316 Stainless Steel
CNC Machining

What Is 316 Stainless Steel?

316 stainless steel is the second most popular stainless steel in the world, right after 304 stainless. It has one key difference: 2–3% molybdenum. That small addition makes a big difference in corrosion resistance.

The molybdenum gives 316 stainless steel much better resistance to chlorides, salt water, and strong acids. It resists pitting — the small holes that form when chlorides attack the surface. That is why 316 is called "marine grade" stainless steel.

316 stainless steel has 16% chromium and 10% nickel. It is tough, weldable, and handles heat up to 1,600°F. It costs about 15–20% more than 304 stainless, but in harsh environments, it lasts much longer.

For CNC machining, 316 stainless is harder to cut than 304. Its machinability rating is 36% of free-cutting brass, compared to 45% for 304 and 78% for 303. It work-hardens aggressively. But with sharp carbide tools, heavy chip loads, and flood coolant, it produces clean parts with tight tolerances. RivCut machines 316 stainless every day.

316 Stainless Steel Properties

Here are the key mechanical and physical properties of 316 stainless steel. These numbers come from ASTM A240 and AMS 5524.

316 vs 316L vs 316Ti: Which Grade Do You Need?

There are three main versions of 316 stainless steel. They share the same corrosion resistance but differ in carbon content and high-temp performance.

Quick rule: If your part will be welded, pick 316L. Most suppliers today sell dual-certified 316/316L stock that meets both specs. If your part runs above 800°F in a chemical environment, 316Ti gives the best creep resistance. For everything else, standard 316 works great.

316 Stainless Steel vs Other Materials

Not sure if 316 is the right pick? Here is how it compares to other common CNC materials.

Key takeaway: Choose 316 stainless when you need the best corrosion resistance of any common stainless grade. If chloride exposure is low, 304 stainless saves you 15–20%. If you need extreme chemical resistance beyond what 316 offers, consider Hastelloy C-276 or titanium Grade 2. If weight matters most, use aluminum 6061.

Industries and Applications for 316 Stainless Steel

316 stainless steel is the go-to material when corrosion resistance matters most. Here are the industries where we machine it most often.

Design Tips for Machining 316 Stainless Steel

316 stainless is the hardest common stainless to machine. It work-hardens more than 304 and gums up tools faster. Here is how to get clean parts at reasonable cost.

Work Hardening

316 stainless work-hardens more aggressively than 304. The surface layer can jump from Rockwell B79 to B95+ after a single light pass. Once hardened, the next pass struggles to cut through, which causes more hardening. This spiral kills tools fast.

• Use heavy chip loads. Every tooth must take a thick chip. A light pass creates heat without removing material, and that hardens the surface.
• Never dwell or rub. Program toolpaths that keep the cutter engaged at a constant chip load. Avoid rubbing on entry and exit moves.
• Replace inserts early. A slightly worn edge creates more heat and less chip. Swap inserts before you see a shiny work-hardened surface.

Chip Control

316 stainless produces tough, stringy chips that are even harder to break than 304 chips. They wrap around tools, scratch surfaces, and jam in pockets.

• Use positive-rake chip-breaking geometry. The right insert geometry curls and snaps the chip before it wraps.
• High-pressure through-tool coolant. 1,000+ psi coolant blasts chips clear of the cut zone. This is the single best investment for 316 stainless machining.
• Peck drilling for deep holes. Break chips with pecking cycles. Full-depth drilling in 316 stainless will pack chips and break the drill.

Coolant

316 stainless has low thermal conductivity (16.3 W/mK) — almost the same as 304. Heat stays at the cutting edge instead of spreading through the part. Without coolant, the tool tip can hit 1,200°F in seconds.

• Flood coolant is minimum. Use 8–10% concentration water-soluble coolant.
• Through-tool coolant is strongly recommended. It cools the cutting edge directly where heat is generated.
• Never machine 316 stainless dry. Dry cutting destroys tools in a single pass and work-hardens the surface beyond recovery.

Design-for-Manufacturability Tips

• Add inside corner radii of 0.040" or larger. 316 stainless puts more stress on small tools. Larger radii let you use stronger cutters.
• Keep wall thickness above 0.080". The higher cutting forces in 316 stainless flex thin walls more than 304 or aluminum.
• Limit pocket depth to 3x width. Deep narrow pockets in 316 cause severe tool deflection and chatter.
• Use standard thread sizes. 4-40, 6-32, 8-32, 10-32, 1/4-20, and 5/16-18 are the cheapest options.
• Consider 303 stainless for non-corrosion-critical features. If a sub-component does not need marine-grade corrosion resistance, making it from 303 stainless saves 30–40% in machining time.

Surface Finishes for 316 Stainless Steel

316 stainless steel accepts the same finishes as 304, but electropolishing is especially effective because it enriches the chromium-to-iron ratio on the surface.

Recommendation: Electropolishing is the best finish for 316 stainless steel parts that need maximum corrosion resistance. It removes the iron-rich surface layer and creates a chromium-rich oxide that is far more protective than passivation alone. For pharmaceutical and semiconductor parts, electropolished 316L is the industry standard.

Tolerances for CNC Machined 316 Stainless Steel

316 stainless steel holds tight tolerances when you manage work hardening. Here is what RivCut holds on every 316 stainless part.

• General features: ±0.005" (±0.127 mm)
• Precision features: ±0.001" (±0.025 mm)
• Critical features: ±0.0005" (±0.013 mm) on request
• Surface finish: 32–125 Ra standard, 16 Ra or better on request
• Flatness: 0.001" per inch on ground surfaces
• Thread tolerances: Class 2A/2B standard, Class 3A/3B on request

Every part gets inspected with calibrated calipers, micrometers, and pin gauges. For tighter requirements, we use CMM inspection and provide a full dimensional report. Material certifications (mill certs), certificates of conformance, and first article inspection reports are available on request.

Why RivCut for 316 Stainless Steel Parts

We machine 316 and 316L stainless steel every day. Here is what makes RivCut the right shop for your project.

• 316 and 316L always in stock. Round bar, flat bar, and plate in dual-certified 316/316L. No waiting for material orders.
• Aggressive work-hardening strategy. Our machinists use heavy chip loads, sharp carbide inserts, and through-tool coolant to prevent work hardening. Your parts come out clean.
• Electropolishing and passivation available. We offer both finishes per ASTM A967, AMS 2700, and ASME BPE standards. No need to send parts to a third party.
• 100% made in USA. Every part is machined in Union City, California. No overseas outsourcing.
• No minimum order. One part or five thousand. Same process, same quality.
• Free DFM review. We flag thin walls, deep pockets, and features that cause work-hardening problems in 316 stainless before you pay anything.

Related Resources

Learn more about stainless steel machining and other materials.