Effect of Tempering Temperature on Microstructure and Properties of NM360 Wear-resistant Steel

Compared with conventional carbon steel, NM360 wear-resistant steel has a higher hardness, double strength and half extension. It can effectively improve the wear resistance of the machinery and prolong its service life.
    
The proper tempering temperature has an important influence on the microstructure and performance of NM360 wear-resistant steel.
    
The effects of tempering temperature on the microstructure and properties of NM360 wear-resistant steel are described as follows.
    
Microstructure. As the tempering temperature increases, the martensite in the microstructure of NM360 wear-resistant steel gradually transforms into a stable body, with the following microstructural changes:
    
1) At low tempering temperature(below 200℃) the tempering effect is not obvious. Under electron microscopic observation, it can be seen that the grains are mainly martensite structure, with some small carbides scattered in the martensite.
    
2) Tempering at 200-400℃ for 2-4h, can make the microstructure dense, some ferrite and pearlitic transformation still exist.
    
3) Tempering at 400-550℃ for 2-4h, the martensite will transform into bainite, tempered martensite and small amount of ferrite, the carbides tend to degrade and even dissolve, and its structure tends to be uniform and dense.
    
4) At 550-650℃, the structure becomes more uniform and fine, the amount of ferrite increases, and the amount of carbide is slight.
    
Mechanical properties. The mechanical properties of NM360 wear-resistant steel are significantly affected by the tempering temperature. The following are the effects of different tempering temperatures on the mechanical properties of the material.
    
    1) At low tempering temperature(below 200℃), its hardness is slightly increased, but its strength, toughness and plasticity are decreased;
    
    2) At 200-400℃, the strength and plasticity are significantly improved, but its toughness is low;
    
    3) At 400-550℃, the strength and toughness are greatly improved, and the hardness is slightly reduced;
    
    4) At 550-650℃, the strength and plasticity are improved, but the toughness is decreased.
    
Conclusion. The proper tempering temperature has a remarkable influence on the microstructure and properties of NM360 wear-resistant steel. It is necessary to accurately design its tempering temperature, so as to improve its performance and better meet the requirements of engineering applications.

---