Stainless Steel 304 CNC Machining Services
304 is the default austenitic stainless: 515 MPa tensile, excellent formability and hygiene, and reliable corrosion resistance in most industrial and food environments.
304, 304L and 304H bar and plate
Tolerances to ±0.05 mm on critical features
Passivation, electropolish and bead blast
What Is Stainless Steel 304?
The general-purpose stainless, when to step up to 316, and how to keep it from work hardening in the cut.
Stainless steel 304 is an austenitic chromium-nickel alloy and the most widely used stainless grade in the world. It offers 515 MPa minimum tensile strength with 40 percent elongation, resists attack from most organic chemicals and food products, and is easily cleaned, which is why it dominates food equipment, architectural hardware and general process plant.
304 or 316
In the annealed condition the two grades are mechanically almost identical; the difference is corrosion resistance. 316 adds 2 to 3 percent molybdenum, raising the pitting resistance equivalent number from about 19 to about 25. Choose 316 for chlorides, seawater, de-icing salt and acidic process streams, and 304 for dry, indoor, fresh-water or food contact service.
Machining notes at a glance
Austenitic stainless work hardens faster than carbon steel. The practical rules are to keep the tool cutting rather than rubbing, use a positive rake and a constant feed, and never dwell. With the right parameters 304 gives a good surface finish, but tool wear is higher and cycle times are longer than for free-machining grades such as 303.
Related capabilities: CNC Machining, CNC Milling, CNC Turning, 5-Axis Machining. Dimensional limits, thread rules and surface roughness grades are listed on the tolerances and specifications page, and volume-based routing is covered under production solutions.
Stainless Steel 304 Mechanical Properties
Typical values at room temperature for the condition most often machined. Use them for material screening, then confirm against the mill certificate for the exact heat and product form.
| Property | Typical value |
|---|---|
| Density | 8.00 g/cm³ |
| Ultimate tensile strength | 515 MPa (75 ksi) minimum |
| Tensile yield strength, 0.2% offset | 205 MPa (30 ksi) minimum |
| Elongation at break | 40% minimum in 50 mm |
| Elastic modulus | 193 GPa |
| Hardness | 201 HB maximum (92 HRB) |
| Thermal conductivity | 16.2 W/m·K at 100 °C |
| Electrical resistivity | 0.72 µΩ·m at 20 °C |
| Melting range | 1400 to 1450 °C |
| Magnetic response | Non-magnetic when annealed |
Typical room-temperature values compiled from public ASM, MatWeb and mill datasheets. Actual values vary with temper, section thickness and product form; request the EN 10204 3.1 certificate for critical applications.
Machining Characteristics of Stainless Steel 304
How the material behaves in the cut, and what that means for tooling, fixtures, cycle time and achievable tolerance.
Work hardening control
Maintain a constant, positive chip load and never let the tool rub. Light cuts on a hardened skin destroy tools quickly and ruin surface finish.
Heat at the cutting edge
Only 16.2 W/m·K conductivity means heat stays at the tool tip. Flood coolant or high-pressure through-tool coolant is standard for drilling and pocketing.
Tooling choice
Sharp carbide with a positive rake, tough substrate and a chip breaker designed for stainless. Replace on a schedule rather than waiting for failure.
Drilling and tapping
Use stub-length drills, peck cycles and generous coolant. Tapping 304 needs the correct tap drill percentage; a work-hardened thread is expensive to recover.
Distortion on thin parts
Austenitic stainless expands more than steel and conducts heat poorly, so thin sections need balanced roughing, low stress clamping and finishing passes.
Grade alternatives
Where tolerances are tight and volume is high, 303 machines far faster. Where weld decay is a risk after welding, 304L is the safer call.
Design and Machining Checklist
Practical rules that reduce cost and scrap on Stainless Steel 304 parts. Share them with your design team before the drawing is frozen.
- Specify 304L if the part will be welded and cannot be annealed afterwards, to avoid sensitisation at the heat-affected zone.
- Never specify a dwell or a zero-feed move in a cycle; the surface hardens instantly and the next pass cuts work-hardened material.
- Deburr and passivate every part; free iron from tooling is the usual cause of rust spots on finished stainless.
- Allow for poor heat dissipation when dimensioning; parts measured hot will read larger than at 20 °C.
- Use coarse threads rather than fine threads in stainless, which is prone to galling during assembly.
- Consider 303 for high-volume turned parts where the small drop in corrosion resistance is acceptable.
Surface Finishing Options
Finishes are selected for corrosion resistance, wear, appearance, electrical behaviour or cleanliness. Specify only what the function needs.
As-Machined
Ra 1.6 to 3.2 µm. Suitable for industrial internals; passivation is still recommended to remove free iron.
Passivation
Nitric or citric acid treatment to ASTM A967 that removes free iron and thickens the passive chromium oxide layer.
Bead Blasting
Uniform satin finish that hides handling marks and gives a consistent non-directional appearance.
Electropolishing
Removes 5 to 40 µm of surface material, dropping Ra by roughly half and leaving a bright, cleanable, low-friction surface.
Mirror Polishing
Mechanical polishing to Ra 0.05 µm or better for pharmaceutical, food contact and decorative architectural work.
PVD and DLC Coating
Thin hard coatings for wear, colour or release properties where the base alloy has insufficient surface hardness.
Typical Applications
Where Stainless Steel 304 is most often specified, and why it wins against the alternatives.
Food and beverage equipment
Mixing vessels, hoppers, chutes, fittings and frames that are cleaned daily with aggressive detergents.
Chemical and process plant
Valve bodies, manifolds, flanges and instrument housings in non-chloride service.
Architectural hardware
Balustrade components, brackets, fixings and decorative trim in dry or indoor atmospheres.
Medical and laboratory devices
Instrument housings, carts, trays and non-implant hardware that must withstand repeated sterilisation.
Automotive and transport
Exhaust brackets, trim, sensor housings and fasteners exposed to weather and road wash.
General industrial machinery
Shafts, collars, spacers, clamps and machine guards where corrosion resistance outweighs material cost.
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