Melting, Slab Casting and Grinding
To make ferritic stainless steels, one needs iron and chromium, and to make austenitic stainless steels, nickel is added to the mixture. This raw material mixture is melted in an electric arc furnace. The molten metal is refined and decarburised in an Argon-Oxygen Decarburiser (AOD) vessel by blowing oxygen, argon and nitrogen into the molten steel. The refined stainless steel is processed through a continuous casting machine to produce stainless steel slabs. The slabs can go through a surface grinding process to remove any possible surface defects. This is our first saleable product.
The slabs are typically between 900mm and 1 600mm wide, 200mm thick, and can be cut to lengths of between 4 and 12m.
The hot rolling process begins at the reheat furnace where the slabs are heated to between 1 100 and 1 300°C, depending on the stainless steel grade. The slabs are then rolled on a reversing four high mill to gauges between 65 and 25mm. Thinner gauges are rolled down further on the Steckel mill. Once the predetermined gauge is reached, the material can either be coiled (black coil, also known as hot band, HR or HRA) or cut into plate (black plate (HRA)). This is our second range of saleable products.
Coil mass is between 20 and 30 tons and the thickness is generally between 3mm and 8mm.
Plate thickness can range between 3 mm and 65 mm.
Annealing and Pickling
The hot rolled products are softened (annealed) and descaled (pickled with acids) to produce a No. 1 finish product. This product has a light grey matt surface finish. No. 1 coil and plate are also saleable products.
Cold Rolling and Finishing
Cold rolling of the No. 1 coils takes place on one of our four Sendzimer mills (Z-mills), which produce smooth, shiny finished, cold rolled stainless steel.
The thickness range of the cold rolled product is between 0,2mm and 6mm.
The material is then annealed (softened) and pickled (and passivated), before it is processed through the skinpass mill, to ensure a smooth surface, known as a 2B finish.
Alternatively, the cold rolled material can be processed to a bright annealed (BA) finish. This is achieved by annealing in a vertical furnace with an inert atmosphere, to retain the bright surface imparted by the cold rolling process.
These cold rolled stainless steel coils can then be cut into smaller coils or sheets, or slit to narrower widths before being packed and shipped to our customers.
Following the cold rolling, annealing and skin passing processes, a material can be given a uniform scratch finish by polishing with abrasive belts.
Click here to view a full description of stainless steel finishes