JPH0517810A - Refining method for high-mn steel - Google Patents

Abstract

PURPOSE:To greatly improve the yield of Mn and to produce the high-Mn steel by executing refining under specific conditions, thereby accelerating the melting of Mn sintered ore from the initial period to the middle period of the refining and minimizing the amt. of slag. CONSTITUTION:Molten iron subjected to a dephosphorization treatment to a product standard [P] or below is charged into a top and bottom blown converter where the MnO-contg. refining slag of the previous time remains. The refining is executed by adding the Mn sintered ore in the initial period of the refining. The porosity of the Mn sintered ore is specified to 30 to 50% and the CaO contained therein to 6 to 30wt.% at this time. Only the auxiliary materials contg. the CaO at the ratio below the value W determined by equation are charged into the furnace from the initial period to the middle period of the refining. The L/L0 by the blasting of oxygen with a lance is maintained at 0.20 to 0.32 from the initial period to the middle period of the refining and at 0.37 to 0.50 in the end period of the refining. Blowing out is stopped at [C] >=0.10%. In the equation, W: the required charging rate of the CaO (kg/T) from the materials exclusive of the Mn sintered ore, Ww: the charging rate of the Mn sintered ore (kg/T), (%SiO2): the content of SiO2 (%) in the Mn sintered ore, (%CaO): the content of the CaO (%) in the Mn sintered ore, L: the denting depth to a steel bath, L0: depth of the steel bath.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses a Mn sinter having a specific porosity and CaO for hot metal that has been dephosphorized to a product grade [P] or lower in hot metal pretreatment and has a high Mn yield. It is a method of refining upper and lower blown converter to obtain

[0002]

2. Description of the Related Art In recent years, with the development of hot metal pretreatment technology,
Less slag refining is the mainstream of refining in converters. Among them, the method of adding Mn to molten steel is a method of performing a smelting reduction by feeding an inexpensive Mn ore into the refining instead of the method of using an expensive Fe-Mn-based alloy after the refining which is conventionally performed. Has become commonplace. M in this converter
As a measure for improving blown Mn using n ore, for example, as described in JP-A-60-9813, a method of introducing Mn ore at the initial stage of refining and refining under less slag, powder coke at the final stage of refining Is added to suppress the reoxidation of Mn in the molten steel and mainly promote the reduction of (MnO) in the slag. However, since Mn ore has a high melting point and is difficult to dissolve in the low temperature region from the early stage to the middle stage of refining, it does not completely dissolve within the limited refining time, and remains in the slag in an undissolved state at the end of refining. , Mn yield was poor, and considerable dissociation was observed in comparison with the equilibrium value (theoretical value) as shown by the dotted line in FIG. As one example of measures for improving the Mn yield, a method of sintering Mn ore in advance and charging it in a converter has been proposed, as described in JP-A-62-33709.

[0003]

However, the above-mentioned Japanese Unexamined Patent Application Publication No.
As described in JP-A-2-33709, if only Mn sintered ore is used, a sufficient dissolution promoting effect cannot be obtained, and Mn cannot be obtained.
We could not expect a significant improvement in yield. Also, M in the slag
There is also a method of leaving the previous refining slag containing MnO in order to effectively utilize n minutes, but it is not sufficient.

Therefore, the present invention has an object to significantly improve the Mn yield by promoting the dissolution of Mn sintered ore from the initial stage to the middle stage of refining and refining with the amount of slag minimized. It is a thing.

[0005]

The present invention has been made in order to solve the above-mentioned problems, and the gist of the present invention is to provide an upper-bottom blowing converter in which the previous refining slag containing MnO was left as a product. In a refining method in which hot metal dephosphorized to the standard [P] or less is charged and Mn sintered ore is added in the initial stage of the refining, the Mn sintered ore has a porosity of 30 to 50% and a content C.
While making aO = 6 to 30 wt%, from the initial stage to the middle stage of refining, only the auxiliary material containing the CaO amount equal to or less than the value W calculated by the following formula was added, and L / L ₀ by lance feeding was 0 from the initial stage to the middle stage of refining. 20 ~ 0.32, the final stage of refining is 0.37 ~
A refining method for high-Mn steel is characterized by refining to 0.50 and stopping at [C] ≧ 0.10%.

W = (W _M × (% SiO ₂ ) /100+1.0) × 5-W _M × (% CaO) / 100 (1) However, W: the required CaO amount input from other than the Mn sintered ore ( k
g / T) W _M : Mn sinter input (kg / T) (% SiO ₂ ): SiO ₂ content in Mn sinter (%) (% CaO): CaO content in Mn sinter Amount (%) L: Depth of steel bath depression, L ₀ : Depth of steel bath

[0007]

In order to improve the Mn yield, it is important to dissolve the Mn sintered ore from the initial stage of refining as described above.
The porosity of the Mn sintered ore is 30 to 50%, the content of CaO is 6 to
It was added as 30 wt% in the initial stage of refining, and the refining pattern in the lance was refined by soft blow in the middle period (molten steel [C] = 2%) immediately after the introduction, and the equilibrium value was significantly increased as shown by the solid line in FIG. Turned out to approach. The reason will be described below.

