Disqualification of Seamless Pipe Mechanical Properties

Keywords:Disqualification of Seamless Pipe Mechanical Properties
Seamless pipe mechanical properties failed mainly in its low elongation and yield point is not obvious, the mechanical properties of the above-mentioned non-conforming product samples for metallurgical testing, found cold drawn pipe spherical pearlite organization and very fine grains ferrite.

Globular pearlite structure is a typical annealing inadequate organization. Normal cold drawing process requirements, the microstructure after annealing should be ferrite and pearlite flaky globular pearlite formation temperature is 750 ~ 830 °C, so the globular pearlite, suggesting that the low annealing temperature, annealing insufficient.

Extremely fine grains of ferrite is also an annealing inadequate organization, and its globular pearlite formation conditions are different. Globular pearlite is formed when the annealing temperature is low, and the very fine ferrite grain structure is appropriate at the annealing temperature and time is short form. After the cold-drawn steel is not annealed fine matrix structure is broken ferrite deformation, internal stress is large and easy to crack, so each drawing between system passes and finished pass after drawing system should be properly annealed recovery grow grains, eliminate stress. If the annealing time is short, the ferrite grains grow too late to recover, it will form a very fine ferrite grains. Under normal conditions the ferrite grain size is generally about 8, and the ferrite grain size of the fine is also finer than 10, the fine grains on the one hand to make a substantial increase in the strength of steel, and lead to plastic reduce. So the grain is too small, the elongation of steel is generally unacceptable.
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