Steel Plate Grades Explained: Q235B, Q355B and International Equivalents

Chinese grade numbers confuse many first-time buyers. This short guide maps the common grades to European and American equivalents and tells you when the upgrade from Q235B to Q355B is actually necessary.

What the numbers mean

Chinese carbon steel grades start with Q (from the Chinese word for "yield strength") followed by the yield strength in MPa. Q235B = 235 MPa yield — the general structural workhorse. Q355B = 355 MPa yield — the higher-strength structural grade that replaced Q345. The letter is the impact-test class (A no test, B 20°C, C 0°C, D −20°C).

International equivalents

These are "equivalent in use" mappings, not paper identities: chemical ranges differ slightly. For code-governed projects, the governing document decides — send us the clause and we will confirm material certificates match it before quoting.

When Q235B is enough (and when it isn't)

Roughly: if your part is sized by stiffness or weldability — brackets, base plates, gussets, machine frames — Q235B is the economical choice and what we stock deepest. Move to Q355B when members are sized by strength: long-span beams, crane structures, heavy mobile equipment, or when weight reduction pays for the premium.

What to check on the MTC

• Heat number matches the markings on the plate you receive
• Yield/tensile/elongation values meet the grade
• Impact test temperature matches your order class (B/C/D)
• Thickness tolerance class — Chinese standard plates carry negative tolerance; if your design needs "full thickness", state it at RFQ

Cutting grades

Both grades laser-cut and flame-cut cleanly. Our steel plate page lists stocked thicknesses from 1.5–16 mm with weights, and our laser cutting service nests your DXF drawings. Cold rolled parts (enclosures, stamped components) are covered on the cold rolled sheet page.