Per: Konrad Krimpelstaetter (Primetals Technologies Austria), Ichiro Maeno (Primetals Technologies AuStria), Gerhard Finstermann (Primetals Technologies AuStria), Hironori Shimogama (Primetals Technologies Japan), Takehiko Saito (Primetals Technologies Japan)
Abstract:
Automobile manufacturers are developing Electrified Vehicles with light steel body structure designs that reduce mass and therefore greenhouse gas emissions over the vehicle’s entire life cycle. This raises the demand for the production and development of Advanced and Ultra High-Strength Steels (AHSS / UHSS) and Electrical Steels with increased permeability and reduced core loss to improve energy conversion efficiency.
To meet this requirements the steel market is tending towards new generations of AHSS with improved formability (3rd generation AHSS) and high-silicon steels with higher strength and thinner products. Therefore, facilities are required to produce these products in higher volumes and under stable operating conditions to achieve the desired high product quality.
With this growing demand for advanced high-strength steels and electrical steels, producers are faced with a unique and interesting challenge in producing materials that strain or exceed the capabilities of existing mill equipment and automation designed to produce low- to medium-carbon sheet. While specialty steel producers have known for decades how to process special high-strength steels and thinner gauges, this equipment typically does not offer the yield and productivity desired by the market, necessitating innovation in re-engineering existing equipment to meet the market demands more economically than new construction. In the case of cold rolling, this can be supported through variable roll geometries, more effective roll-gap lubrication technologies, application of strip heaters (Warm Rolling) to reduce risk for edge crack propagation and strip breaks as well as continuous rolling managed by state-of-the-art automation technologies.
The major lever to improve rolling capability of existing mills is to reduce the work roll diameter especially in the middle stands of a tandem cold rolling mill. This paper contains a historical review and outlook of work roll diameter evolution with respect to harder and thinner steels and introduces two new solutions for the production of AHSS / UHSS and high-Si electrical steels, continuing this history into the future.
For cold rolling heavy reduction of hard materials such as grain oriented or high-grade non grain-oriented electrical steel advanced 20-high cluster mills with very low work roll diameters are applied.
A further lever to support rolling of AHSS / UHSS and high-Si steels is to improve and optimize the roll-gap lubrication, which is of particular importance for hard and/or thin steel products. A new roll-gap lubrication technology allows a flexible adjustment of oil film thickness independent of the rolling speed. This leads to significant advantages for rolling high-strength grades.
The trend to harder and thinner gauges poses more risk for unwanted mill vibrations. To overcome this risk a solution to eliminate gauge chatter supports a high-productivity production of AHSS / UHSS and high-Si electrical steels.
