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AISI 434 / (1.4113)

AISI 434 is an alloy in the ferritic stainless steel class, generally known for moderate corrosion resistance, good machinability and high temperature capability. Its ferritic properties come from its chromium content, and it is mostly used in applications requiring moderate corrosion resistance.​‌​​‌​

AISI 434 offers moderate tensile and yield strength, but is limited compared with the austenitic steels in terms of hardness and wear resistance. Its ferritic structure improves formability and machinability while also having a positive effect on high temperature capability.

Corrosion resistance: It is a variant of AISI 430, the most widely used of the non-hardenable ferritics. The addition of molybdenum increases the general corrosion resistance of the alloy and makes it resistant to attack by dissolved chemicals.​‌​​‌​

Weldability: For weldability, a controlled sulphur content of 0.008% to 0.030% is recommended.

Machinability: For machinability, a controlled sulphur content of 0.015% to 0.030% is recommended.​‌​​‌​

Heat treatment: It combines good heat and oxidation resistance up to 1500 °F (816 °C) with good mechanical properties.

Applications: It is generally used in white goods, automotive, industrial machinery and decorative products, exterior architecture and profile production.​‌​​‌​

1.4113 belongs to the ferritic stainless steel category and offers moderate corrosion resistance, high temperature capability and machinability. Because it does not provide corrosion resistance as high as the austenitic steels, however, it is not suitable for aggressive chemical environments or high wear conditions. It is an ideal choice for applications involving a moderate corrosion risk together with a requirement for high temperature capability.

What AISI 434 Is — the Work One Single Element Does​‌​​‌​

AISI 434 (UNS S43400 / W.Nr. 1.4113 / DIN X6CrMo17-1) is the molybdenum-bearing derivative of 430. Its chemistry is the same as 430 — 16–18 % Cr, low carbon, nickel-free ferritic — with one addition: 0.75–1.25 % molybdenum (0.90–1.40 % on the EN side). The entire reason the alloy exists is that single element, and what it delivers is a single thing: pitting resistance in chlorides.

The mechanism is measurable and fits in one formula. The pitting resistance equivalent number is PREN = %Cr + 3.3 × %Mo. With zero molybdenum, 430 gives PREN = 16–18. For 434, the ends of the ASTM band give 16 + 3.3 × 0.75 = 18.5 and 18 + 3.3 × 1.25 = 22.1. So molybdenum raises PREN by roughly 20–25 % at the same chromium level. That matches exactly the PREN 18.5–22.1 band an independent source publishes for 434 — confirmation that the formula really is being applied.​‌​​‌​

But 434 is a ferritic, and the price of being ferritic is not paid off by molybdenum. It contains no nickel, it is not austenitic, it cannot be hardened by heat treatment, its grains coarsen when welded, it is open to 475 °C embrittlement, and it shows roping (ridging) in deep drawing. 434 is “a slightly better 430” — it is not “a cheap 316”. The difference between those two sentences determines everything else on this page.

Standards by Product Form

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The specification coverage of 434 is built around FLAT PRODUCT, which follows directly from what the material is made for: 434 is an automotive exterior trim sheet. In other product forms the coverage is weak.

Product Forms With NO Standard — the Commercially Valuable Section

434 is a well-known grade name, so it is assumed to exist in every form. It does not.​‌​​‌​

Chemical Composition​‌​​‌​

The difference between ASTM and EN here is real and has measurable consequences. EN demands lower carbon and higher molybdenum — which means EN 1.4113 is a better material than ASTM S43400, and the two are not automatically interchangeable.

Mechanical Properties​‌​​‌​

An honest warning: the MINIMUM values that ASTM A240 sets for S43400 could not be independently verified here. The numbers below are typical / measured values, not specification minimums. If you are going to write minimums into a purchase specification, read them from the current edition of A240.​‌​​‌​

Physical Properties

Heat Treatment and Thermal Stability

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The heat-treatment section for 434 is short because the only thing you can do is anneal it. What matters is what you must not do: ferritic stainless steels have three separate embrittlement mechanisms, and all three are defined by a temperature window.

