Metallographic diagram of 20CrMnTi (gas carbonitriding at 860°C)

?

20CrMnTi is a kind of low-carbon alloy steel that is widely used in the production of different kinds of components. It has good strength, ductility and high wear resistance. It has a combination of high hardness and fatigue strength. It has good high-temperature strength and creep strength.

The microstructure of 20CrMnTi steel is composed of ferrite and pearlite, and its microstructure can be changed by heat treatment, so as to select the appropriate combination of strength and toughness suitable for the application process. Besides, the steel can also be enriched with nitrogen and carbon while maintaining a low carbon content by carburizing, so as to improve its wear resistance and strength.

In the production process of 20CrMnTi steel, gas carburizing and quenching is usually used to improve the combined properties of strength and toughness of the components made by the steel. After austenitizing and quenching, its surface was a typical ferritic and pearlitic structure. Gas carburizing is a process in which components are heated to a certain temperature in a carburizing atmosphere and then carbon is added to the surface to form a supersaturated carbon steel layer. In the carburizing process, nitrogen and carbon are added to the surface of the component to form an alloy steel layer.

The metallographic analysis of 20CrMnTi steel is used to observe the microstructure of the steel. In this experiment, the 20CrMnTi steel was treated by the 860℃ gas carburized and quenched strategy. Its metallographic structure was observed after being polished. The figure shows that the component has two distinct areas. The topmost layer is a martensite layer which has been modified by nitrogen and carbon after being carburized and quenched. The martensitic layer has an equiaxial grain structure. The subsequent rolling layer is composed of pearlite and fine ferrite. There are also some ferritic areas that have not been transformed. The matrix pearlitic structure is the main component in this layer.

In conclusion, the 20CrMnTi steel component produced by gas carburizing and quenching has an excellent combination of strength and toughness, showing potential in high temperature fatigue load and wear resistance. Its metallographic structure has a top layer of martensite layer, which is modified by nitrogen and carbon; and the subsequent rolling layer mainly consists offine ferrite and pearlitic areas. These features show that the component is of high quality.

The microstructure of the 20CrMnTi carburizing steel after being carburized at 860℃ with a gas mixture of carbon and nitrogen is mostly composed of ferrite and a large amount of small grain size and well distributed carbides. The ferrite grains are relatively large and evenly distributed, with low hardness and good ductility. A small amount of pearlite can also be seen, which appears as white bands in the optical microscope. There are various small-sized and well-distributed carbides, which are the product of diffusion reaction between carbon and ferrite during carburizing. It is mainly composed of complex carbides and M2C type carbides. The matrix of the complex carbide consists of M7C3 and M23C6 type carbides, and the M2C type carbide is mainly composed of MC and M6C type carbides. On the cross section of the quenching and tempering specimen, a large amount of martensite can be seen, which form a small isometric compact structure and exhibit dark gray color. The carbide particles are uniformly distributed and precipitated in martensite.

In conclusion, the microstructure of 20CrMnTi carburized steel at 860℃ with a gas mixture of carbon and nitrogen consists of ferrite, pearlite, martensite and various small-sized and well-distributed carbides. The small grain size of the matrix and the uniform and fine distribution of carbides are conducive to the improvement of the performance of the steel and the promotion of the application of the steel.