JPH0617495B2 - Dephosphorizing agent for hot metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a practical and yet inexpensive dephosphorizing agent for hot metal, and particularly, it is carried out in a container such as a torpedo car or a ladle prior to converter refining. The present invention relates to a dephosphorizing agent for hot metal, which is suitable for preliminary dephosphorizing treatment of hot metal and has excellent dephosphorizing properties, but is practical and inexpensive.

(Prior Art) As is well known, since hot metal produced in a blast furnace contains a large amount of phosphorus as an impurity, it is necessary to perform an efficient dephosphorization treatment in the steelmaking process to improve the mechanical properties of steel products. Are being increasingly demanded.

Usually, this dephosphorization process is performed by using a quicklime-based slag-forming agent during oxidation refining such as in a converter together with decarburization, and recently, in the pretreatment of hot metal prior to decarburization and refining in a converter, similar to sulfur, Techniques for removing phosphorus have also been put into practical use.

Conventionally, as a dephosphorizing agent for pretreatment of hot metal, for example, as known from JP-A-55-62112, CaO and C
In general, aCl ₂ or KCl and an oxygen-containing substance (O ₂ gas or iron oxide) are used in combination, or a Na ₂ CO ₃ -based substance is generally used, as known from JP-A-52-127420. is there. In addition, as a dephosphorizing agent of another component type, a CaO—Al ₂ O ₃ type dephosphorizing agent is disclosed, for example, in JP-A-56-108813 and JP-A-59-17.
Those described in Japanese Patent Publication No. 0214 and Japanese Patent Publication No. 56-27569 are known.

(Problems to be Solved by the Invention) The above-mentioned known dephosphorizing agents have the following problems.

First, CaO-CaCl ₂ (or KCl) -based and CaO-CaF ₂ -based Na ₂ CO ₃ -based materials promote the erosion of the refractory lining of the processing container and generate harmful evaporative substances and odorous gases during use. However, the work environment is deteriorated, and the processing of the generated slag requires a large amount of cost.

On the other hand, the CaO-Al ₂ O ₃ system disclosed in Japanese Patent Application Laid-Open No. 56-108813 utilizes a blast furnace slag. The blast furnace slag contains a large amount of SiO ₂ component, and this SiO ₂ not only increases the amount of hot metal dephosphorization slag and increases the slag treatment cost, but also lowers the slag basicity and removes slag between metal and metal. Decrease the phosphorus reaction. Further, since a large amount of sulfur is contained in the blast furnace slag, it is not industrially practical to use the blast furnace slag for de-S treatment in order to utilize it as a treating agent as described in JP-A-56-108813. .

Further, the one described in JP-A-59-170214 is a treating agent which is also intended to remove S at the same time, and is intended for those having a mineral composition of nCaO.mAl ₂ O ₃ such as commercially available calcium aluminate, There are restrictions on the availability of raw materials and there are difficulties in terms of price.

Furthermore, the one described in Japanese Examined Patent Publication No. 56-27569 is intended for use in converter steelmaking, and is different from the hot metal dephosphorization mechanism in which decarburization is suppressed and dephosphorization is preferentially performed. , You can't discuss both at the same level.

That is, the one described in Japanese Examined Patent Publication No. 56-27569 is a self-dissolving slag forming agent which is a substitute for fluorite (CaF ₂ ) which is a slag forming accelerator in the early stage of blowing in converter steelmaking, and its use The purpose is completely different from the beginning. When this is used as a hot metal dephosphorization agent, as is clear from its chemical composition, Fe ₂ O ₃ consumed for decarburization
Since the content is not taken into consideration, the Fe ₂ O ₃ content is too low, the melting point of the final slag becomes high, and a sufficient effect as a hot metal dephosphorizing agent cannot be expected.

(Means and Actions for Solving Problems) The present invention is a dephosphorizing agent for hot metal that advantageously solves the above-mentioned conventional problems, and in particular, during use, the erosion of the refractory lining of the processing container is so great. In addition, since it does not generate harmful gas, it not only harms the working environment, but it also greatly expands the effective use range of the generated slag for fertilizers, etc., and it is practical and naturally possible to remove phosphorus in hot metal preferentially. The purpose is to provide an inexpensive dephosphorizing agent.

