Molten steel component stable control and liquidus temperature measurement method

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a molten steel component stable control and liquidus temperature measurement method, which specifically comprises the following steps: after converter tapping, measuring the content of alloy elements in molten steel, carrying out primary alloy addition in an LF (ladle furnace) according to a chemical component measurement result, re-measuring components and calibrating the amount of molten steel after rough adjustment is completed, and carrying out secondary alloy addition in the LF according to the chemical component measurement result. And second-time alloy adding is conducted on the basis of the calibrated molten steel amount, the content of all the elements meets the conditions after fine adjustment is completed, and the liquidus is calculated through a liquidus temperature model according to the final components. According to the method, the alloy adding types, alloy adding periods and alloy adding amounts of the LF refining furnace and the RH refining furnace are automatically measured and calculated through the model, chemical components of steel types are controlled to be within a narrow range through two-time component adjustment of rough adjustment and fine adjustment, casting blank macrosegregation is reduced, the stability of steel rod performance is improved, the liquidus temperature of molten steel is accurately calculated, and the alloy adding amount of the LF refining furnace and the RH refining furnace is calculated. And process parameters can be accurately formulated for continuous casting.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and particularly to a method for stably controlling the composition of molten steel and measuring the liquidus temperature. Background Art

[0002] As an important industrial material, the properties and application fields of steel are significantly affected by its chemical composition and microstructure. The chemical composition is the main factor affecting the properties of steel. Under the condition of stable process technology, narrow-band control, stability, and uniformity of the chemical composition are the prerequisite for ensuring the properties of steel. The liquidus temperature, as an important physical parameter of steel, has a decisive influence on the processes such as smelting, casting, and heat treatment. However, the traditional method of manually calculating the addition of alloys is affected by the experience of workers. The manual addition of alloys has a large working intensity and a high operation error rate, often resulting in the composition of molten steel exceeding the standard.

[0003] Traditional methods for measuring the liquidus temperature often ignore the complex influence of different components in steel on the liquidus temperature, resulting in the deviation of process parameter settings from the target requirements. Therefore, it is necessary to develop an alloy model that can automatically calculate and configure alloys in the LF refining furnace and the RH refining furnace to ensure the stability of the chemical composition before continuous casting production, with a deviation of carbon (C) of ±0.01%, a deviation of silicon (Si) composition of ±0.02%, a deviation of manganese (Mn) composition of ±0.02%, and other components within a small change range. On the premise of the stability of the chemical composition, a liquidus temperature measurement method model that accurately reflects the composition differences in steel is developed synchronously, which has multiple significances such as economy and efficiency in steelmaking production. Summary of the Invention

[0004] In view of the above technical problems, the present invention overcomes the shortcomings of the prior art and provides a method for stably controlling the composition of molten steel and measuring the liquidus temperature, which can stably control the chemical composition during the steelmaking process, provide an accurate liquidus temperature, reduce the addition amount of alloy components, reduce the processing cost of the process, and reduce the manual labor intensity on the one hand, providing technical support for the setting of continuous casting process parameters and the improvement of slab quality.

[0005] The method for stably controlling the composition of molten steel and measuring the liquidus temperature in this solution includes the following steps:

[0006] (1) After tapping from the converter, measure the content of alloying elements in the molten steel;

[0007] (2) Based on the measurement results of step (1), calculate the types and addition amounts of alloys required for the LF refining furnace and the RH refining furnace respectively through the alloy addition model. The calculation formula of the model is:

[0008]

[0009] Where: W MiLet [[Mi]] be the addition amount (kg) of the alloy containing element [[Mi]]. f Let [[Mi]] be the target component percentage (%) of element [[Mi]] in the molten steel. m Let [[Wb]] be the weight (t) of the molten steel in the ladle, and [[Y]] be the actual analyzed component percentage (%) of element [[Mi]] in the molten steel. Mi Let [[%Mi]] be the percentage (%) of alloying element [[Mi]] in the alloy. The composition control model is loaded into the computer HMI screen to automatically calculate the alloy type and addition amount, so that the molten steel smelted through the LF refining furnace and the RH refining furnace can reach the target composition for continuous casting.

