JPH03153811A - Steelmaking method accompanied with smelting reduction of manganese ore - Google Patents

Abstract

PURPOSE:To raise the concentration of Mn at an end point in a converter after dephosphorizing and to produce a steel having good quality by controlling oxygen blowing velocity, flow rate of furnace bottom gas, flow rate of top blowing stirring gas and slag making agent quantity during period from initial stage to middle stage of blowing. CONSTITUTION:Converter type dephosphorizing furnace 1 and decarbonizing furnace 2 are used. To molten iron 3 poured into the furnace 1, refining agent containing converter slag 4 produced in the furnace 2 and Mn ore as main components, is added, and by top-blowing gaseous oxygen from a lance 6 while executing the bottom blowing gas stirring from blowing nozzles 5, the dephosphorization and the raising of the concentration of Mn in the molten iron are executed. Then, the oxygen blowing velocity is increased to 100-200Nm<3>/hr T during the period from the initial stage to the middle stage of blowing. The flow rate of bottom blowing gas is made to 0.06-0.30Nm<3>/hr T. By controlling the adding timing of the slag making agent and the other, CaO/SiO2 in CaO-SiO2-MnO series slag is made to 0.5-1.2. By this method, the steel containing >= about 0.6% Mn after dephosphorizing refining can be stably produced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention performs highly efficient dephosphorization while minimizing the amount of slag forming agents (quicklime, etc.) used throughout the entire steelmaking process. Melting of manganese ore (including manganese ore), which can be melted and reduced to the maximum extent to raise the end point (Mn) in the converter, making it possible to produce high-quality steel at low cost. This relates to a steel manufacturing method that involves reduction.

(Prior art) Conventionally, the use of slag forming agents (quicklime, dolomite, etc.) in the entire steelmaking process was reduced, and manganese ore was used to raise the converter end point (Mid). etc.), for example, inject a quicklime-based de-#% additive (mainly quicklime - iron oxide - fluorite base) into a torpedo or hot metal transfer pot to dephosphorize the hot metal. After that, the dephosphorized pig iron is poured into a converter, a small amount of normal slag-forming agent such as quicklime is added, and manganese ore (hereinafter referred to as iron-manganese ore) is added to reach the converter end point (Mn). A common method was to increase the

(Problem to be solved by the invention) However, in such conventional methods, (1) quicklime-based flux is used for both hot metal dephosphorization and converter blowing, so the amount of slag forming agent used in the entire steelmaking process is (2) The amount of manganese ore that can be melted and reduced during converter blowing for dephosphorizing pig iron varies depending on the target converter end temperature, but the thermal limit is approximately 15 to 20 kg. , the converter end point [Mn] was about 0.5 to 0.9% by weight at most. Of course, in this case, there is a method of using carbonaceous materials such as coke as a heat source, but there is a problem in that S is mixed in from the carbonaceous materials and there is a limit.

Therefore, as a proposal to solve the above problems, Japanese Patent Laid-Open No. 62-290815 and Japanese Patent Laid-Open No. 639
3813, etc., and later, Japanese Patent Application Laid-Open No. 1-142009 was proposed in order to improve the problem (2) above. The invention proposed in Japanese Patent Application Laid-Open No. 1-142009 is as follows.

(1) In a steelmaking method in which hot metal is refined by using one of two converter-type furnaces with upper and lower blowing functions as a dephosphorization furnace and the other as a decarburization furnace, injection into the dephosphorization furnace is performed. Converter slag generated in the decarburization furnace and a refining agent mainly composed of manganese ore are added to the hot metal, and the temperature of the hot metal is kept below 1400 ° C by blowing oxygen gas upward while stirring the bottom blowing gas. The process involves dephosphorizing the hot metal and raising the hot metal (Mn), and adding a normal slag forming agent and manganese ore to the obtained dephosphorized hot metal and refining it in a decarburization furnace, decarburizing the hot metal and refining the hot metal. End point [Mn
] A steelmaking method characterized by comprising the step of increasing

(2) A steelmaking method involving smelting reduction of manganese ore according to claim 1, wherein the hot metal to be treated has been subjected to preliminary desiliconization treatment to reduce the St content to 0.30% by weight or less;
”.

