UNS S31603 · W.Nr. 1.4404 · X2CrNiMo17-12-2 · 16.0-18.0% Cr – 10.0-14.0% Ni – 2.00-3.00% Mo – C ≤ 0.030% (ASTM A240, A276, A479, A182) or ≤ 0.035% (ASTM A312, A213) – balance Fe. The EN 10088 band for 1.4404 is: C ≤ 0.030%, Cr 16.5-18.5%, Ni 10.0-13.0%, Mo 2.0-2.5%. It is an austenitic stainless steel: NOT PRECIPITATION HARDENABLE, it cannot be hardened by heat treatment; strength is raised only by cold work.
Bought for welded fabrication. Where 304L is not enough in a moderate chloride-bearing environment and where a post-weld solution anneal cannot be carried out: heavy-section welded tanks and vessels, process piping, chemical and pharmaceutical equipment, food and beverage lines.
Forms
Round bar · flat bar · plate · sheet · pipe and tube · forging. All forms supplied to order.
Standards
AMS 5507 (sheet, strip, plate) · AMS 5653 (bars, wire, forgings, mechanical tubing, rings). ASTM: A240 / SA-240 (plate, sheet, strip) · A276 / SA-276 and A479 / SA-479 (bar and shapes) · A312 / SA-312 (pipe, TP316L) · A213 / SA-213 and A249 (tube, TP316L) · A182 / SA-182 (forged flanges and fittings, F316L) · A403 (fittings, WP316L) · A580 (wire) · A484 (general requirements). EN: 1.4404 · 10088-2 · 10088-3 · 10028-7 · 10216-5 · 10217-7 · 10222-5. The AMS numbers are SEPARATE for 316 and 316L and must not be mixed: in sheet, strip and plate AMS 5507 belongs to 316L and AMS 5524 to 316; in bar, wire and forgings AMS 5653 belongs to 316L and AMS 5648 to 316.
Advantage
Intergranular corrosion resistance in the as-welded condition. The carbon ceiling is 0.030% against the 0.08% of 316, that is 2.7 times lower; over the time of a weld heat cycle chromium carbide does not precipitate in practice.
Welding
Filler metal: AWS E316L / ER316L; under AS 1554.6 AZoM states ‘316 and 316L rods or electrodes (or their high silicon equivalents)’. NO PREHEAT IS REQUIRED — the austenitic structure shows no transformation hardening. ASME Section IX P-No 8 (austenitic stainless);
Limits
CHLORIDE STRESS CORROSION CRACKING: the low carbon DOES NOT reduce this risk. Under tensile stress in a chloride-bearing environment it cracks above roughly 50-60 °C (worldstainless, Aalco and AZoM about 60 °C; ASSDA and Outokumpu about 50 °C; ATI about 49 °C). NO SINGLE NUMBER IS GIVEN. SEAWATER: 316L is NOT a seawater material;
Compiled from manufacturer data sheets · confirm against the current specification before ordering
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Standards by Product FormWelding, Heat Treatment and Machining316, 316L and Dual Certified MaterialFrequently Asked Questions
Corrosion resistance: Under normal conditions the corrosion resistance of AISI 316L is far better than that of AISI 304. 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 1000 mg/L of free chlorine in service water at standard temperature and to 500 mg/L above 60 °C.
Temperature capability: 316 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 316L 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 316 is 316, and for 316L it is 316L. When welding thin sections in grade 316, post-weld annealing is not required, but it must be applied on thick sections. For 316L, post-weld annealing is not required even on thick sections (6 mm and above, for example). 316Ti should be preferred over 316 for thick section welds.
Machinability: It has good machinability. Where corrosion resistance is not important, stainless steel products in grades 303 or 430F can be specified.
Heat treatment: AISI 316L stainless steel has certain advantages in terms of heat treatment thanks to its low carbon content. Like other stainless steels of this type, however, it cannot be hardened.
Applications: It is used in food equipment handling highly acidic products, in laboratory benches and equipment, in medical devices, on the exterior facades of architectural structures by the sea (panels, rails and so on), in boat and ship fittings, in chemical transport containers, in heat exchangers, and in bolts, nuts, springs and screws.
