Title

NEW COOLING CONCEPT IN HOT-STRIP MILLS "MICROSTRUCTURE TARGET COOLING"

NEW COOLING CONCEPT IN HOT-STRIP MILLS "MICROSTRUCTURE TARGET COOLING"

Authorship

Weinzierl, Klaus; Burger, Rainer; Smith, Michael

Weinzierl, Klaus

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Burger, Rainer

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Smith, Michael

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DOI

10.5151/2594-5297-0009

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Abstract

The successes of new materials are accompanied by an increase in the requirements that are placed on the classical material, steel. It is not only automotive companies that expect to gain an advantage from thinner but still very strong types of steel sheeting which makes their vehicles more efficient and more environmentally compatible; other branches of industry can also profit from strength-relevant load- bearing structures and energy-absorbing components made of dual-phase, multiphase or high-strength steels such as TWIX and TRIP. In addition to the alloying elements, the cooling section is decisive for the properties of these steels. Precise and highly flexible control of the cooling process in the cooling section is therefore extremely important. Previously, however, all models involving purely phenomenological determination of the transformation process have displayed weaknesses in respect of exact calculation of the temperature curve, especially when transformation occurs on the roller table. Furthermore until recently it has only been possible to stipulate a target coiling temperature, which is derived from a mechanical property target. This is only a rough method to adjust steel properties, especially for changing strip speeds. Siemens VAI has now developed a new cooling section control system which uses the so-called Gibbs' free enthalpy to calculate the steel transformation very precisely on the basis of a thermodynamic model. The new developments in the physical modeling of the steel transformation make it possible to compute temperature and phase fractions along the entire cooling section – in real time. By means of a model-predictive control function, the stipulated time curve of cooling in the cooling section is optimally adhered to for the whole strip within the limits of the plant. This enables Siemens VAI to offer a cooling section that works right on the steel producer’s targets: the microstructure properties of the strip.

The successes of new materials are accompanied by an increase in the requirements that are placed on the classical material, steel. It is not only automotive companies that expect to gain an advantage from thinner but still very strong types of steel sheeting which makes their vehicles more efficient and more environmentally compatible; other branches of industry can also profit from strength-relevant load- bearing structures and energy-absorbing components made of dual-phase, multiphase or high-strength steels such as TWIX and TRIP. In addition to the alloying elements, the cooling section is decisive for the properties of these steels. Precise and highly flexible control of the cooling process in the cooling section is therefore extremely important. Previously, however, all models involving purely phenomenological determination of the transformation process have displayed weaknesses in respect of exact calculation of the temperature curve, especially when transformation occurs on the roller table. Furthermore until recently it has only been possible to stipulate a target coiling temperature, which is derived from a mechanical property target. This is only a rough method to adjust steel properties, especially for changing strip speeds. Siemens VAI has now developed a new cooling section control system which uses the so-called Gibbs' free enthalpy to calculate the steel transformation very precisely on the basis of a thermodynamic model. The new developments in the physical modeling of the steel transformation make it possible to compute temperature and phase fractions along the entire cooling section – in real time. By means of a model-predictive control function, the stipulated time curve of cooling in the cooling section is optimally adhered to for the whole strip within the limits of the plant. This enables Siemens VAI to offer a cooling section that works right on the steel producer’s targets: the microstructure properties of the strip.

Keywords

HOT-STRIP; COOLING;

HOT-STRIP; COOLING;