The invention proposed in JP-A-1-142009 is a method of adding a refining agent mainly composed of converter slag and manganese ore in a dephosphorization furnace. There was no mention of timing or rate of acid delivery. Therefore, for example, regarding the amount of smelting reduction of manganese ore, the increase in [Mn] when the input amount is 10 kg/l under conditions where the slag basicity is 2.5 or more is 0.3 to 0.4 It is difficult to say that the amount of reduction is extremely good as there are many variations, such as about % by weight.

Further, there is little data on input amounts larger than this (for example, 20 kg/or more), and there is a problem in that the amount of reduction in such cases is extremely reduced.

Therefore, in the absence of a heat source, [Mn] after dephosphorization furnace refining
It is a little less than 0.7% by weight at most, and [M
n] remained at about 1.1% by weight. In other words, for steel types with a required [Mn] of 1.2% by weight or more, it is necessary to add ferroalloy at the time of tapping from the decarburization furnace, and the steel manufacturing method proposed in JP-A-1-142009 requires the addition of ferroalloy. It was difficult to say that they were fully enjoying the benefits.

The present invention is an improvement of the invention proposed in JP-A-1-142009, and specifically, the product [Mn] is 1.
In order to obtain steel containing 2% by weight or more without the addition of manganese alloy iron or under similar operating conditions, [Mn] after the dephosphorization furnace can be removed without any particular cost increase, in other words, by improving operating conditions. An object of the present invention is to provide a steelmaking method involving melt reduction of manganese ore, which can increase the amount of manganese ore to 0.8% by weight or more, for example, about 0.8 to 0.9% by weight.

(Means for Solving the Problem) In order to achieve the above object, the present inventors have disclosed
We studied various aspects of the operating conditions in the invention proposed in Publication No. 2009, and made improvements as shown in (1) to (2) below. In other words, the points for improvement are as follows.

■Limited oxygen supply pattern In order to maximize the benefits of reducing ferromanganese by melting and reducing manganese ore, it is desirable to add as much manganese ore as possible within the thermal margin of the dephosphorization furnace. .

However, in that case, the present inventors found that the temperature of the slag-forming agent containing manganese ore is primarily lowered by adding a large amount, and melting of the manganese ore does not apparently proceed.

Therefore, in the present invention, we pay attention to the temperature of this slag-forming agent,
Taking advantage of the hot metal pretreatment method using a converter, in which the oxygen delivery rate can be freely controlled, the oxygen delivery rate from the early to middle stages of blowing is increased to 100 to 22 ONnf/hr -T, and the slag-forming agent is It keeps the temperature high.

■Limitation of bottom blowing gas flow rate pattern As shown in Japanese Patent Application Laid-Open No. 1-142009, the degree of bottom gas agitation when promoting dephosphorization may be the same as in normal upper and lower double blowing combined blowing. Higher flow rate (0°O6~0.30N
It is desirable to set it to n (/sin·T).

Even after the middle stage of blowing when the melting of manganese is completed, it is desirable to continue flowing at the high flow rate from the viewpoint of promoting reduction by strengthening slag-metal stirring.

■ Timing of addition of slag-forming agents and other substances As shown in (■) above, in addition to raising the temperature of the slag-forming agent, it is also natural to consider lowering the melting point of the slag-forming agent when considering the melting of the manganese ore as the top priority. It is an item.

Therefore, in the present invention, in order to lower the melting point to about 1300°C in the CaOSiO-MnO pseudo-shin ternary system, basicity (Cab/Stow) is o, s 4
A slag making method that aims to adjust the amount to approximately 2.0 m, i.e., a method in which manganese ore is melted and reduced under conditions in which the quicklime content is only that supplied from the converter slag that is added before blowing. It is.

