Differences Between Q235 and Q355
Q235 and Q355 are two commonly used types of steel. Their core difference lies in that Q235 is a low-carbon steel with a yield strength of no less than 235MPa, suitable for light-duty structures; while Q355 is a high-strength low-alloy steel with a yield strength of no less than 345MPa, applicable to heavy-load or high-demand scenarios. The two exhibit significant differences in chemical composition, mechanical properties and application fields.
Differences in Chemical Composition
Q235
It is classified as ordinary carbon structural steel. It has a relatively low carbon content (approximately 0.14%-0.22%), with iron and carbon as the main components, plus small amounts of silicon and manganese. It contains low levels of phosphorus and sulfur and no alloying elements.
Q355
It belongs to high-strength low-alloy steel. Its carbon content is slightly lower (around 0.12%-0.20%), but the content of manganese is significantly increased. In addition, micro-alloying elements such as niobium, vanadium and titanium are added to enhance its performance through grain refinement strengthening.
Comparison of Mechanical Properties
Strength
Q235 has a yield strength of ≥235MPa and a tensile strength ranging from 370MPa to 500MPa, with excellent plasticity and toughness (elongation ≥26%).
Q355 has a yield strength of ≥345MPa (≥355MPa under some standards) and a tensile strength of 450MPa to 650MPa. It features higher hardness but slightly lower plasticity and toughness (elongation ≥21%).
Processing Characteristics
Q235 boasts superior weldability and formability, making it suitable for complex processing. Q355 has strong work-hardening performance, yet it tends to fracture during cold deformation and thus requires quenching to improve its strength.
Appearance and Distinguishing Methods
Color and Sparks
Newly cut Q235 shows a blue-gray color, while Q355 appears slightly reddish due to the high manganese content. When ground with an abrasive wheel, Q235 produces round, dark red sparks, whereas Q355 generates bright sparks with branches.
