Steel Basics
Steel is iron + carbon + other stuff. The “other stuff” determines whether it’s cheap structural steel, tough alloy steel, or hardened tool steel. Here’s what you need to know for manufacturing.
Carbon Steel
Just iron and carbon (plus trace manganese, silicon, sulfur, phosphorus). Classified by carbon content:
Low Carbon (Mild Steel): 0.05–0.25% C
| Grade | Tensile (ksi) | Use | Notes |
|---|---|---|---|
| A36 | 58–80 | Structural steel | The default for welded structures. Cheapest. |
| 1018 | 63 | Shafts, pins, fixtures | Easy to machine and weld. Case hardenable. |
| 1020 | 65 | General purpose | Similar to 1018. Common in tube and plate. |
Medium Carbon: 0.25–0.55% C
| Grade | Tensile (ksi) | Use | Notes |
|---|---|---|---|
| 1045 | 91 | Shafts, gears, bolts | Heat treatable. Harder than 1018. |
| 1050 | 100 | Springs, cutting edges | Good balance of strength and toughness. |
High Carbon: 0.55–1.0% C
Hard, strong, wear-resistant, but brittle. Used for springs, cutting tools, wire rope. Difficult to weld.
Alloy Steel
Carbon steel with intentional additions of chromium, molybdenum, nickel, vanadium, etc. for enhanced properties.
| Grade | Tensile (ksi) | Key Property | Common Use |
|---|---|---|---|
| 4130 | 97 | Weldable, heat-treatable | Aircraft tubing, roll cages, structural |
| 4140 | 95–150* | Tough, fatigue-resistant | Shafts, gears, tooling, hydraulic components |
| 4340 | 108–160* | Highest toughness alloy steel | Landing gear, crankshafts, high-stress |
| 8620 | 92 | Case-hardening steel | Gears, pins — hard surface, tough core |
*Range depends on heat treatment condition.
Tool Steel
Designed to make tools — things that cut, form, or shape other materials. Expensive, hard, wear-resistant.
| Grade | Category | Hardness (HRC) | Use |
|---|---|---|---|
| A2 | Air-hardening | 57–62 | Blanking dies, punches, general tooling |
| D2 | Cold work | 58–64 | Stamping dies, slitters, wear plates |
| O1 | Oil-hardening | 57–62 | Cutting tools, gauges, jigs (easy to machine pre-hardened) |
| S7 | Shock-resistant | 50–58 | Chisels, punches, impact tooling |
| H13 | Hot work | 38–53 | Die casting dies, extrusion tooling, hot forging |
| M2 | High-speed | 60–65 | Drill bits, end mills, saw blades |
Free-Machining Steels
Grades with added sulfur or lead for improved machinability. Great for high-volume screw machine work. Terrible for welding.
- 1215: Non-structural, great machinability, cheap. Bushings, spacers, non-critical pins.
- 12L14: Leaded version of 1215. Best machinability of any steel. Restricted in some applications (lead content).
Quick Selection Guide
- Cheapest structural: A36
- General machining: 1018
- Need strength: 4140 (heat treat to spec)
- Need to weld it AND it’s structural: 4130
- Screw machine parts: 12L14
- Tooling/fixtures: A2 or D2
- Springs: 1075 or 1095
Need help picking the right steel? Tell us your application and we’ll recommend the grade.