JPS6235445B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses hot metal that has been dephosphorized to a finished product level through hot metal pretreatment, and reduces converter slag with a carbon-containing substance to recover manganese, thereby increasing the blowout [Mn] and reducing the oxygen content in the steel. It concerns how to reduce the level. In the converter steel manufacturing process, there are top blowing, top blowing, bottom blowing, etc. depending on the oxygen supply form, but since the basic reaction mechanism is the same, the top blowing converter will be described below. In the pure oxygen top-blown converter steelmaking method, pure oxygen is blown onto the pig iron through a lance from the top of the converter, and the reaction is accelerated by the stirring force generated by the collision of the jets, oxidizing impurities in the pig iron and removing these oxides. This is a method of making steel from pig iron by absorbing and removing slag present on the pig iron. When starting converter blowing, CaO-based auxiliary materials, which are the main component of slag, are introduced into the converter and oxygen is blown into the converter. As blowing progresses, silicon in the pig iron is preferentially oxidized to (SiO ₂ ). This (SiO ₂ ) dissolves the solid state CaO and produces an activated slag that can absorb other impurities. During this period, oxidation of [Mn] and [P] also progresses, and they become (MnO) and (P ₂ O ₅ ), respectively, and are absorbed into the activated slag. After the period in which [Si] is preferentially oxidized (so-called "Si blowing"), the oxidation of [C] begins, and the period in which almost all of the blown oxygen reacts with [C] in the pig iron (decarburization) reaching its peak). During this period, the production of (FeO), which contributes to the oxidation of [Mn], [P], etc., slows down, so changes in [Mn] and [P] in the pig iron and slag stop. At the end of the peak decarburization period, slag formation has progressed considerably and a uniform molten slag is formed. (MnO) and (FeO) in the slag are reduced and return to the molten steel [Mn] A phenomenon of upheaval can be seen. After the time when this decarburization rate slows down, oxidation of [Mn] and [P] occurs again as FeO increases,
This results in the production of steel with low [C], [Mn], and [P]. Therefore, in converter refining, it is important to create an appropriate slag from the viewpoint of removing impurities. Low phosphorus steel (finished product [P] 0.02%, especially 0.015
%), conventionally, a large amount of CaO-based auxiliary raw material, which absorbs and removes phosphorus oxides (P ₂ O ₅ ), is input, and in some cases, the slag is discharged during blowing, so that the absorption and removal of phosphorus oxides (P 2 O 5 Methods such as discharging the (P ₂ O ₅ ) from the furnace, introducing new CaO-based auxiliary raw materials, and performing blowing again (so-called double slag method) are used. However, these methods have a limit to the amount of phosphorus that can be reached, and because they strongly promote the oxidation reaction, not only [P] but also [Mn] in the iron-Mn ore added to increase [Mn] is removed by oxidation. As a result, the amount of Mn alloy ferroadded after tapping increases, and therefore, in the conventional method, when obtaining steel with low [P] and high [Mn], the cost becomes high. Moreover, due to the high oxygen level in the steel, deoxidation products from the input ferroalloy increase,
This resulted in an increase in inclusions. The present invention was made to eliminate the above-mentioned drawbacks, and requires the following two configurations. The first step is to pre-treat the hot metal to be charged into the converter and charge the hot metal into the furnace, which has been dephosphorized to the finished product level. The goal is to actively return slag during the period to recover Mn. The present inventors focused on the oxidation reaction form at the final stage of blowing, and added a carbon-containing substance to the slag at this stage for the purpose of reducing (MnO) in the slag and measuring remanganese. As a result, it was confirmed that phosphorus, which has a weaker affinity with oxygen, was preferentially reduced, and the amount of remanganese was very small, which is not preferable for the production of so-called low-phosphorus, high-Mn steel. Therefore, in the present invention, only decarburization is performed in the slag minimum state, and P reduction is suppressed by using hot metal that has been dephosphorized to the finished product level during blowing in which ferromanganese ore is added to increase the blowstop [Mn]. , it is possible to efficiently increase the reduction rate of ferromanganese ore (Mn oxide), further increase the blowout [Mn], and at the same time reduce the oxygen level in the steel through slag reduction. Methods for dephosphorization by pre-treatment of hot metal are already known, but one example is that by adding gas acid, sintered ore, CaO, CaF ₂ , etc. to the hot metal bath after deSi removal and stirring. It is possible to de-P. The contents of the present invention will be explained in more detail below based on the drawings. Figure 1 A, B, and C show an example of the behavior of components in molten iron and slag during pure oxygen top-blowing converter blowing using hot metal that has been dephosphorized ([P] = 0.015%) by hot metal pretreatment. show. As shown in Figure 1A, the point at which the decarburization oxygen efficiency begins to decline after the peak decarburization period (C _B
After point), (FeO) in the slag increases rapidly as shown in (a), and [Mn], which had hitherto encountered
The oxidation of [P] occurs again, and as shown in c, the [Mn] in the molten iron, which had previously increased due to the addition of ferromanganese ore, decreases and transfers to slag. At this stage, according to the method of the present invention, if a carbon-containing substance, such as lump coke, is added to the slag from above the slag, this oxide is reduced and [Mn] returns to the steel.
In this case, if ordinary hot metal with high P content is used,
(P ₂ O ₅ ) in the slag also increases, and this is preferentially reduced, and the reduction of (MnO) becomes slight, but with low P
By using pig iron, (MnO) in the slag can be sufficiently reduced. It is a known technique to increase the gas generated in the converter by adding carbon-containing substances at the early and middle stages of blowing, but the present invention has little effect at the above-mentioned stage.
This is done at the end of the blowing stage, after the peak decarburization stage (after point C _B ). Carbon-containing substances include coke, coal pitch,
When adding carbon sources such as graphite and charcoal from the auxiliary raw material port, there are inhibiting factors such as absorption of exhaust gas from the converter and dissolution into the molten iron due to falling. From the viewpoint of yield, the particle size is preferably about 5 m/m to 30 m/m. Possible feeding methods include upward addition from the auxiliary raw material port or direct injection into the slag. Example In a 100t converter, low-P hot metal shown in Table 2 obtained by removing Si and then deP and S removal from hot metal having the components shown in Table 1 was used, and auxiliary materials shown in Table 3 were used. and performed blowing. As a result, the components shown in Table 4 at the time of blow-off were obtained. According to the present invention, a low phosphorus steel containing about 0.1% higher manganese than conventional methods could be melted in a converter. (1) Blast furnace hot metal components

