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AISI 416 / (1.4005) / UNS S41600 / AMS 5610

Corrosion resistance: The corrosion resistance and surface quality of AISI 416 are lower than those of 1.4006 because of the sulphur addition. It is not suitable for severe corrosive conditions. With corrosion resistance that is not very good, this grade should not be used in corrosive environments.​‌​​‌​

Weldability: Welding is not recommended for this grade, which is both high in chromium and high in sulphur, and welding this material is quite difficult.

Machinability: Thanks to the high sulphur content it contains, this grade is very easy to machine. Grade 416 stainless steel in the annealed condition has very good machinability.​‌​​‌​

Heat treatment: The most important property of this stainless grade is that it can be hardened by heat treatment, and that it machines very easily and quickly in the annealed condition. After heat treatment, however, machinability falls to a certain extent in this grade, so machining is recommended before heat treatment. Among the martensitic steels, AISI 416 offers better properties in terms of weldability, although there are some factors to observe during welding, such as overheating.

Applications: AISI 416 stainless steel is frequently used in the machinery industry, in defence industry components, in automotive parts and in valves. It is suitable for producing screws, nuts, shafts, fittings and similar parts. Carbide or ceramic tooling is recommended for machining.​‌​​‌​

AISI 416 is a martensitic stainless steel that provides high machinability, wear resistance and mechanical strength. Its sulphur content gives very good machinability, but its corrosion resistance is limited. These properties make the steel ideal for applications such as cutting tools, mechanical parts and industrial equipment, while its use in aggressive chemical environments or areas carrying a high corrosion risk is limited.

What AISI 416 Is — a Steel Designed as a Trade-off​‌​​‌​

AISI 416 (UNS S41600 / W.Nr. 1.4005 / DIN X12CrS13) is the sulphurised, free-machining derivative of 410. Its chemistry is the same as 410 — 12–14 % Cr, C ≤0.15 % — with one addition: a minimum of 0.15 % sulphur. That single addition makes it the easiest-machining stainless grade there is and at the same time permanently degrades its corrosion resistance, weldability and formability. 416 is not a performance alloy; it is a deliberate trade-off.

The mechanism is simple and is exactly the logic of 303. Sulphur combines with the manganese in the steel to form manganese sulphide (MnS) inclusions. These are soft, friable islands dispersed through the matrix, and they do three jobs: (1) they break the chip — short controlled chips instead of long stringy ones; (2) they act as a solid lubricant in the cutting zone, lowering tool–chip friction; (3) they lower cutting force and heat — tool life goes up, surface finish improves. On a screw machine running unattended overnight, the combined value of those three effects is large.​‌​​‌​

The price comes from the very same inclusions. MnS particles are discontinuities in the passive film. In chloride environments that is precisely where pitting starts; in the weld pool sulphur forms low-melting-point films that cause hot cracking; in cold forming the inclusions act as crack initiators. These are not defects that can be fixed — they are the unavoidable consequence of what the steel was designed to do.

Standards by Product Form

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Note carefully: the specification coverage of 416 is built around BAR. That is no accident — it follows directly from what the material is. 416 is a bar steel made for the screw machine, and in other product forms it is either absent or severely limited.

Product Forms With NO Standard — the Commercially Valuable Section

This is the section a sales engineer must memorise, and for 416 the list is long. It is exactly where customers get confused: 416 is such a common grade that it is assumed to exist in every form. It does not.​‌​​‌​

Chemical Composition​‌​​‌​

There are two genuine differences between ASTM and EN, and both cause trouble in the field.

Mechanical Properties​‌​​‌​

The mechanical properties of 416 cannot be given in one table, because the material is sold in three different conditions: annealed, cold drawn, and hardened-and-tempered. Under the same bar designation you are buying three different steels.​‌​​‌​

Physical Properties

Published physical data for 416 scatters by roughly 20 % between sources. The scatter itself is shown below.​‌​​‌​

Heat Treatment​‌​​‌​

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The only real advantage of 416 over 410 is machinability; its only real advantage over 303 is THAT IT HARDENS. That is why the heat-treatment section sits at the centre of any decision to buy 416.

