What does the “B” in SM520B mean?

In JIS G3106 the suffix grades A/B/C step up the impact-toughness requirements: A has no mandatory Charpy value, B adds a 0 °C-class Charpy requirement, and C is the most stringent. Chemistry limits are essentially the same across the suffixes.

Grades · Structural & HSLA Steel · SM520B

SM520B

Data verified

SM520B is the 520 MPa tensile class of JIS G3106 weldable structural steel, with yield of at least 365 MPa in thin sections and the same controlled C/Si/Mn chemistry window as SM490. The B suffix adds a Charpy impact requirement that the A grades do not carry.

DINS355J2 / S420 type (near)

AISIA572 Gr.50–60 type (near)

JISSM520B (JIS G3106)

CategoryStructural & HSLA Steel

Chemical composition

Element	Content (%)
C	≤0.20
Si	≤0.55
Mn	≤1.60
P	≤0.035
S	≤0.035

Weight percent, per the governing standard ranges. Actual values per heat are on the mill certificate.

Properties

Tensile strength	520–640 MPa
Yield strength	≥365 MPa (≤16 mm)
Density	7.85 g/cm³
Impact	B grade: Charpy requirement applies per JIS G3106

Heat treatment

Hot rolled or normalized as agreed; no hardening treatment.

Equivalent grades

Standard	Designation
din	S355J2 / S420 type (near)
aisi	A572 Gr.50–60 type (near)
jis	SM520B (JIS G3106)
gb	Q390B (near)

Compare side by side: SM520B vs Q390B · SM520B vs SM490A

Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.

Applications & Processing

Applications: Long-span bridges, high-rise frames, crane girders, heavy welded structures where SM490 sections become too thick.

Processing: Weld with low-hydrogen practice and CEV control from the certificate; preheat by thickness and restraint as for S355/S420-class steels.

FAQ

What does the “B” in SM520B mean?: In JIS G3106 the suffix grades A/B/C step up the impact-toughness requirements: A has no mandatory Charpy value, B adds a 0 °C-class Charpy requirement, and C is the most stringent. Chemistry limits are essentially the same across the suffixes.

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Source: JIS G3106 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.