AISI 430 and AISI 304 represent two different families of stainless steel. From the outside they look the same, but metallurgically they are fundamentally different. The element that separates them is nickel.
Ferritic and austenitic
The composition of AISI 304 contains 8.00–10.50% nickel. Nickel keeps the steel in an austenitic structure at room temperature: that structure is non-magnetic, forms very well and does not become brittle at low temperatures.
In AISI 430 there is practically no nickel (max 0.50%). The structure is ferritic — that is, magnetic, not hardenable, and its deep drawing capability is behind that of 304. In exchange, its coefficient of thermal expansion is much lower (10.4 against 17.2 µm/m·°C) and its thermal conductivity higher (26.1 against 16.2 W/m·K).
There is a difference on the corrosion side as well: the chromium of 430 is close to that of 304 (16–18% against 17.50–19.50%) but, without nickel, its general corrosion resistance is lower. It causes no trouble indoors and in dry environments; in damp, salty or acidic environments 304 is clearly superior.
Comparison in numbers
| PROPERTY | AISI 430 | AISI 304 |
|---|---|---|
| Structure | Ferritic (magnetic) | Austenitic (non-magnetic) |
| Carbon (C) | max 0.12% | max 0.07% |
| Chromium (Cr) | 16 – 18% | 17.50 – 19.50% |
| Nickel (Ni) | max 0.50% | 8.00 – 10.50% |
| Tensile strength Rm | 483 MPa | 500 – 700 MPa |
| Yield strength Rp0.2 | 260 MPa | min 190 MPa |
| Elongation A50 | 22% | min 45% |
| Hardness | max 183 HB | max 215 HB |
| Density | 7.75 g/cm³ | 8.00 g/cm³ |
| Thermal conductivity | 26.1 W/m·K | 16.2 W/m·K |
| Thermal expansion | 10.4 µm/m·°C | 17.2 × 10⁻⁶/K |
| Melting range | 1425 – 1510 °C | 1450 °C |
| UNS | S43000 | S30400 |
| W.Nr (DIN/EN) | 1.4016 | 1.4301 |
| AMS | 5503 · 5627 | 5511 · 5513 · 5560 · 5565 · 5639 · 5647 |
Values are taken from our product datasheets; section thickness and the applied heat treatment regime change the result.
Which one, and when?
AISI 430 is sufficient — white goods panels, interior decoration, lift cabins, kitchen equipment bodies, automotive trim parts, components exposed to heat whose expansion has to stay limited. Since it contains no nickel its cost is markedly lower and it is not affected by swings in the nickel price.
AISI 304 is required — food and beverage equipment, welded tanks and pipes, exterior façade applications, parts formed by deep drawing, anything working in a damp environment. Its forming and welding capability is far better than that of 430.
A practical way to tell them apart: if a magnet sticks it is 430, if it does not it is 304. (Cold-formed 304 can be partly magnetic, so the test should be made on annealed material.)
Neighbouring grades
The free-machining version of 430 is AISI 430F, and its molybdenum-bearing version is AISI 434. For the step above 304, see our AISI 304 – AISI 316 comparison.
Technical datasheets
AISI 430 — chemical composition, mechanical values, standard equivalents
AISI 304 — chemical composition, mechanical values, standard equivalents
Both grades are supplied to order in round bar, flat bar, plate, sheet, pipe and forged forms. Contact us for a quotation.