Microstructural evaluation of APIX80 steels in different thermal cycles

In this work a microstructural evaluation of the influence of thermal cycling was carried out on three API5L X80 grade steels: Nb-Cr Nb-Cr-Mo and Nb-Cr-Mo-V manufactured in Brazil. These steels were manufactured using a controlled thermo-mechanical process without undergoing a subsequent accelerated cooling stage. Microstructural characterisations were carried out under two conditions post-rolling and austenitising at 900oC followed by three (3) thermal cycles: cooling in air (1.5oC/s) in oil (30oC/s) and in water (115oC/s). Data such as TG phase distribution: ferrite bainite and AM hardness and micro-hardness were analysed as well as checking for differences in their substructures: subgrains cells and fine precipitation.