Stainless steel is just one of many classes of steel. Not only does it possess strength and toughness, but it also offers excellent corrosion resistance, good machinability, and welding characteristics. It is regarded as an ideal CNC machining material that combines durability and cost-effectiveness.
This guide will discuss the different types of stainless steel and focus on the most commonly used grades in CNC machining. Next, we will introduce the benefits and challenges of using stainless steel in CNC machining and share practical tips for overcoming these common challenges.
What Is Stainless Steel CNC Machining?
Stainless steel CNC machining is a manufacturing process that uses computer-controlled cutting tools and equipment to precisely shape parts out of stainless steel materials.
Stainless steels are a family of iron-based alloys known for their corrosion resistance, strength, and durability, and are widely used in various industries. CNC machining is a highly automated, precise, and flexible manufacturing process controlled by computer numerical control (CNC) technology. It encompasses a wide range of operations such as cutting, milling, turning, drilling, boring, engraving, and even EDM (electrical discharge machining).
The stainless steel CNC machining process begins with the creation of a computer-aided design (CAD) model of the desired part. This digital design is then converted into machine-readable code using CAM (Computer-Aided Manufacturing) software. The CNC machine reads the code to accurately control the cutting tool's movement, feed rate, spindle speed, and cooling parameters, thereby enabling the automated cutting and shaping of the stainless steel workpiece.
Types of Stainless Steel
Just as there are different types of aluminum alloys, stainless steel is also classified into several categories based on its composition and microstructure. Let’s first take a look at the table below to gain a preliminary understanding：
Type
Composition
Common Grades
Properties
Applications
Austenitic Stainless Steels
▪ 16% to 26% Chromium ▪ 8%to 12% Nickel ▪ 2% to 3% Molybdenum ▪Typically less than 0.10% Carbon
304/304L 316/316L 303 321 347
▪ Excellent corrosion resistance ▪ High ductility and toughness ▪ Outstanding weldability ▪ Moderate resistance to stress corrosion cracking ▪ Non /weak magnetic ▪ No-heat treatable
▪ Food and beverage industry ▪Chemical and pharmaceutical industries ▪ Medical devices ▪ Automotive exhaust systems ▪ Kitchenware and cutlery ▪ Architectural components
Ferritic Stainless Steels
▪ 10.5% to 30% Chromium ▪ Usually Nickel-free ▪ 1% to 2% Molybdenum ▪ Less than 0.08% Carbon
430 409 434 439 446
▪ Good corrosion resistance ▪ Poor low-temperature toughness ▪ Low weldability ▪ High resistance to stress corrosion cracking ▪ Magnetic ▪ No-heat treatable ▪ Cost-effectiveness ▪ High temperature resistance
▪ 18% to 30% Chromium ▪ 1% to 9.5% Nickel ▪ 0.1% to 5% Molybdenum ▪ Usually Carbon-free
2205 2507
▪ Excellent corrosion resistance ▪ High strength and ductility ▪ High resistance to stress corrosion cracking ▪ Typically magnetic ▪ Heat-treatable
▪ Oil and gas equipment ▪ Chemical and marine engineering ▪ Food processing equipment and containers ▪ Construction and bridges
Precipitation Hardening Stainless Steels
Alloying elements like titanium, copper, phosphorus, or aluminum in trace amounts.
17-4 PH 15-5 PH
▪ Highly variable ( curated for specific results） ▪ High strength ▪ Good toughness and ductility ▪ Good corrosion resistance ▪ Heat-treatable
▪ Aircraft structural components ▪ Military and defense ▪ Surgical instruments and orthopedic implants ▪ High-performance automotive parts ▪ Hydraulic systems, shafts, and gears
Austenitic Stainless Steel
Austenitic stainless steel is the most common type, with the 300 series, such as 304 and 316, being its prominent representatives. Its high chromium and nickel content provide excellent corrosion resistance, weldability, and ease of sterilization. However, these grades are more challenging to machine because of their toughness and tendency to work-harden, which increase tool wear and heat generation. Among the 300 series, grade 303 is an exception, as the inclusion of sulfur or selenium improves its machinability.
Ferritic Stainless Steel
Ferritic stainless steel, a member of the AISI 400 family, may have lower corrosion resistance than austenitic stainless steel in certain strong acid or high-chloride environments. However, its superior resistance to stress corrosion cracking in chloride-rich conditions makes it well-suited for marine applications. Additionally, ferritic stainless steel typically requires minimal heat treatment to achieve the desired properties, simplifying processing and manufacturing.
Martensitic Stainless Steel
Martensitic stainless steel offers high strength and hardness due to its higher carbon content, although it has lower corrosion resistance compared to other stainless steel types. One of its standout characteristics is the ability to further enhance these properties through quenching (rapid cooling). This type of stainless steel is commonly used in high-durability applications such as cutlery, surgical instruments, and tools. Grades like 410 and 420 are frequently chosen for their excellent machinability and reliable performance in demanding conditions. Among stainless steels, 416 is the easiest to machine due to its design specifically targeting machinability. This will be discussed in greater detail in the following section.
