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Home > Products > Cold-rolled and surface-coated products > Cold-rolled steel sheets

Cold-rolled steel sheets

Production of semi material for steel sheets

The processing conditions of the preliminary metallurgical stages during the production of the raw steel already determine the quality of the steel grade to be produced. Salzgitter Flachstahl steel is produced using the process chain of blast furnace, oxygen top-blowing converter and continuous casting. This advanced and efficient process technology is backed up by a fully integrated energy supply system. Coke and electricity are produced by the in-company coking plant and power station. Thanks to an efficient combined energy utilisation system the generated secondary energies are fed back into the steelmaking process, thus saving energy.
The flat rolled steel is smelted in the Salzgitter Works in three 220 t L. D. converters using the oxygen top-blowing process combined with state-of-the-art bottom purging technology. This is followed by a treatment of the steel in a ladle-metallurgical centre. Here fine alloying, fine desulphurisation and vacuum treatment are carried out. Salzgitter Flachstahl flat steel is entirely produced by the continuous casting process. Both bow-type continuous casters are equipped with modern alchimist cooling system, narrowest roller spacing strand guides and several bending points. All this represents the latest state-of-the-art.

Sheet qualities

Salzgitter sheet is typified by:

Excellent cold formability
High surface quality especially suitable for surface treatment
Excellent weldability
Excellent strip flatness
Close dimensional tolerances

The manufacturing programme includes cold-rolled drawing, deep-drawing and extra deep-drawing sheets, as well as structural steel grades and fine-grain steel qualities and grades for conventional or direct porcelain enamelling. Specific solutions can be offered, tailored to the particular demands of the application.

Great importance is attached to close relations with the customer. In this way a whole series of new steel types for particular applications was developed in close co-operation with the industries involved in further processing. This highly customer-oriented steel development is one of the reasons why Salzgitter Flachstahl sheet steel possesses optimum usage properties and is recognised as a high-standard quality product.

When using steel sheets, extremely high – and in part very different – material demands result from the wide range of possible later applications. A high standard of quality can only be achieved by keeping the manufacturing parameters within very close limits. In order to guarantee this quality standard an integrated Quality Management System has been established in all process stages. In the steelworks already the properties demanded from the material are determined by means of preset analyses. lt is continued by close co-ordination with the subsequent rolling and heattreatment stages.

Sheet production

Salzgitter Flachstahl has always answered customers’ requests for improved sheet qualities by continental modernisation and improvement of its process technology. Shortly after the start-up of the cold wide strip mill further development programmes were initiated. The expansion and modernisation programmes of the seventies were aiming at improving the economic efficiency, increasing the specific performance, enhancing the sheet quality, and bettering the workplace conditions.
The focus of the heavy investments during the eighties and the nineties was on the field of quality improvement. The production sequence in the cold widestrip mill includes the following: pickling line, tandem mill, annealing facility, skin pass mills and coilslitting and inspection lines..

Pickling lines

In the continuous pickling line and the push-pull pickling line the strip is freed from scale while passing through an acid bath. In order to improve the mechanical breaking of the layer of scale, a stretcher leveller is installed in front of the chemical treatment section. The newly installed turbulence pickler with flat pickling baths reduces the energy requirements of the continuous pickling line by 20 % and thus contributes substantially to the saving of resources. With the new rinsing section and the installation of a new process computer and optimisation system, the quality of the pickled sheet has been further improved with regard to surface cleanness and structure.

Both pickling lines are equipped with electrostatic oiling-machines. The pushpull pickling line has a skin pass mill for thicknesses up to 7,0 mm.

Tandem mill

The central section of the cold-rolling mill is the five-stand tandem mill. The pickled strip is rolled in a single pass to finished thicknesses between 0,35 and 3,0 mm. At this stage final rolling speeds up to 90 km/h are achieved. The first four stands are in four-high design and the fifth stand in six-high design. This plant design, in conjunction with a thickness and strip flatness control system operating in a closed loop, brings about a considerabie improvement to the strip flatness and profile consistency while adhering to the closest possible thickness tolerances.The strip profile is monitored by a measuring roll.
A process computer processes the measured data obtained from the complete rolling train and controls the roll gap and the strip profile using hydraulic roll screwdown mechanisms by bending the work and intermediate rolls, shifting of the intermediate rolls and controlling the roll cooling.
This control system selected for use at Salzgitter can effectively influence the strip profile over a wide range as shown in the diagrams above and opposite. In addition to the good strip flatness the surface cleanness of the cold strip is improved by a separate rolling emulsion circuit for the fifth stand.

