UNS N08904 · W.Nr. 1.4539 · X1NiCrMoCu25-20-5 · ASTM A240 composition: 19.0-23.0% Cr – 23.0-28.0% Ni – 4.00-5.00% Mo – 1.00-2.00% Cu – C ≤ 0.020% – N ≤ 0.10% – balance Fe. The EN 1.4539 band is narrower: 19.0-21.0% Cr – 24.0-26.0% Ni – 4.0-5.0% Mo – 1.2-2.0% Cu. It is a SUPERAUSTENITIC stainless steel: produced by SOLUTION ANNEALING + RAPID COOLING, NOT PRECIPITATION HARDENABLE and not aged; strength is raised only by COLD WORK.
Bought for process equipment where reducing acids and warm chloride environments occur together: sulphuric and phosphoric acid service, pulp and paper, refineries, fertiliser plants, acid pickling lines, seawater-wetted equipment.
Forms
Round bar · flat bar · plate · sheet · pipe and tube · forging. All forms supplied to order.
Standards
THERE IS NO AMS — no AMS number for N08904 could be confirmed in any independent source. ASTM: A240 / SA-240 (plate, sheet, strip) · A276 (bar and shapes) · A479 / SA-479 (bar and shapes for boilers and pressure vessels) · A182 / SA-182 (forged flanges, fittings and valve parts, F904L) · A312 / SA-312 (seamless and welded pipe). EN: 10088-2, 10088-3, 10272. Also NACE MR0175. 1) N08904 HAS BEEN MOVED FROM THE B-SERIES TO THE A-SERIES. N08904 IS NO LONGER in the current grade lists of the nickel-alloy B-series standards: the scope of ASTM B649 is N08925, N08024, N08026, N08031, N08354, N08926, N08936 and R20033 (HT Pipe and…
Advantage
Resistance to reducing acids, and the COPPER behind it. The 1-2% copper addition makes 904L suitable for sulphuric and phosphoric acid service under reducing conditions; this is a mechanism separate from molybdenum or chromium.
Welding
It is weldable. Filler metal: Sandmeyer gives the ’20 25 CuL’ covered electrode and wire; thyssenkrupp states that TIG, MAG, arc, laser beam and submerged arc welding are suitable;
Limits
1) DO NOT EXPECT STRENGTH. In ASTM A479 the tensile minimum of 904L, 490 MPa, is BELOW that of 304 and 316 in the same table (515 MPa); its yield minimum of 220 MPa is 15 MPa above theirs. 904L is not a strength material but a corrosion material.
Compiled from manufacturer data sheets · confirm against the current specification before ordering
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Standards by Product FormWelding, Heat Treatment and Machining904L, 316L and the Super AlloysFrequently Asked Questions
AISI 904L is an alloy in the austenitic stainless steel class, known for its high corrosion resistance and exceptional resistance to rusting.
Corrosion resistance: AISI 904L stainless steel has a chemical composition able to withstand even severely corrosive environments. The bonds formed by the combination of the high chromium, nickel and molybdenum content it carries allow the material to work even in environments that would be severely corrosive. This stainless grade is particularly resistant to sulphuric acid and to heavy chloride environments.
Temperature capability: Although the alloying elements it contains raise corrosion resistance, they lower its heat resistance as they do in other high-alloy materials. It cannot be used above 400 °C.
Weldability: 904L stainless steel can be welded by any method as long as filler of the same grade is used. Its low carbon content minimises the adverse effects of welding during extensive welding.
Machinability: This stainless grade is not a particularly hard material in terms of surface hardness, but the heavy nickel content it carries can cause the chip to wrap.
Heat treatment: It cannot be hardened by heat treatment.
Applications: 904L stainless steel is frequently used in very demanding conditions and in severely corrosive environments. 904L (1.4539) is chosen in acid environments that ordinary stainless steel could not withstand, in the petrochemical industry where severe rusting and corrosion occur, in paper mills, in treatment plants, in gas production and filling plants, in medical applications — in short, everywhere that corrosion resistance must be at the highest level.
