Here's a detailed introduction to Q345, Q345A, Q345B, and Q345C alloy steel plates, covering their definitions, differences, properties, applications, and standards:

1. Overview of Q345 Alloy Steel Plate

Designation Origin:

 

Q: Represents  (Yield Strength in Chinese pinyin).

345: Indicates the minimum yield strength of 345 MPa (applicable to thickness ≤16mm).

Classification (A/B/C/D/E): Denotes different quality grades, primarily distinguished by

 

Type:
Low alloy high-strength structural steel, widely used in general engineering and structural applications.

2. Key Differences Between Q345A/Q345B/Q345C

Grade	Impact Test Temperature	Impact Absorbed Energy (KV2, J)	Max Carbon Content (%)	Max Sulfur/Phosphorus Content (%)	Application Scenario
Q345A	No requirement	-	≤0.20	S≤0.045, P≤0.045	Non-critical structures without impact load
Q345B	20℃	≥34	≤0.20	S≤0.045, P≤0.045	General structures in normal temperature
Q345C	0℃	≥34	≤0.20	S≤0.040, P≤0.040	Structures requiring low-temperature toughness (e.g., northern regions)
Note: Q345D (-20℃) and Q345E (-40℃) exist but are less common in this query.

Core Variations:

Impact Toughness: Grades A to C progressively improve resistance to brittle fracture in lower temperatures.

Impurity Control: Q345C has stricter limits on S/P (sulfur/phosphorus) to enhance ductility and toughness.

3. Chemical Composition

(Typical values for thickness ≤16mm, per GB/T 1591-2018)

 

 Mechanical Properties

Grade	Yield Strength (ReL, MPa)	Tensile Strength (Rm, MPa)	Elongation (A, %)	Bending Test (d=2a)
Q345A/B/C	≥345 (≤16mm)	470-630	≥21	180° bending without cracks

 

 

 

 

 

 

 

 

 

Key Performance Features:

Strength: Higher than ordinary carbon steel (e.g., Q235) but lower than ultra-high-strength grades like Q690.

Weldability: Good due to low carbon content; suitable for most welding methods (e.g., arc welding, gas shielded welding).

Formability: Can be cold-formed, rolled, or machined for complex structural shapes.

 

 

 

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