The directly forming to square tube mills will go through heat treatment steps when making steel pipes. Heat treatment is a common metal material processing technology, which generally includes three processes: heating, heat preservation, and cooling. These processes are connected with each other to achieve different processing effects according to the different requirements of metal materials.

There are many types of steel pipes, and the steel grades (species) used are not the same. The chemical composition of the same variety of steel pipes may also be different, but the steel pipes can meet the relevant technical requirements after the heat treatment of the directly forming to square tube mills. There are mainly five types of heat treatment processes for steel pipes, and we first introduce types 1-3.

1. Quenching + high temperature tempering (also known as quenching and tempering treatment)

The steel pipe is heated to the quenching temperature to transform the internal structure of the steel pipe into austenite, and then rapidly cooled at a speed greater than the critical quenching speed to transform the internal structure of the steel pipe into martensite, and then with high temperature tempering, the steel pipe structure is finally transformed into a uniform Tempered sorbite structure. This process can not only increase the strength and hardness of the steel pipe, but also organically combine the strength, plasticity and toughness of the steel pipe.

2. Normalizing (also known as normalization)

After heating the steel pipe to the normalizing temperature, the internal structure of the steel pipe is completely transformed into austenite structure, and then the air is used as a medium to cool the heat treatment process. Different metal structures can be obtained after normalizing, such as pearlite, bainite, martensite or their mixed structure. This process can not only refine the grains, uniform the composition, and eliminate the stress, but also increase the hardness of the steel pipe and improve its cutting performance.

3. Normalizing + tempering

After the steel pipe is heated to the normalizing temperature, the internal structure of the steel pipe is completely transformed into austenite structure, and then it is cooled in the air and then matched with the tempering process. The structure of the steel pipe is tempered ferrite + pearlite, or ferrite + bainite, or tempered bainite, or tempered martensite, or tempered sorbite. This process can stabilize the internal structure of the steel pipe and improve the plasticity and toughness of the steel pipe.

The directly forming to square tube mills can be used to make steel pipes according to the actual situation to perform the above heat treatment process operations.