[0010] (3) Add the alloy for the first time in the LF refining furnace. After the rough adjustment, re-measure the composition and calibrate the amount of molten steel.

[0011] (4) Based on the calibrated amount of molten steel, add the alloy for the second time. After the fine adjustment, make the content of each element meet: the deviation of C is ±0.01%, the deviation of Si is ±0.02%, and the deviation of Mn is ±0.02%, which provides a prerequisite for accurately testing the liquidus temperature.

[0012] (5) Calculate the liquidus temperature according to the final composition by using the liquidus temperature model.

[0013] (6) Dynamically adjust the continuous casting process parameters according to the calculated liquidus temperature.

[0014] The further limited technical solution of the present invention is:

[0015] Further, the types of alloying elements include at least one of carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), nickel (Ni), chromium (Cr), molybdenum (Mo), vanadium (V), and titanium (Ti).

[0016] Further, the continuous casting process parameters include at least one of the casting speed, the electromagnetic stirring intensity, and the soft reduction amount.

[0017] Further, in the step (5), calculating the liquidus temperature according to the final composition by using the liquidus temperature model specifically obtains the liquidus temperature through the empirical formula between the composition in the steel and the liquidus temperature.

[0018] Further, the empirical formula between the composition in the steel and the liquidus temperature is:

[0019] T = 1536 - (415.3C + 12.3Si + 6.8Mn + 124.5P + 183.9S + 4.3Ni + 1.4Cr), where each element symbol represents the mass percentage content of the element, and the temperature unit is °C. The test results are corrected and calibrated to obtain a more accurate liquidus temperature.

[0020] The beneficial effects of the present invention are as follows:

[0021] The method for stable control of molten steel composition and determination of liquidus temperature proposed by the present invention, based on the results of chemical composition determination, automatically calculates the types of alloys added, the periods of alloy addition, and the amounts of alloy addition in the LF refining furnace and the RH refining furnace by using a model. Through two-stage composition adjustments, namely rough adjustment and fine adjustment, the chemical composition of the steel grade is controlled within a narrow range, reducing the macrosegregation of the continuous casting billet and improving the stability of the through-thickness properties of the steel. By accurately calculating the liquidus temperature of the molten steel, the process parameters for continuous casting, such as casting speed, electromagnetic stirring, and soft reduction amount, can be precisely determined, providing technical support for smooth production and quality improvement. Description of the Drawings

[0022] Figure 1 It is a process flow chart of gear steel production in the specific embodiment of the present invention. Specific Embodiments

[0023] Next, the specific embodiment of smelting 20CrMnTi gear steel in a 130t converter will be further described.

[0024] (1) Develop an alloy addition model on a 130t LF refining furnace and a 130t RH refining furnace to automatically calculate the amount of alloy added to the refining furnace. The model is associated with the alloy bins of the refining furnace, automatically weighs, automatically feeds the materials, and is displayed on the HMI screen to guide the on-site operator to accurately add the alloy.

[0025] (2) Develop a model for automatically calculating the liquidus temperature of molten steel on each continuous caster. The model automatically calculates the liquidus temperature of the molten steel based on the chemical composition of the sample taken out of the refining furnace and is displayed on the HMI screen to guide the setting of continuous casting process parameters.

[0026] (3) The smelting targets for the chemical composition of 20CrMnTi are: (C) 0.20%, silicon (Si) 0.25%, manganese (Mn) 0.95%, chromium (Cr) 1.06%, titanium (Ti) 0.055%, acid-soluble aluminum (Als) 0.015%.

