Stainless Steel 303
Stainless 303 is the most easily machined of all the austenitic grades.
Austenitic steels are highly ductile and have a tendency to work harden and form build up edges on the cutting tools.
The addition of sulphur to the alloy improves its machinability but reduces its corrosion resistance. Nevertheless, it maintains good corrosion resistance in mildly corrosive environments and at temperatures up to about 60oC.
Stainless steel 303 is an austenitic steel. It was developed to give good machining properties by the addition of sulphur. The downside of adding sulphur, which is generally regarded as an impurity to be removed, is a reduction in corrosion resistance, in transverse ductility and notched impact toughness.
The presence of manganese will increase hardness and tensile strength but will further decrease ductility. If these modifications are important you should note that the chemical specifications detail a maximum % of manganese (2.0%) but no minimum. If you require the higher manganese content you will have to specify it.
It is widely used in such things as aircraft fittings, and electrical switch gear.
Stainless 303 is widely used in:
- Nuts and bolts
- Aircraft fittings
- Gears
- Screws
- Shafts
- Electrical switch gear
However, it does have limitations that make it unsuitable for specific applications. Wild it has generally satisfactory corrosion resistance in mildly corrosive environments it is not suited for marine environments where the sulphur inclusions provide sites for the initiation of pitting corrosion and result in rapid deterioration.
In any chloride environment above 60oC 303 is liable to corrosion cracking.
As already noted, welding stainless 303 should be avoided, but if necessary it can be welded with 310 rods. It should be annealed after to dissolve precipitated carbides. It also tends to work harden and speeds should be adjusted accordingly.
It should be annealed after to dissolve precipitated carbides. It also tends to work harden and speeds should be adjusted accordingly.
It also tends to work harden and speeds should be adjusted accordingly.
Machineability
There is no doubt that the primary benefit of Stainless 303 is its machinability. To get the most from this particular quality a few simple rules should be followed:
The low thermal conductivity of austenitic steel means coolants and lubricants must be used, often in large quantities.
- Keep cutting edges sharp. Without sharp tools, you will experience significant work hardening.
- The direction of the cut - conventional milling will tend to result in more work hardening as opposed to "climb" milling
- Keeping swarf clear of the work.
- Careful consideration should be given to chip size.
- The low thermal conductivity of austenitic steel means coolants and lubricants must be used, often in large quantities.
Heat Resistance
303 stainless steel has good heat resistance up to 760oC in intermittent use. It maintains this resistance in continuous use up to 840oC.
See below for problems with carbide precipitation.
However, it does have limitations that make it unsuitable for specific applications. While it has generally satisfactory corrosion resistance in mildly corrosive environments it is not suited for marine environments where the sulphur inclusions provide sites for the initiation of pitting corrosion and result in rapid deterioration.
In any chloride environment above 60oC 303 is liable to corrosion cracking.
As already noted, welding stainless 303 should be avoided, but if necessary it can be welded with 310 rods. It should be annealed after to dissolve precipitated carbides.
It also tends to work harden and speeds should be adjusted accordingly.
| Chemical Element | % Present |
|---|---|
| Carbon (C) | 0.0 - 0.10 |
| Chromium (Cr) | 17.00 - 19.00 |
| Manganese (Mn) | 0.0 - 2.00 |
| Silicon (Si) | 0.0 - 1.00 |
| Phosphorous (P) | 0.0 - 0.05 |
| Sulphur (S) | 0.15 - 0.35 |
| Nickel (Ni) | 8.00 - 10.00 |
| Copper (Cu) | 0.0 - 1.00 |
| Nitrogen (N) | 0.0 - 0.11 |
| Iron (Fe) | Balance |
| Physical | Value |
|---|---|
| Density | 8.03 g/cm³ |
| Melting Point | 1455 °C |
| Thermal Expansion | 17.3 x10^-6 /K |
| Modulus of Elasticity | 193 GPa |
| Thermal Conductivity | 16.3 W/m.K |
| Electrical Resistivity | 0.72 x10^-6 Ω .m |
| Mechanical | Value |
|---|---|
| Proof Stress | 190 Min MPa |
| Tensile Strength | 500 to 750 MPa |
| Elongation A50 mm | 35 Min % |
| Hardness Brinell | 230 Max HB |
303 stainless is also available in a variant 303Se. This employs Selenium as opposed to Sulphur to achieve the better machining properties.
The Selenium improves the forming performance, both hot and cold over the sulphur variant and also provides a smoother finish on the machined surface. In certain environments, this may also improve the resistance to corrosion.
- Tube
- Pipe
- Fittings
- Flanges
- Special Sections
- Sheet
- Plate
- Flat Bar
- Round Bar
- Hollow Bar
- I Beam
- U Channel