UNS S30403 · W.Nr. 1.4307 · X2CrNi18-9 · 17.5-20.0% Cr – 8.0-12.0% Ni – C ≤ 0.030% (ASTM A240, A276, A479, A182, AMS 5647) or ≤ 0.035% (ASTM A312, A213; 0.040% allowed on thin wall) – balance Fe. It is an austenitic stainless steel: NOT PRECIPITATION HARDENABLE, it cannot be hardened by heat treatment; strength is raised only by cold work. Its ONLY difference from 304 is the carbon ceiling.
Bought for welded fabrication: welded tanks, vessels, piping and frame parts where a post-weld solution anneal is not possible. Because the carbon ceiling is 0.030%, carbides do not in practice precipitate at the grain boundaries within the time of a welding thermal cycle;
Forms
Round bar · flat bar · plate · sheet · pipe and tube · forging. All forms supplied to order.
Standards
AMS 5511 (sheet, strip, plate) · AMS 5647 (bar, wire, forgings, mechanical tubing, rings, forging stock). ASTM: A240 / SA-240 (plate, sheet, strip) · A276 / SA-276 and A479 / SA-479 (bar and shapes) · A312 / SA-312 (pipe, TP304L) · A213 / SA-213 and A249 (tube, TP304L) · A182 / SA-182 (forged flanges and fittings, F304L) · A403 (fittings, WP304L) · A580 (wire) · A484 (general requirements) · A666. EN: 10088-2, 10088-3, 10028-7, 10216-5, 10217-7, 10222-5, 10272. The AMS numbers are SEPARATE for 304 and 304L and must not be mixed. Those belonging to 304L are AMS 5511 (flat product) and AMS 5647 (bar, wire, forgings). AMS 5513 and AMS 5639 belong to 304, NOT to 304L.
Advantage
That it can be used as-welded. Its carbon ceiling is 2.3 times lower than that of 304 (0.030% against 0.07%), and this directly limits how much carbon can precipitate in the sensitization band; a post-weld solution anneal is not normally required.
Welding
Filler metal: AWS E308L / ER308L (a low-carbon filler, which must match the carbon ceiling of the base metal); E308 / ER308 and 347 are also used. NO PREHEAT IS REQUIRED — the austenitic structure shows no transformation hardening. ASME Section IX P-No 8 (austenitic stainless).
Limits
CHLORIDE STRESS CORROSION CRACKING: under tensile stress in a chloride-bearing environment it cracks above roughly 60 °C. Atlas Steels, thyssenkrupp, Aalco, Alleima and the buymetal grade sheet give this threshold as about 60 °C; Outokumpu says about 50 °C and ATI about 49 °C (120 °F) — NO SINGLE NUMBER IS GIVEN;
Compiled from manufacturer data sheets · confirm against the current specification before ordering
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Standards by Product FormWelding, Heat Treatment and Machining304 · 304L · 316LFrequently Asked Questions
Corrosion resistance: The corrosion resistance of AISI 304 and AISI 304L in normal atmospheric environments is very good. In hot environments where acid is present, hairline cracking and pitting can form in the internal structure of the material, and above 60 °C stress-induced cracking is possible. It is resistant to 200 mg/L of free chlorine in service water at standard temperature and to 150 mg/L above 60 °C.
Temperature capability: 1.4301 (304) has good oxidation resistance in environments reaching 870 °C intermittently and 925 °C continuously. If the environment is wet and the temperature is between 425 and 860 °C, however, corrosion resistance falls. Because the carbon (C) content of 304L is low, carbide precipitation does not occur in these environments.
Weldability: It shows excellent capability with all welding methods — electrode, gas shielded, wire and so on. The most suitable electrode or wire grade for 304 is 308, and for 304L it is 308L. When welding thin sections in grade 304, post-weld annealing is not required, but it must be applied on thick sections. For 304L, post-weld annealing is not required even on thick sections (6 mm and above, for example).
