The Steel Book.
Production: Information Ofﬁce, SSAB Tunnplåt AB, Luleå Text: Vidén information AB Translation: Ewa Hjelm Proof-reading: Mark Wilcox Design: Formidabel Illustrations: Mediagraﬁk & illustration Photo: Lars Vaksjö, Karin Larsson/SSAB Tunnplåt AB, Per K Olsson, Volvo’s picture library Print: Luleå graﬁska, 2002
Steel for tough demands.
SSAB Tunnplåt is part of the SSAB Group. SSAB Tunnplåt is the largest manufacturer of strip steel in the Nordic region and one of Europe’s leading developers of high-strength strip steels. SSAB Tunnplåt has ore-based steel production in Luleå and strip steel manufacture in Borlänge. This brochure focus on the production in Luleå.
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The world’s most widely used structural material.
Steel is the most useful metal in the world. No other material can meet such a great variety of requirements. Steel is one of the basic ingredients in the development of industry and the whole of society. We come in contact with it everyday – in transportation, sports and leisure, in the kitchen, in schools, hospitals – everywhere.
Steel has to have different properties for different applications. Cars need strip steel with a good formability and an attractive surface ﬁnish. Auto components, such as side impact beams and built-in children’s safety-seats, require high-strength steels that enable the manufacture of strong, yet thin and light constructions. Washing machines need a light, durable steel sheet that stands up to wear. Microwave ovens require sheet with special coatings.
The ice blade on a snow plough must be hard and wear-resistant. Steel sheet that is to be bent into various sections for rooﬁng and facing sheet must be ductile, so that it does not crack when it is bent. Just look around. You’re sure to ﬁnd many more applications, with different demands, in which steel is used.
Making steel with concern for the environment.
All industrial manufacture has an impact on the environment. As long as society develops, steel will be needed. Steel that is scrapped is recycled – a practice followed since the Iron Age. However, society’s demand for steel cannot be met by recycling alone. New steel must be produced from iron ore.
The addition of carbon is required to make hot metal from iron ore. In that process carbon dioxide, one of the greenhouse gases, is formed. Iron and steel production also results in other emissions to the air, water and soil. Reducing emissions and limiting environmental impact are important tasks for SSAB Tunnplåt in Luleå. Since 1980 emissions of dust have been halved and the emission of sulphur has been reduced by 85%. During the same period ammonia and phosphate emissions were reduced by between 80 and 90%. SSAB’s main environmental objective during the 1990s has been to reduce emissions to the air and water. Other important aspects of the environmental effort have been source separation, increased recycling of residual products, life-cycle analyses (LCA), environmental product speciﬁcations, environmental management and restricting the use of harmful chemicals. Future efforts will involve further development of raw materials, processes and products. The environment is a central aspect of all new capital expenditures.
SSAB regularly carries out environmental inspections in the open, investigating, for example, mosses, plants, ﬁsh and other aquatic life, leaks from waste deposits, noise and dust content in the air. Certain tests are conducted on a weekly basis, others at intervals of some years. All results are reported to the environmental protection authorities. An environmental management system is being introduced to systematize the environmental effort and meet customer requirements. The environmental management system includes procedures and documentation that facilitate survey and control over environmental work. Extract from SSAB Tunnplåt’s Environmental Policy: ”Within the Group, all operations shall be conducted in a resource-effective and efﬁcient manner in respect of the use of raw materials, energy and other natural resources. The commercial operations are based on environmental work which contributes to permanent and sustainable development of the use of steel in society.”
The metallurgical processes of iron and steelmak
RAW MATERIALS IRON ORE BECOMES HOT METAL Iron ore pellets, coke and limestone are continuously charged into the blast furnace. Coking plant Coal is imported and transported to Luleå from e.g. Australia, the USA and Canada. The coal is stockpiled in a storage area the size of twelve football ﬁelds. Desulphurization is assisted by the injection of calcium carbide into the hot metal. HOT METAL BECOMES STEEL WHEN SULPHUR AND CARBON ARE REMOVED Hot metal and scrap are mixed in the BOF converter, where oxygen is used to reduce the carbon content. Oxygen Scrap
Coal is heated up for 18 hours, 25% becomes gas and the rest becomes coke. Blast furnace BOF converter
Pellets are produced from iron ore by the mining company LKAB in Malmberget and Kiruna. Every twenty-four hours, three trainloads of iron ore pellets are transported to SSAB Tunnplåt in Luleå.
