Quenching and cooling method for heat treatment of screw fasteners

     Screw fasteners seem to be a simple and small work iron. However, when manufacturing, it is testing the technical strength of a factory. When the screw fasteners are produced, the screw tolerance may be too large in an hour. As a result, it is impossible to assemble, and it is also possible to control the temperature and solution of the surface treatment when the surface of the screw fastener is processed, and it is easy to cause problems with the screw fastener. Today, Shishitong screw manufacturers will briefly introduce the quenching and cooling method for the surface treatment of screw fasteners.

    Extension screw

    The quenching method of the surface treatment of the screw fastener includes the type of quenching cooling medium employed. Cooling time. The final cooling temperature of the screw fastener surface, which is a very important and difficult process to master the quenching and heat treatment of large-size bolt fasteners.

    1. Segregation of carbon alloy elements results in different cooling rates in different regions of the warming member, resulting in different martensite transformation temperatures. Therefore, component segregation must be considered when determining the final cooling temperature of the bolt fastener surface. For the final cooling temperature, time-limited quenching should be used. When cooling to near the dangerous temperature of quenching, the bolt fasteners are taken out from the quenching medium and slowly cooled to prevent the advancement of the structure in some areas.

    Second, the quenching effect of the screw fastener determines the cooling mode and the surface final cooling temperature in the cooling medium. At present, the aqueous solution is made of PAG polymer, the cooling rate is wide, and the concentration is easy to control. For the medium carbon alloy structural steel, the concentration ratio of 9% to 11% is generally adopted, and the mesh belt furnace discharge is free to fall into the cooling tank. The cooling method has a great influence on the cooling speed of the bolt and each section. Except for the segregation of the temperature component, the martensitic transformation temperature is different, and the cooling rate is different, resulting in the non-martensitic transformation of the local region. A tissue specific tolerance along the cross section is produced, and several stress superpositions are prone to cracking of the bolt fasteners.

    The final cold temperature of the surface of the screw fastener is also one of the important reasons for the cracking of the screw fastener. It has been proved that the general quenching crack occurs in the low temperature stage of the late cooling stage. At this time, the screw fastener has no plasticity and the stress cannot be caused. Due to the relaxation of plastic deformation, for some large-section workpieces, due to the fear of impermeability, the cooling time in the cooling medium is too long. This method is undoubtedly prone to cracking. When the chemical composition of steel is constant, the most intense cooling medium is used. It is also difficult to maintain the stability of austenite in a certain cross-section attempt, without precipitation of ferrite and no pearlite transformation, that is, lowering the final cooling temperature, and not improving the overall mechanical properties of the screw fastener, but increasing the quenching. The tendency of cracking, for the medium-carbon alloy steel, the final cooling temperature should not be controlled below 250 °C, and the cooling time should not be too long.