Chemical Composition
DEFENCE METAL
C
Max. 0.03
Mn
Max. 2.00
Si
Max. 0.75
P
Min. 0 · Max. 0.045
S
Max. 0.03
Cr
Min. 16.0 · Max. 18.0
Mo
Min. 2.0 · Max. 3.0
Ni
Min. 10.0 · Max. 14.0
N
Max. 0.10
Mechanical Properties
DEFENCE METAL
Tensile Strength (MPa)
485
Proof Stress (MPa)
170
Elongation A50 mm
40
Hardness Brinell
217 Max HB
Density
8.00 g/cm3
Melting Point
1370 – 1450 °C
Modulus of Elasticity
193 GPa
Electrical Resistivity
740 nΩ.m
Thermal Conductivity
16.3 W/m.K
Thermal Expansion
17.5 x 10-6/K
Standards and Equivalents · AISI 316L
DEFENCE METAL
Trade name
AISI 316L
UNS
S31603
W.Nr (DIN/EN)
1.4404 · 1.4401
AMS
5653 (bar, forgings) · 5507 (plate, sheet, strip)
ASTM
A276 · A479 · A484 · A240
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 5507 (SAE, solution heat treated sheet, strip and plate, SAE 30316L) · ASTM A240 / ASME SA-240 · ASTM A666 · EN 10088-2 · EN 10028-7
Round bar, flat bar (including square and hexagon)
AMS 5653 (SAE, bars, wire, forgings, mechanical tubing and rings, 0.030 max C) · ASTM A276 / ASME SA-276 · ASTM A479 / ASME SA-479 · ASTM A484 (general requirements) · EN 10088-3
Wire
AMS 5653 (includes wire) · ASTM A580 · EN 10088-3. AMS 5690 is defined in its SAE title as SAE 30316, that is 316; no 316L counterpart could be confirmed.
Forging
AMS 5653 (forgings and stock for forgings) · ASTM A182 / ASME SA-182 (F316L) · ASTM A484 · EN 10222-5
Flange
ASTM A182 / ASME SA-182 (F316L) — 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 (WP316L) — wrought fittings · dimensions to ASME B16.9 / B16.11. No separate AMS number for fittings could be confirmed.
Seamless and welded pipe
ASTM A312 / ASME SA-312 (TP316L) · ASTM A358 (welded, for pressure service) · ASTM A409 (large diameter) · ASTM A999 (general requirements) · EN 10216-5 (seamless) · EN 10217-7 (welded). NO AMS number for 316L pipe COULD BE CONFIRMED.
Seamless and welded tube (boiler, superheater, heat exchanger)
AMS 5653 (mechanical tubing) · ASTM A213 / ASME SA-213 (TP316L, seamless) · ASTM A249 (welded) · ASTM A269 (general corrosion service) · ASTM A554 (mechanical tube) · EN 10216-5. AMS 5573 is defined in its SAE title as SAE 30316, that is 316; no 316L counterpart could be confirmed.
The AMS numbers are SEPARATE for 316 and 316L and must not be mixed: in sheet, strip and plate AMS 5507 belongs to 316L and AMS 5524 to 316; in bar, wire and forgings AMS 5653 belongs to 316L and AMS 5648 to 316. Only TWO AMS numbers could be confirmed for 316L: AMS 5507 and AMS 5653. No 316L counterpart was found for tube, pipe or a separate wire number. AMS 5573 and AMS 5690 are defined in their SAE titles as SAE 30316 (316); they must not be ordered in the belief that they are 316L. The EN numbers are for information; the acceptance criteria that apply are those of the specification the order was placed to.
The point most often missed when ordering AISI 316L is that EN 1.4404 and ASTM 316L are not identical. EN 1.4404 caps molybdenum at 2.50% while ASTM S31603 allows up to 3.00%, and the EN sulphur limit is tighter (0.015% against 0.030%). State clearly on the order which one applies.
Standards by Product Form · AISI 316L (S31603 / 1.4404)
Mechanical minimums in the annealed condition (ASTM A240): yield ≥ 170 MPa, tensile ≥ 485 MPa, elongation ≥ 40%, hardness ≤ 217 HB. EN 10088-2 requires yield ≥ 240 MPa and tensile 530–680 MPa for cold-rolled sheet — the EN values are markedly higher than the ASTM minimums, so be clear which standard governs your calculation.
Welding, Heat Treatment and Machining
HEAT TREATMENT — SCHEMATIC
DEFENCE METAL
LOW CARBON — this is the only thing that separates 316L from 316
Step
LOW CARBON — this is the only thing that separates 316L from 316
Summary
This is not a heat treatment step; it explains why the cycle below is THE SAME for all three grades and where the difference comes from.
