Types and definitions of stainless steel corrosion

In many industrial applications, stainless steel can provide today’s satisfactory corrosion resistance. According to the experience of use, in addition to mechanical failure, corrosion of stainless steel is mainly manifested in: a serious form of corrosion of stainless steel is localized corrosion (also known as stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue, and crevice corrosion). These localized corrosion caused by the failure cases account for almost more than half of the failure cases. In fact, many failures can be avoided through proper material selection.

Stress corrosion cracking (SCC): A generic term for the mutual failure of an alloy subjected to stress in a corrosive environment due to the expansion of marring. Stress corrosion cracking has a brittle fracture pattern, but it can also occur in materials with high ductility. The necessary conditions for stress corrosion cracking to occur are the presence of tensile stress (whether residual or applied, or both) and the presence of a specific corrosive medium. The formation and expansion of the pattern is roughly perpendicular to the direction of the tensile stress. This stress value that leads to stress corrosion cracking is much smaller than the stress value required to fracture the material in the absence of a corrosive medium. At the microscopic level, the crack through the grain is called through the grain crack, and along the grain boundary expansion of the crack is called along the grain crack, when the stress corrosion cracking extended to its a depth (here, the stress on the section of the material under load to its fracture stress in air), the material is broken by normal cracking (in ductile materials, usually through the aggregation of microscopic defects). Thus, the section of a part that fails due to stress corrosion cracking will contain a characteristic area of stress corrosion cracking and a “tough nest” area associated with the aggregation of microscopic defects.

Pitting corrosion: is a localized form of corrosion leading to corrosion.

Intergranular corrosion: intergranular boundary is the crystallography of different orientations between the disorderly misalignment of the grain boundary city, therefore, they are a variety of solute elements in steel segregation or metal compounds (such as carbide and δ phase) precipitation precipitation of the favorable area city. Therefore, in some corrosive media, the intergranular boundary may first be corroded is not surprising. This type of corrosion is known as intergranular corrosion, most of the metals and alloys in a particular corrosive medium may present intergranular corrosion.

Crevice corrosion: is a form of localized corrosion, it may occur in the solution stagnation in the crevice or shielding the surface. Such a gap can be formed in the metal-metal or metal-nonmetal joints, for example, in the rivets, bolts, gaskets, valve seats, loose surface deposits, and sea life where the candle is formed.

Full-scale corrosion: is the term used to describe the corrosion phenomenon that occurs in a relatively uniform manner over the entire surface of the alloy. When full-scale corrosion occurs, the village material due to corrosion and gradual thinning, and even material corrosion failure. Stainless steel in strong acids and strong alkalis may show full-scale corrosion. The problem of failure caused by full-scale corrosion is not much of a concern, because, this corrosion can usually predict it by a simple immersion test or by consulting the literature on corrosion.