Why Stainless Steel Is Prone To Rust After Hardening

We are a professional CNC machining factory, the material we can make vary from Aluminum, Stainless steel, Brass, Copper, Titanium, POM, Delrin, Teflon and so on, while some customers always ask why our parts is made of Stainless steel and get rust sometimes, here I’d like to you know why.

There are many kinds of Stainless steel, such as SUS302, SUS303, SUS304, SUS316, Stainless steel 17-4, 17-7, Stainless steel 416, Stainless steel 420... normally they won’t rust in normal environment, but in some poor environment, 302, 303, 17-4 and 17-7 may rust. Because the anti-rust principle of stainless steel mainly relies on a layer of chromium-rich oxide protective film formed on its surface, which can prevent oxygen atoms from penetrating, thus giving stainless steel corrosion resistance. However, there are many reasons for stainless steel to rust, including dust or foreign metal particles of other metal elements attached to the surface, organic juice, substances containing acids, alkalis, and salts, and condensed water in polluted air to form corrosive liquids. These factors can destroy the protective film on the surface of stainless steel, causing iron atoms to precipitate and form loose iron oxide, so that stainless steel begins to rust

Beside, all kinds of stainless steel will rust if it is hardened, especially for Nitrided hardened, nitrogen and chromium form alloy nitrides. Although the hardness of the surface is increased, it also leads to the loss of chromium on the surface, which further promotes the rusting process. Therefore, even if the stainless steel has been hardened, the protective film on its surface may still be damaged if it is used in an improper environment or conditions, resulting in rust. ‌

In order to reduce the rust of stainless steel, it is recommended to clean and scrub the surface of stainless steel frequently to remove attachments and eliminate external factors that cause modification. ‌In addition, keeping the production workshop dry and clean and avoiding a humid environment are also effective measures to reduce the rust of stainless steel.

So next time, when you coated stainless steel part, please be carefully.