The basis of the present invention is to confirm that Al ₂ O ₃ lowers the melting point of CaO even at a relatively low temperature such as the hot metal temperature, and appropriately selects the ratio of CaO and Al ₂ O ₃ . It is based on the finding that dephosphorization takes precedence over decarburization. That is, the gist of the present invention is to promote the dephosphorization reaction by lowering the melting point of the produced slag and the amount of iron oxide required for advancing the dephosphorization reaction of hot metal, lime that stabilizes the dephosphorization product. CaO-Al ₂ O ₃ -containing essential hydrous alumina minerals
A mixture containing Fe _X O _Y as a main component, wherein C in the mixture is
The content ratio of aO and Al ₂ O ₃ is CaO: Al ₂ O ₃ (2.5 to ₂ by weight).
0): 1 and the iron oxide content is 25 to 65 of the mixture.
(Wt%), and the content ratio of SiO ₂ as an impurity was 10% (wt) or less of the mixture.

The present invention will be described in more detail below.

In order to solve the above-mentioned drawbacks of CaF ₂ , CaCl ₂ and KCl as the melting point depressant of CaO, the present inventor selects Al ₂ O ₃ already known to have a similar action and adds it to CaO. When the amount of Al ₂ O ₃ was gradually increased, it was confirmed that Al ₂ O ₃ had a melting point lowering effect of CaO equal to or higher than CaF ₂ and FeO as shown in FIG. 1 up to near the hot metal temperature.

Next, based on these confirmations, an experiment was conducted as to whether Al ₂ O ₃ is effective as a melting point depressant for CaO even in the dephosphorization reaction of hot metal. That is, C: 4.2%, P: 0.14%, S: 0.05%, M
n and Si were melted in the MgO crucible using a 20kHz high-frequency melting furnace to melt 500gr of hot metal having trace components, and set the hot metal temperature to 1
(CaO + Al ₂ O ₃ ): Fe ₂ O ₃ = 5 while maintaining at 350 ℃
Using a 0:50 (weight ratio) CaO-Al ₂ O ₃ -Fe ₂ O ₃ ternary system reagent, every 2 minutes, at a rate of 2 gr, 10 times, 20 gr in total,
Moreover, the state of dephosphorization and decarburization was investigated by changing the ratio of Al ₂ O _{3 to} CaO.

2 and 3, the vertical axis represents the content ratio of phosphorus and carbon in the hot metal, and the horizontal axis represents the elapsed time, showing changes over time in dephosphorization and decarburization. In the figure, ↓ on the horizontal axis indicates the time when the reagent is added, Indicate the types of reagents in which the weight ratio of CaO and Al ₂ O ₃ is changed, as described in the drawings. It is clear from FIGS. 2 and 3 that dephosphorization is significantly progressing in comparison with decarburization, and the present inventor has found that CaO-Al ₂ O ₃ -Fe _X O _Y ternary system. We have obtained a new finding that flux is very effective in dephosphorizing hot metal.

Of this flux The relationship between the ratio, that is, the CaO / Al ₂ O ₃ (weight) ratio and the dephosphorization rate is shown in FIG. From FIG. 4, CaO / Al ₂ O ₃ = 2.5 to 20.0, especially 3.
It can be seen that the optimum composition is in the range of 0 to 9.0. The composition of the generated slag is CaO-Al ₂ O ₃ -Fe _X O _Y
As shown in the figure. From this phase diagram, CaO: Al showing high dephosphorization ability
It can be seen that the slag generated by the flux of ₂ O ₃ = (3.0 to 9.0): 1 is located near the saturation line where CaO precipitates. That is, in the CaO-Al ₂ O ₃ -Fe _X O _Y ternary system, the flux composition that obtains high dephosphorization ability is blended with the composition having the highest P distribution ratio (low Al ₂ O ₃ side) in the low melting point region to react. It is necessary to select a range where the CaO saturation composition (CaO activity = 1) is obtained due to the decrease of Fe _X O _Y with the progress.

