JIS SUS430 Steel: AISI 430 Equivalent — Ferritic Stainless, No Nickel, Magnetic

SUS430 (JIS G4303) is Japan’s most widely used ferritic stainless steel — 16–18% Cr with no intentional nickel addition. Magnetic, non-hardenable by heat treatment, and approximately 30% cheaper than SUS304, it covers indoor architectural components, kitchen appliances, automotive trim, and exhaust systems where the austenitic grades are over-specified. The trade-off is lower corrosion resistance, poor low-temperature toughness, and limited formability compared to SUS304. This guide defines exactly where that trade-off is acceptable — and the two environments where choosing SUS430 over SUS304 leads to rapid failure.

1. International Equivalent Grades

2. Chemical Composition

Source: JIS G4303:2012, ASTM A240/A240M-22, EN 10088-1:2014. The absence of Ni and Mo is the defining feature — and the reason for both lower cost and lower corrosion resistance versus the 300-series austenitic grades.

3. Mechanical Properties

All values for annealed condition. SUS430 cannot be strengthened by heat treatment — only cold work raises hardness, and it cannot be hardened like martensitic grades.

4. Physical Properties

SUS430’s thermal expansion coefficient (~10.4 μm/m·K) is much closer to carbon steel (~11–12) than SUS304’s (~17.2). This is an advantage in dissimilar-metal assemblies and reduces thermal distortion in heated components like exhaust systems.

5. Corrosion Resistance vs SUS304

SUS430 forms a chromium oxide passive film like all stainless steels, but the absence of nickel and molybdenum makes it less stable. The PREN is approximately 16–18 versus ~20 for SUS304 and ~25 for SUS316.

6. Formability & Weldability

Formability

SUS430’s elongation is 22% versus 40% for SUS304. Deep drawing and severe forming operations that are routine with SUS304 can crack SUS430. For sheet metal work requiring significant deformation — deep-drawn sinks, complex housings — SUS304 or the more formable SUS430LX (with Ti/Nb stabilizers) is required.

Weldability

SUS430 welds are more complex than SUS304. The ferritic grain structure grows significantly in the heat-affected zone, causing embrittlement — particularly in sections above 3 mm. Post-weld annealing (750–850°C, air cool) partially restores toughness but cannot fully recover pre-weld ductility. For structural welded fabrication, SUS304 is more reliable. SUS430 welding is acceptable for thin sheet (exhaust components, appliance panels) where the weld zone is not subject to impact loading.

7. Common Mistakes

8. When to Choose SUS430

9. FAQ

Q: Is SUS430 magnetic?

Yes. SUS430 is ferritic and strongly ferromagnetic in all conditions — annealed, cold-worked, or welded. This is why it is used for induction cooktop surfaces and wherever magnetic attachment is needed. SUS304 is non-magnetic when annealed (though cold working induces slight magnetism).

Q: Can SUS430 be hardened?

No — SUS430 cannot be hardened by heat treatment. It is a ferritic grade with insufficient carbon for martensite formation. Cold work increases hardness slightly (up to ~200HBW) but not to the levels achievable with martensitic grades (SUS410, SUS420J2). For hardenable stainless, specify martensitic grades.

Q: Why is SUS430 cheaper than SUS304?

SUS430 contains no nickel (Ni content ≤ 1% residual vs 8–10% in SUS304). Nickel is the most expensive major alloying element in stainless steel, typically contributing 40–60% of the raw material premium over carbon steel. Removing Ni reduces cost significantly while retaining the chromium content needed for basic stainless performance.

Q: Is SUS430 food-safe?

Yes — SUS430 meets food-contact standards (FDA, EU regulation 10/2011) for dry and low-moisture food contact. However, for food processing equipment that uses chloride-based cleaning agents (hypochlorite sanitizers), SUS316 is recommended. SUS430 stains in chloride environments and is difficult to clean to food-grade surface finish requirements once staining occurs.