Stainless Steel

The 300 series family (303, 304, etc.) are austenitic stainless steels (after their crystalline structure) and are the most widely produced grades worldwide. Austenitic stainless grades are known for their high corrosion resistance and high strength across wide temperature ranges. They are not heat-treatable except by cold working, and are generally non-magnetic.

400 series stainless steels are the martensitic family and not as common as austenitic grades. Martensitic steels are extremely strong and tough due to higher carbon content, but more susceptible to corrosion in certain environments.  They can be heat-treated to greatly increase their hardness and are magnetic.

17-4 PH Stainless Steel is a high-strength, highly corrosion-resistant material that maintains its durability up to 1100°F. The PH in its name stands for precipitation-hardened, a type of treatment it undergoes to increase yield strength. It is magnetic and heat treatable to a hardness of approximately Rockwell C50. 17-4 is available in an annealed state, at an H900 temper, and an H1150 temper.

Nitronic 60 is an excellent all-purpose material with superior wear and corrosion resistance. It has a yield strength nearly double that of SS 304 and SS 316, as well as superior oxidation resistance. Popular applications include fasteners, valve stems, seats, pins, bushings, bearings, shafts and rings.

15-5 PH Stainless Steel is a high-strength, high hardness, and highly corrosion-resistant material that maintains its durability up to 1100°F, similar to 17-4 PH Stainless Steel. The PH in its name stands for precipitation-hardened, which is a treatment to increase yield strength. When compared to 17-4, 15-5 offers better ductility and transverse toughness, and is readily weldable.

A286 Stainless Steel is an iron-based super alloy used frequently for engine components. This alloy has excellent corrosion resistance and maintains strength even at high temperatures.

There are four primary stainless steel grades that are best for CNC machining:

• 430F grade stainless steel is a popular grade in machining industries due to the potential for good feeds and speeds. 430F stainless steel is ferritic and it’s similar to 430 with increased sulfur to improve machinability.
• The 300 series family are the most widely used grades. 303 Stainless Steel is the fastest to machine. It maintains good corrosion resistance for industrial machining parts. 303 stainless steel is easily modified, making it ideal for a variety of parts, such as screws, nuts, bolts, gears & shafts.
• Nitronic 60 offers superior wear and corrosion resistance making it an exceptional all-purpose material. It has a yield strength almost double that of stainless steel 304 grade and greater oxidation resistance. Popular uses include valve stems, fasteners, pins, seats, shafts and rings, bushings and bearings.
• 17-4 PH Stainless Steel is a highly corrosion-resistant material with high strength, which maintains durability in high heats. PH, or “precipitation-hardened,” refers to a treatment the material goes through which increases its yield strength. 17-4 PH is magnetic and heat treatable for hardness.

Thin walls require extra care when CNC machining stainless steel. The absolute minimum thickness is 0.5mm for metals. To minimize costs and machining time, it’s recommended to increase the thickness of thin walls to at least 0.8mm. Unless weight is a determining factor thicker walls are more stable and less costly. Thin features are susceptible to vibration, creating extra complexity and requiring considerably more time in machining operations.

Yes, stainless steels tend to be one of the most difficult metals to work with in CNC machining. Stainless steel gets harder over time, instead of wearing, which combined with the high-heat generation in machining stainless steel, can contribute to tool failure. Getting speeds and feeds right as well as proper tooling is key.