JP6028696B2 - Decarburization blowing method for high alloy steel - Google Patents

Description

  The present invention suppresses the scattering of the carbon source introduced into the furnace as a heat source during the decarburization treatment of a steel type having a high alloy component (for example, high alloy steel such as stainless steel) using a converter. Thus, the present invention relates to a decarburization blowing method that improves the yield of carbon source addition while reducing the amount of dust generated.

  In hot metal decarburization processing using a converter, a carbon source is used for melting of scrap and raising the temperature of hot metal, and blowing is performed. As the carbon source, coke containing almost no volatile component is usually used from the viewpoint of preventing ignition during transportation and dust explosion. However, in the decarburization blowing of high alloy steels such as stainless steel, a large amount of cold iron source such as scrap and alloy iron is charged in the furnace, so it should be added for heat compensation during blowing. The required amount of carbon source also increases compared to carbon steel decarburization blowing.

  Coke, which is input as a carbon source for heat compensation, has a small amount of volatile matter, but contains impurity elements that adversely affect the steel material such as P and S. When a large amount of coke is added by smelting, P and S are mixed beyond the allowable range of steel. In particular, stainless steel has a problem that dephosphorization treatment becomes difficult because the P activity is greatly reduced by increasing the P content in the steel.

Therefore, in order to easily perform the dephosphorization treatment, it is necessary to use a carbon source having a small amount of impurity elements (particularly, the P content) as a heat raising material. However, since carbon materials that are suitable as a raw material for coke and have few impurity elements are scarce and expensive, the production cost of coke produced from such carbon materials is unavoidable. .
In addition, when steaming coal with a low P content is used, the content of volatile components is high, so that equipment for preventing ignition and dust explosion is required for transportation facilities and input hoppers.

On the other hand, anthracite is not suitable as a raw material for coke, but it has a low P content. Therefore, as a carbon source for heat compensation in decarburization blowing to obtain high alloy steel (especially stainless steel) from hot metal. Is preferred. Moreover, since anthracite has less volatile content than steam coal, it is not necessary to install a device for preventing ignition or dust explosion in equipment related to storage and transportation.
Therefore, various techniques for decarburization blowing using coal with low volatile content such as anthracite coal have been studied in order to obtain high alloy steel.

For example, Patent Document 1 discloses a technique of using coal having a particle size adjustment and a volatile content of 10% by mass or less in smelting reduction blowing of chromium ore. In this technology, when coal containing a certain concentration of volatile matter is put into the furnace, the coal undergoes thermal collapse, and the fine coal promotes the reduction reaction of chromium oxide present in the slag. It is.
However, since the coal refined by thermal collapse is easily trapped in the exhaust gas discharged from the furnace port and scattered outside the furnace, the amount of dust generated increases and the yield of coal addition decreases. In particular, the dust generated by decarburization blowing to obtain stainless steel contains chromium, and therefore requires a great deal of cost for processing the dust. Therefore, it is necessary to reduce the amount of dust generated.

  In Patent Document 2, in decarburization blowing for obtaining high chromium steel, when anthracite is introduced in the initial stage of decarburization blowing, by reducing the supply rate of oxygen supplied from the top blowing lance, A technique is disclosed in which the linear flow rate of the exhaust gas discharged from the furnace port is reduced to suppress the anthracite from being scattered outside the furnace. However, in this technique, in order to suppress the scattering of the anthracite coal that has been thermally collapsed, it is necessary to reduce the supply rate of oxygen, which is indispensable for decarburization blowing, leading to a reduction in productivity of decarburization blowing.

JP-A-9-227919 JP 2006-233265 A

  The present invention uses a converter to suppress the scattering of the carbon source introduced into the furnace as a heat source during blowing when performing decarburization treatment of a steel type having a high alloy component (for example, stainless steel). It aims at providing the blowing method which can improve the addition yield of a carbon source, reducing the generation amount of dust.

