Carbon steel heat treatment is a metal processing heat treatment method. Its main purpose is to enhance the performance and processing properties of the steel. In simple terms, the steel is heated to a certain temperature, held for a period of time, and then cooled at a certain rate. During this process, the properties of the steel change.

First, annealing:

This is a heat treatment process where steel is heated above the critical temperature AC1 or AC3, held for a certain period of time, and then slowly cooled in the furnace. After this treatment, the steel's structure is closer to the equilibrium state, with lower hardness, which is conducive to cutting processing.

Second, normalizing:

This is a heat treatment process where steel is heated above AC3 or Acm by 30-50℃, held for a certain period of time, and then cooled slowly by air. Due to the slightly faster cooling speed, compared to the annealing structure, there is a relatively higher content of pearlite in the structure, and the lamellar structure is finer. Therefore, the performance has improved. For low-carbon steel, after normalizing, the hardness is increased, which can improve the cutting processing performance and reduce the surface roughness of processing; for high-carbon steel, normalizing can eliminate the network carbides, preparing for spheroidizing annealing and quenching.

Third, quenching:

This is the process of heating steel to above AC3 (for hypereutectoid steel) or AC1 (for hyper-eutectoid steel) by 30-50℃, holding for a certain period of time, and then quickly cooled in different cooling media (faster than the critical cooling speed) to obtain a martensite structure. The hardness and strength of martensite are very high, and it is particularly suitable for materials with high wear resistance requirements for tools and molds. The quenching process has three important parameters: quenching heating temperature, holding time, and cooling speed. If the quenching heating temperature is too high, the grains are likely to become coarse, and defects such as oxidation and decarburization may occur. If the heating temperature is too low, the material hardness may be insufficient due to the presence of ferrite or pearlite in the structure.

Fourth, tempering:

The martensite structure obtained after quenching of steel is hard and brittle. If directly subjected to grinding processing, deformation and cracking may occur. Therefore, tempering is necessary. The tempering temperature depends on the final required structure and performance. According to the heating temperature, tempering is divided into low-temperature, medium-temperature, and high-temperature tempering. Low-temperature is less than 200℃, medium-temperature is between 350-500℃, and high-temperature is between 500-650℃.

In simple terms, the main steps of carbon steel heat treatment are annealing, normalizing, quenching, and tempering. The steelmaking process is very simple, but it causes relatively large environmental pollution. Therefore, in order to protect the environment and other issues, you can try to learn about our heat treatment process cooperation projects on Xianji.com.