The core of on-line controlled cooling technology for hot-rolled seamless steel tubes is to control the phase transformation process of steel tubes through the precise control of the cooling path, and to realize the regulation of different final microstructures such as ultra-fine pearlite, bainite and martensite, thereby obtaining the required high performance steel tube.

As for the control of rolled-state microstructure and properties, ultra-rapid cooling makes the grain of steel tube refined, the microstructure uniformity improved and the strength and toughness of the product improved significantly compared with the original air cooling process.

As for direct quenching, the austenite hardening state with dislocation and substructure formed during rolling and the fine precipitation of carbonitride are fully utilized. The strength of quenched steel is remarkably improved, and the hardenability is about 1.4-1.5 times higher than that of traditional reheat quenching.

The technology can effectively reduce the amount of alloy used in the same grade products by 20-30%, or increase the strength level of the same steel by 50-100 MPa. Meanwhile, by utilizing the waste heat, the energy consumption in the production process is greatly reduced.

The successful construction of the control cooling platform makes the development of high-grade products possible, typical cases:

• The impact toughness at -40℃of 900MPa grade low temperature super high strength structural tube was greatly increased to more than 100J;
• The anti-sulfur performance of 110Ksi grade anti-sulfur tube has reached the international leading level. At the same time, the replacing of twice quenching and tempering process with controlled cooling and once quenching and tempering process has been realized, and the process cost was greatly reduced;
• By using on-line quenching technology to produce high-end seamless line pipe, the surface oxidation of the tube was greatly improved, and the performance was significantly improved compared with off-line quenching;