In most circumstances, machining stainless steel and nickel alloys is more difficult than machining low-alloy steels. However, there are a wide range of compositions, and some grades can have better machinability than mild steel.

The austenitic 300 series stainless steels, like 304/304L and 316/316L, are the most widely utilized stainless steel class. Their good corrosion resistance, formability, and weldability make them suitable for various applications. These characteristics are obtained by alloying nickel with chromium and iron. Adding nickel also results in alloys that work harden rapidly (strengthen through cold work). Therefore, while 300 series stainless steels are the most widely used, they are also the most difficult class of stainless to machine.

Recognizing the tendency for stainless and nickel alloys to cold work is the most important concept to remember when machining these grades. When a tool touches a workpiece to remove stock, it leaves behind a thin, work-hardened layer at the surface. Even though this layer is thin, overcoming the work-hardened layer on subsequent passes could prove to be difficult.

The five guiding principles below are the foundation for good stainless machining practices:

1. Use a heavier feed than what you would typically utilize for mild steels. Heavier feeds are utilized to maintain the cut below the work-hardened surface. Dwelling on the surface or multiple thin cuts should be avoided.
   
   
2. Taking a deeper cut will require more power. The equipment capability for stainless and nickel alloys is about 65% – 75% of that for mild steel. Use a slower speed than with mild steels. This will reduce heat and improve tool life.
   
   
3. Since you are applying greater loads through the tool, the tools and fixtures must be as rigid as possible to avoid chatter and distortion. Minimize overhang or protrusion of both the tool and the workpiece.
   
   
4. Keep tools sharp with recommended rake angles and clearances. Chip breakers may be beneficial for higher nickel-containing alloys.
   
   
5. Proper cutting fluids are critical to maintain adequate lubrication and heat removal. The tool should be flooded with lubricant, which will help remove chips from the work area.

There are many variables in machining operations, so guidelines for speeds and feeds can be used as starting points. Guidelines for speeds and feeds for stainless steels, nickel alloys, and other specialty metals can be found on our website by clicking the below link: