This article conducts a detailed analysis of the factors affecting steel material consumption. By improving the structure of the charging materials, optimizing the slag-making process, reducing the converter splash rate, and strengthening the recovery of internal iron-containing resources, the converter molten steel recovery rate was effectively increased and the consumption of steel materials was reduced.
At present, competition in the steel industry is becoming increasingly fierce, and steel profit margins have been sharply compressed. In order to cope with the challenges brought by the market, measures must be taken to reduce costs and increase efficiency. The consumption of steel materials accounts for more than 70% of the production cost of converter steelmaking, and the quality of steel materials indicators directly reflects the comprehensive technical level and management level of the plant. It is related to the competition of steelmaking plants that focuses on tapping potential and increasing efficiency. The success or failure of activities, therefore reducing steel material consumption is particularly urgent for steelmaking enterprises. This article comprehensively analyzes the actual production situation of the converter line of Lianyang Iron and Steel Co., Ltd. No. 1 Refining and Rolling Plant, and proposes targeted improvement measures. After implementation, significant progress has been made in steel material consumption.
Steelmaking line production status
The converter line of the No. 1 refining and rolling plant currently has three oxygen top-bottom combined blowing converters with a nominal capacity of 100t, one molten iron pretreatment, three argon blowing stations, and two 6-machine and 6-stream arc continuous casting machines. Annual steel production is 3.9 million tons. The main varieties include HRB series, CSP low carbon steel, CSP plain carbon steel, low carbon alloy steel, high carbon high strength steel and other new steel types.
Steel material consumption calculation caliber and current situation
Calculation method of steel material consumption
Steel material consumption (kg/t) = steel material entering the furnace (kg) ÷ qualified steel output (t);
Steel material consumption (t) = molten iron amount (t) + pig iron amount (t) + scrap steel amount (t) + ore (t);
Scrap steel is divided into purchased scrap steel and self-produced scrap steel from the source. Pig iron is added because the steelmaking capacity is greater than the blast furnace production capacity and the amount of molten iron is insufficient. Pig iron blocks are purchased to maximize the converter production capacity.
Current situation of steel material consumption
In 2016, the physical consumption of steel materials in the first refining and rolling mill was 1079.31kg/t, which was significantly better than in previous years.
Main factors affecting steel material consumption
The #6 blast furnace of Lianyang Iron and Steel Co., Ltd. is in the late stage of furnace service. The quality of the molten iron is poor. The amount, temperature and composition of the molten iron slag entering the furnace fluctuate greatly. The volume ratio of the converter is small. It is greatly affected by the quality of the raw materials entering the furnace and the structure of the charging materials. The converter smelting process is prone to splashing, the splashed slag has a large iron content, high flux consumption, high final slag TFe, poor end temperature and composition control, resulting in more returns and interrupted continuous casting, and serious overblowing and high temperature phenomena; The stability of the casting operation is poor and the excess molten steel is lost, which seriously affects the reduction of steel material consumption.
Optimization and improvement measures to reduce steel material consumption
Optimize the structure of the charging materials and implement a loading system based on steel types
Optimizing the structure of the charged steel materials has two main meanings. The first is to propose the optimal steel material structure based on the cost-effectiveness calculation of the steel materials to stabilize the weight of the charged steel materials. After calculating the heat balance of the converter and combining it with practical experience, major improvements were made to the original charging system and the structure of the charging materials.
First, adjust the structure of the charging materials, and through detailed cost accounting, it is proposed to reduce high-priced scrap steel as cold materials, and use the heat of reorganization in the molten iron to add more low-priced cold materials such as iron ore to reduce costs.
Secondly, improve the loading system, because the ore used in the converter for steelmaking will have a certain impact on splashing, output, environmental protection, furnace conditions, etc. In order to improve the operating conditions of the converter, it was decided to reduce the charging amount of the converter and relatively increase the reasonable furnace volume ratio to lay a good foundation for the converter operation. The lower scrap steel ratio made the heat in the furnace surplus, creating favorable conditions for adding low-priced ore. The addition of ore promotes the rapid melting of lime into slag, improves the utilization rate of lime, and lays the foundation for reducing lime consumption.
