The main difference between Q355B and Q345B lies in the execution standards and grade classification. Both Q345 and Q355 are grades of steel material. It is low-alloy steel (C<0.2%) and widely used in construction, bridges, vehicles, ships, pressure vessels, and more.

The Q345B grade marking method: The steel grade consists of three parts: the Chinese pinyin letters representing the yield strength, the yield strength value, and the quality grade symbol.

For example: Q345B, where:

Q - The initial letter of the pinyin for the Chinese character "屈" meaning "yield strength" in steel.

345 - Yield Strength Value, unit MPa

B - Quality Grade B.

When the buyer requires the steel plate to have thickness-direction properties, then add the representation of thickness direction (z) after the specified grade number.

Towards performance level symbols, such as: Q345BZ15.

Q345B Standard: Complies with GB/T1591-2008 "Low-alloy High-strength Structural Steel."

The steel grade consists of the initial letter Q of the Chinese拼音 for "yield strength" (representing "屈"), followed by the specified small yield strength value.

The delivery status code, quality grade symbol, and four other parts make up the composition.

Q355NB. Wherein:

Q--- The initial letter of the Pinyin of the Chinese character for "yield strength" in steel.

Specified small yield strength values, units in MPa (MegaPascals).

N一一一 is in the state of normal fire or hot rolling.

B-grade quality level.

Q355B Execution Standard:

GB/T 1591-2018 "Low-Alloy High-Strength Structural Steel"