405 vs 430 Stainless Steel: Ferritic Grades Compared for Corrosion and Formability

Two Ferritic Grades, Two Different Jobs

405 and 430 are both ferritic stainless steels, both magnetic, and both free of nickel, yet they solve completely different service problems. 405 UNS S40500 is built around 11.5-14.5% chromium plus 0.10-0.30% aluminium, a combination that resists stress corrosion cracking in high-temperature water and mildly aggressive process streams. 430 UNS S43000 carries 16.0-18.0% chromium and no aluminium, which lifts general corrosion resistance and makes it the economical choice for visible, mildly exposed surfaces. Matching the grade to the environment, rather than to price alone, is what keeps fabricated equipment out of premature repair.

Chemical Composition Compared

Element	405 UNS S40500	430 UNS S43000
Chromium	11.5-14.5%	16.0-18.0%
Aluminium	0.10-0.30%	Not intentionally added
Carbon	0.08% max	0.12% max
Manganese	1.00% max	1.00% max
Silicon	1.00% max	1.00% max
Nickel	0.60% max residual	0.75% max residual
Fully ferritic	Yes	Yes

The aluminium addition in 405 is deliberate. It refines and stabilizes the ferritic structure during hot working and heat treatment, reduces the risk of cracking in the as-welded condition, and contributes to the grade's resistance to stress corrosion cracking. 430 relies on chromium alone: the higher level produces a more protective passive film in atmospheric and mildly acidic conditions, which is why it is the default ferritic for decorative and appliance work. European designations are 1.4002 for 405 and 1.4016 for 430.

Corrosion Behaviour in Real Environments

In general atmospheric and fresh-water exposure, 430 is the stronger performer simply because of its higher chromium content. It resists oxidation, staining and general corrosion in rural, urban and lightly industrial atmospheres, and holds up in mildly acidic food contact and detergent environments.

405 wins where mechanical stress and a corrosive medium act together. Its near-pure ferritic structure with aluminium is markedly more resistant to chloride and caustic stress corrosion cracking than 430, and it is used extensively for heat exchanger tube supports, baffles and internals exposed to high-temperature water. Neither grade is suitable for prolonged contact with chlorides in wet, stagnant conditions, and neither should be specified for strong acid service, where a molybdenum-bearing austenitic or duplex grade is required.

Atmospheric exposure, indoor trim, appliance panels: 430 is adequate and economical.

Hot water, steam condensate, mildly caustic streams under stress: 405 is the safer choice.

Marine or chloride-rich wet duty: specify a higher alloyed grade rather than either ferritic.

Mechanical Properties, Formability and Fabrication

Property, annealed condition	405 UNS S40500	430 UNS S43000
Tensile strength	about 415 MPa minimum	about 450 MPa minimum
Yield strength, 0.2% offset	about 205 MPa	about 205-240 MPa
Elongation in 50 mm	about 20%	about 22%
Hardening by heat treatment	Not hardenable	Not hardenable
Cold work response	Moderate	Stronger work hardening

Formability follows the same pattern. 405 bends and rolls readily in the annealed state and tolerates the tight radii needed for baffles and tube supports. 430 forms well at moderate strain but work hardens faster, so deep drawing or severe bending usually calls for an intermediate anneal. Both grades exhibit a ductile to brittle transition and lose toughness at low temperature, so sub-zero service should be reviewed carefully.

Neither grade hardens by heat treatment; strength is controlled by annealing and, where required, by controlled amounts of cold work. Annealing for 405 is carried out in the region that keeps the structure fully ferritic and avoids the embrittling sigma and 475 °C temperature ranges, followed by air cooling. 430 is annealed in similar fashion and then pickled or descaling treated to restore surface corrosion resistance.

405 is the more weld-friendly of the two: thin sections can be welded without preheat and normally need no post-weld heat treatment, which is a decisive advantage for large welded assemblies.

430 welds acceptably but grain growth in the heat affected zone reduces ductility; low heat input, matching ferritic filler or an austenitic filler are used according to the joint design.

Both grades should be cleaned after welding and forming; embedded iron, heat tint and scale become corrosion initiation sites if left in place.

Applications Where Each Grade Fits

405: steam turbine components, heat exchanger tube supports and baffles, pressure vessel internals, chemical processing equipment handling mildly corrosive streams under stress, and welded fabrications that cannot be heat treated after welding.

430: architectural trim and cladding, appliance doors and panels, kitchen and catering equipment, automotive exhaust trim, decorative fasteners, and lower-cost functional parts exposed to indoor atmospheres.

Because both alloys are nickel-free, they also offer a more stable cost base than nickel-bearing grades, which makes them attractive for high-volume fabricated products with moderate corrosion demands.

Frequently Asked Questions

Q: Which grade offers better corrosion resistance, 405 or 430?
In general atmospheric and mildly acidic environments 430 is better because of its higher chromium content. In stressed chloride or caustic media 405 performs better thanks to its aluminium-bearing ferritic structure.

Q: Can 405 or 430 be hardened by heat treatment?
No. Both are ferritic and non-hardenable by thermal treatment; only cold work raises their strength, and annealing is used to restore ductility.

Q: Is 405 easier to weld than 430?
Yes. 405 is designed for welded construction and generally requires neither preheat nor post-weld heat treatment, while 430 needs closer control of heat input to limit grain growth in the heat affected zone.

Q: Are these grades magnetic?
Both are fully ferritic and therefore magnetic in all conditions, which is a normal characteristic rather than a defect.

Q: Which grade should be used for outdoor architectural trim?
430 is the common and economical choice for inland and lightly industrial atmospheres; coastal or heavily polluted sites call for a molybdenum-bearing grade.

Q: What tensile strength can be expected?
Annealed 405 is typically specified at about 415 MPa minimum tensile strength, while annealed 430 is normally specified at about 450 MPa minimum, with elongation around 20-22% for both.