ASTM A36 steel beams are the American standard carbon structural steel, commonly used in structural applications. Its Chinese counterpart is Q235 steel beams, and Q235GJ, a high-performance structural steel, is also sometimes compared because it has a similar strength to A36.
The carbon content is a major factor affecting the strength of steel. For A36 beams, the carbon content gradually increases with the thickness or diameter of the steel, reaching a maximum of 0.29%.
This increase compensates for the decrease in strength that naturally occurs with thicker sections, but it can also reduce weldability and ductility. Therefore, very thick A36 beams are not generally recommended in practical engineering.
In contrast, the chemical composition of Q235 beams does not change with thickness. Instead, Q235 focuses on strict control of sulfur and phosphorus content, two harmful elements in steel. From this perspective, A36 beams are closest to Q235B beams when comparing phosphorus control.
Atmospheric corrosion resistance is another difference. A36 beams contain at least 0.2% copper, which significantly improves corrosion resistance under atmospheric conditions. Q235 beams do not contain copper, so A36 beams generally perform better in outdoor or exposed environments.
In practical applications, A36 beams offer slightly higher corrosion resistance and compensatory carbon content for thicker sections, but welding and forming of very thick beams should be handled carefully.
Q235 beams have stable chemical composition across all thicknesses, strict control of harmful elements, and are cost-effective and widely available, making them a popular choice for general structural applications.
