Views: 16 Author: Site Editor Publish Time: 2020-06-30 Origin: Site
Steel pipes can be used to transport fluids and powdered solids, exchange thermal energy, and make mechanical parts and containers, it is also an economical steel. For example, the use of steel pipes to make grids, pillars and mechanical supports for building structures can reduce the weight and save 20 to 40% of metal, and can realize factory mechanized construction; using steel pipes to make highway bridges can not only save steel, simplify construction, but also greatly reduce The area covered with a protective layer saves investment and maintenance costs.
Steel tubes used as structures sometimes need to undergo heat treatment to meet the different grade requirements of the project. What is the heat treatment process of large-diameter steel pipes?
In the heat treatment process, the reason for the change in the geometry of the large-diameter steel tube is due to the stress of the heat treatment. Heat treatment stress is a relatively complicated problem, which is not only the cause of defects such as deformation and cracks, but also an important means to improve the fatigue strength and service life of the workpiece. Therefore, it is very important to understand the mechanism and change law of heat treatment stress and master the method of controlling internal stress.
So, what is heat treatment stress?
Heat treatment stress refers to the stress generated inside the workpiece due to heat treatment factors (thermal process and structure transformation process). It is self-balanced in the whole or part of the volume of the steel pipe, so it is called internal stress. Heat treatment stress is divided into tensile stress and compressive stress according to the nature of its effect; it can be divided into instantaneous stress and residual stress according to the time of its effect, and it is divided into thermal stress and tissue stress according to the reason for its formation.
The thermal stress is caused by the temperature variation of various parts of the steel pipe during heating or cooling. The surface is always hotter than the core when heating, and the core is slower than the surface when cooling. This is because the absorption and loss of heat are conducted through the surface. Large-diameter steel pipes that do not change in composition and organization state, at different temperatures, as long as the linear expansion coefficient is not equal to zero, will cause changes in specific volume, so in the heating or cooling process, neither fast nor slow.