Why Is Stainless Steel Hard to Machine?

If you’ve ever attempted milling stainless steel, you know it can be a difficult challenge. This high strength alloy steel has the potential to wear tools down quickly. Here’s why machining 303 stainless steel can be a difficult task even for very experienced machinists.

Stainless steel becomes harder during machining

If you’ve ever experienced work hardening during machining, you know it’s tough on your tools. Cutting tools generate a lot of heat, especially when working with an incredibly hard material like stainless steel. Milling stainless steel is a much more difficult process than other metals, and it can lead to scrapped parts, broken tools and major inconveniences. As the friction between the tool and workpiece generates heat, it causes the actual structure of the workpiece material to change. This hardens the material, making already strong stainless steel even stronger.

During work hardening, the heat transfers to the workpiece instead of to the chips being shaved away. This can actually cause deformation to the workpiece. Since stainless steel and other high-temp alloys are prone to work hardening, it requires a special touch to mill these materials.

Chip breaking is difficult with stainless steels

One of the most crucial aspects of machining 303 stainless steel is chip formation. When you’re working with stainless steel, you need to ensure that the material has an optimized microstructure throughout the entire piece. Chip breaking is closely related to this microstructure, and poorly managed chip breaking causes major harm not just to the workpiece itself, but also to your tools. In some cases, they can even be a danger for the machinist.

Chip breaking is tough with stainless steel materials because of their toughness and ductility. Materials with high ductility often have poor chip breaking capabilities. In extreme situations, the chips can actually wrap around the entire workpiece or the tool you’re using. An experienced machinist knows how to perform chip breaking the right way, safely milling stainless steel and cutting it to the desired shape.

Always follow guidelines for machining stainless steels

To safely mill stainless steel, you need to remember the following guidelines:

  • Perform heat treatment before machining to prevent work hardening. The material will be much easier to machine.
  • Provide plenty of lubrication. Lubricating fluid cools the workpiece, taking away heat and lubricating the surface all at once. This is especially ideal when you’re milling stainless steel parts that are very smooth.
  • Use professional cutting tools. If you want professional results, you have to have the tools to get them.
  • Use lower cutting speeds. In general, the faster you cut, the more heat you produce both for the tool and for the workpiece. If you use a lower cutting speed during milling, you reduce the chance for work hardening and also make chip breaking much easier.

Milling stainless steel can be challenging even for the most seasoned machinists. It’s a job that takes years of experience, precision and patience to get right. Contact Evden Enterprises to learn more about metal fabrication processes and procedures.