Duplex Stainless Steel
Duplex stainless steel gets its name from its microstructure, which contains both austenite and ferrite phases. This combination gives it the benefits of both types of stainless steel, including excellent corrosion resistance in chloride and acidic environments, high strength, good ductility, and strong resistance to stress corrosion cracking. However, due to its specialized alloy composition and manufacturing process, duplex stainless steel typically has higher production costs and may exhibit poorer machinability, requiring more careful machining control.
Precipitation-Hardening Stainless Steel
Unlike other stainless steels, which derive their strength from solid solution strengthening (as in austenitic stainless steels) or cold working (as in ferritic stainless steels), precipitation hardening stainless steels gain their strength through the formation of intermetallic compounds such as copper, aluminum, or titanium during heat treatment. After undergoing precipitation hardening heat treatment, PH stainless steels can attain strength levels comparable to high-strength structural steels, with yield strengths typically 3-4 times higher than those of austenitic stainless steels.
Best Stainless Steel Grades for CNC Machining
Here are some of the best stainless steel grades commonly chosen for CNC machining:
Stainless Steel 303
Stainless steel 303, also called free machining stainless steel, is the most machinable grade within the austenitic family. Enhanced with sulfur and phosphorus, it offers improved machinability and cutting performance. These additions allow stable cutting speeds and feed rates during high-speed machining. 303 is widely favored in CNC machining for achieving stringent precision requirements in intricate parts such as precision mechanical components, bearings, valves, bolts, and nuts. Although its corrosion resistance is not as strong as 304 or 316, stainless steel 303 still provides sufficient corrosion resistance for many general applications. It is well-suited for indoor environments and components where extreme corrosion resistance is not required.
Stainless Steel 304
304 is the most versatile and widely used stainless steel in machining tools. With excellent corrosion resistance, it performs reliably in diverse environments, from food processing to chemical manufacturing. Though less machinable than Grade 303, 304 stainless steel balances good machinability with the ability to meet high-precision and complex shape requirements. It also offers excellent weldability and supports common methods such as arc welding and filler wire welding, which ensures versatility for various connection needs.
Stainless Steel 316
After grade 304, grade 316 is the second most widely used and versatile stainless steel. It typically contains around 2–3% molybdenum (Mo), which gives it superior resistance to pitting and crevice corrosion in demanding environments like seawater and aggressive chemicals, compared to 304. Therefore, it is particularly common in high-requirement industries like marine engineering and medical devices. Additionally, it offers excellent formability and weldability. When combined with CNC machining, it can produce complex, high-precision components.
Stainless Steel 416
As previously mentioned, 416 is the easiest stainless steel to machine, primarily due to its high sulfur content. Sulfur forms sulfide inclusions in the steel, which act as "chip breakers" to help cutting tools penetrate smoothly and efficiently remove chips, reducing cutting forces and tool wear. Additionally, 416 has a lower tendency to work-harden, enabling smoother and more consistent cutting while minimizing strain on tools. After heat treatment, it achieves high hardness and good wear resistance, ensuring the reliability of components that require continuous, high-volume operation, such as bearings and valves.
Stainless Steel 17-4 PH
Stainless steel 17-4 PH combines high strength with corrosion resistance. Through precipitation hardening, it achieves mechanical properties comparable to high-strength alloy steel while retaining the corrosion resistance of stainless steel. Its heat treatment process allows flexible adjustment of strength: the material can first be CNC machined in a machinable solution-annealed state, then aged to reach the desired hardness. With well-established material standards and extensive industrial experience, 17-4 PH is widely used in aerospace, defense, oil and gas, and chemical equipment industries. It is a common choice for high-strength, high-reliability components in large-scale production.
Benefits of Stainless Steel in CNC Machining
Regardless of the stainless steel grade, its widespread popularity for machining primarily comes from a unique balance of properties. Below is a concise summary of the key advantages:
Appearance
CNC-machined stainless steel naturally offers a shiny, attractive appearance that can be enhanced through polishing, brushing, or passivation. When properly finished, stainless steel parts take on a sleek, modern look—perfect for kitchen appliances, architectural features, and various consumer products.
Corrosion resistance
Stainless steel alloy has excellent corrosion resistance and is perfect for applications exposed to moisture, chemicals, or saltwater. This is largely due to their chromium content (at least 10.5%), which forms a protective oxide layer that prevents rust and oxidation.
High Strength
Stainless steels are relatively hard, with a high mechanical strength that can be increased further using heat treatments. This strength makes it possible to machine thin-walled or load-bearing components that weaker materials cannot handle. It also enables stainless steel parts to maintain dimensional accuracy and structural integrity even under high-stress environments.
Designed for Improved Machinability
As mentioned earlier, grades 303 and 416 are specifically designed for enhanced machinability by incorporating elements like sulfur, acting as lubricants during cutting. These grades are derived from commonly used stainless steel alloys and modified to improve chip breaking, reduce tool wear, and enhance cutting efficiency.
