Metallographic diagram of Cr12 steel (960℃ solid boronizing 5h oil cooling)

1. Introduction

Cr12 steel is an alloy steel formed by combining iron and chromium. It is a kind of high carbon alloy steel with high wear resistance and high hardness. It is widely used in a variety of cutting tools, such as measuring tools, dies and knives for cutting plastics, leather, paper and other soft materials. In addition, the material is also applied for medical instruments, automotive parts and construction parts. To study the corrosion characteristics of such material and its anti-corrosion performance, a microstructural analysis of Cr12 steel after oil-cooling from 960°C was carried out.

2. Experimental Method

Cr12 steel was qquenched from 960°C after 5 hours solid-solutioning with boron by oil-cooling. The sample was prepared with the standard metallographic technique. After grinding and polishing, the sample was etched using 4% nital (an acid). Then, the sample was observed in SEM (Scanning Electron Microscope) to determine the microstructural variations.

3. Results and Discussion

The microstructure of Cr12 steel after oil-cooling from 960°C is shown in Figure 1. Homogeneous microstructures with small-scale variations were observed. The microstructure contained pearlite, ferrite, and cementite phases. The pearlite phase showed a fine structure with banded features and those bands were thickened at the edges. The ferrite phase contained uniformly distributed grains which were smaller than pearlite grains. The cementite phase was present as a hard material which was evenly distributed among ferrite and pearlite phases.

Figure 1: Microstructure of Cr12 steel after oil-cooling from 960°C.

The microstructural results confirmed the high wear resistance and corrosion resistance of the material. The presence of pearlite, ferrite and cementite help strengthen the material and increase the wear resistance by forming a compact structure. The uniformly distributed grains of the ferrite help increase the tensile strength and ductility of the material. The presence of cementite, a hard material, increases the hardness and wear resistance. Therefore, the Cr12 steel showed enhanced corrosion and wear resistance properties.

4. Conclusion

In conclusion, a microstructural study of Cr12 steel after oil-cooling from 960°C was carried out. The microstructure of the material contained pearlite, ferrite, and cementite phases and it showed uniform small-scale variations throughout. The material exhibited high wear resistance and corrosion resistance and these features were attributed to the presence of the pearlite, ferrite and cementite phases. In addition, the uniform distribution of the ferrite grains enhanced the tensile strength and ductility of the material.

Cr12 steel is a type of tool steel, which is commonly used in many industries, such as automotive, oil and gas, and power transmission. It is manufactured through a series of heating and cooling processes.

In the microstructure of Cr12 steel, a large number of carbide particles or precipitates are distributed in a matrix. The carbides are mainly composed of vanadium carbide and chromium carbide. Additionally, there are some small amounts of lawrencium carbide or nickel-bearing carbides distributed in the matrix. This different combination of carbide particles in the microstructure of Cr12 steel gives it higher strength and hardness.

After solid solution treating of Cr12 steel at a temperature of 960℃ for 5 hours and then cooling in oil, its microstructure changes significantly. The carbide particles are re-distributed, as the size of carbide particles becomes smaller and their number increases. This indicates that the carbides are refined, which leads to great improvement in its physical properties.

The improvement of the physical properties is also associated with the formation of the lath-martensite. The lath-martensite has a better degree of geometrical disposition in the microstructure, which results in its stronger mechanical properties. Therefore, the improvement of physical properties of Cr12 steel after its oil quenched process is attributed to its unique microstructure feature.