JP2958842B2 - Converter refining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter smelting method in steel production,
The present invention relates to a converter refining method in which desiliconization and dephosphorization refining are performed, intermediate waste is discharged, and subsequently decarburization refining is performed.

[0002]

2. Description of the Related Art In recent years, the quality requirements for steel materials have become increasingly severe with the sophistication and diversification of their utilization techniques, and the need for high-purity steel production has been increasing. In response to such demands for the production of high-purity steel, the steelmaking process has attempted to expand the hot metal pretreatment or secondary refining equipment. In particular, since P is efficiently removed from the molten iron at a low temperature level in the molten iron stage, it is common practice to remove P earlier in the molten iron pretreatment step. In this case, the refining vessel has a torpedo car system, a ladle system, or a converter system other than a furnace for decarburization, and in any case, fluxes such as CaO and iron oxide are added upward or injected by an injection system. Nitrogen bubbling agitation or oxygen top blowing is used in combination. For example, JP-A-58-16007
In the “phosphorus dephosphorization / desulfurization method of hot metal” disclosed in Japanese Unexamined Patent Publication (Kokai) No. H07-75, a CaO-based flux is blown into hot metal together with a carrier gas while blowing over oxygen, and after treatment, the slag basicity is 2.0 or more and the iron oxide content is 15 or more. % Hot metal dephosphorization and desulfurization method, characterized in that hot metal dephosphorization is performed so as to be not more than 10%, and thereafter, the upper blowing oxygen is stopped and a desulfurizing material is blown in to perform desulfurization treatment without performing forced slag removal of slag. Have been. Further, in the "Desiliconization Dephosphorization Desulfurization Method of Hot Metal" disclosed in JP-A-62-109908, a dephosphorization flux containing CaO as a main component is added to the surface of the hot metal from an early stage of the hot metal pretreatment, and an iron oxide-based flux powder is added. Of oxygen or a solid oxygen source to the surface of hot metal while blowing gas into the hot metal with a carrier gas, and after the desiliconization period, changing to alkaline flux and performing dephosphorization and desulfurization in parallel , Dephosphorization and desulfurization methods are disclosed. In addition, the "steel making method" disclosed in JP-A-63-195209 uses two upper-bottom blow converters, one of which is a dephosphorizing furnace, the other of which is a decarburizing furnace, and converter debris generated in the decarburizing furnace. There is disclosed a steelmaking method in which is recycled to a dephosphorization furnace, and the dephosphorized hot metal obtained after the hot metal dephosphorization treatment is poured into a decarburization furnace.

[0003]

As described above, in the primary refining process, the desiliconization and dephosphorization steps are performed at the hot metal stage, and the split refining is aimed at improving the efficiency of the decarburization step and improving the productivity in the converter. However, more research has been conducted and steel companies have commercialized them. However, according to the above-described method, a relatively low ultimate P content level can be achieved only by looking at the process capability of lowering P, but the processing time is long and the heat removal during processing is large, A process that is completely satisfactory from the viewpoint of heat margin, such as the fact that it takes time to use, and even if two converters are used, it is inevitable that the molten iron is discharged after treatment and the temperature drops due to recharging into another converter. is not. Furthermore, the recent hot metal dephosphorization treatment further reduces the heat tolerance in the converter process, losing the degree of freedom of the raw materials used, and has a serious problem from the viewpoint of active scrap recycling in the converter in the future.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been changed from a process in which split refining for desiliconization and dephosphorization has been conventionally directed to a pretreatment process to a converter process. It is an object of the present invention to provide an effective smelting method that enables concentration and greatly improves the heat allowance.

That is, according to the present invention, in a method for refining molten iron in a converter having a bottom blowing function, the stirring energy defined by the following equation (1) by the bottom blowing gas is 0.5 KW / T.
Desiliconization of hot metal so that the basicity (% CaO /% SiO ₂ ) of the treated slag is less than 2.0 and the iron oxide content is 5% or more while controlling the flow rate of the bottom blown gas as described above. A gist of the converter smelting method characterized by temporarily stopping blowing, discharging the slag in the furnace by tilting the furnace after performing the phosphorus refining, and performing decarburization blowing after the end of the discharge. Things.

[0006]

(Equation 2)

(Reference: Japan Society for the Promotion of Science, Steelmaking 19th)
Material submitted by the Steelmaking Reaction Council of the 3rd Working Group of the Committee, "Stirring Strength and Metallurgical Reaction of Combined Converters" (Showa 55).

[0008]

[Function] Integrate the hot metal desiliconization and dephosphorization processes into the converter process, and in order to maintain the current low-phosphorous steel production process capacity comparable to the current split refining, quick and thorough dephosphorization slag removal is an essential condition. Becomes That is, it is extremely difficult to remove slag during the hot metal treatment process because of a decrease in yield due to outflow of molten metal at the time of waste, a decrease in productivity due to consumption of waste time, and a high slag removal rate of slag. When the dephosphorized slag having a high P ₂ O ₅ concentration remains, there is a problem that a phosphorus reversion phenomenon occurs.

The present inventors have aimed to improve the efficiency of removing slag after hot metal desiliconization and dephosphorization using a converter and to consolidate the hot metal pretreatment process into the converter process to greatly improve the heat tolerance. R & D. First, the present inventors used a 300 TON converter having a bottom blow function on an actual scale, and
After charging the hot metal of ON, add quicklime and iron ore for dephosphorization, supply top-blown oxygen while performing bottom-blowing agitation, perform desiliconization and dephosphorization, and after dephosphorization, temporarily stop blowing. After performing the intermediate waste by tilting the furnace, a test of continuously performing decarburization blowing was performed. At this time, Si in the hot metal before treatment was 0.40% on average, and P
Is an average of 0.100%, and the temperature after the dephosphorization treatment was set to 1350 ° C. based on the conventional knowledge in order to efficiently promote the dephosphorization reaction. As a result, it was noticed that the bottom gas blowing power and the composition of the slag after the dephosphorization greatly affected the dephosphorization rate and the waste efficiency, and it was found that there was an optimum composition that satisfied both of them.

