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SUS430 vs SUS304: When the Cheaper Ferritic Grade Is Enough

Materials / 5 Sept 2026

SUS430 turns up on drawings for two reasons. Either somebody chose it deliberately to save money, or somebody chose it by accident because a sheet metal part next to it was 430 and nobody questioned it. The second case usually needs correcting. The first case is often the right call and gets overturned by reflex.

Here is where the ferritic grade genuinely works and where it does not.

What makes it different

SUS430 is roughly 16 to 18 % chromium with essentially no nickel. That single fact drives everything:

	SUS430	SUS304
Structure	Ferritic	Austenitic
Nickel	none	8 to 10.5 %
Chromium	16 to 18 %	18 to 20 %
Magnetic	Yes, always	Essentially no, when annealed
Hardenable by heat treatment	No	No
Work hardening rate	Low	High
Thermal conductivity	around 26 W/m·K	around 16 W/m·K
Thermal expansion	around 10.4 µm/m·K	around 17.3 µm/m·K
Machinability index	around 54	around 45
EN number	1.4016	1.4301

Nickel is what makes SUS304 austenitic, non magnetic, tough at low temperature, and expensive. Take it out and you get a cheaper, magnetic, easier cutting grade with less corrosion resistance and much worse behaviour in a weld.

Why it machines better

Three properties combine in your favour.

It barely work hardens. This is the big one. SUS304’s austenite transforms to martensite under strain, so a light pass leaves a hardened skin. Ferritic SUS430 has no such transformation. A rubbing tool leaves a poor finish rather than a hardened layer that ruins the next pass. Shops find it far more forgiving.

Heat leaves the cut. Thermal conductivity is roughly 60 % higher than SUS304. More of the heat goes into the chip and less into the cutting edge, so tool life improves.

Chips behave. SUS430 is less gummy. Built up edge is less of a problem and swarf clears more predictably.

The net effect: an index of roughly 54 against SUS304’s 45, and in practice the gap on the shop floor often feels wider than that, because the forgiveness matters as much as the cycle time. A shop that does not run stainless every week will produce a better SUS430 part than a SUS304 one.

There is one trade off. Ferritic grades tend to tear rather than shear at low cutting speeds, so a fine surface finish takes more attention than on SUS304. Sharp tooling and adequate speed, not slower and heavier.

The cost case

Two savings stack:

The bar. No nickel. Nickel is the expensive and volatile part of the 300 series price, so SUS430 is consistently and substantially cheaper per kilogram, and the gap widens whenever nickel moves.
The cycle. Shorter, with longer tool life.

On a high volume machined part, both matter. On a prototype or a run of five, setup and programming dominate the piece price and the material saving is close to noise. The grade change is worth making at volume and rarely worth arguing about below that.

The three things that rule it out

1. Chlorides, salt, or anything continuously wet. SUS430 has no molybdenum and less chromium than SUS304. Its pitting resistance equivalent is around 17 against SUS304’s 19 and SUS316’s 25. Outdoors, coastal, marine, food processing with brine, any of these and the answer is no.

2. Welding. Ferritic grades suffer grain growth in the heat affected zone, which leaves the weld brittle, and they are also prone to sensitisation. A welded SUS430 assembly is possible with care and the right filler, but if welding is central to the part, SUS304 or SUS304L will give you far less trouble.

3. Low temperature toughness. Ferritic stainless has a ductile to brittle transition, often somewhere near room temperature depending on section thickness. Austenitic grades do not. Anything that has to survive impact when cold should not be SUS430.

Add a softer fourth: anywhere magnetism is a problem. SUS430 is strongly magnetic. If the part sits near a sensor, in a motor assembly or inside a scanner, this rules it out on its own.

Where SUS430 is a genuinely good choice

Indoor hardware, brackets, trim and fasteners
Appliance and kitchen equipment components that stay dry
Decorative parts where a brushed finish is wanted and the environment is benign
Parts where magnetism is wanted, for example something that has to be held by a magnet or sensed as steel
High volume turned parts in a dry environment, where the cycle saving compounds
Applications where low thermal expansion matters, since SUS430 expands at roughly 60 % of SUS304’s rate

That last point is under-used. If a part has to hold a fit against a carbon steel mating component across a temperature range, SUS430’s expansion coefficient is much closer to carbon steel than SUS304’s is.

The substitution conversation

If a drawing says SUS304 and the service is plainly dry and indoor, it is worth asking whether SUS430 would do. The answer belongs to whoever owns the design, not to the shop, and the question to put to them is specific:

Is this part ever wet, ever welded, ever cold, or ever near something magnetically sensitive? If not, SUS430 saves material cost and cycle time.

Four yes or no questions. If all four are no, the substitution is usually safe. If any is yes, stay with SUS304.

Do not make the swap silently at the shop end, and do not accept a quote that has made it for you. A certificate that says 1.4016 against a drawing that says SUS304 is a rejected lot regardless of whether the part works.

What to put on the drawing

SUS430 per JIS G 4303
EN 1.4016 acceptable
Indoor dry service, not for welded assembly
Mill certificate to EN 10204 3.1

That last line about service is not normally drawing content, and it earns its place here. It tells the next engineer who revises the part why the grade was chosen, which stops SUS430 migrating onto a part that goes outside.

For the full grade mapping see the JIS to AISI equivalents table, and for the austenitic comparison see SUS303 vs SUS304 vs SUS316.

Pricing a part and unsure which grade to commit to? Get a quote with the service condition noted and we price both grades if the choice is still open. Within 24 business hours.

Questions

Is SUS430 magnetic?

Yes, strongly. It is ferritic, so it is magnetic in every condition. SUS304 is essentially non magnetic when annealed but becomes slightly magnetic after cold work or heavy machining.

Can SUS430 be hardened?

Not by heat treatment. Ferritic grades do not transform to martensite, so quenching does nothing useful. They can be work hardened to a limited degree, which is not a practical way to harden a machined part.

Does SUS430 rust?

It resists mild indoor atmospheric corrosion well. Outdoors, near salt, or in condensation it will show surface rust far sooner than SUS304. It is a cost grade, not a marine grade.

How much cheaper is it really?

The bar is meaningfully cheaper because there is no nickel in it, and the cycle time is shorter. On a high volume machined part the combined saving is real. On a one off prototype the setup dominates and the saving is small.

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