430 stainless for sheet metal: grade and formability

430 stainless formability is decided by one structural fact: the grade is ferritic, body-centred cubic, and contains no nickel. That makes it cheap, magnetic and dimensionally stable, and it also makes it the least forgiving common stainless sheet in a press or on a brake. A designer who treats 430 as a cheaper 304 will get cracking at the bend line, orange peel on the drawn face, and a part that fails at the weld.

The numbers set the gap. ASTM A240 puts S43000 at 205 MPa minimum yield, 450 MPa minimum tensile and 22% elongation in 50 mm. The equivalent figures for 316L are 170 MPa, 485 MPa and 40%. So 430 is stronger in yield, weaker in ultimate, and has roughly half the stretch before it tears.

That combination is exactly right for a flat panel that gets folded twice and powder coated, and exactly wrong for a deep housing that gets drawn, trimmed and welded. The rest of this guide is the line between those two cases.

Which 430 grade is actually on the quotation?

The base grade is 430 to ASTM A240, UNS S43000, or EN 1.4016. It is 16–18% chromium, up to 0.12% carbon, no nickel and no molybdenum, and it is the sheet behind most brushed appliance fronts, shelf panels and indoor enclosure doors.

Four relatives appear on drawings often enough to name:

The PREN arithmetic shows why the molybdenum variants exist. At 17% chromium with no molybdenum, 430 sits near 17. Adding 1% molybdenum lifts it to about 20, and 2% lifts it to about 24, which is close to 316L at 25. That is the whole point of 434 and 444: they keep the ferritic advantages and buy back the chloride resistance with molybdenum instead of nickel.

430F is a trap on a formed part. The sulphur that makes it machine freely forms manganese sulphide stringers, and those stringers are crack initiation sites in a bend. If a drawing says 430F and the part is bent, the drawing is wrong.

430 stainless formability: bend radius, rolling direction and springback

430 bends to about 0.5 times the thickness when the bend line runs across the rolling direction, and about 1.0 times the thickness when it runs along it. For 1.2 mm sheet that is 0.6 mm and 1.2 mm, and the tighter number is only realistic on a deburred blank with a polished die shoulder.

The direction matters because a ferritic sheet has a strongly directional grain structure and inclusions aligned with rolling. A bend line parallel to the rolling direction puts the outer fibre in tension across those stringers, and the crack starts at the sheet edge where the burr already provides a notch. The practical rule is to lay the bend line across the rolling direction wherever the blank allows it, and to state the rolling direction on the blank drawing so the nest does not rotate the part for yield.

Springback runs higher than on an austenitic grade. The elastic component of springback scales with yield strength divided by modulus, and 430 at roughly 205–240 MPa against 200 GPa gives a ratio about 16% higher than 316L at 170–200 MPa against 193 GPa. On a 90° bend at R/t of 1 that is a fraction of a degree in theory and around 1–2° in a real air bend, which is why the brake programme carries a per-part correction rather than a single global angle.

The bend allowance changes with the K-factor, and the K-factor for 430 sits lower than for an austenitic grade because the neutral axis does not shift as far outward when the section yields. A working value is K 0.42 for 430 against 0.48 for 316L at the same R/t.

Work that through a 90° bend on 1.2 mm sheet at a 1.2 mm inside radius:

• 430 at K 0.42: allowance = (π/2) × (1.2 + 0.42 × 1.2) = 1.5708 × 1.704 = 2.68 mm.
• 316L at K 0.48: allowance = (π/2) × (1.2 + 0.48 × 1.2) = 1.5708 × 1.776 = 2.79 mm.

The 0.11 mm difference per bend is small on one corner and decisive on a box with four bends, because it accumulates into the flange positions. Use the grade-specific K-factor in the flat pattern rather than the value that happened to work on the last stainless job; the bend allowance method sets out the calculation, and the minimum bend radius table compares 430 with the rest of the sheet family.

Thickness range: what 430 will and will not do

The working range for 430 sheet is about 0.4 mm to 1.5 mm. Thin gauge is where the grade earns its place: a 0.8 mm appliance panel is stiff enough, flat enough and cheap enough, and the powder coat covers the surface without the flatness problems that a thinner CRCA panel shows after coating.

Flatness is the constraint that surprises people. A 430 sheet at 0.5 mm has a modulus of 200 GPa, so it is only about 5% less stiff than CRCA at the same thickness, but its yield strength is higher and its residual rolling stress is different. A panel that is flat on the pallet can show a 2–3 mm bow after laser cutting releases the stress, and the bow shows up as a shadow line under a gloss powder coat.

Above 1.5 mm, three things get worse at once: the grade is less available in flat cut-to-length sheet, the bend radius limit becomes an absolute number that is harder to design around, and the blank weight makes manual handling and nesting less efficient. A 2.5 mm part that needs corrosion resistance is usually better in 304 or in coated CRCA than in 430.

Weight is worth calculating before the handling plan. At 7.7 g/cm³, a square metre of 1.2 mm 430 weighs 9.24 kg. The same area in 1.2 mm CRCA weighs 9.42 kg and in 316L 9.60 kg, so the stainless grades are not meaningfully lighter. The reason to choose 430 is corrosion and appearance at a lower alloy cost, not mass.

