Can 304 stainless be bent?
Yes. 304 bends readily on a press brake, but it springs back more than mild steel, work hardens and needs about 50% more tonnage. Give it a generous inside radius.
304 is one of the most formable stainless grades. In the annealed condition it has 40% or more elongation and can be bent to a tight radius without cracking, deep drawn and roll formed. What changes from mild steel is the force and the springback. The tensile strength is about 50% higher, so a given bend takes roughly 1.5 times the tonnage of the same thickness in A36 or CRS, and a shop will size the bend to its brake accordingly. Springback runs about 2-4 degrees on a 90-degree bend instead of 1-2 degrees for mild steel, so the operator overbends or uses bottoming or coining.
Inside bend radius of 0.5 to 1 times the thickness is achievable in annealed sheet along the grain; across the grain, and on half-hard or cold-worked stock, use at least 1t to 1.5t. Bends parallel to the rolling direction are more likely to crack than bends across it, so nesting orientation matters for parts with tight bends. Work hardening is quick: 304 goes from about 200 MPa (30 ksi) yield annealed to well over 500 MPa (75 ksi) after heavy cold work, which is why a second forming operation on an already-formed feature is harder than the first and why flattening a bent part cracks it.
Surface protection matters more than on mild steel because scratches and galling show on a brushed or polished finish and rust does not hide them. Use polyurethane or film-covered tooling and leave the protective PVC film on for cosmetic parts. Tooling that was used on carbon steel leaves iron transfer that later shows up as rust spots; ask for stainless-dedicated or cleaned tooling and passivate afterwards if the part is for wet service.
Press Brake Forming for 304 parts: where to send them
What to specify
- Material condition: 304 or 304L annealed (ASTM A240), 2B or the cosmetic finish, and which face is outside
- Inside bend radius, at least 1t for cross-grain or cosmetic bends, 0.5t only for annealed sheet bent along the grain and accepted with orange peel
- Bend angle tolerance (±1 degree is standard, ±0.5 degree costs more) and flange length tolerance
- Grain direction relative to bends if the part has tight radii or a brushed finish
- Cosmetic requirements: no tool marks on the outside face, film left on, or a post-bend brushing to blend
- Bend reliefs and hole-to-bend distance of at least 2.5t plus the radius, so holes do not distort
- Passivation after forming if the part goes into wet or food service
Pitfalls
- Under-sizing the brake or the die opening: 304 needs about 1.5 times the tonnage of mild steel and can damage tooling meant for it
- Springback surprises when the shop programs mild-steel angles; a first-article bend check saves a scrapped lot
- Cracking on the outside of a tight bend made parallel to the rolling direction
- Tool marks and galling on cosmetic surfaces from bare steel dies
- Iron contamination from shared tooling showing up as rust after a few weeks outdoors
- Trying to re-flatten or re-bend a work-hardened feature; it cracks
Frequently asked questions
- What is the minimum bend radius for 304 stainless?
- About 0.5t along the grain for annealed sheet, 1t across the grain, and 1.5t or more for cold-worked or heavier plate. Cosmetic outside surfaces usually want 1t or more to avoid orange peel and cracking.
- Does 304 stainless spring back more than steel?
- Yes. Expect 2-4 degrees on a 90-degree air bend versus 1-2 degrees on mild steel, and more on thinner gauges and larger radii. Shops compensate by overbending, bottoming or coining.
- Does bending 304 make it magnetic?
- Slightly. Cold work transforms some austenite to martensite, so a bent flange will pick up a magnet a little while the flat sheet does not. It is normal and not a sign of the wrong grade.
