JP3728922B2 - Method for melting molybdenum-containing molten steel - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for melting molybdenum-containing molten steel, and in particular, is a technique that uses inexpensive molybdenum oxide as a molybdenum source, achieves a high molybdenum yield, and melts molybdenum-containing stainless molten steel at a lower cost than before. .
[0002]
[Prior art]
In general, when an alloy material is added to a molten metal during the process of refining the molten metal, an addition method is employed in which the addition yield is high and the molten metal is uniformly mixed in the molten metal. For example, it is considered the same when refining alloy steel such as stainless steel in a converter. Alloy materials such as ferro-chromium, ferro-nickel, and ferro-molybdenum are usually used before or during the refining process. It is thrown in.
[0003]
By the way, in recent years, in order to reduce the production cost of molybdenum-containing steel, attempts to use a large amount of inexpensive raw materials have been actively conducted. In particular, the ferro-molybdenum, which is a molybdenum source, is very expensive and has been replaced by inexpensive molybdenum oxide.
For example, Japanese Patent Publication No. 1-25363 discloses a technique of blowing molybdenum oxide together with a carrier gas through a lance immersed in the molten steel when molybdenum oxide is added to the molten steel. In addition, since the molybdenum oxide to be added is an oxide, in order to facilitate the reduction, the molybdenum concentration is added to the molten steel at the initial stage of converter blowing with a sufficiently high carbon concentration in the molten steel, that is, a strong reducing power. In general, the molybdenum oxide is reduced and the molybdenum is transferred into the molten metal. In this method, molybdenum oxide is sublimated (vaporized) at a relatively low temperature of 700 ° C., so that the faster the reduction, the lower the sublimation loss.
[0004]
[Problems to be solved by the invention]
However, when molten steel is blown using a refining vessel capable of top blowing, bottom blowing, or top bottom blowing of oxygen and a mixed gas containing oxygen, molybdenum oxide may be added at the initial stage of blowing as in the past. It has been found that the amount of molybdenum transferred into the molten steel relative to the amount added, that is, the molybdenum addition yield is at most 92 wt% and does not exceed that. In addition, when adding molybdenum oxide into molten steel, the technology of blowing together with a carrier gas through a lance immersed in the molten steel requires capital investment, and in any case, the advantage of using inexpensive molybdenum oxide cannot be enjoyed. Result.
[0005]
In view of such circumstances, the present invention adds molybdenum oxide, which is a molybdenum source, to the molten metal being decarburized and blown with oxygen or a mixed gas containing oxygen to produce molybdenum-containing molten steel. An object of the present invention is to provide a method for producing molybdenum-containing molten steel that can be remarkably enhanced as compared with the prior art.
[0006]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the inventor diligently studied the timing of addition of molybdenum oxide to the molten alloy in relation to the generation of dust from the hot metal, and completed the present invention.
That is, the present invention provides a molybdenum-containing molten steel that is reduced by adding and adding molybdenum oxide into the molten iron alloy when decarburizing and blowing carbon-containing molten iron alloy with oxygen or an oxygen-containing gas. In the method, molybdenum-containing molten steel characterized by adding molybdenum oxide to the molten iron alloy at a time when the decarburization rate defined by the following formula of the molten iron alloy becomes 0.4 or more and 0.98 or less. This is a melting method.
[0007]
Decarburization rate = ([wt% C] _i − [wt% C]) / ([wt% C] _i − [wt% C] _f )
[Wt% C] _i : Carbon concentration in molten iron alloy at the start of decarburization blowing [wt% C] _f : Carbon concentration in molten steel containing molybdenum at the time of decarburization blowing [wt% C]: Desorption Carbon concentration in molten iron alloy in the course of charcoal blowing Further, the present invention is also a method for producing molybdenum-containing molten steel, wherein the molten iron alloy contains chromium. Here, the above-mentioned molten iron alloy containing carbon (hereinafter, simply referred to as a molten iron alloy) is a case where ordinary steel is melted by decarburization blowing, and at the start of blowing, molten iron as a starting material The alloy has a so-called hot metal composition saturated with carbon, but as the decarburization progresses, the carbon concentration decreases and the molten steel composition is obtained at the time of blowing, so all the states from hot metal to molten steel are expressed in one word. It is a word used for this purpose. In particular, when molten stainless steel or chromium-containing molten steel is produced, chromium is contained in the molten iron alloy. This chromium-containing molten iron alloy is obtained by smelting reduction of chromium ore. Use is preferred.
