The Effects of Surface Modification on the Stress Corrosion Cracking Behavior of 316 Stainless Steel

With the goal of conserving critical metals, the effects of surface modifications on the stress- corrosion cracking resistance of stainless steel has been studied. The stress corrosion cracking behavior of 316 stainless steel in a boiling MgCl₂ solution at 154 C has been investigated with respect to the initial condition and composition of the surface. Changes in the surface were introduced by machining, electropolishing, and ion implantation of silicon, nitrogen, or argon ions into the near-surface region. The time-to-failure and sample potential were measured for each sample following the modification of the surface. Elemental depth profiles of surface films were obtained using Auger electron spectroscopy, and the films and surfaces were characterized by proton induced X-ray emission. Results showed that the surface condition of the sample in terms of either the cold work resulting from machining or the amount of electropolishing is of significant importance to the behavior of the sample. Ion damage induced by argon ion implantation resulted in a reduction in the time-to-failure. Nitrogen ion implantation also reduced the time-to-failure, although it is not clear if this is caused by ion damage or by the presence of the nitrogen. Scanning electron microscopic analyses of nitrogen-implanted samples indicated an explosive release of gas at slip lines which changed the surface morphology. Silicon ion implantation both increased the time-to-failure and reduced the thickness of the film formed on the samples exposed to the boiling MgCl₂ solution.