Mechanism of Internal Fracture of Shot Peened Maraging Steel
Norio KAWAGOISHI, Takanori NAGANO, Michihiko MORIYAMA, Yoshihisa OHZONO and Eiji KONDO
Abstract:Rotating bending fatigue tests were carried out for a shot peened maraging steel in order to investigate the influence of reverted austenite on the internal fracture. Fracture initiated from an internal inclusion regardless of the formation of reverted austenite in long life region, while fracture occurred from a rough surface of specimen in short life region. Although fatigue strength was decreased when surface fracture occurred, that for an internal fracture was increased conversely by the formation of reverted austenite. Many intergranular cracks generated after the formation of flat facets around an inclusion and then fractured by the growth of a surface crack in case of no reverted austenite, while by the formation of reverted austenite intergranular cracking was suppressed and the growth process of an internal crack presented after intergranular cracking. Consequently, an orbit trace was formed clearly at the boundary between the growth of an internal crack and that of a surface crack. Key Words:Fatigue, Maraging steel, Shot peening, Rotating bending, Internal fracture, Reverted austenite, Intergranular crack