ASTM A242/A242M specification covers high-strength low-alloy structural steel shapes, plates, and bars for welded, riveted, or bolted construction intended primarily for use as structural members where savings in weight [mass] or added durability are important. The atmospheric corrosion resistance of the steel in most environments is substantially better than that of carbon structural steels with or without copper addition. When properly exposed to the atmosphere, this steel can be used bare (unpainted) for many applications. This specification is limited to material up to 4 in. [100 mm], inclusive, in thickness.
| Element | Carbon (C), max | Manganese (Mn), max | Phosphorus (p), max | Sulfur (S), max | Copper (Cu), min |
|---|---|---|---|---|---|
| Composition, % | 0.15 | 1 | 0.15 | 0.05 | 0.2 |
| Type | Tensile strength, min, ksi [MPa] | Yield point, min, ksi [MPa] | Elongation in 8 in. [200 mm], min, % | Elongation in 2 in. [50 mm], min, % | |
|---|---|---|---|---|---|
| Plates and BarsA | |||||
| For thicknesses 3⁄4 in.[20 mm], andunder | 70 [480] | 50 [345] | 18B,C | 21C | |
| For thicknesses over3⁄4 to 11⁄2 in. [20 to 40 mm], incl | 67 [460] | 46 [315] | 18B,C | 21C | |
| For thicknesses over11⁄2 to 4 in. [40 to 100 mm], incl | 63 [435] | 42 [290] | 18B,C | 21C | |
| Structural Shapes | |||||
| For flange or leg thicknesses 1.5 in. [40 mm] and under | 70 [485] | 50 [345] | 18C | 21 | |
| For flange thicknesses over 1.5 in. [40 mm] to 2 in. [50 mm], incl | 67 [460] | 46 [315] | 18 | 21 | |
| For flange thicknesses over 2 in. [50 mm] | 63 [435] | 42 [290] | 18 | 21D | |