Section
10 High strength steels for welded structures
10.1 Scope
10.1.1 Provision is made in this Section for hot-rolled, fine-grain treated, weldable high
strength structural steels intended for use in marine and offshore structural
applications. These requirements are not intended to apply to steels for the hull
structure of ships.
10.1.2 The required notch toughness is designated by subdividing the strength levels into
Grades AH, DH, EH and FH.
10.1.3 The steels may be supplied in eight strength levels with minimum yield
stresses of 420, 460, 500, 550, 620, 690, 890 and 960 N/mm2 respectively.
For yield strength level of 890 and 960 N/mm2 grade F is not
applicable.
10.1.4 Steels covered by the scope of these Rules requirements may be supplied either in the
normalised (N), normalising rolled (NR), thermomechanically controlled rolled (TM)
or quench and tempered (QT) condition.
10.1.5 The requirements of this Section are primarily intended to apply to
plates, wide flats, sections, bars and seamless tubulars, generally not exceeding
the thickness limits given in Table 3.10.1 Maximum Thickness Limits.
Steels with a thickness beyond the maximum thickness as given in Table 3.10.1 Maximum Thickness Limits
are to be specially considered by LR.
Table 3.10.1 Maximum Thickness Limits
Steel Grade
|
Condition of supply
|
Maximum thickness (mm) (see Note 1)
|
Plates
|
Sections
|
Bars
|
Tubulars
|
AH42,
AH46
|
N
|
250
|
50
|
250
|
65
|
DH42,
DH46
|
NR
|
150
|
(see Note 2)
|
EH42,
EH46
|
TM
|
150
|
50
|
-
|
-
|
FH42,
FH46
|
QT
|
150
|
50
|
-
|
50
|
AH50, AH55,
|
TM
|
150
|
-
|
-
|
-
|
AH62, AH69
|
DH50, DH55,
|
QT
|
150
|
-
|
-
|
50
|
DH62,
DH69
|
EH50, EH55,
|
EH62, EH69
|
FH50, FH55,
|
FH62,
FH69
|
AH89
|
TM
|
100
|
-
|
-
|
-
|
DH89
|
EH89
|
QT
|
100
|
-
|
-
|
-
|
AH96
|
QT
|
50
|
-
|
-
|
-
|
DH96
|
EH96
|
Note 1. Thicknesses in excess of these limits or those indicated by
‘-’ may be considered for approved applications.
Note 2. The maximum thickness limits of sections and bars produced
by the NR process route are generally lower than those
applicable when manufactured by the N route and are subject to
special consideration by LR.
|
10.2 Manufacture
10.2.1 The steel is to be made to a specification approved by LR which should
include the manufacturing procedure, deoxidation practice, heat treatment and
mechanical properties.
10.2.2 Vacuum degassing treatment shall be applied for all steels with enhanced
through thickness properties and for grades with yield strength level of 690, 890
and 960 N/mm2.
10.2.3 The steel is to be supplied in the fully killed and fine grain treated
condition as detailed in the approved manufacturing specification.
10.3 Chemical composition
10.3.1 The chemical analysis is to be in accordance with the approved
manufacturing specification. All the elements listed in Table 3.10.2 Chemical Composition are
to be reported.
10.3.2 All alloying elements, including residuals, are to be as detailed in the
approved manufacturing specification. Where Boron is added, this is not to exceed
0,005 per cent.
10.3.3 The steel shall contain nitrogen binding elements as detailed in the
approved manufacturing specification.
