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Why does metal injection molding stainless steel rust?

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-06-11 10:00:00
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We also have suffered rust issue on metal injection molding stainless steel products. People feel surprised "stainless steel is not rust, rust is not stainless steel, may be steel problems. In fact, this is a mistake understanding of stainless steel. Stainless steel will rust under certain conditions.

Stainless steel has the ability to resist atmospheric oxidation -- that is, rust, but also has the ability to corrosion in the acid, alkali, salt -- that is, corrosion resistance. However, the corrosion resistance varies with the steel's chemical composition, protective state, service conditions and environment.

Such as stainless steel 304 pipe has absolutely excellent corrosion resistance in the dry and clean atmosphere, but it will soon rust in sea fog once move to seaside which contains a lot of salt. However, 316 steel tubes performed well. Therefore, it is not any kind of stainless steel can resist corrosion in any environment. Stainless steel obtaining the ability to resist corrosion is formed by a very thin, strong and fine stable chromium oxide film (protective film) on its surface to prevent oxygen atoms continue to infiltrate and oxidation. Once for some reason the film is constantly destroyed, the oxygen progens in air or liquid are constantly infiltrated; or the iron atoms are constantly separated from inside metal, forming loose iron oxide, then the metal surface will be constantly corroded.


Stainless steel commonly rust as following situation in daily life:

1.Stainless steel surface contains other metal elements or enclosed dissimilar metal particles. In the moist air, the condensed water between attachment and stainless steel connects them into a microcell, triggering an electrochemical reaction that destroys the protective film, called electrochemical corrosion.

2. Stainless steel surface adhere organic juice (such as melon vegetables, noodle soup, phlegm, etc.), in the case of water and oxygen, constitute organic acid. Organic acid corrodes the metal surface for a long time.

3. Stainless steel surface adhere acid, alkali, salt substances (such as alkali water, splashed white wash), causing partial corrosion.

4. In polluted air (such as air containing a large number of sulfide, carbon oxide, nitrogen oxide), encounter condensed water, form sulfuric acid, nitric acid, acetic acid liquid point, cause chemical corrosion. Tips to ensure that the metal surface is permanently shiny and not corroded, we recommend:

a. it is necessary to clean the stainless steel surface frequently to remove attachments.

b. use 316 stainless steel in seaside area, which can resist the corrosion of sea water.

c. some stainless steel’s chemical composition on the market cannot meet corresponding national standards. Therefore, it will cause rust, which requires users to carefully choose the products of reputable manufacturers. 


For our metal injection molding products, sometime we give priority to recommend 316L materials if product’s application in seaside. Or sometimes based on fully consideration, we will do sandblasting on product surface which is a relative cheap but efficient post process.


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