Steel for CNC Machining
Steel is iron alloyed with carbon, and it is the choice for machined parts that need more strength, hardness, or wear resistance than aluminium can give. Common machining grades run from low-carbon 1018 and medium-carbon 1045 to 304 and 316 stainless steels, which resist corrosion but are slower to cut.
Updated 28 Sep 2026 · 4 min read · By Wyntek
What steel is
Steel is iron with a small amount of carbon, often with other alloying elements. More carbon makes it stronger and harder: 1045 steel has about two and a half times the carbon of 1018 and roughly 30% more tensile strength.
Plain carbon steels carry four-digit SAE/AISI numbers. The 10 prefix marks a plain carbon steel, and the last two digits give the carbon content in hundredths of a percent, so 1018 has about 0.18% carbon and 1045 about 0.45%. Stainless steels are a separate family with at least 10.5% chromium, which protects the surface from rust.
Common machining grades
| Grade | Type | Key alloying | Tensile strength | Yield strength | Typical uses |
|---|---|---|---|---|---|
| 1018 | Low-carbon (mild) steel | 0.14 to 0.20% carbon | 440 MPa (64 ksi) | 370 MPa (54 ksi) | Fixtures, mounting plates, spacers, pins |
| 1045 | Medium-carbon steel | 0.42 to 0.50% carbon | 565 MPa (82 ksi) | 310 MPa (45 ksi) | Shafts, gears, bolts, spindles |
| 304 | Austenitic stainless steel | About 18% chromium, 8% nickel | About 600 MPa (87 ksi) | About 270 MPa (39 ksi) | Brackets, fittings, and housings that must not rust |
| 316 | Austenitic stainless steel | About 17% chromium, 10% nickel, 2% molybdenum | About 570 MPa (83 ksi) | About 260 MPa (38 ksi) | Parts exposed to salt water or chlorides |
Carbon steel figures are AZoM typical values, and they shift with the bar's condition, such as hot rolled or cold drawn. Stainless figures are Outokumpu typical values for hot-rolled plate. Standards guarantee less: 304 and 316 are both specified at a minimum of about 515 to 520 MPa tensile and 205 to 220 MPa yield.
How carbon and stainless steels differ
- Corrosion. Bare carbon steel rusts in damp air. 304 resists most everyday environments, and the molybdenum in 316 improves its resistance to pitting in salt water and other chloride solutions.
- Magnetism. Carbon steels are magnetic. Annealed 304 and 316 are essentially non-magnetic, though cold working makes them slightly magnetic.
- Hardening. 1045 can be flame or induction hardened to about 54 to 60 HRC at the surface. 304 and 316 cannot be hardened by heat treatment, only by cold work.
- Heat flow. Carbon steel conducts heat about three to four times better than stainless: roughly 55 W/m·K against 15 W/m·K.
How steel machines
Steel is harder and stronger than aluminium, so it is cut at lower speeds and wears tools faster. That adds machine time to every feature, and machine time drives the price of a machined part.
Stainless grades are slower again. 304 and 316 are tough and work-harden as they are cut, so they need higher cutting forces than carbon steel and form stringy chips that resist breaking. If a part does not need corrosion resistance, carbon steel is usually quicker to machine.
When to choose steel
- The part needs more strength or hardness than aluminium gives: shafts, pins, gears, and wear surfaces.
- Stiffness matters more than weight. Steel is about three times as stiff as aluminium, so the same shape deflects about a third as much.
- Threads will be screwed in and out many times.
- The part will live in salt water or around chlorides, where 316 stainless is the usual specification.
- If weight matters most, 6061 aluminium is about a third of the density and easier to machine.
Designing parts to machine in steel
- Give internal corners a radius, since milling cutters are round.
- Keep walls generous and pockets shallow. Steel's cutting forces make thin walls and deep pockets slow and hard to hold to size.
- Use tight tolerances only where parts mate. Each tighter tolerance adds machine time to a material that is already slow to cut.
- Save stainless for parts that need corrosion resistance or a non-magnetic material.
- Keep bare carbon steel parts dry or oiled in storage and use, because they rust.
At Wyntek
Wyntek machines steel on Pro plans and up. Upload your file, choose CNC machining and steel, and pick a tolerance class: ±0.2 mm (±0.008 in) standard, ±0.1 mm (±0.004 in) tight, or ±0.05 mm (±0.002 in) precision for suitable features. You see the price in US dollars before you submit, and every part is scanned and inspected before it ships.
Machine a part in steel