What is the cause of stainless steel rust?

304 stainless steel material rust phenomenon, there may be the following reasons:

Chloride ion

Chloride ions are found in many places, such as salt/sweat/seawater/sea breeze/soil, etc. In the presence of chloride ions, the corrosion of stainless steel is faster than that of ordinary mild steel. So there are requirements for the use of stainless steel environment, and the need to wipe often, remove dust, keep clean and dry. In the United States, there is an example: an enterprise with an oak container containing a chloride ion solution, the container has been used for more than 100 years, the last century in the 1990s planned to replace, because the oak material is not modern enough, the stainless steel replacement 16 days after the container due to corrosion leakage.

Solution treatment

The alloy elements do not dissolve into the matrix, resulting in low alloy content and poor corrosion resistance.

Intergranular corrosion

The material, which does not contain titanium or niobium, has a tendency to intergranular corrosion. The intergranular corrosion can be reduced by adding titanium and niobium to the stable treatment. In the air or chemical corrosive medium can resist corrosion of a kind of high alloy steel, stainless steel is a beautiful surface and good corrosion resistance, do not have to go through plating and other surface treatment, and play the inherent surface properties of stainless steel, used in many aspects of steel, usually known as stainless steel. Representative properties of 13 chromium steel, 18-8 chromium nickel steel and other high alloy steel. From the metallographic point of view, because the stainless steel contains chromium and form a very thin chromium film on the surface, this film is separated from the oxygen intrusion in the steel to play a role in corrosion resistance. In order to maintain the corrosion resistance inherent in stainless steel, steel must contain at least 12% chromium. Used for welding. The lower carbon content minimizes the carbide precipitation in the heat-affected zone near the weld, which may lead to intergranular corrosion (welding erosion) of stainless steel in some environments.

Surface marking

Surface mark phenomenon refers to 304 stainless steel deep processing or processing products after grinding, on the surface of the product linear installation or point-like concave mark defects.

Cause: There are foreign bodies on the surface and mold surface, and scars on the surface of the welt pad.

Action: Remove foreign bodies, scars, and peel before processing.

Orange peel phenomenon refers to 304 stainless steel molding products in grinding or other circumstances, the surface of the shape like orange peel phenomenon.

Reason: grinding is not sufficient, the larger the processing of orange peel more serious, raw material grain coarse, heat treatment softening.

Countermeasures: Deep processing products fully grinding, select suitable heat treatment conditions, control the grain size of raw materials.