What is the Q345NH weathering steel plate annealing and normalizing overheating?

Overheat is due to the heating temperature is too high to make the grain obviously grow up, so that after cooling, the structure of the workpiece coarsening, mechanical properties become bad, especially the impact toughness decreased significantly a defect.

The superheated workpiece usually causes the increase of deformation and cracking tendency after heat treatment.
And the heat preservation time is also easy to produce overheating phenomenon.

According to the difficulty of removing superheated tissue by normal heat treatment process, the superheated tissue can be divided into stable superheated tissue and unstable superheated tissue. General superheated tissue can be eliminated by normal heat treatment, which is called unstable superheated tissue. Stable superheated tissue refers to the superheated tissue which cannot be completely eliminated by normal normalizing, annealing and quenching treatment.