Hot metal is regularly tapped from the hearth of the blast furnace. The hot metal is transported to the steel plant in a torpedo car. Slag is tapped into slag ladles.
Transportation to the steel plant
THE STEEL IS FURTHER PROCESSED LIQUID STEEL IS CAST INTO STEEL SEMIS (SLABS) Alloys Oxygen
Alloys At the CAS-OB station (ladle metallurgy) alloys are added and the temperature is adjusted. Liquid steel is tapped into a tundish and then further down into the mould, without interruption. The steel strand is cooled and solidiﬁes as it is pulled down into the strand guide system for subsequent cutting and marking. Mould Argon gas
Slabs are carried by rail to the hot strip mill in Borlänge for further processing. 3 or 4 trains leave for Borlänge every day.
In the RH plant the steel is treated under vacuum to remove impurities. Extremely low carbon contents and a high degree of purity are achieved.
The slabs are cooled and loaded onto a train bound for Borlänge.
Black coal becomes coke.
Coke is required in the blast furnace to get iron from the iron ore. Coke is harder than coal. The coke lumps must be hard and porous, even at high temperatures, to allow reducing gases to pass up through the blast furnace. To ensure a supply of the right quality of coke and high-energy coke oven gas, SSAB Tunnplåt has its own coking plant.
The coke battery consists of 54 coke ovens in a long row. Coal is heated in the narrow, closed ovens. Volatile compounds and gases are distilled from the coal after about 18 hours of heating. The temperature is then over 1000°C and the coal has been converted into coke.
25% of the coal becomes gas which is carried off, cooled and cleaned. When the gas is cleaned, several compounds are removed. These are recovered and then used as raw materials in the chemical industry for making products as different as perfume and asphalt.
Gas holder Cleaned coke-oven gas
The ﬁnished coke is pushed out onto the quencher car and is cooled with water. The large white clouds which can be seen in the sky above the SSAB plant every 15 minutes consist of steam from quenching.
Cleaned coke-oven gas is returned for heating coke ovens.
The interior of the blast furnace
Iron ore becomes hot metal.
To convert iron ore into iron, the oxygen content must be lowered (the ore is reduced). This is achieved by heating, whereby the carbon atoms from coke and coal powder are combined with the oxygen atoms of the ore in a gas ﬂowing up through the blast furnace.
Hot blast is heated air with extra oxygen which is blown into the blast furnace in large quantities to heat and reduce the ore. The air is heated in brick towers (hot stoves) serving as heat exchangers. To heat the hot stoves cleaned gas from the blast-furnace and coking plant processes is used. Air intake Coal powder is injected together with oxygen-enriched air into the lower part of the blast furnace to add carbon and oxygen.
Ore pellets and coke are continuously charged in layers into the top of the blast furnace. Here, limestone, various additives and residual products containing iron, such as dust, ﬂue dust, etc. are also supplied. All this is required, to get a hot metal with the right quality and a slag with the right properties. The slag binds impurities from the hot metal. The layers of ore pellets are slowly preheated and reduced to metallic iron which descends slowly through the blast furnace. The temperature increases further down in the furnace and the iron melts and drips down onto the blast furnace hearth.
1 400 - 1 800o C the ore melts
2 200o C coke burns
The gas from the blastfurnace process is led away and cleaned and then used in the processes.
1 500o C hot metal is The coke lumps are hard, even in tapped out the hottest part of the blast furnace. Gas is formed when oxygen leaves the ore. The gas passes up through the coke lumps. When the iron at the furnace hearth has reached a certain level, it is tapped into so-called torpedo cars. Liquid hot metal is tapped from a blast furnace about ten times every twenty-four hours. Hot metal is brittle and fragile and therefore unsuitable for making products, since it cannot be forged. The hot metal must be further processed into steel.
Hot metal and scrap become steel.
Hot metal becomes steel when the carbon content is reduced below 2%. The addition of alloys gives the steel exactly the composition and the properties desired by the customer. Steel for refrigerators must have different properties than steel that is used for making bridge piers.
After desulphurization the slag is drawn off the surface.
The hot metal arrives at the steel plant from the blast furnace in a torpedo car and is tapped into a hot metal ladle. The volume of hot metal which goes into a hot metal ladle is called a heat.
