Austenitic stainless steels and duplex stainless steels have properties that give them a different machinability compared to carbon steel or ferritic and martensitic stainless steels.
The greatest difference is the high ductility of austenitic stainless steels and duplex stainless steels, as well as their tendency to work harden and form built-up edges on the cutting tool. Moreover, in duplex materials, chip forming is made more difficult by the high strength of these materials.
Sanmac® stainless steel with improved machinability
In Sanmac® stainless steels, machinability has been improved without jeopardizing properties such as corrosion resistance and mechanical strength. The non-metallic inclusions in Sanmac® steels are of great significance to the improved machinability. In addition to sulphides, Sanmac® steels contain oxide inclusions that improve chip breaking and reduce tool wear.
Apart from the material and tool, the machining result is influenced by the machine itself, by the cutting data, coolant, and type of operation.
Cutting fluids
To obtain long insert/tool-life with good chip breaking when turning, a generous flow of cutting fluid should be used. The cutting fluid removes heat from the chip and facilitates chip breaking, at the same time giving improved dimensional stability. In the case of internal machining, chip evacuation is improved if cutting fluid is applied through the cutting tool.
Work hardening
In all machining that involves cutting austenitic and duplex stainless steels, work hardening is more pronounced than in carbon steel or ferritic and martensitic stainless steels. The machined surface becomes harder at the same time as tool-life decreases.
Always observe the following:
- Use modern cutting tools* with suitable geometries for machining austenitic and duplex stainless steels.
- Change the insert regularly. A worn insert causes more severe work hardening.
Mechanical properties
High strength in combination with high ductility in austenitic and duplex stainless steels makes chip breaking more difficult and increases the risk of vibration, which damages the surface and reduces the service life of the insert.
Always observe the following:
- Use stable machines only.
- Make sure that the workpiece is properly secured and use stable tool holders.
- Try to minimize tool overhang - this is especially important in drilling and internal turning.
- In case of vibrations, often a problem during internal turning, use tools with small nose radius even though this increases the risk of plastic deformation at the nose.