EuroWire May 2024

Technical Article

Flexibility, quality and tolerances: results after four years of activity in the Caleotto rolling mill By Lorenzo Angelini, Nicola Bolognani and Andrea Parimbelli, Arlenico SpA, Lecco, Italy; and Andrea Taurino, Fabio Coppola and Francesco Paternoster, SMS group SpA, Tarcento, Italy

Caleotto plans to conduct thorough economic assessments with end users to evaluate the benefits of the smaller diameter wire rods across various applications, including ropes, tyre bead wire, welding wires, automotive and mechanical springs, and cold rolling for shaped products. The cooling process is tailored to different steel grades to achieve desired microstructures, particularly for high-carbon steels where careful temperature control is crucial to obtain fine pearlitic structures. In summary, the advancements in technology and production processes at the Caleotto rolling mill set a significant step towards producing high-quality wire rods with enhanced efficiency and versatility to meet the evolving demands of the steel market. Obtaining a fine pearlitic structure in steel involves rapidly cooling the material from its coiling temperature to the transformation start temperature and then maintaining a constant temperature for the required transformation period. For materials like 4.5mm diameter coils and small diameter products (5.5mm) intended for drawing, this cooling process is adjusted to ensure phase transformation occurs after about 12-15 seconds. The temperature profile along the coil-cooling conveyor for C82D steel grade illustrates this process (Figure 1) . For other steel grades, such as low-carbon or low-alloy steels, the conveyor cooling gradient is slower. This slower cooling aims to achieve a low-hardness ferritic structure necessary for subsequent cold rolling or heading processes.

The steel market has significantly fluctuated in recent years, necessitating adaptability and flexibility. The Feralpi Group, a long-standing player in the Italian steel industry since 1896, has embraced the concept of “green steel” production and has focused on enhancing the production of wire rods from special steel to meet high quality standards. In 2019, the Feralpi Group achieved noteworthy results by utilising the four-stand MEERdrive®Plus sizing block, rolling various steel grades into wire rod products of 4.5 and 5mm diameters in 2023. This technology has paved the way for entering new market segments and enhancing product quality. Through substantial upgrades to the Caleotto rolling mill, SMS group introduced cutting-edge technologies like the MEERdrive Plus finishing/sizing block and a cooling and equalising line equipped with multi-loop technology. The MEERdrive Plus sizing block, with its single-motor drive technology for each stand, offers superior capabilities for producing high-quality wire rods while reducing operational costs and enhancing control over dimensions and temperature. The installation of the MEERdrive Plus sizing block was specifically designed for wire rod products with diameters below 5.5mm, positioning the plant ideally for producing small-diameter products with enhanced productivity. Trials conducted in 2022 and 2023 demonstrated excellent results in dimensional tolerances and mechanical characteristics, particularly with 5mm and 4.5mm diameter wire rods. The process involves a series of stands operating at varying reductions to achieve optimal dimensional tolerances, stability and product quality. Caleotto’s production includes low-, medium- and high-carbon steel for various applications such as cold heading, rope and chain production, springs, boron steel, welding wire, etc. Upgrades to the rolling mill aim to improve dimensional tolerances and microstructure quality through low-temperature finish rolling, enabling the production of the thinnest wire rod in Europe. The smaller diameter wire rods offer significant advantages in downstream processes, such as reduced drawing and annealing requirements, leading to cost savings and improved final product properties. End users benefit from enhanced ductility and plasticity, particularly in rope production and cold-heading applications.

Figure 1: CCT curve for C82D steel

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May 2024