General
Properties
Alloy 317LMN and 317L are molybdenum-bearing austenitic
stainless steels with greatly increased resistance
to chemical attack as compared to the conventional
chromium-nickel austenitic stainless steels such
as Alloy 304. In addition, 317LMN and 317L alloys
offer higher creep, stress-to-rupture, and tensile
strengths at elevated temperatures than conventional
stainless steels. All are low carbon or "L"
grades to provide resistance to sensitization
during welding and other thermal processes. The
"M" and "N" designations indicate
that the compositions contain increased levels
of molybdenum and nitrogen respectively. The combination
of molybdenum and nitrogen is particularly effective
in enhancing resistance to pitting and crevice
corrosion, especially in process streams containing
acids, chlorides, and sulfur compounds at elevated
temperatures. Nitrogen also serves to increase
the strength of these alloys. Both alloys are
intended for severe service conditions such as
flue gas desulfurization (FGD) systems.
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Composition
Chemical Composition
in Weight Percent
per ASTM A240 for Cited Alloys |
| Element |
Type 317L |
Type 317LMN |
| Carbon |
0.03 max |
0.03 max |
| Manganese |
2.00 |
2.00 |
| Silicon |
0.75 max |
0.75 max |
| Chromium |
18.00 - 20.00 |
17.00 - 20.00 |
| Nickel |
11.00 - 15.00 |
13.50 - 17.50 |
| Molybdenum |
3.00 - 4.00 |
4.00 - 5.00 |
| Phosphorus |
0.04 max |
0.04 max |
| Sulfur |
0.03 max |
0.03 max |
| Nitrogen |
0.10 max |
0.10 - 0.20 |
| Iron |
Balance |
Balance |
| UNS
No. |
S31703 |
S31726 |
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Resistance
to Corrosion
Alloys 317L and 317LMN stainless steels
are more resistant to atmospheric and other mild
types of corrosion than conventional chromium-nickel
stainless steels. In general, environments that
are not corrosive to 18Cr-8Ni steels will not
attack alloys containing molybdenum, with the
exception of highly oxidizing acids such as nitric
acid.
Alloys 317LMN and 317L stainless
steels are considerably more resistant than conventional
chromium-nickel types to solutions of sulfuric
acid. Resistance increases with alloy molybdenum
content. These alloys are resistant to sulfuric
acid concentrations up to 5 percent at temperatures
as high as 120°F (49°C). At temperatures
under 100°F (38°C) these alloys have excellent
resistance to solutions of higher concentration.
However, service tests are recommended to account
for the affects of specific operating conditions
that may affect corrosion behavior. In processes
where condensation of sulfur-bearing gases occurs,
these alloys are much more resistant to attack
at the point of condensation than conventional
Alloy 316. The acid concentration has a marked
influence on the rate of attack in such environments
and should be carefully determined by service
tests.
The table below compares the corrosion
resistance of annealed strip samples of 317LMN
and 317L stainless steels in a variety of solutions
related to the process industries as well as standard
ASTM tests. Data on Alloy 316L and Alloy 276 are
presented for comparison.
| Corrosion Resistance
in Boiling Solutions and ASTM Tests |
Test
Solution |
Corrosion
Rate in Mils per Year (mm/y)
for Cited Alloys |
Alloy
316L |
Alloy
317L |
Alloy
317LMN |
Alloy
276 |
20%
Acetic Acid |
0.12
(<0.01) |
0.48
(0.01) |
0.12
(<0.01) |
0.48
(0.01) |
45%
Formic Acid |
23.41
(0.60) |
18.37
(0.47) |
11.76
(0.30) |
2.76
(0.07) |
10%
Oxalic Acid |
48.03
(1.23) |
44.90
(1.14) |
35.76
(0.91) |
11.24
(0.28) |
20%
Phosphoric
Acid |
0.06
(0.02) |
0.72
(0.02) |
0.24
(<0.01) |
0.36
(0.01) |
10%
Sulfuric Acid |
635.7
(16.15) |
298.28
(7.58) |
157.80
(4.01) |
13.93
(0.35) |
10%
Sodium
Bisulfate |
71.57
(1.82) |
55.76
(1.42) |
15.60
(0.40) |
2.64
(0.07) |
50%
Sodium
Hydroxide |
77.69
(1.92) |
32.78
(0.83) |
85.68
(2.18) |
17.77
(0.45) |
ASTM
A262
Practice B
(FeSO4H2SO4) |
26.04
(0.66) |
20.76
(0.53) |
17.28
(0.44) |
264.5
(6.72) |
ASTM
A262
Practice C
(65% HNO3) |
22.31
(0.56) |
19.68
(0.50) |
16.32
(0.42) |
908.0
(23.06) |
ASTM
A262
Practice E
(Cu•CUSO4•H2SO4) |
Pass |
Pass |
Pass |
Pass |
The low carbon (less than 0.03%)
of these alloys effectively prevents sensitization
to intergranular corrosion during thermal processes
such as welding or forging. The higher chromium
contents of 317LMN and Alloy 317L stainless steels
also provide superior resistance to intergranular
attack. It should be noted that prolonged exposure
in the range 800 to 1400°F (427-816°C)
can be detrimental to intergranular corrosion
resistance and may also cause embrittlement due
to precipitation of sigma phase. The higher nitrogen
content of the 317LMN alloy retards the precipitation
of sigma phase as well as carbides.
| Pitting Resistance Equivalents |
| Alloy |
PRE |
Alloy 316
|
25 |
| Alloy 317L |
30 |
| Alloy 317LMN |
38 |
| Alloy 625 |
52 |
| Alloy C276 |
69 |
High molybdenum and nitrogen contents
can significantly improve pitting resistance as
illustrated in the preceding table of Pitting
Resistance Equivalents (PRE). The PRE is based
on the results of corrosion tests in which it
was found that nitrogen was 30 times more effective
than chromium and approximately 9 times more effective
than molybdenum in enhancing chloride pitting
resistance.