  In the initial stage of decarburization blowing to obtain high alloy steel, the present inventors have reduced the concentration of chromium oxide, iron oxide, etc. in the slag, so that the carbon source is not necessarily refined by thermal decay and reduced. It is not necessary to promote the reaction, but rather, various brands and types of carbon sources from the viewpoint that it is important to suppress thermal decay (ie, refinement) in order to suppress the scattering of carbon sources outside the furnace. Was put into the hot metal in a small experimental melting furnace, and then collected with a bag filter, and the amount of scattering was measured.

  In addition, the exhaust velocity of the small melting furnace is adjusted so that the linear velocity of the gas flow discharged from the furnace port of the small melting furnace is equivalent to the normal converter operation, and the particle size of the dust collected by the bag filter is adjusted. As a result of the investigation, most of the fine particles having a particle size of 3 mm or less accounted for. That is, the carbon source that has been put into the furnace and refined by thermal collapse is caught in the exhaust gas and scattered from the furnace port as dust.

In addition, it has been found that a carbon source having a volatile content of 3% by mass or less suppresses refinement due to thermal collapse of the input carbon source.
From the above results, in decarburization blowing to obtain high alloy steel, in order to suppress the scattering of dust, by using a carbon source having a volatile content of 3% by mass or less, it was introduced into the furnace. It was found that it is important to suppress thermal collapse when doing so. Moreover, since the scattering of dust is suppressed by suppressing the thermal collapse of the carbon source, there is no need to reduce the supply rate of oxygen supplied from the top blowing lance, and the productivity reduction of decarburization blowing of high alloy steel Can also be prevented.

The present invention has been made based on such knowledge.
That is, the present invention relates to an anthracite having a volatile content of 2.7 % by mass or less for heat compensation in a decarburization blowing method in which hot metal is decarburized to obtain high alloy steel using a converter. This is a decarburization blowing method that is put into the converter.
In the decarburization blowing method of the present invention, it is preferable to add scrap to the converter as the iron source in addition to the hot metal, and as anthracite, supply the oxidizing gas with particles adjusted to a particle size of less than 3 mm. It is preferable to supply from a charcoal charging lance provided separately from the blowing lance. Further, through the carbonaceous material charged run scan by supplying the fuel gas and oxygen gas, a burner flame formed at the tip of the carbonaceous material charged lance, it is preferable to blowing particles anthracite the burner flame.

  According to the present invention, when performing decarburization processing of a steel type (for example, stainless steel, etc.) with a large amount of alloy components using a converter, it is possible to suppress scattering of the carbon source input into the furnace as a heat source during blowing. Therefore, since the yield of carbon source can be improved while reducing the amount of dust generated, there are significant industrial effects such as improving productivity.

It is sectional drawing which shows typically the example of the converter to which this invention is applied. It is a graph which shows the relationship between the volatile matter of a carbon source, and a scattering rate.

In order to obtain high alloy steel such as stainless steel, when decarburizing and blowing the hot metal, in addition to the hot metal preliminarily treated and low phosphorous, after the stainless scrap and ferrochrome are charged into the converter Then, oxygen is supplied from the top blowing lance, a carbon source is further charged, and the inside of the converter is heated by the combustion heat. At this time, in this invention, in order to suppress that a carbon source refines | miniaturizes by thermal collapse, anthracite is used as a carbon source whose volatile content is 2.7 mass% or less. As described above, if the content of volatile components of anthracite is 2.7 % by mass or less, refinement due to thermal collapse is suppressed. In addition, the risk of fire and dust explosion is low, and no special equipment modification is required. Therefore, the volatile content is 2.7 % by mass or less.

  Furthermore, when adding from an on-furnace addition hopper, anthracite coal classification may be performed to remove fine particles having a particle size of less than 3 mm. When using anthracite mixed with fine particles with a particle size of less than 3mm, it is put into the furnace and before it reaches the hot metal surface, it is caught in the upward flow of exhaust gas and scattered as dust or is sucked into the dust collector. This is because there is a large proportion. In order to prevent an increase in the amount of dust generated due to the scattering of fine particles of anthracite coal or a decrease in the addition yield of anthracite coal, it is also possible to reduce the supply rate of oxygen supplied from the top blowing lance. However, this may reduce the productivity of decarburization blowing. Therefore, it is preferable to introduce a carbon source having a particle size of 3 mm or more into the converter. On the other hand, when the particle size of the carbon source exceeds 100 mm, there is a problem that the reactivity is lowered, and therefore the particle size is preferably in the range of 3 to 100 mm.

