Method of acquisition
Therefore, according to the above principle, a series of corrosion resistant alloys are obtained industrially by alloying. There are generally three corresponding methods.
(1) To improve the thermodynamic stability of a metal or alloy, that is, to add an alloying element having high thermodynamic stability to a metal or alloy which is not corrosion resistant, to form a solid solution and to improve the electrode potential of the alloy and to enhance corrosion resistance. For example, if Au is added to Cu and Cu, Cr or the like is added to Ni, it is such. However, this method of adding precious metals in large quantities is limited in the application of industrial structural materials.
(2) Adding easily passivable alloying elements such as Cr, Ni, Mo, etc., can improve the corrosion resistance of the base metal. A chromium-based stainless steel can be obtained by adding an appropriate amount of Cr to the steel. Experiments have shown that in stainless steel, the amount of Cr should generally be greater than 13% to resist. The higher the Cr content, the better the corrosion resistance. Such stainless steels have good corrosion resistance in oxidizing media, but have poor corrosion resistance in non-oxidizing media such as sulphuric acid and hydrochloric acid. This is because the non-oxidizing acid does not easily form an oxide film on the alloy, and at the same time dissolves the oxide film.
(3) Adding an alloying element that promotes the formation of a dense corrosion product protective film on the surface of the alloy is another way to obtain a corrosion resistant alloy. For example, steel is resistant to atmospheric corrosion due to the protective effect of the structure of the structure of iron oxyhydroxide (FeOx·(OH)3-2x). The addition of Cu and P or P and Cr to the steel promotes the formation of such a protective film, whereby Cu, P or P, Cr can be used to form a low alloy steel resistant to atmospheric corrosion.
Metal corrosion is the most dangerous spontaneous process in the industry. Therefore, the development and application of corrosion resistant alloys have great social and economic value.
Previous: How Was Inconel 718 Created?