Machinability: Grade 1.4301 (304) is the most frequently used and most versatile stainless steel in the world. It has excellent formability and weldability. The austenitic structure of 304 allows deep drawing without intermediate annealing, which is why it is chosen for products requiring deep drawing such as sinks, gas flues and saucepans.
Heat treatment: Because of its low carbon (C) content it cannot be hardened by heat treatment.
Applications: Food processing equipment; kitchen, boat and vehicle equipment (sinks, fittings, pans, handrails and so on); architectural facade cladding (panels, rails and so on); chemical transport containers; heat exchangers; and the production of bolts, nuts, screws and springs.
Chemical Composition
DEFENCE METAL
C
304 0.0 – 0.07 · 304L 0.0 – 0.03
Mn
304 0.0 – 2.0 · 304L 0.0 – 2.0
Si
304 0.0 – 1.00 · 304L 0.0 – 1.00
P
304 0.0 – 0.05 · 304L 0.0 – 0.05
S
304 0.0 – 0.03 · 304L 0.0 – 0.02
Cr
304 17.50 – 19.50 · 304L 17.50 – 19.50
Ni
304 8.00 – 10.50 · 304L 8.00 – 10.50
Fe
304 Balance · 304L Balance
N
304 0.00 – 0.11 · 304L 0.00 – 0.11
Mechanical Properties
DEFENCE METAL
Tensile Strength (MPa)
500 – 700
Proof Stress (MPa)
175 min
Elongation A50 mm
45 Min %
Hardness Brinell
215 Max HB
Density
8.00 g/cm3
Melting Point
1450 °C
Modulus of Elasticity
193 GPa
Electrical Resistivity
0.72 x 10-6 Ω.m
Thermal Conductivity
16.2 W/m.K
Thermal Expansion
17.2 x 10-6/K
Standards and Equivalents · AISI 304L
DEFENCE METAL
Trade name
AISI 304L
UNS
S30400 · S30403
W.Nr (DIN/EN)
1.4307 · 1.4301
AMS
5511 · 5513 · 5560 · 5565 · 5639 · 5647
ASTM
A276 · A479 · A484
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
AMS 5511 (SAE, solution heat treated sheet, strip and plate) · ASTM A240 / ASME SA-240 · ASTM A666 · EN 10088-2 · EN 10028-7
ASTM A182 / ASME SA-182 (F304L) — forged flanges, fittings and valve parts · dimensions to ASME B16.5 / B16.47 · EN 10222-5. No separate AMS number for flanges could be confirmed.
Fitting
ASTM A403 / ASME SA-403 (WP304L) — wrought fittings · dimensions to ASME B16.9 / B16.11. No separate AMS number for fittings could be confirmed.
Seamless and welded pipe
No AMS number of its own for 304L pipe or tube could be confirmed by four sources (see the specification note). ASTM A312 / ASME SA-312 (TP304L) · ASTM A358 (welded, for pressure service) · ASTM A409 (large diameter) · ASTM A999 (general requirements) · EN 10216-5 (seamless) · EN 10217-7 (welded)
Seamless and welded tube (boiler, superheater, heat exchanger)
No AMS number of its own for 304L pipe or tube could be confirmed by four sources (see the specification note). ASTM A213 / ASME SA-213 (TP304L, seamless) · ASTM A249 (welded) · ASTM A269 (general corrosion service) · ASTM A554 (mechanical tube) · EN 10216-5
The AMS numbers are SEPARATE for 304 and 304L and must not be mixed: AMS 5513 sheet, strip and plate 304; AMS 5511 sheet, strip and plate 304L; AMS 5639 bar, wire and forgings 304; AMS 5647 bar, wire and forgings 304L. AMS 5560 (seamless tubing) and AMS 5565 (welded tubing) are defined in their SAE titles as 30304, that is 304; no 304L counterparts could be confirmed. The EN numbers are for information; the acceptance criteria that apply are those of the specification the order was placed against.
When ordering AISI 304L the specification must be quoted together with the product form; the same grade is sold under different standard numbers as sheet, bar, pipe and forgings. The EN equivalent is 1.4307 — the frequently seen 1.4306 is also 304L, but with a different nickel and chromium range (see below).