Note
THE REAL DIFFERENCE between 316 and 316L IS THE CARBON BAND — nothing else. The chromium (16.0-18.0%), nickel (10.0-14.0%) and molybdenum (2.00-3.00%) bands of the two grades are the same in ASTM A240; 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: 0.08% for 316, 0.030% for 316L. That ceiling sets how much carbon can precipitate inside the sensitization band. Because the carbon is lower, carbide precipitation in 316L is far slower and does not occur in practice over the time of a weld heat cycle; the PRICE of that is yield strength: in ASTM A240, 205 MPa for 316 against 170 MPa for 316L, 35 MPa lower. 316Ti reaches the same end not by lowering the carbon but by binding it with titanium, and does not pay that price.
Requirement
C ≤ 0.030% (ASTM A240, A276, A479, A182, EN 1.4404) · C ≤ 0.035% (ASTM A312, A213)
DEFENCE METAL
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 chromium carbides back 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 call for the material in this condition.
Temperature
The sources differ at the ends of the band, EACH WITH ITS NAME: worldstainless grade sheet 1010-1120 °C · Aalco 1010-1120 °C · AZoM 1010-1120 °C · ATI 1040-1175 °C (1900-2150 °F) · Jacquet 1040-1175 °C · thyssenkrupp 1.4404 1030-1110 °C · Outokumpu 1000-1100 °C · Sandmeyer at least 1038 °C (1900 °F). NO SINGLE NUMBER IS WRITTEN AND NO AVERAGE IS TAKEN. The practical envelope is about 1010-1175 °C. THE SPECIFICATION FLOOR IS SEPARATE and it is the binding one: ASTM A312, A213, A479 and A182 require at least 1040 °C (1900 °F).
Time
No single soak time could be confirmed by four independent sources, so none is given. The time is set by getting the whole section to temperature; extending it brings no benefit, it brings grain growth.
Cooling
RAPID COOLING IS MANDATORY — it is not a preference, it is a metallurgical condition. Water quench or rapid air/gas cooling. The purpose is to pass the roughly 816-427 °C range before carbides can precipitate again (ATI, Jacquet). ATI gives the measure this way: the metal must be cooled from the annealing temperature to black heat in less than three minutes. ASTM A312, A213 and A479 say ‘quenched in water or rapidly cooled by other means’; ASTM A182 requires solution annealing plus quenching. Slow cooling voids the treatment: the part stays inside the sensitization band.
Purpose
After hot and cold forming; to restore corrosion resistance after welding; to recover 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 WITH ITS NAME: TWI states that most austenitic stainless steel weldments do not require postweld heat treatment, and gives about 400 °C for partial relief, about 1000 °C for stress corrosion cracking resistance and above 1000 °C for full solution annealing · AZoM says below 400 °C gives only partial relief, 425-925 °C is effective but carries a sensitization risk, and the full answer is a solution anneal at about 1080 °C · Alloy Wire gives 250 °C / 1 hour / air for 316Ti wire. PRACTICAL RULE: do not hold the part in the sensitization band in order to relieve stress; either do a partial relief well below the band (about 400 °C) or go to a full solution anneal and cool rapidly.
DEFENCE METAL
Range to avoid
Step
SENSITIZATION BAND — chromium carbide precipitation (M23C6)
Temperature
The sources differ at the ends of the band, EACH WITH ITS NAME: ATI 427-816 °C (800-1500 °F) · Jacquet 427-816 °C · worldstainless grade sheet 425-860 °C · Aalco 425-860 °C · AZoM 425-860 °C · Alleima 450-850 °C · Abrams 450-850 °C. NO SINGLE NUMBER IS WRITTEN AND NO AVERAGE IS TAKEN. The practical envelope is about 425-870 °C.
Note
A REGION TO AVOID. It is NOT a hardening step; this alloy is not precipitation hardenable. In this band chromium precipitates at the grain boundaries as chromium carbide (M23C6); the region next to the boundary is depleted in chromium and the material becomes open to intergranular corrosion (sensitization). Because the carbon ceiling of 316L is 0.030%, precipitation is far slower and does not occur in practice over the time of a weld heat cycle. BUT THE BAND DOES NOT GO AWAY: on the scale of long-term service the carbon still precipitates. For a part that will run for long periods in the 425-870 °C band the right grade is not 316L but the titanium-stabilized 316Ti.