The three embrittlement windows — the real problem with ferritics

Welding

434 can be welded, but saying it “welds well” would be misleading. The sources conflict here, and the conflict itself is informative.​‌​​‌​

Machining and Forming

434 is a sheet material; its main manufacturing route is forming, not metal removal. So in this section forming behaviour matters at least as much as cutting parameters.​‌​​‌​

Corrosion — Where It Is Good, Where It FAILS

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The corrosion story of 434 fits in one sentence: the molybdenum is enough for road salt, and it is not enough for seawater.

Let the number speak: PREN​‌​​‌​

Using PREN = %Cr + 3.3 × %Mo:
430 (no Mo): 16–18
434 (ASTM band): 18.5 – 22.1 — exactly the band an independent source publishes for 434
434 (EN band, Mo ≥0.90 %): the lower end rises to 19.0
316: about 24 and above
F53 super duplex: above 40
What to take from this: 434 sits above 430 and below 316 — and where in that gap it sits depends on which end of the molybdenum band the heat came from. Between a heat at the bottom (Mo 0.75 %) and one at the top (Mo 1.25 %) the PREN difference is 3.6 points — and on a salted road that is a measurable difference in service life. On a critical application, write a molybdenum minimum into the purchase specification.

Where 434 IS good​‌​​‌​

Automotive exterior trim and de-icing salt — its home ground. An automotive steelmaker’s own product brochure puts it plainly: 430 bright anneal is for “interior or fully encapsulated products”; where protection against de-icing salt is needed, “Type 434 and 436 with molybdenum are typically required”. Window bezels, roof trim, pillar posts, wheel covers.
Fresh water and weak acids/alkalis. A database rates 434 “excellent” in those environments.
Chloride stress corrosion cracking (SCC). This is the one area where ferritics genuinely beat austenitics. Austenitic stainless steels such as 304 and 316 crack under stress in hot chloride environments — one of the most expensive failure modes in industry. Ferritics are effectively immune to that mechanism. So despite its lower PREN, 434 can be more reliable than 316 in a hot chloride plus stress combination. That is a genuine engineering argument that almost no distributor page bothers to make.
Thermally cycled applications. Its expansion coefficient is about two thirds of 316’s and close to carbon steel; on parts joined to carbon steel the differential expansion stress is far lower.
Oxidising environments and scaling resistance. 17 % chromium gives good scale resistance at elevated temperature.

Where 434 FAILS — read this list before quoting​‌​​‌​

1. Seawater and stagnant high chlorides. PREN 18.5–22.1 is not enough for that. A database rates seawater performance only as “good” — not excellent. For immersion, stagnant salt water and hot chlorides you need 316, F53 or F55.
2. Crevice geometries. Chloride concentrates and pH falls inside a crevice; 434’s PREN does not cope with that local condition. Salt water collecting inside closed trim profiles is the most common field failure.
3. Inorganic acids. A database places these on the “restricted” list.
4. Sour service (H₂S). The same database rates sour oil and gas environments as “restricted”. Do not quote 434 for sour service.
5. Unstabilised welded joints. This is 434’s greatest weakness. During welding Cr₂₃C₆ precipitates at the grain boundaries and intergranular corrosion begins. In a ferritic, sensitisation is far faster than in an austenitic. Every joint without post-weld annealing or a stabilised grade is at risk.
6. Continuous service between 375 and 525 °C. 475 °C embrittlement. Toughness collapses, hardness rises. A 17 % chromium ferritic is markedly susceptible.
7. Long exposure between 550 and 800 °C. Sigma phase. Both toughness and corrosion resistance fall. Molybdenum accelerates sigma formation — 434 is worse than 430 here.
8. Low temperature and impact loading. Ferritics show a ductile-to-brittle transition close to room temperature, rising with thickness. The published minimum service temperature sits somewhere between −73 and −43 °C, and that uncertainty is itself a warning. Do not use 434 in cryogenic or cold-climate impact service.
9. Cosmetic deep drawing. Roping is more pronounced than in 430, and on polished exterior trim that is a visible defect.
10. Anywhere high strength is required. It cannot be hardened. Yield sits in the 300–440 MPa band and cannot be raised except by cold work.
11. As a pressure-boundary material. ASME coverage could not be verified here, and ferritics have low creep strength. Use an austenitic in a pressure vessel.
12. Surfaces not cleaned after welding. Scale and heat tint leave a chromium-depleted layer. The steelmaker is explicit: it must be thoroughly cleaned after welding.

