The short answer

• 430 is a ferritic stainless steel with chromium but essentially no nickel. It is magnetic, inexpensive, and suited to dry, indoor environments.
• 304 is austenitic, with roughly 18% chromium and 8% nickel. It is the general-purpose grade: food equipment, kitchenware, architectural work, chemical containers.
• 316 is austenitic like 304, but with 2–3% molybdenum. That addition is what buys resistance to chlorides — coastal atmospheres, de-icing salts, seawater splash, chlorinated water and many chemical process streams.
• 201 is austenitic too, but substitutes manganese for part of the nickel. It is cheaper than 304 and correspondingly less corrosion-resistant.

If you only remember one line: 304 fails where chloride is present; 316 is the answer to chloride. 430 is a different family altogether.

A grade number is not a quality rating

The three-digit numbers come from older AISI naming and carry no inherent ranking. They describe composition and structure, not "how good" a steel is.

A well-specified 430 sheet performs exactly as intended in the application it was designed for. A 304 sheet used in the wrong environment is a liability. The number tells you what the alloy is — the environment tells you whether it is right.

Austenitic vs ferritic: the difference that explains everything else

Stainless steel is not one material. It is a family of iron alloys with at least roughly 10.5% chromium, and the chromium content plus the other alloying elements determine the crystal structure.

Austenitic (304, 316, 201) — a face-centred cubic structure stabilised by nickel (and, in 201, by manganese and nitrogen). Austenitic steels are non-magnetic in the annealed condition, highly ductile, and easy to form and weld. They work-harden rapidly, which makes them strong in forming but harder to machine.

Ferritic (430) — a body-centred cubic structure with no nickel stabiliser. Ferritic steels are magnetic, lower in ductility, cheaper, and have better thermal conductivity with lower thermal expansion than austenitic grades.

That single structural difference predicts most of the behaviour described later in this article: magnetism, weldability, ductility, thermal behaviour and cost.

Composition compared

Typical specified limits for the same product form (cold rolled sheet and strip):

Two things stand out.

First, 316 and 304 have almost the same chromium range. The chromium is not what separates them — the molybdenum is.

Second, nickel is the cost driver. 430 contains effectively none. 201 stretches a small amount of nickel with manganese. 304 needs 8–10.5%. 316 needs 10–14% plus molybdenum. Because nickel and molybdenum are the most expensive elements in the alloy, this is also the order of price, and it is why grade substitution is such a persistent issue in the market.

Values above are typical specification limits for cold rolled sheet and strip. Exact limits vary with standard, thickness and finish — always confirm against the applicable standard and the mill test certificate for a specific order.

What composition does to corrosion resistance

Stainless steel resists corrosion through a passive chromium-oxide layer that repairs itself in the presence of oxygen. Chloride ions attack that layer locally, producing pitting and crevice corrosion — the failure mode that matters most in practice.

The industry uses a simple ranking number for this, PREN (Pitting Resistance Equivalent Number):

PREN ≈ Cr + 3.3 × Mo + 16 × N

Run the typical values through it and the picture becomes concrete:

• 430 — chromium only, no molybdenum: the lowest resistance of the four
• 304 — high chromium, no molybdenum: good general resistance, weak against chlorides
• 316 — same chromium range as 304, but molybdenum lifts it well clear of 304
• 201 — chromium comparable to 304, but a less stable passive layer in aggressive conditions

This is why the practical rule works: chloride decides between 304 and 316. Fresh water, most foods, mild atmospheres and indoor service sit comfortably with 304. Coastal air, road salt, swimming pool atmospheres, brine, and chloride-bearing process chemicals call for 316.

Note that PREN is a comparative ranking, not a pass/fail test. Temperature, concentration, oxygen availability and surface condition all shift the outcome.

Mechanical properties at a glance

The counter-intuitive row is the first one. 201 shows the highest yield strength and 430 the lowest ductility — but this does not make 201 "stronger" in a useful sense. Higher yield in 201 comes largely from its manganese and nitrogen content and its rapid work-hardening; it also means more springback and more tooling load during forming.

For deep drawing and severe forming, the austenitic grades' 40% elongation is the number that matters. 430's 22% tells you it will not tolerate the same forming severity, which is why 430 is usually specified for flat or lightly formed parts — appliance trim, decorative panels, utensil bodies.

Both 304 and 316 have good strength retention at elevated temperature, with 316 holding up better because molybdenum improves high-temperature creep behaviour.

The magnetism question

"Is 304 stainless steel magnetic?" is one of the most common questions — and the answer is genuinely counter-intuitive.

Annealed 304 and 316 are non-magnetic. Cold-worked 304 can be noticeably magnetic. When austenitic steel is bent, drawn, rolled or spun, part of the austenite transforms into martensite, which is magnetic. A deep-drawn sink or a heavily deformed fastener may attract a magnet while still being perfectly correct 304.

430 is magnetic regardless, because its ferritic structure is magnetic by nature.

This matters commercially, because a magnet is often (wrongly) used as a scrap-yard test for grade. A magnet cannot distinguish good 304 from bad 304, and it will flag correctly-manufactured cold-worked parts as suspect.

Heat, welding and the "L" grades

Sensitisation. Hold 304 or 316 in roughly the 450–850 °C range — during welding, for example — and chromium carbides can precipitate at the grain boundaries. The chromium is then locally depleted, and the steel becomes vulnerable to intergranular corrosion.

The countermeasure is the low-carbon variants:

• 304L — carbon limited to 0.030% max
• 316L — carbon limited to 0.030% max

Lower carbon leaves too little carbon to form the carbides, so the chromium stays in solution. On welded assemblies that cannot be annealed afterwards, 304L or 316L is the normal specification. Where welding is light and post-weld annealing is possible, standard 304 or 316 remains perfectly serviceable and slightly stronger.

Welding 430 is a different problem. Ferritic grades are prone to grain growth in the heat-affected zone, which reduces toughness. 430 can be welded, but the process is normally restricted to thinner gauges with controlled heat input — not the general-purpose fabrication duty that 304 and 316 handle routinely.

Surface finishes on coil and sheet

Because the finish controls both appearance and corrosion performance, it is worth knowing the standard designations used on stainless coil and sheet:

Roughness matters beyond appearance: a rougher surface traps deposits and moisture, which is where pitting starts. Smoother finishes are generally more corrosion-resistant in the same grade — which is why 2B is often specified for process equipment rather than a decorative finish.

Where each grade belongs

430 Appliance trim and panels, washing machine drums, automotive trim, kitchenware bodies, indoor decorative sheet, dry indoor environments. Avoid coastal, chlorinated or wet service.

304 Kitchen and food processing equipment, sinks, cookware, architectural sheet and handrail, chemical and dairy containers, brewery equipment, general fabrication. The right answer for most indoor and fresh-water applications.

316 / 316L Marine and coastal architecture, de-icing and road-salt exposure, swimming pool and spa environments, pharmaceutical and medical equipment, pulp and paper processing, food plants using chloride-based cleaning agents, welded process pipework.

201 Decorative indoor sheet, low-cost kitchenware, furniture trim — where the environment is mild and cost pressure is high. Substituting 201 for 304 in a wet or coastal application is one of the most common and most expensive specification errors in the market.

The takeaway

Grade selection is an environment question, not a prestige question. Identify the chloride exposure, the forming severity, whether the part will be welded, and what finish the surface needs — then the grade almost selects itself.

If you are working with stainless steel coil or sheet and want the composition and mechanical data for a specific grade, finish and thickness, send us the requirement and we will come back with the specification and the mill test certificate format for that order.