The composition satisfying this condition is CaO: Al ₂ O ₃ = 2.5 to 20.0: 1.
(Weight) Especially 3.0-9.0: 1 (weight), Fe _X O _Y
Is in the range of 25 to 65%, especially 30 to 60%.

Furthermore, the present inventor, based on the above findings, pays attention to natural bauxite, red mud which is a waste product of the aluminum industry, etc. as an inexpensive Al ₂ O ₃ source that can be industrially used, and quick lime, bauxite and / or red mud, As a typical example of conventional flux, CaO-CaF ₂ -Fe ₂ was used as a typical example of conventional flux by using a powder mixture of iron oxide as a flux and conducting the experiment under the same conditions as in FIGS. 1 and 2.
Comparative experiments of O ₃ system and CaO-CaF ₂ -CaCl ₂ -Fe ₂ O ₃ system,
Each surveyed the status of dephosphorization and decarburization. FIGS. 6 and 7 show changes with time in dephosphorization and decarburization when various fluxes were used. In the figure Is a mixture of the present invention, containing bauxite, red mud, and bauxite + red mud as quick lime, iron oxide, and Al ₂ O ₃ sources, respectively. Is a CaO-Al ₂ O ₃ -Fe ₂ O ₃ ternary reagent, and ○ and ◇ are respectively
Shows a conventional CaO-CaF ₂ -Fe ₂ O ₃ system and _{CaO-CaF 2 -CaCl 2 -Fe 2} O 3 based flux, the components ratio is as shown FIG. 6, in Figure 7.

As is clear from FIGS. 6 and 7, when bauxite and red mud were used (CaO / Al ₂ O ₃ compared to the CaO-Al ₂ O ₃ -Fe _X O _Y system using pure reagents). = 3/1), the dephosphorization rate is lowered. This is due to the effects of SiO ₂ and TiO ₂ in bauxite and red mud, and if the amount of CaO is increased to cancel this, CaO / Al ₂ O ₃ = 5/1), CaO-Al ₂ O ₃ -F using pure reagent
An effect equivalent to that of the e _X O _Y (CaO / Al ₂ O ₃ = 3/1) system can be obtained. In addition, CaO- which has been used as a hot metal dephosphorization agent
Compared with CaF ₂ -Fe ₂ O ₃ -based and CaO-CaF ₂ -CaCl ₂ -Fe ₂ O ₃ -based dephosphorization agents, they are completely equivalent. Therefore, it was confirmed that a mixture using natural bauxite and red mud which is a waste product of the aluminum industry is also useful.

The reasons for limiting the dephosphorizing agent of the present invention will be described below.

The dephosphorizing agent of the present invention is a ternary system of CaO-Al ₂ O ₃ -Fe _X O _Y ,
When these components are selected on an industrially practical level, the amount of iron oxide necessary for proceeding the dephosphorization reaction, lime that stabilizes the products such as P ₂ O ₅ produced by dephosphorization, and lime. A hydrated alumina mineral that lowers the melting point of is essential. And
In order to obtain an excellent dephosphorization rate of 75 to 80%, it is essential to appropriately select the ratio of both CaO and Al ₂ O ₃ components, as is clear from FIG. That is, as mentioned above, the dephosphorization rate is 80%.
CaO: Al ₂ O ₃ = (3.0-
9.0): 1 (by weight) is required. If the dephosphorization rate is slightly sacrificed, CaO: Al ₂ O ₃ = (2.5-20.
0): 1 (weight) is sufficient. This is the second feature of the present invention.

Further, as suggested from FIG. 6, it is better that the incidental amounts of SiO ₂ and TiO ₂ coming from the hydrated alumina mineral (bauxite, red mud, etc.) as the source of Al ₂ O ₃ are as small as possible.

