Study on the static and dynamic fracture mechanism of different casing-drilling steel grades

The tensile and impact properties of three different types of casing drilling steels were investigated. Results show that P110 exhibits a higher yield and ultimate tensile strength compared with the N80 and K55 specimens. All tensile fractures follow the dimple fracture mechanism. The impact toughness values of N80 and P110 steels show no remarkable difference. However, both N80 and P110 absorb up to about five times the impact energy absorbed by the K55 specimen. The impact fractures of the K55 and P110 steels exhibit cleavage and ductile fracture mechanisms, respectively, whereas N80 steel primarily follows quasi-cleavage and ductile fracture mechanisms. The microstructures underneath the tensile fracture surface show noticeable deformation compared with those underneath the impact fracture surface. K55 steel microstructure variance in the tensile process is affected by the size of the inclusions as well as by the orientation relative to the inclusion and the normal stress.