Effect of Residual Stress on Stress Corrosion Behavior of Industrial Pure Iron Formed by Selective Laser Melting

Industrial pure iron specimens were formed by selective laser melting and subjected to solution at different temperatures (650, 800, 950 ℃) and aging at 400 ℃ to control residual stresses. The slow strain rate tensile test of the formed specimens was carried out in NaCl solution with different NaCl mass fractions (3.5%, 5.0%, 10.0%). The effect of residual stress on stress corrosion behavior of formed specimens was studied. The results show that the high residual tensile stress in the deposited (before solution + aging treatment) specimens enhanced its stress corrosion sensitivity at relatively high Cl⁻ concentration (mass fraction not less than 5.0%). With the increase of Cl⁻ concentration, the stress corrosion sensitivity of the deposited specimens increased. After solution and aging treatment, the residual stress decreased, the stress corrosion sensitivity decreased at relatively high Cl⁻ concentration. With the increase of Cl⁻ concentration, the stress corrosion sensitivity of specimens after 650,950 °C solution and aging treatment changed little,and the stress corrosion sensitivity of spcimens after 800 °C solation and aging trentment decreased first and then increased. The stress corrosion sensitivity of the specimens with residual stress close to zero (solution temperature was 800 °C) was lower at relatively high Cl⁻ concentration than those with relative high residual stresses. The tensile fracture of the specimens with a high residual tensile stress was brittle fracture. With the decrease of residual stress, dimples appeared on the fracture surface. When the residual stress was close to zero or transformed into compressive stress (solution temperature was 950 °C), the tensile fracture was brittle-ductile fracture.