Characteristics, Processing Performance, and Manufacturing Process Details of Q345E Seamless Square and Rectangular Steel Pipes

First, the Material Characteristics and Chemical Composition of Q345E Seamless Square and Rectangular Steel Pipes.

Q345E seamless square and rectangular steel pipes use low-alloy high-strength structural steel Q345E as the core material, with strict control over its chemical composition:

Carbon: ≤0.18%, ensuring the basic strength of the steel; Silicon: 0.20%~0.60%, improving oxidation resistance; Manganese: 1.00%~1.60%, enhancing toughness and weldability; Phosphorus and Sulfur: both ≤0.025%, reducing brittleness;

Alloying elements: Vanadium: 0.02%~0.15%, Niobium: 0.015%~0.06%, Aluminum: ≥0.015%, refining grains through microalloying to improve strength and low-temperature toughness.

Low-Temperature Toughness: The "E" grade of Q345E indicates that it maintains excellent impact performance (longitudinal impact value ≥27J) even at -40℃, making it suitable for low-temperature applications such as polar engineering and LNG storage tanks.

Second, Mechanical and Technological Properties of Q345E Seamless Square and Rectangular Steel Tubes

1. Mechanical Properties of Q345E Seamless Square and Rectangular Steel Tubes:

Yield Strength: ≥345MPa for wall thickness ≤16mm, ≥325MPa for 16mm~30mm, ≥295MPa for ≥30mm;

Tensile Strength: 490~675MPa;

Elongation: ≥22%;

Hardness: Brinell hardness (HB) ≤217, Rockwell hardness (HRC) ≤15.

2. Processing properties of Q345E seamless square and rectangular steel pipes:

Weldability: Low sulfur and phosphorus content (both ≤0.025%). Low-hydrogen welding materials and preheating (100~150℃) and heat treatment are required during welding to avoid cold cracking.

Cold bending performance: No cracks after 180° cold bending, meeting the requirements for processing complex geometries.

Fatigue resistance: Fatigue life is improved through optimized grain size (level 8 or above), suitable for cyclic loading conditions.

Third, Production Process and Quality Control of Q345E Seamless Square and Rectangular Steel Pipes.

1. Production Process of Q345E Seamless Square and Rectangular Steel Pipes:

- Hot Rolling: Suitable for large-specification square and rectangular steel pipes (side length ≥ 100mm), rolled at 1150℃ with a compression ratio of 6:1 to ensure grain refinement;

- Cold Drawing and Finishing: Suitable for small-specification pipes (side length < 100mm), three-pass cold drawing process, surface roughness Ra ≤ 3.2μm, wall thickness tolerance ±0.2mm;

- Heat Treatment: Normalizing (880~940℃) + tempering to eliminate internal stress and improve toughness.

2. Quality Control of Q345E Seamless Square and Rectangular Steel Pipes:

Three-level Testing System: Raw material spectral analysis; online ultrasonic flaw detection (detection accuracy of Φ0.8mm flat-bottomed hole); finished product mechanical testing (3000kN universal testing machine).

3. Standard Certifications for Q345E Seamless Square and Rectangular Steel Tubes: Compliant with GB/T 8162, GB/T 6728-2017, ASTM A500, or EN10210 standards. Some manufacturers have passed ISO3834 welding system certification.

Fourth, Specifications and Weight Calculation of Q345E Seamless Square and Rectangular Steel Tubes.

1. Common Specifications of Q345E Seamless Square and Rectangular Steel Tubes:

Small Diameter: 30×40×4mm (suitable for light structures); Medium Diameter: 150×150×10mm (for building frames);

Large Diameter: 300×300×20mm (suitable for bridge main beams).

2. Weight Calculation Formula for Q345E Seamless Square and Rectangular Steel Tubes:

Square and Rectangular Steel Tubes: Weight (kg/m) = 4 × Wall Thickness × (Side Length − Wall Thickness) × 0.00785;

Rectangular Steel Tubes: Same as above, substitute the length and width dimensions.

Fifth, Application Areas and Advantages of Q345E Seamless Square and Rectangular Steel Pipes.

1. Building Structures: High strength (yield strength ≥ 345MPa) and good seismic resistance, suitable for high-rise buildings, stadiums, etc.

2. Bridge Engineering: High bending and torsional strength, lightweight (30% weight reduction compared to solid steel), enhancing bridge spans.

3. Mechanical Manufacturing: Good weldability and cold-bending performance, suitable for dynamic load components such as crane booms and vehicle frames.

4. Energy Transmission: High-pressure resistance (pressure rating up to PN160), corrosion resistance (surface can be galvanized or powder-coated), suitable for oil and natural gas pipelines.