Standards by Product Form · AISI 304L (S30403 / 1.4307)
Mechanical minimums in the annealed condition (ASTM A240 / A276): yield ≥ 170 MPa, tensile ≥ 485 MPa, elongation ≥ 40%, hardness ≤ 201 HB / ≤ 92 HRB. EN 10088-2 requires yield ≥ 200 MPa, tensile 500–700 MPa and elongation ≥ 45% for hot-rolled plate.
Welding, Heat Treatment and Machining
HEAT TREATMENT — SCHEMATIC
DEFENCE METAL
CARBON CEILING — the single reason for the 304 / 304L difference
Step
CARBON CEILING — the single reason for the 304 / 304L difference
Summary
This is not a heat treatment step; it explains why the cycle below is THE SAME for both grades and where the difference comes from.
Note
THE REAL DIFFERENCE between 304 and 304L IS THE CARBON BAND — nothing else. The chromium (17.5-20.0%) and nickel bands of the two grades overlap in practice in the same specifications; the heat treatment cycle is THE SAME; the solution annealing temperature and the cooling requirement are THE SAME. The only variable that changes is the carbon ceiling: 0.07-0.08% for 304, 0.030% for 304L. That ceiling sets how much carbon can precipitate in the sensitization band. Because the carbon is lower, carbide precipitation in 304L is far slower and does not occur in practice within the time of a welding thermal cycle; THE PRICE is yield strength: in ASTM A240 the minimum is 205 MPa for 304 and 170 MPa for 304L, i.e. 35 MPa lower.
SOLUTION ANNEAL — this is the only valid heat treatment
Step
SOLUTION ANNEAL — this is the only valid heat treatment
Summary
It reverses cold work, takes carbides 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, A312, A213 and A182 all require the material in it.
Temperature
1010-1120 °C (1850-2050 °F). Sources: Atlas Steels 1010-1120 °C · thyssenkrupp 1010-1120 °C · Aalco 1010-1120 °C · ATI 1010-1121 °C (1850-2050 °F) · AK Steel 1038-1121 °C (1900-2050 °F) · Alleima 1040-1100 °C · Outokumpu 1050 °C. THE SPECIFICATION FLOOR IS SEPARATE: ASTM A312, A213 and A182 require a minimum of 1040 °C (1900 °F).
Time
No single soak time could be confirmed by four independent sources, so none is given. What was found, source named: buymetal grade sheet, 90 minutes per 25 mm of thickness. In practice the time is set by how long the full section takes to reach temperature; extending it brings no benefit, only grain growth.
Cooling
RAPID COOLING IS MANDATORY — not a preference but a metallurgical requirement. Water quench, or rapid air/gas cooling. The purpose is to pass through roughly 816-427 °C before carbides re-precipitate (ATI). Water quenching is required for heavy sections (AK Steel). ASTM A312 and A213 state ‘quenched in water or rapidly cooled by other means’; ASTM A182 requires ‘solution treat and quench’, cooled in a liquid medium down to 260 °C (500 °F). Slow cooling voids the treatment: the part sits inside the sensitization band.
Purpose
After hot and cold forming; on 304, to recover corrosion resistance after welding; to rescue a part that has been held in the sensitization band.
In an austenitic structure stress relieving has to be done without passing through the sensitization band. That is why there is no single standard recipe.
Note
NO SINGLE NUMERICAL RECIPE IS GIVEN — no temperature/time pair could be confirmed by four independent sources. What was found, EACH SOURCE NAMED: AK Steel 399 °C (750 °F) for 0.5-2 hours for cold-worked parts · buymetal grade sheet 400 °C maximum for 304, 450-600 °C for 60 minutes for 304L · AZoM below 400 °C only partial relief, 425-925 °C effective but carries the sensitization risk, full cure is a ~1080 °C solution anneal · Acme Alloys about 900 °C for adequate stress relief · TWI: ‘most austenitic stainless steel weldments do not require postweld heat treatment’, around 400 °C for dimensional stability, around 1000 °C for stress corrosion cracking resistance. PRACTICAL RULE: do not hold the part inside the sensitization band to relieve stress; either relieve partially well below the band (approximately 400 °C), or go up to a full solution anneal and cool rapidly.
