Effects of different austenitization treatments on K IC,K ISCC,and other mechanical properties of 300M steel bar

The effects of different austenitization treatments on the plane strain fracture toughness K_IC, the stress corrosion threshold stress intensity factor K_ISCC, the fatigue crack growth rate, and the transverse tensile properties of 300M bar have been investigated over the tempering range 230°–560°C. Rapid austenitization and high-temperature austenitization treatments have been compared with the conventional heat treatment, since these treatments have been reported to increase the K_IC of medium-carbon steels without impairing their tensile strengths. For the standard 320°C temper, rapid austenitization decreased K_IC but increased the tensile strength and 0·2% proof stress, whereas high-temperature austenitization treatments increased K_IC up to 30%, slightly decreased the 0·2% proof stress, and above 1130°C caused a 50% decrease in the reduction in area. Neither the K_ISCC nor the fatigue crack growth rates in 1M NaCl, were affected by austenitization treatment. Reasons for the observed K_IC variations with austenitization treatment are discussed.