Stainless steel type 1.4305, popularly known as grade 303 is the most readily machinable austenitic grade stainless steel. This is due to urge presence of Sulphur in the composition. The downside to this improved machinability is the sulphur decreases corrosion resistance and slightly reduces the steel’s toughness, giving it a lower corrosion resistance than grade 304. Even with a reduced toughness it is still very high as with other austenitic steel grades.
Due to its machinability, 303 is used in parts that require extensive machinery such as:
Nuts and bolts
|Chromium (Cr)||17.00 – 19.00|
|Nickel (Ni)||8.00 – 10.00|
|Manganese (Mn)||0.0 – 2.00|
|Copper (Cu)||0.0 – 1.00|
|Silicon (Si)||0.0 – 1.00|
|Sulphur (S)||0.15 – 0.35|
|Nitrogen (N)||0.0 – 0.11|
|Carbon (C)||0.0 – 0.10|
|Phosphorous (P)||0.0 – 0.05|
Stainless steel grade 1.4305/334 also corresponds to, but may not be a direct equivalent of the following designations:
|Proof Stress||190 Min MPa|
|Tensile Strength||500 to 750 MPa|
|Elongation A50 mm||35 Min %|
|Hardness Brinell||230 Max HB|
Due to the addition of Sulphur, pitting corrosion can occur where it is present, decreasing the corrosion resistance below that of 304. Despite this, 303’s corrosion resistance is still good in mild environments. In environments where chloride is present and over 60c, pitting and crevice corrosion occurs, and 303 is not suitable for use in marine environments.
Grade 303 is extremely well suited for machining, and this can be enhanced by using the following techniques:
• Cutting edges must be kept sharp. Dull edges cause excess work hardening.
• Cuts should be light but deep enough to prevent work hardening by riding on the surface of the material.
• Chip breakers should be employed to assist in ensuring swarf remains clear of the work
• Low thermal conductivity of austenitic alloys results in heat concentrating at the cutting edges. This means coolants and lubricants are necessary and must be used in large quantities.