Stainless vs Carbon Steel in CNC Machining Applications

Understanding the Two Material Families

What Is Carbon Steel?

Carbon steel typically contains:

• 0.05–0.6% carbon

• Small amounts of manganese and silicon

• Minimal alloying

Common CNC machining grades include:

• AISI 1018 / C45

• 1045

• 1144 stressproof

Typical uses: shafts, brackets, frames, structural parts.

What Is Stainless Steel?

Stainless steels contain:

• ≥10.5% chromium for corrosion resistance

• Nickel and molybdenum in austenitic grades

Common CNC machining grades include:

• 303, 304, 316

• 410, 420

• 17-4 PH

Typical uses: valves, medical components, marine hardware.

Real Shop-Floor Comparison Test

A contract manufacturer ran controlled turning trials on Ø50 mm bars:

• 1045 carbon steel (HB 200)

• 316 stainless steel (HB 180)

Using identical carbide inserts:

Conclusion: Stainless required slower speeds and caused significantly higher tooling cost.

Machinability Comparison

Winner for ease of machining: Carbon steel ✅

Corrosion Resistance and Service Environment

• Carbon steel rusts unless coated or painted

• Stainless resists corrosion naturally

• 316 outperforms carbon steel in marine or chemical exposure

Winner for corrosive environments: Stainless steel ✅

Strength and Heat Treatment

Carbon steel:

• Easy to heat treat

• Widely available

• Cost-effective in pre-hard states

Stainless:

• 17-4 PH offers excellent strength after aging

• Austenitic grades (304/316) are non-magnetic and tough

• Martensitic grades (420) can be hardened

Cost Comparison in CNC Machining

From procurement audits:

Winner for cost efficiency: Carbon steel ✅

Design Flexibility and Tolerance Control

Both materials can achieve tight tolerances, but:

• Stainless requires sharper tools and better thermal control

• Carbon steel is more forgiving

When to Choose Stainless Steel for CNC Machining

Choose stainless if:

• Parts face corrosion or chemicals

• Cleanliness is critical (food/medical)

• High temperature resistance needed

• Aesthetic surface finish matters

When to Choose Carbon Steel for CNC Machining

Choose carbon steel if:

• Environment is dry

• Protective coating is acceptable

• Budget is tight

• High volumes required

• Post-machining heat treatment planned

FAQs: Stainless vs Carbon Steel CNC Machining

Is stainless steel always harder to machine?

Austenitic grades like 304/316 are significantly harder to machine; 303 and 17-4 PH are much friendlier.