JPH0442451B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides at least one of Mn, P and S.
Regarding a method that can highly accurately estimate the concentration of more than one component in molten steel at the end of blowing, the method is based on the concentration of the above components in molten steel measured during blowing. The present invention relates to a method of increasing the accuracy of estimating a blowout component by adding the following factors. [Prior art] In conventional converter operation, the molten steel in the converter is sampled at the time when it reaches the stop, and the components of the molten steel (especially C, Mn, P, S, etc.) are analyzed. Operations have been managed by checking whether these meet the target standards, re-blowing if they fail, and tapping the steel only after passing the test. However, with the conventional method, it takes at least 5 minutes to complete the component analysis after blow-off.
As a result, (a) not only does the molten steel supply pitch from the converter to the continuous caster slow down, which becomes an important overflow path for improving production capacity, but also (b) the residence time of molten steel in the furnace becomes slower. The combined effects of the long contact time with the refractories and the need to set the blow-off temperature higher than necessary due to the risk of temperature drop while waiting for the steel to be tapped lead to rapid damage to the converter refractories. I had a problem. Therefore, in recent years, in converter operation, studies have been progressing toward adopting a system in which the component analysis after blow-stopping is omitted and steel is tapped immediately (hereinafter referred to as rapid steel tapping). The shortcomings mentioned in b) are being resolved. However, in carrying out rapid steel tapping operations, it is a major prerequisite to establish a technique for estimating the composition of molten steel at the time of blow-stopping without performing a component analysis, that is, a technique for estimating the blow-off composition. If this estimation technology is inaccurate or (a) it incorrectly determines that the target composition has not been achieved even though it is in fact achieved, unnecessary reblowing may be required. (b) When the steel extraction is carried out with the judgment that the target composition has been achieved even though in reality the target composition has not been achieved. teeth,
A problem arises in that products that do not meet the standards are manufactured. Therefore, there is a need to improve the accuracy of the estimation technique, and the following proposals have been made. () A method in which molten steel is sampled using a sublance at the time of blow-off, the freezing point is measured, and the carbon concentration is estimated from that value. () A method of sampling molten steel during blowing and estimating the end-of-blowing phosphorus concentration using the following formula based on the analytical value of the adjacent concentration (Japanese Patent Application Laid-Open No. 105512/1983). [P] _S = [P] _B −αt ...(1) However, [P] _S : Phosphorus concentration in blow-stop molten steel [P] _B : Phosphorus concentration in molten steel during blowing α: Coefficient t: Time of sampling Time from to the end of blowing () Sampling the molten steel during blowing, C,
The concentration of Mn, P, and S in the molten steel is analyzed, and the carbon concentration [C] _S
Estimate. And C and Mn in molten steel,
The following formula showing the relationship between P and S [M] = α _M ([C] - A _M ) ^kM + β _M ... (2) where [M]: Mn, P, S concentration in molten steel A, K: constant [C]: Concentration of C in molten steel α _M , A _M , k _M : Constant β _M : Using the minimum value of [M] reached when the carbon concentration in molten steel is reduced, β _M in the above formula is Based on factors xi such as blowing conditions, sample analysis values collected during blowing, and molten steel temperature at each point, the following formula β _M = a _OM + ΣaiM・Xi ... (3) where aiM: is determined by the coefficient. And [C] in the above formula (2),
By substituting [M] and β _M , the coefficient α _M in equation (2) is determined, and the carbon concentration [C] _S in the blow-blown molten steel estimated above is determined by substituting [M] and β M into equation (2). A method of estimating the value of [M], that is, Mn, P, and S in blow-stopped molten steel by substituting [C]
3611). () At the time of blow-off, a sublance is applied, the oxygen partial pressure in the molten steel is estimated by an oxygen sensor based on an oxygen concentration battery, and the operating conditions such as auxiliary raw materials are estimated.
Adding xi to the factors, the following formula, [M] _S = a ₀ [O] _F + Σ (a _i x _i ) + K ... (4) where [M] _S : Mn, P, S in blow-stopped molten steel Concentration [O] _F : Oxygen partial pressure in molten steel _aO , _ai : Coefficient K: Estimate Mn, P, and S concentrations at the time of blow-off using constants. [Problems to be Solved by the Invention] The methods () to () above each have the following drawbacks. First, the method in () can only be applied to the estimation of carbon concentration, and moreover, in the low carbon region ([C]≦0.10%) where the dependence of liquidus temperature on [C] is small ([C]≦0.10%), σ =
