Heat Treatment Methods For Sanitary Pipe Fittings

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Hot rolling and cold rolling are the two most commonly used processes for forming steel or steel plates, and are also the most basic heat treatment methods for steel. Heat treatment can have a great impact on the structure and performance of Sanitary Butterfly Valve. The rolling of steel is mainly hot rolling, and cold rolling is only used to produce small steel and thin plates. The following introduces the differences between them.

1. Hot rolling

Benefits: It can destroy the casting structure of the 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 is mainly reflected in the rolling direction, so that the steel is no longer an isotropic body to a certain extent; the bubbles, cracks and looseness formed during pouring can also be welded under high temperature and pressure.

Disadvantages: 1. After hot rolling, the non-metallic mixture inside the steel (mainly sulfides and oxides, and silicates) is pressed into thin sheets, and the phenomenon of stratification (interlayer) occurs. Delamination greatly deteriorates the tensile properties of steel along the thickness direction, and there is a possibility of interlayer tearing when the weld is tightened. The local strain induced by weld tightening often reaches several times the yield point strain, which is much larger than the strain caused by load.

2. Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress without external force. Hot-rolled steel sections of various cross-sections have this kind of residual stress. Generally, the larger the cross-sectional size of the steel section, the greater the residual stress. Although residual stress is self-balanced, it still has a certain effect on the performance of steel components under external forces. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc.

2. Cold rolling

It refers to the processing of steel plates or steel strips into various types of steel at room temperature through cold processing such as cold drawing, cold bending, and cold drawing.

Advantages: fast forming speed, high output, no damage to coating, can be made into a variety of cross-sectional forms to meet the needs of application conditions; cold rolling can make steel produce great plastic deformation, thereby increasing the yield point of steel.

Disadvantages: 1. Although there is no hot plastic compression during the forming process, there are still residual stresses in the cross section, which will definitely affect the overall and local buckling properties of the steel.

2. The cold-rolled steel section is generally an open section, which makes the free rotation stiffness of the section low. It is easy to rotate when bent, and it is easy to bend-torsion buckling when compressed, and the torsion resistance is poor.

3. The wall thickness of cold-rolled steel is small, and there is no thickening at the corners where the plates are connected, so the ability to withstand local concentrated loads is weak.

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