True stainless steel products should last for hundreds of years without rust. However, stainless steel that we have seen in the market can still rust and corrode, but in general, the corrosion rate is very slow. Such tests have been done: Two pieces of stainless steel, each weighing 20 grams, and plain carbon steel were put together in dilute nitric acid and boiled for a day or two. As a result, ordinary steels were strongly corroded, leaving only 13.6 grams of weight, while stainless steel weighed 19.8. Grams. Because stainless steel does not easily rust, many corrosion-resistant equipment in chemical plants are made of stainless steel.
Whether stainless steel is rusted or not, the content of chromium is the key. China's stipulated minimum chromium content in stainless steel can not be less than 12%. Because stainless steel contains a relatively high proportion of chromium, its surface is always in a passivated state under normal conditions (neutral and alkaline). This means that a protective film with a tight structure protects it from rust. If the chromium content is low, that is, poor quality stainless steel, the surface can not produce a sufficiently close passivation film, can not play a protective role, this stainless steel still rust. In another case, stainless steel encounters highly active substances (such as salt in daily life, etc.) and contains high chlorine or fluoride ions. Even if the stainless steel contains high quality stainless steel, the surface of the passive film will be destroyed. The surface of the stainless steel is in an active state. At this time, the stainless steel not only rusts but also dissolves heavy metal ions harmful to the body.