Determination of crack growth rate and threshold for caustic cracking (KIscc) of a cast iron using small circumferential notched tensile (CNT) specimens

A novel fracture mechanics technique has been employed for the determination of crack growth rate and threshold stress intensity factor (KIscc) for stress corrosion cracking (SCC) using small circumferential notch tensile (CNT) specimens. The technique was applied successfully for testing SCC susceptibility of spheroidal graphite (SG) cast iron in 5 M NaOH at 100 and 120 °C. Crack growth rate of SG cast iron in 5 M NaOH solution at 100 and 120 °C has been determined at different stress intensity factors (KI), and the KIscc have been determined to be 11.2 and 9 MPa m1/2, respectively. The surfaces of fractured specimens have been examined by scanning electron microscopy (SEM) in order to establish intergranular propagation of stress corrosion cracks. CNT testing is a simple, relatively fast and cost-advantageous approach for generating crack growth rate and KIscc data.