Guide
304 vs 430 stainless: when is magnetic 430 a safe substitute for 304?
430 stainless is a ferritic chromium stainless steel with no deliberate nickel addition: per ASTM A240 it carries 16.0 to 18.0% chromium and no more than 0.75% nickel, against 17.5 to 19.5% chromium and 8.0 to 10.5% nickel for austenitic 304. That missing nickel is why 430 costs less, why it is magnetic, and why it forms, welds and resists corrosion differently from 304.
By Saola Manufacturing engineering team · Published · Updated
The 304 vs 430 stainless question usually arrives from purchasing: a supplier offers 430 as a cheaper alternative, or a cost-down review asks whether the bracket, cover or trim panel really needs 304. Sometimes 430 is the better engineering answer, not just the cheaper one. Sometimes it is a quiet downgrade that shows up a year later as rust spotting on a coastal installation or a cracked weld. This guide covers what actually differs between the two grades, how to use magnetism properly (and how not to), where 430 is a sound substitute, where it is not, and how to write the drawing callout and the RFQ so the material you receive is the material you approved.
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What is the real difference in 304 vs 430 stainless?
304 is an austenitic chromium-nickel steel and 430 is a ferritic chromium steel, so they differ in crystal structure, not just in recipe. Structure decides magnetism, ductility, toughness, weldability and thermal behavior, while chromium content does most of the work on corrosion.
Nickel stabilizes the face-centered cubic austenite structure in 304 at room temperature. Without it, 430 stays body-centered cubic ferrite, the same structure as carbon steel. The British Stainless Steel Association classification note sums up the trade: the ferritics are a low-cost type with more limited corrosion resistance, toughness, formability and weldability than the austenitics, and they cannot be hardened by heat treatment.
The differences engineers notice in practice follow directly. Per ASTM A240, annealed 304 sheet must reach a minimum elongation of 40% while 430 needs only 22%, so 304 stretches much further before it splits. Per ASTM A240 both grades share a minimum yield strength of 205 MPa, while 304 carries the higher minimum tensile strength. 304 also work hardens far more as it is formed or cut, as the association’s machinability note below explains. And 430 expands less and conducts heat better, as the table shows.
| Property | 304 (UNS S30400) | 430 (UNS S43000) |
|---|---|---|
| Family / structure | Austenitic (FCC) | Ferritic (BCC) |
| Chromium | 17.5–19.5% | 16.0–18.0% |
| Nickel | 8.0–10.5% | 0.75% max |
| Carbon | 0.07% max | 0.12% max |
| Tensile strength, min | 515 MPa | 450 MPa |
| Yield strength, min | 205 MPa | 205 MPa |
| Elongation, min | 40% | 22% |
| Response to a hand magnet, annealed | Negligible | Strong |
| Density | 7.9 g/cm³ | 7.7 g/cm³ |
| Thermal conductivity at 100 °C | 15 W/m·K | 26 W/m·K |
| Thermal expansion, 0–200 °C | 16 × 10⁻⁶/K | 10.5 × 10⁻⁶/K |
| Hardenable by heat treatment | No (cold work only) | No |
Why is 430 magnetic, and can a magnet tell 304 from 430?
430 is magnetic because ferrite is ferromagnetic, and annealed 304 is not because austenite is paramagnetic. A magnet can tell the two families apart, but it cannot prove a part is 304.
The association’s note on magnetic properties of ferritic grades describes 430 as a “soft” ferromagnetic grade, one that magnetizes and demagnetizes more easily than the hardenable martensitic grades, which is why ferritic grades are used for solenoid cores where good corrosion resistance is also required. Its companion note on austenitic grades gives a relative permeability of roughly 1.003 to 1.05 for fully annealed austenitic steel, and explains that cold work and composition can raise it by forming martensite or retaining ferrite.
That second point is where incoming inspection goes wrong. A deep-drawn 304 sink, a roll-formed edge or a cold-headed 304 screw can pull a magnet noticeably, and an inspector who treats “magnetic” as “not 304” will reject good parts. The opposite failure is worse: chromium-manganese austenitic grades such as 201 are also nonmagnetic, carry far less nickel than 304 and are cheaper, so a magnet will pass them as 304. A magnet sorts ferritic from austenitic; only chemistry identifies the grade. Use the mill test report for the heat, and a handheld XRF reading for nickel and manganese when you need to verify a lot.
If the part must be nonmagnetic for function, near a sensor, a compass or an MRI room for example, say so on the drawing as a measurable requirement with a stated maximum permeability and a test method such as ASTM A342, and state the condition after forming. If the part must be magnetic, as with a knife rack, a magnetic catch or an induction cooktop base layer, 304 will not do the job and 430 is the obvious choice.
How much less corrosion resistant is 430 than 304?
Meaningfully less in wet, chloride or outdoor service, where 430 rust-spots and pits sooner than 304. In dry or mildly humid indoor service the difference rarely matters, and 430, unlike 304, is not prone to chloride stress corrosion cracking.
