JPS63255312A - Method for refining in converter - Google Patents

Abstract

PURPOSE:To facilitate melting of steel kind having comparatively high Mn and low S steel and to remarkably improve the yield, by executing oxidizing refining of dephosphorization and decarbonization to molten iron and next executing recovery of Fe and/or Mn and desulfurization by reducing refining. CONSTITUTION:The dephosphorizing treatment to less than the presetting P content for the product and next the decarbonizing refining to the prescribed C content are executed to the molten iron after tapping off from a blast furnace. Slag making agents of Fe-Si series reducing agent, lime, fluorite, etc., are charged, and the reducing refining is executed by gas stirring, and oxides of Fe and/or Mn, etc., generated or charged at the decarbonizing refining process, are reduced and recovered, and also desulfurizing treatment is executed. Then, slag basicity (CaO/SiO2) is to come at least more than 1.7, in order to obtain recovery of Mn and Fe in the slag and the desulfurizing treatment. By this method, all available elements from the discharging slag in a converter are recovered, and reduction of ferro-manganese consumption and the desulfurizing treatment can be executed.

Description

[Detailed description of the invention] [Industrial application field] The present invention separates the refining process after blast furnace tapping into oxidation refining and reduction refining to efficiently recover Fe, Mn, etc. and desulfurization treatment. This invention relates to a converter refining method that makes it possible.

C Prior Art] After blast furnace tapping, the hot metal is dephosphorized in a preliminary treatment process using a quicklime-based slag-forming agent, and the subsequent dephosphorization process in the converter blowing process is reduced.
Instead, attempts have been made to introduce Mn ore in converter blowing and to add Mn, which is an effective alloying element, to molten steel at low cost by melt reduction. For example, a method to increase the Mn recovery rate by controlling operating conditions (Japanese Patent Publication No. 61-159
No. 23), or a method of injecting a reducing agent into the slag to recover Mn (Japanese Patent Application Laid-open No. 60-238408) has already been proposed.

[Problem that the invention seeks to solve]

However, the quicklime-based slag forming agent used in hot metal pretreatment has a low desulfurization reaction, with a desulfurization rate of only about 50%, and furthermore, when an attempt is made to improve the dephosphorization rate, the desulfurization ability decreases. For this reason, in the case of steel types that require low sulfur content as in recent years, desulfurization treatment is performed before or after dephosphorization treatment, but while dephosphorization and decarburization treatment are oxidation refining, desulfurization treatment is Because it is a reduction refining process, resulfurization occurs from the desulfurization slag during the subsequent dephosphorization and decarburization treatments, causing problems in the melting of ultra-low sulfur copper and the like.

Furthermore, when attempting to recover Mn from the slag mentioned above, carbonaceous materials such as coke are used as reducing substances, but since the use of coke increases the amount of sulfur in molten steel, the amount of coke itself used is limited. This has become a major obstacle in efforts to recover Mn.

The present invention was made in view of the above circumstances, and its purpose is to separate the refining process after blast furnace tapping into oxidation refining and reduction refining, and to dephosphorize it.

To provide a converter refining method capable of performing oxidation refining for decarburization, and then performing reduction refining to recover Mn, etc., which is an effective component element for steel, recover iron, etc. lost by deoxidation or oxidation, and also perform desulfurization treatment. It is in.

Means for Solving Problem c] In the present invention, after decarburizing and refining hot metal that has been previously dephosphorized to below the product phosphorus concentration to a predetermined coal concentration, a reducing agent, Add the slag forming agent and adjust the slag basicity (Ca
O/SiO□) is set to 1.7 or more to reduce and recover oxides such as Fe and/or Mn produced or introduced in the decarburization refining process, and also performs a desulfurization treatment.

[Effect]

According to the present invention, all of the effective components can be recovered from the converter discharge slag, and the amount of Mn alloy iron can be reduced and desulfurization treatment can be performed.

[Refining contents]

Each process will be specifically explained below.