Table 3.10.2 Chemical Composition
Chemical Composition
|
Condition of supply/Steel
Grade
|
N/NR
|
TM
|
QT
|
AH42
|
EH42
|
AH42
|
EH42
|
AH42
|
EH42 FH42
|
DH42
|
EH46
|
DH42
|
FH42
|
DH42
|
EH46 FH46
|
AH46
|
|
AH46
|
EH46
|
AH46
|
EH50 FH50
|
DH46
|
|
DH46
|
FH46
|
DH46
|
EH55 FH55
|
|
|
AH50
|
EH50
|
AH50
|
EH62 FH62
|
|
|
DH50
|
FH50
|
DH50
|
EH69 FH69
|
|
|
AH55
|
EH55
|
AH55
|
DH89 EH89
|
|
|
DH55
|
FH55
|
DH55
|
DH96 EH96
|
|
|
AH62
|
EH62
|
AH62
|
|
|
|
DH62
|
FH62
|
DH62
|
|
|
|
AH69
|
EH69
|
AH69
|
|
|
|
DH69
|
FH69
|
DH69
|
|
|
|
AH89
|
DH89
|
AH89
|
|
|
|
|
EH89
|
AH96
|
|
Carbon % max
|
0,20
|
0,18
|
0,16
|
0,14
|
0,18
|
Manganese %
|
1,0~1,70
|
1,0~1,70
|
1,70
|
Silicon % max
|
0,60
|
0,60
|
0,80
|
Phosphorus % max (see Note 1)
|
0,030
|
0,025
|
0,025
|
0,020
|
0,025
|
0,02
|
Sulphur % max (see Note 1)
|
0,025
|
0,02
|
0,015
|
0,010
|
0,015
|
0,010
|
Aluminium total % min (see Note 2)
|
0,02
|
0,02
|
0,018
|
Niobium % max (see Note 2)
|
0,05
|
0,05
|
0,06
|
Vanadium % max (see note 3) 0,20
|
0,20
|
0,12
|
0,12
|
Titanium % max (see Note 3)
|
0,05
|
0,05
|
0,05
|
Nickel % max (see Note 4)
|
0,80
|
2,00 (see Note 4)
|
2,00 (see Note 4)
|
Copper % max
|
0,55
|
0,55
|
0,50
|
Chromium % max (see Note 3)
|
0,30
|
0,50
|
1,50
|
Molybdenum % max (see Note 3)
|
0,10
|
0,50
|
0,70
|
Nitrogen % max
|
0,025
|
0,025
|
0,015
|
Oxygen ppm max (see Note 5)
|
Not applicable
|
Not applicable
|
50
|
Not applicable
|
30
|
Note 1. For sections
the P and S content can be 0,005 per cent higher than the value
specified in the Table,
Note 2. The total
aluminium to nitrogen ratio shall be a minimum of 2:1, When
other nitrogen binding elements are used, the minimum Al value
and Al/N-ratio do not apply,
Note 3. Total
Nb+V+Ti ≤ 0,26 % and Mo+Cr ≤0,65%, not applicable for QT
steels,
Note 4. Higher Ni
content may be approved at the discretion of LR,
Note 5. The
requirement on maximum Oxygen content is only applicable to
DH89; EH89; DH96 and EH96.
|
For steel grades H46 and higher, CET may be used instead of
Ceq at the discretion of the manufacturer, and is to be calculated
according to the following formula:
For TM and QT steels with carbon content not exceeding 0,12 per cent, the cold
cracking susceptibility Pcm for evaluating weldability may be used instead of
carbon equivalent of Ceq or CET at the manufacturer’s discretion, and
is to be calculated using the following formula:
Table 3.10.3 Maximum Ceq, CET and Pcm values
Steel yield strength level/Condition of supply
|
Ceq (%)
|
CET
(%)
|
Pcm
(%)
|
Plates
|
Sections
|
Bars
|
Tubulars
|
all
|
all
|
t≤50
(mm)
|
50<t≤100
(mm)
|
100<t≤250
(mm)
|
t≤50
(mm)
|
t≤250
or
d≤250
(mm)
|
t≤65
(mm)
|
all
|
all
|
H42N/NR
|
0,46
|
0,48
|
0,52
|
0,47
|
0,53
|
0,47
|
N/A
|
H42TM
|
0,43
|
0,45
|
0,47
|
0,44
|
N/A
|
N/A
|
H42QT
|
0,45
|
0,47
|
0,49
|
N/A
|
N/A
|
0,46
|
H46N/NR
|
0,50
|
0,52
|
0,54
|
0,51
|
0,55
|
0.51
|
0,25
|
|
H46TM
|
0,45
|
0,47
|
0,48
|
0,46
|
N/A
|
N/A
|
0,30
|
0,23
|
H46QT
|
0,47
|
0,48
|
0,50
|
N/A
|
N/A
|
0.48
|
0,32
|
0,24
|
H50TM
|
0,46
|
0,48
|
0,50
|
N/A
|
N/A
|
0,32
|
0,24
|
H50QT
|
0,48
|
0,50
|
0,54
|
N/A
|
0,50
|
0,34
|
