Effects of high temperature austenitization on fracture, fatigue and stress corrosion cracking behavior of cast and forged high strength steels II: Fatigue and stress corrosion cracking behavior

Abstract

The effects of high temperature austenitization (h.t.a.) on fatigue crack growth rate (FCGR) and stress corrosion cracking (SCC) behavior have been studied in a high strength cast steel. Compared with the behavior of a forged steel with the same chemical composition and heat treatment, h.t.a. reduced the FCGR of both steels in the whole range of applied cyclic stress intensity Δϰ, including the near-threshold regime, linear growth and static mode regimes, but the cast steel had a slightly lower growth rate than the forged steel. A higher threshold stress intensity ϰ ISCC of SCC crack growth and lower crack growth rate (da/dt) II were also obtained in both h.t.a. forged and cast steels, but a more significant improvement was revealed in the forged steel. The microstructural origins of the difference in FCGR and SCC behavior of the forged and cast steels have been explored. The high fracture toughness and reduced intergranular segregation are responsible for the lower FCGR in the h.t.a. cast steel, whereas the larger austenite grain size of the h.t.a. forged steel is the dominant factor for its better SCC resistance. The h.t.a. is a desirable heat treatment technique for high strength cast steel owing to the concurrent improvement in monotonic fracture, FCGR and SCC resistance.