Based on the above improvement points (1) to (2), the present inventors conducted further studies and completed the present invention.

Here, the gist of the present invention is a steelmaking method in which hot metal is refined by using one of two converter type furnaces having both upper and lower blowing functions as a dephosphorization furnace and the other as a decarburization furnace. There it is,
Converter slag generated in the decarburization furnace and a refining agent mainly composed of manganese ore are added to the hot metal injected into the dephosphorization furnace, and oxygen gas is blown upward while stirring the bottom blowing gas to adjust the temperature of the hot metal. Hot metal dephosphorization and hot metal [M
n], and the obtained dephosphorized hot metal is charged with a normal slag-forming agent and manganese ore and refined in a decarburization furnace to decarburize the hot metal and increase the molten iron refining end point [Mnl]. In a steelmaking method characterized by including a step of
At the same time, the bottom gas flow rate is 0.06 to 0.3Nr.
rf/+win HT, and further CaO-5CaO-
A steelmaking method involving smelting and reduction of manganese ore, characterized by controlling the top and bottom blowing agitation gas flow rate and the slag 11qI so that the Can/5ift of the 5-inch slag is 0.5 to 1.2. It is.

Furthermore, in the present invention described above, the hot metal to be treated is Si
The higher the Si content in the hot metal, which may have been preliminarily desiliconized to a content of 0.3% by weight or less,
The slag basicity in the dephosphorization furnace decreases and the dephosphorization ability decreases,
This is because the total amount of quicklime etc. used increases. Therefore, the Si content of the hot metal is preferably adjusted to 0.3% by weight or less, preferably 0.2% by weight or less.

FIG. 1 conceptually shows the preliminary treatment of hot metal using a converter that implements the steelmaking method involving smelting reduction of manganese ore according to the present invention, that is, a converter-type furnace 1 (dephosphorization furnace).
Using the furnace 2 (decarburization furnace), a refining agent mainly composed of converter slag 4 generated in the furnace 2 and Mnn Mangoku fluorite) is added to the hot metal 3 injected into the furnace 1, and the stirring gas While bottom-blowing gas is stirred from the blowing nozzle 5, oxygen gas is blown upward from the lance 6 to maintain the temperature of the hot metal 3 below 1400°C, and in the process of dephosphorizing the hot metal and raising the Mnl of the hot metal. In order to maximize the smelting reduction of manganese ore, improvements in (1) and (2) above are carried out.

The improvement points (1) to (2) of the present invention are conceptually shown in Fig. 2.
0 N rrr/hr-T, (2) setting the bottom blowing gas flow rate to 0.06 to 0.3 ON rrr/hr-T, and (2) adding the slag agent and other timing as shown in Fig. 2. By controlling as shown, CaO-5rO1MnO
The CaO/SiO2 ratio of the system slag is 0.5 to 1.2.

(Operation) The configuration and operation of the present invention will be explained in detail. In addition, in this specification, unless otherwise specified, "%"
” shall mean “% by weight”.

1. Acid feeding pattern The acid feeding pattern of the present invention described above (acid feeding rate: 100-2
2ONm'/hr-T) and the conventional oxygen supply pattern (acid supply rate: 50-95Nm!/hr)
An example of the temperature change due to -T) is shown in FIG.

The results of temperature measurement at specific time intervals are plotted, and according to the conventional oxygen supply pattern, a considerable change of 1M degree occurs with the addition of manganese ore, especially in the initial stage of manganese ore. This tendency is noticeable when inputs are made.

When manganese ore is added in portions, the temperature drop is somewhat alleviated, but basically the same tendency remains. Furthermore, when adding in portions, there is not enough time to reduce manganese in the slag-forming agent into hot metal within the limited blowing time, so there is a drawback that even if it is melted, the amount of reduction will be small.

