Disqualification of Seamless Pipe Mechanical Properties

The unqualified mechanical properties of seamless steel pipe mainly in its low elongation, yield point is not obvious, the mechanical properties of the above unqualified products metallographic examination and found that the cold-drawn tube spherical pearlite and fine grain ferrite .


Spherical pearlite is a typical lack of annealed tissue. Normal cold drawing process requirements, microstructure after annealing ferrite and pearlite flake should be spherical pearlite, forming a temperature of 750 ~ 830 ° C, spherical pearlite, indicating that the annealing temperature is low, the lack of annealing.


Very small ferrite is also insufficient annealing organization, the spherical pearlite formation conditions are different. When the annealing temperature is low, the formation of spherical pearlite, annealed annealing temperature suitable, fine grains, time is short. Cold-drawn steel after annealing, the matrix microstructure, ferrite deformation and destruction, internal stress, easy to crack, after drawing the drawing between the various passes and the final mold should be properly annealed to restore grain growth, eliminate stress. When the annealing time is short, ferrite grains grow too late to recover easily and form fine ferrite grains. Under normal conditions, the ferrite grain size is generally about 8, the fine grain ferrite grain size is greater than 10, fine grain on the one hand so that the steel strength is greatly increased, resulting in plasticity decreased. Therefore, the grain is too small, steel elongation is generally unacceptable.