Corrosion resistance of stainless steel and its types?

1、 Type and definition of corrosion

In many industrial applications, stainless steel can provide satisfactory corrosion resistance.

It is mainly manifested in: a serious form of stainless steel corrosion is local corrosion (i.e. stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue and crevice corrosion).

Stress corrosion cracking (SCC): refers to the general term of mutual failure of stressed alloys due to strong linear expansion in corrosive environment. Stress corrosion cracking has brittle fracture morphology, but it may also occur in high toughness materials. The necessary conditions for stress corrosion cracking are the existence of tensile stress (whether residual stress or external stress, or both) and specific corrosion media. The formation and expansion of the profile are roughly perpendicular to the direction of tensile stress. The stress value causing stress corrosion cracking is far less than the stress value required to break the material without corrosive medium. Microscopically, cracks passing through grains are called transgranular cracks, and cracks propagating along grain boundaries are called intergranular cracks. The stress reaches its breaking stress in the air), and the material breaks in the form of normal cracks (in ductile materials, it is usually through the aggregation of microscopic defects). Therefore, the part that fails due to stress corrosion cracking will contain the characteristic area of stress corrosion cracking and the "pit" area related to the accumulation of microdefects.

Pitting: It is a local corrosion form that causes corrosion.

Intergranular corrosion: grain boundary is the boundary of disorderly interwoven grains with different directions. Therefore, they are beneficial to the segregation of various solute elements or metal compounds (such as carbides and δ Phase). Therefore, in some corrosive media, it is not surprising that the grain boundary may be corroded first. This kind of corrosion is called intergranular corrosion. Most metals and alloys may have intergranular corrosion in some corrosive media.

Gap corrosion: It is a local corrosion form, which may occur in the gap or shielding surface where the solution is stagnant. This gap can be formed at metal-to-metal or metal-to-non-metal joints, such as rivets, bolts, washers, seats, loose surface deposits and marine biological candles.

Corrosion: A term used to describe the corrosion phenomenon that occurs in a relatively uniform manner on the entire surface of the alloy. When corrosion occurs, the village material will gradually become thinner due to corrosion, and even the material will fail due to corrosion.