(1) Hot metal pretreatment Dephosphorization treatment is performed to obtain a preset phosphorus concentration as a finished product or a lower phosphorus concentration.

The processing conditions are not particularly limited as long as the above-mentioned conditions can be achieved, and the processing may be carried out by appropriately selecting the location and method conventionally practiced. If especially necessary, after dephosphorization treatment,
A method involving hot metal desulfurization treatment may also be used.

Examples of places where dephosphorization is performed include blast furnace casthouses, torpedo cars, hot metal pots, converters, etc.Fluxes used include CaO-based, Na-based, 0-based, and other fluxes that have high dephosphorizing ability but are accompanied by an increase in sulfur. A dephosphorizing agent such as Ca5On may also be used.

(II) Top-bottom blowing converter Refined hot metal that has undergone dephosphorization treatment until the phosphorus concentration is at or below the predetermined concentration for the finished product is transferred to the top-bottom blowing converter and further processed as follows. The refining process is first oxidation refining i) decarburization treatment and then reduction refining 1
i) Recovery of Fe and/or Mn and desulfurization treatment are performed.

The reason why a top-bottom blowing converter is used is that it can easily satisfy the stirring conditions required in the reduction refining process.

i) Decarburization is carried out until the carbon concentration of hot metal reaches a predetermined value (usually about 0.10%). - Carbon materials such as coke are used for heating, but even if the amount used increases and the sulfur contained in this increases, no problems will occur because desulfurization treatment will be performed later.

In addition, in decarburization treatment, an appropriate amount of slag is used to reduce the evaporation loss of Fe, but the basicity of slag is around 2.5 to 3.5 because it affects the recovery rate of Mn after decarburization. Set. It should be noted that if the amount of slag is increased, the amount of reducing agent required for subsequent reduction refining will increase, so it is usually desirable to set the amount of slag to about 20 to 40 kg/l.

Figure 1 is a graph showing the relationship between the amount of slag and the evaporation loss of Pe, with the horizontal axis representing slag i (kg/ton) and the vertical axis representing the evaporation loss of Fe (kg/ton). It is. As is clear from this graph, the evaporation loss decreases as the amount of slag increases up to 20 kg/).
It can be seen that the evaporation loss hardly changes even if the amount exceeds tons.

On the other hand, Figure 2 is a graph showing the relationship between the amount of slag and the reducing agent consumption rate, with the horizontal axis representing slag (kg/) and the vertical axis representing the amount of reducing agent (Fe-5i) required. (kg/)ton).

As is clear from this graph, when the amount of slag exceeds 40 kg/ton, the amount of required reducing agent increases rapidly. Therefore, from Fig. 1.2, it can be said that the slag amount is desirably 20 to 40 kg/).

Figure 3 is a graph showing the relationship between the slag basicity and the Mn recovery rate after decarburization, and the horizontal axis shows the slag basicity (Cab/5
ift), and the Mn recovery rate (%) after decarburization is plotted on the vertical axis. As is clear from this graph, it is desirable that the slag basicity is about 2.5 to 3.5.

1i) Fe and/or Mn recovery and desulfurization treatment The molten steel that has been decarburized to a predetermined carbon concentration is charged with a Fe-5i reducing agent, slag-forming agents such as quicklime, fluorite, and dolomite, and gas Stirring is performed to perform reduction refining, and oxides such as Fe and/or Mn produced or introduced during the decarburization refining process are reduced and recovered, and a desulfurization treatment is also performed.

The reducing agent may be any substance containing Si, Af, C, etc., and may be selected depending on the target carbon content of the steel to be manufactured. Particularly in the case of molten steel with a high carbon concentration, inexpensive reduction refining can be performed by using carbon itself as a reducing agent.

In addition, the slag basicity (CaO/5iOz) is the M in the slag.
n, at least 1.7 to achieve Fe recovery and desulfurization treatment. Therefore, when using a reducing agent containing Si, basicity is adjusted by adding CaO to prevent erosion of the furnace wall.