When using natural hydrous alumina minerals (bauxite, diaspore) and red mud, which is a waste product of the aluminum industry, as alumina sources, SiO ₂ <5%, Al ₂ O ₃ = 50 for bauxite and diaspore as hydrous alumina minerals. ~
70%, Fe ₂ O ₃ = 15 to 20%, TiO ₂ = 1 to 2%, and compounded water of about 15 to 25% is abundant in a wide variety and is inexpensive. Red mud has SiO ₂ = 10-20%, Al ₂ O ₃ = 20-
25%, Fe ₂ O ₃ = 30-40%, TiO ₂ = 5-8%, Na ₂ O
It has a composition of about 8 to 15%, and is a waste resource of the aluminum industry which has never been used. And the sixth
As is clear from the figure, the dephosphorization rate is worse when red mud containing a large amount of SiO ₂ is added to the flakes.As is well known, especially SiO ₂ is a melt during hot metal dephosphorization. Since the basicity of the slag is reduced, the dephosphorization efficiency is reduced, and the amount of produced slag is increased, in consideration of increasing the cost of post-treatment of the produced slag, it is better that the amount of SiO ₂ is less,
As its upper limit, the proportion of the components in the dephosphorizing agent mixture of the present invention is 10% by weight, preferably 7%. This is the third feature.

Iron oxide is necessary in an amount sufficient to promote dephosphorization, and its proportion in the dephosphorization agent is at least 25% by weight, and especially 30% is necessary and too much. When the relative proportion of CaO decreases, Since the phosphorus product cannot be fixed stably, its upper limit is 65.
%, Preferably 60%. Examples of iron oxide that can be used include iron ore, mill scale, smelting dust (steel making furnace, blast furnace dust, etc.), iron oxide powder, and the like.

Either limestone or quicklime may be used as lime,
In the case of limestone, since the endothermic reaction is decomposed in the hot metal, the hot metal temperature is lowered. From this point, quicklime is preferable.

As mentioned above, hydrous alumina minerals that are readily available and practical as resources, as described above, contain 50 to 70% of Al ₂ O _3, natural bauxite, diaspore, and red mud, which is a waste resource of the aluminum industry. Alumina or the like can be used.

Since these hydrous alumina ores usually contain 15 to 25% of compound water, if they are used as they are, the hot metal temperature will drop, and it will also cause fume generation, which will harm the working environment. Calcination at 550 to 600 ° C. is effective not only for removing water but also for removing trace volatile components such as Zn, Pb and the like.

In the use of the dephosphorizing agent of the present invention, it is effective for dephosphorization by adding it from the upper side of the processing vessel by the slag-metal reaction, but especially by using a carrier gas such as N ₂ from the upper side of the processing vessel to the hot metal. The effect of preferential dephosphorization is enhanced when the lance is soaked or is sprayed and added into the hot metal through a nozzle provided at the bottom of the container. Further, when the hot metal temperature is lowered during the treatment, or when a higher hot metal temperature is required, it can be used in combination with gaseous oxygen by suspending it in gaseous oxygen and blowing it. When blowing with a carrier gas, like the other known treating agents, it is preferable that the dephosphorizing agent of the present invention has its shape and particle size appropriately adjusted depending on its usage.

(Example) Example 1 An inner diameter of 46 mmφ and a height of 100 using a high-frequency furnace of 35 kw.
Melt pig iron 500gr in a MgO crucible of mmφ and set the hot metal temperature to 1
Maintained at 350 ± 10 ° C.

The composition of the dephosphorizing agent is CaO + Al ₂ O ₃ : Fe ₂ O ₃ = 50: 50 (weight)
In addition, 6.95 gr of quick lime, 4.55 gr of bauxite, and 8.5 gr of mill scale were mixed so that CaO: Al ₂ O ₃ = 3: 1 (weight). Incidentally, SiO _{2 in the} mixed dephosphorizing agent
= 0.58% (weight). This dephosphorizing agent was used as C: 4.
2%, P: 0.14%, S: 0.05% Added to 500gr of hot metal with traces of Si and Mn traces, and 10 minutes after the addition was completed, a sample of hot metal was analyzed. C: 3.3%, P: 0.05
The dephosphorization rate was 4%, S: 0.042%, and about 61%.

Example 2 Using the same experimental equipment and hot metal conditions as in Example 1, the composition of the dephosphorizing agent was (CaO + Al ₂ O ₃ ): Fe ₂ O ₃ = 60: 40 (weight) and
CaO: Al ₂ O ₃ = 9: 1 (by weight) quicklime 10.
17 gr, bauxite 1.54 gr, red mud 1.54 gr, and mill scale 6.75 gr were mixed. Incidentally, SiO ₂ = 1.5% in the mixed dephosphorizing agent. When a sample of hot metal was analyzed 10 minutes after the addition of the dephosphorizing agent, C: 3.4.
%, P: 0.028%, S: 0.039%, about 80
The dephosphorization rate was%.

