Mild Steel CNC Machining: 10xx to 12xx Grades

We offer mild steel CNC machining in plain carbon 10xx steels and in the free-machining 11xx and 12xx series. This page helps you choose between a plain carbon grade and a free-machining one, and explains the welding trade-off. It also pairs each finish with the rust protection it gives and shows how to write the callout so the quote matches the part. Mild steel is a common low-cost choice for brackets, frames, spacers and fixtures.

Which carbon steel series do you machine?

We machine all three series by CNC milling and CNC turning. Steel sheet parts are cut on our laser cutting service and bent on the sheet metal side. The exact grade is confirmed in your quote.

Mild steel10xx, 11xx, 12xx

Plastics and other materials on request. The exact grade is confirmed in your quote.

The four-digit numbers come from the SAE system, set out in SAE J403 (SAE International). The first two digits give the type of steel, and the last two give the average carbon content in hundredths of a percent, so 1018 has about 0.18% carbon (PMPA).

How do the carbon steel series compare?

The main choice is between plain carbon steel, which welds well, and free-machining steel, which cuts faster but shouldn’t be welded. Sulfur is added to the 11xx and 12xx series to make them machine more easily (PMPA), and the same sulfur makes them poor for welding (PMPA).

Series	What it is	Machining	Welding	Example grades	Best for
10xx	Plain carbon steel	Low-carbon grades can be gummy; chips are harder to control	Good for low-carbon grades	1018, 1045	Welded parts, frames and brackets
11xx	Resulfurized	Easier, thanks to added sulfur	Not recommended	1117, 1144	Turned parts with some strength
12xx	Resulfurized and rephosphorized, some leaded	Easiest of the three	Not recommended	1215, 12L14	High-volume turned parts that won’t be welded

Example grades are labels, not a list of what we stock. 1045 sits at the top of the 10xx range and is a medium-carbon steel, not a true mild steel (PMPA). The mill certificate that ships with your parts gives the composition and properties for the batch you receive.

How does mild steel machine?

Low-carbon steel is easy to cut but can be gummy, with long, stringy chips that are hard to break (PMPA). Free-machining grades break chips more easily, which is why they’re chosen for turned parts with many features.

What that means for your part:

Turned parts in volume. A 12xx grade can cut cycle time on shafts, pins and fittings that won’t be welded. Ask about it in the quote.
Welded assemblies. Keep to 10xx. The machining is a little slower, but the weld is sound.
Bar condition. Cold-finished bar, covered by ASTM A108, is supplied for machining (ASTM International). Name it on the drawing if your customer requires it.
Hardness. If the part needs case hardening or a hardness range, write it on the drawing, and the quote confirms how the part will be made and treated.

Which finishes stop mild steel from rusting?

Bare mild steel rusts, so most machined steel parts get a coating. The right one depends on where the part works and whether it will be painted later.

Finish	Why you’d choose it on mild steel	Watch for
Zinc electroplating	Corrosion protection on small parts and fasteners	Not for steels harder than about 46 HRC, because of hydrogen embrittlement (ASTM B633)
Nickel or chrome electroplating	Wear resistance or a bright finish	Confirm the plating type and thickness in the quote
Powder coating	Durable color on brackets and frames	Masking needed on threads and fits
Painting	Color, or a primer for later painting	Masking needed on threads and fits
Bead blasting	Even matte surface, often before coating	Not a rust protection on its own
As-machined	Parts that will be oiled or coated later	Bare steel rusts in storage and transit

ASTM B633 is the standard most drawings cite for zinc plating on steel (ASTM International). It warns that steels above 1,700 MPa (247 ksi), about 46 HRC, shouldn’t be zinc plated to it.

Our full list of finishes:

As-machined
Bead blasting
Anodizing Type II
Anodizing Type III (hard anodizing)
Powder coating
Brushing
Passivation
Electroplating (nickel, chrome, zinc)
Painting

How do you call out mild steel on a drawing?

Write the grade, the bar condition and the finish. For example (an example callout, not a recommendation): “Steel 1018, cold finished to ASTM A108, zinc plate to ASTM B633”. ASTM A29 covers the general requirements for hot-wrought carbon steel bar (ASTM International).

What to put on the drawing or in your message:

Grade, such as 1018 or 12L14. “Mild steel” alone can mean several grades, and the quote is clearer with a number.
Bar condition, cold finished or hot rolled, if it matters.
Finish, with the plating standard and any surfaces to mask.
Welding, if the part will be welded, so no free-machining substitute is used.

Every order comes with a mill certificate that traces the metal to its batch, along with QC inspection and ISO 9001 documentation.

Standard QC inspection
Material certification (mill certs)
ISO 9001 documentation

Questions buyers ask about mild steel CNC machining

Is 1018 or 12L14 better for a turned part?

12L14 machines more easily, because it is a leaded, resulfurized free-machining steel. Choose 1018 if the part will be welded, since free-machining steels shouldn’t be welded (PMPA).

Is 1045 mild steel?

Not strictly. Its 0.45% average carbon makes it a medium-carbon steel (PMPA). We machine it as part of the 10xx series.

Can I weld 1215 or 12L14?

It’s not recommended. The sulfur that makes them easy to machine causes slaggy, crack-prone welds (PMPA). Use a plain low-carbon grade for welded parts.

Does zinc plating make steel brittle?

Plating can put hydrogen into steel, and hardened steel is most at risk. ASTM B633 says steels above about 46 HRC shouldn’t be zinc plated to it (ASTM International). If your part will be hardened before plating, say so on the drawing.

What is the difference between mild steel and carbon steel?

Mild steel is low-carbon steel, one part of the wider carbon steel family. The last two digits of the grade show how much carbon it has (PMPA).

Will I get a material certificate?

Yes. A mill certificate comes with every order, so the grade traces back to the batch the metal came from.

Need more hardness or wear resistance? See tool steel CNC machining. For corrosion resistance without a coating, compare stainless steel CNC machining, or see all the metals we machine and what CNC machining is.

Sources

SAE International, J403 Chemical Compositions of SAE Carbon Steels (named; homepage linked), https://www.sae.org/, accessed 2026-10-20.
PMPA, Basics of the North American Steel Grade System: Carbon, https://www.pmpa.org/basics-of-the-north-american-steel-grade-system-carbon-2/, accessed 2026-10-20.
PMPA, 3 Reasons To Not Weld Free Machining Steels, https://www.pmpa.org/3-reasons-to-not-weld-free-machining-steels/, accessed 2026-10-20.
ASTM International, A29, A108 and B633 (named; homepage linked), https://www.astm.org/, accessed 2026-10-20.