Metallographic diagram of 45 steel (rack)

The microstructure of 45 steel (rack) is analyzed by optical instrument microscope. The size of the sample is 7 mm × 7 mm. The results of the observation are shown in Fig. 1.

Fig. 1 shows that 45 steel has a ferrite and pearlite structure. The volume fraction of ferrite is 73.5%, which is represented by gray color, and the volume fraction of pearlite is 26.5%, which is represented by light gray. It can be seen from the figure that the structure of the sample is relatively uniform, and the ferrite and pearlite are well-distributed.

As the graphite nodules contained in 45 steel are not very obvious, the network structure of proeutectoid ferrite still exists, and a large number of black points appears in the matrix of ferrite. These black points are graphite flakes, and the size of the graphite flakes is relatively small. The surface of the graphite flakes is oxidized to form a layer of oxide coating.

There are some inclusions in the sample, but their number is relatively small and their shape is not consistent. Inclusions in the sample include MnS, Si, CaS and other sulfides and oxides.

It can be seen from the observation that the surface of 45 steel shows loose bubble holes, which are caused by improper heat treatment or inadequate quenching process, so that some parts of the steel are overheated and form small bubbles.

The sample is poured, and the grain size of 45 steel is coarse, mostly distributed in medium coarseness, with an average of about 8.4μm. Although the grain size of 45 steel is large, the coarse grains are well-distributed, the texture of the sample is not blocky, and the texture is uniform and delicate.

In summary, the microstructure of 45 steel (rack) is analyzed by optical instrument microscope. The results show that the sample has a ferrite and pearlite structure, and many graphite flakes are dispersed in the matrix of ferrite. The graphite flakes are oxidized to form a layer of oxide coating. There are some inclusions in the sample. The surface shows bubble holes, caused by improper heat treatment. The grain size of 45 steel is coarse, mostly distributed in medium coarseness, with an average of about 8.4 μm.

The Microstructure of 45 Steel

45 steel, also known as medium carbon steel, is an important material used in many industrial areas. It is a two-phase ferrite-cementite microstructure that has important mechanical properties. A microstructure of 45 steel is obtained by heat treatment, which determines its mechanical properties.

The structure of 45 steel is composed of ferrite and pearlite. The ferrite is also known as alpha-iron and can be found as a white or grayish solid. It is a soft, ductile and malleable solid that has a body-centered cubic crystal structure. The pearlite is formed from a mixture of the ferrite and cementite and appears as a lighter gray color in a microstructure. It has a lamellar microstructure, composed of alternating layers of ferrite and cementite that give it excellent strength and hardness.

The mechanical properties of 45 steel are determined by its specific chemical composition and heat treatment. Its strength and hardness can be further improved by adding alloying elements such as molybdenum, chromium, vanadium and manganese. The heat treatment also helps to modify the microstructure of 45 steel and further increase its strength.

Heat treatment of 45 steel can also be used to optimize its properties for specific applications. For instance, the microstructure of the steel can be adjusted to provide better wear resistance, fatigue strength and machinability. In its annealed form, 45 steel is ductile and soft and can be used for many different purposes. It is particularly useful for knurling and for manufacturing spur gears and other types of machine elements.

In conclusion, 45 steel is a two-phase ferrite-cementite microstructure that has important mechanical properties. It is composed of ferrite and pearlite, and its properties can be improved by alloying elements and heat treatment. It is used for various applications including the production of spur gears and other machine elements.