The initiation and propagation of chloride-induced transgranular stress-corrosion cracking (TGSCC) of 304L austenitic stainless steel under atmospheric conditions

• Cracking consistent with corrosion enhanced plasticity model of Magnin.
• Cracking stress threshold is 10 MPa, substantially lower than current guidance.
• Humidity threshold for cracking is 30%.
• Measured length of cracks very dependent on polishing practice.
• Cracking could occur at 290–300 K, based on measured activation energy.

Bending tests were used to investigate the stress-corrosion cracking of 304L stainless steel in a corrosive atmosphere containing magnesium chloride. Initially smooth specimens showed multiple closely spaced cracks after exposures of up to 500 h. These showed threshold stresses of 10 MPa and a threshold humidity of 30%. Cracking rates increased with stress but were a maximum at plastic strains of 2%. Examination of cracks using focussed ion beam milling and electron diffraction indicated a multi-stage mechanism of propagation via preferential oxidation of slip planes. The apparent activation energy was 34 kJ mol−1 in the temperature range 333–363 K.