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) and no ageing diagram has been drawn. The heat treatment is THE SAME for 316, 316L and 316Ti. The difference shown on the card comes not from heat treatment but from THE LOW CARBON of 316L. The time axis is not to scale; no published TTT/CCT curve was used. The sources differ on the solution annealing temperature; no single number is written and the range is given with the source names. The binding figure is the specification floor (≥1040 °C). No single numerical recipe is given for stress relieving; no temperature/time pair could be confirmed by four independent sources. A stabilizing anneal is MEANINGLESS on 316L: there is no titanium to bind the carbon. The stabilizing anneal applies only to 316Ti.
Welding
GTAW (TIG), GMAW (MIG), SMAW, submerged-arc, flux-cored, plasma and resistance welding are all applicable; oxy-acetylene welding is not recommended. The filler is ER316L (AWS A5.9) or E316L-16 / E316L-17 covered electrodes (AWS A5.4). No post-weld heat treatment is required — that is the whole purpose of the low carbon. Filler metals are formulated to contain a small amount of delta ferrite to prevent hot cracking. Copper and zinc contamination must be strictly avoided; they form low-melting compounds that cause weld cracking. Remove scale and heat tint with a stainless steel wire brush, and pickle and passivate for corrosive service — skipping this step is the single most common cause of corrosion failures at welds in the field.
Heat treatment
The structure is austenitic; it cannot be hardened by heat treatment. Strength is raised only by cold work. The only treatment applied is solution annealing: 1040–1175 °C in ASTM practice, 1020–1120 °C in EN practice, followed by water quenching or rapid cooling. The critical point is to pass quickly through the 816–427 °C band — from annealing temperature to black heat in under three minutes. The sensitisation (chromium carbide precipitation) range is 427–816 °C. Hot working is done at 927–1204 °C; forging starts at 1150–1205 °C and finishes at 927–955 °C.
Machining
The governing problem is work hardening. If the tool dwells or rubs, the surface hardens and the next pass becomes impossible. The rule: low cutting speed with a heavy, steady feed; never interrupt the feed and never let the tool idle in the cut. Sharp tooling, positive rake, rigid clamping and an amply powered machine are essential. Chips are ductile and stringy, so chip-breaker geometry is needed. Thermal conductivity is low, so use a generous, continuous flow of coolant. 316L machines slightly more easily than 316 because of its lower carbon; the work-hardening behaviour is the same.
316, 316L and Dual Certified Material
The only structural difference is carbon — but the consequences bear directly on purchasing:
316 · 316L · Dual Certified Comparison
DEFENCE METAL
Carbon
316: ≤ 0.08% · 316L: ≤ 0.030%
Yield strength (min)
316: 205 MPa · 316L: 170 MPa
Tensile strength (min)
316: 515 MPa · 316L: 485 MPa
Post-weld heat treatment
316: may be needed in heavy sections · 316L: not required
Intergranular corrosion as welded
316: at risk · 316L: resistant
Dual certified (316/316L)
Carbon held ≤0.030% while nitrogen restores strength above the 205 MPa yield minimum of 316 — meets both specifications at once
Limit of dual certification
It does not satisfy 316H (the H grade requires C 0.04–0.10% and a coarse grain size)
Continuous service above 450 °C
316L is not used; 316 or 316H is required
Rule of thumb: for welded fabrication, medium to heavy sections and corrosive service the default is 316L. At ambient temperature in non-corrosive service the two grades behave identically. If a certificate says “316/316L”, always check the carbon line — if it is not ≤0.030% it is not genuine dual certification.
Other members of the same family: AISI 304L (no molybdenum, more economical), AISI 316Ti (titanium stabilised, high temperature), AISI 904L (super austenitic, acid resistance).
Frequently Asked Questions
Is 316L suitable for seawater? What is its PREN?
The PREN is roughly 24 (304: ~19, 317L: ~30). It is not suitable for continuous seawater service. Seawater contains around 19,000 ppm chloride, while the practical chloride limit for 316L in water is of the order of 2,000 ppm. The real risk is pitting and crevice corrosion, which starts quickly under gaskets, under bolt heads and under marine fouling. Genuine seawater service calls for super austenitic 6Mo grades (254 SMO, AL-6XN), super duplex (2507) or 904L.
A magnet sticks to it — is the material counterfeit?
