304 Stainless Steel Sheet Fabrication
304 is the stainless sheet that most fabricated parts are made from, and it holds that position by being good at everything without being best at anything. It bends tightly, it welds easily, it resists corrosion in fresh water, food service and most mild chemicals, and it is available everywhere in every finish. Where a part needs spring, 301 is the grade; where it needs chloride resistance, 316 is; where it needs to be cheap and weldable and formed, 304 is the default — and it is the right default far more often than not.
Specification at a glance
- Material family
- Austenitic stainless steel, non-hardenable, low carbon option available
- Composition
- ~18–20% chromium, ~8–10.5% nickel; carbon ≤0.08% (304) or ≤0.03% (304L)
- Tensile
- Roughly 505–515 MPa annealed; yield around 205 MPa
- Formability
- Excellent — tight bends, deep draws, complex formed shapes
- Typical minimum bend radius
- Roughly 0.5–1× thickness annealed
- Work hardening
- Moderate — bends gain strength, and springback is a real forming consideration
- Corrosion resistance
- Good in fresh water, food service and most mild chemicals; not a chloride grade
- Weldability
- Excellent — specify 304L for welded parts
- Magnetic
- Essentially non-magnetic annealed; slightly magnetic after cold forming
- Mill finishes
- 2B, BA, No. 4 brushed and others, with passivated or electropolished finishes applied after fabrication
- Typical thickness
- Evaluated per drawing
- Fabrication route
- Cut, bent, formed and welded as one job on our own floor; specialist operations through our vetted partner network
- Finishing
- Deburring, passivation, electropolishing, brushing, polishing to drawing
- MOQ
- From 50 pieces, samples from 1 piece
- Lead time
- Samples 5–10 days; production 25–35 days after sample approval
The safe choice, and why it usually is
304 sheet is specified more often than any other stainless because it fails at nothing. The property set is unremarkable in each individual respect and excellent in combination.
| Property | 304 sheet | What it means for a fabricated part |
|---|---|---|
| Formability | Excellent | Tight bends, deep draws, complex shapes |
| Weldability | Excellent | Assemblies are straightforward |
| Corrosion | Good — fresh water, food, mild chemicals | Adequate for most fabricated equipment |
| Availability | Universal | Every finish, thickness and form, everywhere |
| Work hardening | Moderate | Bends gain strength, springback is real |
| Chloride resistance | Poor | The one limit that matters most often |
The one row that catches people out is the last. 304 is not a chloride grade, and chloride exposure in fabricated equipment is common — coastal installations, de-icing salt, bleach-based sanitisers, and process fluids that contain chlorides. Where that applies, the grade is 316 or 316L.
Forming 304: good, with springback
304 forms very well in the annealed condition, with minimum bend radii of roughly 0.5 to 1 times the material thickness. That is among the tighter radii of the common fabrication metals, and it is a large part of why 304 dominates formed stainless work.
The one forming consideration that is specific to the austenitic grades is springback. Every metal springs back when the bending force is released, but 304 work-hardens as it is formed — so the material in the bend is stronger and springier when the operation finishes than when it started. That makes the springback larger and less predictable than on a mild steel.
The practical answers:
- Overbend by a calculated amount, rather than expecting the part to come off the tool at the intended angle
- Consider bottoming or coining rather than air bending where the angle matters
- Agree the bend allowance in DFM, so the flat pattern accounts for both the bend radius and the springback before the blank is cut
The same work-hardening is why a formed 304 part is stronger at its bends than in its flat panels — and why a bend that is going to be reworked should be considered carefully, since re-bending already-hardened material can crack it.
Welding: the 304L rule
304 welds very readily, and a welded fabrication should still be specified as 304L.
Welding heats a band of metal beside the joint into the range where chromium combines with carbon to form chromium carbides at the grain boundaries. Those carbides pull chromium out of the surrounding metal, and chromium is what forms the passive film — so a narrow band beside the weld ends up less protected than the rest of the part and corrodes first. That is sensitisation.
304L holds carbon below about 0.03%, low enough that the carbides cannot form. That is why the L grade is specified whenever a part is welded and then returned to service without a post-weld solution anneal — which, on a fabricated sheet assembly, is essentially always.
A great deal of 304 sheet is dual-certified 304/304L, meaning the same heat satisfies both specifications. Where that is the case, the question settles itself and no trade has to be weighed.
