Effect of Silicate and Phosphate on the Fatigue Crack Growth Rates in Type 403 Stainless Steel in Concentrated Sodium Chloride and Sodium Hydroxide Solutions Available to Purchase

Corrosion fatigue crack growth rates of a quenched and tempered Type 403 stainless steel were measured in concentrated sodium hydroxide and sodium chloride solutions, with and without the addition of sodium silicate and sodium phosphate as potential inhibitors, using compact tension specimens (CTS). All tests were performed at 100 C with a sinusoidal loading wave form at R = 0.5 and at frequencies of 0.1,1.0, and 10.0 Hz. Tests in air were also conducted to obtain the base line data for fatigue crack growth rates (FCG). At open circuit potentials, corrosion fatigue crack propagation rates were highest in concentrated sodium chloride solution. The environmental enhancement of fatigue crack growth became more evident as the frequency was decreased in both 10 mol kg⁻¹(m) sodium hydroxide and saturated (6.6 mol kg⁻¹) sodium chloride solutions. Both sodium phosphate and sodium silicate at the concentrations used in this work showed no beneficial effect on the corrosion fatigue crack growth rates for Type 403 stainless steel in 10 mol kg⁻¹ NaOH solution. However, the addition of sodium silicate and sodium phosphate showed inhibiting effects in 6 mol kg⁻¹ sodium chloride solution. The inhibiting actions of these compounds were strongly concentration dependent. A crack growth rate equivalent to that in air was found upon addition of 0.5 m Na₃PO₄ or 0.5 m Na₂SiO₃ to sodium chloride solution.