DEFENCE METAL
Range to avoid
Step
SENSITIZATION BAND — carbide precipitation (M23C6)
Temperature
The sources diverge at the ends of the band, EACH IS NAMED: ATI 427-816 °C (800-1500 °F) · Atlas Steels 425-860 °C · thyssenkrupp 425-860 °C · Aalco 425-860 °C · buymetal grade sheet 450-850 °C · Acme Alloys 480-815 °C (900-1500 °F). NO SINGLE NUMBER IS GIVEN AND NO AVERAGE WAS TAKEN. Practical envelope: approximately 425-870 °C.
Note
ZONE TO BE AVOIDED. This is NOT a hardening step. Chromium carbide (M23C6) precipitates at the grain boundaries in this band. Because the carbon ceiling of 304L is 0.030%, there is little carbon available to precipitate and precipitation is far slower: over the time the grain boundaries spend hot during welding, sensitization does not occur in practice. THE BAND DOES NOT DISAPPEAR FOR 304L; IT STILL APPLIES IN LONG-TERM SERVICE — it is harmless only on the time scale of a weld.
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 NOT PRECIPITATION HARDENABLE and cannot be hardened by heat treatment. There is NO AGEING STEP such as H900 or H1075 and no ageing diagram has been drawn. Strength is raised only by COLD WORK; heat treatment lowers it. This alloy IS NOT PRECIPITATION HARDENABLE. There is NO ageing step (H900, H1025, H1075, H1150 and the like); no such diagram has been invented. The heat treatment is THE SAME for 304 and 304L. The difference shown on the card comes not from heat treatment but from THE CARBON BAND. The time axis is not to scale; no published TTT/CCT curve was used. The ends of the sensitization band differ between sources; no single number is written and every source is named. No single temperature/time recipe for stress relieving could be confirmed by four independent sources; what was found is given with the source named.
Welding
It welds readily by all standard processes: GTAW, GMAW, SMAW, submerged-arc, flux-cored, plasma, laser and resistance welding. The filler is ER308L (AWS A5.9) or E308L-16 / E308L-17 covered electrodes. No post-weld heat treatment is required. The filler must be an “L” grade; plain ER308 raises the carbon in the weld metal and cancels the benefit of the low carbon base. The thermal expansion of austenitic steels is about 1.5 times that of carbon steel, so distortion and residual stress are high — tack closely and keep heat input low. Do not omit back purging at the root, and clean off scale and heat tint after welding.
Heat treatment
It is fully austenitic and cannot be hardened by heat treatment; strength is raised only by cold work. The treatment applied is solution annealing at 1010–1120 °C followed by rapid cooling. The critical point is to pass quickly through the 815 → 425 °C band; thin sections cool in air, heavy sections are water quenched. The sensitisation range is 425–870 °C, with the fastest precipitation between 550 and 800 °C. Hot working is carried out between 900 and 1200 °C. Standard delivery condition: solution annealed and descaled to ASTM, +AT to EN.
Machining
The fully austenitic structure makes it harder to machine than carbon steel, and work hardening is pronounced. A light cut, rubbing, or letting the tool dwell leaves a hardened layer on the surface that blunts the tool on the next pass. A steady, adequate depth of cut is essential — the tool must cut beneath the hardened layer. Use sharp, positive-rake coated carbide tooling, rigid clamping and minimum tool overhang, with a generous, high-pressure coolant supply. Chips are long and ductile, so chip-breaker geometry is needed. Where better machinability is required, grades optimised for machining within the same chemical limits are preferred; free-machining 1.4305 (303) has poor corrosion resistance and is not suitable for welding.
304 · 304L · 316L — Which and When?
The decision turns on two questions: is there a post-weld corrosion risk, and are chlorides present?