Chemical Composition
DEFENCE METAL
C
Max. 0.02
Mn
Max. 2.00
Si
Max. 1.00
P
Max. 0.045
S
Max. 0.035
Cr
Min. 19.00 · Max. 23.00
Mo
Min. 4.00 · Max. 5.00
Ni
Min. 23.00 · Max. 28.00
Cu
Min. 1 · Max. 2
Mechanical Properties
DEFENCE METAL
Tensile Strength (MPa)
490
Proof Stress (MPa)
220
Elongation A50 mm
36
Hardness Brinell
150 Max HB
Density
7.90 g/cm3
Melting Point
1300 – 1390 °C
Modulus of Elasticity
190 GPa
Electrical Resistivity
952 nΩ.m
Thermal Conductivity
11.5 W/m.K
Thermal Expansion
15 μm/m
Standards and Equivalents · AISI 904L
DEFENCE METAL
Trade name
AISI 904L
UNS
N08904
W.Nr (DIN/EN)
1.4539
ASTM
A182 · A262 · A479 · B649
Available forms
Round bar · Flat bar · Plate · Sheet · Tube · Forgings All forms are supplied to order.
Standards by Product Form
STANDARDS BY PRODUCT FORM
DEFENCE METAL
Product form
Standards
Plate
NO AMS · ASTM A240 / ASME SA-240 · EN 10088-2 · EN 10028-7 (A240 confirmed via Metalcor and ISSF)
Sheet and strip
NO AMS · ASTM A240 / ASME SA-240 · EN 10088-2
Round bar, flat bar (including square and hexagon)
NO AMS · ASTM A276 · ASTM A479 / ASME SA-479 · ASTM A484 (general requirements) · EN 10088-3
Forging
NO AMS · ASTM A182 / ASME SA-182 (F904L) · EN 10222-5
Flange
NO AMS · ASTM A182 / ASME SA-182 (F904L) · dimensions to ASME B16.5 / B16.47 · EN 10222-5 · EN 10272
Seamless and welded pipe
NO AMS · ASTM A312 / ASME SA-312 · EN 10216-5 (seamless) · EN 10217-7 (welded)
OLD B-SERIES NUMBERS — SHOULD NOT BE USED
N08904 IS NOT in the current grade lists of ASTM B625 and ASTM B649 (HT Pipe, Ferrobend). Old datasheets and some vendor pages still write ‘SB649 N08904’; orders should be placed against the A-series.
There is NO AMS number for N08904; ASTM is given directly. N08904 has been moved from the nickel-alloy B-series to the stainless A-series. Orders should not be placed against the SB625 / SB649 numbers found on old datasheets. 904L is not an AISI number; what binds is UNS N08904 and 1.4539.
There is an important change to be aware of when ordering 904L: ASTM moved N08904 out of the B-series nickel alloy standards into the A-series stainless standards. The reason is stated in ASTM’s own text — iron is the largest element by mass percent in this grade. Most datasheets in circulation still quote the old B numbers; the B/SB numbers remain valid on legacy projects, but new orders should use the A-series number.
Standards by Product Form · AISI 904L (N08904 / 1.4539)
DEFENCE METAL
Sheet · Plate · Strip
ASTM A240 / A480(formerly B625) · EN 10088-2 · EN 10028-7
Bar · Wire
ASTM A479 / A484(formerly B649) · EN 10088-3
Seamless pipe · tube
ASTM A312 · A269(formerly B677) · EN 10216-5
Welded pipe
ASTM A312(formerly B673) · EN 10217-7
Welded tube
ASTM A249(formerly B674)
Heat exchanger tube
ASTM A213
Mechanical tube (EN)
EN 10296-2
Fittings
EN 10253-3 · EN 10253-4
Welding wire
AWS A5.9 ER385(20 25 CuL)
Welding electrode
AWS A5.4 E385-16 · E385-17
Mechanical minimums in the solution-annealed condition (ASTM): yield ≥ 220 MPa, tensile ≥ 490 MPa, elongation ≥ 35%, hardness 70–90 HRB. EN 10088-2 requires yield ≥ 220 MPa and tensile 520–720 MPa for plate. On chemistry the EN 1.4539 range is narrower than ASTM N08904 (Cr 19–21% against 19–23%, Ni 24–26% against 23–28%).