That is, as shown in FIG. 1, the waste rate is affected by the bottom blowing gas agitation force, and even with the same slag composition, when the bottom blowing agitation energy is 0.5 KW / T or more, the waste efficiency is rapidly improved. You can see that. This is because the slag forming level is increased by the bottom blowing gas, and the slag is more actively discharged from an earlier stage at the time of intermediate waste.

Further, as shown in FIG. 2, under the same bottom stirring condition, the dephosphorization rate largely depends on the slag basicity after the treatment, and the higher the basicity, the higher the dephosphorization rate. Above, no improvement is seen, and at a basicity of 2.0 or more, a decrease in the waste rate is seen. This is presumed to be related to the slag formation rate of the slag, and an increase in basicity inhibits slag formation, lowers the fluidity of the slag, and greatly affects the slag discharge property. Furthermore, from the viewpoint of ensuring productivity, the dephosphorization time must be as short as possible.In the temperature range of the hot metal pretreatment level, high basicity operation is not appropriate from the viewpoint of slagging time, and the results of this test Therefore, it is determined that a composition having an analyzed basicity of less than 2.0 after treatment is optimal.

The desiliconization reaction proceeds by supplying an oxygen source, and the desiliconization and dephosphorization can be easily and continuously performed by controlling the amount of supplied oxygen according to the Si level before the treatment. . Drainage is performed from the furnace port by tilting the furnace,
The slag time was 5 to 7 minutes until the hot metal began to flow out.

Here, the waste rate is defined as the ratio of the amount of waste to the amount of slag generated in the furnace. The amount of waste is the actual weighed value, and the amount of slag generated in the furnace is determined based on the amount of quicklime introduced into the furnace. The value calculated by the following equation (2) was used in consideration of the slag analysis value and the slag conversion rate.

[0014]

(Equation 3)

Next, it is obvious that the iron oxide concentration in the slag is preferably as low as possible from the viewpoint of the yield of iron, but the dephosphorization reaction is promoted or the fluidity of the slag is secured to improve the waste rate. It is necessary to secure the necessary minimum content.
Further, as shown in FIG. 3, the iron oxide concentration in the slag depends on the stirring force of the bottom gas, and the stirring energy is 0.5K.
Above W / T, the iron oxide concentration in the slag is about 5 to 15%.

The dephosphorization rate and the waste rate targeted this time are 80% and 85%, respectively, which are the phosphorus level before the treatment and the suppression of the recovery of P during the decarburization blowing performed continuously after the intermediate waste. Are set according to the following conditions, which vary depending on the conditions. The same applies to the temperature after the dephosphorization treatment. Hereinafter, examples of the present invention will be described.

[0017]

EXAMPLE A hot iron of 290 to 300 TON was charged into a 300 TON top-bottom blowing converter having a bottom blowing tuyere at the bottom of the furnace, and CO _{2 was} blown from the bottom blowing tuyere and oxygen was blown from the top blowing lance. The applied examples are shown in Tables 1 and 2 (continuation of Table 1). FIG. 4 shows a process flow of the present invention. Conventional methods 1-3
Is an example in which the slag basicity after dephosphorization treatment is 2.0 or more, or the slag is refined by reducing the stirring power, and Examples 4 to 7 are carried out according to the present invention. Of SiO ₂ amount, and other furnace residual slag SiO ₂ amount, etc. to produce than pretreated hot metal Si concentration for basicity adjustment it can be easily performed by turning on the quick lime content accordingly.

As can be seen from the results in this example, the application of the present invention makes it possible to greatly increase the intermediate waste rate after the dephosphorization treatment as compared with the conventional method, In the decarburization step performed in the above, the re-P is suppressed, and desiliconization, dephosphorization and decarburization refining in one furnace can be sufficiently performed.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

As is clear from the above embodiments, the present invention is directed to a desiliconization and dephosphorization refining method using an upper-bottom blower by improving the efficiency of slag discharge after dephosphorization. The decarburization refining can be performed continuously, and the effects of greatly reducing the number of steps, improving the heat allowance, and improving the iron content yield can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between bottom blow stirring energy and waste rate.

FIG. 2 is a diagram illustrating a relationship among slag basicity, a P removal rate, and a waste rate.

FIG. 3 is a diagram illustrating a relationship between bottom blowing stirring energy and iron oxide content in slag.

FIG. 4 is a diagram showing a process flow of the present invention.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-5-140627 (JP, A) JP-A-1-47011 (JP, A) JP-A-4-99213 (JP, A) JP-A-1- 283311 (JP, A) ISIJ International, Vol. 31, No. 11, pp. 1322-1328 (1991) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21C 5/28 C21C 1/02 110 C21C 1/04 101 C21C 5/34

Claims (1)

(57) [Claims] 1. A method for refining hot metal in a converter having a bottom-blowing function, wherein the flow rate of the bottom-blown gas is adjusted so that the stirring energy defined by the following equation (1) is 0.5 KW / T or more. Controlled slag basicity (% C
aO /% SiO ₂ ) is less than 2.0 and the iron oxide content is 5
% After desiliconization and dephosphorization of hot metal,
A converter refining method characterized by temporarily stopping blowing and discharging slag in the furnace by tilting the furnace, and subsequently performing decarburization blowing after finishing the waste. (Equation 1)