BFI VDEh-Betriebsforschungsinstitut GmbH

Initial situation:

A good surface quality and ideal segregation behaviour in as-cast products are key subjects during continuous casting. Surface quality is influenced by initial solidification in the meniscus as well as subsequent treatment in the secondary cooling zone; while, segregation is mainly influenced by cooling rate. Therefore, an adequate control of cooling rates in the caster as a function of online measurements and predictive tools is of particular interest to steelmakers. Automatic surface monitoring systems are not built-in at existing casters; the surface quality has to be assessed by visual inspection with the aid of callipers. Thus, no online changes are possible since the surface quality data is acquired long time after casting, when operators can only do remedial but not preventive treatment of defects.

Project targets:

The main objectives were:

• Development and industrial implementation of novel monitoring techniques to provide earlier/online process and quality information for operators and process engineers.
• Identification of defects under critical situations when casting micro-alloyed/low carbon billets and stainless-steel slabs.
• Most advanced Digital Twin for modelling the continuous casting behaviour and use it as testbench to develop optimization guidelines.

Innovative approaches:

The following innovative aspects were addressed:

• Application of newly developed surface quality measurement techniques at industrial continuous casters to produce a unique database of surface quality data and corresponding casting process data.
• Enhancement of resolution and accuracy of strand surface temperature measurements in the strand by innovative combination of thermal-camera, active adaptive optics, and simultaneous transmission coefficient determination of the optical path.
• Technology transfer and development of an advanced topography characterisation technique for measurement on as-cast products with potential to be installed directly in the caster for measurement of oscillation marks and cracks in hot samples with accuracy up to 50 μm.
• Application of linear EMS and correlation of cooling rates to segregation and casting conditions for optimal surface and internal quality.
• Innovative modelling technique able to predict heat transfer and strand shell formation as a function of slag infiltration to provide more detailed cooling-rate predictions instead of the usual approach of fitting thermocouple measurements which lead to pre-conditioning of heat fluxes.

Benefits for the industry:

The industrial benefits were focused on productivity, costs cutbacks, reducing environmental footprint and enhancing the working conditions of personnel performing quality inspections on as-cast products. All these are directly related to the new possibilities to monitor and model the CC process to optimize casting conditions and make better decisions to improve product quality by reducing or even eliminating defects. The development of new sensors and modelling techniques gives a strategic edge to European producers and suppliers as well as improving the internal know-how.