First, the hot metal is desulphurized. Calcium carbide is injected through a lance which is dipped deep down into the melt. A chemical reaction is thereby started in which the sulphur reacts with calcium and the compound is bound in a slag on the surface of the melt. At this stage, for each heat, operators know the sulphur level that must be reached in order to match the customer’s speciﬁcations for the ﬁnished steel.
The slag is a residual product which is partly recycled.
Oxygen is required to lower the carbon content.Gaseous pure oxygen is blown under high pressure on the surface of the molten metal and the carbon content is reduced to below 2%. The hot metal then becomes steel. The carbon content of the steel is reduced to the right level to match the customer’s speciﬁcations. The carbon content of most steel produced at SSAB Tunnplåt in Luleå is below 0.1%. Scrap Oxygen
Other impurities, such as phosphorus and vanadium, are bound in a slag on the surface. The steel is tapped into a ladle and the slag remains in the BOF converter. At the same time as the steel is tapped into a steel ladle, the preliminary addition of alloys (different metals), as speciﬁed in the order, is made. The slag is poured over into special slag ladles and most of it is re-used as raw material in the blast-furnace process.
The desulphurized hot metal is poured into a BOF converter (Basic Oxygen Furnace) together with scrap and the carbon content is reduced, i.e., the iron is decarburized into steel.
At this stage the steel in the ladle has to be further processed to satisfy demands on material properties in the end product. There are hundreds of different steel grades. Steel grades are given their special properties in two different processes, called CAS-OB and RH. The analysis (the exact composition of different ingredients) and the temperature are ﬁnely adjusted.
In the CAS-OB process a ceramic bell is lowered into the ladle. Argon gas is added from the bottom to stir the steel bath and protect the steel from the oxygen in the air. To reach the desired speciﬁcation of the heat, alloys are added in the form of metal pieces, or by using a long metal wire which is fed down into the liquid steel.
Vacuum valve Alloys
Here, 200 to 300 different steel grades are manufactured, all according to the requirements of different customers and ﬁelds of application.
In the RH plant a very clean steel with extremely low carbon or hydrogen content is produced. The steel bath circulates under vacuum. Carbon reacts with oxygen and the compound, carbon monoxide is removed. Hydrogen from the steel is also removed to the gas phase. The values are carefully measured and are reduced to the levels speciﬁed by the customer. Steel grades with the lowest carbon content are extremely soft and are used for advanced pressing of parts for cars, etc.
Continuous casting into slabs.
Ladle after ladle of molten steel is cast without interruption. This is possible because the steel runs from the ladles into an intermediate reservoir, the tundish. From there, the steel is tapped into a mould through a submerged nozzle at a regular speed. Great care is taken to register the steel grade being tapped into the tundish, so as to enable identiﬁcation of each steel slab manufactured.
Ready-treated molten steel runs in a uniform ﬂow via the tundish
The slabs are loaded onto railway cars and transported to SSAB Tunnplåt’s rolling mills in Borlänge. Three or four trainloads of slabs leave Luleå every day. The time from order to delivery of ﬁnished strip product to the customer is 16 to18 days.
down into the continuous casting machine, which consists of a mould – a rectangular funnel with adjustable sides – followed by a strand guide system.
The steel is cooled and solidiﬁes slightly against the surface of the mould and is pulled down into the strand guide system. There, the steel is further cooled with water and solidiﬁes successively. The solidiﬁed steel strand is cut into 11-meter lengths, slabs, as it leaves the casting machine. Each slab has an identiﬁcation number and is manufactured for a certain customer and a certain purpose. The slabs are allowed to cool and then inspected. If required, surface cracks can be removed.
At SSAB Tunnplåt in Luleå 4.5 million tonnes of iron ore pellets, coal, scrap, limestone and alloys are used annually. Most of the solid material becomes steel. Only four percent becomes residual products which are dumped. The rest is re-used in the process or is sold externally.
