The way alloy elements exist in steel
1. The alloying elements interact with the carbon in the steel to form carbides in the steel. The alloying elements interact with carbon in the steel. They can be divided into two categories:
(1) An element which does not form a carbide (referred to as a non-carbide forming element), and includes nickel, silicon, aluminum, cobalt, copper, and the like. Since these elements have a lower binding force to carbon than iron, they cannot be combined with carbon in steel, and they have no significant effect on the structure of carbides in steel.
(2) An element forming a carbide (referred to as a carbide forming element), and depending on the strength of binding to carbon, the carbide forming element can be classified into three types.
1) Weak carbide forming elements: Manganese manganese has a slightly stronger binding force to carbon than iron. Manganese is added to steel and generally does not form special carbides (carbides with a structure different from Fe3C are called special carbides) but are dissolved in cementite.
2) medium-strong carbide forming elements; chromium, molybdenum, tungsten
3) Strong carbide forming elements: vanadium, niobium and titanium have extremely high stability. For example, TiC starts to slowly dissolve above 1 000 C when quenching and heating. These carbides have extremely high hardness, for example, in high speed steel. Vanadium is added to the V3C to make it more wear resistant.
2. The alloying element is dissolved in ferrite (or austenite) and exists in steel as a solid solution.
3. Alloying elements are combined with nitrogen, oxygen, sulfur, etc. in steel, and are present in steel in the form of non-metallic inclusions such as nitrides, oxides, sulfides, and silicates.
4. Free form, ie insoluble in iron, insoluble in compounds: lead, copper
