Stainless Steel 304 Hex Bar is specified for machined parts, fasteners, fittings, and general engineering work where corrosion resistance and consistent mechanical performance are required. The grade is identified as UNS S30400 and EN 1.4301, with applicable ASTM and ASME specifications defining chemical, mechanical, dimensional, and testing requirements. Material selection should also consider the required condition and size.
What Is a Stainless Steel 304 Hex Bar?
A hex bar carries six flat sides around a central axis, giving a hexagonal cross-section instead of a round profile. Grade 304 is an austenitic stainless steel, and the flat faces let a wrench or collet grip the bar without slipping. Suppliers list stainless steel 304 hex bars within their standard hex bar range alongside round and square sections. The grade resists corrosion in most atmospheric conditions and welds with standard austenitic filler wire.
Key Properties of Stainless Steel 304 Hex Bar
The properties below decide how a 304 hex bar performs on a machine shop floor.
- Corrosion resistance – Chromium forms a passive layer that resists rust in air, water, and mild chemicals.
- Strength – Cold-drawn 304 can have higher strength than annealed material.
- Ductility – A minimum elongation of 40 percent lets the bar bend without cracking.
- Formability – The bar cold forms into brackets and fittings without a separate annealing step.
- Weldability – Standard TIG or MIG welding with 308 filler joins the bar without special preheat.
- Machinability – Flat faces grip cleanly in a collet, and the bar machines well with coolant.
- Temperature performance – 304 holds useful strength to around 870°C and resists scaling.
Stainless Steel 304 Hex Bar Chemical Composition
Chemical limits for the 304 hex bar follow ASTM A276, and results vary within these ranges by heat.
| Element | Typical Range / Max (%) |
|---|---|
| Chromium (Cr) | 18.0 – 20.0 |
| Nickel (Ni) | 8.0 – 10.5 |
| Carbon (C) | ≤ 0.08 |
| Manganese (Mn) | ≤ 2.00 |
| Silicon (Si) | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulphur (S) | ≤ 0.030 |
| Nitrogen (N) | ≤ 0.10 |
| Iron (Fe) | Balance |
| Molybdenum (Mo) | Not added |
Chromium and nickel set the corrosion resistance and structure, while low carbon limits carbide formation at welds.
Mechanical Properties of SS 304 Hex Bar
These values apply to the bar in the annealed condition per ASTM A276 and ASME SA479.
| Property | Typical Value (Annealed) | Spec Reference |
|---|---|---|
| Tensile strength | ≥ 515 MPa (≥ 75,000 psi) | ASTM A276 / A479, Type 304 |
| Yield strength (0.2% offset) | ≥ 205 MPa (≥ 30,000 psi) | ASTM A276 / A479 |
| Elongation | ≥ 40% in 50 mm (2 in.) | ASTM A276 / A479 |
| Hardness | ≤ 201 HB (≤ 92 HRB) | ASTM A276 / A479 |
304 Stainless Steel Hex Bar Sizes and Dimensions
Size selection starts with the across-flats measurement, which determines fit with collets and sockets.
- Across-flats dimension – The distance between two parallel flat faces is used when ordering a hex bar.
- Length – Standard mill lengths span 3 to 6 metres, with shorter cuts on request.
- Standard and custom sizes – Common across-flats range from 6 mm to 50 mm, with larger sections cut to order.
- Dimensional tolerances – ASTM A484 sets the tolerance class, and cold-drawn stock holds a tighter tolerance than a hot-finished bar.
Types and Finishes of 304 Hex Bars
A few processing and finishing options exist, and the choice affects surface and cost.
- Cold-drawn hex bars – Cold drawing tightens tolerances and raises strength, the common choice for precision stock.
- Hot-finished hex bars – A hot-finished bar carries a rougher surface and looser tolerance and is used for larger sections.
- Polished / machined finishes – A machined or polished surface removes mill scale from parts left visible in assembly.
- Bright bar finish – Bright finish pairs cold drawing with a bright anneal, suited to food and pharma equipment.
How Are Stainless Steel 304 Hex Bars Manufactured?
Hex bar production moves through seven stages from raw billet to certified bar.
- Billet / raw material preparation – Mills start from cast billet with chemistry checked against the 304 spec.
- Hot working – The billet is hot-rolled or forged into the hex profile above 1000°C.
- Cold drawing where applicable – Cold drawing pulls the hot-worked bar through a hex die to tighten size and raise strength.
- Straightening – Roller or press straightening removes bow left from hot working or drawing.
- Cutting – Bar is cut to stock or custom length on cold saws.
- Surface finishing – Pickling, polishing, or bright annealing sets the final surface texture.
- Inspection – Each lot is checked for chemistry, dimensions, and properties before certification.
What Are the Applications of Stainless Steel 304 Hex Bar?
304 hex bar is used across eight industries where corrosion resistance and machinability both matter.
- Fasteners – Hex bars become bolts, nuts, and studs, where the flats serve as the wrenching surface.
- Machined components – Shops turn the bar into bushings, spacers, and fittings without a separate forming step.
- Valves and fittings – Small valve bodies and fitting components draw on a hex bar for the flat gripping sections.
- Shafts and hardware – Short shafts, pins, and hardware use the bar where a round profile is not needed.
- Food-processing equipment – Fittings and fasteners in food plants use 304 hex bars for washdown resistance.
- Chemical equipment – Hex bar forms fittings in chemical plants handling mild, non-chloride fluids.
- Architectural components – Railings and brackets use the bar where flat faces suit bolted connections.
- General engineering – Workshops keep 304 hex bars on hand for one-off fittings and repair parts.
304 Hex Bar vs 316 Hex Bar
Both grades share a close mechanical profile, but molybdenum sets them apart in aggressive service.
| Parameter | 304 Hex Bar (UNS S30400) | 316 Hex Bar (UNS S31600) |
|---|---|---|
| Molybdenum | None | 2 – 3% |
| Corrosion resistance | Good in mild, indoor, and freshwater conditions | Better in chloride-rich and marine environments |
| Chloride tolerance | Up to about 200 ppm at ambient temperature | Up to about 1,000 ppm |
| Typical use | Indoor, architectural, and freshwater service | Marine, coastal, and chemical process service |
How to Choose the Right 304 Hex Bar
A few factors decide whether a 304 hex bar fits a job, worth checking before ordering.
- Required size – Confirm the across-flats dimension and length, since custom cuts add lead time.
- Application – Match the bar to its use, whether a fastener, a machined part, or hardware.
- Mechanical load – Check the load against annealed yield strength and specify cold-drawn stock for higher strength.
- Corrosion environment – Review chloride exposure, since 304 is not suited to saltwater or high-chloride fluids.
- Machining requirements – Confirm whether the job needs a cold-drawn bar for tolerance or a hot-finished bar for rough machining.
- Finish – Pick a bright or polished finish for visible parts and a mill finish for coated parts.
- Applicable ASTM / ASME / EN standard – Specify ASTM A276, ASME SA479, or EN 10088 depending on the project and documentation needs.
- Material certification – Request a mill test certificate with heat number, chemistry, and mechanical results before the order ships.