Finishing a fabricated 304 assembly
Passivation is the standard step. It removes free iron smeared into the surface by cutting, forming and welding, and restores the chromium oxide film.
On a welded assembly the sequence matters: heat tint must be removed before passivation, not after. Heat tint is not a cosmetic discolouration — it is a chromium-depleted oxide layer sitting exactly where the sensitisation risk already is. Mechanical cleaning, pickling or electropolishing all serve; the order is clean first, passivate second.
Beyond passivation, the common routes:
- Electropolishing — smoother, brighter surface for hygienic and low-contamination service
- Polishing and brushing — directional or reflective finishes for visible parts
- A chemical conversion coating or paint where a specific colour or additional protection is wanted
The mill finish — 2B, BA, No. 4 brushed — is the starting point, and it is worth specifying, because the finish a part starts from affects how much work the final finishing operation takes.
Formed-feature rules
Because 304 forms well, the geometric rules around a bend are moderate — but they still apply, and they are where formed stainless parts most often fail inspection.
Holes and slots must clear the bend. A hole inside the bend zone distorts as the material stretches around the radius, and it comes out oval or torn. The working rule is to keep a hole at least a distance of roughly two-and-a-half times the material thickness plus the bend radius away from the bend line — measured from the edge of the hole, not its centre. 304 tolerates less clearance than a mild steel would, because it work-hardens as it forms and the stretch is less evenly distributed.
Flanges have a minimum length. A flange shorter than roughly four times the material thickness cannot be formed reliably, because the press brake tooling has nothing to grip and the bend does not develop properly. Where a design calls for a very short return flange, the answer is usually to redesign it rather than to specify a tighter tool.
Bend relief prevents tearing. Where a bend runs into a corner or up to an edge, a small relief notch at the end of the bend line stops the material tearing as it is stretched. On 304 the relief is standard practice rather than optional, because the hardened material in the bend has limited stretch left.
Grain direction affects the achievable radius slightly. A bend made with the rolling grain has less ductility to spend than one made across it, so where a part has a tight radius the orientation of the flat pattern is worth agreeing.
Plan for springback rather than correcting it. The overbend, the bend allowance and the angle tolerance are set in the flat pattern before the blank is cut. Correcting an angle after the part is formed means re-bending already-hardened material, which risks cracking it.
Where 304 sheet is the right choice
- Food and beverage equipment and kitchen fabrications
- Equipment enclosures, covers and machine guards
- Tanks, vessels, hoppers and ducting in benign service
- Architectural, trim and visible fabricated parts
- Brackets, mounting panels and general fabricated assemblies
- Welded assemblies of any kind in fresh water, food or mild chemical service
- Any fabricated part where no single requirement is extreme — which is most of them
Where 304 sheet is the wrong choice
The part sees chlorides. Salt water, coastal air, bleach, de-icing salt and chloride process fluids pit 304. 316 or 316L is the grade.
The part’s function is to store energy or hold tension. 304 does not work-harden enough to make a spring. 301 is the grade.
The part has to be hardened. Austenitic stainless cannot be hardened by heat treatment. Where hardness or wear resistance is required, a martensitic or precipitation-hardening grade is the answer.
The weld will be left with heat tint and no cleaning step. A welded 304 assembly with heat tint left on it will corrode at the weld. The cleaning step is part of the specification, not an option.
Non-magnetic behaviour is a hard requirement and the part is heavily formed. Cold forming makes 304 slightly magnetic. State the requirement if it exists.
Strong chlorides or hot concentrated chemicals are in service. Those duties are beyond what 304 handles, and naming the chemical and temperature is what allows the right grade to be found.
What to put on the drawing
| Instead of | Write |
|---|---|
| Stainless sheet | 304, or 304L for a welded fabrication |
| 304, welded | Specify 304L, or check whether the stock is dual-certified |
| 304, bend radius and angle | State the angle and the tolerance — springback is larger than on mild steel |
| 304, chloride service | Wrong grade — 316 or 316L |
| 304, needs spring | Wrong grade — 301 is the forming stainless |
| 304, welded and exposed | State the finish — heat tint comes off before passivation |
| 304, hygienic service | Specify electropolishing or a defined passivated finish |
| 304, needs to stay non-magnetic | Heavy forming makes it slightly magnetic — say so if it matters |
The three lines that decide most 304 sheet parts are whether chlorides are present, whether the assembly is welded, and the bend radius and angle tolerance. The first decides whether 304 is the right grade at all. The second decides the L. The third is the forming review, and on an austenitic grade it is where springback has to be planned rather than corrected.
