Metallographic diagram of 45 steel (annealed state)

Astm A455 Steel Microstructure Analysis

ASTM A455 steel is a low-alloy low-carbon steel that is often used in structural and construction applications. The alloy is annealed at medium temperatures, which makes it soft, malleable, and durable. Its main component elements are steel, iron, and carbon, and secondary alloying elements are sulfur, phosphorus, manganese, and silicon. Its chemical composition varies depending on the production process, but it typically has a carbon content of about 0.2%, and manganese of about 1.2%, both of which are relatively low.

The microstructure of ASTM A455 steel is composed of ferrite and pearlite. The ferrite is in a body-centered cubic (BCC) lattice structure and is either ferrite or pearlite. The pearlite is made up of alternating plates of ferrite and cementite, and is typically finer than the ferrite grains.

The microstructure of the steel depends on a number of factors including temperature, cooling rate, and composition. In annealing, higher temperatures result in finer carbide forms and softer steel. Lower annealing temperatures and slow cooling rates result in a coarser carbide form, harder steel, and poor toughness. High annealing temperatures, on the other hand, result in a softer steel but poor toughness. In general, steel produced with a low carbon content and slow cooling results in a finer pearlite and ferrite microstructure, softer steel, and better toughness.

The ASTM A455 steel is a low-alloy steel with a low carbon content, and it is used for both structural and construction applications. Its chemical composition varies according to the production process, but typically contains low levels of carbon and manganese, and sometimes also includes sulfur, phosphorus, and silicon. Its microstructure consists of ferrite and pearlite with small carbide forms, and it typically has good toughness and wear resistance. Annealing the steel at medium temperatures results in a softer steel and better toughness, while lower annealing temperatures and slower cooling rates produce a coarser carbide form and harder steel with poorer toughness. This steel is best suited for applications where strength and good toughness are needed.

20CrMnTi is a traditional Chinese structural alloy steel, belonging to medium hardening steel with simple steel production process, quenching and tempering after normalizing. It has good mechanical properties and reliable performance, and has been widely used in the manufacture of axles, gears, connecting rods and other important components, and enjoys a good market reputation.

The metallographic examination of 20CrMnTi steel (annealed state) is mainly based on the white etching effect. The white etching area is gray-white, distributed thin, and the ferrite structure is floating. The white edge particles are finely distributed and the particles are slightly curved, showing the characteristics of pearlite. In addition, there are also martensite, bainite and small amounts of carbides distributed in white etching area.

In addition, the fatigue fracture surface of 20CrMnTi steel (annealed state) is observed, and it can be seen that there are transgranular fractures in the fracture surface. The fracture surface has obvious dimples, smooth rounding, and no signs of cleavage twins. It can be analyzed that there are a large number of unreinforced cementite in the fracture surface and there are a small number of carbides, which are distributed in an radial arrangement.

Overall, metallographic examination of 20CrMnTi steel (annealed state) shows a certain degree of global white etching effect, mainly distributed as ferrite, pearlite, martensite and bainite, as well as a small amount of carbides. In addition, the fatigue fracture surface has a large number of unreinforced cementite and a small number of carbides, arranged in a radial direction.