Steels_ Metallurgy and Applications, Third Edition

182 Steels: Metallurgy and Applications

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Time reduced to its value at the end of the first stage

CCT diagram

J.I II

Figure 2.21 Tempcore process- thermal evolution in different parts of a 25 mm bar,
finished rolled at 9000C (After Economopoulos et al. 28)

applies particularly to large-diameter bars which are finished at a high temperature

and it is claimed 28 that the length of the cooling facility can be reduced by 70%

by reducing the finishing temperature from 1050 to 900"C.

The Tempcore process is relatively cheap and provides the required mechanical

properties in steels of low carbon equivalent. For these reasons, it is gradually

superseding the cold-twisted and micro-alloyed products.

Steel bridges

In the UK, bridge construction is dominated currently by reinforced concrete and

only about 15% of bridges are based on steel, compared to about 80% in Japan.

According to Simpson, 29 one reason for this situation is that the design codes

for steel bridges are complex and not easy to use. However, Simpson also points

out that the failure during construction of three box girder bridges in the 1970s

has also contributed to the lack of steel construction. In order to regain market

share, steel suppliers and fabricators are attempting to improve the attraction of

steel by providing cheaper and more effective forms of corrosion protection and

by developing methods of construction that will allow faster erection schedules.

Design against brittle fracture

In the UK, the design and construction of bridges is covered by BS 5400: Part 3"

1982 Steel concrete and composite bridges. This code involves the use of the

complex limit state approach for the calculation of design stresses and therefore