1, the fatigue phenomenon of steel refers to the phenomenon that steel breaks after a period of time under repeated or periodic stress, especially below its yield point. This fatigue fracture is different from the fracture of steel under large stress, which usually leads to brittle fracture or plastic deformation.
2. Fatigue fracture of steel usually occurs in stress concentration areas, such as mechanical joints, welding points and screw holes. Under the repeated action of stress, these areas will gradually form tiny cracks and expand, eventually leading to overall fracture. The occurrence of fatigue fracture is often related to the internal microstructure of steel, such as inclusions, grain boundaries and dislocations.
3. The occurrence of fatigue phenomenon is related to the magnitude of stress, the number of stress cycles, the minimum stress value in stress cycles and the microstructure of steel. In order to prevent fatigue fracture, methods such as improving steel microstructure, reducing stress concentration area, reducing stress amplitude and increasing minimum stress value can be adopted.
4. Fatigue strength calculation and fatigue life prediction are needed for steel materials such as bridges, buildings and ships that bear repeated or periodic stresses. This can be achieved by fatigue test and finite element analysis. At the same time, for important structural components or key components, regular inspection and maintenance are needed to ensure their safety and reliability.
The refining method of steel is as follows:
1. BOF steelmaking: BOF steelmaking is a steelmaking method in which molten iron, scrap steel and ferroalloy are used as main raw materials and molten steel is obtained through BOF smelting. In the process of converter steelmaking, the oxidation reaction of silicon and manganese in molten iron mainly produces heat, and ferroalloy is added to adjust the composition of steel. Converter steelmaking has the advantages of high production efficiency and low cost, but the composition control is not as accurate as that of open hearth furnace.
2. EAF steelmaking: EAF steelmaking takes scrap steel as the main raw material, and molten steel is obtained by arc heating and melting raw materials. In the process of EAF steelmaking, electric energy is converted into heat energy, and a small amount of molten iron or ferroalloy is added to adjust the composition of steel while melting scrap steel. Electric arc furnace steelmaking has the advantages of wide adaptability of raw materials and controllable components, but the production efficiency is relatively low.
3. Oxygen converter steelmaking: Oxygen converter steelmaking is to replace air with oxygen in the converter and generate molten steel through the reaction of iron ore or iron-containing raw materials with oxygen at high temperature. Oxygen converter steelmaking has the advantages of high production efficiency, low energy consumption and controllable composition. , but the investment is large and the operational technical requirements are high.