For adjusting the particle size, any industrially used method can be used, but it can be conveniently adjusted by sieving. That is, adjust the particle size to between 3 and 100 mm by using an anthracite sieve with a sieve of 100 mm or less and a sieve with a sieve of 3 mm or more and using the sieve. Can do.
Further, when supplying fine anthracite having a particle size of less than 3 mm, it is preferable that the anthracite be introduced into a region where there is a downward jet from the upper blowing lance (hereinafter referred to as a downward oxygen jet region) so as not to be sucked into the upward exhaust gas flow. .

  Further, as shown in FIG. 1, the present inventors, in a converter 1 having a carbon material charging lance 2 and an upper blowing lance 3 for charging fine anthracite coal having a particle size of less than 3 mm, are located above the central axis of the carbon material charging lance 2. The horizontal distance from the central axis of the blow lance 3 is D (mm), and the vertical distance between the tip position of the charcoal charging lance 2 and the tip position of the upper blow lance 3 is H (mm). It has been found that by arranging H and H so as to satisfy H ≧ 1.1D, it is possible to supply granular anthracite into the downward oxygen jet region.

  Furthermore, fuel gas and oxygen gas are supplied to the charcoal charging lance 2, a flame (hereinafter referred to as a burner flame) is formed at the tip of the charcoal charging lance 2, and anthracite particles are blown into the burner flame. As a result, the anthracite particles are heated by the burner flame, and serve as a heat transfer medium to transfer heat to the molten metal (not shown) in the converter 1. As a result, the heat receiving efficiency is improved, the amount of carbon material required for heating is reduced, and the generation of dust (so-called bubble burst dust) generated from the molten metal can be reduced.

  Moreover, in this invention, since anthracite is used as a carbon source, it can decarburize with a carbon material with little P content, and is suitable for the decarburization blowing of hot metal for obtaining stainless steel.

<Example 1>
First, using anthracite particles classified to a particle size of 3mm or more, hot metal (1200 ° C), stainless scrap, and ferrochrome were charged into a converter with a capacity of 150 tons. A carbon source was added and decarburized and blown to produce stainless steel. The types of carbon sources charged into the converter and the volatile content thereof were as shown in Table 1, and were 2.7 mass%, 3.0 mass%, 4.3 mass%, 5.8 mass%, and 10.2 mass%, respectively. For further comparison, Table 2 shows the coke with a volatile content of 1.4% by mass and the detailed analysis values of the carbon source sample used in this experiment for reference. The input amount was adjusted within a range of 10 to 20 tons depending on the amount of stainless steel scrap or ferrochrome charged, and the temperature inside the furnace was raised.

Further, when the C content of the hot metal in the converter was estimated to be about 1.5% by mass from the time of decarburization blowing, a sample was taken and the C content (hereinafter referred to as measured C content) was measured. . Further, the flow rate, CO concentration, and CO ₂ concentration of the exhaust gas discharged from the furnace port were measured with an exhaust gas analyzer, and the decarburization amount (hereinafter referred to as analytical decarburization amount) was calculated based on the obtained data. On the other hand, a decarburization amount (hereinafter referred to as an actual decarburization amount) was calculated based on the actual measurement value of the input amount of the carbon source and the actual C content.

