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.