Annealing and sheet conditioning

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Results of surface cleanness after annealing

After cold-rolling the coil is annealed in order to remove the strain hardening in the material caused by the cold-rolling process. Salzgitter Flachstahl thus meets the increasingly stringent demands of the customer in this respect. With the introduction of high convection furnaces which were added to complement our conventional stack annealing furnaces, the uniformity of the material properties and the surface cleanness have been increased.

Skin pass rolling mills and finishing shop

The annealed coils are then transferred to the skin pass mills where they are passed through roughened rolls at very low reduction degrees of approx. 0,5% to 2,0% and provided with a predetermined surface roughness on the sheet. In this way subsequent formation or the application of paint or other coating materials is improved.

The skin pass mills possess hydraulic screwdown mechanisms and automatic elongation controls.

The elongation is measured by means of deflector rolIs which are installed ahead of and behind the skin pass stand. The related automatic pressure and rolling force control unit ensures a constant elongation along the complete coil length.
A tension leveller is directly connected to skin pass mill 1 so that both skin passing and straightening can be carried out in a single process, if increased coil flatness is required. In the conditioning line of the cold-rolling mill modern coil slitting and inspection lines are available. Here the coil edges are trimmed or the coils are slit to the ordered width, marked and electrostatically oiled to prevent corrosion. For this purpose atomised ionised oil particles are deposited evenly on the coil in a layer which can be accurately controlled.
In the conditioning lines the coil weight can be adapted to suit the ordered weight using the efficient Preplap transverse seam welder. Salzgitter Flachstahl can supply coils up to a max. weight of 32 t.

Plant overview
Cold-rolling mill and surface treatment

Cold-rolling mill
Pickling lines
Continuous pickling line
HCl pickling solution
Coil width: 900 - 1.880 mm
Coil thickness: 1,5 - 6,0 mm
Max. pickling speed: 260 m/min

Push-pull pickling line
HCl pickling solution
Strip width: 900 - 1.550 mm
Strip thickness: 1,5 - 12,5 mm
Max. pickling speed: 90 m/min

Rolling mill equipment

	Stands	Drive	Barrel length	Coil width	Coil thickness	max. rolling speed
		KW	mm		mm	m/min
Tandem mill	4x4-high / 1 six-high	29400	2030	900 - 1880	0,35 - 3,0	1425
Skin pass mill 1 / 2	1x4-high	1200 / 2100	2030 / 1600	900 - 1880 / 1500	0,5 - 3,0	1200 / 1500
Skin pass mill 3	2x4-high	2 x 1000	2030	900 - 1880	0,3 - 3,5	1500

The rolling trains are equipped with: hydraulic screwdown mechanisms, roll bending units, process computer, thickness and flatness control, automatic control of skin pass degree, fast-acting roll changers.

Annealing plant

Stack annealing furnaces for conventional annealing of tightly wound and loose coils; high-convection annealing.

Conditioning lines

Cold-strip stretcher leveller in combination with skin pass mill 1; one strip slitting and three recoiling lines for strip widths of between 40 and 1.850 mm, max. coil weight 32 t, with electrostatic oiling.

Surface treatment of sheet steel

The Salzgitter cold-rolling mill supplies the surface treatment plants with high-quality starting material.

Surface-coated sheet – Salzinc® – is a composite material combining the good qualities of different materials, namely steel as the basic material and the wide range of coating materials such as zinc, special alloys, paints, plastics and foils.

The favourable properties of sheet steel in respect of

its strength
its cold-forming and elastic behaviour
its weldability

are effectively supplemented by the corrosion resistance of the coating materials, and the range of applications of the sheets is thus considerably extended.

The multitude of surface-coated sheet products is extremely large. A considerable role is played by the various galvanising processes. Zinc guarantees a high level of corrosion protection, which remains effective even after damage to the paint coat and the zinc layer of a car body component, for example. A protective layer is formed at the damaged spot. The self-protection is based on an electro- chemical reaction between iron and the baser zinc.

Surface treatment lines

	Coil width	Coil thickness	max. troughput	Coating system
	mm	mm	m/min
Hot-dip galvanising	900 - 1850	0,4 - 4,0	185	Salzinc®-F
Electro-galvanising	900 - 1850	0,5 - 2,0	180	Salzinc®-E
Coil coating	900 - 1850	0,4 - 2,0	120	Salzinc®-K

Production equipment and facilities

Cold strip mill
Surface coating

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