ASTM A36 steel is a widely used American standard carbon structural steel, and in H-beam form it is one of the most common structural materials in the construction and industrial sectors.
Its closest national standard equivalent is Q235 carbon structural steel. Additionally, Q235GJ, a high-performance structural steel widely adopted in recent years, is often compared because its strength level is similar to that of A36.
Chemical Composition & Strength Characteristics
Carbon content is the primary factor influencing the strength of structural steel.
A distinctive feature of ASTM A36 is that its carbon content increases with the thickness (or section size) of the steel, reaching up to 0.29% at maximum. Because thicker H-beams tend to experience reduced mechanical strength due to internal defects inherent to larger sections, A36 compensates for this by increasing carbon content to maintain strength levels.
However, higher carbon content also affects weldability and ductility negatively.
Therefore, in practical engineering applications, overly large or excessively thick A36 H-beams are not recommended if high weldability or toughness is required.
Comparison with Q235 / Q235B / Q235GJ
In contrast, the chemical composition of Q235 does not vary with the thickness of the section. Instead, its quality grades (A, B, C, D, E) focus on reducing harmful elements such as sulfur (S) and phosphorus (P).
In terms of impurity control, A36 is roughly equivalent to Q235B.
Atmospheric Corrosion Resistance
An important difference is the copper (Cu) content:
A36 steel contains ≥0.20% copper
Q235 steels typically do not contain copper
Copper significantly enhances atmospheric corrosion resistance.
Therefore, A36 H-beams outperform Q235 H-beams in outdoor exposure and weathering conditions, making them more suitable for bridges, outdoor structures, and long-term installations.