The term “475 °C embrittlement” is being misused here

One European producer page, writing that 416 must not be tempered between 425 and 525 °C, calls the effect “475 °C embrittlement”. That terminology is wrong and it creates confusion. 475 °C embrittlement is a phenomenon of high-chromium FERRITIC and duplex stainless steels, caused by the demixing of a chromium-rich α′ phase — it is the problem of grades such as 430 and 434. 416 is martensitic, and the effect there is classical TEMPER EMBRITTLEMENT: carbides and impurities segregating to the grain boundaries of tempered martensite. The practical outcome is the same (do not temper in that band) but the mechanism differs, and the name confusion puts a ferritic grade and 416 in the same category. And in 416 that band has a second cost that ferritics do not have: loss of corrosion resistance. Chromium carbide precipitation depletes chromium at the grain boundaries, and in a sulphurised steel the already limited passivity weakens further.​‌​​‌​

Welding — 416 IS NOT WELDED

The heading of this section is not a warning but a conclusion. 416 was not designed to be welded and welding it is not recommended. The producer’s own statement is unambiguous: “similar to any sulphur bearing stainless steel, the welding of 416 should be avoided since the high sulphur content can result in cracking”. A second European producer says the same: “welding is discouraged, especially autogenous methods”.​‌​​‌​

Why — two separate mechanisms operating at once

1. Sulphur-driven hot cracking (solidification cracking). Sulphur concentrates in the last liquid to solidify in the weld pool and forms low-melting sulphide films at the grain boundaries. As the bead contracts those films are still liquid and separate under tensile stress. The result is a longitudinal crack running down the centre of the bead. This cannot be cured by filler selection — the sulphur comes from the base metal.
2. Martensitic hardening and hydrogen cracking. 416 is an air-hardening 13Cr martensitic. The heat-affected zone transforms to hard, brittle, untempered martensite. That is the classic 410 problem, and in 416 it is superimposed on the sulphur embrittlement.
These two mechanisms do not cancel; they multiply. Welding 416 means combining the two worst weldability characteristics in a single material.​‌​​‌​

Machining — the Reason 416 Exists​‌​​‌​

There is a very common confusion here, and it has to be cleared up first. Two different “machinability” numbers circulate for 416, and both are correct, because they measure different things.

Corrosion — Where It Is Good, Where It FAILS​‌​​‌​

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The honest opening sentence: a European producer’s own datasheet for 1.4005 says that it is “probably the least resistant to corrosion of all of the stainless steel grades”. That was not written by a competitor; it was written by the company that makes the material. Opening a 416 sale with that sentence prevents most of the complaints that come later.

The mechanism: why an MnS inclusion starts a pit​‌​​‌​

The protection of a stainless steel is the chromium oxide passive film on the surface. That film only works while it is continuous. MnS inclusions break that continuity in three separate ways:
1. Physical discontinuity. Over an inclusion the passive film is either absent or very weak. For a chloride ion that is a direct point of entry.
2. The inclusion itself dissolves. MnS dissolves at a lower potential than the surrounding matrix. When it does, it leaves a micro pit — that is, a crevice. Inside that crevice chloride concentrates and pH falls.
3. The dissolution products acidify the local environment. Sulphur species (sulphide, thiosulphate) go into solution and prevent repassivation. Once a pit opens it feeds itself and does not close.
The result: the pitting resistance of 416 is measurably lower than sulphur-free 410 at the same chromium level, and the difference does not show up in the chemical analysis table. Sulphur is a corrosion variable, not just a manufacturing variable.