0,25
|
H55TM
|
0,48
|
0,50
|
0,54
|
N/A
|
N/A
|
0,34
|
0,25
|
H55QT
|
0,56
|
0,60
|
0,64
|
N/A
|
0,56
|
0,36
|
0,28
|
H62TM
|
0,50
|
0,52
|
N/A
|
N/A
|
N/A
|
0,34
|
0,26
|
H62QT
|
0,56
|
0,60
|
0,64
|
N/A
|
0,58
|
0,38
|
0,30
|
H69TM
|
0,56
|
N/A
|
N/A
|
N/A
|
0,36
|
0,30
|
H69QT
|
0,64
|
0,66
|
0,70
|
N/A
|
0,68
|
0,40
|
0,33
|
H89TM
|
0,60
|
N/A
|
N/A
|
N/A
|
0,38
|
0,28
|
H89QT
|
0,68
|
0,75
|
N/A
|
N/A
|
N/A
|
0,40
|
N/A
|
H96QT
|
0,75
|
N/A
|
N/A
|
0,40
|
N/A
|
Note N/A = Not applicable
|
10.4 Mechanical tests
10.4.1 For steels in the normalising rolled (NR) or thermomechanically
controlled rolled (TM) conditions, one tensile test is to be made for each batch of
25 tonnes or fraction thereof. Additional tests are to be made for every variation
of 10 mm in the thickness or diameter of products from the same cast. One set of
three Charpy V-notch impact tests specimens are to be taken from each piece. A piece
is to be regarded as the rolled product from a single slab or billet, or from a
single ingot if this is rolled directly into plates. Charpy V-notch impact test
specimens from plates and flats with a finished width more than 600 mm are to have
their axes transverse to the main rolling direction.
10.4.2 For normalised (N) and quenched and tempered (QT) plates, one tensile
test piece and a set of three Charpy V-notch impact test specimens are to be taken
from each plate as heat treated. Charpy V-notch impact test specimens from quenched
and tempered plates and flats with a finished width more than 600 mm are to have
their axes transverse to the main rolling direction.
10.4.3 For sections, bars and tubulars, one tensile test piece and one set of
three Charpy V-notch impact test specimens are to be taken from each batch of 25
tonnes or fraction thereof. Additional tests are to be made for every variation of
10 mm in the thickness or diameter of products from the same cast. For sections, the
thickness to be considered is the thickness of the product at the point at which
samples are taken for mechanical tests. A piece is to be regarded as the rolled
product from a single slab or billet, or from a single ingot if this is rolled
directly into sections, bars or tubulars.
10.4.4 For material with a thickness in excess of 50 mm, impact tests shall be
taken at the quarter thickness (t/4) location and additionally at mid-thickness
(t/2) location. As an alternative to a full thickness or a sub-sized flat tensile
specimen, the specimens are to be located at a position lying at a distance of t/4
from the surface and additionally at t/2 for thickness above 100 mm or as near as
possible to these positions.
10.4.5 For steels designated with improved through thickness properties, through
thickness tensile tests are to be performed in accordance with the requirement of
Ch 3, 8 Plates with specified through thickness properties.
Through-thickness tensile strength is required to be not less than 80 % of the
specified minimum tensile strength.
10.4.6 The results of the tests are to comply with the appropriate requirements
of Table 3.10.4 Mechanical Properties for acceptance purpose.
