Steels_ Metallurgy and Applications, Third Edition

Low-carbon strip steels 115

-30. , ...................

-4O

60

70

-80 ,

-10 0

Bond TT (~

TT = transition temperature

II

Curve Fk: Y =-64.4+0.71x RA2 = 0.70

I ' I ' ii i I ' iii I I '

10 20 30

Figure 1.114 Relation between brittle transition temperature measured using the crushed
cup and the bend test methods (After Henning 173)

tendency to SCWE, ~79 but not sufficient to have a noticeable detrimental effect
on the r value.

Strip steel in automotive applications

The automotive industry is the most important single market for steel strip and
has provided the greatest stimulus and challenge for the development of new
products, new ways of using them and greater product consistency. In spite of the
competition from aluminium alloys and plastics, steel has maintained its position
as the predominant material for the car body and structural components due to
its good formability, high modulus of elasticity, ease of welding and relatively
low cost. Various grades of steel now comprise 50-60% of the vehicles weight.
Since the 1970s, however, significant changes have taken place in the selection
of strip steels for automotive construction:

1. The need to reduce fuel consumption and fume emissions while maintaining
   structural performance.


2. The need to improve corrosion performance to be able to provide customers
   with better warranties against structural and cosmetic deterioration.


3. The need to improve passenger safety.

Reduced fuel consumption may clearly be achieved by improved engine effi-
ciency, but it has also been achieved by reducing vehicle weight. Figure 1.115
shows, for the top 30 registered European cars, how the kilometres travelled per
litre increases with decreasing weight, but also shows that, for a given weight,
there was a general increase from 1982 to 1992 due to other reasons. Clearly, a