Therefore, according to the present invention, even if manganese ore is initially charged, the temperature of the slag forming agent can be maintained at 1300°C or higher, which is perfect from the viewpoint of melting manganese ore. .

Once the entire amount of manganese ore has been melted, it is desirable to reduce the oxygen delivery rate in order to ensure time for reducing the manganese in the slag, and this is also effective in suppressing unnecessary decarburization.

It goes without saying that it is most desirable to change the oxygen feeding rate in accordance with the amount of manganese ore added, but a slight timing difference does not pose much of a problem, so there is no particular need to limit the timing of the change.

In addition, the oxygen supply rate from the early stage to the middle stage of blowing should be adjusted to 100~
The reason for limiting it to 220 Nrrr/hrT is 100
This is because if it is less than Nrrf/hr・1, the temperature of the slag forming agent will not rise sufficiently and the effect of the present invention cannot be obtained.
On the other hand, if it exceeds 220 Nm'/hrT, decarburization in the dephosphorization furnace occurs excessively, and the thermal margin in the subsequent decarburization furnace decreases.

2. Bottom blowing gas flow rate pattern Bottom blowing gas flow rate is 0.03Nm'/min -T and 0.1
For the two cases of '5 Nm''/sin・T, the following hot metal conditions (oxygen feed rate: 17ONm''/hr-T, Ca
Figure 4 shows the transition of hot metal [Mn] in O/SiO2:2.5), and the effect of the bottom blowing gas flow rate is clearly visible in both the melting period before the addition of quicklime and the reduction period after the addition. There is.

The reason why the upper limit of the bottom blowing gas flow rate was set at 0.30 Nn (/min・T) is that even if the flow rate exceeds this, the effect will be saturated, and the life of the bottom refractory will be shortened. Furthermore, when carbon dioxide gas is selected as the gas species, an endothermic effect occurs due to the reaction with hot metal carbon.

On the other hand, the reason why the lower limit is set at 0.06 Nm''/sin·T is that if the value is smaller than this value, there is a possibility that the melting of manganese will be insufficient.

Of course, as shown in JP-A-1-142009, the stirring gas injected from the bottom of the furnace may be any gas other than carbon gas, such as argon or -carbon oxide, and if these are used, the endothermic reaction will not occur. Of course there isn't.

3. Timing of addition of slag forming agent, etc. As mentioned above, in the CaO-MnO-3in, pseudo-ternary system, the basicity (CaO/SiO2) is 0.5 to 1.
By adjusting the melting point to about 2, there is a region where the melting point of the slag-forming agent decreases to 1300° C. as shown in FIG.

Specifically, blowing is started under the condition that the quicklime content is only the amount supplied from the converter slag added before blowing, and the manganese ore is melted. In other words, the CaO in the converter slag is the sum of the expected amount of Si islands from hot metal [S1] and 5iotit in the converter slag.
The amount of converter slag is controlled according to the value of hot metal (Si) so that the value divided by the amount falls within the range of 0.5 to 1.2.

Of course, since fluorite is added as part of the slag-forming agent, it is fully expected that the melting point will be even lower than the melting point shown in Figure 5, but the overall trend is as shown in Figure 5. be.

After the manganese ore has been melted, quicklime is added and the manganese reduction process begins. The reason for this is JP-A-1-142
As shown in Publication No. 009, the higher the slag basicity, the more easily manganese oxide is reduced, and as shown in Figure 6, this tendency is strongest in the region where the slag basicity is 2.5 or more. This is to make it constant.

Furthermore, as shown in Figure 4, hot metal after adding quicklime [
Mn] has a tendency to rise again, which supports the results shown in Figure 6 well.

In this way, it is possible to obtain dephosphorized hot metal in which the amount of [11 nl] has been increased in the dephosphorizing furnace.

