Abstract
The effect of solution pH on the corrosion fatigue behaviour of a low carbon steel (S15C) has been investigated in an aerated HCl-NaCl-NaOH aqueous solution environment, adjusted for a constant ionic strength of 0.5 at 25°C, over the range of pH0.5 to pH13.7. The main results obtained are as follows:
(1) In the acidic range (pH<4), the corrosion fatigue strength decreased monotonically as solution pH was decreased. In the strongly alkaline range (pH>13) a marked increase in corrosion fatigue strength was observed.
(2)In the middle pH range (pH4 to pH13) a maximum in corrosion fatigue strength was observed at pH5 to pH6, falling off to a local minimum at pH9 to pH12. This effect was most marked in the tests with a low cyclic stress amplitude, giving a large number of cycles to failure, and hence longer time for corrosion. The local minimum at pH9 to pH12 is thought to be due to a few deep corrosion pits, which were produced from localized pittings and acted as stress concentrators and crack initiation sites.
(3) The corrosion fatigue fracture surface was predominantly intergranular in nature, although the specimens, fatigued in the passivating high pH (pH>13) region and in air, were both characterized by the fracture surface with fatigue striations and secondary cracks.
(4) The fatigue lives obtained were compared with the results of corrosion tests in the identical corrosive environment under both flowing and stationary conditions.
