1. Heat treatment

Heat treatment processing refers to a metal thermal processing process in which the material is heated, insulated and cooled in a solid state to obtain the desired structure and function. During the progression from the Stone Age to the Bronze and Iron Ages, the role of heat treatment became known.

As early as 770 BC to 222 BC, Chinese people have discovered in production practice that the function of steel will change due to the influence of temperature and pressure deformation. The softening of white cast iron is an important process for making agricultural tools.

2. Heat treatment method

Metal heat treatment process can be roughly divided into three categories: overall heat treatment, surface heat treatment and chemical heat treatment. According to the different heating medium, heating temperature and cooling method, each category can be divided into several different heat treatment processes. Different heat treatment processes are used for the same metal to obtain different arrangements and thus have different functions.

Steel is a widely used metal in industry, and the microscopic arrangement of steel is also more complicated, so the heat treatment process of steel is complicated. Overall heat treatment is a metal heat treatment process that heats the entire workpiece and then cools it at an appropriate rate to obtain the required metallographic structure to change its overall mechanical properties. The overall heat treatment of steel generally has four basic processes: annealing, normalizing, quenching and tempering.

Heat treatment is a metal thermal processing process in which the metal material is heated, kept warm and cooled in a certain medium, and its performance is controlled by changing the surface or internal metallographic structure of the material. Several commonly used heat treatment process methods are described below.

Commonly used heat treatment methods are as follows:

1. Normalizing: Heat the steel or steel parts to an appropriate temperature above the critical point AC3 or ACM for a certain period of time and then cool in the air to obtain a heat treatment process of pearlite structure.

2. Annealing annealing: heat the hypoeutectoid steel workpiece to 20-40 degrees above AC3, after holding for a period of time, slowly cool with the furnace ((or cool in sand or lime) to below 500 degrees and cool in air heat treatment process.

3. Solution heat treatment: Heat the alloy to a high temperature single-phase region and hold it at a constant temperature, so that the excess phase is fully dissolved into the solid solution, and then rapidly cooled to obtain a supersaturated solid solution.

4. Aging: After the alloy is subjected to solution heat treatment or cold plastic deformation, its function changes with time when it is placed at room temperature or slightly higher than room temperature.

5. Solid solution treatment: to fully dissolve various phases in the alloy, strengthen the solid solution and improve the toughness and corrosion resistance, eliminate stress and soften, so as to continue processing and forming.

6. Aging treatment: heating and keeping the temperature at the precipitation temperature of the strengthening phase, so that the strengthening phase is precipitated, hardened, and the strength is improved.

7. Quenching: A heat treatment process in which the steel is austenitized and then cooled at an appropriate cooling rate, so that the workpiece undergoes martensite and other unstable structural transformations in the entire or certain range of the cross section. 50CrVA spring steel 880°C oil quenched metallographic arrangement

8. Tempering: The quenched workpiece is heated to an appropriate temperature below the critical point AC1 for a certain period of time, and then cooled in a manner that meets the requirements to obtain the required design and performance.

9. Carbonitriding of steel: Carbonitriding is the process of entering carbon and nitrogen together into the surface of the steel. Traditionally, carbonitriding, also known as cyanidation, is currently widely used in medium-temperature gas carbonitriding and low-temperature gas carbonitriding (ie, gas soft nitriding). The primary purpose of medium temperature gas carbonitriding is to improve the hardness, wear resistance and fatigue strength of steel. Low-temperature gas carbonitriding is mainly nitriding, and its primary purpose is to improve the wear resistance and seizure resistance of steel.

10. Ion nitriding The process of nitriding using the glow discharge that occurs between the workpiece (cathode) and the anode in a nitriding atmosphere below one atmosphere is called ion nitriding. Its characteristics are: fast nitriding speed; easy control of arrangement, small brittleness of nitrogen layer; small deformation; easy maintenance, energy saving; less pollution.

11. Quenching and tempering treatment: It is generally customary to combine heat treatment with quenching and high temperature tempering as quenching and tempering treatment. Quenching and tempering treatment is widely used in various important structural parts, especially those connecting rods, bolts, gears and shafts that work under alternating loads. After quenching and tempering, a tempered sorbite structure is obtained, and its mechanical properties are better than the normalized sorbite structure with the same hardness. Its hardness depends on the high temperature tempering temperature and is related to the tempering stability of the steel and the size of the workpiece section, generally between HB200-350.

12. Brazing: a heat treatment process in which two workpieces are bonded together with solder. With the development of modern science and technology and the continuous development of heat treatment technology, it has brought greater convenience to industrial enterprises, while traditional thermal processing technology always requires a lot of resources and raw materials to be processed. High-quality metal workpieces are produced, and a lot of waste will occur in the process, the use of raw materials is not sufficient, etc. However, today's ion nitriding furnace can save energy and emissions during the process of ion nitriding heat treatment. There are fewer pollutants and gases, and operational efficiency is also increased. It is another important creation in the history of heat treatment.