JPH06108136A - Production of low p and low s foundry pig iron - Google Patents

Abstract

PURPOSE:To efficiently produce a low P and low S foundry pig iron having the aimed component composition by adjusting dephosphorizing agent, after-blowing scale and top-blowing oxygen quantities in dephosphorizing process after desiliconizing. CONSTITUTION:In the dephosphorizing process executing after desiliconizing treatment and removal of the desiliconized slag, the CaO-base dephosphorizing agent is used. Together with this, according to the aimed C and S contents in the foundry pig iron, the dephosphorizing agent, after-blowing scale and top-blowing oxygen quantities are adjusted so as to satisfy the equations I and II. At the time of the execution, according to the components in the molten pig iron after the removal of desiliconized slag, by introducing each supplying quantity of the preset dephosphorizing agent, after-blowing scale and top-blowing oxygen into the equation I, the decarbonizing content is calculated and deducted from the C content in the molten pig iron. This result is compared with the aimed C content in the foundry pig iron. In the case of being the excess or the shortage to the decarbonizing content, one or more kinds of each supplying quantity among the dephosphorizing agent, after-blowing scale and top-blowing oxygen are adjusted to secure the aimed C content. In the same way, S content after dephosphorization is calculated from the equation II and each supplying quantity is adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for economically and efficiently producing low P / low S cast pig iron having a controlled C and S content.

[0002]

2. Description of the Related Art A low P / low S cast pig iron has been conventionally manufactured by sequentially performing three steps of Si removal, P removal and S removal in a hot metal pretreatment step. That is, the hot metal discharged from the blast furnace is first subjected to a de-Si treatment, then the slag containing a high concentration of SiO ₂ is discharged, and then the P removal treatment is carried out so that the P in the hot metal falls within the component specifications. A low-P / low-S cast iron pig is obtained by removing S from the pretreatment process.

However, in these methods, no consideration is given to the amount of C [C] in the hot metal in each processing step, and the [C] of the cast iron shows a considerable variation from batch to batch. Nevertheless, the actual condition is that the [C] of the obtained low P / S cast iron pig is as soon as it is completed, and no fine adjustment of [C] has been made.

That is, in the dephosphorization process performed after desiliconization,
A large amount of oxygen (or air) is blown up to accelerate de-P, and scale is supplied into the hot metal for temperature adjustment and final P amount adjustment at the final stage, so [C] is slightly added in this step. It's difficult to adjust. On the other hand, S in cast pig iron
With respect to the amount [S], it is difficult to simultaneously adjust [S] within the standard in the above-mentioned P removal step, so a method of adjusting [S] in the subsequent S removal step is adopted. In the S-removing step, soda ash or the like is added as a S-removing agent in order to achieve low nitrogen content, and
Since it is necessary to remove slag, not only the total treatment process becomes long and the production efficiency is lowered, but also the temperature drop of the hot metal becomes large and the casting yield is adversely affected.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its purpose is to achieve low P
-When manufacturing low S cast iron, it is possible to adjust the components of [C] and [S] in the hot metal at the same time in the P removal step after Si removal. S
It is intended to establish a method capable of efficiently producing cast pig iron.

[0006]

The structure of the present invention which has been able to solve the above-mentioned problems is a de-P process performed after removing Si and removing Si slag when producing low P / low S cast iron. , Using CaO-based de-P agent,
Depending on the target C amount and target S amount of the cast pig iron, the following [I]
The gist is to adjust the amount of P-removing agent, the amount of post-blown scale, and the amount of top-blown oxygen so as to satisfy the formula and the formula [II].

C removal amount (%) = 0.42 x P removal agent amount (kg / ton) +1.1 x post-blown scale amount (kg / ton) +6.7 x top-blown oxygen amount (Nm ³ / ton) + 4.9 / 100 … [I] S amount after dephosphorization (%) = 0.41 × amount of S before deoxidation (%) × 10 ³ -0.19 × amount of dephosphorization agent (kg / ton) + 0.59 × amount of top-blown oxygen (Nm ³ / (Ton) + 10.8 / 1000… [II]

[0008]

In the present invention, the hot metal discharged from the blast furnace is received by a ladle or a mixed pig car to remove Si, remove slag from Si, and remove P.
Perform hot metal pretreatment in this order. That is, in the Si removal step, for example, solid oxygen (Fe ₂ O ₃ etc.) or the like is blown as a Si removal agent by an injection method or the like, but in this step, Si removal and Mn progress simultaneously, so that Si reduction and M reduction are achieved.
n-ization is achieved.

Then, in order to efficiently proceed with the de-Ping performed thereafter, the de-Si slag having a high SiO ₂ concentration is discharged to the outside of the system by a drucker or the like. In the conventional example, low P and low S are achieved by sequentially performing the P removal and S removal steps thereafter.
However, this method has a problem that the finished C content becomes unstable in addition to the problems of production efficiency and guarantee of the temperature of the hot metal as described above.

