peči 110 120 100 80 60 10 V - ------ 1 1 Mv \ t| 1 iT 1 '-N. \ - - 1 i 1 T 1 •. \ \ 11 1 , , r. , , ^ 1 0,9 vO O X 0,8 c" •H 0,6 a 0 0,5 a nJ 0,1 C C CC 0,3 J 2000 Figure 1: Evolution of production of BFs (upper part of the picture) and weight of converters (lower part of the picture) from 1950 Slika 1: Razvoj proizvodnje plavžev (zgornji del slike) in kapaciteta konvertorjev (spodnji del slike) od leta 1950 production unit was also increased by about three times in the years from 1965 to 1972. By charge preheating and coke addition into converters the energy balance was improved and thereby the charging of solid input increased up to 60%2 which further increased the rentabil-ity. New development diminished the consumption of coke in a production line BF - converters under 300 kg/t steel, as vvell as other costs. Parallelly, improvements in EAF were also introduced. The power of transformers was increased and charge preheating introduced. The la-dle metallurgy (secondary steel making) enabled the dis-charge of furnace after melting3, diminished the con- ■■ El.pouer ESDuration of prooessEZl Ocnsuipticn of electrodes 128 112 156 170 181 198 212 226 210 Production priče, DM/t Figure 3: Relationship furnace capacity versus production priče for different levels of salaries. A - production costs without salary, B -gross salary of 700 DM per worker, C - gross salary of 4200 DM per worker Slika 3: Razmerje med kapaciteto peči in proizvodna cena za različne nivoje plač. A - proizvodni stroški brez plač, B - brutto plača 700 DEM. C - brutto plača 4200 DEM sumption of energy and electrodes, and shortened the melting time as shown in Figure 2. A number of improvements in the electric steel production has increased the rentability of the process and since then low priced steel are produced in average EAFs4'5-6'7,8. The influence of EAF size on production priče is shovvn in Figure 35-6. Curve A refers to the production costs without salary, curve B to a gross salary of 700 DM and curve C to a gross of 4200 DM per worker and month. Ali efforts to increased the rentability of open hearth steel elaboration by oxygen injection proved to be unsuc-cessful. Oxygen intensification is used either by injection of enriched air during charging and heating or by inject-ing oxygen during melting and refining. Air is enriched vvith oxygen up to 27% and the time of charging and soaking is diminished up to 30%. Further air enriching leads to no shortening of charging and soaking time be-cause of energy consuming dissociation of gas compo-nents CO2 and H2O in the furnace. The decarburization rate due to oxygen injecting into the melt depends upon open hearth size9. In Figure 4, the necessary heat flow in dependence upon open hearth capacity and the percent-age of slag in relation to the mass and rate of decarburization are shown. Directions in the figure represent heat flow because of combustion of CO evolving from the melt at various carbon combustion rates (Vc). Curve A in Figure 4 shows the maximal possible heat flow, curve B the flow with 15% of slag, curve C the flovv with 6% of slag, and curve D the heat flow for keeping the empty furnace at operation temperature. In smaller-size furnaces the decarburization rate (Vc) of about 2,5% C/h while in greater furnaces the rate of 1% C/h can be reached. Higher decarburization rates vvith heat flows greater than that shown by the curve A would lead to a furnace pressure greater than that a!lowed and Capacity of the furnace, t Figure 4: Relationship heat flow versus the capacity of OHFs for different decarburization rates and different quantities of slag. A -maximally possible heat flow, B - heat flow with 15% of slag, C - heat flow with 6% of slag, D - heat flow at operating temperature of the empty furnace Slika 4: Razmerje med toplotnim tokom in kapaciteto Siemens Martinovih peči za različne hitrosti razogljičenja in različne količine žlindre. A - največji toplotni tok, B - toplotni tok pri 15 % žlindre, C -toplotni tok pri 6 % žlindre, D - toplotni rok pri prazni peči cause several consequences. The converter decarburization rate reaches about 8% C/h. The total increase of maximal productivity of steel by oxygen injection in OHF is about 40%. The basic reason for stopping the open hearth steel production is the low productivity, es-pecially in small-size OHFs, hence higher costs than by converter and electric furnace processing but not - as sometimes claimed - because of higher costs of energy. 4 Croatian and world steel production since 1973 The production of steel in Sisak Ironworks until 1973 was about 350000 tpy, 280000 tpy in OHFs and 70000 tpy in EAF. Steel processing plants needed about 550000 tpy of steel, therefore, 200000 tpy were purchased. With the aim to become less dependent of external suppliers, the steel making plants were reconstructed to increase the production of steel up to 410000 tpy. BFs were reconstructed and their size enlarged from 150 to 202 m3, which increased the pig iron production by about 16%. The planned increase of open hearth production has never been achieved. On the contrary, it remained on the same level as before the reconstruction, vvhile manufac-turing costs increased because of inefficient oxygen in-jecting as well as more consumption of refractory lining and ferroalloys, and smaller output. Greater consumption of refractory lining and smaller slopping is a normal con-sequence of oxygen injection in the melt that has to be economically justified by increased manufacture. Greater consumption of ferroalloys, is a consequence of vvrong utilization of injected oxygen. Oxygen was also injected during the melting process. This was a non competent decision because of the small share of molten charge. It was not possible to coordinate the temperature in some melts with the