Abstract
Torsional corrosion fatigue tests were carried out on S35C carbon steel to clarify the influence of pH in the test solution which contains HCl+NaCl or NaOH+NaCl. The following conclusions were drawn:
(1) The fatigue strength at 107 cycles showed a maximum at pH 4, and then increased monotonically with pH. It is considered that the pH value in the test solution, initially at pH 4, increased with test duration, and the site of crack initiation was changed from the cathode area to the bottom of the corrosion pits.
(2) The fatigue strength in the solution of pH 4 and 7.7 was decreased with the addition of NaCl, but it did not affect at pH 1 and 13.7. It is because electrical conductivity is not changed at pH 1 and passive film is formed at pH 13.7.
(3) The reduction of fatigue strength with NaCl concentration (>0.005 wt percent) was more remarkable at pH 7.7 than at pH 4. The critical concentration of NaCl, below which NaCl has no effect on fatigue strength, appeared to be 0.005 wt percent in both pH solutions.
