Threshold stress intensity factor and crack growth rate for stress corrosion cracking of simulated heat affected zone in caustic solution

The threshold stress intensity factor for stress corrosion cracking (KIscc) of the simulated heat affected zone (HAZ) of mild steel in caustic solution has been determined using circumferential notch tensile (CNT) technique. The HAZ microstructure produced upon manual metal arc welding of grade 250 steel was simulated over a length of 35 mm of CNT specimens, using a thermo-mechanical simulator. Inter- and trans-granular stress corrosion cracking has been confirmed using a scanning electron microscope. The results presented here validate the ability of CNT technique for the determination of KIscc of HAZ and Base metal. Crack growth rates have also been determined using CNT technique. Further, the effect of microstructures on KIscc and crack growth rate is discussed in the present study. The determined KIscc of Base metal and simulated heat affected zone in 30% caustic solution is 24 and 45 MPa m1/2, respectively.