| Alloy
317LMN
Sandmeyer Steel Company has the only North American
stock of 317LMN stainless steel plate in thicknesses
from 3/16" through 1/2".
317LMN (UNS S31726)合金是以钼为基础的奥氏体不锈钢，具有很强的抗化学侵
蚀能力。另外，与常规的不锈钢相比，317MN 合金具有更高的延展性、抗应力断
裂、在高温下较高的耐压强度。它是低碳等级或L 等级， 这个等级具有在焊接期
间及热处理过程中抗敏化作用性能。M 和N 分别指较高的钼及镍含量。钼和镍含
量使其具有较强的抗斑蚀和裂隙腐蚀能力，尤其是在高温的含有酸、氯化物、硫
化合物溶液中。氮含量提高了其强度。这个不锈钢合金在所有的标准等级的不锈
钢中抗水腐蚀能力最高。
Specs:
317LMN
General Properties
Composition
Resistance to Corrosion
Oxidation Resistance
Fabrication
Heat Treatment
Welding
Mechanical Properties
Physical Properties
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 |
| Molybden |
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 |
*Optional
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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 Alloys 316L and AL276 alloy are resented 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 |
| 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) |
Type 317L
|
0.0007
|
0.0377
|
0.0500 |
| 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 |
Type 317L |
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 (20°C, 68°F) 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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