What is the chemical composition of Q235B

According to GB/T 700-2006, the "Carbon Structural Steel" standard, the chemical composition (melting composition, mass fraction%) of Q235B is clearly defined. It primarily includes the following elements and their content ranges:
I. Main Alloying Elements and Contents
Carbon (C): ≤0.20%
Carbon is a key element in determining steel strength. Q235B has a low carbon content, ensuring a certain level of strength while also achieving good ductility and weldability (excessive carbon increases brittleness and reduces weldability).
Silicon (Si): ≤0.35%
Silicon is a deoxidizer. Proper addition can increase the strength and hardness of steel, but excessive levels can reduce ductility and toughness, so strict control is required.
Manganese (Mn): ≤1.40%
Manganese is a strengthening element that significantly increases the strength and toughness of steel, while also improving its hot and cold working properties. It is one of the key alloying elements in Q235B. II. Harmful Elements and Limitations
Sulfur (S): ≤0.045%
Sulfur is a harmful element in steel. It easily forms low-melting-point sulfides with iron, causing "hot brittleness" (fracture) during high-temperature processing. Therefore, its content must be strictly limited.
Phosphorus (P): ≤0.045%
Phosphorus is also a harmful element. It can make steel brittle at low temperatures ("cold brittleness") and reduce impact toughness. Therefore, it must be kept at a low level.
III. Other Notes
Minor adjustments in composition are permitted based on steel thickness, rolling process, and other factors, but must remain within the overall standard range.
Residual elements such as nitrogen and oxygen are not specified, but are generally controlled during the smelting process through processes such as deoxidation to ensure stable steel properties.
Strict control of these components is the foundation for Q235B to achieve the comprehensive properties of "moderate strength, good ductility, and excellent weldability," enabling it to meet the needs of a wide range of applications in construction, machinery, and other fields.