Heat treatment method of sanitary pipe fittings
Hot rolling and cold rolling are the two most commonly used processes for forming steel or steel plates, and they are also the most basic heat treatment methods for steel. Through heat treatment, they can have a great influence on the structure and performance of steel. Hot rolling is used as the tension for steel rolling Mainly, cold rolling is only used for the production of small section steel and thin plates. Let me introduce the difference between them.
First, hot rolling
Benefits: It can destroy the casting structure of the steel ingot, refine the grains of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved. This improvement tension is reflected in the upward direction of rolling, so that the steel is no longer isotropic to a certain extent; the bubbles, cracks and looseness formed during casting can also be welded under the action of high temperature and pressure.
Disadvantages: 1. After hot rolling, the non-metallic mixture inside the steel (strain is sulfide and oxide, and another silicate) is pressed into thin slices, showing signs of delamination (interlayer). The delamination greatly deteriorates the tensile properties of the steel along the thickness, and there may be interlayer tearing when the weld is tightened. The local strain induced by welding seam tightening often reaches several times the yield point strain, which is much larger than the strain caused by the load.
2. Slag stress caused by uneven cooling. The dross stress is a stress that balances itself in the absence of external forces. Hot-rolled steel of various cross-sections has this type of dross stress. The larger the cross-sectional size of ordinary steel, the greater the dross stress. Although the slag stress is self-balanced, it still has a positive effect on the performance of the steel member under the action of external forces. Such as deformation, stability, anti-complexion and other aspects are likely to produce bad luck.
Second, cold rolling
refers to the cold-drawing, cold-bending, cold-drawing and other cold processing of steel plates or steel strips into various types of steel at room temperature.
Benefits: fast forming speed, high output, and without damaging the coating, can be made into a variety of cross-sectional situations to meet the needs of the use conditions; cold rolling can cause the steel to produce a large plastic deformation, thereby improving the steel's Yield point.
Disadvantages: 1. Although there is no hot plastic compression in the forming process, there is still slag stress in the cross section, which will definitely affect the characteristics of the steel group and local buckling.
2. The style of cold-rolled steel is usually an open section, which makes the free rotation rigidity of the section lower. Rotation is easy to occur when bending, bending and torsion buckling is easy to occur under compression, and the torsion resistance is poor.
3. The wall thickness of the cold-rolled steel is small, and there is no thickening at the corners where the plates are joined, and the ability to be subjected to local convergence loads is weak.