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What is the difference between Q235 and Q345B?
The primary difference between Q235 and Q345B lies in their chemical composition, mechanical properties, and typical applications, as they are two different grades of steel in the Chinese GB standard.
1. Strength:
- Q235: A low-carbon structural steel with a yield strength of 235 MPa. It is suitable for general-purpose applications where high strength is not critical.
- Q345B: A low-alloy structural steel with higher strength, offering a yield strength of 345 MPa. It is used for applications requiring greater load-bearing capacity and toughness.
2. Composition:
- Q235: Primarily consists of carbon, manganese, phosphorus, and sulfur. It has a lower carbon content, which provides good weldability but limits its strength.
- Q345B: Contains alloying elements like manganese, silicon, and sometimes trace amounts of vanadium or niobium. These elements enhance its strength, toughness, and resistance to deformation.
3. Mechanical Properties:
- Q235: Moderate tensile strength (375–500 MPa) and good ductility, making it suitable for basic structural uses.
- Q345B: Higher tensile strength (490–675 MPa) and better impact resistance, allowing it to perform well in dynamic or harsh conditions.
4. Weldability:
Both Q235 and Q345B have good weldability due to their low carbon content. However, Q345B may require pre-heating or post-weld heat treatment in thick sections due to its higher strength and alloy content.
5. Applications:
- Q235: Used in simple structural components like beams, plates, and rods in low-stress environments such as construction and manufacturing.
- Q345B: Preferred for higher-stress applications like bridges, heavy machinery, pressure vessels, and pipelines where additional strength and durability are essential.
6. Cost:
Q345B is typically more expensive than Q235 due to its enhanced properties and alloying elements.
Summary: Choose Q235 for basic structural applications where cost and ease of fabrication are priorities. Opt for Q345B when higher strength, toughness, or load-bearing capacity is required.
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