No. In the annealed condition 316L is non-magnetic, but cold work (bending, drawing, deep drawing, heavy machining) transforms part of the austenite into deformation martensite, and that phase is ferromagnetic. The effect is most pronounced at bend radii, on drawn bar surfaces and at cut edges. 316L is markedly more stable in this respect than 304, because nickel and molybdenum stabilise the austenite. A magnet test is not a valid way to verify 316L; verification is by spectrometer analysis and the mill certificate. Where low magnetic permeability is mandatory, a final solution anneal restores it.
What is the difference between 1.4404 and 1.4435?
Both are 316L; the difference is in the alloy range. 1.4435 has molybdenum 2.50–3.00% (1.4404: 2.00–2.50%) and nickel 12.5–15.0% (1.4404: 10.0–13.0%). Higher molybdenum means better pitting resistance, higher nickel means less delta ferrite. For that reason 1.4435 is supplied with a guaranteed delta ferrite content to the BN2 (Basler Norm 2) specification and is called for in pharmaceutical, bioprocess and urea plants. Both fall inside the ASTM S31603 limits, so an order for “316L” may bring either — if low ferrite is required, write “EN 1.4435, delta ferrite guaranteed to BN2” on the order.
STRENGTH VALUES
DEFENCE METAL
Condition
Hardness
Yield MPa
Tensile MPa
Elongation
ASTM A240 / ASME SA-240 · plate, sheet and strip
217 HBW max. · 95 HRB max.
170
485
40%
ASTM A276 / ASME SA-276 · bar and shapes, hot-finished and annealed (Condition A)
A276 gives no hardness ceiling for 316L
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 (F316L)
—
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 (485 / 170 MPa); THE QUANTITIES THAT DIFFER ARE ELONGATION AND REDUCTION OF AREA (40% on plate, 35% on pipe and tube, 30% on forgings). That is a difference of test-piece geometry and specification acceptance criteria, not of the material. The shortfall of 30 MPa in tensile and 35 MPa in yield against 316 IS THE PRICE OF LOW CARBON, and the design calculation is made with these lower minimums. COLD-WORKED TEMPERS ARE NOT IN THIS TABLE: ASTM A276 carries separate minimums for Conditions B and S that vary with diameter, and having been found in a single source they have NOT been put on the card. 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 quantities that differ are elongation and reduction of area. The 30 MPa in tensile and 35 MPa in yield that are missing against 316 are the price of low carbon; the calculation is made with these lower minimums. A hardness ceiling was found only in A240 (217 HBW / 95 HRB) and A213 (192 HBW / 200 HV / 90 HRB). The ASTM A479 elongation and reduction of area minimums could not be confirmed by four sources and are left blank; the values found are in the ‘atlananlar’ list.
316 — 316L — 316TI COMPARISON
A · CARBON AND TITANIUM — ASTM A240 composition table (SAME TABLE). This is where the three grades start to differ.
ASTM A240 / ASME SA-240 composition table. All three UNS numbers are in this table.
DEFENCE METAL
Criterion
AISI 316
AISI 316L
AISI 316Ti
Difference
Carbon (C) ceiling
0.08% max.
0.030% max.
0.08% max.
316L carries 2.7 times LESS carbon than 316. The carbon of 316Ti is THE SAME as 316 — 316Ti solves the problem with titanium, not by lowering carbon.
Titanium (Ti)
Not in the specification
Not in the specification
5×(C+N) minimum, 0.70% maximum
This is the ONE element that sets 316Ti apart. Titanium ties up the carbon as TiC, so the carbon is not free to form chromium carbide.
Chromium (Cr)
16.0-18.0%
16.0-18.0%
16.0-18.0%
NO DIFFERENCE
Nickel (Ni)
10.0-14.0%
10.0-14.0%
10.0-14.0%
NO DIFFERENCE
Molybdenum (Mo)
2.00-3.00%
2.00-3.00%
2.00-3.00%
NO DIFFERENCE. Molybdenum is the same in all three; it is what separates the 316 family from 304 in pitting resistance, not what separates these three grades from each other.
ASTM A479 / ASME SA-479 heat treatment requirement; every austenitic grade falls under the same row. ASTM A312 and A213 state the same requirement.
DEFENCE METAL
Criterion
AISI 316
AISI 316L
AISI 316Ti
Difference
Type of treatment
Solution anneal + rapid cooling
Solution anneal + rapid cooling
Solution anneal + rapid cooling
NO DIFFERENCE — NONE OF THE THREE IS PRECIPITATION HARDENABLE. None of them has an ageing step such as H900 or H1075.
