Carbon Steel CNC Machining Services
Low and medium carbon steel remains the lowest-cost structural metal: 440 MPa tensile in 1018, weldable, heat treatable and available in every product form.
1018, 1045, 4140 and 12L14 stock
Tolerances to ±0.05 mm on critical features
Black oxide, zinc plating and nitriding
What Is Carbon Steel?
Choosing between 1018, 1045, 4140 and 12L14, and how to protect steel parts from corrosion.
Carbon steel is the workhorse of mechanical engineering. AISI 1018 is a low-carbon grade with 440 MPa ultimate tensile strength in the cold-drawn condition, excellent weldability and the lowest material cost of any structural metal. Where higher strength or wear resistance is needed, 1045 and the alloy grade 4140 are stepped in, and where the part is turned at high volume, 12L14 free-machining steel cuts cycle time dramatically.
Which carbon steel to specify
Use 1018 for brackets, shafts, spacers, mounts and welded structures. Use 1045 for higher-strength shafts, gears and pins that can be quenched and tempered. Use 4140 where through-hardening and fatigue strength are required in larger sections. Use 12L14 for high-volume turned parts, accepting that it is not weldable and has lower ductility.
Corrosion is the one real weakness
Plain carbon steel rusts. Every part needs a plan: black oxide for indoor and oiled service, zinc or nickel plating for general industrial use, powder coating for outdoor equipment, or nitriding and hard chrome where wear matters more than appearance. Tell us the service environment on the drawing and we will match the finish to it.
Related capabilities: CNC Machining, CNC Milling, CNC Turning, 5-Axis Machining. Dimensional limits, thread rules and surface roughness grades are listed on the tolerances and specifications page, and volume-based routing is covered under production solutions.
Carbon Steel Mechanical Properties
Typical values at room temperature for the condition most often machined. Use them for material screening, then confirm against the mill certificate for the exact heat and product form.
| Property | Typical value |
|---|---|
| Density | 7.87 g/cm³ |
| Ultimate tensile strength | 440 MPa (64 ksi) |
| Tensile yield strength | 370 MPa (54 ksi) |
| Elongation at break | 15% in 50 mm |
| Elastic modulus | 205 GPa |
| Brinell hardness | 126 HB |
| Thermal conductivity | 51.9 W/m·K |
| Machinability rating | About 70, against AISI 1212 at 100 |
| Melting range | 1420 to 1460 °C |
| Weldability | Excellent for 1018, limited for 1045 and 12L14 |
Typical room-temperature values compiled from public ASM, MatWeb and mill datasheets. Actual values vary with temper, section thickness and product form; request the EN 10204 3.1 certificate for critical applications.
Machining Characteristics of Carbon Steel
How the material behaves in the cut, and what that means for tooling, fixtures, cycle time and achievable tolerance.
Stable, predictable cutting
1018 machines consistently with standard carbide, produces manageable chips and holds tolerance well, which is why it is the default for fixtures and machine parts.
Heat treatment options
1018 can be case hardened to about 42 HRC in thin sections. 1045 and 4140 are through-hardened and tempered to the specified core strength.
Welding and fabrication
1018 welds with any common process and needs no preheat in thin sections, which makes it the standard for welded frames and brackets.
Surface speed and tool life
Medium carbon grades are more abrasive than leaded steel. Expect shorter tool life on 4140 in the hardened condition and plan a finishing strategy accordingly.
Dimensional stability
Cold-drawn bar holds dimension well but carries residual stress. Stress-relieved stock is specified for parts with heavy, uneven material removal.
Corrosion protection required
Black oxide, zinc plating, phosphate or powder coat must be specified on the drawing; bare steel will rust in transit.
Design and Machining Checklist
Practical rules that reduce cost and scrap on Carbon Steel parts. Share them with your design team before the drawing is frozen.
- Specify 12L14 instead of 1018 for high-volume turned parts; the lead addition cuts cycle time substantially.
- Choose 4140 when the part needs through-hardening, fatigue strength or wear resistance in sections over 25 mm.
- Always specify a corrosion protection finish; even indoor parts rust during shipping and storage.
- Call out stress-relieved stock for parts with asymmetric material removal to avoid distortion after machining.
- Use coarse threads in steel where assembly speed matters, and avoid very fine threads in hardened grades.
- Allow grinding stock if the part is hardened after machining and must return to a tight tolerance.
Surface Finishing Options
Finishes are selected for corrosion resistance, wear, appearance, electrical behaviour or cleanliness. Specify only what the function needs.
As-Machined
Ra 1.6 to 3.2 µm. Requires an oil film or immediate plating, since bare steel begins to oxidise quickly.
Black Oxide
1 to 2 µm conversion coating giving a uniform black appearance and mild corrosion resistance for indoor and oiled service.
Zinc Plating
5 to 25 µm sacrificial coating, usually with a clear or yellow chromate, the default for industrial hardware.
Electroless Nickel
Uniform 5 to 50 µm nickel-phosphorus layer providing corrosion and wear resistance with no line-of-sight limitation.
Powder Coating
60 to 120 µm polymer layer for outdoor equipment, with far better impact and UV resistance than wet paint.
Nitriding and Hard Chrome
Case hardening or 5 to 50 µm chrome for shafts, pins and sliding surfaces where wear life drives the specification.
Typical Applications
Where Carbon Steel is most often specified, and why it wins against the alternatives.
Shafts, pins and spindles
Drive shafts, locating pins, pivot pins and spindles, frequently turned, hardened and ground.
Structural brackets and frames
Welded machine frames, mounting brackets and base plates where stiffness and low cost dominate.
Gears, sprockets and cams
Power transmission components machined from 1045 or 4140 and heat treated to the required core strength.
Jigs, fixtures and tooling
Fixture bodies, drill bushings, clamps and weld jigs used on the shop floor.
Fasteners and hardware
Studs, bolts, collars, hubs and couplings produced in volume on turning centres.
Agricultural and construction equipment
Wear plates, linkage components and mountings that are usually powder coated or zinc plated for outdoor service.
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