JPH03120307A - Steelmaking method - Google Patents

Abstract

PURPOSE:To efficiently execute dephosphorizing and decarbonizing reactions in molten steel with common use of small quantity of slag making agent by suitably controlling oxygen top blowing refining in a converter for dephosphorizing at the time of refining the molten steel with two sets of the oxygen top and bottom combined blowing converters for dephosphorizing and decarbonizing. CONSTITUTION:At the time or producing the molten steel from molten iron by using two sets of the oxygen top and bottom combined blowing converters, oxidizing molten slag 4 from the converter 2 for decarbonizing is charged into the converter 1 for dephosphorizing, and by blowing CO2 gas from a bottom blowing nozzle 5, the molten iron 3 is stirred, and by blowing O2 gas from a top blowing lance 6, P in the molten iron 3 is oxidized into P2O5 to make this the stable molten slag with CaO in the slag making agent, and the dephosphorization is executed. By making O2 charged energy expressed in equation I from the top blowing lance in the dephosphorizing furnace 1 1500-2000W/m<3> molten iron, the dephosphorization is executed while allowing C to remain in the molten iron. This dephosphorized molten iron is charged into the converter 2 for decarbonizing and the new slag making agent is added and C in the dephosphorized molten iron is oxidized and decarbonized with the gas stirring from the bottom nozzle 5 and oxygen blowing from the top blowing lance 6 to refine the molten iron into the molten steel, and the oxidizing molten slag at this time is supplied and used into the dephosphorizing furnace 1. The dephosphorizing and decarbonizing reactions are executed with a small quantity of slag making agent.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention relates to a steel manufacturing method for stably producing high-quality steel with a small amount of slag-forming agent (quicklime, etc.) used. .

<Prior art and its challenges> In recent years, in order to meet the high quality requirements and low price requirements for various steel materials, great efforts have been made to develop, for example, means to stably melt low-phosphorus steel at even lower costs. However, under these circumstances, the applicant has previously proposed a method for refining hot metal that can achieve highly efficient dephosphorization while minimizing the amount of slag-forming agents (quicklime, etc.) used throughout the entire steelmaking process. As shown in Fig. 1, two converter type furnaces having both upper and lower blowing functions were used, and one of them was used as dephosphorization furnace 1 and the other as decarburization furnace 2. A refining agent 4' whose main component is the converter slag 4 generated in the decarburization furnace 2 (the converter slag may be used in either a molten state or a solidified state) is added to the hot metal 3 injected into the furnace 1. At the same time, the hot metal is dephosphorized while maintaining the required hot metal temperature by top-blowing oxygen gas with the lance 6 while bottom blowing gas is stirred using the stirring gas injection nozzle 5. JP-A No. 62-290815) proposes a "steel manufacturing method involving two-stage countercurrent catalytic refining of dephosphorized slag-metal," which consists of decarburizing and final dephosphorizing hot metal in a decarburizing furnace 2. This opens the door to providing high-quality steel with a low P content at a low cost while using a small amount of slag forming agent.

However, through numerous operational results since then, the present inventors have found that when carrying out the above-mentioned "steel manufacturing method involving countercurrent two-stage catalytic refining of dephosphorized slag and metal," sometimes during decarburization furnace refining, We have come to recognize the fact that it may be difficult to secure the desired hot metal temperature, or there may be insufficient dephosphorization in the dephosphorization furnace refining.

Therefore, the inventors of the present invention have removed the factors that cause the hot metal temperature to be maintained and the dephosphorization rate to become unstable as described above, and have developed a "dephosphorization slag-metal solution" that uses only a small amount of slag and is extremely advantageous in terms of cost. We have begun new research aimed at further stabilizing the operation of the ``steelmaking process that involves two-stage catalytic refining.''

Means for Solving the Problem> The inventor's research conducted to achieve the above object revealed that ``The reason why it is sometimes difficult to secure the desired hot metal temperature in decarburization furnace refining is that When the top blowing oxygen intensity is too high, the amount of decarburization of the hot metal increases, and the thermal energy on the decarburization furnace side decreases.On the other hand, the reason why dephosphorization is sometimes insufficient in dephosphorization furnace refining is due to dephosphorization. It has become clear that this is because the top-blowing oxygen intensity in furnace refining is too low, resulting in insufficient oxygen potential to be supplied to the slag or hot metal.

For this reason, the present inventor conducted further research by repeating numerous experiments in order to find out whether or not there are dephosphorization furnace refining conditions that can stably prevent the defective dephosphorization and insufficient hot metal temperature. , ``In the steelmaking process involving countercurrent two-step catalytic refining of dephosphorized slag-metal,'' dephosphorization can be achieved by adjusting the energy input by top-blowing oxygen from the top-blowing lance during dephosphorization furnace refining to a specific range. In phosphor furnace refining, it is possible to perform sufficient dephosphorization while suppressing decarburization of hot metal as much as possible, and as a result, the [P] level is a desired low value and a high [C] that can exert sufficient thermal energy. We were able to obtain the knowledge that it will be possible to stably supply hot metal to the decarburization furnace."

The present invention has been made based on the above-mentioned knowledge, etc., and it is based on the above-mentioned findings. In a steelmaking process in which a refining agent mainly composed of converter slag generated in a decarburization furnace is added to hot metal injected into the phosphorization furnace to carry out countercurrent two-step contact refining of dephosphorization slag and metal, the dephosphorization furnace During refining, the input energy of oxygen gas introduced from the upper oxygen lance to the surface of the hot metal bath as shown in Fig. 2 is calculated by the formula % formula % (value per volume of hot metal calculated from 1500 to 220
By adjusting to 0 W/rd, carbon loss in the hot metal is suppressed and dephosphorization is stabilized, making it possible to produce low-phosphorus steel of stable quality at low cost and with good operability.

