Reasons for rusting of 304 stainless steel
The rust phenomenon of 304 stainless steel material may have the following reasons:
Chloride ions exist widely, such as salt/sweat/seawater/sea breeze/soil and so on. In the presence of chloride ions, stainless steel corrodes rapidly, even more than ordinary low carbon steel. Therefore, there are requirements for the use environment of stainless steel, and it needs to be wiped frequently to remove dust and keep it clean and dry. (In this way, he can be rated as "improper use".) There is an example in the United States: a company used an oak container to hold a solution containing chloride ions. The container has been used for nearly a hundred years and was planned to be replaced in the 1990s. , Because the oak material is not modern enough, the container leaked due to corrosion 16 days after the replacement with stainless steel.
Alloy elements are not dissolved into the matrix, resulting in low alloy content in the matrix structure and poor corrosion resistance.
This titanium- and niobium-free material is prone to intergranular corrosion. The addition of titanium and niobium, together with stabilization treatment, can reduce intergranular corrosion. A high-alloy steel that can resist corrosion in the air or in chemically corrosive media. Stainless steel has a beautiful surface and good corrosion resistance. It does not need to undergo surface treatment such as color plating, but instead exerts the inherent surface properties of stainless steel. It is used in many A type of steel, commonly referred to as stainless steel. The representative performance is high alloy steel such as 13 chrome steel and 18-8 chrome nickel steel. From the metallographic point of view, because the stainless steel contains chromium, a very thin chromium film is formed on the surface, which isolates the oxygen from the steel and plays a role in corrosion resistance. In order to maintain the inherent corrosion resistance of stainless steel, the steel must contain more than 12% chromium. For occasions where welding is required. The lower carbon content minimizes carbide precipitation in the heat-affected zone near the weld, which can lead to intergranular corrosion (weld erosion) of stainless steel in some environments.
The phenomenon of surface marks refers to the occurrence of wire-mounted or point-shaped pit marks on the surface of 304 stainless steel after deep processing or grinding of processed products.
Reason: There are foreign objects on the surface and mold surface, and there are scars on the surface of the blanking pad.
Countermeasures: Remove foreign bodies, scars, and orange peel by fully grinding before processing.
The orange peel phenomenon refers to the phenomenon that the surface of 304 stainless steel moldings has a shape like orange peel under grinding or other conditions.
Reason: Insufficient grinding, the larger the processing, the more serious the orange peel, the coarse grains of the raw materials, and the softening of heat treatment.
Countermeasures: Fully grind the deep-processed products, select suitable heat treatment conditions, and control the grain size of the raw materials.