[M] - STAINLESS STEELS (STAINLESS STEEL)

Stainless steels are alloy steels with a chromium (Cr) content above 12%, to which their high corrosion resistance is due.

Machining stainless steel presents challenges due to the following properties:

• Work hardening: During machining, stainless steels tend to harden due to deformation, making further machining more demanding.
• Low Thermal Conductivity: They have low thermal conductivity, resulting in heat concentration in the cutting zone during machining.
• High Ductility: Especially the austenitic types (e.g. 304, 316), have high plasticity and ductility compared to other steels. This is an important factor in machining because during cutting part of the material deforms plastically.

The low thermal conductivity and high ductility contribute to the formation of a particularly "sticky" (sticky -gummy) burr. These burrs tend to adhere to the cutting edge, reducing its performance and accelerating tool wear.

In machining technology and specifically according to VDI 3323 they are classified into:

M 12 - Ferritic Stainless Steels

(400 series - Unhardened, Annealed)

• Microstructure:
• Carbon content less than 0.1%C. The chromium steel has a ferritic structure and is not hardened.
• Machinability:
• Burrs: Continuous and long
• Tool wear: Moderate
• Cutting type: Moderate cutting speeds, moderate feed
• Surface quality: Good
• Water-soluble cutting fluid is recommended

M 13 - Martensitic Stainless Steels

(400 series - Hardened)

• Microstructure:
• Magnetic - hardened stainless steels. An example is stainless steel used for manufacturing tools such as a caliper, Stainless Hardened
• Machinability:
• Burrs: Continuous, hard and difficult to remove
• Tool wear: High
• Cutting type: low cutting speeds, low feed
• Surface quality: Moderate
• High-quality water-soluble cutting fluid is recommended

M 14 - Austenitic Stainless Steels

(300 series - Common INOX)

• Microstructure:
• Stainless steels with an additional alloying element, nickel Ni, exhibit an austenitic structure even at ambient temperatures. They are non-magnetic and offer the highest corrosion resistance among steels. The best-known grades are 304 and 316
• Machinability:
• Burrs: Continuous, "sticky" and particularly difficult to remove
• Tool wear: Very high
• Cutting type: very low cutting speeds, moderate feed
• Surface quality: Good
• Water-soluble cutting fluid is recommended specifically for austenitic stainless steel