As a key connecting element in mechanical equipment and structure, the performance stability of fasteners is crucial to the normal operation and safety of the entire equipment. Especially in the high temperature environment, the creep resistance of fasteners is particularly important. The creep resistance of fasteners refers to their ability to resist plastic deformation under high temperature. In a high temperature environment, fasteners are susceptible to thermal expansion, thermal fatigue, high temperature corrosion and other factors, resulting in a decline in creep resistance, thereby affecting the safety and stability of the entire equipment. Therefore, it is of great practical significance to study the creep resistance of fasteners in high temperature environment.
The creep resistance of fasteners is closely related to their material, structure and manufacturing process. Strength ratio is an important parameter to reflect the plastic deformation ability of materials under static load, while thermal fatigue refers to the phenomenon of fatigue cracks in materials under cyclic heat load. Under high temperature environment, the creep resistance of fasteners is mainly affected by thermal expansion, thermal fatigue, high temperature corrosion and other factors.
Representative fastener materials were used in this experiment, including low carbon steel, medium carbon steel and high carbon steel. These materials have good strength and stability under high temperature environment and can meet the experimental requirements. The experimental equipment includes universal testing machine and high temperature furnace, which can simulate the high temperature environment from normal temperature to 600℃, and carry out long-term heat exposure experiments.
Before the experiment began, chemical composition analysis, metallographic microstructure observation and hardness testing were performed on all samples to ensure the consistency of material properties of the samples. Subsequently, the sample is placed in a high temperature furnace, heated to a preset high temperature environment at a rate of 10 ° C /min, and maintained for a certain time to simulate the heat exposure process of fasteners in actual use. During the experiment, the tensile and compressive stress of the sample were tested by the universal testing machine, and the stress-strain curves at different temperatures were recorded, and the deformation of the sample was observed. At the same time, in order to simulate the cyclic load conditions in actual use, it is also necessary to carry out thermal cycling treatment on the sample during the experiment to simulate the thermal fatigue process at different temperatures.
Through the collation and analysis of the experimental data, the following conclusions are drawn:
In high temperature environment, the creep resistance of low carbon steel is the best, the creep resistance of medium carbon steel and high carbon steel is poor. This is because the lattice structure of low carbon steel is relatively simple, and the binding force between atoms is weak, so it is not easy to creep at high temperatures. The lattice structure of medium carbon steel and high carbon steel is more complex, and the binding force between atoms is strong, so it is easy to creep at high temperatures.
With the increase of temperature, the yield strength and tensile strength of all materials decreased gradually. This is because at high temperatures, the thermal motion between atoms intensifies, leading to a reduction in the stress inside the material, which reduces the yield strength and tensile strength of the material.
At the same temperature, the thermal fatigue treated material has better creep resistance than the untreated material. This may be because thermal fatigue treatment can increase the internal stress of the material, thereby improving the creep resistance of the material.
In this experiment, the creep resistance of fasteners under high temperature environment was studied, and the following conclusions were drawn:
The creep resistance of fasteners at high temperature is closely related to their materials. Low carbon steel has better creep resistance, medium carbon steel and high carbon steel have worse creep resistance.
With the increase of temperature, the yield strength and tensile strength of fasteners are gradually reduced.
Fasteners after thermal fatigue treatment have better creep resistance than untreated fasteners.
In practical applications, fasteners often need to work in a high temperature environment for a long time, so improving their creep resistance is of great significance to ensure the safety and stability of the equipment. According to the results of this experiment, in order to improve the creep resistance of fasteners, the following measures can be taken:
Choose materials with better creep resistance to make fasteners, such as mild steel.
The fasteners are heat treated to improve their internal structure and increase their creep resistance. For example, advanced surface treatment technologies such as vacuum heat treatment or plasma nitriding technology are used to improve the hardness and wear resistance of fasteners.
In the design and manufacturing process, the size and thickness of the fastener should be minimized to increase its structural stiffness and stability to reduce the probability and degree of creep. At the same time, the fit and support form should be selected reasonably to reduce the degree of stress concentration
