The chemical composition of ASTM A36 is defined by a range for key elements, ensuring the desired mechanical properties and weldability. The composition is determined by heat analysis. The following table outlines the typical and maximum percentages for primary elements:
| Element | Content (Typical / Maximum) | Purpose / Effect |
|---|---|---|
| Carbon (C) | 0.25 – 0.29% / ≤0.25% | Primary hardening element; increases strength but reduces ductility and weldability. |
| Manganese (Mn) | ~1.03% / 0.80–1.20% | Increases strength and hardness; combats brittleness from sulfur. |
| Phosphorus (P) | ≤ 0.040% | Impurity; increases strength but severely reduces ductility and impact toughness (causes cold shortness). |
| Sulfur (S) | ≤ 0.050% | Impurity; improves machinability but harms ductility and weldability (causes hot shortness). |
| Silicon (Si) | ~0.28% / ≤0.40% | Deoxidizer added during steelmaking; increases strength. |
| Copper (Cu) | ≥0.20% (when required) | Improves atmospheric corrosion resistance (in "copper-bearing" grades). |
| Iron (Fe) | Balance (~98-99%) | Base metal. |
The specification allows the carbon content to be as high as 0.29%, which, compared to common cold-rolled steels like 1018 (max ~0.18% C), makes A36 slightly harder and stronger but less ductile and more challenging to form or stamp. This composition classifies A36 as a mild/low-carbon steel.