SS · stainless
Stainless Steel 304 / 304L
Work-hardens faster than the tool can cut if the feed drops. Published index around 45% against B1112 = 100%. Everything about machining it is about keeping the tool engaged.
Quoting this material
- Typical lead time
- 7–12 working days
- Condition
- Annealed (or cold drawn bar with higher tensile)
- Achievable finish
- Ra 1.6 µm typical · Ra 0.4 µm best
Choosing between two grades? 304 vs 316L compared →
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
Work-hardens faster than the tool can cut if the feed drops. Published index around 45% against B1112 = 100%. Everything about machining it is about keeping the tool engaged.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength | 505 | MPa |
| Yield strength (0.2%) | 215 | MPa |
| Elongation | 40 | % |
| Hardness | 201 | HB |
| Thermal conductivity | 16.2 | W/m·K |
| Modulus of elasticity | 193 | GPa |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Annealed (or cold drawn bar with higher tensile)
Heat treatment
Not hardenable by heat treatment. Annealing after welding or heavy cold work restores ductility and relieves stress; it does not strengthen.
Achievable surface finish
Ra 1.6 µm
Ra 0.4 µm
Passivation after machining is standard for corrosion-critical parts; electropolishing gives a smoother, cleaner surface than mechanical polishing alone.
Tooling and cutting parameters
Cutting speed
- 100–180 m/min (carbide)
Feed
- 0.10–0.25 mm/rev turning · 0.08–0.15 mm/tooth milling
Tooling
- AlTiN or TiAlN coated carbide, sharp positive geometry, strong corner radius
Coolant
- Flood, high pressure ideally, aimed at the cutting edge
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Food and beverage equipment
- Chemical process pipework and fittings
- Architectural and marine hardware
- Pharmaceutical clean-service parts
- Heat exchanger components
DFM notes for this grade
- Never take a light finishing pass to “clean up” a dimension - that is exactly the cut that work-hardens the surface and ruins the finish
- On thin walls, the material work-hardens as it deflects, so support it and take fewer, deeper cuts
- Threading and tapping are the slowest operations on a 304 part; a form tap instead of a cut tap changes the cycle time and the tool life
Questions buyers ask
- What is 304L and should I specify it?
- The low-carbon variant, held under 0.03% carbon. It matters if the part is welded: 304 can sensitise in the heat-affected zone and start corroding at the grain boundaries, while 304L does not. For a machined part that is never welded, the difference is not worth the price.
- Why is my drawing’s 304 part so much more expensive than the 303 quote I got elsewhere?
- Because the two are not the same material to machine. 303 runs at roughly 1.7× the cutting speed and the tools last longer, so a quote that looks 35% cheaper often is a 303 quote for a part specified in 304. Ask what material is in the quote.
Grades we would quote instead
316L
3/10Harder to machine than 304 and it galls more, but it is the grade for chlorides, medical and marine.
303
6/10The free-machining austenitic, and the reason the rest of the family looks so hard by comparison.
321
4/10A stabilised austenitic - same machining character as 304 with a little more bite, and the titanium addition is there to stop sensitisation at high temperature.