According to the present invention, molybdenum oxide is added at a time when the decarburization rate is 0.4 or more and 0.98 or less, so that the dust loss of molybdenum is reduced in order to avoid the time when dust is generated in the first half of blowing. In addition, the addition yield is improved because the carbon concentration at the end of blowing is low, that is, the addition is avoided when the reducing power is weak, and the sublimation loss is reduced.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the form of the present invention will be described with the background of the present invention.
First, the inventor has investigated why the yield of molybdenum decreases when molybdenum oxide is used as a molybdenum source. In other words, the material balance was investigated by converter refining with a gas bottom blowing function. As a result, almost no molybdenum remains in the slag formed by refining, and as shown in FIG. 2, it is contained in molten iron alloy (hot metal), refining dust, or refining dust. I knew that.
[0009]
Therefore, the inventor continuously investigated the time course of the dust generation rate during decarburization blowing and the carbon concentration in the molten iron alloy (hot metal), and obtained the relationship shown in FIG. According to FIG. 3, it can be seen that the dust generation rate rapidly decreases after the decarburization rate is almost the maximum just before 0.4. That is, from this, it became clear that the conventional addition time of molybdenum oxide was the time when the dust was dissipated. It was also found that the loss of molybdenum oxide due to dust can be significantly reduced if molybdenum oxide is added when the decarburization rate is 0.4 or more and the dust generation rate is reduced.
[0010]
Furthermore, the inventor investigated the molybdenum yield when molybdenum oxide was added at various concentrations of carbon in molten steel at the end of the blow smelting, and obtained the results shown in FIG. According to this result, the yield of molybdenum increases as the carbon concentration in the hot metal when molybdenum oxide is added decreases, reaches a maximum when the decarburization rate is 0.98, and further decreases as the carbon concentration decreases. It can be seen that the yield decreases again. The reason for this decrease again is that when molybdenum oxide is added in a region where the decarburization rate exceeds 0.98, the rate of reduction of molybdenum oxide is low because of less carbon, rather the sublimation loss increases, and the molybdenum addition yield increases. It is because it will fall.
[0011]
Therefore, the inventor decided to add molybdenum oxide when the decarburization rate is 0.4 or more and 0.98 or less in order to solve such a problem. FIG. 1 shows the relationship between the decarburization rate and molybdenum yield when molybdenum oxide is added at each carbon concentration.
[0012]
【Example】
TCM13 steel (1 wt% Mo-9 wt% Cr) was melted using an upper bottom blow converter with a capacity of 160 tons. When the carbon in the hot metal is lowered from 5.5 wt% to 0.12 wt% by decarburization blowing with ordinary oxygen gas, the carbon in the hot metal is 0.4 wt% (decarburization rate 0.95) Then, molybdenum oxide was added to the hot metal by dropping. And oxygen blowing was continued and it was set as said molybdenum containing molten steel. The performance of the operation was evaluated by molybdenum yield and is shown in FIG.
[0013]
From FIG. 5, compared to the conventional method of adding molybdenum oxide at the early stage of decarburization, according to the melting method according to the present invention, the addition yield of molybdenum is improved by 2% in absolute value. Is clear.
[0014]
【The invention's effect】
As described above, according to the present invention, molybdenum yield can be improved by 2% in the production of molten molybdenum-containing steel using molybdenum oxide as a molybdenum source.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing the results of investigation of molybdenum addition yield by adding molybdenum oxide at various carbon concentrations in hot metal during the decarburization blowing process of hot metal.
FIG. 2 is a diagram showing a material balance relating to the amount of molybdenum in conventional decarburization blowing.
FIG. 3 is a graph showing changes over time in dust generation rate and carbon concentration in molten iron in the conventional melting of molten molybdenum steel.
FIG. 4 is a diagram showing molybdenum yield when molybdenum oxide is added at various carbon concentrations at the end of blowing.
FIG. 5 is a diagram showing molybdenum yield when molybdenum oxide is added at the beginning and end of decarburization blowing.

Claims (2)

When decarburization blowing the molten iron alloy in an oxygen or oxygen-containing gas containing carbon, was charged adding molybdenum oxide in the molten iron alloy, the melting method including molybdenum molten steel to reduce,
Molybdenum-containing molten steel is produced by adding molybdenum oxide to the molten iron alloy when the decarburization rate defined by the following formula of the molten iron alloy becomes 0.4 or more and 0.98 or less. Method.
Decarburization rate = ([wt% C] _i − [wt% C]) / ([wt% C] _i − [wt% C] _f )
[Wt% C] _i : Carbon concentration in molten iron alloy at the start of decarburization blowing [wt% C] _f : Carbon concentration in molybdenum-containing molten steel at the time of decarburization blowing [wt% C]: Desorption Carbon concentration in molten iron alloy during charcoal blowing   The method for melting molybdenum-containing molten steel according to claim 1, wherein the molten iron alloy contains chromium.

Images