Welding, Heat Treatment and Machining
HEAT TREATMENT — SCHEMATIC
DEFENCE METAL
1 · SOLUTION ANNEAL — this is the only valid heat treatment
Step
1 · SOLUTION ANNEAL — this is the only valid heat treatment
Summary
It reverses cold work, takes precipitated phases into solid solution, renews the grain structure and restores corrosion resistance. IT DOES NOT RAISE STRENGTH, IT LOWERS IT. This is the delivery condition; ASTM A240, A276, A479, A182 and A312 all call for the material in this state.
Temperature
The sources and the specifications diverge on the band ends, ALL UNDER THEIR SOURCE NAME: ISSF/worldstainless 1090-1175 °C · Sandmeyer 1060-1140 °C (1940-2084 °F) · Virgamet 1050-1150 °C · ASTM A182 (F904L) 1100-1150 °C (2010-2100 °F) · ASTM A312 1040-1100 °C · ASTM A240 a minimum of 1010-1120 °C. NO SINGLE NUMBER IS WRITTEN, NO AVERAGE IS TAKEN. The practical envelope is roughly 1040-1175 °C; whichever specification the order is placed against, that specification’s own band governs.
Time
No numerical soak time could be confirmed in four independent sources, so NONE IS WRITTEN. The time is set by getting the whole section to temperature.
Cooling
RAPID COOLING IS MANDATORY — it is a metallurgical requirement, not a preference. ISSF says ‘cool rapidly’; Sandmeyer says ‘quench’; ASTM A182 calls for a water quench; ASTM A312 and A240 say ‘water quench or rapid cool by other means’; MW Alloys says ‘solution anneal followed by rapid quench is the usual mill process’. The aim is to pass quickly through the temperature range in which intermetallic phases (sigma, chi, Laves) could precipitate.
Resulting hardness
Specification ceilings: 90 HRB / 200 HBW max. for ASTM A240, A182 and A312 (HT Pipe); Boltport gives 95 HRB max. for A240 — the two numbers are not the same and the conflict is recorded. Sandmeyer’s typical measurement is 70-90 HRB. On the EN side Metalcor and Virgamet give ≤230 HB.
DEFENCE METAL
2 · POST-WELD HEAT TREATMENT — usually NOT REQUIRED
Step
2 · POST-WELD HEAT TREATMENT — usually NOT REQUIRED
Summary
This step is skipped on most jobs. The reason is the carbon ceiling: C ≤ 0.020% is lower even than that of 304L, so grain boundary carbide precipitation does not in practice occur during the welding thermal cycle.
Temperature
No separate temperature is given because it is not required. If it is carried out, the solution annealing band of step 1 is used.
Time
Not applicable.
Cooling
Rapid cooling if it is done. ISSF says ‘no pre-heat should be used and in most cases post weld heat treatment is also not required’; Steelinox and Virgamet point the same way.
Resulting hardness
No change is expected. WARNING: because the fully austenitic structure contains no ferrite, the hot cracking risk is real; the answer is not heat treatment but low heat input and faster cooling (thyssenkrupp).
DEFENCE METAL
3 · COLD WORK — the ONLY way to raise strength
Step
3 · COLD WORK — the ONLY way to raise strength
Summary
This is NOT a heat treatment step; it is placed in the diagram so that it is not confused with one. 904L is not precipitation hardened and is not aged.
Temperature
Room temperature (cold drawing / cold rolling).
Time
Not applicable.
Cooling
Not applicable.
Resulting hardness
Hardness and strength rise while elongation falls. The numerical minimums of the cold-worked tempers of 904L could not be confirmed by four independent sources and are therefore NOT in the diagram. Cold work also leaves residual stress and raises susceptibility to stress corrosion cracking; the advantage of 904L in that area should not be spent on cold work.