The coking plant produces raw materials of different kinds In the coking plant 75% of the coal becomes coke and 25% evaporates as gas. When the coke-oven gas is cleaned, a number of products are recovered which are then sold as raw materials for use in other manufacturing processes. Sulphur, for example, can be used to make sulphuric acid for paper mills; tar is used for making pitch, tar oils, etc., and crude benzene is used in plastics manufacture. Recovery of iron in residual products Residual products from the different process steps contain ferrous material. This iron is subjected to magnetic separation and reintroduced into blast furnaces or converters. Dry dust and small iron fragments become briquettes in a briquetting plant. The briquettes, together with iron ore pellets, coke and limestone, are part of the burden in the blast furnace. Fewer and safer landﬁlls To landﬁll waste means to deposit it in a controlled outdoor ground site, once known as a dump. The volume of landﬁlled waste per tonne of produced
steel at SSAB Tunnplåt continues to decrease. An ever greater amount of the residual products containing iron is reintroduced into the manufacture of hot metal and steel. Other material, which cannot become iron, is for example slag from the blastfurnace process. That slag can be sold and used as a ﬁlling material in road construction. However, some waste must be landﬁlled. SSAB Tunnplåt has its own controlled landﬁll sites for this waste. The material in the landﬁlls is sorted to the greatest possible extent for possible future recovery. Legislation Public authorities have issued about 50 environmental conditions with which steel producers must comply. Various environmental tests and analyses are done every day to ensure that these conditions are satisﬁed. They are made both by SSAB Tunnplåt’s own environmental laboratory and by external companies and agencies.
In the processes at SSAB Tunnplåt in Luleå large volumes of gas are formed. After cleaning, the gas is reused in the manufacture of coke, iron and steel. Excess gas is delivered to LuleKraft – a combined power and district-heating plant – via a long gas pipe. LuleKraft uses the gas to produce district heating and electric powers.
About 20,000 households and a number of industries and ofﬁce premises in Luleå are heated by surplus gas from SSAB. District heating is also supplied to the hospital in Sunderbyn. In addition to the production of power and district heating, approximately 35 million kilowatt-hours of steam are produced and delivered to SSAB Tunnplåt for use in the steelmaking process. Development and investments, for example in a coolant supply line from the Lule River, mean that more and more gas can be utilized instead of being burnt in the ﬂare.
Man and machines.
People Plants and technical equipment need maintenance. People also need a certain ‘maintenance’. In order for co-workers to experience job satisfaction and develop in the workplace, there must be room both for commitment and change. Individual discussions take place with all employees at regular intervals and form the basis of personal development plans. The Company Health Service works with, for example, exercise and medical check-ups as a preventive measure. SSAB Tunnplåt’s sports centre is open to all employees and has a bowling-alley, weight training and many other facilities. The Company Health Service also treats any medical conditions that may have resulted from work. The plant Maintenance includes all activities that are routinely carried out to keep the equipment in operation over time, as well as incidental repair or replacement of parts that apt to break down sometimes. Not only do small spare parts need to be replaced. A single valve can weigh as much as four tonnes. About a third of all employees at SSAB Tunnplåt in Luleå work with maintenance.
Maintenance of machines and plant is both preventive and planned, i.e. for example, cleaning and lubrication must be done at regular intervals to ensure proper function of equipment and parts must be replaced according to schedule, before they break down. The aim is for steel production to proceed without disturbances and standstills. Maintenance means keeping a step ahead at all times. All production facilities at SSAB Tunnplåt in Luleå are regularly inspected according to different schedules. Repairs due to an unplanned shutdown cost 100 to 1000 times more than preventing or remedying the fault at an early stage. An efﬁcient and preventive maintenance programme requires knowledge and the commitment of all employees. • Operators may discover minor changes, such as an oil leak or a noise, and report it. • Maintenance personnel who work close to the operation measure, analyse and remedy faults. • The personnel working with common maintenance do major work, such as replacing parts or doing repairs in a workshop. • Purchasing and store personnel see to it that proper tools and spare parts are available.
Europe’s leading manufacturer of high-strength steels.
SSAB Tunnplåt Luleå is a relatively small steel plant. This enables us to develop special steel grades for the customer and to quickly adapt production, so that even small quantities of a steel grade can be produced proﬁtably. The focus is on high-strength steels.
In Luleå we are good at producing steel with higher and higher yield strength. This makes it possible to manufacture thinner and lighter designs. Since the steel plant in Luleå is small compared to those of competitors around the world, special steel grades can be made in small quantities for customers with special requirements. Example: A company in Barcelona in Spain sells turnkey warehouse solutions, including buildings, shelves, automatic lift trucks and computer systems. They wanted to offer their customers more efﬁcient warehousing that occupies less space and requires fewer trucks. To achieve this, they had to build taller structures that would accommodate the same volume of stored goods in a smaller area. The problem was that the steel used for the shelving did not meet their requirements, so they contacted SSAB Tunnplåt.
