THE EFFECT OF DELTA-FERRITE CONTENT ON THE STRESS-CORROSION CRACKING OF AUSTENITIC STAINLESS-STEELS IN A SULFATE-SOLUTION

The susceptibility to stress corrosion cracking of a CF3 cast austenit ic stainless steel, heat treated to generate a range of delta-ferrite contents, and weld metal that contained either 0 or 6% delta-ferrite h as been assessed in a buffered, sulphate environment at 250 degrees C using slow strain rate and constant displacement tests under open circ uit conditions and at various applied electrode potentials. The suscep tibility to cracking of the CF3 material decreased with increasing del ta-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% delta-ferrite weldment but had little effect on the 6% weldment. Bolt-loaded WOL data for the weldmen ts indicated that the plateau crack growth rates were higher and the K -Iscc values lower for the 0% than the 6% delta-ferrite material. Plat eau crack growth rates were similar to 10(-7) mm/s for the 6% delta fe rrite weldment and similar to 10(-5) mm/s for the 0% delta ferrite wel dment. For the test conditions investigated, the CF3 steel was less su sceptible to stress corrosion cracking than either of the weldments.