The estimation accuracy is only about 0.02%. Next, the method in () is an estimation method based on the assumption that [P] in molten steel depends only on the blowing time, and is an effective method if there are no changes in the steel type or operating conditions. It cannot be applied when the phosphorus concentration varies with each charge, and it can only be used to estimate the phosphorus concentration. The method in parentheses can be used to estimate the concentrations of Mn, P, and S, but the estimation accuracy for each element is σ (Mn) =
0.0149%, σ(P) = 0.00177%, σ(S) = 0.00151
%, and it has the disadvantage that it cannot be safely applied to steel types with strict composition standards or steel types that are subject to severe dephosphorization conditions in converters. Finally, the method () is particularly useful in low carbon regions, and the accuracy of estimating C concentration is σ =
It is good at 0.0073%, but when looking at other components, σ (Mn) = 0.0165%, σ (P) = 0.00294%, σ
(S) is only about 0.00102%, and the scope of application is narrow as in the case of (). As mentioned above, there is no known technology that can estimate the Mn, P, and S concentrations with high precision in the high-carbon and low-carbon regions, especially at the time of blow-off, and rapid tapping operations are adopted in the converter refining method. The ratio is still low. The present invention has been made in consideration of the above-mentioned circumstances, and has been made by establishing a technology that can estimate with high precision the concentrations of Mn, P, and S at the end of blowing in converter furnace blowing. The purpose is to contribute to improving the rapid steel extraction ratio. [Means for solving the problem] The present invention that achieves the above object is as follows:
A sample of molten steel was collected during converter blowing, and Mn, P
and S, the concentration [M] _B of at least one component in the molten steel during blowing is measured,
In the method of estimating the concentration [M] _S of the relevant component in the blow-off molten steel using the results, (1) the amount of auxiliary raw materials, (2) the amount of blowing oxygen used from the time of collecting the molten steel sample until the blow-off, (3) ) Residual oxygen amount in slag calculated from oxygen balance, (4) Oxygen partial pressure in molten steel measured at the end of blowing, (5) Temperature of molten steel at the end of blowing (6) Carbon concentration at the end of blowing (7) Select at least one or more items from a group of operational items consisting of hot metal conditions, and add the factors related to the selected items to the concentration in the molten steel during blowing [M] _B to form the following regression formula [M ] _S = [M] _B + ΣαXi + constant ... [] In the formula [M] _S : Concentration in molten steel at the end of blowing [M] _B : Concentration in molten steel during blowing α: Coefficient Xi: (1) to (7) above The gist of the present invention is to estimate the concentration of the relevant component in blow-out molten steel based on factors related to one or more items selected from a group of operational items. [Function] Regarding the reactions of Mn, P, and S in the steel bath during oxygen blowing, the following reactions can be considered. [Mn] + (FeO) = (MnO) + Fe 2 [P] + 4 (caO') + 5 (FeO) = (CaO') ₄・P ₂ O ₅ + 5Fe (CaO) + [FeS] = (CaS) + ( FeO) [S] + 2[O] = SO ₂ (gas) Therefore, the controlling factor for the concentration of Mn, P, and S in the steel bath at the time of blow-off is the hot metal condition (amount and composition of hot metal - especially Mn, P, S concentration), the amount of slag, and the distribution relationship of each component between molten steel and slag. Among these, a more detailed analysis of the distribution relationship between molten steel and slag reveals that the slag composition (especially the CaO concentration and
SiO ₂ concentration), oxygen partial pressure in the system (specifically, FeO concentration in slag, oxygen partial pressure in molten steel), molten steel temperature and carbon concentration at the time of blow-off are important controlling factors. Therefore, the present inventors base their estimation on the Mn, P, and S concentration information in molten steel obtained from molten steel sampled during blowing, and in addition to these, (1) the amount of auxiliary raw materials, (2) Amount of blowing oxygen after the above-mentioned intermediate sampling (3) Amount of residual oxygen in the slag at the end of blowing (4) Partial pressure of oxygen in the molten steel at the end of blowing (5) Temperature of molten steel at the end of blowing (6) At the end of blowing Carbon concentration (7) Considering how the concentration in molten steel changes until blow-off using the above formula (5), which was statistically created by combining one or more factors selected from the hot metal conditions. put in,
We decided to estimate the final concentration in molten steel at the time of blow-out. In order to perform more accurate estimation, it is recommended to add all of the above seven items as factors. Targeting sampled molten steel during blowing