Where 416 IS good​‌​​‌​

Fresh water, steam, dry air. Indoor atmospheric conditions including high humidity.
Many petroleum products. Oil, fuel, hydraulic fluid — as long as they carry no chloride and no water.
Soaps, solvents, mould atmospheres, many organic acids.
Weak alkalis.
In which condition is corrosion resistance best? The producer states that the 416 HT condition (27–31 HRC) is the optimum for both machinability and corrosion resistance. The reason is that in the correct tempering window carbides precipitate finely and dispersed rather than at grain boundaries.
Surface treatment is decisive. For 416 passivation is not optional but effectively mandatory: per ASTM A380, 20–50 % nitric acid plus 2–6 wt % sodium dichromate, 25–40 minutes at 20–50 °C. Free iron smeared onto the surface during machining and exposed sulphides are removed by this step. Unpassivated 416 behaves markedly worse than passivated 416.

Where 416 FAILS — read this list before quoting​‌​​‌​

1. Chlorides and seawater. An absolute exclusion. Salt spray, marine atmosphere, chlorinated water, road salt. Producer pages put “NaCl saline mist” and “seawater” on the restricted list — which in practice means “do not use”. For marine service there are 316, F53 and F55.
2. Crevice geometries. The producer warns explicitly: “avoid crevice designs”. Under gaskets, threaded joints, interference fits, under deposits. 416 already has microscopic crevices (dissolved MnS voids); adding a macroscopic one compounds the problem.
3. Acids. Nitric, phosphoric, sulphuric and acetic acid are all on the restricted list.
4. Welding. See the welding section above. A welded 416 part carries both cracking and corrosion risk.
5. Parts tempered between 400 and 600 °C. That band lowers both impact resistance and corrosion resistance. Here the heat-treatment records matter as much as the material certificate.
6. Roughly machined, unpassivated surfaces. A rough surface, exposed MnS and free iron all accelerate corrosion. The producer’s advice: “maintain smooth, contamination-free surfaces”.
7. Food and pharmaceutical contact surfaces. A sulphurised steel pits quickly against cleaning chemicals — especially chlorinated disinfectants — and a pit is a bacterial refuge that cannot be cleaned. Those applications use 316L.
8. Sour service (H₂S). 416 is not accepted for sour service under NACE MR0175. For sulphide stress cracking, a sulphurised and hardened martensitic is the worst possible combination. If you need a sour-service 13Cr, that is 415.
9. Deep drawing and heavy cold forming. Not corrosion but a mechanical limit: MnS inclusions initiate cracks. 416 can be bent but not deep drawn.
10. Cryogenic and low-temperature impact service. No verified low-temperature toughness data could be found for a sulphurised martensitic, and the microstructure is not suited to it. If there is a low-temperature impact requirement, do not quote 416.

Frequently Asked Questions​‌​​‌​

We make our parts from 303 but they need to be a bit harder. Can we switch to 416?

Technically yes — and this is exactly the reason 416 exists. But you lose three things, and none of them comes back.
What you gain is clear: 303 is austenitic and cannot be hardened by heat treatment — outside of cold work there is no way to raise its strength. 416 is martensitic: quenched it reaches 41–43 HRC and tempering sets it wherever you want. The typical working point is Condition T, 27–31 HRC, tensile 890–1035 MPa. Far above cold-drawn 303.
The first thing you lose is corrosion resistance. 303 is an 18Cr-8Ni austenitic; 416 is a 13Cr martensitic. Five points less chromium and no nickel at all. A producer writes on its own 1.4005 datasheet that it is “probably the least resistant to corrosion of all of the stainless steel grades“. If your part sits in a damp environment, gets washed with cleaning chemicals, or occasionally meets salt water, this switch will be visible in the field.
The second is magnetic response. 303 is effectively non-magnetic (it picks some up from cold work). 416 is ferromagnetic in every condition. If the part sits near a sensor, passes through a magnetic separator, or needs MR compatibility, that alone is grounds for exclusion. Conversely, if you run magnetic fixturing on the assembly line, it may be an advantage.
The third is cutting speed. Published speed tables give 303 about 150 SFM and 416 about 95 SFM — so your cycle time goes up. Even though 416’s relative machinability rating (85 %) is higher than 303’s (78 %), that rating also measures tool life and chip breaking; in raw speed, 303 is faster. Cost the machine hours in.
And a fourth point that gets forgotten: switching to 416 means you are also buying a heat treatment step. Hardening, tempering, probably straightening, and certainly passivation. Add those to the part price; the price per kilo of the material is misleading.​‌​​‌​

Our datasheet says 416 is “the most machinable stainless” but 303 runs faster on our machines. Which is right?

