Transgranular Stress Corrosion Cracking of Mild Steel in 0.5N H₂SO₄ + 0.005N Kl Solution — Stress Corrosion Behavior Under Constant Crosshead Speed Test

Investigation of stress corrosion cracking (SCC) of mild steel in 0.5N H₂SO₄ + 0.005N Kl was carried out using a constant crosshead speed method at room temperature. Smooth specimens tested at a crosshead speed of 5 × 10⁻² mm/minute, and notched specimens tested at 10⁻² mm/minute, cracked transgranularly at a slightly anodic polarization (approximately 0.04 V < η_a <0.07 V), in which general corrosion of mild steel was somewhat inhibited by I⁻ ions. These specimens did not show appreciable susceptibility to SCC when tested at a high crosshead speed of 10⁻¹ mm/minute for the smooth specimens and 2.5 × 10⁻² mm/minute for the notched specimens at an anodic polarization of η_a = 0.06 V. The relationship between crack length and SCC test time was examined. The results showed that the cracks nucleated after a test time of 1 hour, and they propagated linearly with time initially, and rapidly after 3 hours. Transgranular cracking of mild steel in the present study was not preceded by hydrogen embrittlement but by active path corrosion.