These modifications are made possible by stainless steel’s inherent alloying flexibility. The base composition of iron, chromium, and nickel can be adjusted with elements such as sulfur, selenium, or molybdenum to tailor properties for specific applications, including machinability.
Hygienic and Easy to Clean
Stainless steel’s non-porous surface is simple to sterilize and maintain. That’s why it’s an ideal material for medical instruments, food handling, and pharmaceutical equipment. Its smooth, corrosion-resistant finish also requires less upkeep than many other metals, further enhancing its appeal in applications demanding high cleanliness.
Challenges of Stainless Steel in CNC Machining
While stainless steel offers many advantages, it also presents several challenges in CNC machining due to its material properties and composition. These challenges include:
Work Hardening Tendency
Work hardening is a phenomenon where stainless steel becomes harder during machining. Austenitic stainless steels are particularly prone to work hardening, which increases tool wear and can negatively impact the quality of the finished product if not properly managed.
Higher Cutting Forces and Tool Wear
The toughness of stainless steel — while beneficial for durability— typically demands higher cutting forces than softer metals. This can lead to slower cutting speeds, increased energy consumption, and greater strain on tooling.
Chip Management
Austenitic stainless steels often produce long, stringy chips that are difficult to break. Poor chip evacuation can lead to machine downtime and damaged surfaces.
Overheating
Stainless steel has relatively low thermal conductivity, causing heat to build up at the cutting zone. This can accelerate tool wear, affect dimensional accuracy, and potentially damage the workpiece.
Tips to Overcome Challenges
Use sharp, wear-resistant tools made of carbide or coated materials.
Apply optimized cutting parameters, including slower cutting speeds and higher feed rates.
Use coolant systems to dissipate heat effectively and reduce tool wear.
Employ rigid machine setups to minimize vibrations and improve surface finish.
Select free-machining grades, such as 303 or 416, for applications where machinability is a priority.
Common Stainless Steel CNC Machining Processes
Stainless steel's versatility and durability make it compatible with a wide range of CNC machining processes. Here are the most common machining processes used with stainless steel:
CNC Milling
CNC milling is the primary method for machining stainless steel, using high-speed rotating cutting tools to produce complex shapes, pockets, and contours with precision. Due to stainless steel’s high work-hardening rate, standard tools and feeds are often insufficient. It is recommended to use carbide tools and adopt a patient approach by reducing feeds and speeds to minimize tool wear and maintain accuracy. Adequate cooling is also essential to dissipate heat and prevent thermal damage during machining.
CNC Turning
CNC turning is an excellent choice for producing cylindrical or round components with tight tolerances and smooth finishes. The process involves rotating the stainless steel workpiece while stationary cutting tools shape it, making it particularly effective for machining austenitic stainless steel. Turning allows for faster material removal but may cause the workpiece to bind with the cutting tool. To prevent this, it's crucial to minimize tool overhang, use sharp tools, and select inserts with positive rake angles. Additionally, operating at lower cutting speeds helps reduce work hardening, ensuring precision and efficiency.
CNC Drilling
CNC drilling is commonly used to create precise holes in stainless steel workpieces, often combined with milling or turning as part of a secondary machining process. This process is employed to produce threaded or multi-feature components, such as screw holes for secondary assembly or decorative features for aesthetic purposes. Drilling stainless steel requires careful attention to tool selection and machining parameters to achieve accuracy and maintain surface integrity.
CNC Laser Cutting
CNC laser cutting uses high-powered lasers, such as CO2 or fiber lasers, to cut or engrave stainless steel sheets and thin parts with exceptional precision. This process delivers clean cuts with minimal waste, making it ideal for both decorative and structural applications. It can cut stainless steel effectively without much heat buildup, preserving the material's integrity and ensuring high-quality results.
CNC Grinding
CNC grinding is a precise process used to achieve ultra-smooth finishes and tight tolerances, especially for parts like surgical instruments or optical components. Using abrasive wheels, grinding improves surface finish, removes small amounts of material for accuracy, eliminates welding burrs, and sharpens cutting edges, ensuring both functionality and aesthetics.
Wire EDM (Electrical Discharge Machining)
For intricate shapes or hard-to-machine stainless steel grades, wire EDM is highly effective. It uses electrical discharges to cut material without mechanical stress, which makes it perfect for precision components in aerospace, medical, and tooling industries. While slower than conventional methods, it performs well at creating complex geometries, though additional surface finishing may be needed.
Best Stainless Steel Machining Services at Chiggo
While stainless steel can be more challenging to work with, its advantages often outweigh the difficulties. With its excellent combination of strength, durability, and cost-effectiveness, it remains a top choice for producing robust, high-performance products. However, machining stainless steel demands significant expertise to ensure optimal results. That’s why designers should choose a trusted CNC machine shop like Chiggo, which specializes in high-quality stainless steel machining backed by years of expertise.If you’re considering stainless steel for your next project, reach out to Chiggo for a tailored quote.
