Continuous cooling transformation behaviour of high strength microalloyed steels for linepipe applications

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Continuous cooling transformation behaviour of high strength microalloyed steels for linepipe applications

Manohar, P.A. / Chandra, T.

Continuous cooling transformation (CCT) behaviour of microalloyed steels containing two different levels of Mn+Si additions is investigated in undeformed and thermomechanically processed conditions using dilatometry. The deformation schedule used in the dilatometer is designed to simulate controlled rolling procedures for the production of plates. CCT diagrams are constructed. Effects of thermomechanical processing (TMP), accelerated cooling and composition on gamma transformation start temperature (Ar3), phase transformation kinetics, CCT diagrams and microhardness are investigated. The results show that TMP accelerates the onset of gamma/alpha transformation (Ar3 is raised), but the progress is retarded. Significant retardation is observed during the final 30 % of the transformation reaction. Increase in cooling rate lowers Ar3 and accelerates the progress of transformation. The steel with higher Mn+Si addition exhibits lower Ar3, sluggish transformation kinetics and higher hardnesses compared with steel with lower Mn+Si addition. Increase in cooling rate increases the microhardness while TMP lowers it.