Selection Guide · Austenitic Stainless Steels
DEFENCE METAL
Carbon
304: ≤ 0.08% · 304L: ≤ 0.030%
Yield strength (min, A240)
304: 205 MPa · 304L: 170 MPa
Intergranular corrosion after welding
304: chromium carbide precipitates in the HAZ, risk of weld decay · 304L: resistant
Dual certified 304/304L
Carbon held ≤0.030% while nitrogen lifts yield above 205 MPa — meets both specifications at once
1.4307 versus 1.4306
Both are 304L. 1.4306 has Ni 10–12% and Cr 18–20% (1.4307: Ni 8–10.5%, Cr 17.5–19.5%). 1.4306 is preferred for deep drawing and where low magnetic permeability matters; the mechanical minimums are identical
304L is sufficient
Atmospheric, indoor, clean water, food, beverage and dairy service; chloride below ~50–100 ppm and temperature below ~50 °C
Chloride above ~50–100 ppm, coastal atmosphere, salt-laden environments, chloride service above 50 °C, sulphuric or phosphoric acid processes
Sustained high temperature
The low carbon of 304L reduces creep strength; 304H or a stabilised grade such as AISI 321 is required
Frequently Asked Questions
Can 304L be supplied in place of 304?
Consider the two aspects separately. On corrosion, 304L can always safely replace 304; its lower carbon adds margin in the as-welded condition. On strength, no: to ASTM A240 the minimum yield strength of 304L is 170 MPa against 205 MPa for 304. A part designed to the 304 value in a pressure vessel or load-bearing calculation cannot be made in 304L. The reverse — 304 supplied against an order for 304L — is unacceptable in welded, corrosive service. The standard solution is dual certified 304/304L material.
Is post-weld heat treatment required?
No — that is the entire purpose of the low carbon. Focus instead on three things: the filler must be an “L” grade (ER308L / E308L), the root must be back purged, and heat tint and scale must be removed after welding (pickling and passivation). The oxide layer at the weld is the most common field error that reduces corrosion resistance, independently of chemistry. Solution annealing only becomes relevant if the material will sit in the 425–870 °C band during service.
Up to what temperature can 304L be used in chloride service?
The practical limit: do not use it above about 50 °C in chloride-bearing aqueous service. Under full immersion, stress-corrosion cracking is rare below 60 °C, but failures have been reported at chloride levels as low as 10 ppm. In evaporation zones, at wet–dry interfaces and under salt deposits that temperature threshold does not apply — chloride concentrates locally to hundreds of ppm and cracking has been seen close to room temperature. Tensile stress is necessary for cracking, but it need not come from an external load: weld residual stress alone is enough. Note also that moving to 316L does not solve this — both grades sit at similar nickel levels and are equally susceptible to chloride cracking; the answer is a ferritic, duplex or high-nickel alloy.
STRENGTH VALUES
DEFENCE METAL
Condition
Hardness
Yield MPa
Tensile MPa
Elongation
ASTM A240 / ASME SA-240 · plate, sheet and strip
201 HBW max. · 92 HRB max.
170
485
40%
ASTM A276 / ASME SA-276 · bar and shapes, hot-finished and annealed (Condition A)