Different steel types have different smelting end-point requirements. Formulating different ratios of molten iron and scrap steel according to different steel types is helpful to accurately hit the end-point composition and temperature and reduce blow loss during the smelting process.
It can be seen from the test data, as shown in Table 1, that with the increase in molten iron consumption, the total charging amount remains unchanged. By adjusting the ore addition
The amount (adjusted according to the physical heat of molten iron, Si content and smelting end temperature control conditions), the metal yield is increased, and the consumption of steel materials is significantly reduced.
Table 1 Consumption of steel materials under different furnace charging structures
| Plan | molten iron;t | pig iron;t | scrap steel;t | Molten iron;kg/t | Pig iron;kg/t | Scrap steel;kg/t | Ore;kg/t | Steel material consumption;kg/t |
| 1 | 95 | 0 | 15 | 957.78 | 0.00 | 130.69 | 3.15 | 1081.62 |
| 2 | 96 | 0 | 14 | 965.25 | 0.00 | 120.40 | 4.82 | 1080.46 |
| 3 | 97 | 0 | 13 | 972.68 | 0.00 | 110.16 | 6.47 | 1079.32 |
| 4 | 98 | 0 | 12 | 980.08 | 0.00 | 99.98 | 8.12 | 1078.18 |
Optimize the slagging process and reduce lime consumption
Lime is the main raw material for converter slag making. The process of melting lime into slag requires a large amount of FeO and heat. A large amount of lime will inevitably increase the cost of steel materials. Therefore, a refining and rolling mill made the following optimizations to the slagging system.
Control of lime addition amount
In order to accurately control the amount of lime added to the converter and avoid unnecessary waste and quality and cost fluctuations caused by insufficient addition, we must first strengthen the maintenance and inspection of metering equipment to improve metering accuracy. Secondly, a corresponding static mathematical calculation model was established based on the composition and temperature of the molten iron entering the furnace, as well as the composition and temperature of different steel end points, which effectively avoided waste of lime and insufficient addition.
Limestone steelmaking and less slag steelmaking
Since ore added to the converter is prone to splashing, in order to balance the smelting heat of the converter, the amount of ore added should be appropriately reduced to control splashing and reduce production costs. Through continuous exploration, the feasibility of using limestone to make steel in the first refining and rolling mill was verified, and the purpose of reducing the cost of converter steelmaking was achieved. The physical and chemical indicators of limestone are shown in Table 2.
Table 2 Physical and chemical indicators of limestone
| Granularity range | CaO | SiO2 | P | S |
| 10～30mm | ≥52% | ≤2% | ≤0.04% | ≤0.04% |
With the improvement of hot metal conditions, Lianyang Iron and Steel Co., Ltd. No. 1 Refining and Rolling Plant promptly reduced the amount of lime added based on the composition of the hot metal. Through continuous exploration, the average alkalinity of the final converter slag decreased, reducing the amount of converter slag, thereby reducing the consumption of steel materials.
In 2016, by optimizing the flux structure (trying not to use high-priced self-produced light burning, increasing the consumption of lower-priced limestone, and reducing the consumption of higher-priced lime), the amount of lime added was controlled according to the conditions of the molten iron. When the molten iron Si ≤ 0.60%, Medium carbon steel is based on lime + limestone ≤ 26kg/t (limestone is converted at 0.56); when molten iron Si ≥ 0.60, double slag operation is used or the amount of scrap steel is increased. In 2016, the converter lime consumption was 11.49kg/t lower than in 2015. The total Flux consumption is reduced by 8.24kg/t (limestone is not converted), steel material consumption and flux costs are significantly reduced, see Table 3.
