JPS609813A - Refining method by increasing blown-out mn in converter - Google Patents

Abstract

PURPOSE:To increase blown-out Mn and to decrease the oxygen level in a steel by dephosphorizing the molten iron to be charged into a converter by a preliminary treatment and reducing positively slag at the attenuation period of decarburization reaction in the end period of converter refining. CONSTITUTION:A low P molten iron dephosphorized to a product level by a preliminary treatment is used as the above-described molten metal in the stage of charging the molten iron and ferruginous manganese ore into a converter, performing oxygen blowing and obtaining a steel contg. high blown-out Mn. A powder and granular or lumped C-congt. material is added from above in the attenuation period of decarburization reaction in the end period of converter refining so as to arrive at a slag layer and to reduce the slag layer, thereby restoring Mn. The reduction of P is thus suppressed and the reducing rate of ferruginous manganese ore (MnO) is effectively increased, by which the blown-out Mn is much increased and at the same time oxygen level in the steel is decreased by the reduction of the slag.

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 the converter slag with a carbon-containing substance to recover manganese. let it rise;
and a method for reducing oxygen levels in steel.

In the converter steel manufacturing process, there are top blowing, top bottom blowing, bottom blowing, etc. depending on the oxygen supply form, but the reverse is / /%/.

Since the basic converter 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 stirring force generated by the collision of the jets accelerates the reaction, oxidizes impurities in the pig iron, and removes these oxides from the pig iron. This is a method of making steel from pig iron by absorbing and removing the slag present above.

At the start of converter blowing, Ca, the main component of slag, is
O-based auxiliary raw materials are introduced into the converter, and oxygen is blown into the converter.

As blowing progresses, silicon in the pig iron is preferentially oxidized (Si02). This (5i02) dissolves the solid state CaO and produces an activated slag that can absorb other impurities. At this time [:Mn':l
, [P] also progresses, resulting in (MnO) and (P2
It is absorbed into the activated slag in the form of O3).

After the period in which [Si] is preferentially oxidized (so-called "St blowing"), the next oxidation of K (C) begins, and the period in which almost all of the blown oxygen reacts with [C] in the pig iron (decarburization) reaching its peak).

2- During this period, (M
n), [P] stops changing.

At the end of the peak decarburization period, the slag progresses rapidly and a uniform molten slag is formed.
A phenomenon of upheaval (Mn:) in which nO) and (Fed) are reduced and returned to the molten steel is observed.

After the time when this decarburization rate slows down, the oxidation of [Mn] and [P] is actively carried out again as FeO increases, and [Ca, C
M+1), (results in the production of steel with low Pl. Therefore, in converter refining, it is important to create an appropriate slag from the viewpoint of removing impurities.

Low phosphorus steel (finished product [P'3≦θL3, also known as θθ/jchi]
When melting P2O3, conventionally a large amount of CaO-based auxiliary raw materials to be absorbed and removed by the phosphorus oxide CP2 (P2O3
) is discharged from the furnace, new CaO-based auxiliary raw materials are introduced,
Methods such as blowing again (the so-called double slug method) are used. However, these methods have a limit to the amount of phosphorus that can be reached, and they do not strongly promote the oxidation reaction [P
] as well as iron M added to increase [Mn].
[Mr+] in the n ore is also removed by oxidation, and the amount of Mn alloy iron added after tapping increases. Therefore, in the conventional method, [P
) is low and [Mn:] is high, the cost is high. Furthermore, due to the high oxygen level in the steel, deoxidation products from the input alloy iron increased, leading to an increase in inclusions.

The present invention was made to eliminate the above-mentioned drawbacks, and requires the following β configurations.

The first step is to charge the hot metal into the converter (hot metal that has been pretreated and dephosphorized to the finished product level). The aim is to actively reduce 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 (M n O) in the slag and measuring remanganese. As a result, phosphorus, which has a weak affinity for oxygen, is preferentially reduced, and only a small amount of remanganese is produced, so-called low phosphorus and high Mn.
It was confirmed that the steel was not suitable for melting.

