Kinetics of thermal aging and its effect on the proneness of hull steels to brittle failure

Abstract

1. The hull steels 10GN2MFA and 15Kh2NMFA-A have little proneness to aging) this is in keeping with the requirements that modern shell materials have to fulfill. 2. The activation energy of the process of thermal aging (Q=70–80 kJ/mole) is close to the activation energy of diffusion of carbon in ferrite. The magnitude of the activation energy, and also the nature of the change of strength and fracture toughness make it reasonable to assume that in the steels 15Kh2NMFA-A and 10GN2MFA the aging process is determined by the state of the carbide phase. 3. The use of the constant in the Khollomon equation (α=3.5–4.5), which was experimentally established for the temperature range 250–400°C, and 10GN2MFA upon aging. 4. Aging for up to 6500 h causes a shift of the temperature dependence of the fracture toughness of steel 15Kh2NMFA-A into the range of higher temperatures, and it also increases fracture toughness at low temperatures (below −100°C).