The present work evaluates the sulfide corrosion cracking susceptibility of nanostructured bainitic steel with a dual-phase structure of bainite and retained austenite. Notch Tensile Slow Strain Rate Testing (NTSSRT) method was employed to assess the threshold stress intensity values (KISSCC). Microscopic morphology and analysis of fracture surface were carried out by scanning electronic microscope (SEM). Hydrogen sulfide (H2S) concentration with the range from 0.02 mole% to 35 mole% and pH value of 3.5 and 5.5 were controlled in 1% sodium chloride (NaCl) solution using sodium acetate/acetic acid buffer solution.

The results show that KISSCC values are much lower in a more acidic environment. Heat treatment makes nanostructured steel more susceptible to SSC. Many secondary cracks were observed on the fracture surface, which may initiate from quasi cleavage caused by hydrogen in brittle fracture region. Inclusions can accelerate the crack propagation and failure process. Microscopic observation shows cracks can initiate from or arrested in austenite. Further relation between crack propagation and microstructure can be explored by employing Electron Backscatter Diffraction (EBSD) technique.

Subject
Hydrogen sulfide, Hydrogen concentration, Notches, Crack initiation, Fracture surfaces, Corrosion cracking, Stress cracking, Acidity, Steel, Brines, Sulfide stress cracking, Austenite, Hydrogen
Keywords:
Nanostructured steel, sulfide stress corrosion cracking, pH, hydrogen sulfide concentration
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2021
Association for Materials Protection and Performance (AMPP)
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