Here, the refining agent added to the dephosphorization furnace is "mainly composed of converter slag generated in the decarburization furnace," but in addition to the above-mentioned converter slag, it also contains iron oxide, fluorite, etc. as basic subcomponents. In addition to these, quicklime, dolomite, limestone, etc. may be additionally blended.

In addition, the stirring gas blown from the furnace bottom nozzle is CO2.
, Ar, CO+ Nz, Oz or air can be used.

In the present invention, the input energy of the oxygen gas input from the upper oxygen lance to the surface of the hot metal bath during dephosphorization furnace refining is limited as described above because the input energy per volume of hot metal due to oxygen top blowing is ε.

When ε9. Even if the current exceeds 2200 W/rrr, the dephosphorization rate is determined by the mass transfer rate on the source side, so further improvement in the dephosphorization rate cannot be expected. This is because it causes a lack of thermal energy during refining. However, if you want operational stability in the − layer,
If possible, use the above ε9. is preferably adjusted to 1,600 to 2,100 W/n.

Next, the present invention will be explained in more detail with reference to Examples.

<Example> Weight percentage: CH4.6%, St: 0.10%,
Mn: 0.33%, P: 0.105%,
Hot metal (1300°C) having a composition of S: o, oos% and the balance consisting of Fe and unavoidable impurities was poured into a top and bottom double blowing combined blowing converter as a dephosphorization furnace, and in the same manner as above. The converter slag generated in the decarburization furnace is cooled and solidified.
A refining agent consisting of 20 kg/T crushed to a particle size of n or less, 14 kg of quicklime of the same particle size, and 10 kg/T of fluorite was added, and the mixture was mixed with bottom-blown gas using CO□ and at various blowing intensities. Dephosphorization was carried out for 12 minutes while blowing 0□ from the top blowing lance.

We investigated the dephosphorization rate and amount of decarburization of hot metal by this dephosphorization treatment,
The results are shown in FIGS. 3 and 4, respectively.

First, Fig. 3 is a graph showing the results of investigation of hot metal dephosphorization rate and top blowing oxygen intensity.
．． When the value of is less than 1,600 W/%, the oxygen potential in the slag supported by the top-blown oxygen begins to become insufficient, and when the value falls into the region of εV<1,500 W/n, this tendency becomes significant and dephosphorization becomes difficult. It is clear that this will lead to defects.On the other hand, if εVa≧1600W/rr
In the region of r, the dephosphorization rate is determined by the rate of mass transfer on the source side, and it is therefore clear that there is no need to increase the top-blowing oxygen intensity.

In addition, Figure 4 is a graph showing the results of an investigation of the amount of hot metal decarburized and the top blowing oxygen intensity, and the result shows that the amount of decarburized increases as the energy input into the hot metal bath increases. There is. This is because as the energy input by oxygen top blowing increases, the proportion of oxygen that displaces the slag and directly reaches the molten iron surface to selectively cause the decarburization reaction increases. Therefore, it can be seen that in order to secure carbon as a source of thermal energy in decarburization furnace refining, consideration must be given not to increase the top blowing oxygen intensity too much.

(Summary of Effects) As explained above, according to the present invention, it is possible to stably produce high-grade low-phosphorus steel at low cost with a small amount of slag-forming agent used, and The operating conditions are extremely useful industrially, as they are expected to greatly contribute to ensuring stable operation when applied to other types of outside-furnace refining (using processing vessels such as hot metal pots) that also use top-blown oxygen. effect is brought about.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a "steel manufacturing method involving countercurrent two-stage catalytic refining of dephosphorized slag-metal using two upper and lower double-blown combined blowing converters." FIG. 2 is a schematic diagram illustrating how the top blowing lance is used. FIG. 3 is a graph showing the relationship between hot metal dephosphorization rate and top blowing oxygen intensity. FIG. 4 is a graph showing the relationship between hot metal decarburization amount and top blowing oxygen intensity. In the drawings: 1... Dephosphorization furnace, 2... Decarburization furnace. 3... Hot metal, 4... Converter slag. 4'...Dephosphorization slag whose main component is converter slag. 5... Stirring gas blowing nozzle, 6... Lance.

Claims (1)

[Scope of Claims] One of the two converter type furnaces having upper and lower blowing functions is a dephosphorization furnace and the other is a decarburization furnace, and the hot metal injected into the dephosphorization furnace is heated to a decarburization furnace. In the steelmaking process, which involves countercurrent two-step contact refining of dephosphorized slag and metal by adding a refining agent mainly composed of converter slag generated in the converter, the slag is injected into the surface of the hot metal bath from the upper oxygen lance during dephosphorizing furnace refining. The input energy of oxygen gas is 1500~2 as the value per volume of hot metal calculated by the following formula.
A rope making method characterized by adjusting the power to 200 W/m^3 to suppress carbon loss in hot metal and stabilize dephosphorization. ε_v_r=6.32×10^-^7×cosξ×Qo
_2^3×M/V_L×n^2×d_e^3×H [However, ξ: Lance opening angle (rad), d_e: Lance tip exit diameter (mm), n: Number of lance holes, H: Lance height (mm), V_L: Molten steel volume (m^2), Qo_2: Top blowing oxygen flow rate (Nm^2/min), M: oxygen molecular weight]