Mechanical properties of thick sheets of X70 API 5L grade steel produced from heavy slab

Abstract

This work investigated the microstructure and mechanical properties of 40 mm thick sheets of low-carbon (0.06-0.07 wt.%C) (Cr, Ni, Mo, V, Nb)-micro-alloyed steel, produced from heavy slab in order to comply with the requirements of X70 (API 5L) grade. It was found that applying a heavy slab of increased thickness is feasible for the production of thick ( 30 mm) steel sheets intended for oil/gas pipelines. Using a 300 mm thick slab increases its rolling reduction by 12-36 % when producing 40 mm thick sheets which enabled the better deformation to eliminate the cast structure in the axis zone of the billet. This resulted in structure refining which enhances the lowtemperature impact behaviors (Charpy V-notch test, DWTT) of steel ensuring compliance with an X70 (API 5L) grade.