Steels_ Metallurgy and Applications, Third Edition

Low-carbon strip steels 37

and a supplier in order that a particularly difficult customer requirement can be
satisfied.
It is convenient to present information on mild steels and higher-strength steels
in separate sections even though they may be closely related. Metallic-coated
steels and organic-coated steels are also covered in separate sections.

Mild or low-strength steels

BS 1449 was the definitive specification in the UK for carbon and
carbon-manganese steels in the form of plate sheet and strip. The last version
of this specification - BS 1449 Section 1.1' 1991 - is still in force and provides
brief details of both hot-rolled (HR) and cold-reduced (CR) grades. A summary
of this information is given in Table 1.2. It is understood, however, that BS
1449 should only be used to specify hot-rolled grades and this specification will
eventually be withdrawn in favour of European standards.
The cold-rolled and annealed carbon steel flat products supplied for cold
forming in Europe are covered by European standard EN 10130:1991 and desig-
nated Fe P01 to Fe P06 but with Fe P02 missing. The most important feature of
these grades is their formability, with grade Fe P06 having the highest forma-
bility and Fe P01 the lowest formability as indicated in Table 1.3. The higher
grades, therefore, have stringent requirements for r value and n value. The other
main difference between the grades concerns the acceptable strain ageing limit.
The Fe P06 grade is regarded as being completely non-ageing, whereas a small
degree of ageing is regarded as acceptable for grades Fe P03 to 5, provided the
steel remains suitable for use after storage for up to six months. An even higher
degree of ageing is acceptable for grade Fe P01.
Each grade may be obtained from either continuous or batch annealing, but
the chemistry and prior processing needed to provide the necessary properties
from the two methods are usually, but not always, different.
There are two main types of mild steel. The first is the more traditional steel
described as aluminium-killed (AK) steel in which the carbon is relatively free

Table 1.2 BS 1449:1991 Section 1.1 (General specification)

Grade Rolled condition Quality C% max. Mn% max

1 HR EDDAK 0.08 0.45

CR

HR EDD 0.08 0.45

CR

HR DD 0.1 0.5

CR

HR D or F 0.12 0.6

CR

14 HR FL 0.15 0.6

15 HR C 0.2 0.9

Key: EDDAK, extra deep drawing, Al-killed; EDD, extra deep drawing; DD, deep

drawing; D or F, drawing or forming; FL, flanging; C, commercial.