DEFENCE METAL
SERVICE TEMPERATURE CEILING — about 550 °C (ISSF). NO NUMERICAL PRECIPITATION BAND IS GIVEN.
Step
SERVICE TEMPERATURE CEILING — about 550 °C (ISSF). NO NUMERICAL PRECIPITATION BAND IS GIVEN.
What happens
In a highly alloyed fully austenitic structure, long high-temperature service can lead to intermetallic phase (sigma, chi, Laves) precipitation, which lowers toughness and corrosion resistance. CLASSICAL CHROMIUM CARBIDE SENSITIZATION DOES NOT APPLY IN PRACTICE to 904L, because the carbon ceiling is 0.020%, lower even than that of 304L (Steelinox, Virgamet, MW Alloys, ISSF).
As named in the source
ISSF/worldstainless gives an explicit service ceiling for this grade: it ‘should not be used above about 550 °C’. Against that, West Yorkshire Steel gives 1000 °C as the safe scaling temperature for continuous service, and thyssenkrupp tabulates the modulus of elasticity only up to 500 °C. These three statements DO NOT MEASURE THE SAME QUANTITY (a structural limit, an oxidation limit and a table limit); NO AVERAGE IS TAKEN. The 550 °C limit from ISSF should be used as the design ceiling.
Mechanism warning
A NUMERICAL INTERMETALLIC PRECIPITATION BAND (for example 650-1000 °C) COULD NOT BE CONFIRMED BY FOUR INDEPENDENT SOURCES AND IS NOT GIVEN; it is recorded in the ‘atlananlar’ list. No invented band has been written. The practical rule to know is this: rapid cooling after the solution anneal exists precisely to prevent those phases from precipitating, and slow cooling damages the material.
The scheme is schematic; the time axis is NOT to scale. No published TTT/CCT curve was used, so no curve is drawn. THIS ALLOY IS AUSTENITIC: it is produced by SOLUTION ANNEALING + RAPID COOLING, it is NOT PRECIPITATION HARDENABLE and it is not aged. There is NO hardening step such as H900 or H1075 and none is drawn. The ONLY way to raise strength is COLD WORK; heat treatment lowers it. The scheme is schematic; the time axis is not to scale. This alloy is NOT PRECIPITATION HARDENABLE; there is no ageing step. Rapid cooling after the solution anneal is mandatory; its purpose is to prevent intermetallic precipitation. Post-weld heat treatment is usually not required; the reason is the C ≤ 0.020% ceiling. A numerical intermetallic precipitation band could not be confirmed by four sources and is not given.
Welding
TIG, MIG, covered electrode, submerged-arc, flux-cored, plasma and laser welding are all applicable. No preheat is required and post-weld heat treatment is not normally applied. The low carbon preserves intergranular corrosion resistance in the as-welded condition. The usual fully austenitic rules apply: heat input no more than 1.2 kJ/mm, interpass temperature no more than 100 °C, and root shielding gas is mandatory.
Choice of filler: for most service the matching ER385 / E385-16 is sufficient; that wire is already slightly over-alloyed (Mo 4.2–5.2% against 4.0–5.0% in the base metal). For severe chloride-pitting environments, equipment entering service in the as-welded condition, and aggressive duties such as flue gas desulphurisation, the nickel-base ERNiCrMo-3 (Alloy 625) is preferred. The reason: molybdenum segregates to the interdendritic regions during solidification, the dendrite cores become depleted, and the local pitting resistance of the weld metal falls below that of the base metal. An over-alloyed filler compensates for that gap.
Heat treatment
The grade is fully austenitic with no precipitation hardening or martensitic transformation; it cannot be hardened by heat treatment and is non-magnetic. The only treatment applied is solution annealing, practically at 1060–1150 °C followed by rapid cooling or quenching. Critical warning: harmful intermetallic phases (sigma, chi) precipitate within minutes between 800 and 900 °C. Cooling therefore cannot be slowed, and service in that band is not permitted. Hot working is carried out between 850 and 1150 °C and must be followed by solution annealing. The standard delivery condition is solution annealed and quenched.