Table 3.10.4 Mechanical properties for
acceptance purpose
Steel grade
|
Yield Stress
N/mm2 min
(see Notes 1
and 2)
|
Tensile Strength
N/mm2
|
Elongation on
5,65
%min
(see Note 3)
|
Charpy V-notch impact test
|
Nominal thickness (mm)
|
Average energy J Minimum
|
≥3≤50
|
>50≤ 100
|
>100≤150
|
>150≤250
|
≥3≤50
|
>50≤ 100
|
>100≤150
|
>150≤250
|
T
|
L
|
T
|
L
|
AH42
DH42
EH42
FH42
|
420
|
390
|
365
|
365
|
520~680
|
520~680
|
470~650
|
470~650
|
19
|
21
|
28
|
42
|
AH46
DH46
EH46
FH46
|
460
|
430
|
390
|
390
|
540~720
|
540~720
|
500~710
|
500~710
|
17
|
19
|
31
|
46
|
AH50
DH50
EH50
FH50
|
500
|
480
|
440
|
-
|
590~770
|
590~770
|
540~720
|
-
|
17
|
19
|
33
|
50
|
AH55
DH55
EH55
FH55
|
550
|
530
|
490
|
-
|
640~820
|
640~820
|
590~770
|
-
|
16
|
18
|
37
|
55
|
AH62
DH62
EH62
FH62
|
620
|
580
|
560
|
-
|
700~890
|
700~890
|
650~830
|
-
|
15
|
17
|
41
|
62
|
AH69
DH69
EH69
FH69
|
690
|
650
|
630
|
-
|
770~940
|
770~940
|
710~900
|
-
|
14
|
16
|
46
|
69
|
AH89
DH89
EH89
|
890
|
830
|
-
|
-
|
940~1100
|
940~1100
|
-
|
-
|
11
|
13
|
46
|
69
|
AH96
DH96
EH96
|
960
|
-
|
-
|
980~1150
|
-
|
-
|
-
|
10
|
12
|
46
|
69
|
Symbols
|
T = Transverse
|
L = Longitudinal
|
Notes
|
Impact tests are to be made on
the various grades at the following temperatures:
- AH grades 0°C
- DH grades -20°C
- EH grades -40°C
- FH grades -60°C
Note 1. For
tensile test either the upper yield stress (ReH) or where
ReH cannot be determined, the 0,2 per cent proof stress
(Rp0,2) is to be determined.
Note 2. The
ratio of actual yield strength to tensile strength shall not
exceed 0,94. A higher yield strength to tensile strength
ratio may be acceptable on a project specific basis, subject
to special consideration.
Note 3. For full
thickness flat test specimens with a width of 25 mm and a
gauge length of 200 mm the elongation is to comply with the
minimum values shown in Table 3.10.5 Elongation minimum
values for a width of 25 mm and a 200 mm gauge
length.
|
Table 3.10.5 Elongation minimum values for a width of 25 mm and a 200 mm gauge
length
Thickness (mm)
(See Note
1)
|
≤10
|
>10
≤15
|
>15
≤20
|
>20
≤25
|
>25
≤40
|
>40
≤50
|
>50
≤70
|
Elongation (%)
|
Strength
levels
|
|
|
|
|
|
|
|
H42
|
11
|
13
|
14
|
15
|
16
|
17
|
18
|
H46
|
11
|
12
|
13
|
14
|
15
|
16
|
17
|
H50
|
10
|
11
|
12
|
13
|
14
|
15
|
16
|
H55
|
10
|
11
|
12
|
13
|
14
|
15
|
16
|
H62
|
9
|
11
|
12
|
12
|
13
|
14
|
15
|
H69
(see
note 2)
|
9
|
10
|
11
|
11
|
12
|
13
|
14
|
H89
H96
|
See Note 3
|
Note 1. The tabulated elongation minimum values are the
requirements for testing specimen in transversed direction.
Note 2. Re-test can be carried out on the standards proportional
test specimen witha gauge length of
L0=5.65√S0 to meet the
requirement of Table 3.10.4 Mechanical Properties for
acceptance purpose when the elongation does not meeting
the requirement in this table. See Ch 2, 2.4 Equivalent
elongations.
Note 3. Steel with strength level of 89 and 96 shall be tested by
proportional specimens witha gauge length of
L0=5.65√S0.
|
10.5 Identification of materials
10.5.1 The particulars detailed in Ch 3, 1.12 Identification of materials are to be
marked on each piece which has been accepted and, for ease of recognition, are to be
encircled or otherwise marked with paint.
10.6 Certification of materials
10.6.1 At least two copies of each test certificate are to be provided. They are
to be of the type and give the information detailed in Ch 3, 1.13 Certification of materials and,
additionally, are to state the specified maximum Ceq, CET or
Pcm. As a minimum, chemical composition is to include the contents of any
grain refining elements used and of the residual elements as detailed in Table 3.10.2 Chemical Composition.
|