Frequently Asked Questions​‌​​‌​

We use 430 and the parts corrode on salted roads. Will switching to 434 fix it?

Largely yes, and this is exactly the reason 434 exists. But with two warnings.
The gain is real and measurable. The only difference between 430 and 434 is molybdenum, and pitting resistance comes directly from it. Using PREN = %Cr + 3.3 × %Mo: 16–18 for 430, 18.5–22.1 for 434. An automotive steelmaker has turned this into policy in its own brochure: 430 bright anneal is for “interior or fully encapsulated products”; where de-icing salt protection is needed, “Type 434 and 436 with molybdenum are typically required”. So the damage you are seeing is expected behaviour, and the right answer really is molybdenum.
First warning: where in the band the molybdenum sits matters. ASTM S43400 leaves molybdenum free between 0.75 % and 1.25 %. A heat from the bottom gives PREN 18.5, one from the top gives 22.1 — a 3.6 point difference. Write a molybdenum minimum into the purchase specification (for example ≥1.00 %). Alternatively, ask for dual certification to EN 1.4113: EN’s molybdenum minimum is already 0.90 %, and its carbon ceiling is lower too (0.08 % against 0.12 %).
Second warning: if the part is welded, molybdenum is not enough. 434 is an unstabilised ferritic; welding precipitates chromium carbide and intergranular corrosion starts. On a salted road that progresses faster than pitting. If your part is welded, the right answer is not 434 but niobium-stabilised 436. Same molybdenum, plus weld safety.
A third, commercially important point: the same steelmaker reports that a grade with 19–21 % chromium, C ≤0.02 %, niobium-stabilised and MOLYBDENUM-FREE offers salt resistance comparable to 434/436 — with better weldability and formability. If the molybdenum price is high, investigate that route.​‌​​‌​

434 is sold as “cheap 316”. Can we really use it instead of 316?

No — and that analogy leads to one of the most expensive mistakes in the field. But there is an interesting exception.
Why not, on four grounds:
1. Insufficient pitting resistance. 434: PREN 18.5–22.1. 316: about 24 and above. In a chloride environment that is a critical difference, not a matter of “slightly less” — once the pitting threshold is crossed, damage starts; below it, nothing starts at all.
2. Weldability. 316 can be welded and used as welded; unstabilised 434 sensitises during welding and demands post-weld annealing.
3. Formability. 316 is austenitic, work hardens strongly and deep draws. 434 ropes and has limited work-hardening capacity.
4. Low-temperature toughness. 316 stays ductile down to cryogenic temperatures. 434’s ductile-to-brittle transition is close to room temperature. There is no comparison to make.
Now the exception — and it genuinely matters. Where chloride stress corrosion cracking (SCC) is the risk, 434 is BETTER than 316. Austenitic stainless steels crack under tensile stress in hot chloride environments — above about 60 °C in chloride-bearing water this is a classic failure mode, and it is sudden, widespread and not visible in advance. Ferritic stainless steels are effectively immune to it. So in a hot, chloride-bearing, stressed application — a heat exchanger tube, a hot water tank, a steam condensate line — a ferritic such as 434 can outlast 316, despite its lower PREN.
The correct sales sentence: “434 is not the cheap alternative to 316. 434 is the better version of 430, and a genuine alternative to 316 where chloride SCC is the risk. If you need general chloride resistance, formability or weldability, buy 316.”​‌​​‌​

We weld our 434 sheet parts and corrosion starts at the weld. What is wrong?