Although the method for measuring the Mn, P, and S concentrations is not limited, the cantback analysis method (for example, pulse analysis measurement method using a vacuum type issuance analyzer) is recommended as an effective means. Item (1) above is an item designed at the start of blowing, and item (2) is an item that can be easily grasped as blowing results, so information regarding these two items will be It can be obtained without any particular difficulty. Next, item (3) can be calculated using the following formula. ΔO _S =∫ ^t _t1 {(Input oxygen - Output oxygen)} dt However, t ₁ : The period of sampling during the above Input oxygen: Calculated from the amount of blowing oxygen and the amount of oxygen in the auxiliary material Output oxygen: The amount of oxygen in the exhaust gas The calculation method for residual oxygen in slag is not limited to the above formula, but when calculating using the above formula, it is not affected by the amount of oxygen contained in the residual slag from the previous charge, and the calculation period is short. Therefore, the sensor error is reduced, and it is used as a highly accurate blowing control parameter. Regarding item (4), a sublance is applied at the time of blow-off, and the oxygen partial pressure (hereinafter referred to as [O] _F ) in the molten steel is measured using an appropriate oxygen sensor. Although the present invention is not limited to the mechanism of the oxygen sensor, if a method is adopted in which an oxygen concentration battery is attached to the tip of the supplement, measurements can be made by immersing it in molten steel. Compared to a method in which various measurements are made using the method, significant time savings can be achieved. Item (5), the temperature of molten steel at the time of blow-off, can be easily measured using a sublance, or in some cases, the value estimated using a known method for converter dynamic control may be used. It can also be adopted as is. The carbon concentration at the end of blowing, which is item (6), can be determined by estimating the carbon concentration based on the solidification temperature of a sample of molten steel collected using a supplement, or by using the aforementioned dynamic control method. Examples of estimation methods and the like are given. As for hot metal conditions, item (7), the amount of hot metal, which is the main raw material for blowing, and the concentrations of Mn, P, and S in the hot metal are selected from the initial data and used. The most important of measurement items (1) to (7) in the present invention is the oxygen partial pressure in molten steel [O] _F described in (4).
However, when the present inventors were previously researching a technology to estimate the Mn, P, and S concentrations in blow-blown molten steel based on [O] _F , they found that in the low carbon region, the calculated values and the measured values were different. Although a correlation was found between
In the high carbon region, the slag becomes overoxidized, resulting in a non-equilibrium state between the slag and the molten steel, and the calculated values and actual measurements do not match at all, making it impossible to estimate using [O] _F in the high carbon region. In contrast, in the present invention, samples are taken during blowing, the Mn, P, and S concentrations in the molten steel are quickly analyzed, and the factors (1) to (6), excluding (4) above, are added to the data to determine the end of blowing. By estimating the Mn, P, and S concentrations at the same time, the estimation accuracy was extremely high. [Example] Fig. 1 is a flowchart of an example of estimating components by the method of the present invention. , Mn, P, and S are sampled from the molten steel and subjected to cantback analysis. On the other hand, the sub-lance is also immersed at the time of blow-off, and the molten steel temperature and [O] _F are measured and input into the CPU along with the above-mentioned cantback analysis results, where calculations are quickly performed, compared with the target components, and the steel is tapped. Determine whether or not it is possible. And if it fails, it will be re-blown. In addition, since the present invention does not control the end of blowing itself by cantback analysis of the sample, the end of blowing is carried out as planned, and the Mn, P, and S concentrations at that time are not determined by direct concentration analysis. Both are methods that can be estimated quickly and with high accuracy. Example 1 Using a 240-ton vertical blowing converter, blowing was planned for the purpose of obtaining high carbon steel having the composition specifications shown in Table 1. First, 250 tons of hot metal pretreated with the components shown in Table 2 were charged into a converter. Blowing began, and 3 tons of quicklime, 2 tons of lightly calcined dolomite, and 0.9 tons of fluorite were charged. Thirteen minutes after the start of blowing, a molten steel sample was collected using a sublance and analyzed for Mn, P, and S.
The blowing process ended 2.5 minutes after the sample was collected.
Molten steel temperature was measured using a sublance. In this charge, the sample analysis value, the amount of quicklime, light calcined dolomite, and fluorite input, and the amount of input oxygen at the end of the blow from the time of sample collection (blowing oxygen,
entrained air) and output oxygen amount (CO,
Based on the residual oxygen amount of 412Nm ³ calculated from the difference in CO ₂ ) and the molten steel temperature of 1680℃ measured at the blowstop,
When Mn, P, and S of the blowhole were estimated using equation (5), the values shown in Table 3 were obtained. Since P and S satisfied the composition specifications in Table 2, tapping started immediately, and Mn
For this, Mn alloy iron was added to meet the standard composition. Note that C was estimated using the conventional method (). We also collected molten steel samples when measuring the molten steel temperature using a sub-lance at the blowstop, and analyzed them separately, and the values shown in Table 4 were confirmed, confirming that estimation by this method is highly accurate even for high carbon steel. did.

