Tianjin Brisk Steel is one of the manufacturers of Cold Formed ERW Rectangular Hollow Section in China. Our products are mainly exported to the Middle East, Southeast Asia, Europe, New Zealand, and other regions.If you would like to learn more about our products, feel free to contact us and send your purchase list.
Technical of Rectangular Steel Tube
Sourcing structural hollow sections for international industrial codes requires a clear understanding of the mechanical and metallurgical principles behind the product:
- The High-Frequency Induction (HFI/ERW) Process: Our RHS lines utilize premium structural carbon steel strip coils that are progressively cold-rolled into shape at room temperature. The longitudinal seam is continuously forged using high-frequency electrical resistance. This molecular bonding process requires zero filler metals, ensuring the weld line retains structural characteristics identical to the parent steel body.
- The Structural Cold-Forming Advantage: Cold forming work-hardens the steel matrix, naturally increasing both the yield strength and tensile strength of the section compared to its raw sheet state. This provides an incredibly cost-effective alternative to hot-finished profiles for the vast majority of general civil and industrial framing applications.
Mainstream Heat Treatment Processes
Annealing (+A)
- Process: Heating and holding at temperature, followed by slow cooling.
- Function: Eliminates residual stresses from cold bending or welding; softens the material; enhances plasticity for bending and stamping (prevents cracking during bending).
- Applications: Furniture, decorative items, bent structural components (e.g., black annealed square hollow sections).
Normalizing
- Process: Heating to a critical temperature followed by air cooling.
- Function: Refines grain structure and homogenizes the microstructure; improves strength, toughness, and machinability.
- Applications: General mechanical structures, brackets/supports.
Quenching and Tempering (Q&T)
- Process: High-temperature quenching → rapid cooling (oil or water) → tempering at 500–650°C.
- Advantages: Balances high strength and high toughness; offers significantly superior fatigue resistance and load-bearing capacity compared to standard square tubes.
- Applications: Construction machinery, lifting equipment, heavy-duty steel structures, vehicle chassis.
Stress Relief Annealing
- Function: Specifically eliminates internal stresses caused by welding seams or cold forming processes; prevents subsequent deformation or cracking.
Key advantages over standard SHS:
- Uniform internal microstructure; significantly reduced stress concentration at the corners.
- Relieved residual stress minimizes deformation during subsequent welding or machining.
- Quenched and tempered versions offer significantly higher yield and tensile strength, enabling lightweight, load-bearing applications.
- Annealed versions offer excellent ductility, suitable for pipe bending, folding, and stamping.
- Superior fatigue performance, making them ideal for equipment subject to dynamic loads.
- Heat treated square hollow sections with full body quenching & tempering for high load machinery.
- Stress-relief annealed SHS eliminates forming residual stress for easy bending & fabrication.
- Normalized square hollow sections comply with EN 10219 & ASTM A500 for structural construction.
FAQ
Q: How does a heat-treated SHS tube compare to a standard cold-formed SHS tube during heavy field welding?
A: During field welding on heavy cold-formed SHS, the extreme heat of the weld arc creates an uneven temperature gradient that reacts with the locked-in cold-forming stresses. This often results in localized distortion or micro-cracking in the Heat-Affected Zone (HAZ). A heat-treated SHS has no residual stresses to release, ensuring that the HAZ cools evenly and retains high toughness without requiring intensive pre-heating cycles.
Q: What is the impact of post-forming heat treatment on the "Yield Strength" profile of the tube corners?
A: Cold forming artificially boosts the yield strength in the corners of a square tube via strain hardening, but at the expense of material elongation and impact resistance. Post-forming normalizing resets the crystal structure. While this slightly lowers the artificial hardness spike in the corners, it establishes a uniform yield strength across the whole section and dramatically boosts material ductility (Elongation ≥22%), ensuring safe energy absorption under overload conditions.
Q: Why is heat-treated SHS specifically mandated for mobile crane booms and mining equipment?
A: Mobile crane booms and heavy mining structures experience intense, repetitive dynamic loads and severe vibration. Under these conditions, any internal manufacturing stresses or hard, brittle corners act as initiation sites for fatigue cracks. Heat-treated SHS provides an isotropic, fine-grain microstructure with uniform toughness, giving the chassis high resistance to dynamic fatigue failure over long operational lifespans.
Q: How does your factory verify that full-body normalization has been achieved throughout heavy-wall square tubes?
A: We enforce strict metallurgical quality control. In addition to continuous furnace temperature recording, samples from every heat-treated production lot are subjected to Microstructural Metallographic Analysis under optical microscopes to verify complete grain refinement. This is complemented by full-body Hardness Testing across flat and corner zones, destructive Charpy Impact Testing, and 100% Ultrasonic Testing (UT) to guarantee defect-free internal structure.
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