201 HBW max. · 92 HRB max.
170
485
40% · reduction of area 50%
ASTM A479 / ASME SA-479 · bar and shapes for boilers and pressure vessels, annealed
ASTM A182 / ASME SA-182 · forged flanges, fittings and valve parts (F304L)
—
170
485
30% · reduction of area 50%
EVERY 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: the tensile and yield minimums are the same for every product form; THE ONLY QUANTITY THAT DIFFERS IS ELONGATION (40% on plate, 35% on pipe and tube, 30% on bar and forgings). That is a difference of test-piece geometry and specification acceptance criteria, not of the material. COLD-WORKED TEMPERS ARE NOT IN THIS TABLE. ASTM A276 carries separate minimums, varying with diameter, for cold-finished annealed bar (Condition A) and for strain-hardened Conditions B and S; those numbers could be found in only ONE independent source, so they did not pass the four-source threshold and they have NOT been put on the card or in the diagram (details are in the ‘atlananlar’ list). The metallurgy to know is this: in this alloy the only way to raise strength is cold work; cold work lowers elongation and raises susceptibility to stress corrosion cracking. If a cold-worked temper is to be ordered, the minimums must be read from the specification’s own table together with the diameter range. No row is a typical value; every row is a specification minimum. The tensile and yield minimums are the same for every product form (485 / 170 MPa); the only quantity that differs is elongation. A hardness ceiling was found only in A240, A276 and A213; no hardness ceiling fit for the card could be confirmed in A312, A479 or A182. Cold-worked temper minimums could not be confirmed by four sources and are therefore not in the table. There is no AMS row: the numerical minimums of the AMS specifications could not be confirmed by four independent sources.
304 — 304L COMPARISON
A · CARBON — ASTM A240 composition table (SAME TABLE). This is the ONLY reason for the difference.
ASTM A240 / ASME SA-240, Table 1 (composition). Both UNS numbers are in this table.
DEFENCE METAL
Criterion
AISI 304
AISI 304L
Difference
Carbon (C) ceiling
0.07% max.
0.030% max.
304L is 2.3 times lower. Every other element is in practice in the same band.
Chromium (Cr)
17.5-20.0%
17.5-20.0%
NO DIFFERENCE
Nickel (Ni)
8.0-10.5%
8.0-12.0%
The upper limit is higher for 304L to keep the austenite balance; it is not the reason for the corrosion difference.
ASTM A182 / ASME SA-182, heat treatment table. F304 and F304L are subject to the same row requirement.
DEFENCE METAL
Criterion
AISI 304
AISI 304L
Difference
Treatment type
Solution treat and quench
Solution treat and quench
NO DIFFERENCE — neither is precipitation hardenable
Minimum temperature
1040 °C (1900 °F)
1040 °C (1900 °F)
NO DIFFERENCE
Cooling
Quench in a liquid medium
Quench in a liquid medium
NO DIFFERENCE
D · SENSITIZATION RESISTANCE — mechanism; NOT numerical laboratory data
This block is not a laboratory table; it is the direct consequence of the carbon difference in block A and the common statement of the producer technical bulletins. No numerical sensitization time/temperature curve could be confirmed by four independent sources, so NONE IS GIVEN.
DEFENCE METAL
Criterion
AISI 304
AISI 304L
Difference
Intergranular corrosion resistance after welding
The weld heat can precipitate carbides at the grain boundaries; on heavy sections and multi-pass welds the risk is real. A post-weld solution anneal is needed to recover the resistance.
It can be used as-welded; a post-weld solution anneal is not normally required.
This is 304L’s ONLY IMPORTANT PRACTICAL ADVANTAGE.
Long-term service in the 425-870 °C band
Not recommended if aqueous corrosion resistance is required afterwards.
Because the carbon is low, precipitation is far slower, but THE BAND DOES NOT DISAPPEAR; it still applies in long-term service. In addition, the elevated-temperature strength of 304L is lower than that of 304.
304L wins on the time scale of a weld; it does not win in long-term high-temperature service.
RULE: every block in this diagram is read from A SINGLE TABLE OF A SINGLE SPECIFICATION. Different specifications are not compared on the same row. Both UNS numbers (S30400 and S30403) are WITHIN THE SCOPE of the specifications below, that is, they are listed side by side in the same tables under the same acceptance criteria. THE BLOCKS ARE NOT SUMMED AND NOT PUT ON ONE AXIS. Each block is read from a single table of a single specification; the blocks are not summed. The comparison rests only on specification minimums and composition ceilings; no typical value was used. A numerical corrosion laboratory comparison (for example an ASTM A262 time / mass-loss table) could not be confirmed by four independent sources and is therefore not in this diagram. In short: 304 gives the higher yield minimum (205 MPa); 304L gives intergranular corrosion resistance after welding. The choice is between those two things.
