Steels_ Metallurgy and Applications, Third Edition

228 Steels: Metallurgy and Applications

9 As-rolled, as-rolled and softened, and micro-alloyed C and CMn steels

(Section 2).

9 Through hardening boron steels (Section 3).

9 Case hardening steels (Section 4).

9 Stainless and heat resisting steels (Section 5).

Acknowledging that the standard contains a large number of grades, this edition
of BS 970 has continued the practice of separating the steels into two categories.
Category 1 steels are the recommended series of steels for use in new designs and
in established designs whenever possible and are printed throughout the standard
in normal (upright) type. Category 2 steels make up the remainder and are shown
in italic (sloping) type.
The old En numbering system which became established after the Second
World War was withdrawn some years ago and replaced by a logical, if complex,
system which is outlined below.
In all designations, apart from those for stainless steels, the last two digits
indicate the mean of the specified carbon content.
Each designation carries a letter which defines the supply requirements:

. M- for steels to specified mechanical properties
. H - for supply to hardenability requirements
9 A - when supplied only to a specified analysis

In carbon and carbon - manganese steels, the first three digits indicate the mean
of the manganese content and examples are shown in Table 3.4.
Free-cutting steels are now included in BS 970: Part 3:1991 Bright bars for
general engineering purposes. In these grades, the first three digits are in the
range 200 to 240 and the second and third digits indicate the minimum or mean
of the sulphur content multiplied by 100 (Table 3.5).
In the case of stainless steels, the designations reflect the well established AISI
system. Thus the first three digits are in the 300 or 400 ranges, representing the

Table 3.4

Grade C% Mn% Supplied to

060A62 0.6-0.65 0.5-0.7 Analysis only

080H46 0.43-0.5 0.6-1 Hardenability requirements

150M36 0.32-0.4 1.3-1.7 Mechanical properties

Table 3.5

Grade C% Mn% S% Supplied to

226M44 0.4-0.48 1.3-1.7 0.22-0.3 Mechanical properties