The machining of stainless steels is often regarded as difficult. This is due to the fact that certain stainless steels, but far from all of them, are characterized by material properties that result in the cutting edge being exposed to severe conditions when machining.
Machinability is a complex concept that embraces several factors, and not just the question of tool wear. In addition to the effect of the material on tool wear, i.e. on tool life, it is also necessary to consider its effect on the magnitude of cutting forces, chip shape and surface quality of the machined surface when considering the overall machinability of a material.
The special material properties of stainless steels affect all four machinability factors: in general, it can be said that the higher the alloy content of a stainless steel, the more difficult it is to machine. The special properties that make stainless steels difficult to machine occur to a greater or lesser extent in all grades of stainless steels, but are most marked in the austenitic and ferritic-austenitic grades. They can be summarized in five points:
- Stainless steels work-harden considerably
- Stainless steels have low thermal conductivity
- Stainless steels have high toughness
- Stainless steels tend to be sticky
- Stainless steels have poor chip-breaking characteristics