The cold brittleness (or low temperature brittleness tendency) of the cold-drawn tube is expressed by the ductile-brittle transition temperature Tc. The TC of high-purity iron (0.01%C) is -100 ℃ , and it is completely brittle below this temperature. Most of the alloying elements in cold-rolled precision bright steel pipes increase the ductile-brittle transition temperature and cold-brittle tendency of cold-rolled precision bright steel pipes. The ductile fracture of cold-rolled precision bright steel pipe above room temperature is dimple fracture, and the brittle fracture at low temperature is cleavage fracture.
The reasons for the low temperature embrittlement of cold drawn tubes are:
(1) When the dislocation generated by the dislocation source is blocked by obstacles (such as grain boundaries and second aliquots) during the deformation process, the local stress exceeds the theoretical strength of the cold-rolled precision bright steel pipe, resulting in microcracks.
(2) Several stacking dislocations synthesize a microcrack at the grain boundary.
(3) The reaction at the intersection of two {110) slip bands leads to fixed dislocations %26lt; 010%26gt;, forming wedge-shaped microcracks that can crack along the {100} cleavage plane.
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