The difference between the measured decarburization amount and the analytical decarburization amount obtained in this way is regarded as the amount of carbon source scattered outside the furnace, and the ratio of the carbon source scattered amount (ton) to the input amount (ton) The scattering rate (%) is shown in Table 1. The scattering rate is a value calculated by the following formula. The relationship between the volatile content of the carbon source in Table 1 and the scattering rate is shown in FIG.
Scattering rate (%) = 100 x scattering amount (ton) / input amount (ton)

In addition, the P content in the hot metal before the start of decarburization blowing and the P content in the molten steel after the end of decarburization blowing are measured, and the amount of increase in the P content resulting from decarburization blowing is shown. Also shown in FIG. The P content increase amount is a value calculated by the following equation.
P content increase (mass%) = P content in molten steel (mass%) − P content in hot metal (mass%)
As is apparent from Table 1 and FIG. 2, if the volatile content of the carbon source is in the range of 3% by mass or less, the scattering rate of the carbon source is kept low, and if the volatile content exceeds 3% by mass, the scattering rate is Increased significantly.

In addition, when coke was used as the carbon source (Comparative Example 1), the scattering rate was kept low because the volatile content was 3% by mass or less, but due to decarburization blowing. P content increased.
When anthracite is used as a carbon source (Invention Examples 1 and 2 and Comparative Examples 2 to 4), the increase in P content due to decarburization blowing is 0.002 to 0.004 mass%, and coke is used. It was low compared with the comparative example 1 (P content increase amount 0.011 mass%) used. Inventive Examples 1 and 2 having a volatile content of 3% by mass or less had a scattering rate of 9.5 to 11%, whereas Comparative Examples 2 to 4 having a volatile content exceeding 3% by mass were scattered. The rate was 19-35%.

<Example 2>
Next, decarburization blowing was performed using fine anthracite particles having a particle size of less than 3 mm as a heating material. The charcoal material used was investigated by changing the content of volatile matter in the same manner as in Example 1 using an under-sieving material obtained by classifying anthracite coal with a sieve having a sieve size of less than 3 mm. Regarding the addition method, a method of adding from the furnace hopper and a method of charging using a carbon material charging lance installed separately from the top blowing lance for supplying oxygen gas were investigated. When using a carbon material input lance, the horizontal distance D between the center axis of the top blow lance and the center axis of the carbon material input lance is 1 m (= 1000 mm), and the tip position of the carbon material input lance and the top blow lance The distance H in the vertical direction from the tip position was variously changed. Table 3 shows the relationship between D and H as D / H.

When added from the furnace hopper, the scattering rate of charcoal increased. Moreover, when using the carbonaceous material input lance, the carbon material scattering rate decreased as the position of the carbonaceous material input lance was lowered. In addition, when the tip of the carbonaceous material charging lance is placed in the downward oxygen jet region formed by the upper blowing lance, the scattering rate of the carbonaceous material is further reduced.
Furthermore, fuel gas and oxygen gas were supplied to the charcoal charging lance to form a burner flame at the tip of the charcoal charging lance, and anthracite particles were blown into the burner flame. As a result, the heat receiving efficiency of the molten metal in the converter was improved, and the amount of the heating carbon material and the heating oxygen could be reduced. As a result, bubble burst dust generated from the molten metal was reduced.

  As described above, according to the present invention, it has been confirmed that in the decarburization blowing performed in a converter to obtain stainless steel, the scattering of the carbon source can be suppressed. As a result, it is possible to improve the yield of carbon source addition while reducing the amount of dust generated.

1 Converter 2 Charging material lance 3 Top blowing lance

Claims (4)

In a decarburization blowing method in which hot metal is decarburized to obtain high alloy steel using a converter, anthracite having a volatile content of 2.7 % by mass or less is used in the converter for heat compensation. A decarburizing and blowing method characterized by being put into a slag.   The decarburization blowing method according to claim 1, wherein scrap is charged into the converter as an iron source in addition to the hot metal. 3. The decarburization according to claim 1, wherein particles having a particle size adjusted to less than 3 mm are supplied as anthracite from a carbon material charging lance provided separately from an upper blowing lance for supplying an oxidizing gas. Blowing method. The fuel gas and oxygen gas are supplied through the charcoal charging lance to form a burner flame at the tip of the charcoal charging lance, and the anthracite particles are blown into the burner flame. 3. The decarburization blowing method according to 3.

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