People from the marketing department in Borlänge and the steel plant in Luleå met with the customer to discuss needs and demands. SSAB provided the solution: a high-strength steel with the required width. This was a steel grade with exactly the right carbon content and exactly the right mix of alloys: a vanadium-alloyed, high-strength steel. Now the company in Barcelona can build all of its warehouses with high, strong shelf systems that are slender and space-saving.
Competitiveness Small-scale production, short delivery times and people who are experienced in working with many special steel grades are competitive advantages for SSAB Tunnplåt. Our customers appreciate short delivery times and high quality. In future we will be even more renowned for our close co-operation with customers. By producing new and unique steel grades we will be helping our customers to improve their products even more. About 800 million tonnes of steel are produced in the world annually, of which just over 2 million tonnes are produced at SSAB Tunnplåt’s plant in Luleå. Strong customer relations are important for future competitiveness. The home market of Swedish steel is usually considered to be within the radius of daily railway trafﬁc. Northern Italy, for example, is an important export market for steel from SSAB Tunnplåt.
Steelmaking is a high-tech business that is based on both science and experience. Certain data cannot be measured, because measuring devices cannot withstand the high temperatures. To be able to understand what is happening in the liquid iron or steel you have to combine a lot of input and output data in complicated computer models that are built up around calculations and practical knowledge. As one of the researchers at SSAB Tunnplåt in Luleå says, ”It is easier to measure the composition of the surface of the moon than to measure the composition inside the blast furnace”.
Research and development (R&D) are conducted by researchers and development engineers who work with various short-term and long-term projects within the production units. Sometimes it is a question of solving everyday problems, sometimes of coming up with entirely new methods to make processes more efﬁcient. To solve a problem, development engineers can co-operate with works operators and the pellet supplier, LKAB, or with the customer who uses the steel. Often, we co-operate with researchers from universities in Sweden and abroad, or with other steel producers via the branch association Jernkontoret (the Swedish Steel Producers’ Association). Another partner in development is Mefos, a research institute with pilot scale facilities in Luleå. R&D are carried out in the following areas: • Product development – to produce new steel grades corresponding to market demands. • Operating stability – to avoid interruptions and quality
deviations. • Process development – to produce as much steel as possible with the minimum consumption of energy, alloys, etc. • Environmental development – to minimize environmental impact. • Training/education of personnel – to improve competence throughout the organization.
Example: An example of an R&D project is the injection of slag formers directly into the blast furnace as a complement to adding slag formers from the top. If the composition of the slag needs to be adjusted and changes are only made from the top, it takes at least eight hours before the change is noticeable in the hot metal tapped from the blast furnace. However, if slag formers could be injected into the blast furnace in the same way as coal powder, the change would be noticed much faster.
Objectives and skills.
To achieve continuous improvement SSAB Tunnplåt applies management by objectives. All employees are actively involved in discussing various targets and results are compared with objectives each month.
It is difﬁcult to navigate the course ahead merely by looking in the rear-view mirror. Having future targets to aim at encourages employee commitment and participation. Targets are set for each unit, department, and crew. One overall target is to improve production efﬁciency. The success ratio can be measured, for example, by the amount of hot metal produced per man-hour and year. One man-hour is equal to one worked hour per employee, distributed equally over all occupational groups. As production efﬁciency increases, so does the amount of hot metal/man-hour. The target is to achieve uniform operation without disturbances. This can be measured in number of heats per twenty-four hours in the steel plant. A heat is the quantity of hot metal/steel which a steel ladle can hold, i.e. 114 tonnes. The more uniform the operation, the more heats per twenty-four hours.
Skills development It is important for each individual to learn new things and to develop. Not only do the people at SSAB Tunnplåt in Luleå set output targets, they also set targets for their own personal development. To some people the target can be an upper secondary school education, to others a thesis for a doctorate. There are a lot of possibilities and opportunities for study in a number of basic subject areas, such as mathematics, English, physics and computer science. Some use distance tuition, while others attend separate courses during their leisure hours. The form is adapted to suit the work and family situation. An important strategy for all development which takes place in the production units is that everyone should learn more about the company as a whole. Each person learns how his or her own tasks are related to preceding and subsequent production steps. This gives everyone a better understanding of how their own work affects the work of others.
SSAB Tunnplåt AB, SE-971 88 Luleå, Telephone +46 (0)920 920 00, Telefax +46 (0)920 927 14, www.ssabtunnplat.com, www.ssab.se