Effect of accelerated cooling after controlled rolling on the hydrogen induced cracking resistance of line pipe steel.

Abstract

The effect of accelerated cooling after controlled rolling on the hydrogen induced cracking (HIC) resistance of line pipe steels produced from continuously cast slabs was examined, and the relation between HIC resistance and the microstructure in the segregated zone at the mid-thickness of plate was clarified. The optimization of accelerated cooling conditions reduced the volume fraction of high carbon martensite or upper bainite formed in the segregated zone, and this resulted in significant improvement of HIC resistance. The above result can be explained by the model that the high cooling rate as well as the optimized start and stop temperatures in accelerated cooling suppress the rejection of carbon from the non-segregated area to segregated zone during the austenite to ferrite transformation causing the more uniform profile of carbon distribution in the through-thickness direction of plate.