It is well known that the manufacturing process of stainless steel screws usually have four types: molding, grinding, cleaning and heat treatment. Then, the top three steps of the screw have been processed, why should the heat treatment process? Is a stainless steel screw or a carbon steel high strength bolt? In fact, after the first three steps, there is still a certain residual stress in the screw, the thread is extended inwardly, and the heat treatment can be improved when the heat treatment is improved; in addition, the stainless steel screw is made of low carbon steel, and the carbon treatment . The main purpose of heat treatment is to increase the surface containing carbon, which further improves the strength of the surface, anti-mobility, tensile resistance, and wear resistance, and improve the life of the stainless steel screw.
In general, heat treatment is divided into preliminary heat treatment and final heat treatment. The purpose of screw pretreatment heat treatment is to improve process performance, eliminate internal stress, and prepare the gold phase to the final heat treatment. The heat treatment process includes annealing, normal fire, aging, quenching and tempering.
1. About the annealing and normal fire of the stainless steel screw: used for hot processing blanks, carbon steel containing more than 0.5% carbon steel and alloy steel to reduce hardness, easy to cut; for carbon steel and alloy steel containing less than 0.5% carbon, Using normal fire treatment, the hump is avoided when the hardness is too low. Annealing and annealing can fine grain, uniform tissue, ready for subsequent heat treatment. Annealing and normalizing usually scheduled after the blank manufacturing and roughing.
2. Screw aging: Mainly used to eliminate internal stress generated during blank manufacturing and processing. For a generally accurate part, an aging treatment can be arranged prior to finishing. For parts having high precision requirements, arrange two or more aging processing, simple parts cannot be processed. For some precision parts with poor stiffness, in order to eliminate internal stress generated in the machining, the processing accuracy of the part is made, and multiple aging processing is performed between roughing and semi-finishing. The axial part of the fastener is processed after normalization.
3. Quenching and tempering of stainless steel screws: This process is high-temperature tempering after quenching. Uniform and small temper tissue can be obtained to prepare a deformation of the surface quenching and nitriding treatment of the lower process. Therefore, quenching and tempering can also be used as preheating treatment. After tensioning, the comprehensive mechanical properties of fasteners are better, and the product that requires lower hardness and wear resistance can serve as the final heat treatment process.
4. Final heat treatment: The final heat treatment of stainless steel screws is to improve hardness, wear resistance, strength, and related mechanical properties.
5. Quenching: Divided into surface quenching and overall quenching. Different, surface quenching is widely used due to small deformation, oxidation and decarbonation. It has the advantages of high external strength, good wear resistance, good internal toughness, strong impact resistance. In order to improve the mechanical properties of surface quenching, the preheating treatment must be hot treatment such as quenching tempering or normal fire.
Process is: Upper material forging normal fire (annealing) - roughing and quenching tempering semi-finishing surface quenching processing.
6. Carburizing quenching: Suitable for low carbon steel and low alloy steel to improve the amount of carbon containing the surface of the part, improve the hardness after quenching, while the core remains a certain strength and high toughness and plasticity. Carburizing is divided into whole-carburization and local carburization. When local carburization, the non-carburizing site should take anti-seepage measures. Copper plated or processed anti-seepage materials are generally selected. The carburizing quenching is large, and the depth of carburizing is generally between 0.5 to 2 mm. This process is arranged between semi-finishing and finishing.
Process is: Upper material forging
When partial carburizing but non-carburized parts, the cutting processes should be carried out prior to quenching after carburizing after cutting the long-induced process.
7. Nitrogen nitrogen treatment: the nitrogen atom penetrates into the metal surface to give a layer of nitrogen-containing compound. The nitrogen nitrogen nitrogen nitrogen can improve the surface hardness, wear resistance, fatigue strength and corrosion resistance of the part. Due to the low nitriding temperature, small deformation, the nitrid layer is thin (generally less than 0.7 mm-41; the nitriding process should be arranged as much as possible. In order to reduce nitrogen nitrogen-nitriding deformation, it is generally necessary to perform stress elimination and high temperatures after cutting.
In summary: carbon steel, high-strength screw, high strength nut and high strength gasket more suitable for heat treatment.
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