BAOWU OPEN INNOVATION

The on-line controlled cooling technology and direct quenching technology for hot-rolled seamless steel tube

The controlled cooling technology is an effective way for on-line control of hot-rolled steel microstructure and property. It has been widely used in hot-rolled plate, strip steel, rod wire, shaped steel and other fields, and played a key role in product microstructure control and comprehensive performance improvement

However, due to the characteristics of the circular section of steel tube, the high-strength homogenization cooling technology for hot-rolled seamless steel tubes has not yet been effectively broken through. Industrial application of controlled cooling is becoming a bottleneck of high-efficiency and energy-saving production technology for hot-rolled seamless steel tubes. Baosteel took the lead in the world to propose the application of controlled cooling technology to the production of hot-rolled seamless steel tubes and cooperate with the Northeastern University to carry out research and development work on technology and equipment. Relying on PQF 460 production line, Baosteel developed an on-line controlled cooling pilot plant and carried out several rounds of technical research and tests in 2014. Baosteel have successively broken through a series of technical problems such as high-strength homogenization cooling mechanism of circular section steel, key technology of equipment development, process strategy and its precision control. The first set of industrialized controlled cooling equipment for hot-rolled seamless steel tubes was successfully put into production in April 2016.

Efficient and precise control of cooling

Baosteel hot-rolled seamless steel tube on-line controlled cooling platform features high-intensity uniform cooling of circular section steel, precise automatic control of cooling path, self-learning of cooling parameters, and direct quenching (DQ) capability. It has the advantages of high temperature control accuracy after cooling, high cooling uniformity, good tubular shape after cooling, matching various hot rolling production rhythms, and free switching between controlled cooling and conventional rolling processes.

Accurate microstructure regulation

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.

Reduction Production

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.

High-grade product development based on controlled cooling platform

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;

Application effect

Currently, Baosteel has successfully realized the large-scale production of hot-rolled seamless steel tubes exceeding 150,000 tons by using on-line controlled cooling technology. Rolled-state microstructure of the seamless steel tube has been greatly improved, and the performance has been significantly promoted, production cost was reduced effectively.