Q235 is a material of ordinary carbon structural steel. Q represents the yield limit of this material. The following 235 refers to the yield value of this material, which is around 235MPa. And as the thickness of the material increases, its yield value decreases.
Because the carbon content is moderate, the overall performance is good, the strength, plasticity and welding properties are well matched, and it has a wide range of uses. It consists of Q+number+quality grade symbol+deoxidation method symbol. Its steel number is prefixed with “Q”, which represents the yield point of the steel. The following number represents the yield point value, and the unit is MPa. For example, Q235 represents a carbon structural steel with a yield stress (σs) of 235 MPa. If necessary, symbols indicating the quality grade and deoxidation method can be marked after the steel number. The quality grade symbols are A, B, C, and D respectively. Deoxidation method symbols: F represents boiling steel; b represents semi-killed steel; Z represents killed steel; TZ represents special killed steel. Killed steel may not be marked with symbols, that is, both Z and TZ may be unmarked. For example, Q235-AF represents Grade A boiling steel. Special-purpose carbon steel, such as bridge steel, marine steel, etc., basically uses the representation method of carbon structural steel, but a letter indicating the purpose is appended to the end of the steel number. The complete expression method is: Q235–Quality grade symbol·Deoxidation method symbol. The quality grades are divided into A, B, C, and D. In order, A grade has the poorer quality and D grade has the highest quality. The deoxidation method symbols are F, b, Z and TZ, which respectively represent boiling steel, semi-killed steel, killed steel and special killed steel. However, in the grade representation method, the symbols Z and TZ can be omitted.
The different grades of Q235A, Q235B, Q235C and Q235D mainly represent different impact temperatures. A means no impact, B is above 20 degrees, C is above 0 degrees, D is above 20 degrees, the difference between A to E refers to the difference in impact temperature in their performance. They are: Q235A grade, which does not require impact toughness test; Q235B grade, which is subject to normal temperature (20°C) impact toughness test; Q235C grade, which is subject to 0°C impact toughness test; Q235D grade, which is subjected to -20°C impact toughness test. The impact toughness test uses Charpy V-shaped notch specimens. The impact toughness index is Akv. The above-mentioned B, C and D grade steels are required to achieve Akv≥27J under their respective different temperature requirements. At different impact temperatures, the impact values are also different.
The sulfur content of A, B, C, and D decreases in order; A and B have the same sulfur content, C has the second highest sulfur content, and D has the least sulfur content.
Q235 chemical composition:
Q235 is divided into four levels: A, B, C and D (GB/T 700-2006)
Q235A grade contains C ≤0.22% Mn ≤1.4% Si ≤0.35% S ≤0.050% P ≤0.045%
Q235B grade contains C≤0.20% Mn≤1.4% Si ≤0.35% S ≤0.045% P ≤0.045% (with the consent of the purchaser, the carbon content may not exceed 0.22%)
Q235C grade contains C ≤0.17% Mn ≤1.4% Si ≤0.35% S ≤0.040% P ≤0.040%
Q235D grade contains C ≤0.17% Mn ≤1.4% Si ≤0.35% S ≤0.035% P ≤0.035%
Q235 deoxygenation method:
F, b, and z can be used to represent boiling steel, semi-killed steel, and killed steel respectively. Grade A and Grade B steel each have three deoxidation methods: F, B and Z. Grade C steel only has killed steel, and Grade D steel has only special killed steel. Boiling steel is steel with incomplete deoxidation and poor plasticity and toughness. Welded structures made of this material are prone to cracks in the joints when subjected to dynamic loads. It is not suitable to work at low temperatures, as hardening may occur sometimes. In contrast, killed steel is fine and uniform, with good plasticity and toughness.
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