Both are right, and the confusion comes from two different indices being published with the same percent sign.
Index one: the AISI relative machinability rating. Reference B1112 free-machining steel = 100 %. This rating weighs tool life, chip-breaking behaviour and achievable surface finish together. On that scale 416 = 85 % is first among stainless steels and 303 = 78 % is second.
Index two: the cutting-speed index. Same B1112 = 100 % reference, but it measures only the applicable cutting speed. On that scale 416 annealed is 95 SFM (54 %) and 303 is 150 SFM (75 %). 303 is clearly faster.
Not a contradiction — physics. 416 is martensitic and harder; hard material is cut at lower speed. But 416 breaks the chip far better, galls less, wears the tool less and is more dimensionally stable. 303 is austenitic: it runs fast but work hardens, produces stringy chips and builds up edge on the tool.
Practical consequence: on short, simple parts 303 gives the faster cycle. On long, multi-operation, tight-tolerance, unattended work, 416 is more predictable and cheaper overall — because there are fewer tool changes, fewer chip jams and less dimensional drift. The right comparison is not parts per hour but good parts per shift.
And remember: on both indices 416 is roughly 1.5× better than its sulphur-free sibling 410. 416’s true benchmark is not 303 but 410.​‌​​‌​

The customer wants us to weld a 416 part. “Just a small tack weld,” he says. Should we?

No — and put the reason in writing, because the liability comes back to you later.
The welding problem in 416 is not a skill problem; it is a metallurgy problem. Two mechanisms operate simultaneously.
The first is sulphur-driven hot cracking. Sulphur concentrates in the last liquid to solidify in the weld pool and leaves low-melting sulphide films at the grain boundaries. The bead contracts as it cools; those films are still liquid and separate under tensile stress. This cannot be fixed by filler metal — the sulphur comes from the base metal and mixes into the pool. A tack weld does not remove the problem; it merely makes the crack smaller and invisible.
The second is martensitic hardening. 416 is an air-hardening 13Cr steel. The narrow band around the tack transforms to untempered, hard and brittle martensite. If hydrogen is present (damp electrode, oily surface, moisture in the shielding gas) delayed cracking arrives days later.
The third is corrosion, and it is usually overlooked. The weld and the heat-affected zone lose what passivity they had. Even if the part looks sound right after welding, the first corrosion will start in that band.
If you are forced into it, damage limitation: filler E309 / ER309 (European equivalent 1.4833), preheat 200–300 °C, shielding gas free of hydrogen and nitrogen, post-weld stress relief at 650–675 °C or full annealing at about 790 °C, followed by mechanical cleaning and passivation of the weld zone. But that is damage control, not a procedure.
The right engineering answer: do not make a welded part from 416. Either solve the assembly mechanically (screws, pins, interference fits, brazing), or make the component that gets welded from 410 or 415, or look for a sulphur-free free-machining alternative. Welding a free-machining steel cancels every reason you had for choosing it.​‌​​‌​

Our 416 parts started rusting six months after assembly. Did we get the wrong material?

Most likely the material was right and a step in the process was skipped. There are four things to check, in order.
1. Were the parts passivated? For 416, passivation is not optional. During machining, free iron is transferred onto the surface from tooling, machine ways and chip conveyors, and the cut also exposes MnS inclusions at the surface. Both start rusting when they meet moisture. The correct treatment is 20–50 % nitric acid plus 2–6 wt % sodium dichromate, 25–40 minutes at 20–50 °C, per ASTM A380. Unpassivated 416 rusts within six months — that is expected behaviour, not a defect.
2. What is the surface roughness? A roughly machined surface means more exposed inclusions and more micro-crevices. The producer’s advice is explicit: “maintain smooth, contamination-free surfaces, avoid crevice designs”.
3. What was the tempering temperature? If the part was tempered between 400 and 600 °C, its corrosion resistance has been reduced, even if nobody intended it. That band damages both impact resistance and passivity. Ask your heat treater for the furnace record. It can be more informative than the material certificate.
4. Is the environment actually the one you expected? 416 is fine in fresh water, steam, dry air and most petroleum products. If chloride is present — salt spray, road salt, chlorinated cleaner, perspiration — 416 was the wrong grade from the start. Six months is a realistic life for 416 in a chloride environment.
What to do: in the short term, re-passivate the parts and reduce the surface roughness. In the long term, if there is chloride in the environment, change grade: 303 if there is no hardness requirement, 415 or 17-4 PH if there is. You cannot make 416 chloride-resistant by passivating it; passivation only lets the material reach its own limit.​‌​​‌​

