​What are the Characteristics of Stainless Steel Machining?

What are the Characteristics of Stainless Steel Machining?

Stainless steel has high chromium (Cr) and nickel (Ni) content. For stainless steels where manganese (Mn) replaces nickel, the manganese content is primarily high.

Precisely because the content of Ni (or Mn) and Cr in stainless steel is about ten times higher than in ordinary carbon steel, although the tensile strength and yield limit of stainless steel are not significantly higher—sometimes even lower—than those of ordinary steel, other performance indicators of stainless steel, such as elongation, reduction of area, and impact value, are higher than those of ordinary carbon steel and alloy steel.

Under the influence of cutting temperature, the strength and hardness of the metal at the shear zone in ordinary steel decrease significantly as the temperature rises, facilitating the cutting process. In contrast, the strength and hardness of stainless steel do not decrease noticeably at high temperatures. Consequently, the cutting forces during stainless steel machining are substantial.

When machining stainless steel, not only is a significant amount of heat generated, but the thermal conductivity of stainless steel is also low (approximately ½–⅓ that of ordinary carbon steel), resulting in poor heat dissipation conditions. This leads to high tool temperatures, greatly affecting tool life. Stainless steel has strong adhesion and welding tendencies, making it prone to built-up edge formation during cutting, which hinders achieving a smooth machined surface. Additionally, stainless steel has a strong work-hardening tendency; if cutting conditions are inappropriate, tool wear accelerates. The chips from stainless steel are difficult to break and curl, easily causing clogging during cutting, which degrades surface finish, damages the machined surface, and chips the cutting edge.

To address the characteristics of stainless steel cutting, tool materials with high hardness, good anti-adhesion properties, and high strength should be selected. For carbide tools, grades containing tantalum (Ta) or niobium (Nb), such as YG8, should be chosen. For high-speed steel tools, cobalt-containing grades are preferable. A reasonable tool geometry should be selected: for stainless steel with low hardness and high plasticity, larger rake and relief angles should be used. Measures to promote chip curling (such as chip breakers) should be implemented, and the tool should have sufficient chip pocket space to ensure smooth chip evacuation. Reasonable cutting conditions must be determined: use a larger feed rate (greater than the work-hardened layer thickness) and a lower cutting speed. The depth of cut should exceed the work-hardened layer left by the previous process.

It is essential to maximize the rigidity of the machine tool, workpiece, and tooling system. Select cutting fluids with good anti-adhesion and heat dissipation properties.