【table】 (2) Converter capacity: Pure oxygen top-blown converter 100ton (3) Composition of charged hot metal

【table】 (4) Charging hot metal temperature: 1375℃ (5) Amount of auxiliary raw materials used

[Table] Conventional method Under the conditions (1) to (5) above, blowing was carried out using the blowing method shown in Figure 2. Method of the Invention The blowing method as shown in FIG. 3 was carried out under the conditions (1) to (5) above. The amount of coke input in Figure 3 is 7Kg/TS. The results of the experiment as described above are shown in Table 4.

【table】 [Brief explanation of the drawing]

Figure 1 A, B and C are graphs showing examples of decarburization oxygen efficiency and component behavior in slag and molten iron.
3 and 3 are charts showing the blowing patterns of the conventional method and the method of the present invention in Examples.

Claims (1)

[Claims] 1 When hot metal and Mn-containing materials are charged into a converter and subjected to oxygen blowing using a slag-forming agent to obtain steel with a high blowout Mn, the hot metal is decomposed to a finished product level through preliminary treatment. To regenerate Mn by using P-polluted low-P hot metal and adding powder, granular, or lumpy carbon-containing substances upward during the decarburization reaction decay period at the end of converter refining to reach the slag layer and reduce the slag. A blow-stop Mn ascending refining method in a converter characterized by the following.