Today we will discuss the differences in characteristics between Q345A, Q345B, Q345C, Q345D and Q345E steel materials.
Q345 refers to a type of steel material. It is a low alloy steel (C<0.2%), widely used in structures such as buildings, bridges, vehicles, ships and pressure vessels.
The 'Q' represents the yield point of this material, with the number 345 indicating a yield value of around 345MPa. This yield value decreases as the material thickness increases.
Q345 offers good overall mechanical properties, decent low temperature performance, and excellent plasticity and weldability.
It is used in medium and low pressure vessels, oil tanks, vehicles, cranes, mining machines, power stations, bridges and other structures designed to support dynamic loads, mechanical parts, building structures and metallic structural components in general.
It can be used in hot-rolled or standard conditions and is suitable for various structures in cold regions below -40°C.
1. Grade classification
Q345 can be divided into classes Q345A, Q345B, Q345C, Q345D and Q345E, each representing a different impact temperature:
- Class Q345A is not impact tested.
- The Q345B undergoes impact testing at room temperature (20°C).
- The Q345C is impact tested at 0°C.
- Q345D is tested at -20°C.
- Q345E is tested at -40°C.
Different impact temperatures will result in different impact values.
2. Chemical Composition
- Q345A: C≤0.20, Mn ≤1.7, Si≤0.55, P≤0.045, S≤0.045, V 0.02~0.15.
- Q345B: C≤0.20, Mn≤1.7, Si≤0.55, P≤0.040, S≤0.040, V 0.02~0.15.
- Q345C: C≤0.20, Mn≤1.7, Si≤0.55, P≤0.035, S≤0.035, V 0.02~0.15, Al≥0.015.
- Q345D: C≤0.20, Mn≤1.7, Si≤0.55, P≤0.030, S≤0.035, V 0.02~0.15, Al≥0.015.
- Q345E: C≤0.20, Mn≤1.7, Si≤0.55, P≤0.025, S≤0.025, V 0.02~0.15, Al≥0.015.
3. Comparison with 16Mn
Q345 steel was developed as a replacement for various types of steel, including 12MnV, 14MnNb, 18Nb, 16MnRE, 16Mn and more, not just 16Mn steel. The chemical composition of 16Mn and Q345 is not exactly the same.
Of greater importance is the difference in the dimensions of the thickness grouping according to different yield strengths, which will inevitably cause changes in the allowable stress of certain thickness materials.
Therefore, it is not suitable to simply apply the allowable stress of 16Mn steel to Q345 steel; instead, the allowable stress must be redetermined based on the new thickness grouping dimensions of the steel material.
The main constituent elements of Q345 steel are essentially the same as those of 16Mn steel. The difference is the addition of alloy elements V, Ti, Nb. These elements refine the grain, greatly increase the steel's toughness, and substantially improve the steel's overall mechanical properties.
This is why Q345 steel can be thicker. Therefore, the overall mechanical performance of Q345 steel should be better than that of 16Mn steel, especially its low temperature performance, which 16Mn steel lacks. The allowable stress of Q345 steel is slightly higher than that of 16Mn steel.
4. Performance Comparison
- Mechanical properties of Q345D seamless pipe: Tensile strength: 490-675, Yield strength: ≥345, Elongation: ≥22.
- Mechanical properties of Q345B seamless pipe: Tensile strength: 490-675, Yield strength: ≥345, Elongation: ≥21.
- Mechanical properties of Q345A seamless pipe: Tensile strength: 490-675, Yield strength: ≥345, Elongation: ≥21.
- Mechanical properties of Q345C seamless pipe: Tensile strength: 490-675, Yield strength: ≥345, Elongation: ≥22.
- Mechanical properties of Q345E seamless pipe: Tensile strength: 490-675, Yield strength: ≥345, Elongation: ≥22.
5. Product Series
Compared to Q345A, B, C steel, Q345D steel has a lower test temperature for low-temperature impact work, better performance and smaller amounts of P and S harmful substances. However, its market price is higher.
Q345D Definition:
① Composed of Q + number + quality grade symbol + deoxidation method symbol.
Its steel number is prefixed with “Q”, representing the yield strength of the steel, and the following number indicates the value of the yield strength, in MPa. For example, Q235 indicates carbon structural steel with a yield point (σs) of 235 MPa.
② If necessary, the steel number may be followed by symbols indicating the quality grade and deoxidation method. The quality grade symbols are A, B, C and D.
Deoxidation method symbols:
- F represents boiling steel; b denotes semi-finished steel;
- Z means dead steel;
- TZ means dead special steel.
Dead steel does not need to be marked, i.e. Z and TZ do not need to be marked. For example, Q235-AF represents grade A boiling steel.
③ Carbon steel for special uses, such as bridge steel or marine steel, basically adopts the expression method of carbon structural steel, but the steel number ends with a letter indicating the use.
