304 Stainless Steel
CNC Machining

What Is 304 Stainless Steel?

304 stainless steel is the most widely used stainless steel in the world. It makes up more than 50% of all stainless steel produced. You see it in kitchen sinks, food processing machines, chemical tanks, and hospital equipment.

It gets its name from its composition: 18% chromium and 8% nickel. That is why it is also called 18-8 stainless. The chromium creates a thin oxide layer on the surface that stops rust. The nickel makes it tough and easy to form.

304 stainless steel is food-safe and FDA-approved for contact with food. It resists most acids, cleaning chemicals, and salt water in mild conditions. It handles heat up to 1,500°F in continuous service. It welds easily and does not need heat treatment after welding.

For CNC machining, 304 stainless steel is a fair choice. It cuts slower than aluminum or free-machining 303 stainless. It work-hardens fast, which means the surface gets harder as you cut it. But with the right tools and speeds, it produces clean parts with tight tolerances. Most CNC shops machine 304 stainless every day.

304 Stainless Steel Properties

Here are the key mechanical and physical properties of 304 stainless steel. These numbers come from ASTM A240 and AMS 5513.

304 vs 304L vs 304H: Which Grade Do You Need?

There are three main versions of 304 stainless steel. They look the same, but they differ in carbon content. That difference matters when you weld or use the part at high temperatures.

Quick rule: If your part will be welded and used in a corrosive environment, pick 304L. If your part runs above 800°F, pick 304H. For everything else, standard 304 works great.

304 Stainless Steel vs Other Materials

Not sure if 304 stainless is the right choice? Here is how it stacks up against other common CNC materials.

Key takeaway: Choose 304 stainless when you need corrosion resistance, weldability, and food-safety at a moderate cost. If you only need fast machining and corrosion does not matter much, use 303 stainless. If you need better chemical resistance, use 316 stainless. If weight matters most, use aluminum 6061.

Industries and Applications for 304 Stainless Steel

304 stainless steel is used in almost every industry. Here are the most common applications we machine at RivCut.

Design Tips for Machining 304 Stainless Steel

304 stainless steel work-hardens fast. That means the surface gets harder every time the cutter passes over it. Here are the tips that save you time and money.

Work Hardening

The biggest challenge with 304 stainless is work hardening. When the cutter rubs instead of cutting, the surface layer hardens. The next pass has to cut through harder material, which causes more rubbing, which causes more hardening. It is a spiral that kills tools and wrecks surface finish.

• Always use a positive chip load. Never let the cutter dwell or rub. Each tooth must take a real chip.
• Use sharp tools. Replace inserts before they get dull. A dull tool rubs instead of cutting.
• Avoid light passes. A finishing pass that is too light will rub and harden the surface. Use 0.010" minimum depth of cut.

Chip Control

304 stainless makes long, stringy chips that wrap around the tool and clog the cut. This scratches the surface and can break the tool.

• Use chip-breaking insert geometry. The grooves on the insert face curl and break the chip.
• Increase feed rate. A thicker chip breaks more easily than a thin one.
• Use through-tool coolant. High-pressure coolant blasts chips out of the cut zone.

Coolant

304 stainless has low thermal conductivity (16.2 W/mK). Heat builds up at the cut zone instead of spreading through the part. Coolant is not optional.

• Flood coolant at a minimum. Use 6–10% concentration water-soluble coolant.
• Through-tool coolant is better. It reaches the cutting edge where heat is worst.
• Never machine 304 stainless dry. It will work-harden, gall, and destroy your cutter in seconds.

Design-for-Manufacturability Tips

• Add inside corner radii of 0.030" or larger. Sharp corners need EDM, which adds cost and time.
• Keep wall thickness above 0.060". Thin walls flex more in stainless than in aluminum because of higher cutting forces.
• Limit pocket depth to 4x width. Deep pockets in 304 stainless cause 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.
• Specify 303 stainless for non-critical parts. If corrosion resistance and weldability are not critical, 303 machines 70% faster and costs less.

Surface Finishes for 304 Stainless Steel

304 stainless steel accepts many surface finishes. The right finish depends on your application — cosmetic, corrosion, or functional.

Recommendation: Passivation is the most important finish for 304 stainless steel parts that will see moisture or chemicals. It costs little and significantly improves corrosion resistance. We recommend it for all 304 stainless parts unless your application is purely dry and indoor.

Tolerances for CNC Machined 304 Stainless Steel

304 stainless steel holds tight tolerances well once you account for work hardening. Here is what RivCut holds on every 304 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 and certificates of conformance are available on request.

Why RivCut for 304 Stainless Steel Parts

We machine 304 stainless steel every day. Here is what makes RivCut the right shop for your project.

• 304 stainless always in stock. Round bar, flat bar, and plate in standard and 304L grades. No waiting for material.
• Work-hardening expertise. Our machinists know how to keep chip loads constant and tools sharp. Your parts come out clean, not work-hardened.
• Passivation in-house. We passivate per ASTM A967 / AMS 2700 without sending parts out. Faster delivery, lower cost.
• 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 features that cause work hardening, tool breakage, or unnecessary cost before you pay anything.

Related Resources

Learn more about stainless steel machining and other materials.