Pitting resistance rises with chromium, and per ASTM A240 the 16.0 to 18.0% chromium range of 430 starts below the 17.5 to 19.5% range of 304, with no molybdenum or meaningful nitrogen to help. The association’s PREN note explains the ranking formula and is explicit that it ranks grades but cannot predict whether a grade will suit a given application. In practice, the industry brochure The Ferritic Solution charts 430 below 304 for localized corrosion, places the stabilized ferritics such as 439 slightly below 304, and shows that only molybdenum-bearing ferritics such as 444 beat 304.
What that means for a part:
- Indoor, dry or wiped clean: appliance panels, range hoods, interior trim, enclosures and brackets inside equipment. 430 is normal here and performs well.
- Outdoor inland, rained on and free to drain: 430 will usually show light surface staining over time where 304 stays cleaner. Acceptable on hidden parts, often not on visible ones.
- Coastal, road salt, pool air, chlorinated cleaners: 430 is the wrong choice, and even 304 may be marginal. This is 316 territory.
- Warm chloride service under tensile stress: here the ferritic grade has a genuine advantage. The same brochure lists among the ferritic advantages that, unlike austenitics, ferritics are not prone to stress corrosion cracking.
Surface finish and crevices matter as much as grade. A rough or contaminated 430 surface rusts faster than a clean, smooth one, and any joint that traps water will find the weaker grade first.
How do 304 and 430 compare for forming, welding and machining?
304 is the better stretch-forming and welding grade, while 430 draws well, springs back less and machines more easily. Unstabilized 430 is the weak link wherever a part is welded or must stay tough.
- Forming. The ductility gap in the table is real: 304 tolerates stretch forming, tight flanges and embossing that would split 430. The ferritic brochure notes that ferritics have higher limiting drawing ratios than austenitics, so 430 is good at pure deep drawing, and that it springs back less in bending. Its known cosmetic defect is ridging, or roping: lines parallel to the rolling direction after forming, which matter on visible polished parts. Titanium-stabilized 430Ti or 439 is the usual upgrade where drawing depth or surface quality is marginal.
- Welding. 304 welds readily, with 304L used where sensitization in the heat-affected zone is a concern. Standard 430 is unstabilized, so welding can sensitize the heat-affected zone and leave it prone to intergranular corrosion, and ferritic welds can also lose toughness through grain coarsening. Stabilized grades such as 439 or 430Ti were developed for welded ferritic parts, and a user case study in the brochure reports that articles with welded seams needed a higher-chromium grade than standard 430.
- Toughness and section size. Ferritic steels lose impact toughness at low temperature and in thick sections, which is why the association’s classification note says available section sizes are restricted by toughness. Keep 430 to sheet, strip and light bar, and avoid it for impact-loaded parts in cold climates.
- Machining. 430 has much lower work hardening than 304, so it is the easier of the two to cut, although still harder to machine than mild steel; the association’s note on machinability by steel family explains both points. For heavily machined parts there is also 430F, a sulfur-bearing free-machining version bought to ASTM A582 rather than A276.
- Heat and thermal cycling. Lower expansion and higher conductivity mean 430 distorts less when heated and holds its oxide scale better under repeated heating, which is why it is common in burners, griddles and heating appliance parts.
When is 430 a sound substitute for 304, and when is it not?
430 is a sound substitute for parts that live indoors or dry, are formed rather than stretched, are not welded or are welded only lightly, and either need magnetism or do not care about it. It is not a substitute for wet, outdoor, food-acid or chloride service, for heavily welded assemblies, or for parts specified nonmagnetic.
A short screening checklist before approving the change:
- Environment. Will water, salt or cleaning chemicals sit on the surface? If yes, stay with 304 or go higher.
- Appearance. Is the part visible to the end customer? Light staining that is harmless on a hidden bracket can drive warranty claims on a front panel.
- Forming. Does the part pass its forming trial in 430 without splits or visible ridging? Run the trial on production-gauge material, not on a sample from a different mill.
- Joining. Is the part welded? If so, consider 439 or 430Ti rather than standard 430, and qualify the weld.
- Function. Does anything depend on the part being nonmagnetic, or on it being magnetic?
- Mating parts. Will a 430 part sit against 304 or 316 hardware in a wet joint? The less noble grade corrodes first in the crevice, so match grades or keep the joint dry.
- Governing standards. If a food-equipment, sanitation or customer material standard applies, check what grades it permits; approval for appliance trim does not carry over to a food zone.
On cost, the brochure’s main argument for ferritics is that they carry no expensive nickel, so their price is lower and far less exposed to nickel price swings. That saving is real, but it is a material-cost saving only. Extra finishing, a changed weld procedure or a field failure can consume it quickly, so compare the whole part cost rather than the sheet price.
How should a drawing call out 304 or 430 stainless?
Name the grade by UNS number, the product specification, the condition and the surface finish, and say whether substitution is allowed. “SS”, “stainless” or “18/0 stainless” on its own is not a material specification.
