Section
9 Stainless steel forgings
9.1 General
9.1.1 Forgings in austenitic and duplex stainless steels are acceptable for the
construction of marine structures, machinery, pressure vessels and piping systems in
ships. They may also be accepted for elevated temperature service in boilers. The
allowable number and size of indications in the reference area are given in Table 5.2.3 Steel forgings surface
inspection. This Table is also
applicable to austenitic stainless steel and ferritic-austenitic (duplex) stainless
steel forgings, for the purposes of assessing surface indications.
9.1.2 Austenitic stainless steel forgings are suitable for applications where the design
temperature is not lower than -165°C.
9.1.4 Duplex stainless steels forgings are suitable for applications where the design
temperature is not lower than -20°C.
9.1.5 Where it is proposed to use alternative steels, particulars of the specified chemical
composition, mechanical properties and heat treatment are to be submitted for
approval.
9.2 Chemical composition
9.3 Heat treatment
9.3.1 All materials
are to be supplied in the solution treated condition.
9.4 Mechanical tests
9.4.3 For austenitic
stainless steel forgings, impact tests may be omitted subject to prior
agreement with LR.
9.5 Mechanical properties for design purposes
9.6 Non-Destructive Examination
9.6.1 Non-destructive
examination is to be carried out in accordance with the requirements
of the approved forging drawing and specification or as otherwise
agreed between the manufacturer, purchaser and Surveyor.
9.7 Corrosion tests
9.7.1 Where corrosive conditions are anticipated in service, for grades 304, 316
and 317 intergranular corrosion tests are required in accordance with Ch 2, 9.1 Intergranular corrosion test. Such tests may also be required for grades
304L, 316L and 347.
9.7.2 Where corrosive conditions are anticipated in service, for duplex stainless
grades pitting corrosion tests are required in accordance with Ch 2, 9.2 Pitting corrosion test . Unless otherwise specified, the test temperatures
shall be 20°C for S31803 and 30°C for S32750.
Table 5.9.1 Chemical composition of stainless
steel forgings
Type of steel
|
Chemical composition % (see Note)
|
C
|
Si
|
Mn
|
S
|
P
|
Cr
|
Mo
|
Ni
|
Others
|
Austenitic
|
304L
|
0,03
|
1,000
|
2,000
|
0,030
|
0,045
|
18,0–20,0
|
-
|
8,0–13,0
|
-
|
304
|
0,08
|
18,0–20,0
|
-
|
8,0–11,0
|
-
|
316L
|
0,03
|
16,0–18,0
|
2,0–3,0
|
10,0–15,0
|
|
316
|
0,08
|
16,0–18,0
|
2,0–3,0
|
10,0–14,0
|
|
317
|
0,08
|
18,0–20,0
|
3,0–4,0
|
11,0–15,0
|
|
347
|
0,08
|
17,0–20,0
|
–
|
9,0–13,0
|
Nb >10xC ≤1,10
|
|
Duplex
|
UNS S 31803
|
0,03
|
1,00
|
2,00
|
0,020
|
0,030
|
21,0–23,0
|
2,5–3,5
|
4,5–6,5
|
N 0,08–0,20
|
UNS S 32750
|
0,03
|
0,80
|
1,20
|
0,020
|
0,035
|
24,0–26,0
|
3,0–5,0
|
6,0–8,0
|
N 0,24–0,32 Cu 0,50
|
Note Where a single value is shown (and not a range of values),
the value is to be taken as maximum.
|
Table 5.9.2 Mechanical properties for
acceptance purposes: stainless steel forgings
Type of steel
|
Tensile strength
N/mm2 minimum
|
1,0% proof stress
N/mm2 minimum
|
Elongation on 5,65
√So % minimum
|
Reduction of area %
minimum
|
Charpy V-notch impact tests
|
Test temperature
oC
|
Average energy
J
|
Austenitic
|
304L
|
485
|
170
|
30
|
50
|
–196
|
41
|
304
|
515
|
205
|
316L
|
485
|
170
|
316
|
515
|
205
|
317
|
515
|
205
|
347
|
515
|
205
|
Duplex
|
UNS S 31803
|
620
|
450
|
25
|
45
|
–20 (see Note)
|
41
|
UNS S 32750
|
800
|
550
|
15
|
40
|
Note Charpy V-notch impact tests are to be carried
out at a temperature 5°C below design temperature or -20°C, whichever is
lower.
|
Table 5.9.3 Mechanical properties for design
purposes: austenitic stainless steels
Grade
|
Nominal 1% proof stress (N/mm2) at a
temperature of
|
100°C
|
150°C
|
200°C
|
250°C
|
300°C
|
350°C
|
400°C
|
450°C
|
500°C
|
550°C
|
600°C
|
650°C
|
700°C
|
304L
|
168
|
150
|
137
|
128
|
122
|
116
|
110
|
108
|
106
|
102
|
100
|
96
|
93
|
316L
|
177
|
161
|
149
|
139
|
133
|
127
|
123
|
119
|
115
|
112
|
110
|
107
|
105
|
316LN
|
238
|
208
|
192
|
180
|
172
|
166
|
161
|
157
|
152
|
149
|
144
|
142
|
138
|
321
|
192
|
180
|
172
|
164
|
158
|
152
|
148
|
144
|
140
|
138
|
135
|
130
|
124
|
347
|
204
|
192
|
182
|
172
|
166
|
162
|
159
|
157
|
155
|
153
|
151
|
—
|
—
|
|