The first thing to understand is that A36 and 1018 are specified under two completely different systems, and this affects how you think about each material.[1][2]
| Property | A36 | 1018 | 12L14 |
|---|---|---|---|
| Specification system | ASTM (mechanical) | SAE/AISI (chemical) | SAE/AISI (chemical) |
| What it guarantees | Minimum yield strength (36 ksi) | Chemical composition (0.15–0.20% C) | Composition + free-machining additives |
| Typical supply condition | Hot rolled | Cold drawn | Cold drawn |
| Primary product form | Plate, shapes, structural sections | Round bar, flat bar, hex bar | Round bar, hex bar |
| Surface finish | Rough, black mill scale | Smooth, bright (cold drawn) | Very smooth, bright |
| UNS designation | K02600 | G10180 | G12144 |
The processing condition is at least as important as the grade designation. Hot rolling produces steel at elevated temperature — the final product has a rough, dark mill scale surface, looser dimensional tolerances, and lower strength. Cold drawing pulls the bar through a die at room temperature, which work-hardens the material, tightens the dimensions, and produces a smooth bright surface.[2]
| Property | Hot Rolled (A36 typical) | Cold Drawn (1018 / 12L14 typical) |
|---|---|---|
| Surface finish | Rough black mill scale — must be machined off | Smooth, bright — may be usable as-received |
| Dimensional tolerance | Loose (ASTM A6 tolerances) | Tight (typically ±0.002–0.004" on bar) |
| Yield strength | 36 ksi (A36 minimum) | 54 ksi (1018 CD typical) / 60 ksi (12L14 CD) |
| Tensile strength | 58–80 ksi | 64 ksi (1018 CD typical) / 78 ksi (12L14 CD) |
| Ductility | Higher (20% elongation) | Lower (15% elongation) — work hardened |
| Internal stress | Low — stress relieved by hot working | Higher — can warp during heavy machining |
| Cost | Lower | Higher (additional processing step) |
A36 in hot rolled plate. 1018 and 12L14 in cold drawn bar. These are the conditions you will most commonly encounter from distributors.[1][2][3]
Toggle between properties. 4140 prehardened included as a reference for when you need to step up to alloy steel.[1][2][3]
ASTM A36 is the most widely used structural steel in the United States. It is specified by mechanical properties (36 ksi minimum yield), not by exact chemistry. This means A36 plate from two different mills can have different carbon content, different manganese, and machine differently. The standard covers plate, bar, shapes (angles, channels, beams), and sheet piling. It is almost always hot rolled, which gives it a rough, black mill scale surface that must be machined off before finishing.[1]
A36 is available in bar form, but it is far less common than A36 plate. When you order "mild steel round bar" from a distributor, you will almost always receive 1018 cold drawn, not A36 bar. A36's primary domain is plate, structural shapes, and welded fabrications where the rough surface is acceptable and will be painted, galvanized, or left as-is.
SAE 1018 is specified by chemical composition under the SAE J403 standard: 0.15–0.20% carbon, 0.60–0.90% manganese. It is almost always supplied as cold drawn bar (often called C1018 or "1018 CRS" for cold rolled steel). The cold drawing process pulls the hot rolled bar through a die at room temperature, which work-hardens the material, increases strength, tightens dimensional tolerances (typically ±0.002–0.004"), and produces a smooth, bright surface.[2]
1018 is the default "mild steel bar" for machined components. It machines cleanly, welds readily, and can be case hardened (carburized) to produce a hard, wear-resistant surface over a tough core. It cannot be through-hardened to high hardness because of its low carbon content. When you need more strength than 1018 can provide, the next step up is 4140 alloy steel.
SAE 12L14 is a resulfurized, rephosphorized, leaded carbon steel engineered for maximum machining speed. The "12" indicates a resulfurized/rephosphorized series, the "L" indicates lead addition, and "14" indicates the approximate carbon content (0.15% max). The lead (0.15–0.35%) acts as an internal solid lubricant at the cutting interface, and the sulfur (0.26–0.35%) forms manganese sulfide inclusions that break chips into short, manageable pieces. The result is a steel that machines at nearly twice the speed of 1018 with better surface finish and dramatically longer tool life.[3]
The trade-off is significant: 12L14 cannot be welded. The lead and high sulfur cause hot cracking and porous, brittle weld joints. It also cannot be meaningfully heat treated or case hardened. It is purely a machining material for parts that will be turned, drilled, and finished, then used as-machined. It is the standard material for high-volume screw machine products.
A36 in hot rolled condition, 1018 and 12L14 in cold drawn condition. 4140 prehardened (28–32 HRC) included as the next step up when carbon steel isn't strong enough.[1][2][3][4]
| Property | A36 (HR) | 1018 (CD) | 12L14 (CD) | 4140 PH (ref) |
|---|---|---|---|---|
| Specification | ASTM A36 | SAE 1018 | SAE 12L14 | SAE 4140 |
| Specified by | Mechanical properties | Chemical composition | Chemical composition | Chemical composition |
| Carbon content | 0.25–0.29% (typical) | 0.15–0.20% | 0.15% max | 0.38–0.43% |
| Tensile strength | 58–80 ksi400–550 MPa | 64 ksi440 MPa | 78 ksi540 MPa | 130 ksi896 MPa |
| Yield strength | 36 ksi (min)250 MPa | 54 ksi370 MPa | 60 ksi415 MPa | 100 ksi690 MPa |
| Elongation | 20% | 15% | 10% | 18% |
| Hardness | ~120 HB | ~126 HB | ~163 HB | 28–32 HRC |
| Machinability (vs 1212=100%) | 72% | 70% | 170–190% | 65% |
| Weldability | Excellent | Excellent | Poor — do not weld | Good (preheat) |
| Case hardenable? | Yes | Yes (carburize) | No (lead interferes) | N/A (through harden) |
| Surface (as-received) | Rough, black scale | Smooth, bright | Very smooth, bright | Smooth, bright |
| Dimensional tolerance | Loose (ASTM A6) | Tight (±0.002–0.004") | Tight (±0.002–0.004") | Tight |
| Contains lead? | No | No | Yes (0.15–0.35%) | No |
| Food/water contact safe? | With coating | With coating | No — lead | With coating |
| Relative cost (bar) | $ (plate) | $ | $$ | $$ |
Our team at C&W machines A36 plate, 1018 cold drawn bar, and 12L14 free-machining bar daily. We can advise on grade selection, recommend when to step up to alloy steel, and coordinate plating or coating when corrosion protection is needed.
