The effect of delta-ferrite content on the stress corrosion cracking of austenitic stainless steels in a sulphate solution

Abstract

The susceptibility to stress corrosion cracking of a CF3 cast austenitic stainless steel, heat treated to generate a range of delta-ferrite contents, and weld metal that contained either 0 or 6% delta-ferrite has been assessed in a buffered, sulphate environment at 250°C using slow strain rate and constant displacement tests under open circuit conditions and at various applied electrode potentials. The susceptibility to cracking of the CF3 material decreased with increasing delta-ferrite content in the range 2–7% and the 0% delta-ferrite weldment was more susceptible to cracking than the 6% weldment. Sensitization increased the susceptibility of the 0% deltaferrite weldment but had little effect on the 6% weldment. Bolt-loaded WOL data for the weldments indicated that the plateau crack growth rates were higher and the K Iscc values lower for the 0% than the 6% delta-ferrite material. Plateau crack growth rates were ~ 10 −7 mm/s for the 6% delta ferrite weldment and ~ 10 −5 mm/s for the 0% delta ferrite weldment. For the test conditions investigated, the CF3 steel was less susceptible to stress corrosion cracking than either of the weldments.