Probably nothing was done “wrong” — 434 is an unstabilised ferritic and this is expected behaviour. But it is worth separating which of three mechanisms is operating.
1. Sensitisation (the most likely cause). During welding Cr₂₃C₆ precipitates at the grain boundaries and depletes chromium in the adjacent region. That narrow chromium-poor strip is no longer stainless and intergranular corrosion begins. In a ferritic this is far faster than in an austenitic: carbon solubility in ferrite is very low and diffusion is very fast, so while sensitisation takes hours in an austenitic it can happen in seconds during weld cooling in a ferritic. ASTM S43400’s C ≤0.12 % ceiling magnifies the risk.
2. Surface cleanliness. Weld scale and heat tint leave a chromium-depleted layer beneath them. The steelmaker is explicit: after welding the part must be thoroughly cleaned. Skip that step and corrosion starts in that band even without sensitisation.
3. Galvanic couple. If you used an austenitic filler (308L / 309L), the weld metal and the ferritic base metal sit at different potentials. In a salty, wet environment that sets up a galvanic cell.
What to do — three options, in increasing cost:
Option 1: post-weld annealing. 750–800 °C followed by RAPID cooling. Chromium diffuses back into the depleted zone and sensitisation is removed. The rapid cool is essential — slow cooling walks the part through the 475 °C and sigma bands. But this does not restore the coarsened heat-affected-zone grain; that toughness loss is permanent.
Option 2: reduce heat input. Faster travel, narrower beads, lower amperage. No submerged arc welding. This narrows the sensitised band but does not eliminate it.
Option 3 — the real answer: change grade. Niobium-stabilised 436 carries the same molybdenum as 434 but ties the carbon up as NbC; it PREVENTS intergranular corrosion during welding. That is the steelmaker’s own statement. It also ropes less. Choosing 434 for a part that will be welded is bringing forward a cost you will pay later.
And an intermediate fix: ask for dual certification to EN 1.4113 instead of ASTM alone. EN’s carbon ceiling is 0.08 % against ASTM’s 0.12 % — the sensitisation risk drops measurably. It does not replace stabilisation, but it is a free improvement.​‌​​‌​

We want 1.4113 for a solenoid valve core. Is standard 1.4113 good enough?

No — and this is a distinction that is easily missed when writing the order.
Standard EN 1.4113 / X6CrMo17-1 is a corrosion-resisting structural material. It is ferromagnetic, yes — but its soft magnetic properties (coercivity, maximum permeability, saturation polarisation) are not defined in the specification and are not checked heat by heat. In a solenoid core those properties are the function of the part, not a by-product.
One European producer offers a separate grade for this: 1.4113 IL. The published analysis is C ~0.03 %, Si ~0.6 %, Mn ~0.60 %, S ≤0.015 %, Cr ~18 %, Mo ~1.1 %. Note the difference: carbon has been cut far below the standard ceiling (0.08 %) and chromium pushed to the top of the band. The reason is direct physics: carbon, nitrogen and inclusions pin magnetic domain wall motion — they raise coercivity and lower permeability. In a soft magnetic material all of those are undesirable.
The published magnetic values: coercive field <240 A/m, maximum relative permeability >1300, saturation polarisation >1.5 T. Tensile strength in the soft annealed condition is 400–600 MPa. Do not publish those figures for standard 1.4113 — they belong to a special melt and cannot be guaranteed from standard material.
Why is this grade chosen? The application the producer names: pneumatic and hydraulic solenoid valves with higher corrosion resistance requirements, such as medical equipment. So the molybdenum is there for corrosion reasons, not magnetic ones: the valve body sits in a permanently damp or repeatedly cleaned environment. High molybdenum and low sulphur raise pitting resistance — that is the producer’s own stated reasoning.
What to do: if you have a magnetic specification, order the producer grade by name and with its magnetic values; do not simply write “1.4113”. And put the annealing condition into the order too: soft magnetic properties are extremely sensitive to the final anneal, and cold work in a machined part raises coercivity — so the final anneal must come AFTER machining.​‌​​‌​