Common datasheet errors — check these before you place an order

1. The EN equivalent is printed as 1.4401 — WRONG. A widely mirrored producer datasheet lists the specification as “ISO/EN 10088-3 (1.4401/1.4005)”. 1.4401 is 316, an entirely different material (austenitic, 17Cr-11Ni-2Mo). The only EN counterpart of 416 is 1.4005 / X12CrS13.
2. Thermal conductivity is given in impossible units. One distributor page prints “171.8 Btu·ft/ft²·hr·°F” for 416. That is above the conductivity of silver and is impossible. The unit was most likely meant to be Btu·in/ft²·hr·°F. The correct magnitude is 25–30 W/m·K.
3. The annealed row pairs 517 MPa tensile with 262 HB hardness. 262 HB corresponds to roughly 900 MPa tensile, not 517 MPa. In that row the hardness is a CEILING and the tensile is a TYPICAL value. Do not read them as one material condition.
4. Sulphur is written as an upper limit. In the ASTM/AISI definition S ≥0.15 % is a MINIMUM — a guaranteed floor. Some pages write it as “S max 0.15”. That inverts what the material is. EN 1.4005 by contrast gives both limits: 0.15–0.35 %.
5. The carbon minimum is forgotten. ASTM S41600 has NO carbon minimum (only ≤0.15 %); EN 1.4005 HAS one (0.08–0.15 %). For a part that will be hardened this difference is decisive: a heat of S41600 at 0.06 % C conforms and will not reach the expected hardness. For hardened work, ask for dual certification to 1.4005.
6. The term “475 °C embrittlement” is used for 416. A European producer page names the 425–525 °C forbidden band that way. 475 °C embrittlement is a phenomenon of FERRITIC and duplex stainless steels (α′ demixing). The effect in 416 is TEMPER EMBRITTLEMENT. Same practical outcome (do not temper in that band), different mechanism.
7. The forbidden tempering band is given three different ways. 400–580 °C, 400–600 °C and 425–525 °C. Publish the conservative envelope: 400–600 °C. The intersection of all three, 425–525 °C, is absolutely forbidden.
8. “Highest machinability” is confused with cutting speed. On the relative rating scale 416 = 85 % (first among stainless steels). On the cutting-speed scale 416 = 54 % and 303 = 75 %. They measure different things and both are correct. Use the speed index when programming the machine.
9. Molybdenum is shown as if it were part of the composition. Mo ≤0.60 % is a PRODUCER OPTION, not a mandatory alloying element. Unless it is explicitly required in the order, its presence cannot be guaranteed — and do not base a corrosion calculation on it.
10. “416 plate to ASTM A240” gets quoted. S41600 is not in the A240 grade list. A single source cites ASTM A895 for free-machining stainless flat product, but that could not be independently verified. In practice 416 flat product is sold to mill specification in limited sizes.
11. Two different property sets circulate for the hardened condition. ASTM A582 typical: 758/586 MPa, 248–302 HB; producer band: 890–1035 / 760–895 MPa, 27–31 HRC. The gap is not small. State in the purchase order which set you are buying.
12. 416 and 416Se are treated as the same thing. 416Se (S41623) is selenium-bearing and differs from sulphurised 416: better cold forming and hot working, higher surface quality, higher price and harder to source. Do not order them under the same part number.​‌​​‌​

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