Metal heat treatment processes can be roughly divided into three categories: overall heat treatment, surface heat treatment and chemical heat treatment. Depending on the heating medium, heating temperature and cooling method, each category can be divided into several different heat treatment processes. Using different heat treatment processes, the same metal can obtain different structures and thus have different properties. Steel is the most widely used metal in industry, and the microstructure of steel is also the most complex, so there are many types of steel heat treatment processes.
Overall heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate speed to change its overall mechanical properties. The overall heat treatment of steel generally includes four basic processes: annealing, normalizing, quenching and tempering.
1.Annealing
Annealing is to heat the workpiece to an appropriate temperature, adopt different holding times according to the material and workpiece size, and then slowly cool it. The purpose is to make the internal structure of the metal reach or approach an equilibrium state, or to release the internal stress generated in the previous process. Obtain good process performance and service performance, or prepare the structure for further quenching.
2.Normalizing
Normalizing or normalizing is to heat the workpiece to a suitable temperature and then cool it in the air. The effect of normalizing is similar to that of annealing, except that the obtained structure is finer. It is often used to improve the cutting performance of materials, and is sometimes used to meet certain requirements. Not high parts as final heat treatment.
3.Quenching
Quenching is to heat and maintain the workpiece, and then quickly cool it in a quenching medium such as water, oil or other inorganic salt solutions, organic aqueous solutions.
4.Tempering
After quenching, the steel becomes hard but at the same time becomes brittle. In order to reduce the brittleness of steel parts, the quenched steel parts are kept at an appropriate temperature above room temperature and below 650°C for a long time, and then cooled. This process is called tempering. Annealing, normalizing, quenching, and tempering are the “four fires” in overall heat treatment. Among them, quenching and tempering are closely related and are often used together and are indispensable.
“Four Fires” have evolved different heat treatment processes with different heating temperatures and cooling methods. In order to obtain a certain strength and toughness, the process of combining quenching and high-temperature tempering is called quenching and tempering. After some alloys are quenched to form a supersaturated solid solution, they are kept at room temperature or a slightly higher temperature for a longer period of time to improve the hardness, strength or electromagnetic properties of the alloy. This heat treatment process is called aging treatment.
The method of effectively and closely combining pressure processing deformation and heat treatment to obtain good strength and toughness of the workpiece is called deformation heat treatment; heat treatment performed in a negative pressure atmosphere or vacuum is called vacuum heat treatment, which not only enables The workpiece will not be oxidized or decarburized, and the surface of the treated workpiece will be kept smooth and clean, improving the performance of the workpiece. It can also be chemically heat treated by penetrating agent.
At present, with the increasing maturity of laser and plasma technology, these two technologies are used to apply a layer of other wear-resistant, corrosion-resistant or heat-resistant coatings on the surface of ordinary steel workpieces to change the surface properties of the original workpiece. This new The technique is called surface modification.
Post time: Mar-31-2024