The temperature of the onset of
crevice corrosion as determined in a modified
AST G-48B test is a useful means of ranking the
relative resistance of stainless and nickel-base
alloys. The Critical Crevice Corrosion Temperatures
table that follows demonstrates that crevice corrosion
resistance for austenitic stainless steels increases
with the alloy's molybdenum and nitrogen content.
Crevice Corrosion in
a Simulated
FGD System Environment |
| Alloy |
Weight
Loss (g/cm2)
for Tests* at Cited Temperatures |
24°C
(75°F) |
50°C
(122°F) |
70°C
(158°F) |
Alloy 317L
|
0.0007
|
0.0377
|
0.0500 |
| Alloy 317LMN |
0.0000 |
0.0129 |
0.0462 |
| Alloy 625 |
0.0000 |
0.0000 |
0.0149 |
| Alloy C276 |
0.0000 |
0.0001 |
0.0004 |
*72-hour exposure based on ASTM
G-48B procedure using the following solution:
7 vol.%H2SO4, 3 vol%HCI,
1 wt% CuCl2, 1 wt%FeCl3
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Oxidation
Resistance
The chromium-nickel-molybdenum steels all have
excellent resistance to oxidation and a low rate
of scaling in ordinary atmospheres at temperatures
up to 1600-1650°F (871-899°C).
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Fabrication
The physical and mechanical properties
of 317LMN and Alloy 317L stainless steels are
similar to those of more conventional austenitic
stainless steels and can, therefore, be fabricated
in a manner similar to Alloys 304 and 316.
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Heat
Treatment
Forging
The recommended initial temperature range is 2100-2200°F
(1150-1205°C) with a finishing range of 1700-1750°F
(927-955°C).
Annealing
317LMN and Alloy 317L stainless steels can be
annealed in the temperature range 1975-2150°F
(1080-1175°C) followed by an air cool or water
quench, depending on thickness. Plates should
be annealed between 2100°F (1150°C) and
2150°F (1175°C). The metal should be cooled
from the annealing temperature (from red/white
to black) in less than three minutes.
Hardenability
These grades are not hardenable by heat treatment.
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Welding
The use of an overalloyed filler is suggested
to maintain corrosion resistance in the as-welded
condition. Filler metals containing at least 6%
molybdenum are suggested for welding Alloy 317L
and a filler metal with at least 8% molybdenum,
such as Alloy 625, is suggested for 317LMN. In
applications where it is not possible to use an
overalloyed filler metal or to perform a post-weld
anneal and pickle treatment, the severity of the
service environment should be carefully considered
to determine if the properties of autogenous welds
(weld made without a filler) are satisfactory.
The optimum corrosion resistance of autogenously
welded 317LMN and Alloy 317L stainless steels
is obtained by post-weld annealing and pickling.
ASTM A-380 "Recommended Practice for Descaling
and Cleaning Steel Surfaces" is suggested
for more information.
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Mechanical
Properties
The ASTM specified minimum tensile properties
and maximum hardness for annealed plate, sheet,
and strip products are shown in the following
table.
Minimum
Mechanical Properties per
ASTM A-240 for Cited Alloys |
| Property |
Alloy 317L |
Alloy 317LMN |
Ultimate
Tensile Strength, ksi (MPa)
|
75
(515)
|
80
(550) |
| 0.2%
Yield Strength, ksi (MPa) |
30
(205) |
35
(240) |
| %
Elongation in 2" (5.1 cm) |
40 |
40 |
| Hardness,
Maximum |
217BHN |
-- |
| UNS
No. |
S31703 |
S31726 |
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Physical
Properties
The physical property data which follows represent
the iron-chromium-nickel-molybdenum class of stainless
steels. For all practical purposes, the data are
applicable to 317LMN and Alloy 317L stainless
steels. All properties are at room temperature
(68°F, 20°C) unless stated otherwise.
Density
|
0.29
8.0
|
lb/in3
g/cm3 |
| Modulus
of Elasticity |
29•106
200 |
psi
Gpa |
| Melting
Range |
2410 to 2550
1320 to 1400 |
° F
°C |
Thermal
Conductivity
68 to 212°F
20 to 100°C |
100.8
14.6 |
Btu/ft2-hr-°F-in
Watts/m- K |
Coefficient
of Thermal Expansion
77°F (25°C) to:
212°F (100°C)
932°F (500°C)
1832°F (1000°C) |
9.2 (16.5)
10.1 (18.2)
10.8 (19.5) |
10-6/°F (10-6/°C)
10-6/°F (10-6/°C)
10-6/°F (10-6/°C) |
| Specific
Heat |
0.11
0.46 |
Btu/lb-°F
J/g-°K |
| Electrical
Resistivity |
31.1
0.79 |
µ-ohm-in
µ-ohm-in |
Magnetic
Permeability
Fully annealed
0.5" plate
65% cold-worked 0.5"
plate |
1.0028
1.0028 |
µ at H = 200 oe
µ at H = 200 oe |
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