Matched by chemical composition and mechanical properties, not a formal equivalence claim. Always verify against the applicable standard before substitution.
Chemical Composition (%)
C
Si
Mn
Cr
S
P
0.30-0.35
0.10-0.35
0.65-0.80
0.85-1.15
<=0.050
<=0.050
Mechanical Properties
Tensile Strength
≥695 MPa (45 tons/sq in, converted)
Yield Strength
≥525 MPa (34 tons/sq in, converted)
Elongation
≥22%
Hardness
201-255 HB
Condition
Hardened and tempered R, ruling section 4 in (lowest-strength condition of the standard)
More data from BS 970:1955
From the standard
Condition of material on delivery
A
Bars and billets for forging as rolled or forged unless order states otherwise.
B
Forgings and drop-forgings finally heat treated unless order states otherwise.
C
Bars for machining finally heat treated unless order states otherwise.
D
Bright bars finally heat treated, before or after cold work at manufacturer option, unless order states otherwise.
Source: BS 970:1955, Part 2, En 18B (page 90)
Mechanical properties
Condition
Ruling section or size (in)
Tensile strength (tons/sq in)
Yield stress (tons/sq in)
Elongation (%)
Izod impact (ft lb)
Brinell (HB)
Proof stress 0.2% (tons/sq in), when requested
Hardened and tempered R
4
45
34
22
40
201-255
32
Hardened and tempered S
2 1/2
50
38
20
40
223-277
36
Hardened and tempered T
1 1/8
55
44
18
40
248-302
41
Values as printed in BS 970:1955; tensile strength, yield stress and proof stress in tons/sq in, Izod in ft lb. Minimum unless a range is shown.
Source: BS 970:1955, Part 2, En 18B (page 91)
Heat treatment
Harden (oil or water)
850/880 C
Temper
suitable temperature between 550 C and 700 C
Note
Steels in the upper part of the composition range should not be water hardened unless special precautions are taken.
Temperatures in degrees C as printed.
Source: BS 970:1955, Part 2, En 18B (page 90)
Notes
Note
Special applications; composition only. Mechanical properties not part of contractual obligations.
Source: BS 970:1955, Part 2, En 18B
Status in the 1955 edition
Status
Deleted by Amendment 7
Reason
Amendment 7 (Sep 1970): direct hardening alloy steels moved to BS 970 Part 2:1970
BS 970:1955 was amended up to Amendment 10 (June 1972); steels were moved to the revised Parts 1 to 5 and deleted from this edition.
Source: BS 970:1955, Amendment slips 6 to 10
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