First, when the porosity of the Mn sintered ore is set to 30% or more, the Mn yield is remarkably improved as shown in FIG.
It is considered that this is because the contact interface area between the Mn sintered ore and the slag is expanded and the melting is promoted. However, when the porosity exceeds 50%, the strength is decreased, powder is generated during transportation, and the powder is sucked into the exhaust gas recovery equipment when charging the converter, so that it cannot be used in an actual machine. The porosity referred to here is a value measured by the vacuum packing method.

Secondly, the addition of CaO makes it possible to lower the melting point of Mn sinter, but if the amount is less than 6%, the melting point lowering effect is not sufficient, and conversely if it exceeds 30%. This is because the strength of the Mn sintered ore itself is reduced. Third, L / L ₀ by lance acid transfer from the early stage to the middle stage of refining
(L: depth of indentation of steel bath, L ₀ : depth of steel bath) is 0.20
The soft blow of 0.32 is carried out so that the oxygen injected from the lance hits mainly the boundary part between the slag and the molten steel (the unmelted Mn sintered ore floats in this part), and the heat of the slag This is to secure a margin and promote the dissolution of the Mn sintered ore existing at the boundary between the slag and the molten steel into the slag.

Next, suppression of reoxidation of [Mn] in the molten steel at the final stage of refining is important for improving the Mn yield. Therefore, the refining pattern at the final stage of refining (molten steel [C] ≤1%) is used as a hard blow. , It is necessary to stop with molten steel [C] ≧ 0.10%. Firstly, L by lance acid transfer toward the final stage of refining
The reason why / L ₀ is set to 0.37 to 0.50 as a hard blow is that the oxygen injected from the lance hits the molten steel mainly, so that the oxidation degree in the slag at the end of refining increases sharply. This is to suppress reoxidation of [Mn] in the molten steel.

Regarding the blow stop [C], [C] <0.
This is because FeO, which is an index of the degree of oxidation in the slag, rapidly increases at 10% and reoxidation of [Mn] occurs due to the reaction between [Mn] in the molten steel and FeO in the slag. Further, in addition to the promotion of dissolution and the suppression of reoxidation, the amount of Mn contained in the slag can be reduced by reducing the amount of slag to the limit, thereby further improving the Mn yield. For this purpose, the content of [P] in the hot metal is set below the product specification in advance, and in addition to this, the CaO-based auxiliary material to be added during refining is added
n distribution (the ratio of Mn content in slag to Mn content in molten steel) is minimized so that blow-stop basicity of slag is 4 and only for basicity adjustment, and the value obtained by the above formula (1) W
It is the amount necessary to obtain the following CaO amount.

[0012]

EXAMPLES Examples 1 to 3 are shown in Table 1, and Comparative Examples 1 to 3 are shown in Table 2.
Indicates. It can be seen that in Examples 1 to 3, a high Mn yield of about 70% is obtained. Comparative Example 1 is a case where Mn sinter having a low porosity of 27% is used, and the Mn yield is 65%.
Stays in.

In Comparative Example 2, the refining pattern was L (depth of steel bath dent) / L due to lance acid transfer from the initial stage to the middle stage of refining.
_This is an example of a hard blow of ₀ (steel bath depth) of 0.375, and the Mn yield is about 65%. Comparative Example 3
Is an example in which the amount of CaO required from other than the Mn sintered ore is set to an amount exceeding the value calculated by the above formula (1) (W calculated value), and the Mn yield remains at 65%.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

As described above, according to the present invention, the hot metal dephosphorized to the product specification [P] or less by the hot metal pretreatment is used.
By using Mn ore that has been pre-sintered with regulated porosity and CaO content, the refining pattern is optimized, and the amount of auxiliary materials other than Mn sintered ore is limited to a minimum, resulting in a conventional Mn yield. Compared with the method, it can be increased by about 5%, and the merit of reducing the amount of quick lime used in the converter can be enjoyed, and the effect is extremely large.

[Brief description of drawings]

[Figure 1] [Mn] in the steel bath from the start of refining to the end of refining
It is a figure which shows the behavior of.

FIG. 2 is a diagram showing a relationship between porosity of Mn ore and Mn yield.

Claims (1)

Claims: 1. At the beginning of the refining process, the upper and bottom blowing converter in which the previous refining slag containing MnO is left, is charged with dephosphorized hot metal below the product specification [P]. In the refining method of adding Mn sinter, the porosity of the Mn sinter = 30-50
%, CaO content = 6 to 30 wt%, and from the initial stage of smelting, L / L ₀ by lance acid transfer from the initial stage of smelting from the initial stage of smelting Refining with 0.20 to 0.32 in the middle stage and 0.37 to 0.50 in the final stage of refining, [C] ≧ 0.10%
A method for refining high-Mn steel, characterized in that _{W = (W M × (%} SiO 2) /100+1.0) × 5-W M × (% CaO) / 100 (1) where, W: must put the amount of CaO from non Mn sinter (k
g / T), W _M : Mn sintered ore input amount (kg / T) (% SiO ₂ ): Mn sintered ore SiO ₂ content (%) (% CaO): Mn sintered ore CaO Content (%) L: Depth of steel bath dent, L ₀ : Depth of steel bath