Therefore, in the present invention, as a means for solving all of these problems at once, it is possible to perform S removal at the same time and adjust the C content in the P removal step performed after the removal of the Si slag, and the P content, It is intended to establish a method capable of producing a low-P / low-S cast iron pig whose S content and C content are adjusted with good productivity.

That is, in the present invention, first, Si removal is performed as a P removal agent.
Using a CaO-based de-P agent that also functions, depending on the target C amount and target S amount of the cast pig iron, the amount of the de-P agent and the post-blowing are performed so as to satisfy the above formulas [I] and [II]. Adjust the scale and top-blown oxygen. That is, the amount of de-C and the amount of de-S when performing de-P using a CaO-based de-P agent are
It has a close relationship with the amount of de-P agent (kg / ton), the amount of post-blown scale (kg / ton) and the amount of top-blown oxygen (Nm ³ / ton), and controls each of these amounts during de-P treatment. By doing so, it was found that the C content and S content of the obtained cast pig iron could be adjusted well.

Therefore, in carrying out the present invention, the respective supply amounts of the P-removing agent, the post-blown scale and the top-blown oxygen which are set in advance in accordance with the hot metal component after the removal of the Si slag are introduced into the above formula [I]. Then, the C removal amount is calculated and subtracted from the C content of the hot metal, and the result is compared with the target C content of the cast iron. As a result, when there is an excess or deficiency in the C removal amount, the P removal agent, the post-blown scale,
The target C amount is secured by increasing / decreasing one or more of each supply amount of top-blown oxygen.

However, since each of the above-mentioned supply amounts affects not only the C-depletion amount but also the S-content after the P-depletion, similarly, the preset supply amounts of the P-depleting agent, the post-blown scale and the top-blown oxygen are similarly set. Is introduced into the above formula [II] to calculate the S content after P removal,
Depending on the excess / deficiency of the S removal amount, one or more of the above supply amounts are increased / decreased while being linked to the correction value of the C removal amount according to the above formula [I].

After the composition of the hot metal after the removal of the de-Si slag has been clarified, these calculations are carried out promptly by a computer or the like based on the analyzed values,
The C amount and S amount after P removal will be adjusted quickly and almost accurately according to the target value.

Thus, it is possible to obtain C by performing only one P removal process.
Content and S content can be adjusted at the same time, production efficiency can be improved, and the decrease in hot metal temperature in the pretreatment process can be suppressed to a minimum.
-It becomes possible to obtain low S cast iron.

Examples of the present invention will be shown below, but the present invention is not limited by the following examples, and any modifications may be made within a range that is compatible with the purpose of the invention. It is included in the technical scope of the present invention.

[0017]

EXAMPLE Using two kinds of hot metal having chemical compositions after removing Si and removing Si slag as shown in Table 1,
Aiming at obtaining cast pig iron having the target component composition shown in Table 2, the values are applied to the above formulas [I] and [II] to be used in the depurification step, and the CaO-based depurifying agent, the post-blown scale, Each supply amount of top-blown oxygen was calculated, each supply amount shown in Table 3 was determined, and P removal processing was performed. The obtained cast iron,
The composition of the components is as shown in Table 4, and S content, P content, Si
Cast iron that satisfies the target composition is obtained not only in the amount of C but also in the amount of C.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

EFFECTS OF THE INVENTION The present invention is configured as described above, and it is possible to adjust the C removal amount and the S removal amount at the same time in the P removal step after Si removal, and the pretreatment for producing cast pig iron is It is remarkably simplified, the productivity is improved, the heat release during the pretreatment is suppressed, the casting yield is improved, and the C content can be controlled as desired, so that the quality of the cast pig iron is stabilized. It is possible to obtain various benefits according to practical use.

Claims (1)

[Claims] 1. When manufacturing low P / low S cast pig iron,
De-P treatment performed after de-Si treatment and de-Si slag removal
In the process, a CaO-based de-P agent is used, and according to the target C amount and target S amount of the cast pig iron, the de-P agent amount and the post-blown scale are satisfied so as to satisfy the following formulas [I] and [II]. A method for producing a low-P / low-S casting pig iron characterized by adjusting the amount and the amount of top-blown oxygen. C removal rate (%) = 0.42 x P removal agent amount (kg / ton) +1.1 x post-blown scale amount (kg / ton) +6.7 x top-blown oxygen amount (Nm ³ / ton) + 4.9 / 100… [I ] S amount after P removal (%) = 0.41 x S amount before P removal (%) x 10 ³ -0.19 x P removal agent amount (kg / ton) + 0.59 x Top blown oxygen amount (Nm ³ / ton) + 10.8 / 1000… [II]