The most critical step in the production of high-strength bolts

The high-strength bolt grades produced by our factory include metric 8.8, 10.9, 12.9, ASTM  standard UNC Gr5 , 8 grades. The high-strength nuts include metric 8 and 10 grades, and  ANSI standard grade 5 and G8 , all of which require heat treatment

Quenching and tempering refers to a heat treatment process used to improve the comprehensive mechanical properties of steel materials. After quenching, it is subjected to high-temperature tempering treatment. The purpose is to achieve a good combination of strength and toughness in steel components, with both high strength and excellent toughness, plasticity, cutting performance, etc. Some alloy steels or low-alloy steels must undergo quenching and tempering to obtain good comprehensive properties, and these steels can also be called quenched and tempered steels. After quenching and tempering treatment, ductile iron can not only improve strength, but also enhance hardness and wear resistance

brief introduction
Quenching and tempering treatment refers to the dual heat treatment method of quenching and high-temperature tempering, which aims to make the workpiece have good comprehensive mechanical properties. High temperature tempering refers to tempering between 500-650 ℃. Most quenched and tempered parts work under relatively large dynamic loads, bearing the effects of tension, compression, bending, torsion, or shear. Some surfaces also have friction, requiring certain wear resistance, and so on. In short, the parts work under various composite stresses. These types of parts are mainly structural components of various machines and mechanisms, such as shafts, connecting rods, bolts, gears, etc. They are widely used in manufacturing industries such as machine tools, automobiles, and tractors. Especially for large components in heavy machinery manufacturing, quenching and tempering treatment is more commonly used. Therefore, tempering treatment plays a very important role in heat treatment. The performance requirements for quenched and tempered parts in mechanical products vary depending on their stress conditions. Generally speaking, various quenched and tempered parts should have excellent comprehensive mechanical properties, that is, a suitable combination of high strength and high toughness, to ensure the long-term smooth operation of the parts.
Steps and principles
Quenching is the first step process, and the heating temperature depends on the composition of the steel. The quenching medium is selected based on the harden ability of the steel and the size of the steel component. After quenching, steel has high internal stress and is very brittle. Tempering is necessary to eliminate stress, increase toughness, and adjust strength. Tempering is the most important process for standardizing the mechanical properties of quenched and tempered steel. The curve of various steel mechanical properties changing with tempering temperature, also known as the tempering curve of steel, can be used as a basis for selecting tempering temperature. For high-temperature tempering of certain alloy quenched and tempered steels, attention should be paid to preventing the occurrence of the second type of tempering brittleness to ensure the performance of the steel.
application
Quenching and tempering treatment is widely used for structural parts that require excellent comprehensive performance, especially for working under alternating loads, such as automobile shafts and gears, turbine shafts and compressor discs of aircraft engines, etc. Structural steel parts that require induction heating quenching are usually quenched and tempered before surface quenching to obtain small and uniform martensite, which is beneficial for the surface hardening layer and can also achieve good comprehensive mechanical properties in the core. Nitrided parts that undergo quenching and tempering treatment before nitriding can improve the processing performance of steel and prepare the structure for nitriding. In order to achieve high smoothness of the measuring tool before quenching, eliminate stress caused by rough machining, reduce quenching deformation, and make the hardness after quenching high and uniform, quenching and tempering treatment can be carried out before precision machining. For tool steels with network carbides or coarse grains after forging, quenching and tempering treatment can be used to eliminate the carbide network, refine the grains, and improve the machinability by spheroidizing the carbides, preparing the microstructure for the final heat treatment.
Processing technology
The heat treatment process of steel includes methods such as annealing, normalizing, quenching, tempering, and surface heat treatment. Among them, tempering includes high-temperature tempering, medium temperature tempering, and
Low temperature tempering. Reheating quenched steel to a certain temperature and then cooling it using a certain method is called tempering. The purpose is to eliminate the internal stress generated by quenching, reduce hardness and brittleness, and achieve the expected 

mechanical properties.
Quenching and tempering usually refers to the heat treatment process of quenching and high-temperature tempering to obtain tempered martensite. The method is to first quench, with a quenching temperature of Ac3+30-50 ℃ for hypoeutectoid steel; Eutectoid steel is Ac1+30~50 ℃; Alloy steel can slightly improve compared to carbon steel. After quenching, tempering can be carried out at 500-650 ℃.
Quenched and tempered steel
The so-called quenched and tempered steel generally refers to medium carbon steel with a carbon content of 0.3-0.6%. Parts made of this type of steel generally require good comprehensive mechanical properties, that is, maintaining high strength while also having good plasticity and toughness. People often use modulation treatment to achieve this goal, so people habitually refer to this type of steel as quenched and tempered steel. It should be noted that sometimes quenched and tempered steel also refers to the process of adding manganese and silicon during the smelting of steel, and attention should be paid to the difference.

Ningbo Zhongli bolts manufacturing co.ltd has its own heat treatment equipment that allows us to control the quality ourselves, which is very friendly to customers with high quality requirements. After heat treatment, we will test the hardness, tensile strength, and elongation of bolts and nuts We have our own testing laboratory. We mainly produce GB, DIN, ASTM high-strength bolts and nuts. Including hexagonal bolts GB5782/5783, DIN931/933,DIN912,DIN6914,EN14399, A325,A193 B7,2H NUTS, Hexagonal nut DIN934 , DIN6915,A563, Flat pad DIN125, DIN6916,F436.