CNC Machining Stainless Steel: The Benefits, Drawbacks, and Best Alloys

by | Apr 28, 2023 | CNC Machining, Machining Materials

Stainless steel is just one of many classes of steel. It’s best known for its strength and durability, even in wet or corrosive environments. This makes it a very popular metal for both consumer products and industrial applications.

This article explains the many benefits of using stainless steel for your products and the challenges of working with it. We’ll also provide an overview of a few of the best stainless steel alloys for machined parts.

Benefits of CNC Machined Stainless Steel

Caliper measuring stainless steel flange

CNC machining is a precise and effective manufacturing method for a wide range of materials, including metals and non-metals. The popularity of stainless steels as a machining material mostly comes from their unique balance of properties.

Stainless steels are relatively hard, with a high mechanical strength that can be increased even further using heat treatments. To add to their impressive mechanical durability, stainless steel parts are very resistant to corrosion and chemical deterioration. They can even maintain their impressive properties at higher temperatures that cause many other materials to weaken or even melt.

Generally speaking, the primary alternatives for designers considering stainless steels are aluminum or titanium alloys. Depending on the alloys used and the conditions they experience, they can all offer impressive corrosion resistance.

The strength, hardness, machinability rating, and temperature resistance of stainless steel alloys lie somewhere between aluminum and titanium. Stainless steel however is also often cheaper than either aluminum or titanium alloys and has better weldability. But that doesn’t mean it doesn’t also present a few challenges.

Challenges of Machining Stainless Steel

Carbide endmill tool for CNC machining stainless steel

Despite its impressive balance of beneficial properties, CNC machining stainless steel does come with a few obstacles. Austenitic stainless steels in particular are prone to work hardening during machining which can make them even harder. This increases tool wear and can negatively impact the quality of the finished product if machinists are not familiar with machining stainless.

Additionally, stainless steel tends to have a lower thermal conductivity that allows heat to build up at the cut area. Without adequate cooling and the proper cutting parameters, these temperatures can be high enough to cause sensitization of the stainless steel. Depending on where the stainless steel part is being used, this could mean intergranular corrosion and stress corrosion cracking.

Despite these challenges, experienced machinists with the right tools and equipment can reliably create high-quality parts when CNC machining stainless steel.

Best Stainless Steel Alloys for Machining

In a previous article, we highlighted 10 different steel alloys that are excellent choices for making machined parts. Of those alloys, 4 out of 10 were stainless steels:

Alloy Type Description Advantages Disadvantages Applications
SS 303 Free Machining Stainless Steel One of the most readily available and highly machinable of all austenitic grades of stainless steel. Excellent machinability, good corrosion resistance, moderate cost. Cannot be hardened by heat treatment. Not suitable for marine applications. Electronic hardware, nuts and bolts, screws, aircraft fittings, bushings.
SS 416 Free Machining Stainless Steel Offers superior machinability to any other stainless steel. Outstanding machinability, moderate corrosion resistance, good strength. Not suitable for chlorine or marine environments. Poor weldability and limited availability. Valves, pump shafts, gears, nuts, bolts.
SS 304 Stainless Steel One of the most common stainless steels alloys available with good weldability. Good machinability, weldability, and cost. Excellent corrosion resistance. Susceptible to stress corrosion cracking in some applications above 60°C. Some other stainless steel alloys offer better resistance to pitting and crevice corrosion. Food handling, utensils, automotive parts, architectural applications, heat exchangers, screws.
SS Grade 17-4 PH Stainless Steel It is a grade of martensitic precipitation-hardened stainless steel, containing up to 30% chromium. Very high toughness, strength, and corrosion resistance. Requires efficient and careful heat treatment. Nuclear reactors, aircraft turbines, oil and gas applications.


Using Stainless Steel for Machined Products

Inside Gensun Precision machine shop

Stainless steel is an excellent choice for creating strong and durable products. It offers a great combination of properties at a reasonable cost. And producers with concerns about machining efficiency can opt for an alloy like SS 416 that has better machinability.

Overall, while stainless steels can be a bit more challenging to work with, the benefits are often worth it. That’s why designers should choose a reliable CNC machine shop like Gensun to create high-quality stainless steel products at an affordable cost.

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