Difference between SA662 Grade B and Grade C steel plate

SA662 Grade B and Grade C are ASME/ASTM carbon-manganese-silicon steel plates designed for moderate to low-temperature pressure vessels, differing mainly in their mechanical properties (strength/toughness) and chemical compositions, with Grade C generally offering higher strength and toughness than Grade B, often used in critical low-temperature applications, while Grade B serves general moderate/low-temp needs, both requiring specific heat treatments like normalization, especially for thicker plates, to meet performance standards.

Chemical Composition

Carbon Equivalent: Ceq = 【C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15】%

Carbon Equivalent: Ceq = 【C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15】%

Mechanical Property

Key Differences & Similarities

Standard: Both fall under ASME SA-662/A-662M for pressure vessel steel.

Application: Used for manufacturing pressure vessels for moderate and lower temperature service.

Material Type: Carbon-Manganese-Silicon (C-Mn-Si) alloy steels.

Heat Treatment: Often supplied normalized, especially for thicker plates (over 40mm), but can be ordered normalized or stress relieved.

Grade B (SA662 Gr. B)

Characteristics: Good mechanical properties for general moderate/low-temp use.

Typical Tensile Strength: Around 450-585 MPa.

Typical Yield Strength: ≥295 MPa.

Grade C (SA662 Gr. C)

Characteristics: Higher strength and impact toughness, specifically suited for demanding low-temperature environments.

Typical Tensile Strength: Often in the 480-620 MPa range.

Typical Yield Strength: ≥295 MPa (can be higher than Grade B).

In Summary

While both are excellent pressure vessel steels, Grade C is a higher-performance variant of the SA662 specification, offering superior properties for colder service conditions compared to Grade B, which is a strong, general-purpose choice for moderate-to-low temperatures.