Changes in Corrosion Resistance of 18%Cr-12%Ni-Type Stainless Steels After Sensitization Available to Purchase

Intergranular corrosion resistances of 18%Cr-12%Ni-2.5%Mo and 18%Cr-12%Ni-0.64%Ti austenitic stainless steels annealed at 723 K to 1,223 K were examined by two electrochemical potentiostatic reactivation (EPR) methods (single-loop and double-loop) and by the Strauss test. The 18%Cr-12%Ni-0.64%Ti steel was subjected to three thermal cycles in a device for simulating thermal-deformation welding cycles prior to annealing. The time-temperature sensitization diagrams for the analyzed steels were constructed. Corrosion resistances of the steels were related to results of phase analysis performed with the help of energy dispersive x-ray spectroscopy (EDX) and electron diffraction. The M₂₃C₆ carbide was found to be the dominant phase responsible for the sensitization of both investigated steels. The sensitizing effect of σ-phase was considered to be a secondary influence, particularly in Ti-stabilized steel.