People usually understand steel that does not rust literally as stainless steel, but academically, this is not the case.

We usually refer to steel that does not rust in weakly corrosive media such as atmosphere and fresh water as stainless steel, while steel that is corrosion-resistant in harsh corrosive media such as acid, alkali, salt, and seawater is called acid resistant steel. The former may not be resistant to harsh corrosive media corrosion, while the latter both have rust resistance due to their sufficient chromium content. Therefore, stainless steel is a general term for both, also known as stainless acid resistant steel.

Research has shown that as the chromium content in steel increases, its corrosion resistance improves. When the chromium content reaches a certain proportion, a thin, colorless, transparent, and smooth chromium rich oxide film will automatically form on the surface of the steel to prevent rusting. This layer of film is very stable and can quickly repair itself even if damaged, known as a self passivation film.

The corrosion resistance of stainless steel depends on the alloying elements contained in the steel, and chromium is the basic element that gives stainless steel corrosion resistance. In addition to chromium, commonly used alloying elements include nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., to meet the requirements of various applications for the microstructure and properties of stainless steel.

The current national standards stipulate that steel with stainless steel and corrosion resistance as its main characteristics, and chromium content ≥ 10.5% and carbon content ≤ 1.2%, is called stainless steel.