The on-line heat treatment of steel after rolling is generally divided into the following three steps:

1. Quenching stage.

This process consists of a water cooling system arranged in a rack. Reasonable and effective water-cooling equipment can make the rolling stock cool vigorously here. On the surface of the rolled product, the cooling value exceeds the critical value of martensite, so a martensite structure can be formed on the surface.

2. Tempering stage.

At this time, after the rolled product is exposed to the air after passing through the water cooling system, the heat of the core will be transferred to the surface layer, and the surface will be tempered, so-called self-tempering.

3. Cooling stage.

This stage occurs later, mainly because the austenite in the core undergoes an isothermal phase transformation to obtain the final metallurgical state.

On-line heat treatment is an effective method to improve the quality, which can improve the internal structure of the rolling stock, thereby obtaining better mechanical strength. The on-line heat treatment of the rolled product can form the martensite structure on the surface layer by quenching, and externally pass the heat of the core to self-temper the martensite on the surface layer to obtain the tempered martensite structure on the surface layer. Due to the cooling of the surface layer of the core, the temperature drop is large, and the resulting pearlite structure is refined. This not only increases the hardness of the surface layer, but also improves the core structure. In addition, in-line heat treatment can enhance the mechanical properties of the steel sheet and reduce the content of carbon and alloying elements. Online heat treatment is a combination of controlled heating, controlled rolling and controlled cooling into a complete energy-saving production process, so it can save a lot of energy and reduce costs.