FIG. 4 is a graph showing the relationship between residual MnO in slag and slag basicity, where the horizontal axis shows the slag basicity (CaO/
5iOz), and Mn0 (%) is plotted on the vertical axis. Figure 5 is a graph showing the relationship between desulfurization index (S)/(S) and slag basicity, with the horizontal axis representing slag basicity CaO/5iOz and the vertical axis representing (S)/(S). This is a great indication. As is clear from Figures 4 and 5, Mn
It can be seen that it is desirable to have a slag basicity of 1.7 or more in order to increase the recovery rate and at the same time perform sufficient desulfurization treatment.

A non-oxidizing gas such as Ar or N is used as the stirring gas. In addition, since the amount of gas affects the basic unit of reducing agent,
It is preferable that the uniform mixing time τ of the steel bath calculated by the following formula be set to 50 seconds or less.

τ=800ε-0・4 Q:il stirring gas flow! (Nm'/min) Wg: Molten steel amount (tons) T: Steel bath temperature (K) 2: Bath depth cm) Figure 6 shows the stirring gas and reducing agent when the slag amount is 20 to 40 kg/min. This is a graph showing the relationship with basic unit,
The horizontal axis represents the uniform mixing time (seconds) of molten steel, and the vertical axis represents the reducing agent (kg/). As is clear from this graph, when the uniform mixing time is longer than 50 seconds, the amount of reducing agent used increases rapidly, so it is better to set the stirring gas amount so that the uniform mixing time is approximately 50 seconds or less. I understand.

It goes without saying that after the above-mentioned treatments (I) and (II), the composition of the alloying elements may be adjusted in the furnace by taking advantage of the fact that there is no risk of oxidation of the alloying elements.

〔Example〕

Using a 21-ton capacity converter with a top-bottom blowing structure, Ar was blown into it at a rate of I Nm3/min through two bottom-blowing tuyeres, and blowing was carried out to obtain steel with a predetermined composition including Mn while stirring. did.

In the blowing process, 50 kg of Mn ore is initially charged, 10 kg of Fe-5i is used as a reducing agent, and quicklime is used as a slag forming agent.
15 kg of dolomite, 10 kg of dolomite, and 4 kg of fluorite were charged. The amount of slag at this time was approximately 25 kg/), and the basicity (CaO/5iOz) was 2.9.

Table 1 shows the transition of each component composition before and after decarburization treatment and after reduction refining.

As is clear from Table 1, if we compare the Mn composition after decarburization and after reduction, it can be seen that Mn is as high as 0.48%. When steel was tapped at the end of the decarburization process using the conventional method and the conventional method, it was confirmed that the yield improved by approximately 1.55% when using the method of the present invention. This is presumed to be due to the improvement and the effect of adding Fe-5i as a reducing agent.

〔effect〕

・As described above, in the method of the present invention, it is possible to easily and inexpensively produce steel types with relatively high Mn content without using Mn-based alloy iron, and it is also possible to produce low-sulfur steel. The present invention has excellent effects, such as being easy to carry out and greatly improving the yield.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between slag amount and Fe evaporation loss, Figure 2 is a graph showing the relationship between slag amount and reducing agent consumption, and Figure 3 is the relationship between slag basicity and Mn recovery rate. Figure 4 is a graph showing the relationship between residual MnO in slag and slag basicity, Figure 5 is a graph showing the relationship between desulfurization index and slag basicity, and Figure 6 is a graph showing the relationship between the amount of stirring gas and reducing agent. It is a graph showing the relationship with quantity.

Claims (1)

[Claims] 1. After decarburizing the hot metal that has been previously dephosphorized to below the product phosphorus concentration and decarburizing it until it reaches a predetermined carbon concentration, a reducing agent and a slag-forming agent are added to it to reduce the slag basicity (CaO/SiO_
2) A converter refining method characterized in that oxides such as Fe and/or Mn produced or introduced in the decarburization refining process are reduced and recovered by setting 1.7 or more, and a desulfurization treatment is performed.