Effect of Tempering Temperature on Microstructure, Hardness, Toughness and Impact Abrasive Wear Properties of Medium Car

Steel is widely used in all areas of civil engineering, and its mechanical properties such as hardness, toughness and impact abrasive wear properties are essential for successful application.
    
Tempering is a heat treatment process used to alter the mechanical properties, structure and microstructure of a material. It is carried out in order to improve the mechanical properties of a steel. One of the most important steels used in civil engineering is medium carbon low alloy steel ZG30Cr2SiMnMo and in this study, the effect of tempering temperature on its microstructure, hardness, toughness and impact abrasive wear properties were studied.
    
To investigate the effect of tempering temperature on microstructural and mechanical properties of the medium carbon low alloy steel ZG30Cr2SiMnMo, a range of tempering temperatures (150°C, 200°C and 250°C) were selected. The results of hardness tests showed that the hardness of the sample decreased with increasing tempering temperature. The highest hardness value was at 150°C and the lowest value was at 250°C. Similarly, impact abrasive wear tests showed a decrease in wear index with increasing tempering temperature. The wear index decreased from 3.36 at 150°C to 2.91 at 250°C. The results of toughness tests also revealed that the tempering temperature significantly affects the toughness of the medium carbon low alloy steel. The toughness reached a maximum of 148.12MPa at 150°C, and decreased gradually to 86.1MPa at 250°C.
    
Microstructure of the medium carbon low alloy steel ZG30Cr2SiMnMo at different tempering temperatures
    
The microstructural observations revealed that an increase in tempering temperature caused the dissolution of excess carbide precipitates. Figures 1 and 2 show the microstructure of the samples tempered at 150°C and 250°C respectively. As can be seen from these figures, an increase in tempering temperature from 150°C to 250°C resulted in an increased grain size of the ferrite and increased dissolution of carbides. The results of this study show that the tempering temperature has a significant effect on the microstructure and mechanical properties of the medium carbon low alloy steel ZG30Cr2SiMnMo.
    
Hardness of the medium carbon low alloy steel ZG30Cr2SiMnMo at different tempering temperatures
    
In conclusion, increasing tempering temperature from 150°C to 250°C has a visible effect on the microstructure and mechanical properties of medium carbon low alloy steel ZG30Cr2SiMnMo. The microstructural changes showed an increased grain size of the ferrite and increased dissolution of carbides. Hardness and toughness decreased with increasing tempering temperature, and the wear index also decreased. This study provides valuable information about the effect of tempering temperature on medium carbon low alloy steel and can be used as a guide for selection of appropriate tempering temperatures for mechanical applications.

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