After this, as disclosed in JP-A-1-142009, a slag-forming agent, manganese wire, and stones are usually added and refined in a decarburization furnace to decarburize the hot metal and reach the final point of refining [ Mn
What is necessary is to increase l.

Furthermore, when carrying out the present invention, it is preferable to perform a preliminary desulfurization treatment on the applied hot metal if possible.

The first reason is that desulfurization progresses extremely slowly in this method, but on the other hand, when hot metal that has not been desulfurized in advance is used, the S content in the converter slag increases, This is because there is also a concern that the molten steel S content in the next charge may be increased. Note that the preliminary desulfurization may be performed by any of the commonly used hot metal desulfurization methods.

The present invention will be explained in more detail with reference to examples in comparison with comparative examples.

Example 1 250T of desiliconized and desulfurized hot metal having the components shown in the upper row of Table 1 was poured into a dephosphorization furnace, and 25kg of converter slag generated in the decarburization furnace and 11kg/l of fluorite were added. , particle size 30m
After adding 15.3 kg of manganese ore with a particle diameter of less than 100 m, a dephosphorization treatment was performed for 9 minutes to prepare a sample as an example of the present invention.

Table 1 Table 2 The operating conditions in Example 1 are as shown in the section of the present invention example in Table 2. Each item was implemented.

(Left below) Compared to the comparative example described below, although a slightly smaller amount of manganese ore is used, the [Mnl after treatment is high and the input manganese yield in the dephosphorization furnace is approximately 55% and 25%.
Improvements have been made.

Example 2 If the restrictions on sulfur concentration in steel types are relatively loose,
As shown in JP-A-1-142009, about 60% of desulfurization progresses in the dephosphorization furnace. Therefore, there is no need to desulfurize the hot metal in advance.

250T of desiliconized hot metal having the composition shown in the upper row of Table 3 was poured into the dephosphorization furnace, and 25kg of converter slag generated in the decarburization furnace was added.
In addition to 10 kg/l of fluorite, 24.3 kg of manganese ore with a particle size of 30 m or less was added, and dephosphorization was performed for 9 minutes.

Table 3 Comparative Example 250 tons of hot metal having the composition shown in the upper row of Table 4, which had been desiliconized and desulfurized in advance, was poured into an upper and lower double blowing composite blowing converter used as a dephosphorization furnace. 25kg of converter slag generated in a similar type of decarburization furnace after being cooled and solidified and crushed to a particle size of 30IIIL or less, 17.7kg/L of manganese ore with a similar particle size, and 10kg of fluorite.
Dephosphorization treatment was carried out for 10 minutes by adding heto.

The reason why the amount of manganese ore is large compared to Example 1 in Table 4 is that the temperature of the hot metal before the dephosphorization treatment is high because there is no temperature drop accompanying hot metal desulfurization. Despite the large amount of manganese ore, the input manganese yield was comparable to that of Example 1, and after the dephosphorization treatment [Mnl≧0.9% was achieved.

Note that the operating conditions are as shown in the invention example in Table 2, and there is no difference from Example 1.

As shown in the Comparative Example section of Table 2, the operating conditions in the comparative example were as follows: the oxygen supply rate was constant at 6ONm+3/hr・T, and the bottom blowing gas flow rate was as low as 0.03Nm'/5in-T. , further added with a slag-forming agent and manganese ore.

Although [Mn] increases after dephosphorization, the amount of increase is small and even considering the manganese in the converter slag generated from the decarburization furnace, the input manganese yield in the dephosphorization furnace is approximately 30%. and is very low.

Here, FIG. 7 shows the relationship between the amount of manganese ore added in the dephosphorization furnace and the input manganese yield, including other examples.

As a result of the effects of the present invention, the manganese yield has been improved by 20% or more regardless of the amount of manganese ore added.

As a result, despite the addition of a relatively small amount of manganese ore in the decarburization furnace as shown in Example 1.2, after the decarburization furnace (
Mn, l exceeds 1% to 1.2%.

