Are ASTM A36, A572 Gr 50, S355, Q355 and SS400 Equivalent? Similar, Not Interchangeable

Short answer

ASTM A36, GB Q235, JIS SS400 and EN 10025 S275 are often grouped as "mild structural steel", and ASTM A572 Grade 50, EN 10025 S355 and GB/T 1591 Q355 are often grouped as "higher-strength structural steel". They are similar, not identical. Minimum yield strength, tensile range, chemistry limits, impact testing and thickness rules differ between standards, so a substitute grade should only be used when the project engineer accepts it in writing and the mill test certificate (MTC) shows the values the drawing requires.

The standards behind each grade

• ASTM A36/A36M – carbon structural steel for shapes, plates and bars (United States).
• ASTM A572/A572M – high-strength low-alloy columbium-vanadium structural steel; Grade 50 is the grade most often specified for beams.
• EN 10025-2 – non-alloy structural steels (Europe); S275 and S355 with sub-grades JR, J0, J2 that indicate the impact-test temperature.
• GB/T 700 – carbon structural steel (China), including Q235 with quality grades A, B, C, D.
• GB/T 1591 – high-strength low-alloy structural steel (China). The 2018 edition replaced Q345 with Q355.
• JIS G 3101 – rolled steels for general structure (Japan), including SS400.

The number in the European, Chinese and A572 grade names is the nominal minimum yield strength for the thinnest thickness range (for example 355 MPa for S355 and Q355, 50 ksi for A572 Grade 50). A36 is named after its 36 ksi minimum yield. SS400 is named after its minimum tensile strength of 400 MPa, not its yield strength.

Why "equivalent" grades are not drop-in substitutes

1. Thickness dependence. EN 10025 and GB/T standards reduce the minimum yield strength as flange or plate thickness increases. Two grades that match at thin sections can differ at thick sections.
2. Impact toughness. S355J2 and Q355D require Charpy impact tests at low temperature; A36 and SS400 do not include an impact requirement by default. If the design needs toughness, specify the sub-grade and test temperature.
3. Chemistry and weldability. Carbon, manganese and carbon-equivalent limits differ. SS400 does not set limits for carbon or manganese, which matters for welded structures.
4. Section dimensions. American W-shapes (ASTM A6), European HE/IPE sections and Chinese HW/HM/HN sections (GB/T 11263) use different size series. A grade substitution often also means a size substitution, which must be checked by the designer.

How to specify the grade in an RFQ

• State the standard and the edition, the grade and any sub-grade (for example "EN 10025-2 S355J2").
• State the section designation and the standard for dimensions and tolerances.
• List any extra tests the design needs (impact test temperature, through-thickness properties, chemistry limits).
• Ask whether an alternative grade is acceptable, and who must approve it.
• Request the MTC; we provide it per order. Third-party inspection can be arranged per order.

SHEDAR supplies structural steel sourced to order through our established supply channel in China. Grade, section and testing are confirmed per order and per drawing.

FAQ

Is ASTM A36 the same as Q235 or SS400?

No. They are commonly compared as mild structural steels, but their yield, tensile, chemistry and impact rules differ. Use one in place of another only with the engineer's approval.

Is S355 equivalent to A572 Grade 50 and Q355?

They have similar nominal minimum yield strengths at thin sections, but thickness rules, impact sub-grades and chemistry limits differ. Compare the actual standard requirements with the design.

What replaced Q345?

GB/T 1591-2018 replaced Q345 with Q355.

Which document proves the grade?

The mill test certificate (MTC) for the heat or lot, checked against the ordered standard. We provide the MTC per order, and third-party inspection can be arranged per order.

Can you supply a grade to a standard not listed here?

Send the standard, grade and drawing. Availability and testing are confirmed per order.