Example 3 Using the same experimental equipment and hot metal conditions as in Example 1, the composition of the dephosphorizing agent was (CaO + Al ₂ O ₃ ): Fe ₂ O ₃ = 40: 60 (weight) and CaO:
6.24 g of quick lime so that Al ₂ O ₃ = 5: 1 (weight)
r, 1.70 gr of bauxite, 1.70 gr of red mud, and 10.36 gr of mill scale were mixed. The SiO ₂ content in the mixed dephosphorization agent was 1.68%. When a sample of hot metal was analyzed 10 minutes after the addition of the dephosphorizing agent, C:
The amount was 3.27%, P: 0.033%, S: 0.04%, and the dephosphorization was 76%.

Examples 4 to 6 Table 1 shows examples in which the dephosphorizing agent of the present invention was applied to the treatment on an actual scale.

(Effects of the present invention) As described above, the dephosphorizing agent of the present invention promotes preferential dephosphorization while suppressing decarburization of hot metal, and thus the conventional CaO-CaF ₂ -Fe ₂ O ₃ system or CaO-CaF is used. _2- CaCl ₂ -Fe ₂ O ₃ system or Na ₂ C
A dephosphorization rate comparable to that of O ₃ type dephosphorizers can be achieved. Further, in use, since the work environment is not contaminated by the harmful gas generated by eroding the refractory lining of the processing container, which is a drawback of these conventional dephosphorization agents, not only the cost required for these measures can be saved. The bauxite, red mud, etc., which are the raw materials of the melting point depressant of the dephosphorizing agent of the present invention, are resource-rich and inexpensive. Further, since the produced slag treated with the dephosphorizing agent of the present invention has less harmful components than the conventional slag, there is a possibility that the application range to cement raw materials, fertilizers, roadbed materials, etc. can be greatly expanded. Therefore, the dephosphorizing agent for hot metal of the present invention is practical and extremely useful on an industrial scale.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the melting temperature and the addition amount of various CaO melting point depressants to be added to CaO, and FIG. 2 is the CaO-Al ₂ O of the present invention.
Diagram showing dephosphorization status of hot metal by _3- Fe ₂ O ₃ -based dephosphorizer, No. 3
The figure is also a diagram showing the decarburization state of hot metal, FIG. 4 is a diagram showing the relationship between CaO / (CaO + Al ₂ O ₃ ) in the dephosphorizing agent of the present invention and the dephosphorization rate, and FIG. 5 is CaO-Al ₂ The ternary phase diagram of the O ₃ -Fe _X O _Y flux, FIG. 6 is a diagram showing the comparison of the dephosphorization state of the hot metal between the dephosphorizing agent of the present invention and the conventional dephosphorizing agent, and FIG. 7 is also the same. It is a figure which shows the comparison of the decarburization situation.

Claims (3)

[Claims] 1. An amount of iron oxide necessary for promoting a dephosphorization reaction of hot metal, lime for stabilizing a dephosphorization product, and hydrous alumina mineral for lowering the melting point of the produced slag to accelerate the dephosphorization reaction. A mixture containing CaO-Al ₂ O ₃ -Fe _X O _Y system as a main component, and the content ratio of CaO and Al ₂ O _{3 in} the mixture is CaO: Al ₂ O ₃ = (2 0.5 to 20): 1, the iron oxide content is 25 to 65% by weight of the mixture, and the content of SiO ₂ as an impurity is 10% by weight or less of the mixture. Phosphorus. 2. The hot metal dephosphorization agent according to claim 1, wherein at least one of quicklime as lime and natural bauxite, diaspore, red mud and purified alumina as hydrated alumina mineral is used. Dephosphorizing agent. 3. A dephosphorizing agent for hot metal according to claim 1 or 2, which is a dephosphorizing agent for hot metal obtained by calcining a hydrated alumina mineral.