Of course, it is usually about 15 to 20 kg/l due to the heat margin of the decarburization furnace.
Since manganese ore can be added, it is easy to produce molten steel with a high end point [Mn] in accordance with the manganese standard of the steel type.

(Effects of the Invention) With the configuration as explained above, the present invention enables the production of 0.6% or more of In particular, if high-temperature hot metal can be used without pre-desulfurization, it is possible to produce hot metal with a high [Mn] content of 0.9% or more.

Therefore, even if the amount of manganese ore used in the decarburization furnace is not excessive, in other words, even without using carbon materials, it is possible to easily achieve [Mn] of 1% or more after the decarburization furnace.
It is possible to reduce the amount of ferromanganese used by 18 to 10 kg/l.

Furthermore, as shown in JP-A-1-142009, the decarburization furnace slag can be reused, and the amount of slag forming agent required throughout the steelmaking process can be significantly reduced, making it extremely useful industrially. It brings about an effect.

Note that, in the present invention, as shown in the examples, no heat margin expander such as carbon material is used.

As mentioned above, it is 1% even without using carbon materials etc.
This is because molten steel with a Mn content of 1.2% or more can be produced stably, but in recent years, the number of Mn has been increasing [Mn] 21
．． It goes without saying that carbonaceous material may be used in the dephosphorization furnace to enjoy the merit lift even in 5% high manganese steel.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of hot metal pretreatment using a converter that implements the method of the present invention; Fig. 2 is a schematic explanatory diagram of the blowing process according to the present invention in a dephosphorization furnace of the above process; The figure is a graph showing the change in slag temperature in the dephosphorization furnace when the blowing method according to the present invention is carried out; Figure 4 is a graph showing the change in manganese concentration during blowing; Figure 5 is a graph showing changes in the concentration of manganese during blowing; A graph showing the melting point distribution of -3ing system slag: Figure 6 is a graph showing the relationship between Mn distribution ratio and slag basicity in the dephosphorization furnace; and Figure 7 is a graph showing the input manganese yield in the dephosphorization furnace. It is a graph showing the relationship between the amount of manganese ore added and the amount of manganese ore added. 1: Dephosphorization furnace 2: Decarburization furnace 3: Hot metal 4: Converter slag 4°: Dephosphorization slag mainly composed of converter slag 5: Stirring gas injection nozzle 6: Lance Figure 1! L5, Figure 2, Part 2 (Cab) / (SiOJ)

Claims (2)

[Claims] (1) A steelmaking method in which hot metal is refined by using one of two converter-type furnaces having both upper and lower blowing functions as a dephosphorization furnace and the other as a decarburization furnace, and in which the hot metal is refined into the dephosphorization furnace. A refining agent mainly composed of converter slag and manganese ore generated in the decarburization furnace is added to the injected hot metal, and the temperature of the hot metal is kept below 1400 ° C by blowing oxygen gas upward while stirring the bottom blowing gas. A process of dephosphorizing the hot metal and raising the hot metal [Mn], and adding a normal slag forming agent and manganese ore to the obtained dephosphorized hot metal and refining it in a decarburizing furnace, decarburizing the hot metal and refining the hot metal. In a rope manufacturing method characterized by including a step of increasing the end point [Mn], the oxygen supply rate from the early to middle stages of blowing is set at 100 to
220 Nm^3/hr・T, and the furnace bottom gas flow rate was 0.06 to 0.3 Nm^3/min. T, and CaO/Si of CaO-SiO_2-MnO system slag
A steelmaking method involving melt reduction of manganese ore, characterized by controlling the flow rate of top and bottom blowing stirring gas and the amount of slag forming agent so that O_2 is 0.5 to 1.2. (2) The steelmaking method involving smelting reduction of manganese ore according to claim 1, wherein the hot metal to be treated has been subjected to a preliminary desiliconization treatment to reduce the Si content to 0.3% by weight or less.