Callouts that leave nothing to interpretation look like this:
- “MATERIAL: STAINLESS STEEL UNS S43000 (TYPE 430) SHEET PER ASTM A240/A240M, ANNEALED, 2B FINISH PER ASTM A480/A480M. NO SUBSTITUTION WITHOUT WRITTEN APPROVAL.”
- “MATERIAL: STAINLESS STEEL UNS S30400 (TYPE 304) SHEET PER ASTM A240/A240M, ANNEALED, NO. 4 FINISH PER ASTM A480/A480M, GRAIN DIRECTION AS SHOWN. FERRITIC GRADES NOT ACCEPTABLE.”
- “MATERIAL: UNS S30400 OR S43000 SHEET PER ASTM A240/A240M, SUPPLIER’S OPTION, ONE GRADE PER LOT, GRADE MARKED ON PACKAGING.” Use this only when the screening checklist above passes for both.
A few details behind those notes. Sheet and strip are bought to ASTM A240 with surface finishes such as 2B, BA and No. 4 defined in ASTM A480; bar is bought to ASTM A276, and 430F bar to A582. In EN and JIS supply chains the equivalents are 1.4016 to EN 10088 and SUS430 to JIS G4305 for sheet, and 1.4301 and SUS304 for 304. If you accept those, list them on the drawing rather than leaving the choice to the supplier. If the part needs passivation, cite ASTM A967/A967M and let the finisher choose a treatment suited to a 400-series grade, because baths that suit 304 can etch ferritic and free-machining grades. Finally, ask for a mill test report with every lot; an EN 10204 3.1 certificate shows the heat chemistry, which is the document that proves the nickel is there or is not.
What should the RFQ say, and can Saola make 304 or 430 parts?
The RFQ should name the grade, specification, finish, any accepted equivalents and the service environment, and say whether 430 may be offered as an alternative. Stainless steel is not named among the materials Saola currently lists as running, so confirm scope at drawing review rather than assuming it.
Writing the environment into the RFQ (“indoor appliance panel, dry” or “outdoor coastal enclosure”) lets a supplier flag a grade mismatch before quoting, and asking for a 430 alternative as a separate line keeps the price comparison honest. The RFQ package guide lists the rest of what to send.
On our own scope, the stamping page names brass strip and 6061-T6 aluminum sheet as the materials run most often, and for steel it asks for the grade and gauge on the drawing so the partner stamping plant can confirm it can run that material before quoting; stainless is not named there. The bar materials listed on the CNC turning page are alloy and free-machining steels, aluminum and silicon bronze, without 304 or 430. The surface finishing page lists the finishes our partner plants apply, and passivation is not on it. Material certification for the grade used is available on request, as the quality page describes. If your part is stainless, send the drawing through the quote page anyway; the first review will say plainly whether the material is within scope rather than quoting work that cannot be made to print.
Frequently asked
Is 430 “real” stainless steel?
Yes. Stainlessness comes from chromium, not from nickel or from being nonmagnetic, and 430 carries enough chromium to form a passive film. It is simply a less corrosion resistant grade than 304, suited to milder service.
Is 18/0 stainless the same as 430?
Usually, in cookware and tableware marketing, “18/0” means roughly 18 parts chromium and no nickel, which describes 430. It is a trade label, not a specification, so the drawing and purchase order should still name UNS S43000 and the product standard.
My 304 parts are slightly magnetic. Were they made from the wrong grade?
Not necessarily. Cold work from drawing, bending, heading or heavy machining can turn some of the austenite in 304 into magnetic martensite, especially at edges and corners. Check the mill test report and, if in doubt, an XRF reading for nickel before rejecting the lot.
Can 430 be hardened like 410 or 420?
No. 430 is ferritic and cannot be hardened by quenching; it gains only modest strength from cold work. If a part needs a hard edge or wear surface, a martensitic grade is the family to look at, with the trade-off of lower corrosion resistance.
Will 430 cause galvanic corrosion when fastened with 304 hardware?
The two grades are close in the galvanic series, so the risk is low in dry service. In a wet chloride joint the less resistant 430 will usually be the one to stain or pit in the crevice, so match grades or keep the joint dry and sealed.
Sources
- ASTM A240/A240M-26, Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications, ASTM International, 2026
- ASTM A276/A276M-25, Standard Specification for Stainless Steel Bars and Shapes, ASTM International, 2025
- ASTM A342/A342M-26, Standard Test Methods for Permeability of Weakly Magnetic Materials, ASTM International, 2026
- ASTM A967/A967M-25, Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts, ASTM International, 2025
- The Ferritic Solution: Properties, Advantages, Applications, International Stainless Steel Forum, hosted by the British Stainless Steel Association, accessed October 2026
- Classification of stainless steels, British Stainless Steel Association, accessed October 2026
- Magnetic properties of ferritic, martensitic and duplex stainless steels, British Stainless Steel Association, accessed October 2026
- Magnetic properties of austenitic stainless steels, British Stainless Steel Association, accessed October 2026
- Calculation of pitting resistance equivalent numbers (PREN), British Stainless Steel Association, accessed October 2026
- Influence of steel family (type) on machinability, British Stainless Steel Association, accessed October 2026