Weldability: why 430 rarely ships as a welded assembly

430 is weldable in the sense that an arc will fuse it. It is not a welded assembly grade, and the reason is metallurgical rather than procedural.

The carbon content runs up to 0.12%, which is high for a stainless, and the chromium carbides that form at the grain boundaries in the heat-affected zone leave a chromium-depleted band next to the weld. That band corrodes first. The same heat cycle coarsens the ferrite grains, and the coarse grain structure has low toughness, so a restrained joint can crack as it cools.

Three consequences follow for a drawing:

1. Use a stabilised grade if the part is welded. 430Ti or 439 adds titanium or niobium, which ties up the carbon as a stable carbide and leaves the chromium in solution. 444 does the same with molybdenum added for chloride resistance.
2. Keep heat input low and preheat only where the section demands it. A 1.2 mm lap joint needs a fast, small weld, not a slow one; a 3 mm tee may need 150–200 °C preheat to avoid a hard, crack-prone zone.
3. Do not plan a post-weld anneal unless you have a furnace with atmosphere control. A 780–830 °C anneal would restore ductility, but it also scales the surface and distorts a thin panel, and we do not run that treatment in-house.

A 309L filler helps with dilution and is the common choice for joining 430 to carbon steel, but it does not fix a 430-to-430 joint that the design should not have asked for. If a part needs to be welded, formed and coated, 304 is the grade that does all three without a caveat.

Thermal and magnetic behaviour that decides the part

430 expands at about 10.4 × 10⁻⁶ per kelvin against 16.0 for 316L and 17.3 for 304. Over a 1,000 mm panel and a 150 K temperature rise, that is 1.56 mm of growth against 2.40 mm for 316L, a difference of 0.84 mm. On a single part that is irrelevant; on a stainless frame with mixed grades it changes the fit at every joint, and it is the reason a 430 panel bolted to a 304 frame should have slotted holes.

Thermal conductivity is the other direction. 430 conducts at about 26 W/m·K against 16 for 316L and 50 for carbon steel. That makes 430 cut and weld faster than 316L but still slower than CRCA, and it makes a 430 panel less prone to local hot spots under a weld than an austenitic grade.

Two limits matter for service temperature:

• 475 °C embrittlement. Prolonged exposure between about 400 °C and 550 °C makes the ferrite brittle at room temperature. A 430 exhaust shroud or oven panel that runs in that band is a wrong application.
• Low-temperature toughness. The ductile-to-brittle transition for 430 sits near room temperature, so impact toughness at 0 °C and below is poor. It is not a cold-climate structural grade.

Magnetism is absolute. 430 is ferromagnetic in the annealed, formed and welded condition, because the body-centred cubic lattice stays magnetic at room temperature. That is an advantage for a sensor target or a magnetic clamp and a disqualification for a part that must not disturb a field.

How Ganesh runs 430 sheet

430 cuts on the 12 kW fibre laser with the 40 ft × 16 ft bed, up to 20 mm, and the grade takes a nitrogen assist cleanly because there is no nickel to stabilise a heavy oxide on the cut face. Bending runs on the 200 T, 5-axis brake with the 4,450 mm bed and Delem control, which holds the part number, the angle correction and the bend sequence, so a repeat release does not inherit the springback of a different grade. Press work from 20 T to 300 T covers the shallow forms and the pierced features that a 430 panel usually needs.

Deburring matters more on 430 than on CRCA because the burr on a ferritic edge is harder and the bend starts there. The bending capability page sets out the bed and thickness envelope, and the custom parts range covers the 0.8–40 mm window across stainless, CRCA, aluminium, brass and copper.

The plant holds ISO 9001:2015 and ISO 14001:2015, and the seven-tank pretreatment and powder line are on the same site, which is what makes a coated 430 panel practical rather than a two-supplier exercise.

What to put on the 430 drawing

1. Grade and standard: 430 to ASTM A240 or IS 6911, with the mill certificate and the heat number on the first lot.
2. Thickness with a tolerance, and the flatness limit after cutting rather than at the mill.
3. Rolling direction on the blank, with the bend lines drawn across it.
4. Inside bend radius and bend direction for each corner, not a single note.
5. Surface finish: 2B, BA or No. 4, and the Ra if the face is visible.
6. Weld or no weld, because that one line decides whether 430 is available or whether the part moves to 439.
7. Magnetic requirement, stated either way, because a sensor or a reed switch will not forgive an assumption.

Send the blank layout with the rolling direction marked to request a quotation. We review the bend lines and the draw ratio before the tool is cut, which is cheaper than reviewing them after the first thousand parts.

When 430 is the wrong grade

430 is wrong for any welded structural part, for chloride service outdoors, for a draw deeper than about 1.8 times the blank-to-cup ratio in one pass, and for service between 400 °C and 550 °C. It is also wrong where the part must be non-magnetic.

The 430 corrosion and finish guide covers the environmental limits in detail, and the case against 430 sets out the failure modes and the substitution route. The materials and grades hub holds both alongside the rest of the grade set.