Metallographic diagram of 20 steel (surface galvanized after carbonitriding and quenching)

C20 steel is a low carbon content C-Mn steel which possesses excellent machinability of similar steels such as CK20 without providing any appreciable strength or wear resistance. C20 steel is coated with a zinc plating layer on its surface to protect against corrosion. The zinc-plated layer is generally very thin and is applied after the steel has been hardened in a controlled atmosphere.

In order to understand the microstructure of C20 steel, a metallurgical analysis using an optical microscope and/or a scanning electron microscope (SEM) is necessary. A typical C20 steel microstructure is composed of a finely grained ferrite matrix with various amounts of pearlite, bainite and martensite inclusions. The pearlitic regions in the matrix have a coarser grain size than the ferrite regions. The amount of pearlite present depends on the prior heat treating procedure(s). The presence of bainite and martensite is reflective of more severe heat treating.

The presence of free carbon as well as an extremely flakey primarily elemental alloy layer will be observed on the surface of a polished and etched C20 steel sample. The most dominant feature on the observed surface of the sample will be the iron grain boundaries that contain the particles of iron, manganese and other elements.

To understand thoroughly the metallurgical characteristics of C20 steels, a metallurgical analysis is needed. This analysis forces the use of specific tools such as the optical microscope, scanning electron microscope, hardness testers, tempering microscopes, etc.

The optical microscope allows for the evaluation of the primary structural constituents of the C20 steel sample such as the ferrite and pearlite. Additionally, the optical microscope allows for the evaluation of the inclusions present in the sample and their size, distribution, and type.

The scanning electron microscope (SEM) is particularly useful in the analysis of the surface characteristics of the C20 steel specimen. The SEM provides a maximum magnification of up to 500,000 times and is capable of providing a detailed analysis of the microstructure of the C20 steel sample. The SEM allows for the evaluation of the elemental composition of the material as well as the presence of inclusions and oxides due to heat treatment.

By using hardness tester, it is possible to analyze the strength properties of the C20 steel sample. Hardness testers provide values in HRC or HRB units that indicate the material’s resistance to abrasion and cutting. Additionally, the hardness tester allows for transitioning the properties of the samples from one condition to another (such as from an annealed condition to a hardened condition).

The tempering microscope is particularly useful in evaluating the structure of the material after peeling or cold working. The tempering microscope provides information on the austenite grain size, distribution, and geometry. It also allows for the determination of the tempering temperature and its effect on the shape and substructure of the material.

In conclusion, the metallurgical analysis of C20 steel provides substantial information about the characteristics of the material. The wide array of features of the C20 make it an excellent material for a variety of applications. An optical microscope, scanning electron microscope, hardness testers, and tempering microscopes are some of the important tools necessary for undertaking a comprehensive analysis of this material.

This is a brief introduction to 20# steel (carbon-nitrogen alloy, quenching and tempering, and galvanizing surface).

20# steel is a kind of carbon-nitrogen alloy structural steel. It is easy to cut, with medium plasticity, good surface quality and small size allowance. In quenching and tempering treatment, the hardness can be up to HRC45. After galvanizing, the corrosion resistance of parts can be enhanced, so that they can be used in special environments such as electrical environment, acid, alkali and salt.

The main element of 20# steel is 0.17-0.24% of carbon and 0.17-0.37% of nitrogen. Other elements are C, Si, Mn and Cr. In terms of mechanical properties, the tensile strength of 20# steel is not lower than 410 MPa, and the yield strength is not lower than 245 MPa. The allowable stress is 175~204MPa, the Brinell hardness is 119~150HB, and the elongation is not lower than 30%.

The microstructure of the galvanized 20# steel is ferrite and pearlite. The ferrite proportion is about 30-40%, the pearlite proportion is about 50-60%, and the rest are carbide and inclusion. The grain size is from 0.15 to 2.00mm, and the non-metallic inclusions are dominated by phosphide particles, which are distributed in the network form.

20# steel has good versatility and applicability, and is widely used in engineering machinery and automobiles, manufacturing industry and daily life. Therefore, it has been widely used in the production of various engineering structures and components such as bridges and buildings, ships, vehicles, boilers, chemical machinery, nuclear power plants, and liquid pipelines.