[0027] (4) When smelting 20CrMnTi in a 130t converter, after the converter smelting is completed and the steel is tapped, measure the contents of the main alloying elements such as carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), nickel (Ni), chromium (Cr), molybdenum (Mo), vanadium (V), and titanium (Ti) in the steel after tapping, and obtain the converter end-point carbon (C) of 0.06%, silicon (Si) of 0.02%, manganese (Mn) of 0.06%, phosphorus (P) of 0.008%, sulfur (S) of 0.013%, and other minor residual alloying elements.

[0028] (5) After the chemical composition of the tapped steel is out, use the model formula to calculate the target chemical composition of the first batching of molten steel to the refining furnace. The model formula is as follows:

[0029]

[0030] Automatically plan the first alloy addition plan. The added alloy amounts are 130 Kg of carbon powder, 1000 kg of silicomanganese, 220 kg of low-carbon ferromanganese, and 2200 kg of low-carbon ferrochrome.

[0031] Table 1 Alloy element recovery rate

[0032]

[0033] (6) After the molten steel reaches the LF refining furnace, the composition is (C) 0.15%, silicon (Si) 0.14%, manganese (Mn) 0.70%, chromium (Cr) 0.92%, and trace residual titanium (Ti) content.

[0034] (7) According to the composition control gap, the model further calculates the gap between the added alloy amount and the target composition, calibrates the amount of molten steel in the ladle, and finds that the amount of molten steel in the ladle is 132 t. After re-verifying the amount of molten steel, start to roughly adjust the chemical composition of the molten steel.

[0035] (8) According to the new amount of molten steel, repeat steps (5), (6), and (7) for the second alloy addition plan, perform a rough adjustment of the chemical composition. The model automatically calculates the alloy addition amounts as 66 kg of carbon powder, 830 kg of silicomanganese alloy, 330 kg of low-carbon ferrochrome, 220 kg of ferrotitanium, and 200 kg of aluminum pellets. Through adjustment, the chemical composition of the molten steel reaches the target composition, and the deviation from the target composition is small.

[0036] (9) Repeat step (8) to finely adjust the composition, and the composition gets closer to the target, meeting the requirements within a narrow range.

[0037] (10) Before the qualified molten steel is poured into the continuous casting, according to the sampled composition at the refining station, the liquidus line model corrects and calibrates the chemical composition results according to the liquidus line formula T = 1536 - (415.3C + 12.3Si + 6.8Mn + 124.5P + 183.9S + 4.3Ni + 1.4Cr +...), and calculates that the liquidus line temperature of this furnace of steel is 1510 °C, 2 °C lower than the liquidus line of the steel grade at 1512 °C, and more accurately calculates the liquidus line temperature.

[0038] (11) Calculate the superheat of the molten steel based on the liquidus line temperature calculated in step (10). Increase the superheat by 2 °C to guide the setting of the continuous casting drawing speed under different superheat parameters. Since the superheat is on the high side, lower the drawing speed by one gear for production. Under the condition of high superheat, increase the cooling intensity of the secondary cooling water, increase the end electromagnetic stirring intensity by 50 A, and increase the soft reduction amount by 1 mm for setting, etc.

[0039] For different heats in the continuous casting and continuous pouring process, steps (4) to (11) above are continuously and repeatedly adopted, so that the chemical composition fluctuations of different heats are within a relatively small range. The control of composition and temperature throughout the steelmaking process is in a dynamically stable control state.

[0040] In the embodiment of the present invention, based on the results of chemical composition determination, the model automatically calculates the alloy addition type, alloy addition period, and alloy addition amount of the LF refining furnace and the RH refining furnace. Through two-component adjustments of rough adjustment and fine adjustment, the chemical composition of the steel grade is controlled within a relatively narrow range, reducing the macrosegregation of the slab and improving the stability of the through-thickness performance of the steel. By accurately calculating the liquidus temperature of the molten steel, the process parameters for continuous casting can be accurately determined, such as casting speed, electromagnetic stirring, soft reduction amount, etc. It provides technical guarantee for smooth production and quality improvement.

