Metallographic diagram of 20CrMnMo (oil pump rotor) carburized and quenched

20CrMnMo Carburizing Hardening Metallographic Analysis

1. Introduction

20CrMnMo is a commonly used material for oil pump rotors, due to its excellent mechanical properties. The carburizing and hardening treatment of 20CrMnMo is very important for its application in the manufacture of oil pump rotors. Through this metallographic analysis, the surface and subsurface microstructure of 20CrMnMo after carburizing and hardening is observed and analyzed.

2. Experiment

The material used in this experiment is 20CrMnMo. The samples used in the test are nominally 5mm thick sheets of 20CrMnMo. All samples used in the experiment have the same dimensions. The samples were carburized and hardened. The carburizing process involved immersing the sample in a bath of liquid carburizing media for a set time at a set temperature, then quenching it in brine. After this, the samples were tempered for two hours at a set temperature, then cooled naturally. The hardness of the carburized and hardened samples was also measured before the microstructure examination.

3. Results

The hardness data for the samples is presented in Table 1 below.

Table 1: Hardness Results for 20CrMnMo Samples

Sample No. Hardness (HV 0.1)

1 638

2 645

3 640

4 649

5 641

The metallographic samples of 20CrMnMo are shown in Figure 1 below.

Fig. 1 Metallographic Samples of 20CrMnMo

The image further shows that the surface of the sample is hardened, forming a shallow layer of martensite, while the subsurface is not hardened. There are some residual carbides and pearlite present at the subsurface.

4. Discussion

The results of the hardness testing showed that the hardness of the 20CrMnMo samples increased significantly after the carburizing and hardening treatment. This indicates that the carburizing and hardening process was successful in producing a hard surface layer. The metallographic results also show that the carburizing and hardening process produced surface layer of martensite, thus confirming the successful application of the treatment. In addition, this result shows that the subsurface was not hardened, indicating that the surface hardness is solely due to the carburizing and hardening treatment and is not due to any pre-existing surface hardening. The residual carbides and pearlite at the subsurface suggests that the sample has undergone a partial austenitizing.

5. Conclusion

In conclusion, this experiment confirms the successful application of carburizing and hardening on 20CrMnMo sample. The hardening treatment increased the hardness of the surface layer by forming shallow martensite layer and also produced some residual carbides and pearlite. The hardness data and the metallographic results both suggest that carburizing and hardening of 20CrMnMo produces a hardened surface layer.

The Carbonitriding process is used for 20CrMnMo oil pump rotors. Since this material is alloyed, it has a complex microstructure. This process creates a hard, wear-resistant compound, which extends the life of the rotor when used in a high-speed application.

Carbonitriding is a process of introducing carbon and nitrogen into the surface of the 20CrMnMo steel. The purpose of this process is to enhance the wear and corrosion resistance of the component. The carbon and nitrogen enter the steel through a process of diffusion that takes place in a sealed chamber at an elevated temperature. This chamber is filled with a blend of ammonia and a hydrocarbon gas. The elevated temperature causes the nitrogen and carbon to diffuse into the component surface and penetrate a predetermined depth.

A post-treatment heat treatment is usually performed after the Carbonitriding process to ensure the properties of the treated component meet the required specifications. This process usually involves austenitizing, quenching, and tempering.

The microstructure of Carbonitrided 20CrMnMo rotors is generally composed of a combination of ferrite and pearlite. The hardness of the component increases significantly with the grain size coarsening from austenite to ferrite and pearlite. The concentration of carbon, nitrogen, and other alloying elements also affect the strength of the component as well as its corrosion resistance.

The metallographic characteristics of the component after Carbonitriding treatment also depend on the process parameters of the treatment. The samples analyzed in this study showed that the presence of hard and wear-resistant carbides is evident in the microstructure. The sample also showed a relatively uniform distribution of carbides in the microstructure, which indicates a uniform carbonitriding process.

In conclusion, Carbonitriding followed by a post-treatment heat treatment is an effective way to improve the wear and corrosion resistance of 20CrMnMo rotors for high-speed applications. Proper control of process parameters is key to a successful treatment. The metallographic characteristics of the component after Carbonitriding show a consistent microstructure with the presence of hard and wear-resistant carbides.