Why was the new national standard changed to Q355?
Answer: GB/T 1591-2018 (implemented on February 1, 2019), the yield strength was increased to 355MPa, and the composition was slightly adjusted.
12. What is the common thickness range for Q345?
Answer: 6–200mm, commonly 6/8/10/12/16/20/25/30/40/50mm.
13. What are the delivery conditions?
Answer: Hot-rolled (most common), normalized, TMCP (controlled rolling and controlled cooling, E grade).
14. Why is Q345A rarely used?
Answer: No impact requirements, high levels of harmful elements, cannot be used for welding critical structures.
15. Which grade is used for pressure vessels?
Answer: Special grade Q345R, corresponding to C/D/E; cryogenic vessels must be E grade.