Machining
The work-hardening rate is high, and the high nickel content makes chips ductile and sticky with a tendency to built-up edge. 904L is markedly harder to machine than 304 or 410. The rule set: a rigid machine and fixture, sharp positive-rake tooling, low cutting speed with a high, steady feed, never letting the tool linger on the workpiece (a dwell means a work-hardened surface and a hard layer for the next pass), and a generous high-pressure coolant supply.
904L, 316L and the Super Alloys — Which and When?
The real argument for 904L is not chloride resistance but resistance to reducing acids. The copper addition (1–2%) stabilises the passive film in media such as sulphuric and phosphoric acid — an advantage the 6Mo and duplex grades cannot offer.
Selection Guide · Chloride and Acid Resistant Grades
316L: 20 ±2 °C · 904L: 62 ±3 °C · 2507: 84 ±2 °C (same test method)
Sulphuric acid
904L is one of the few stainless steels offering full resistance up to 35 °C across the whole 0–100% concentration range in dilute sulphuric acid. In boiling 10% H₂SO₄ its corrosion rate is roughly six times lower than that of Type 316
Hydrochloric acid
Use of 904L is limited
Reducing acids dominate
904L — the only group where the copper addition gives an advantage
Chloride and pitting dominate
254 SMO (PREN 43) or AL-6XN — the typical seawater threshold is PREN > 40, which 904L does not reach
Chloride plus high strength
2507 super duplex — its yield strength is about 2.5 times that of 904L, reducing wall thickness; but its service temperature is limited to 250 °C
Stress-corrosion cracking
With 23–28% nickel, the chloride SCC resistance of 904L is far higher than that of 304L and 316L
ASME design temperature limit
371 °C
Frequently Asked Questions
My specification says ASTM B625 but the supplier sent an A240 certificate — is this the wrong material?
No. ASTM determined that iron is the largest element by mass percent in N08904, reclassified the grade as a stainless steel and transferred it from the nickel alloys committee to the stainless committee. The transfers are: B625 → A240/A480, B649 → A479/A484, B673 → A312, B674 → A249, B677 → A269/A312. This note appears explicitly in the scope section of the current B625, B649, B673, B674 and B677 editions. The B/SB number remains valid on legacy projects; use the A-series number on new orders.
I have a seawater line — is 904L enough?
The typical specification threshold for seawater is PREN > 40; at PREN ≈ 34, 904L is below that threshold, and its critical crevice temperature is only of the order of 10 °C — which makes it risky in warm seawater wherever crevice geometry exists, such as flanges, under gaskets and at tube-to-tubesheet joints. Decision rule: if reducing acids (sulphuric, phosphoric) dominate, choose 904L; if chloride and pitting dominate, choose 254 SMO or AL-6XN; if chloride is combined with a requirement for high strength and reduced wall thickness, choose 2507 super duplex. Note that 2507 is limited to 250 °C in service, while 904L has no such wall (ASME 371 °C).
Should I weld 904L with matching ER385 or with an Inconel 625 filler?
For most service ER385 / E385-16 is sufficient; molybdenum segregation in 904L is milder than in the 6Mo grades, and ER385 is already slightly over-alloyed. Move to the nickel-base ERNiCrMo-3 (Alloy 625) in these cases: severe chloride-pitting environments, equipment entering service in the as-welded condition without solution annealing, and aggressive duties such as flue gas desulphurisation. In either case keep heat input ≤ 1.2 kJ/mm and interpass temperature ≤ 100 °C, and use root shielding gas; preheat and post-weld heat treatment are not required.
