Microstructure Analysis of ZG25, ZG35, ZG45 and ZG55 High Strength Bolts
Introduction
High strength bolts are widely used for connecting mechanical components subject to loads to one another, such as crane booms, high-rise buildings, large ships, and bridges. ZG25, ZG35, ZG45, and ZG55 are four common materials used for high strength bolts. This report is aimed to analyse their microstructure under FIRE treatment, which stands for Fire corrosion Improvement and Regrinding Enhanced. In this report, the macrostructure, martensitic phase, and microstructure elements of the four materials are closely examined.
Macrostructure
All four samples ZG25, ZG35, ZG45, and ZG55 are grey in colour before regrinding. Under FIR treatment, the samples become brighter in colour due to the polish caused by the grinding process. The surface of these samples become smooth and shiny, indicating a high degree of machining accuracy in the manufacturing process. All four samples have similar macrostructure, which includes a head and a threaded shaft. The heads of the samples contain a hexagonal cross section, and the threaded shafts taper down in size. The overall shape and size of the high strength bolts remain unchanged after the FIR treatment.
Martensitic Phase
The martensite phase is the major component of all four samples. Its principal characteristics are its high strength, hardness, and hardness to wear. After FIR treatment, the martensite phase in these samples must be thinned. This thinning removes the defects which are caused by high heat, thereby improving the performance of the material. This thinning also affects the overall strength and wear resistance of the material. The thinning to such a degree usually results in a decrease of strength and hardness but can still remain in its constructive use.
Microstructure Elements
The microstructure elements of ZG25, ZG35, ZG45, and ZG55 are mainly periodic structures which contain intermetallic compounds, carbides, nitrides, and other elements. Those elements have a profound influence on the mechanical properties of the high strength bolts. The microstructure of the samples is mainly composed of ferrite, carbide, and manganese sulphide. The martensite phase, together with intermetallic compounds and carbides, form a microstructure grid. This grid supports the other elements and provides stability to the material.
The intermetallic compounds and carbides in the samples are mainly found around the grain boundaries. Their contents can be very different from one sample to another. The intermetallic compounds are mainly composed of iron, chromium, sulphur, and phosphorus. The carbides mainly contain chromium, tungsten, and vanadium. Those elements enhance the hardness and wear resistance of the material, making them suitable for use in applications requiring high temperature and corrosion resistance.
Conclusion
The microstructure of the ZG25, ZG35, ZG45, and ZG55 high strength bolts has been analysed under FIRE treatment. The analysis reveals that the macrostructure of these materials remains unchanged after the process, while the martensitic and microstructure elements have changed. The principal microstructure elements include ferrite, carbide, and manganese sulphide. The intermetallic compounds and carbides are mainly found around the grain boundaries and they have a profound influence on the mechanical properties of the material.
