1. Q: What material is GB/T 712 AH690 steel pipe made of?
A: It is a high-strength steel for hull structures specified in the Chinese national standard (GB/T 712). AH690 indicates a yield strength of 690 MPa or higher. It is an ultra-high-strength steel with excellent weldability, low-temperature toughness, and corrosion resistance. It is specifically designed for use in critical load-bearing structures such as ships and marine engineering.
2. Q: What are its chemical composition and mechanical properties?
A:
Composition: Low-carbon (C ≤ 0.18%) as a base, with alloying elements such as Mn, Ni, Cr, and Mo added to enhance strength and toughness.
Performance: Yield strength ≥ 690 MPa, tensile strength ≥ 770-940 MPa, elongation ≥ 14%, and excellent low-temperature impact toughness (maintaining high toughness even at -40°C).
3. Q: What are its main applications?
A: It is primarily used in large vessels (such as aircraft carriers and LNG carriers), offshore platforms, and submarine pressure hulls, where material strength, impact resistance, and seawater corrosion resistance are extremely demanding.
4. Q: What are its advantages over ordinary ship plate steel (such as AH36)?
A:
Higher strength: AH690's yield strength is nearly twice that of AH36 (355 MPa), significantly reducing structural weight.
Better low-temperature toughness: Suitable for polar vessels or deep-sea equipment.
More stringent welding procedures: High-strength welding consumables and preheating measures are required to prevent cold cracking.
5. Q: What precautions should be taken when purchasing or using it?
A:
Confirm the delivery status (such as quenching and tempering heat treatment).
Check third-party test reports (especially impact test and Z-axis properties).
Follow specific welding procedures to avoid embrittlement in the heat-affected zone.