Common datasheet errors — check these before you place an order

1. A yield strength with a botched unit conversion. A widely mirrored datasheet gives “yield 50 ksi (290 MPa)” for 434. 50 ksi is 345 MPa, not 290. The same page converts the tensile correctly (80 ksi = 655 MPa). Check the conversion yourself; that page is copied in many places online.
2. Thermal conductivity in an impossible unit. The same page prints “15.1 Btu-in/ft²-hr-°F”. That works out to ~2.2 W/m·K, which is impossible for a stainless steel. The correct magnitude is 23–27 W/m·K (i.e. ~160–190 Btu-in/ft²-hr-°F).
3. ASTM A240 minimums are confused with typical values. Figures such as 538 / 441 MPa / 32 % / 89 HRB that you see on datasheets are typical measured values, not specification minimums. The A240 minimums for S43400 could not be independently verified on this page — if you are writing minimums into an order, read them from the current edition of the standard.
4. A factor-of-two scatter in yield strength is being ignored. Published values run from 245 MPa to 441 MPa. The cause is most likely product form and degree of cold work. Do not pick a design value; ask the mill for heat data.
5. ASTM and EN chemistries are assumed identical. Carbon: ASTM ≤0.12 %, EN ≤0.08 %. Molybdenum: ASTM 0.75–1.25 %, EN 0.90–1.40 % (0.90–1.30 % in one source). EN is narrower and better. A heat of S43400 from the bad end of the band is not 1.4113.
6. A product called “ASTM A268 TP434” gets quoted. TP434 was not seen in the A268 grade list in two separate sources. The listed grades revolve around TP405, TP409, TP410, TP430, TP439, TP444 and TP446. Confirm from the current edition of the standard before ordering.
7. “No preheat or PWHT required for welding” is published as an absolute rule. One database says that; welding-technology sources recommend 100–200 °C preheat and 750–800 °C post-weld annealing. The conflict is contextual: it is true for thin trim sheet and false for heavy section and corrosion-critical joints.
8. The maximum service temperature is given as four different numbers. 816 °C (oxidation), 750–800 °C (maximum service), 880 °C (“mechanical”), 410 °C (“corrosion”). They measure different things. The 410 °C figure is most likely the lower edge of the 475 °C embrittlement band; the 816 °C figure is scaling resistance only, and there is no useful mechanical strength left up there. Label every number with what it measures.
9. Soft magnetic values are attributed to the standard grade. The figures coercivity <240 A/m, µr max >1300, saturation >1.5 T belong to one producer’s special melt (1.4113 IL, C ~0.03 %, Cr ~18 %). They cannot be guaranteed for standard 1.4113.
10. “434 is hardenable” gets printed. It is not. The ferritic structure does not transform to martensite. The C ≤0.12 % ceiling is misleading: the partial martensite that can form at high temperature is not a heat-treatment route but a welding problem.
11. The molybdenum addition is presented as “316-level corrosion resistance”. 434: PREN 18.5–22.1. 316: ~24 and above. Molybdenum lifts 434 above 430, not up to 316.
12. 434 and 436 are treated as the same grade. 436 is 434 plus niobium stabilisation (Nb ≥5 × C, ≤0.80 %). The molybdenum is the same but welding behaviour and roping tendency differ. On a part that will be welded or deep drawn, that distinction decides the job.​‌​​‌​

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