Q: What do Q235 and Q345 designate?
A: They are Chinese steel grade designations per GB/T standard. 'Q' stands for Yield Strength (Qu fu dian). The number indicates the minimum yield strength in MPa at ≥16mm thickness. Q235 has ≥235 MPa, Q345 has ≥345 MPa.
Q: What is the main mechanical difference?
A: The primary difference is the yield and tensile strength. Q345 has significantly higher strength (higher load-bearing capacity) than Q235.
Q: Are they equivalent to common international grades?
A: Approximately, Q235 is similar to ASTM A36, S235JR, SS400. Q345 is similar to ASTM A572 Gr.50/51, S355JR, SM490.
Q: What are their chemical compositions?
A: Both are carbon-manganese steels. Q235 has lower C, Mn, and micro-alloy (like V, Nb) content. Q345 has higher Mn and often contains micro-alloys for strength.
Q: Which one has better weldability?
A: Generally, Q235 has better weldability due to its lower Carbon Equivalent (CE). Q345 requires more controlled welding procedures (pre/post-heat may be needed for thick sections).
