JP2018109213A - Method and apparatus for desulfurizing molten steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and stably melt a low-S steel having S concentration of 50 ppm or less using a smaller amount of desulfurization flux by RH-PB method without using fluorite CaF, which has a large environmental load.SOLUTION: When a molten steel 2 is desulfurized by RH-PB method, an eccentric lance 13 in which the central direction of the powder injection direction is inclined with respect to the direction of the center axis of the lance is used as a top-blown lance. The distance L from a lance hole 18 of the eccentric lance 13 to the intersection point between the extension of the center axis of the eccentric lance 13 and the recycling molten steel 2 is 1.5 to 3.5 m. A powdery desulfurization flux 14 containing no fluorite is blown toward the surface of the molten metal within the range of 1 m away from directly above the reflux gas blowing tuyere 7 in the horizontal direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a molten steel desulfurization method and a desulfurization apparatus.

  The influence of impurity elements in steel materials on the quality of steel materials is significant, and development of technology for reducing impurity elements is required due to the recent increase in demand for upgrading steel materials. Among the impurity elements, sulfur in molten steel (hereinafter referred to as “S”) includes solute elements in molten steel and sulfide inclusions (non-metallic particles such as oxides and sulfides remaining in the steel). Generated).

  Inclusions in the steel material have properties different from those of the base material, and therefore become a starting point of destruction of the steel material or cause a decrease in the corrosion resistance of the steel material. For this reason, the production | generation of a sulfide type inclusion is suppressed by reducing the S concentration in molten steel. For example, in pipe materials that require sour resistance and HIC resistance, including oil well pipes and line pipes, molten steel having a low S concentration with an S concentration of 40 ppm or less is required.

  As a method for producing molten steel having a low S concentration, molten steel decarburized in a decarburizing furnace is taken out in a ladle and desulfurized in a secondary refining facility in the next step.

  Secondary refining consists of (a) degassing under reduced pressure atmosphere that enables degassing of molten steel for the purpose of reducing or controlling the concentration of carbon, hydrogen, nitrogen, etc., and (b) impurity elements in molten steel And refining (reaction between flux and molten steel) by adding a flux or solvent for the purpose of removing inclusions and inclusions.

  Conventionally, the processing of the above items a and b has been performed in separate processes for functional differentiation, but from the viewpoint of reducing manufacturing costs, consolidating manufacturing facilities, and increasing production efficiency, a single refining facility is used. Development of multi-functional refining method using slag is required. In response to this, a desulfurization method in an RH vacuum degassing apparatus has been developed.

  FIG. 9 is an explanatory diagram showing a situation where the molten steel 2 is refined by the RH vacuum degassing apparatus (hereinafter also referred to as “RH apparatus”) 1.

  As shown in FIG. 9, the RH device 1 includes a vacuum chamber 4 installed above a ladle 3 that accommodates molten steel 2, an ascending pipe 5 and a descending pipe 6 provided below the vacuum tank 4, and an ascending This is a refining facility provided with a reflux gas injection tuyere 7 provided in the pipe 5, and the molten steel 2 is blown upward by blowing the reflux gas 8 from the reflux gas injection tuyere 7, and the riser 5, the vacuum tank 4, It is mainly used for melting steel grades that require degassing treatment by refluxing the downcomer 6 and the ladle 3 in this order, and it is widely used at home and abroad as a secondary refining equipment because of its high productivity. It has been.

  Then, in order to perform desulfurization in the RH apparatus 1, CaO is mainly formed from the powder top blowing lance 9 disposed in the vacuum tank 4 on the molten steel 2 refluxed in the vacuum tank 4 of the RH apparatus 1. The powdered desulfurization flux 10 to be blown is blown to cause CaO to react with S in the molten steel, so that CaS is dissolved and precipitated at the interface of the particles (CaO particles) of the desulfurization flux 10 to remove the particles. Hereinafter, this desulfurization method is also referred to as “RH-PB method”.

  However, it is known that the reaction efficiency of desulfurization in the RH apparatus 1 is lower than the reaction efficiency of the desulfurization method using other reaction apparatuses. The reason is that CaO particles blown in the vacuum chamber 4 are sucked and dissipated in the exhaust system 11 of the vacuum chamber 4, and the CaO particles are difficult to get wet in the molten steel 2, so It is known that the reactivity of CaO particles with molten steel 2 is low.

