Steels_ Metallurgy and Applications, Third Edition

2 Steels: Metallurgy and Applications

removed. At the time of writing, this process has not yet reached the stage of
routine production.
The motor industry, among others, has provided an important stimulus to
the steel industry to further improve the mechanical attributes of strip steel,
including gauge control, flatness, surface cleanliness and roughness. The motor
industry, however, has also helped to stimulate the development of mild steel
with improved formability and of some of the wide range of high-strength and
coated strip steels that are now available. The building industry has also played
its part and there has been a spectacular growth in the use of profiled, organic-
coated, galvanized steel sheet for architectural roofing and cladding, particularly
for industrial buildings. The galvanized steel lintel has also now substantially
replaced the reinforced concrete lintel in domestic housing.

General processing considerations

Developments in steelmaking, the use of vacuum degassing and other secondary
steel making techniques enable the steel to contain much more controlled levels
of the important elements carbon, nitrogen, sulphur, aluminium and manganese
than were available previously. Very low levels of the first three of these elements,
down to below 0.003%, are now also easily obtained if required. In many cases,
however, higher levels must be used to give the properties needed.
The most common of the existing process routes for the conversion of liquid
steel into a usable sheet form are summarized in Figure 1.1. Prior to about 1970,

Electric arc

steelmaking

I

Thin slab casting

Basic oxygen steelmaking

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Secondary steelmaking

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Continuous casting

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Slab reheating

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Hot rolling

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Hot coiling

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Pickling

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Cold rolling

Thin strip casting

I / Future?

Batch annealing Continuous annealing Hot dip coating

Temper rolling Temper rolling

~ ~ /

1

Tin coating Electrolytic coating

Organic coating

Figure 1.1 Process route- low-carbon steel strip