Controlled rolling and cooling can reduce the consumption of alloys and reduce the production cost. Therefore, it is being promoted in the production of seamless steel tubes, and a variety of processes such as on-line normalization, on-line quenching, and online rapid cooling are preliminarily formed.
1, online normalization process
On-line normalization, also known as on-line normalizing, is the process of obtaining a uniform metallurgical structure after the tube is rolled in the austenite phase after air-cooling or forced cooling in the austenite phase.
The process includes two phase transitions:
1) The waste pipe is cooled from 1100°C to 550°C, and the austenite in the steel is transformed into ferrite + pearlite;
2) After the cooled seamless steel pipe is reheated, the ferrite + pearlite in the steel is transformed into austenite.
Through the on-line normalization, it can not only make the steel structure uniform and refine the grain, but also improve the comprehensive mechanical properties of the seamless steel pipe.
2, online quenching process
1) Austenitic stainless steel tube
Austenitic stainless steel tube quenched online, also known as in-line solid solution, is the solid solution of C element in the austenite structure to form a single austenite structure. Solution temperature is generally 1000-1150 °C. Cooling methods can use water, oil, air cooling and so on.
2) Carbon steel, low alloy steel pipe
It refers to the quenched and tempered heat treatment process by directly quenching the waste heat after rolling and then tempering it online. This process can greatly save energy.
3, online rapid cooling process
It is a new generation process based on ultra-fast cooling technology. It refers to the process of directly performing heat treatment after the finish rolling mill by using the residual heat after rolling. It is to strengthen and cool the austenite after rolling, and quickly cool the metal to the vicinity of the ferrite transformation temperature in a short time. Inhibition of austenite grain growth, as much as possible to maintain the hardened state of austenite.
The rapid cooling on line has obvious effects in improving the seamless steel pipe structure, improving the comprehensive mechanical properties of the seamless steel pipe, refining the surface grains, and improving the fatigue crack propagation resistance.