Microstructure and properties of NM360 high-strength wear-resistant steel welded joints

NM360 high-strength wear-resistant steel is an ideal material for various important components in various industries such as mining, petrochemical, cement and energy due to its excellent wear resistance, impact resistance and high strength. Since the base material of NM360 steel is austenite and its welding is difficult, welding is often encountered in the fabrication processes of components of NM360 steel. The welding joint of NM360 steel needs to possess excellent wear resistance, impact resistance, and strength to ensure the reliability and safety of the components. In this article, the microstructure and properties of NM360 high-strength wear-resistant steel welded joints are discussed.
    
Microstructure and Alloying
The microstructure of NM360 steel welded joints mainly consists of martensite, ferrite and bainite. The martensite is formed by the rapid cooling process at the welding seam. The martensite is hard and brittle, so it can improve the wear resistance of the welding joint. The ferrite is formed by the slow cooling process after welding. The ferrite exhibits low hardenability and low wear resistance. The bainite is required to improve the strength and toughness of the welding joint. The bainite structure is achieved by optimal alloying which is controlled by the cooling process.
    
SEM photograph of the microstructure of the welded joint
    
The figure above shows the microstructure of the welded joint of NM360 high-strength wear-resistant steel. It can be seen that the microstructure mainly consists of martensite and ferrite with a small amount of bainite. The bainite can be identified by the presence of an fine network of interlaced ferrite and carbide particles.
    
Mechanical Properties
The mechanical properties of NM360 high-strength wear-resistant steel welded joints are mainly determined by its microstructure. The mechanical properties of the welding joint must be excellent to ensure the reliability and safety of components. The hardness and toughness of NM360 steel welded joint are improved by the optimal alloying, which is controlled by the cooling process. The microstructure of NM360 steel welded joint consists of martensite, ferrite and bainite, which exhibits high hardness and toughness. The hardness of the welded joint is HRC45-50 and the impact toughness is above 40J. The fatigue strength and tensile strength of the welded joint are 770MPa and 1000MPa, respectively. The wear resistance of the welding joint is excellent and its wear resistance is up to 2.5 times that of the base material.
    
In conclusion, the microstructure of NM360 high-strength wear-resistant steel welded joint mainly consists of martensite, ferrite and bainite. The martensite can improve the wear resistance of the welded joint while the bainite is essential to improve the strength and toughness. The optimal alloying controlled by the cooling process can improve the hardness and toughness of welding joint. The fatigue strength, tensile strength and wear resistance of the welded joint are excellent.

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