Abstract
Sulfide cracking of mild steel at a constant strain rate of 4.4×10−5 sec−1 in H2S solutions was studied by scanning electron microscopy. Particular attention was given to effects of pH, applied potential and temperature on the morphology of the fracture surface of the steel. The following results were obtained.
(1) The mild steel specimens exhibit mainly transgranular quasi-cleavage fracture at the open circuit potential in acidic H2S solutions.
(2) The specimens also show mainly transgranular quasi-cleavage fracture when a large quantity of hydrogen is absorbed by cathodic polarization, while under anodic polarization or at high pH, a ductile dimple pattern becomes predominant on the fracture surface.
(3) Nucleation sites of cracks appear to be carbides in the pearlite, inclusions or grain boundaries.
(4) Intergranular corrosion and cracks are observed on the steel surface. However, intergranular corrosion does not lead to the rupture of the steel.
It follows from above results that the sulfide cracking of mild steel is attributed to hydrogen embrittlement.
