Mechanical Technology January 2016

⎪ Special report ⎪

Left: Following reheating to between 1 100 and 1 300°C, depending on the stainless steel grade, the slabs are rolled on a reversing four-high mill to gauges of between 65 and 25 mm. Above: Cold rolling of the No. 1 coils takes place on one of four Sendzimer mills (Z-mills), which produce smooth, shiny finished, cold rolled stainless steel. The thickness range of the cold rolled product is between 0.2 mm and 6.0 mm. Below: The rolled material is then annealed (softened), pickled and passivated, before it is processed through the skinpass mill, to ensure a smooth surface, known as a 2B finish.

Ferrochrome plant next door, according to the needs of the stainless steel melt being processed. This significantly reduces the logistics costs for both par- ties and, directly linked to Columbus’ EAF furnace control system, improves compositional control. The just-in-time approach also reduces the amount of post-processing required at Samancor – to solidify and crush the Ferrochrome – and the melting energy required per batch of stainless. Melting To make ferritic stainless steels, es- sentially, only iron and chromium are needed, but for austenitic stainless steels, nickel is added to the mix. “Our compositional control is among the best in the Acerinox Group,” says Matthews, “and we are also able to switch between different material grades several times per day, giving us a flexibility to respond to urgent or special requirements from anywhere in the world,” he adds. From the EAF, the molten metal is transferred to one of two 100 t Argon- Oxygen Decarburisers (AODs). There, by blowing oxygen, argon and nitrogen into the molten steel, the stainless steel is refined. Oxygen decarburises the steel, but this process is exothermic, which increases the melt’s temperature. Argon and/or nitrogen are bubbled through the mix to accurately control the tempera- ture and to optimise the decarburisation process. Reducing agents, such as silicon and aluminium, are added to recover some of

Mechanical Technology — January 2016

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