Post-rolling control cooling process for hot-rolled H-shape steel

Abstract

The invention provides a post-rolling control cooling process for hot-rolled H-shape steel. The hot-rolled H-shape steel enters a cooling device after the rolling is finished, an upper nozzle and a lower nozzle are respectively aligned with upper / lower R parts of the hot-rolled H-shape steel to carry out water spray cooling, and a left nozzle and a right nozzle are respectively aligned with left / right flank centers of the hot-rolled H-shape steel to carry out water spray cooling. The invention is characterized in that the pressure of cooling water is within 0.7 to 1.2MPa, the water quantity is within 1,200 to 2,000m3 / hour, the cooling rate is within 75 to 150 DEG C / s and the cooling time is within 3 to 5 seconds; and the hot-rolled H-shape steel is cooled to 20 to 30 DEG C above the martensitic phase transformation point of the corresponding steel grade after the rolling under the temperature of 850 to 1,000 DEG C is finished. By adopting the cooling process in the invention, the actual grain size of ferrite at the core part of the hot-rolled H-shape steel can be refined from 8-10 grades to 10-12 grades, and a tissue of bainite plus sorbite can be formed on the surface of the hot-rolled H-shape steel, thereby obviously improving the strength and toughness of the hot-rolled H-shape steel and improving the yield strength of the hot-rolled H-shape steel by more than 70MPa.

Description

technical field [0001] The invention belongs to the technical field of steel rolling, and in particular relates to a post-rolling controlled cooling process for hot-rolled H-shaped steel. Background technique [0002] At present, the H-beam hot rolling production line has not yet formed a mature cooling theory and cooling process technology, which has become the bottleneck of industrial production. This is mainly due to the complexity of the cross-sectional shape of the H-beam, and its on-line cooling is prone to residual water at the waist and uneven cooling, which will affect the cross-sectional shape and performance uniformity of the rolled piece, and the product is prone to internal and external expansion and deformation. Web waves, cracks and other defects. [0003] In recent years, this technology has attracted the attention of domestic and foreign enterprises and scientific research institutes, and research reports have been reported in some countries such as Japan, ...

AI Technical Summary

Problems solved by technology

However, the technology is still immature, and there are problems such as uneven cooling and deformation of the rolled piece.

And in our country, users are not easy to accept steel products strengthened by quenching after rolling and self-tempering process. They think that the tempered layer formed after quenching and self-tempering will reduce the performance of steel products. The main problems are: the yield strength ratio of steel products is large; welding performance Decrease; the stress aging of steel is large

Therefore, this technology cannot be popularized and applied in our country.

[0004] "Steel Rolling" magazine, 2004, No. 5, pages 15-17, published a paper titled "Research on Controlled Cooling Process of Hot-rolled H-shaped Steel", which disclosed a gas mist controlled cooling device after hot-rolled H-shaped steel. Using water vapor atomization cooling, the water pressure is 0.20-0.25MPa, the air pressure is 0.15-0.25MPa, the water flow is 200-350L / h, and the air flow is 9.5-15.0m 3 / h, the cooling rate is 15-30°C / s, the maximum cooling rate is only 30°C / s, the structure of the product is ferrite + pearlite, which is the same as that after general air cooling, but the ferrite content increases, and the iron The ferrite grains are on average 0.5 finer than the air-cooled ferrite grains, and the yield strength of the product is increased by about 50 MPa. Due to the low cooling rate, the improvement of product strength, toughness and other performance indicators is limited.