Stress-corrosion cracking behavior of an 18 Pct Ni maraging steel

Stress-corrosion cracking of an 18 pct Ni maraging steel in aqueous solutions was studied using precracked cantilever beam specimens. By appropriate heat treatments, six different structures having the same yield strength were obtained. Although significantly different plane strain fracture toughness values (K _Ic ) resulted, it was found that the threshold plane strain stress intensity (K _Iscc ) was the same for all structures.K _Iscc had the same value in 3 pct NaCl at various pH values, in 1N H₂SO₄, and in distilled water. Specimens tested in 3 pct NaCl under both anodic and cathodic applied potentials also exhibited this sameK _Iscc value. Fractographic inspection of the crack surfaces revealed no apparent differences due to changes in solution, pH, or applied potential. The crack path was intergranular in all cases. However, specimens austenitized at 1500°F exhibited crack branching, whereas in specimens austenized at much higher temperatures branching no longer occurred. Aging time and temperature seemed to change only the time to failure. The mechanism most consistent with all observations appears to be hydrogen cracking.