BS 970 (Part 1):1983 708A40: 708A40 is an alloy steel grade specified in BS 970 Part 1:1983 (Table 6, category 2). Section three of the standard advises that category 1 steels be used for new designs and established designs whenever possible.
Matched by chemical composition and mechanical properties, not a formal equivalence claim. Always verify against the applicable standard before substitution.
Chemical Composition (%)
C
Mn
Cr
Mo
P
S
0.38-0.43
0.75-1.00
0.90-1.20
0.15-0.25
<=0.035
<=0.040
More data from BS 970 (Part 1):1983
From the standard
Other composition limits
Phosphorus and sulphur
P 0.035 max, S 0.040 max, alloy steels (clause 1.7.2.1)
Residual elements: see clause 1.7.3.
Source: BS 970 (Part 1):1983, clause 1.7.2.1
Mechanical properties by heat treatment condition
Condition
Limiting ruling section (mm)
Rm (N/mm2)
Re min (N/mm2)
A min (%)
Izod min (ft lbf)
KCV min (J)
Rp0.2 min (N/mm2), when specifically ordered
HB
Q
250
625-775
450
15
25
28
430
179-229
Q
150
625-775
480
18
15
16
465
179-229
R
250
700-850
495
15
25
28
480
201-255
R
150
700-850
525
17
40
50
510
201-255
S
100
775-925
585
15
40
50
570
223-277
T
63
850-1000
680
13
40
50
665
248-302
U
29
925-1075
755
12
35
42
740
269-331
V
19
1000-1150
850
12
35
42
835
293-352
W (note 11)
13
1075-1225
940
12
30
35
925
311-375
Values as printed in Table 6 for the limiting ruling section shown. Rp0.2 applies when specifically ordered (note 10). 1 N/mm2 = 1 MPa. Note 11: often ordered in the softened condition for machining and subsequent heat treatment to achieve these specified mechanical properties.
Source: BS 970 (Part 1):1983, Table 6
Comparison with earlier editions
BS 970:1970/72 designation
Not listed
BS 970:1955 En No.
None
Appendix D note 47: where a comparison is made the steels are not necessarily equivalent. 'Not listed' means the earlier edition has no entry under this designation.
Source: BS 970 (Part 1):1983, Appendix D
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