EVERY ASTM ROW IS A SPECIFICATION MINIMUM for room temperature; these are NOT typical values, and a typical value never goes into a calculation. BECAUSE THIS ALLOY IS NOT PRECIPITATION HARDENABLE, the rows are split by SPECIFICATION and PRODUCT FORM, not by ageing condition; there is NO condition column such as H900 or H1075. NOTE 1: the tensile minimum (490 MPa) and the elongation minimum (35%) are the same for every ASTM product form; the only quantity that differs is the YIELD MINIMUM (215 or 220 MPa), and that is not a difference of measurement but of how the metric equivalent of the same 31 ksi value is rounded from one specification to another. NO AVERAGE IS TAKEN. NOTE 2: the yield value on the EN 10088 side (≥230 MPa) is HIGHER than on the ASTM side. The two systems set different floors for the same material; whichever specification the order is placed against, that table governs. COLD-WORKED TEMPERS ARE NOT IN THIS TABLE. In the chart, a value given as a range is drawn at its lower bound; the full range is in the table. The rows are split by specification and product form; there is no ageing condition column. The 490 MPa tensile and 35% elongation are the same for every ASTM form. The yield minimum shows a rounding difference between 215 and 220 MPa; no average is taken. The EN 10088 yield floor (≥230 MPa) is higher than the ASTM floor. Cold-worked tempers are not in the table.
904L — COMPARED WITH 304, 316, 303 AND NITRONIC 50 · AND THE 6 MO DISTINCTION
CRITERION: (A) STRENGTH — ASTM A479 / A479M annealed bar SPECIFICATION MINIMUMS, FROM ONE AND THE SAME TABLE, at room temperature. (B) CORROSION RESISTANCE — the Cr, Mo, N and Cu contents taken from the composition tables of the same specifications, together with PUBLISHED PREN values (formula: PREN = %Cr + 3.3×%Mo + 16×%N, NeoNickel). (C) corrosion rates and a critical crevice corrosion temperature measured by a single laboratory in the same tests (Sandmeyer). THE BLOCKS ARE NOT SUMMED AND NOT PUT ON ONE AXIS.
A · STRENGTH — ASTM A479/A479M annealed bar minimums (SAME TABLE, Boltport)
The values are SPECIFICATION MINIMUMS, not typical values.
DEFENCE METAL
Criterion
AISI 904L
AISI 304
AISI 316
Nitronic 50
AISI 303
Difference
Tensile strength minimum (MPa)
490
515
515
690
NOT WITHIN A479
904L carries the LOWEST tensile minimum in this table — 25 MPa below 304 and 316.
Yield strength minimum 0.2% (MPa)
220
205
205
380
NOT WITHIN A479
904L is only 15 MPa above 304/316. Strength is NOT the reason to buy 904L.
Elongation minimum
35%
30%
30%
35%
NOT WITHIN A479
904L is 5 points more ductile than 304 and 316.
B · COMPOSITION AND CORROSION — ASTM specification tables and published PREN values
The composition figures are taken from the tables of ASTM A240 (304, 316, N08904, S31254), ASTM A479/A276 (S20910) and ASTM A582 (S30300). PREN WAS NOT CALCULATED.
DEFENCE METAL
Criterion
AISI 904L
AISI 304
AISI 316
Nitronic 50
AISI 303
254 SMO (S31254)
Difference
Molybdenum (Mo)
4.00-5.00%
none
2.00-3.00%
1.50-3.00%
none
6.00-7.00%
The molybdenum of 904L is about twice that of 316 and about three quarters of that of 254 SMO. THIS IS WHERE THE 6 Mo LINE LIES.
Nitrogen (N)
≤0.10% (A CEILING, not a deliberate addition)
≤0.10%
≤0.10%
0.20-0.40% (DELIBERATE)
not specified
0.18-0.25% (DELIBERATE)
In 904L nitrogen is a ceiling; in 254 SMO and Nitronic 50 it is a deliberate alloying element. Its coefficient in the PREN formula is 16, so its effect is large.
Copper (Cu)
1.00-2.00% (DELIBERATE)
not specified
not specified
not specified
≤1.00%
0.50-1.00%
This is the distinguishing element of 904L; its resistance to reducing sulphuric and phosphoric acid comes from copper.
