The most common mistake made between AISI 434 and AISI 430 is to assume 434 is “430 with more chromium”. It is not: the two steels have exactly the same chromium band (16.00–18.00 %). The one deliberate difference is molybdenum.
What does the molybdenum buy?
Molybdenum increases resistance to pitting corrosion in chloride-bearing environments. In AISI 434 molybdenum runs from 0.75 to 1.25 % (ASTM S43400) or 0.90 to 1.40 % (EN 1.4113); AISI 430 has none at all.
The International Stainless Steel Forum’s approximate relationship makes the difference concrete: one extra percent of molybdenum increases pitting corrosion resistance as much as about 3.3 percent of extra chromium.
The classic application is automotive exterior trim. Cleveland-Cliffs describes 430 as “the entry-level 17 % chromium ferritic that provides acceptable corrosion resistance to mild conditions”, used primarily for interior or fully encapsulated parts, and notes that where added protection from de-icing salts is needed, the more corrosion-resistant Type 434 and Type 436 grades are typically required.
Compared in figures
| PROPERTY | AISI 434 (1.4113) | AISI 430 (1.4016) |
|---|---|---|
| Structure | ferritic | ferritic |
| Chromium (Cr) | 16.00 – 18.00 % | 16.00 – 18.00 % |
| Molybdenum (Mo) | 0.75 – 1.25 % (ASTM) 0.90 – 1.40 % (EN) | none |
| Carbon (C) | 0.08 % max (EN 1.4113) | 0.08 % max (EN) / 0.12 % max (ASTM) |
| Manganese (Mn) | 1.00 % max | 1.00 % max |
| Magnetic | yes | yes |
| Hardens by heat treatment | no | no |
| Chloride / road salt resistance | higher | lower |
| Typical use | exterior trim, visible parts | interior, encapsulated parts |
Welding and forming
Both grades can be welded by the common fusion and resistance methods, but post-weld annealing is required to restore ductility and corrosion resistance in the heat-affected zone.
A small but commercially important note on forming: Cleveland-Cliffs observes that 434 has a slightly greater tendency to “roping” during forming than the niobium-stabilised grades (435 Mod, 436). This should be taken into account on deep-drawn parts with a visible surface.
What to watch when ordering
EN 1.4113 and UNS S43400 are not identical.
Molybdenum is 0.90–1.40 % in EN and 0.75–1.25 % in ASTM. Material certified to 1.4113 always meets S43400’s molybdenum requirement; the reverse is not true — a heat at 0.75 % molybdenum passes S43400 and fails 1.4113. The carbon ceiling differs too (0.08 % in EN, 0.12 % in ASTM A240).
Two further warnings
1. 434’s ASTM A240 annealed proof strength minimum is genuinely disputed: SSINA gives 240 MPa (35 ksi), Ulbrich gives 205 MPa (30 ksi). Write into your specification which value you design to, and its source.
2. If de-icing salt resistance is all you need, 434 is not the only option: Cleveland-Cliffs states that the molybdenum-free 19 % chromium grade 435 Mod (UNS S44500) offers similar de-icing salt resistance to 434 and 436. Ask about it when obtaining quotations.
Where are they used?
AISI 434: automotive exterior trim and mouldings, wheel covers, beltline and pillar trim, window bezels, appliances, architectural components, hot water tanks, solar water heaters, visible exhaust parts, range hoods and catering equipment.
AISI 430: domestic appliances, kitchen equipment, architectural interior trim, food and dairy equipment, interior or encapsulated automotive parts.
Designations, standards and AMS equivalents
The same steel is called different things depending on which system you are speaking in. Most ordering and certification confusion starts here, so a short summary:
- AISI — the American Iron and Steel Institute’s grade naming (410, 316L and so on). It is the most widely used name in everyday use, but on its own it is not a purchasing specification: composition and mechanical requirements are defined in the ASTM standards.
- UNS — the Unified Numbering System operated jointly by ASTM and SAE (S41000 and so on). It is the number used for ordering and certification in North America, and it is more precise than the AISI name.
- W.Nr / EN — the European material number (1.4006 and so on) and EN name (X12Cr13 and so on). This is the governing designation in Europe. It is usually only an approximate equivalent of the AISI grade; carbon, sulphur or molybdenum limits frequently differ.
- AMS — SAE’s Aerospace Material Specifications. An AMS specification binds not only the composition but also the melting practice, the product form, the heat treatment condition and the inspection requirements. In aerospace and defence orders this is the designation that governs.
| DESIGNATION | AISI 434 | AISI 430 |
|---|---|---|
| AISI / trade name | AISI 434 | AISI 430 |
| EN material no. (W.Nr) | 1.4113 | 1.4016 |
| UNS number | — | S43000 |
| AMS specifications | — | AMS 5503 · AMS 5627 |
| Product page | AISI 434 technical page | AISI 430 technical page |
Two reminders. First: an AMS number is specific to a product form and condition. The same grade may have separate AMS specifications for bar, sheet and forgings, so establish which product form you need before calling up an AMS number.
Second: the AISI name, material number, UNS and AMS data in the table above are the designations shown on Defence Metal’s product pages. If you are working to a different edition of a standard or to a different product form, state the material number and the specification edition explicitly on your order.