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Ferritic Stainless Steel

Ferritic stainless steels are 11–18 % chromium (up to 27 % in 446) with little or no nickel and low carbon, so they keep the body-centred-cubic structure of iron: magnetic, not hardenable by heat treatment, and with a thermal expansion close to carbon steel rather than the 300 series. 430 yields about 300 MPa annealed with 450–600 MPa tensile — similar to 304 — but with less toughness in thick sections and far less work-hardening.

Popular ferritic stainless grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
4303105007.7FairGoodTrim, panels and brackets in dry or indoor service
4092504507.7GoodVery goodExhaust systems, heat shields, mufflers
4393104857.7FairVery goodWeldable 17 % Cr sheet; 430 replacement
4413204807.7FairExcellentHot-end exhaust and manifolds to 950 °C
4443504907.8FairGoodHot-water tanks; 316-level pitting, no SCC
4463505507.5FairPoorOxidation and sulfur gases to 1,100 °C
4343655307.7GoodGoodAutomotive trim with road-salt exposure

All 85 ferritic stainless grades

Choose ferritic stainless for

Appliance and architectural trim, exhaust systems, heat shields, brackets and enclosures, solenoid and magnetic parts, hot-water tanks (444) and furnace hardware in sulfur-bearing gas (446) — wherever a magnetic, low-nickel grade with modest corrosion resistance does the job at lower cost than 304.

Look elsewhere when

The part is welded thicker than about 3 mm or deep-drawn severely (304 or 304L), sees marine or chloride exposure beyond what 444 handles (316L or 2205), must be hardened (410 or 420), needs toughness below −20 °C or in thick plate (austenitic), or will be turned in volume (430F).

Yield strength against max service temp, Ferritic (400 series, low C) among every stainless steel grade

No materials in view have both of these properties.

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Ferritic stainless by application

Exhaust and heat shields
409 for cold-end pipes, mufflers and shields; 441 (or 439) for manifolds and converter shells that run hotter; 446 for burner and furnace hardware.
Trim, panels and enclosures
430 in 2B or bright-annealed finish for appliance fronts, kick plates and brackets; 434 outdoors on cars; 439 where the panel is welded.
Hot water and mild chlorides
444 for water heaters, heat-exchanger tubes and food equipment where 304 would stress-crack and 316 is more than the job needs.
Magnetic and structural parts
430 and 3Cr12 (1.4003) for solenoid housings, magnetic cores and utility structural sections that only need to outlast painted carbon steel.

Working with ferritic stainless

Machining
Slightly easier than 304 — less work-hardening, shorter chips, cutting speeds roughly 60–70 % of mild steel. 430 smears at low speed; 430F is the free-machining version for turned parts.
Welding
Weldable by TIG and MIG with 430 or 309L filler, but the heat-affected zone coarsens and turns brittle in unstabilized 430 above about 3 mm. Use stabilized 439, 441 or 444 for welded sheet; keep heat input low and do not hold at 400–550 °C, where 475 °C embrittlement sets in.
Forming
430 bends and draws well — the low work-hardening rate means less springback than 304 — but roping and ridging show on stretched panels, so specify ridging-controlled sheet for cosmetic drawn parts. Toughness drops sharply below room temperature in plate over about 6 mm.
Finishing
Bright-annealed and brushed finishes are the reason 430 sells; passivate (ASTM A967) after machining. Lower chromium means 409 develops a brown tint outdoors — accepted on exhausts, unacceptable on trim, where 430 or 434 is the minimum.

Other stainless steel series

Ferritic Stainless Steel — frequently asked

What is ferritic stainless?

Ferritic stainless steels are 11–18 % chromium (up to 27 % in 446) with little or no nickel and low carbon, so they keep the body-centred-cubic structure of iron: magnetic, not hardenable by heat treatment, and with a thermal expansion close to carbon steel rather than the 300 series. 430 yields about 300 MPa annealed with 450–600 MPa tensile — similar to 304 — but with less toughness in thick sections and far less work-hardening.

Which grade of ferritic stainless should I use?

430 (17 % Cr) is the general trim, panel and bracket grade wherever the environment is indoor or dry. 409 (11 % Cr, titanium-stabilized) is the exhaust and heat-shield grade — it discolours but does not perforate to about 700 °C. 439 and 441 are stabilized 17–18 % chromium grades that weld without grain growth, 441 adding niobium for hot-end exhaust to about 950 °C. 444 (18 % Cr, 2 % Mo) matches 316 for pitting and resists the chloride stress-corrosion cracking that 316 does not, for hot-water tanks and heat exchangers. 434 and 436 add molybdenum to 430 for automotive trim; 446 carries 23–27 % chromium for oxidation and sulfur-bearing atmospheres to 1,100 °C.

Which grade of ferritic stainless is the strongest?

1.4525 has the highest yield strength in the series at 620 MPa; 1.4515 follows at 540 MPa. Values are for each grade's default condition.

Which grade of ferritic stainless is easiest to machine?

1.4523 (machinability very good, 75/100), then 430FSe (66/100).

Is ferritic stainless heat-treatable?

No. These grades are strengthened by cold work and softened by annealing, not by heat treatment; the conditions are listed on each grade page.

430 or 304 for trim and enclosures?

430 has no nickel, is magnetic, forms with less springback and has almost the same strength as 304. It pits sooner in chlorides, welds only in thin sections and cannot be deep-drawn as hard. Indoors, in dry or occasionally wet service, 430 is fine; outdoors near the coast, in food processing, or when the enclosure is welded from plate, choose 304 or 316L.

Why are exhausts 409 rather than 304?

409 is the cheaper alloy, expands only about two thirds as much per degree (less distortion and fatigue at the joints), and its titanium stabilization survives welding. It is also far less prone to chloride stress-corrosion cracking from road salt. It does rust to a brown patina, which is accepted under a car; for visible tips 304 or 441 is used.