Comprehensive Analysis of Q345E Seamless Square Steel Pipe

First, Material Properties and Chemical Composition of Q345E Seamless Square Steel Pipe

Q345E seamless square steel pipe is made from the low-alloy, high-strength structural steel Q345E. Its chemical composition is strictly controlled:

Carbon: ≤0.18% to ensure the steel's basic strength; Silicon: 0.20%-0.60% to enhance oxidation resistance; Manganese: 1.00%-1.60% to enhance toughness and weldability; Phosphorus and Sulfur: ≤0.025% each to reduce brittleness.

- Alloying Elements: Vanadium 0.02%-0.15%, Niobium 0.015%-0.06%, Aluminum ≥0.015%. Microalloying refines grain size, improving strength and low-temperature toughness.

- Low-temperature toughness: Q345E's "E" grade indicates excellent impact resistance (longitudinal impact value ≥27J) at -40°C, making it suitable for low-temperature applications such as polar engineering and LNG storage tanks.

Second, the mechanical and processing properties of Q345E seamless square steel tubes.

1. Mechanical properties of Q345E seamless square steel tubes:

- Yield strength: ≥345 MPa for wall thickness ≤16 mm, ≥325 MPa for wall thicknesses 16 mm to 30 mm, and ≥295 MPa for wall thicknesses ≥30 mm;

- Tensile strength: 490 MPa to 675 MPa;

- Elongation: ≥22%;

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

2. Processing Performance of Q345E Seamless Square Steel Pipe:

- Weldability: Low sulfur and phosphorus content (≤0.025%) requires the use of low-hydrogen welding consumables, along with preheating (100-150°C) and heat treatment to prevent cold cracking.

- Cold Bending: No cracking after 180° cold bending, meeting the processing requirements of complex geometries.

- Fatigue Resistance: Optimized grain size (grade 8 and above) improves fatigue life, making it suitable for cyclic loading conditions.

Third, Q345E Seamless Square Steel Pipe Production Process and Quality Control

1. Q345E Seamless Square Steel Pipe Production Process:

- Hot Rolling: Applicable to large-sized square steel pipes (side length ≥ 100mm), high-temperature rolling at 1150°C, with a compression ratio of 6:1, ensuring grain refinement;

- Cold Drawing Finishing: Applicable to small-sized square steel pipes (side length < 100mm), a three-pass cold drawing process, surface roughness Ra ≤ 3.2μm, wall thickness tolerance ±0.2mm;

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

2. Q345E Seamless Square Steel Pipe Quality Control:

- Three-Level Inspection System: Raw material spectral testing (spectrometer); online ultrasonic flaw detection (detection accuracy Φ0.8mm flat-bottom hole); finished product mechanical testing (3000kN universal testing machine).

- Standard Certification: Complies with GB/T 8162, GB/T 6728-2017, ASTM A500, or EN10210 standards. Some manufacturers have ISO 3834 welding system certification.

Fourth, Specifications and Weight Calculation of Q345E Seamless Square Steel Tube

1. Common Specifications of Q345E Seamless Square Steel Tube:

Small Diameter: 30 × 40 × 4 mm (suitable for lightweight structures);

Medium Diameter: 150 × 150 × 10 mm (suitable for building frames);

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

2. Formula for Calculating the Weight of Q345E Seamless Square Steel Tube:

- Square Steel Tube: Weight (kg/m) = 4 × Wall Thickness × (Side Length - Wall Thickness) × 0.00785;

- Rectangular Steel Tube: Same as above, substituting the length and width for the correct dimensions.

Fifth, the application fields and advantages of Q345E seamless square steel pipe

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

(2) Bridge engineering: high bending and torsional strength, light weight (30% lighter than solid steel), and enhanced bridge span.

(3) Machinery 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 level can reach PN160), corrosion resistance (surface can be galvanized or sprayed), suitable for oil and natural gas pipelines;