Heating-free direct rolling technology for long sections

1. The background and purpose of the research

The energy consumption of the iron and steel industry accounts for about 23% of the country's total industrial energy consumption and 16.1% of the country's total energy consumption. The energy consumption of the rolling process accounts for about 10% of the total energy consumption of the steel industry. Therefore, the study of energy-saving and consumption-reducing technologies in the rolling process is of great significance for reducing energy consumption per ton of steel in my country. In recent years, although my country’s newly constructed long section steel rolling production lines generally use energy-saving technologies such as hot delivery and hot charging, on-line accelerated cooling, and endless rolling, my country’s low-level steel rolling production lines still account for a considerable proportion, making my country’s overall The energy consumption index of the steel rolling process is relatively high.

In hot rolling production, billet heating energy consumption is high in the rolling process. Taking a typical bar mill production energy consumption as an example, billet heating consumes about 80% of the energy, and the energy consumption for steel rolling only accounts for about 15%. With the application of energy-saving technologies, the proportion of energy consumption used for billet heating has gradually decreased, but it is still maintained at a high level. Therefore, the energy saving potential of ordinary steel rolling process mainly comes from the heating furnace. The long-section direct rolling technology enables the steel billet after continuous casting to be directly sent to the rolling mill for rolling without passing through the heating furnace or even supplementary heating. Without calculating the energy consumption of the heating furnace, the energy saving effect on the steel rolling process is significant.

 

2.Technical solutions

The core of the long-section direct rolling technology lies in the connection of continuous casting and rolling processes, and its foundation is the stable production of high-speed continuous casting and the stability control of the rolling process. The guarantee of continuous casting technology should realize defect-free billet production, higher casting speed, and stable production process; the guarantee of steel rolling technology should realize the temperature connection with the billet, partial induction heating, and high rigidity rolling with larger temperature window , Performance stability control and other technologies.

The long-section direct rolling technology solves the contradiction between low-energy production and high-quality products in the long-section non-heating rolling production process. It can realize the direct rolling process of continuous casting billets in short, medium and long distances. Realize low energy consumption production and significantly reduce production costs.

 

Figure 1: Schematic diagram of direct rolling technology for long sections

3.Main innovative achievements

(1)Control technology of continuous casting billet with high temperature, constant temperature and constant quantity

By studying the temperature field of the billet at different R angles, the breakout prediction model and control system, the co-design of the layout of the casting machine, the casting speed, and the cutting of the billet, the temperature difference between the head and the tail of the billet does not exceed 50℃, and the billet tapping temperature Stable production of high temperature continuous casting slabs above 1000℃.

Figure 2: High-speed production with constant temperature and constant volume of continuous casting slab

Figure 3: Hydraulic cutting at the end of metallurgical length after on-site multi-process optimization

(2) Long section casting-rolling interface billet queuing control technology

Based on the method of queuing theory, the continuous casting billet queuing system of the multi-strand continuous caster under different production processes was constructed, and the factors such as different molten steel volume, different flow numbers, and different fixed lengths were studied for the continuous casting billet conveying process at the casting-rolling interface. And rolling rhythm. This model can optimize the production rhythm of different production lines and improve the straight rolling rate and output.

(3)Long profile green and low energy consumption casting-rolling connection technology

According to the different distances, different plane positions, and different height differences between the continuous casting machine and the rolling mill of different steel enterprises, the methods of non-heating rolling, induction heating, and high-temperature billet soaking are selected to make the head, tail, and cross section of the continuous casting billet The temperature difference between the surface and the core of the product meets the production requirements and realizes the efficient connection of various on-site process arrangements. The straight rolling rate of a typical production line reaches 99%.

Figure 4: Performance stability control technology for billet direct rolling

(4)The performance stability control technology of long profile without heating rolling

Aiming at the influence of the chemical composition difference of different heats in the same pass and the temperature fluctuation caused by the connection of the casting-rolling interface on the mechanical properties of long sections in the non-heating rolling process, high-rigidity temperature-controlled rolling, variable-speed rolling, and post-rolling are studied. The cooling path and other processes balance the effects of microalloying elements and metallurgical structure on the mechanical properties of long profiles, and realize that the fluctuation of the yield strength of the same pouring second long profile does not exceed 10%.

Figure 5: a) Direct rolling production without uniform temperature control b) Direct rolling production with uniform temperature process control

4.Application situation

During the "Twelfth Five-Year Plan" period, the Institute of Metallurgical Technology of Central Iron and Steel Research Institute undertook the national science and technology support program "Steel Enterprise Long Section Direct Rolling Technology Project Demonstration". To tackle key technical issues such as quality control technology for long sections without phase change before production, finally, Guangdong Yuebei United Iron and Steel Co., Ltd. has successfully built a long section straight rolling demonstration line with an annual output of 500,000 tons. The demonstration line mainly produces HRB400 and HRB400E rebars, with specifications ranging from Φ20 to Φ35. The continuous casting machine of the demonstration line is well matched with the steel rolling process, the continuous casting billet is stable at high temperature, and the temperature fluctuation is less than 50 ℃. The heating furnace was eliminated on the production line of the demonstration line, and the rolling temperature was 900～1100℃. The demonstration line has realized the continuous production of continuous casting billet direct rolling, with a direct rolling rate of 99% and a product qualification rate of 100%.