Corrosion Resistance Of Stainless Steel

- Nov 20, 2018 -

                                                                                                                                    ------------From HongWang

1. Type and definition of corrosion

 

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

 

According to the experience in use, apart from mechanical failure, corrosion of stainless steel is mainly manifested in: a serious corrosion form of stainless steel is local corrosion (i.e. stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue and crevice corrosion).

 

These local corrosion caused by the failure of almost half of the failure cases.

 

In fact, many failure accidents can be avoided by reasonable selection of materials.

 

Stress corrosion cracking (SCC) : a general term used to describe the alternate failure of a stress bearing alloy in a corrosive environment due to the expansion of grains.

 

Stress corrosion cracking has brittle fracture morphology, but it may also occur in ductile materials.

 

The necessary conditions for the occurrence of stress corrosion cracking are the presence of tensile stress (either residual stress or external stress, or both) and a specific corrosion medium.

 

The profile is formed and expanded roughly perpendicular to the direction of tension stress.

 

This stress value, which results in stress corrosion cracking, is much smaller than that required for material fracture in the absence of corrosive media.

 

In the micro level, through the crack in grain called transgranular crack, and the cracks along the grain boundary expansion graph called the intergranular crack, when the stress corrosion cracking extended to one depth (here, the load stress on the section of materials to achieve its fracture stress) in the air, the material is according to the normal crack (in ductile material, usually through microscopic defect aggregation) and disconnect.

 

Therefore, the section of a part that fails due to stress corrosion cracking will contain characteristic areas of stress corrosion cracking and "dimple" areas associated with the polymerization of microdefects.

 

Pitting corrosion is a form of partial corrosion that results in corrosion.

 

Intercrystalline corrosion: intergranular boundary is a boundary city of disordered intergranular mixtures of different crystalline orientations. Therefore, they are favorable regions for the precipitation of various solute elements or metal compounds (such as carbide and sulfide) in steel.

 

Therefore, it is not surprising that in some corrosive media, grain boundary may be corroded first.

 

This type of corrosion is called intercrystalline corrosion, and most metals and alloys may present intercrystalline corrosion in a specific corrosive medium.

 

Crevice corrosion: a form of partial corrosion that may occur in a crevice where the solution is stagnant or within the surface of the shield.

 

Such a gap can be formed at the metal-to-metal or metal-to-nonmetal joint, for example, at the point where the rivet, bolt, gasket, seat, loose surface sediment, and sea life meet the candle.

 

Total corrosion: a term used to describe corrosion on the entire surface of an alloy by comparing spoons.

 

When overall corrosion occurs, the village materials gradually become thin due to corrosion, or even the corrosion failure of materials.

 

Stainless steel may show overall corrosion in strong acid and strong base.

 

Failure problems caused by full-scale corrosion are less of a concern because such corrosion can usually be predicted by simple immersion tests or by referring to corrosion literature.

 

2. Corrosion resistance of various stainless steels

 

304: is a universal stainless steel, which is widely used in the manufacture of equipment and parts requiring good comprehensive performance (corrosion resistance and molding).

 

304L: a variant of 304 stainless steel with low carbon content, used for welding applications.

 

The lower carbon content minimizes the amount of carbide that is precipitated in the heat affected zone near the weld, which may lead to intercrystalline corrosion (weld erosion) in some environments of the stainless steel.

 

The 309S and 310S are variants of 309 and 310 stainless steel, which differ only in the low carbon content, in order to minimize the amount of carbon precipitated near the weld.

 

330 stainless steel has a very high carburization resistance and thermal shock resistance.

 

Type 316 and type 317: stainless steels contain aluminum, so the resistance to pitting corrosion in Marine and chemical industrial environments is much better than that of type 304 stainless steels.

 

Among them, type 316 stainless steel consists of low carbon stainless steel 316L, high strength stainless steel 316N containing nitrogen and easy cutting stainless steel 316F with high sulfur content.

 

321, 347 and 348 are stainless steel stabilized by titanium, niobium, tantalum and niobium respectively.

 

348 is a kind of stainless steel suitable for nuclear power industry.

 

Contact: Una Chen

WuXi XiChu Stainless Steel Co.,Ltd

Mobile: +86-18961715099

Mailbox: xc01@xichustainless.com

Add: B2-135,Stainless Steel Market, No.82 North XueDian Road

         City Wuxi, JiangSu, 214000,China


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