【table】

【table】

【table】

[Table] Example 2 When melting high-carbon steel using a 240-ton vertical blowing converter, a sample of molten steel was collected during blowing using a sublance, and the Mn, P, and The S concentration was measured. On the other hand, the auxiliary materials (quicklime, fluorite,
Dolomite), the amount of oxygen used in blowing from the time of sample collection to the end of the blowing process, the amount of residual oxygen in the slag calculated from the oxygen balance, and the temperature of molten steel, were added as factors, and the statistically calculated equation (5) was used. The P concentration at the end of blowing was determined and used as the estimated value. Figure 2 is a graph showing the correlation between estimated values and actual values, σ = 0.00151%
It was possible to estimate with high accuracy. Example 3 A 240-ton converter was used to produce low carbon steel having the composition specifications shown in Table 5. First, 25 tons of scrap was added to the converter, and then 225 tons of hot metal with the composition shown in Table 6 was added to the converter.
A ton was charged. Blowing began, and 9 tons of quicklime, 4 tons of lightly calcined dolomite, and 0.8 tons of fluorite were charged.
Twelve minutes after the start of blowing, a molten steel sample was collected using a sublance and analyzed for Mn, P, and S. The blowing process ended 2.5 minutes after the sample was taken;
Molten steel temperature and [O] _F were measured using a sublance. Here, the analysis value of the sample, the amount of quicklime, light calcined dolomite, and fluorite added, the amount of blowing oxygen used from the time of sample collection to the blowstop of ^2000Nm3 , the molten steel temperature measured at the blowstop of 1660℃, and [O] _F
Using equation (5) with 750ppm as a factor, the Mn of the blowhole,
When P and S were estimated, the values shown in Table 7 were obtained. Since P and S met the composition specifications in Table 1, tapping began immediately, and Mn alloy iron was added to meet the specifications for Mn. In addition,
C was estimated using the conventional method (). In addition, when measuring the molten steel temperature and [O] _F using a sub-lance at the blowstop, take a sample of the molten steel.
Separate analysis revealed the values shown in Table 8, confirming that estimation by this method is highly accurate even for high carbon steel.

【table】

【table】

【table】

[Table] Example 4 When melting low carbon steel with C≦0.30% using a 240-ton vertical blowing converter, a sample of molten steel was collected during blowing using a sublance, and the molten steel was analyzed by cantback analysis. The Mn, P, and S concentrations were measured. On the other hand, the amount of auxiliary raw materials (quicklime, fluorite, dolomite) put into the charge, the amount of blowing oxygen used from the time of sample collection to the end of blowing, and the temperature and temperature of molten steel measured using a sublance at the end of blowing.
Adding the concentration as a factor, the Mn and P concentrations at the end of blowing were determined using the statistically determined equation (5) and used as estimated values. FIG. 3 is a graph showing the correlation between the estimated value and the measured value for Mn, and an excellent correlation with high accuracy of σ = 0.0093% was observed. FIG. 4 is a similar graph for P, and an excellent correlation with a high accuracy of σ=0.00145% could be recognized. Table 9 compares the estimation accuracy in the case of low carbon steel when similar estimation is made based on [O] _F and the case of the present invention, and the estimation accuracy of the present invention is superior. It can be seen that this shows accuracy.

[Table] [Effects of the Invention] Since the present invention is configured as described above, the Mn, P, and S concentrations in blow-finished molten steel can be estimated in a short time without taking the time required for direct analysis. The estimation accuracy is high regardless of whether the steel is low carbon steel or high carbon steel. Therefore, even steel types with strict composition standards, such as low-phosphorus steel, can be incorporated into the rapid tapping system, contributing to increasing the rate of adoption of rapid tapping.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing the estimation procedure according to the embodiment of the present invention, FIG. 2 is a graph showing the relationship between the estimated value and the measured value of P concentration in high carbon steel, and FIG.
The figure is a graph showing the relationship between the estimated value and the measured value of the Mn concentration in low carbon steel, and FIG. 4 is the graph showing the relationship between the estimated value and the measured value of the P concentration in the low carbon steel.

Claims (1)

[Claims] 1. Collecting a molten steel sample during converter blowing,
A method of measuring the concentration [M] _B of at least one component among Mn, P, and S in molten steel during blowing, and using the results to estimate the concentration [M] _S of the component in molten steel at the end of blowing. (1) Amount of auxiliary raw materials, (2) Amount of blowing oxygen used from the time of molten steel sample collection to the end of blowing, (3) Amount of residual oxygen in the slag calculated from the oxygen balance, (4) Measured at the end of blowing. (5) Temperature of molten steel at end of blow, (6) Carbon concentration at end of blow, (7) Select at least one item from the group of operation items consisting of hot metal conditions, and The following regression formula is constructed by adding the factors related to the items to the concentration in the molten steel during blowing [M] _B [M] _S = [M] _B + ΣαXi + constant ...[] In the formula, [M] _S : Concentration in molten steel at the end of blowing [M] _B : Concentration in molten steel during blowing α: Coefficient Xi: Based on factors related to one or more items selected from the operation item group consisting of (1) to (7) above A method for estimating a component at the end of a converter, comprising estimating the concentration of the component in the end of molten steel.