carbon content at the end of the refining process. The rate of decarburization was 1,0 to 1,5% C/h and ferroalloys were added also with the aim to heat up the melt to the necessary temperature10. If the planned production increase had been achieved, it would have been failure from the stand point of increase of economy and of profitability. Namely, the share of expensive pig iron was increased by about 16% and, since it was produced in out-of-date BFs, it was 2,5 times more expensive than steel scrap. Back in 1973 BF units were world-wide producing up to 12000 tpd - the Sisak unit only 300 tpd - and con-verters about 350 tph. By the planned enlargement of OHF the efficiency would have been 28 tph per OHF. The productivity of EAFs was then about 80 tph and there was a clear tendency for further enlargement so that to day productivity of larger EAFs reaches up to 200 tph. The only way to increase the quantity of steel up to about 200000 tpy using the existing BFs was to built up oxygen plant and an adequate converter using 200000 tpy of molten pig iron. This could have been achieved with less investments than through open hearth process intensification by oxygen. Scrap could have been used both, in OHFs vvithout addition of oxygen and in the 30-ton EAF, and achieve the needed 500000 tpy of steel8. This version was not considered although it would have given the wanted increase of production as well as an increase of efficiency and profitability, although stili under vvorld levels. That efftciency and profitability were not sufficiently considered is evident. The planned construc-tion of two BFs of about 1000 m3 was unprofitable because furnaces of about 3000-4000 m3 were already in operation in several countries. According to the criteria of profitability Sisak Iron-works had no conditions for steel manufacture by means of BF and converters. A 4000 m3 BF would produce of about 9000 tpd of pig iron and would require three times more raw materials to be transported to Sisak. Beside the increased transport costs, the railway ca-pacity in existence was also questionable. The only prof-itable orientation for the manufacturing of low priced steels required by the actual structure of products are 100-ton EAFs which achieve a production cheaper by about 70 DM/t than in 45-ton furnaces (Figure 3). The company policy was that it is megalomanic to build large production units for low priče steel although such units remarkably increase the profitabi!ity. "Megalomanic products", in which the priče of steel sometimes partici-pates more than 80%, were never abandoned. The ineffi-ciency cannot be significantly improved in the existing rolling mills with their actual products because the priče difference between steel manufactured with modern processes and steel produced in Sisak Ironworks is about 280 DM/t. 5 Possible production of steel for rolled products in Croatia The present steel production in EAFs in Croatia is achieved in three furnaces (Sisak and Split) with the maximal production of about 200000 tpy. This makes it expensive (great consumption of energy and electrodes, maintenance costs and costs for operators' salaries) in re-lation to great EAFs producing up to 1500000 tpy of steel. At the production of 600000 tpy, the production per worker is three times greater. The production of about 200000 tpy in smaller EAFs would be more expen-sive than the production of 600000 tpy in a 100-ton EAF by about 84 DM/t of steel. The processing costs in EAFs for 200000 tpy of steel would be about 224 DM/t, while, by 600000 tpy would be about 140 DM/t". For this rea-son world-wide facilities greater than 500000 tpy are used for low priced steel production4. The casting costs of a greater quantity of steel are also lower. In Figure 512, the costs of production of since 1982 and of steel scrap in Germany are shown. The evolution of costs is also valid for steel plates and welded pipes, vvhich have a similar priče as concrete steel. The tendency of costs lovvering is stronger than that for the prices of steel scrap used in EAFs. Ever smaller differences between the priče of charge and costs of production are met in larger EAFs vvith capacity of (0,5 - 1,0) x 106 tpy (mini Ironvvorks)". Maximal pig iron production in BFs in Sisak Ironvvorks is 230000 tpy. Using converters, preheating the converter charges, and injection of coke, as already mentioned, 50% of steel scrap could be charged and that vvould en-able a production of about 400000tpy of steel. At pig iron priče of 448 DM/t (priče vvhen BFs vvere in operation) and at the priče of 131 DM/t of scrap in Figure 5 in 1991, the total charge priče is 448 x 0,5 + 131 x 0,5 = 289,5 DM/t. The processing costs in 50-ton converter vvith charge preheating are about 77 DM/t of steel, as shovvn in Figure 6, vvhich vvas dravvn using data in ref.3 and I3. Curve A refers to costs vvithout and curve B to costs vvith charge preheating. Unfortunately Croatia disposes of two small and out-of-date BFs of 202 m3 in-stead of one larger-sized, vvhich could produce cheaper iron and lovver the priče of steel products. The priče of steel scrap and its processing costs about 506 DM/t in 1992 shovvn in Figure 5 refer to the production in larger EAFs. At small steel producing EAFs (200000 tpy), the processing costs in EAFs vvould be higher by about 84 DM/t. Steel casting and producing costs are also lovver at higher manufacturing. At smaller steel production by the electric are technology the costs are about the same as the costs of 50% charges consist-ing of molten pig iron from the existing BFs and 50% converter preheated and processed solid steel scrap. Using the data in Figure 3 and Figure 6 the costs of charging and steel making have been estimated and (DM /1) 1.000 m 4-> to o o c o •H 4-> O D ■g u D. "S n) a m s., o o 0) ■P O