2009•Cailiao rechuli xuebaoRequires access
Effect of Mo addition on microstructure and CCT curves of Nb microalloyed pipeline steel
Huang Jian, Qingyou Liu
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Abstract
CCT curves of Nb microalloyed and Nb-Mo microalloyed X80 pipeline steels were determined.Microstructure of the steels under different processing conditions were investigated by means of optical microscope,scanning electronic microscopy and transmission electron microscopy.The results show that microstructure of the steels changes from polygonal ferrite and quasi-polygonal ferrite to acicular ferrite with increase of cooling rates and the grains are refined at the same time.Significant change of the microstructure is observed at low cooling rates,when cooling rates exceed 5℃/s,microstructure which consists of acicular ferrite and M-A islands remains unchanged,but it becomes more uniform and M-A islands are finer and more dispersed.Mo addition is able to make transformation line of acicular ferrite of CCT curves right shift and promotes formation of acicular ferrite.