Metallographic diagram of 35CrMo (quenched and tempered)

Figure-1 is a micrograph of a 40CrNiMoA structural steel material (martensite) processed at 900C. The micrograph was taken with a magnification of 1000X. The etching used was 5% Nital. As shown in Figure-1, a uniform microscopic structure can be observed. Grain boundary walls are clearly visible in the center of the grain boundary. On the left side of the structure, some large grains can be seen while on the right side of the structure, the grains are smaller in size. The alloying elements in this material are chromium and nickel, which can be observed as dark patches that are surrounded by lighter areas.

Observing the structure carefully, it is possible to notice that most of the grains are aligned in one direction, indicating a bimodal grain size distribution. A closer examination of the material reveals that small pro-eutectoid carbide particles can be seen distributed throughout the microstructure. The carbide particles have dark contrast with the base material, which can be identified as chromium-rich particles. These particles form along the grain boundaries and act as barriers or inhibitors against grain growth.

Threaded structures can be seen throughout the material. It is likely that the material has been cold-worked to improve its mechanical properties. Cold-working introduces mechanical stresses that give rise to the threaded structures seen within the microstructure.

In conclusion, this micrograph of the 40CrNiMoA structural steel material shows a bimodal grain size distribution, with small pro-eutectoid carbide particles distributed throughout the microstructure. The material has likely been cold-worked to improve its mechanical properties, as indicated by the threaded structures present throughout the material.

35CrMo is a type of alloy steel that is widely used in the manufacture of machine parts and tools. It is a popular material because it has the properties of high strength, good toughness, strong wear resistance and corrosion resistance, and high heat resistance.

The microstructure of 35CrMo steel contains grains of ferrite and pearlite, with a small amount of carbides, which contribute to its excellent mechanical properties. By heat treating 35CrMo steel, its grains can be made more uniform, resulting in further improved mechanical properties.

In terms of metallography, 35CrMo steel is composed of ferrite and pearlite and several other components. After heat treatment, the reticular components of ferrite are transformed into block components, the ferrite grains become longer and thinner, the pearlite becomes thinner and more uniform, and the internal stress is reduced due to the different volumetric contraction coefficients of different phases.

In addition, small particles of carbide can be observed in the photographed area. These carbides are segregated from the solid solution of the iron element, and are easy to gather in the grain boundary, in order to improve wear resistance and hardenability.

In short, depending on the heat treatment process and the specific requirements of the application, 35CrMo steel can be further annealed or quenched, tempered and normalized to meet various requirements. The heat treatment process can improve the microstructure of the 35CrMo alloy steel and its mechanical properties, making it an excellent material for the manufacture of machine parts and tools.