Minimum temperature
1040 °C (1900 °F)
1040 °C (1900 °F)
1040 °C (1900 °F)
NO DIFFERENCE
Cooling
Quenched in water or rapidly cooled by other means
Quenched in water or rapidly cooled by other means
Quenched in water or rapidly cooled by other means
NO DIFFERENCE
Additional step
None
None
STABILIZING ANNEAL — only meaningful on 316Ti (see the heat treatment diagram)
This is the only structural difference in the heat treatment cycle of the three grades.
D · SENSITIZATION RESISTANCE — mechanism; this is NOT numerical laboratory data
This block is not a laboratory table; it is the direct consequence of the carbon and titanium difference in block A and is the common statement of the producers’ technical bulletins. No numerical sensitization time/temperature curve could be confirmed by four independent sources, so NONE IS GIVEN.
DEFENCE METAL
Criterion
AISI 316
AISI 316L
AISI 316Ti
Difference
Mechanism
None — the carbon is free
The carbon ceiling is lowered (0.030%); there is little carbon to precipitate
Titanium ties the carbon up as TiC; the carbon cannot form chromium carbide
316L REDUCES the carbon, 316Ti BINDS it. Two different routes to the same end.
Intergranular corrosion resistance after welding
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.
Can be used as-welded; a post-weld solution anneal is not normally required.
Can be used as-welded; thyssenkrupp states that ‘due to the Ti-alloy, resistance to intergranular corrosion is guaranteed after welding’.
On this row 316L and 316Ti are both ahead of 316.
LONG-TERM service in the 425-870 °C band
Not recommended if corrosion resistance in an aqueous environment is wanted afterwards.
Precipitation is much slower, but THE BAND DOES NOT GO AWAY; in long-term service the carbon still precipitates. The high temperature strength of 316L is also lower than that of 316.
The titanium stays bound at temperature as well. Alleima and Abrams put this as the prevention of intergranular corrosion during prolonged holding in the 450-850 °C range; ATI states that the alloy ‘can be used for extended periods at elevated temperatures without compromising its corrosion resistance’.
THE REAL ADVANTAGE OF 316Ti IS ON THIS ROW. 316L wins over the short heat cycle of a weld; 316Ti wins in long-term elevated temperature service.
Price paid in yield strength
Does not pay it (205 MPa)
Pays it (170 MPa)
Does not pay it (205 MPa)
This is the criterion that separates the three grades in one sentence: 316Ti gives the sensitization resistance of 316L while KEEPING the yield minimum of 316.
E · HIGH TEMPERATURE CEILING — no single number is given, the sources are named instead
This block is NOT read from a single table of a single specification; producer bulletins and code sources use different criteria. For that reason the block is given as A LIST OF NAMED SOURCES rather than a numerical comparison, and it is not put on the same axis as the other blocks.
DEFENCE METAL
Criterion
AISI 316
AISI 316L
AISI 316Ti
Difference
Oxidation resistance (non-pressure)
worldstainless, Aalco, AZoM: 870 °C in intermittent service, 925 °C in continuous service
worldstainless, Aalco, AZoM: the same band is given as for 316
thyssenkrupp UK 925 °C continuous / 870 °C intermittent · Alleima 850 °C in air, 750 °C in steam · Abrams 850 °C in air · Outokumpu about 800 °C non-pressure · Virgamet 870 °C
The sources differ; no single number is written.
Pressure vessel code ceiling
ATI and Jacquet: 816 °C (1500 °F) for ASME Section VIII, Division 1
ATI and Jacquet: 454 °C (850 °F) for ASME Section VIII, Division 1
Not confirmed by four independent sources — not given. Outokumpu writes that pressure code design values are given up to 400 °C.
This 362 °C gap between 316 and 316L was found in TWO sources (ATI, Jacquet) and did not pass the four-source threshold; it is given here with the source names for the record and has not been put on the card as a number.
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. All three UNS numbers (S31600, S31603, S31635) 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 ARE NOT PUT ON ONE AXIS. Every block is read from a single table of a single specification; different specifications are not mixed on one row. The heat treatment cycle is THE SAME for all three grades. The difference does not come from heat treatment: it comes from the carbon band in 316, from low carbon in 316L and from titanium stabilization in 316Ti. Molybdenum is 2.00-3.00% in all three grades; the pitting resistance difference is between the 316 family and the 304 family, not between these three grades. Block E is not a numerical comparison; because the sources differ, it is given with the source names. No row is a typical value; every number in block B is an ASTM A240 specification minimum.
