Flaw detection requirements?
Important structures: UT (ultrasonic) Class I; Pressure vessels: UT+MT/PT.
Relationship with 16Mn?
Q345 = old 16Mn (old grade), same composition/properties, only standard updated.
High-temperature performance?
Stable at long-term ≤**450℃**; strength decreases significantly >500℃, unsuitable for high-temperature pressure applications.
Fatigue performance?
Good, fatigue limit ≈170–200MPa, suitable for dynamic loads (bridges/cranes).
Hardness?
HB 150–180, lower than quenched and tempered steel, easy to machine.