Study on M/A islands in pipeline steel X70

Chunming Wang, Xingfang Wu, Jie Liu, and Ning’an Xu Materials Science and Engineering School, University of Science and Technology Beijing, Beijing 100083, China Anshan Iron & Steel Group Corporation, Anshan 114021, China

摘 要：<正>The fine structure of M/A islands in pipeline steel X70 has been studied by transmission electron microscope （TEM）. It is shown that the M/A islands are about 1-2 μm in size and distribute at the grain boundary of irregular massive ferrite or acicular ferrite in the microstructure of the steel undergoing TMCP （thermo-mechanical controlled processing）. The analysis of diffraction contrast shows that the M/A islands consist of retained austenite and some martensite lamellae different in size and orientation. The microt winning and midrib exist in the lamella of lenticular martensite, which exhibit the typical character of high-carbon martensite. The influences of TMCP parameters on M/A islands have been studied carefully. With the increase of the cooling speed, the amount of M/A islands decrease slightly and the morphology of M/A islands changes to thin dispersive short bars from thick irregular long strips.

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