Therefore, in the present invention, in the blowing process in which only decarburization is performed in the slag minimum state and ferromanganese ore is added to increase the blowstop [Mn], it is possible to reduce P by using hot metal that has been dephosphorized to the finished product level. ferromanganese ore (M oxide
A method of dephosphorizing O by pre-treatment of hot metal is already known, which can efficiently increase the reduction rate of (n) to further increase the blowout [Mn] and at the same time reduce the oxygen level in the steel through slag reduction. However, to give an example, for example, if there is a presence in the hot metal bath after de-Station,
DeP can be easily removed by adding sintered ore, Cab, Ca-F2, etc. and stirring.

The contents of the present invention will be explained in more detail below with reference to the drawings.

Figure 1 (7), (a) and (ii) In molten iron and slag during pure oxygen top-blowing converter blowing using hot metal dephosphorized (CP) = θθ/j%) by K1 hot metal pretreatment An example of the component behavior of is shown below. As shown in Figure 1 (7), after the peak decarburization period has passed,
After the point at which the decarburization oxygen efficiency begins to decrease (CB point), (
As shown in b), (Fed) in the slag increases rapidly,
The oxidation of [Mn] and [P] that had occurred up until then occurred again, and as shown in (?) Transition. 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) is returned to the steel. In this case, if ordinary hot metal with high P content is used,
(P2O3) in the slag also increases, and this is preferentially reduced, resulting in a slight reduction of (MnO), but by using low P pig iron, (MnO) in the slag can be sufficiently reduced. be.

It is a known technique to add carbon-containing substances in the early and middle stages of blowing to increase the gas generated in the converter, but the present invention has little effect during the above period, and the decarburization peak period has passed. (
08 points and above) Performed at the final stage of blowing.

Coke, coal, pitch, -Otsuichi graphite, charcoal, etc. are selected as carbon-containing substances.When the carbon source is added through an auxiliary raw material port, etc., it is dissolved into the molten iron by suction of exhaust gas from the converter and falling. Therefore, from the viewpoint of yield in the slag layer, the particle size is preferably about S% to 3θ%.

Possible charging methods include upward addition from the auxiliary raw material port or direct injection into the slag. Example 10 In a converter, hot metal having the components shown in Table 1 was subjected to Si-removal P and S-removal treatment. Blowing was carried out using the low P hot metal shown in Table 3 obtained in the above manner and the auxiliary raw materials shown in Table 3.

As a result, the components shown in Table 9 at the time of blow-off were obtained.

According to the present invention, a low phosphorus steel having a higher θ/manganese ratio than conventional methods can be produced in a converter.

(1) Blast furnace hot metal composition / Table (2) Converter capacity: Pure oxygen top-blown converter / θθton (3)
Charged hot metal composition Table 2 (4) Charged hot metal temperature: /373'C (5) Amount of auxiliary material used Table 3 Conventional method Under the conditions (1) to (5) above, blowing as shown in Fig. It was conducted using the training method.

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 7k.
g/T-8.

The results of the above tests are shown in Table 7.

Table 7: Molten steel composition and slag composition during blow-stopping

[Brief explanation of drawings]

Figure 1 (7) (a) and ((Foundation) are graphs showing examples of decarburization oxygen efficiency and component behavior in slag and molten iron. Figures 2 and 3 are examples of the conventional method and the present invention. This is a chart showing the blowing pattern of the method.

Claims (1)

[Claims] When hot metal and Mn-containing materials are charged into a converter and oxygen blowing is performed to obtain steel with a high blowout Mn, low P hot metal that has been dephosphorized to a finished product level through preliminary treatment is used as the hot metal, and A blowing furnace in a converter characterized in that five grains or lumps of carbon-containing material are added upward during the decarburization reaction decay period at the end of furnace refining to reach the slag layer and reduce the slag to achieve Mn recovery. Refining method to increase stop Mn.