Section
2 Forgings for ship and other structural applications
2.1 Scope
2.1.1 This Section
gives the specific requirements for carbon-manganese steel forgings
intended for ship and other structural applications such as rudder
stocks, pintles, etc.
2.1.2 Where it
is proposed to use an alloy steel, particulars of the chemical composition,
mechanical properties and heat treatment are to be submitted for approval, see
Ch 5, 1.4 Chemical composition 1.4.3.
2.2 Chemical composition
2.2.1 For forgings to which structural items are to be attached by welding or
which are intended for parts of a fabricated component, or are to be weld cladded or may
be subject to weld repair in service, the chemical composition of ladle samples is to
comply with Table 5.2.1 Chemical composition limits for
hull steel forgings:
Table 5.2.1 Chemical composition limits for
hull steel forgings
Steel type
|
Composition in percentage mass by mass maximum
unless shown as a range
|
C
|
Si
|
Mn
|
P
|
S
|
Cr
|
Mo
|
Ni
|
Cu
See Note 2
|
Total
residuals
|
C,
C-Mn
|
0,23
Max.
See Note 1
|
0,45
Max.
|
0,30-1,50
|
0,035
Max
|
0,035
Max
|
0,30
Max
See Note 2
|
0,15
Max
See Note 2
|
0,40
Max.
See Note 2
|
0,30
Max.
|
0,85
Max.
|
Alloy
See Note 4
|
Note
3
|
0,45
Max.
|
Note
3
|
0,035
Max.
|
0,035
Max.
|
Note
3
|
Note
3
|
Note
3
|
0,30
Max.
|
-
|
Note 1: The carbon
content may be increased above this level provided that the carbon
equivalent (Ceq) is not more than 0,41%, calculated using the
following formula:
Note 2: Elements are
considered as residual elements.
Note 3: Specification is
to be submitted for approval.
Note 4: The contents of
all alloying elements and significant impurities detailed in the
specification are to be reported.
|
2.2.3 For C and C-Mn steel forgings not intended for welded construction, the
carbon content may be 0,65 per cent maximum.
2.2.4 Where alloy steel forgings are intended for welded constructions, the proposed chemical
composition is subject to approval by LR.
2.3 Heat treatment
2.3.1 Forgings are to be supplied in one of the following conditions:
- Carbon and carbon-manganese steels:
- Fully annealed.
- Normalised.
- Normalised and tempered.
- Quenched and tempered.
- Alloy steels:
- Normalised.
- Normalised and tempered.
- Quenched and tempered.
For all types of steel, the tempering temperature is to be not less than 550°C.
2.3.2 The delivery condition shall meet the design and application requirements.
It is the manufacturer’s responsibility to select the appropriate heat treatment method
to obtain the required mechanical properties.
2.4 Mechanical tests
2.4.2 Where a forging
exceeds both 4 tonnes in mass and 3 m in length, tensile test specimens
are to be taken from each end. These limits refer to the `as forged'
mass and length but exclude the test material.
2.4.3 Unless otherwise
agreed between the manufacturer and the Surveyor, the test specimens
are to be cut in a longitudinal direction.
2.4.5 For large
forgings, where tensile tests are taken from each end, the variation
in tensile strength is not to exceed 70 N/mm2.
2.4.6 For rudder stocks, pintles, and rudder coupling keys and bolts, the minimum
specified yield strength is not to be less than 200 N/mm2, see
Table 13.2.1 Rudder material factor,
k in Pt 3 Ship Structures (General)
of the Rules and Regulations for the Classification of Ships, July 2022.
Table 5.2.2 Mechanical properties for ship and other structural applications
Steel
type
|
Tensile strength Rm min. N/mm2
|
Yield
stress Re min. N/mm2
|
Elongation A5 min. %
|
Reduction of area Z min. %
|
Charpy V-notch impact test
See Notes 1 &
2
|
Long.
|
Tang.
|
Long.
|
Tang.
|
Test
temperature (0C)
|
Minimum average energy (J)
|
Long.
|
Tang.
|
C and
C-Mn
|
360-480
|
180
|
28
|
20
|
50
|
35
|
0
|
27
|
18
|
400-520
|
200
|
26
|
19
|
50
|
35
|
440-560
|
220
|
24
|
18
|
50
|
35
|
470-590
|
235
|
23
|
17
|
45
|
35
|
480-600
|
240
|
22
|
16
|
45
|
30
|
520-640
|
260
|
21
|
15
|
45
|
30
|
560-680
|
280
|
20
|
14
|
40
|
27
|
600-750
|
300
|
18
|
13
|
40
|
27
|
Alloy
|
550-670
|
350
|
20
|
14
|
50
|
35
|
600-750
|
400
|
18
|
13
|
50
|
35
|
650-800
|
450
|
17
|
12
|
50
|
35
|
Note 1. Special consideration may be given to
alternative requirements for Charpy V-notch test, depending on design
and application, and subject to agreement by LR.
Note 2. For ships with ice class notation:Impact
tests are required for rudder stocks intended for ships with ice class
notation 1AS FS(+), IAS FS, 1A FS(+), 1A FS, 1B FS(+), 1B FS, 1C FS(+)
and 1C FS. The tests are to be carried out for all steel types at
minus 10°C and the average energy value is to be minimum 20J
(longitudinal test). One individual value may be less than the
required average value provided that it is not less than 70% of this
average value.
|
2.5 Non-Destructive Examination
2.5.1 Surface inspections are to be carried out by visual examination and magnetic
particle testing (or liquid penetrant testing where appropriate), for the purpose of
detecting relevant indications and assessing them against the accept/reject criteria
stated in Ch 5, 2.5 Non-Destructive Examination 2.5.4. Personnel engaged
in visual examination are to have sufficient knowledge and experience; however, they may
be exempted from formal qualification requirements.
2.5.3 For the purpose
of evaluating indications, the surface is to be divided into reference
areas of 225 cm2. The area is to be taken in the most unfavourable
location relative to the indication being evaluated.
2.5.4 The allowable number and size of indications in the reference area is given
in Table 5.2.3 Steel forgings surface
inspection.
Table 5.2.3 Steel forgings surface
inspection
Inspection zone
|
Maximum number
of indications
|
Type of indication
|
Maximum
number each type
|
Maximum
dimension, mm
|
I
|
3
|
Linear
|
0, see Note
|
–
|
Non-linear
|
3
|
3,0
|
Aligned
|
0, see Note
|
–
|
II
|
10
|
Linear
|
3,
see Note
|
3,0
|
Non-linear
|
7
|
5,0
|
Aligned
|
3, see Note
|
3,0
|
Note Linear or aligned indications are not permitted on bolts,
which receive a direct fluctuating load, e.g. main bearing bolts,
connecting rod bolts, crosshead bearing bolts and cylinder cover
bolts.
|
2.5.5 Volumetric
inspection is to be carried out by ultrasonic testing using the contact
method.
2.5.6 Ultrasonic
testing is to be carried out on rudder stocks having a finished diameter
of 200 mm or greater.
|