Send the drawing through the request a quote form and the reply comes back within 24 hours with DFM feedback — including a note on the grade, the bend radii and allowances, the weld route and the finishing sequence where any of them need settling.
Frequently asked
- What is 304 stainless steel sheet used for?
- Food and beverage equipment, kitchen and catering fabrications, equipment enclosures and covers, tanks and vessels, ducting and ventilation, architectural and trim work, brackets and mounting panels, machine guards, and general fabricated assemblies in benign or mildly corrosive service. It is the sheet grade that most fabricated stainless parts are made from.
- What bend radius does 304 sheet need?
- In the annealed condition, roughly 0.5 to 1 times the material thickness — among the tighter radii of the common fabrication metals, and one of the reasons 304 forms so well. The achievable radius depends on thickness, the bend direction relative to the sheet's rolling grain, and the bend method, so it is agreed per drawing in DFM. Bending across the grain is generally more forgiving than bending with it.
- What is springback, and why does it matter on 304?
- Springback is the amount a formed part springs back toward its original shape once the bending force is removed. Every metal does it, but 304 work-hardens as it is formed, so the material in the bend is stronger and springier than it was when the operation started — which makes the springback larger and harder to predict than on a mild steel. The practical answers are to overbend by a calculated amount, to use a bottoming or coining operation rather than air bending, and to agree the bend allowance in DFM so the flat pattern accounts for it.
- Should I specify 304 or 304L for a welded fabrication?
- 304L, if the assembly is welded and then put into service without a post-weld solution anneal. Welding heats a band of metal beside the joint into the range where chromium combines with carbon to form carbides at the grain boundaries, and those carbides pull chromium out of the surrounding metal — leaving a narrow band that corrodes first. The low-carbon L grade holds carbon low enough that the carbides cannot form. A great deal of 304 sheet is dual-certified 304/304L, in which case the question settles itself.
- Does 304 resist chlorides?
- No — and this is the limit that most often catches people out. 304 handles fresh water, food contact, indoor atmospheres and most mild chemicals well, but salt water, coastal air, bleach, de-icing salt and chloride process fluids will pit it. Where the part sees chlorides, the grade is [316 or 316L](/materials/stainless-steel-316-sheet-metal-fabrication/), which carries molybdenum for exactly that reason.
- Is 304 stainless sheet magnetic?
- In the annealed condition it is essentially non-magnetic. Cold forming — bending, drawing, rolling — converts some of the austenite to martensite and makes the formed part slightly magnetic, so a heavily formed 304 part can show noticeable magnetism. The effect is smaller than on [301](/materials/stainless-steel-301-sheet-metal-fabrication/), which transforms far more readily, but it is real. If non-magnetic behaviour is a requirement, state it on the drawing.
- How is fabricated 304 finished?
- Passivation is the standard step: it removes free iron smeared into the surface by cutting, forming and welding, and restores the natural chromium oxide film. On a welded assembly, heat tint must be removed before passivation rather than after, because heat tint is a chromium-depleted oxide layer sitting exactly where the corrosion risk already is. Beyond passivation, the common finishes are electropolishing for hygienic service, and brushing or polishing for visible parts — with the mill finish (2B, BA or No. 4) as the starting point.
- Why is 304 not the best choice for a spring?
- Because it does not work-harden enough to make one. [301](/materials/stainless-steel-301-sheet-metal-fabrication/) carries less nickel and slightly more carbon, so it transforms far more of its structure to martensite when formed and develops considerably higher strength from the same bend. A 304 spring would either be too weak or too large. Where the part's function is to store energy or hold tension, 301 is the grade.
- Is 304 food safe?
- 304 is the standard stainless for food and beverage equipment, and it is widely used in that service. The relevant points are that the surface should be passivated or electropolished for hygienic work, that the material must not be left with free iron contamination from tooling, and that chloride-based cleaning agents — which are common in food plants — will attack it. Where a plant cleans with chlorinated sanitisers, 316L is the better specification, and that is a question worth settling at the enquiry rather than after the equipment is built.
Related pages
Stainless Steel 304 in other processes
Other Stainless Steel materials
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