[0041] Significance of narrow-band control of composition and accurate control of superheat of molten steel in the steelmaking process:

[0042] Improve the purity of steel. Narrow-band control helps to reduce the oxygen content and other impurity elements in steel, such as inclusions like Al2O3, thereby improving the fatigue strength and service life of steel. Research shows that inclusions in steel can cause contact fatigue damage and bending fatigue fracture of gear steel, affecting the service life of automotive gears.

[0043] Narrow hardenability bandwidth control. Narrow-band control can significantly reduce the hardenability bandwidth of gear steel, which is crucial for ensuring the dimensional accuracy after gear heat treatment and reducing operating noise. Narrowing of the hardenability bandwidth contributes to the consistency of gears during carburizing treatment, thereby improving the contact strength and bending strength of gears.

[0044] Refine grains to improve toughness. Through aluminum-nitrogen microalloying, the austenite grains of gear steel can be refined, improving the toughness and crack propagation resistance of the steel. Fine austenite grains can reduce heat treatment deformation and improve the fracture resistance of the steel.

[0045] Optimize mechanical properties. Narrow-band control not only improves the mechanical properties of gear steel, but also includes its fatigue strength, wear resistance, and corrosion resistance, which are crucial for ensuring the long-term stable operation of gears.

[0046] Narrow-band control of the chemical composition of gear steel is a key technology to improve the quality and performance of gears, and is of great significance for meeting the operating requirements of high-demand automobiles and other mechanical equipment.

[0047] In addition to the above embodiments, the present invention may have other implementation manners. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A method for stabilizing the composition of molten steel and determining the liquidus temperature, characterized in that: The following steps are involved: (1) After the converter is tapped, the content of alloying elements in the molten steel is determined; (2) Based on the measurement results of step (1), the alloy type and addition amount required for the LF refining furnace and the RH refining furnace are calculated respectively by the alloy addition model, and the calculation formula of the model is: Where: W Mi is the amount of alloy containing Mi element, [Mi] f is the target composition percentage of Mi element in molten steel, [Mi] m is the actual analysis composition percentage of Mi element in molten steel, Wb is the weight of molten steel in the ladle, and Y Mi is the yield of alloying element Mi, %Mi is the percentage of alloying element Mi in the alloy; (3) Carry out the first alloy addition in the LF refining furnace, re-determine the composition and calibrate the amount of molten steel after completing the rough adjustment; (4) Based on the calibrated amount of molten steel, a second alloy addition is performed, and after fine-tuning, the content of each element meets the following requirements: C deviation ±0.01%, Si deviation ±0.02%, and Mn deviation ±0.02%; (5) calculating the liquidus temperature using a liquidus temperature model based on the final composition; (6) Dynamically adjust the continuous casting process parameters according to the calculated liquidus temperature.

2. The method for stabilizing the composition of molten steel and measuring the liquidus temperature according to claim 1, characterized in that: The alloy element type includes at least one of C, Si, Mn, P, S, Ni, Cr, Mo, V, and Ti.

3. The method for stabilizing and controlling the composition of molten steel and measuring the liquidus temperature according to claim 1, characterized in that: The continuous casting process parameters include at least one of casting speed, electromagnetic stirring intensity, and soft reduction.

4. The method for stabilizing and controlling the composition of molten steel and measuring the liquidus temperature according to claim 1, characterized in that: In the step (5), the liquidus temperature is calculated according to the final composition using the liquidus temperature model, and specifically the liquidus temperature is obtained by an empirical formula between the composition in the steel and the liquidus temperature.

5. The method for stabilizing the composition of molten steel and measuring the liquidus temperature according to claim 4, characterized in that: The empirical formula between the composition and liquidus temperature of the steel is: T=1536-(415.3C+12.3Si+6.8Mn+124.5P+183.9S+4.3Ni+1.4Cr), where the symbol of each element represents the mass percentage content of the element, and the temperature unit is ℃.

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