EFFECT OF COOLING RATE ON MICROSTRUCTURE OF DEFORMED AND UNDEFORMED X80 PIPELINE STEELS
Received date: 2010-01-05
Revised date: 2010-04-16
Online published: 2010-08-10
Supported by
Supported by the Fundamental Research Funds for the Central Universities (No.N090607002), National Natural Science Foundation of China (No.50474015) and State Key Laboratory Self–determination Foundation (No.RAL–SD–2008–2)
The effects of cooling rate and deformation on microstructures of an X80 pipeline steel were investigated by thermo–mechanically simulated tests heated up to the same temperature and cooled at different rates under 0 and 0.7 true strain deformation. The results reveal that the start temperature for bainite transformation will be increased by 30—80 ℃higher under 0.7 true strain than under no deformation. But the increase of cooling rate depresses the start temperature for bainite transformation and accelerates the progress of its transformation. It is found that the microstructure of the cooled samples without deformation is all composed of bainite with prior austenite grain boundaries (PAGB), but it is complicated for the cooled samples under 0.7 true strain. In the range of 1—40 ℃/s, with the increase of cooling rate, microstructures appeare successively such as polygonal ferrite, quasi–polygonal ferrite, massive ferrite, granular bainite, acicular ferrite (+ granular bainite) and athy bainite. Full martnsite steel can be acheved by quenching. Under current experiment conditions, acicular ferrite can be obtained n the steel at cooling rates of 10—20 ℃/s. In this cooing ate range, the fraction of high angle grain boundaries (HAGBs) inceases and the grain size decreases with the increase of cooling rate.
DENG Wei , DIAO De-Wen , QIN Xiao-Mei , DU Lin-Xiu , GAO Xiu-Hua , GAO Xin . EFFECT OF COOLING RATE ON MICROSTRUCTURE OF DEFORMED AND UNDEFORMED X80 PIPELINE STEELS[J]. Acta Metall Sin, 2010 , 46(8) : 959 -966 . DOI: 10.3724/SP.J.1037.2010.00005
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