Abstract
Low-carbon high-strength steel was investigated by ultra fast cooling (UFC) processing. The results have shown that the microstructures of both steels were all composed of quasi polygonal (QF), acicular ferrite (AF) and granular bainite (GB). The mechanical properties of low-carbon steel all meet the standard requirements of linepipe steels, this is attributed to the effect of the ferrite grain refinement which is resulted in UFC processing. MA islands are more finely dispersed in steel B. Nanoprecipitates which were likely to form at lower temperatures during or after UFC in steel B are finer and more dispersed than those in steel A. Therefore, steel B has higher ultimate tensile strength (UTS) and yield strength (YS). The Charpy absorbed energy (AK) of steel B exhibited a high value. This is because the amount of AF in steel B is much more than that in steel A. A great deal of acicular ferrite grain boundary inhibit growing cleavage crack in steel B.
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