Nickel (Ni)
23.0-28.0%
8.0-10.5%
10.0-14.0%
11.5-13.5%
8.0-10.0%
17.5-18.5%
The high nickel is the source of resistance to chloride stress corrosion cracking (ISSF).
Carbon (C) ceiling
≤0.020%
≤0.07%
≤0.07%
≤0.06%
≤0.15%
≤0.02%
The carbon ceiling of 904L is lower even than that of 304L; this is why no post-weld heat treatment is needed.
Published PREN value
35 (ISSF/worldstainless)
19 (Langley Alloys)
25 (Langley Alloys, for 316L)
no single published value found
no single published value found
no single published value found
ISSF states that a PRE of 35 means ‘good resistance to warm sea water and other high chloride environments’. The values were published by separate organizations and were not measured in one table; they are used for ranking, not for calculation.
C · CORROSION RATES — ONE LABORATORY, THE SAME TESTS (Sandmeyer Steel)
It is the table of a single organization, so NO separate ‘corrosion’ diagram was made; it is given inside the comparison under the source name. Different rows are different environments and are not summed.
DEFENCE METAL
Criterion
AISI 904L
AISI 316
AISI 304
Nitronic 50
AISI 303
Difference
20% HNO3 + 4% HF pickling acid, 25 °C (mm/year)
0.47
>6
not in the table
not in the table
not in the table
In the same test 904L corrodes at least twelve times more slowly than 316L.
Wet-process phosphoric acid, 60 °C (mm/year)
1.2
>5
not in the table
not in the table
not in the table
The same table gives 0.05 mm/year for 254 SMO — the 6 Mo grade is ABOVE 904L in this environment.
The same table gives 2 °C for 317L and 35 °C for 6Mo (N08367). 904L sits between 316L and 6Mo.
Fatty acid column, tall oil distillation, 253 °C (mm/year)
0.056
0.88 (316L)
not in the table
not in the table
not in the table
The same table gives 0.29 mm/year for 317LMN.
D · SERVICE CLASS — qualitative, not numerical
This is the common statement of manufacturer technical bulletins; it is not a laboratory table.
DEFENCE METAL
Criterion
AISI 904L
AISI 304
AISI 316
Nitronic 50
AISI 303
254 SMO (S31254)
Difference
Alloy class
Superaustenitic (high Ni + Mo + Cu)
Standard austenitic
Standard austenitic with Mo
Nitrogen-strengthened austenitic
Sulphur-bearing free-machining austenitic
6 Mo superaustenitic
904L and 254 SMO ARE NOT THE SAME CLASS; molybdenum and deliberate nitrogen separate them.
How is strength raised?
Cold work
Cold work
Cold work
Nitrogen + cold or warm work
Cold work
Cold work
NONE OF THEM IS PRECIPITATION HARDENABLE; none has an ageing step.
Post-weld heat treatment
Usually NOT REQUIRED (C ≤ 0.020%)
A solution anneal may be needed on heavy sections
May be needed on heavy sections
Usually not required
Not welded
Usually not required
The low carbon of 904L is a direct manufacturing advantage in welded fabrication.
DEFENCE METAL
Additional information
Compared with
AISI 904L (N08904 · 1.4539) — AISI 304 (S30400) — AISI 316 (S31600) — AISI 303 (S30300) — Nitronic 50 (S20910 · XM-19) — 254 SMO (S31254, for the 6 Mo distinction only)
RULE: every block is read from A SINGLE SOURCE TABLE. 303 IS ABSENT from block A because ASTM A479 does not cover free-machining grades. 254 SMO appears only in the composition block, to show the distinction that ‘904L is not a 6 Mo grade’. Every block is read from a single source table; the blocks are not summed. 904L is not a strength material; it carries the lowest tensile minimum in block A. 904L is NOT a 6 Mo grade; the molybdenum and deliberate nitrogen difference is seen in block B. Block C is the laboratory table of a single organization, so no separate corrosion diagram was made.