Table 3 Comparison of lime consumption and total flux consumption in two years
| month | lime;kg/t | Flux;kg/t | ||
| 2015 | 2016 | 2015 | 2016 | |
| 1 | 45.11 | 30.13 | 62.28 | 61.41 |
| 2 | 47.36 | 30.59 | 66.30 | 58.55 |
| 3 | 46.83 | 27.00 | 64.97 | 48.10 |
| 4 | 43.38 | 27.65 | 62.90 | 49.56 |
| 5 | 45.44 | 27.65 | 64.87 | 51.06 |
| 6 | 45.70 | 25.39 | 64.51 | 50.90 |
| 7 | 45.97 | 27.72 | 65.22 | 49.78 |
| 8 | 45.14 | 27.99 | 63.08 | 53.75 |
| 9 | 34.58 | 30.10 | 55.28 | 50.96 |
| 10 | 31.73 | 33.96 | 56.59 | 52.60 |
| 11 | 31.39 | 35.65 | 54.89 | 54.11 |
| 12 | 31.11 | 37.22 | 50.26 | 59.52 |
| all | 41.45 | 29.96 | 61.44 | 53.20 |
Control of TFe in slag
The amount of converter slag is calculated based on 80kg. For every 1% increase in converter final slag TFe, steel material consumption will increase by 0.42kg/t steel. Therefore, reducing the TFe content of converter final slag is beneficial to reducing steel material consumption. To this end, by increasing the carbon pulling rate at the end of the converter (C ≥ 0.08%), reducing the number of post-blow and over-blow heats in the converter, and ensuring the end-point lance pressing time (the corresponding lance pressing time is determined according to different steel types), the entire blowing process can be ensured. On the premise of processing good slag, the TFe content of the final converter slag has been effectively reduced. The situation in the past two years is shown in Table 4.
Table 4 Converter end-point carbon pulling rate (C≥0.08%) and final slag
| 2015 | 2016 | ||
| Carbon pulling rate; % | TFe;% | Carbon pulling rate; % | TFe;% |
| 68.56 | 11.95 | 77.93 | 11.60 |
Reduce converter splash and reduce the amount of scattered slag under the furnace
Splash is a phenomenon that is difficult to avoid in the converter production process. Since splash contains a large amount of metal, the more violent the splash, the higher the consumption of steel materials. The factors that affect the converter splash mainly include the converter furnace volume ratio, the structure of the charge, the silicon content of the molten iron, etc. In view of these factors, with the goal of not splashing, measures such as operation and management refinement are adopted to comprehensively tackle the problem of splashing and slag scattering. The improvement in quantity is shown in Table 5.
Table 5 Amount of loose slag under converter furnace
| Bulk slag volume in 2015; kg/t | Bulk slag volume in 2016; kg/t |
| 40.54 | 27.43 |
Strengthen internal management and reduce the loss of iron-containing resources
Recycling is mainly reflected in the recycling of iron-containing resources such as loose slag under the furnace, slag trays/cans, and ladle rims. By strengthening management and formulating special recycling management regulations, the loss of iron-containing resources has been reduced, and the consumption of steel materials has been effectively reduced. The recycling situation is shown in Table 6.
Table 6 Iron-containing resource recovery
| 2015 | 2016 | ||
| Furnace bottom slag recovery ratio | Other iron-containing resources | Furnace bottom slag recovery ratio | Other iron-containing resources |
| 39.52% | 6.43kg/t steel | 50.71% | 8.06kg/t steel |
Application effects
Through the above-mentioned technical improvements and management, the flux consumption of Lianyuan Iron and Steel Co., Ltd. No. 1 Refining and Rolling Plant has been continuously reduced, the converter process control has become more controlled, and production has gone more smoothly. With the improvement of various indicators, the consumption of steel materials has been significantly reduced. The consumption of steel materials is shown in the table 7.
Table 7 Steel material consumption control situation
| Steel material consumption in 2015; kg/t | Steel material consumption in 2016; kg/t |
| 1098.03 | 1079.31 |
Conclusion
There are many factors that affect the consumption of steel materials. This article combines the production practice of a refining and rolling mill to optimize the process and strengthen internal refined management in terms of the converter loading system, slag making system, final slag TeO control, etc., which are summarized as follows. What time is it:
a. Reasonable calculation and refined management of steel materials to achieve process control are of guiding significance for reducing steel material consumption.
b. Promote standardized operations and unify the converter shaking operation mode to create good conditions for the improvement of various indicators.
c. Improve the measurement accuracy of various materials, making it possible to scientifically reduce the consumption of steel materials.
d. Reducing steel material consumption is a systematic project. In addition to optimizing operations and improving management levels, efforts must also be made to systematically reduce the tapping temperature, increase the life of the tundish, and reduce various continuous casting accidents.