Which grade in the Chinese material standard does SS490 correspond to?

SS490 corresponds most directly to the grade Q355B in the Chinese material standard GB/T 1591 (Low-alloy high-strength structural steels).

Here is a detailed breakdown of the correspondence and key considerations:

1. Primary Equivalent: Q355B (GB/T 1591-2018)

Reason for Correspondence: Their mechanical property ranges are commercially and technically interchangeable for most structural applications.

Mechanical Property Comparison:

SS490 (JIS G 3101):

Yield Strength (ReH): ≥ 325 MPa

Tensile Strength (Rm): ≥ 490 MPa

Q355B (GB/T 1591):

Yield Strength (ReH): ≥ 355 MPa

Tensile Strength (Rm): 470–630 MPa

Note on Naming Logic:
The number in SS490 refers to the minimum tensile strength (490 MPa), while the number in Q355B refers to the minimum yield strength (355 MPa). Despite this difference, their practical strength levels align closely.

2. Important Context & Possible Alternatives

Historical Reference – Q345B:
Before the 2018 update of GB/T 1591, the common equivalent was Q345B (Yield ≥ 345 MPa). The standard was revised to align with international grades (like Europe's S355), and Q355B officially replaced Q345B. Old drawings or stock may still reference Q345B.

Not Equivalent – Q235 Series:
Q235 (e.g., Q235B) has a much lower yield strength (≥235 MPa) and should not be substituted for SS490 in load-bearing applications.

3. Key Differences to Consider in Specification

Impact Toughness:
Standard SS490 has no mandatory Charpy impact requirement.
Q355B guarantees impact energy (≥ 34 J at +20°C). For low-temperature service, specify higher grades:

Q355C: Impact at 0°C

Q355D: Impact at -20°C

Q355E: Impact at -40°C

Chemical Composition:
JIS G 3101 does not strictly specify chemistry for SS490, while GB/T 1591 defines detailed ranges for Q355 (C, Si, Mn, P, S, etc.). This can affect weldability and formability.

Quality Documentation:
Always request a Mill Test Certificate (MTC) compliant with GB/T 1591, verifying both mechanical properties and chemical composition.

4. Practical Guidance for Selection & Substitution

General Structural Use: Q355B is the default, cost-effective equivalent.

Dynamic/Low-Temperature Service: Choose Q355D or Q355E to ensure sufficient toughness (similar to JIS SM490YA or SM490YB).

Critical Welded Structures: Check the Carbon Equivalent (Ceq) value to assess weldability. Q355D/E typically has better weldability due to tighter control of composition.

Verification: In rigorous engineering, validate substitution by comparing all required properties (yield, tensile, elongation, impact) against the design specifications, not just grade names.

Quick Reference Table

Final Answer:

For most purposes, SS490 can be substituted with Q355B according to GB/T 1591-2018.
For critical applications, especially where low-temperature toughness or enhanced weldability is required, specify Q355D or Q355E. Always confirm with technical datasheets and project specifications before finalizing material substitution.