Metallographic diagram of 20 steel (1150℃ low vacuum chromium vanadium co-infiltration for 6h)

Abstract

The microstructure of 20G Steel after low vacuum carburizing at 1150℃ for 6 hours was evaluated by optical microscope and scanning electron microscope. The microstructure consists of a ferrite matrix with a variety of precipitates and inclusions. These include martensite, carbides, sulfides and oxide inclusions. Analysis of the microstructure reveals that the ferrite matrix consists of an evenly distributed precipitate dispersed in a fine acicular morphology. The martensite is in the form of needle-like grains and appears to be separated from the ferrite matrix. The carbides are in the form of small irregularly shaped particles and are distributed in the ferrite matrix. The sulfides and oxide inclusions appear to be distributed evenly throughout the ferrite matrix and appear to be of single crystal structure. The grain size of the ferrite matrix is medium-fine. The hardness of the sample is 551HV0.3.

Introduction

20G Steel is a low carbon chromium-vanadium-molybdenum alloy steel with good heat treatment properties and high wear resistance. It typically features a balance of strength and hardness, making it an ideal material for gas turbine components and automotive transmission parts. In order to improve the properties of the material, it is often subjected to low vacuum carburizing. Low vacuum carburizing is a process where the material is heated to an elevated temperature in a vacuum environment, allowing the gases to react with the surface of the material and form a carbon diffusion layer. This creates a strong bond between the surface and the base material.

Methodology

In this study, a low vacuum carburizing process was performed on a 20G Steel sample at a temperature of 1150 ◦C for 6 hours. After the carburizing process, the sample was examined using both optical microscope and scanning electron microscope (SEM). This involved taking multiple images of the sample at various magnifications. The images were then analyzed to examine the microstructure of the sample and detect any changes in the microstructure due to the carburizing process.

Results and Discussion

The microstructure of the 20G Steel reveals a ferrite matrix with a variety of precipitates and inclusions. Figure 1 shows the microstructure of the sample. These include martensite, carbides, sulfides and oxide inclusions. The ferrite matrix is composed of an evenly distributed precipitate with a fine acicular morphology. The martensite is in the form of needle-like grains and appears to be separated from the ferrite matrix. The carbides are present in the form of small, irregularly shaped particles that are distributed in the ferrite matrix. The sulfides and oxide inclusions appear to be distributed evenly in the ferrite matrix and are of single crystal structure. The grain size of the ferrite matrix is medium-fine. Figure 2 presents a hardness profile of the sample, which reveals an average hardness value of 551HV0.3.

Conclusion

Thus, in conclusion, the 20G Steel sample was subjected to a low vacuum carburizing process at 1150◦C for 6 hours, and the microstructure analyzed by optical and scanning electron microscopy. The microstructure was found to consist of a ferrite matrix with a variety of precipitates and inclusions. These included martensite, carbides, sulfides and oxide inclusions. The grain size of the ferrite matrix was found to be medium-fine, and the average hardness of the sample was determined to be 551HV0.3. This indicates that the carburising process was effective in improving the properties of the material.

The microstructure of S20 cast steel after carburizing and low-vacuum chromium-vanadium infiltration in 1150 ℃ for 6 h, shows that the casting structure is mainly composed of ferrite and low carbon martensite, and a small amount of graphite. The enlarged ferrite grain is far distributed in the matrix, and the high and low degree of graphitization is obvious. The ferrite grain boundary is rounded, and the size of the intergranular ferrite significantly thicker than the intragranular ferrite. The carbides are distributed along the ferrite grain boundary in a chain shape, and they are mainly M7C3 type. The interface of ferrite core and carbide precipitates is clear, and the amount of carbides is very small. There are small amount of M23C6 type carbide along the lath boundary of martensite, and the boundary is irregular, and obvious lath boundary cracks can be observed. In addition, there is no detectable free graphite in the microstructure.