Mechanical Technology January 2016

Mechanical Technology — January 2016

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Special report

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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