  Further, when the blowing amount of the desulfurization flux 10 is large, not only the melting cost increases, but also the amount of Al added from the alloy addition hole 12 to compensate for the temperature drop of the molten steel 2 increases. However, melting costs will increase. For this reason, the desulfurization reaction efficiency per unit use amount of the desulfurization flux 10 is also required to be high.

Conventionally, in order to solve this problem, by using fluorite CaF ₂ as the desulfurization flux 10, Cs (referred to as sulfide capacity, indicating the S distribution relationship between slag and molten steel) is high with high basicity, By reducing the melting point, a slag having the property of becoming a liquid phase and easily increasing the reaction interface area was generated, and the de-S reaction between the flux and the molten steel 2 was dramatically improved.

  However, fluorine contained in fluorite is known to cause environmental pollution, and from the viewpoint of environmental regulations in recent years, there is a demand for a fluorine-free steelmaking process. Therefore, there is a need for a technique for improving the reaction efficiency of the desulfurization flux 10 in a vacuum degassing apparatus such as the RH apparatus 1 having low desulfurization capability without using fluorine and melting ultra low S steel.

  However, if fluorite is not used for the desulfurization flux 10, it is inevitable that the de-S reaction efficiency tends to decrease due to aggregation of the desulfurization agent and a decrease in the reaction interface area.

  In Patent Document 1, oxygen or an oxidizing gas is sprayed from the top blowing lance 9 to the bath surface of the molten steel 2 in the vacuum chamber 4 and aluminum or an aluminum-containing reducing agent is added. The desulfurization flux 10 containing at least 1 kg / ton of the desulfurization flux 10 as a main component is sprayed, or, in addition to the above treatment, the bath depth of the molten steel 2 staying in the vacuum chamber 4 is lowered to reduce the blown desulfurization flux. 10 powder is circulated between the vacuum tank 4 and the ladle 3 together with the molten steel, so that the molten steel 2 is desulfurized efficiently and in a short time without causing contamination, and the sulfur concentration is 3 to 5% by mass. An invention for melting steel is disclosed.

In Patent Document 2, when vacuum degassing is performed on the molten steel 2 that has been deoxidized by the RH device 1, a carrier gas is used together with a carrier gas from a lance 9 that is vertically inserted from the upper part of the vacuum chamber 4. In addition, after desulfurization treatment was performed by blowing desulfurization flux 10 mixed with CaO and CaF ₂ or the like to lower the melting point, the molten steel 2 was increased to a pressure level that would not stop the reflux, and calcium alloy grains were added to the alloy. An invention is disclosed in which high-clean steel is efficiently melted by adding the holes 12 to the molten steel 2 in the vacuum chamber 4.

JP-A-5-287359 JP-A-7-70628

  However, in the inventions disclosed by Patent Documents 1 and 2, an extremely low S steel having an S concentration of 40 ppm or less is obtained by using the RH device 1 without using fluorite having a large environmental load, and having a smaller unit of desulfurization flux 10. It cannot be efficiently and stably melted at the amount used.

  The present invention is listed below.

(1) Ascending the molten steel by blowing a reflux gas upward from a reflux gas blowing tuyere provided in a riser pipe provided in a lower part of a vacuum tank placed above a ladle containing molten steel It is arranged inside the vacuum chamber (specifically, the central portion in the horizontal plane of the vacuum chamber) while refluxing in the order of the tube, the vacuum chamber, the downcomer provided at the bottom of the vacuum chamber, and the ladle. In the method of desulfurizing the molten steel by blowing a powdery desulfurization flux onto the molten steel surface to be recirculated from the powder blasting lance,
As the powder top blowing lance, an eccentric lance in which the center direction of the powder blowing direction is inclined with respect to the direction of the lance central axis with respect to the lance spray angle,
The distance from the lance hole of the powder blowing lance to the intersection of the extension of the central axis of the powder blowing lance and the refluxed molten steel is 1.5 to 3.5 m,
A method for desulfurizing molten steel, in which the powdery desulfurization flux is blown toward the molten metal surface located within a distance of 1 m in the horizontal direction from immediately above the reflux gas blowing tuyere.

(2) The molten steel desulfurization method according to item 1, wherein the lance spray angle θ satisfies the expressions (1) and (2).
tanθ ≦ R / (Hlance-Y) (1)
{Rn + LH- (αn + Y) × tanθ '} / (Hlance-Y) ≦ tanθ (2)
However,
Bath depth Y = Hs + Ls-α (m)
Molten steel height Hs = (Pa-Pr) / ρg (m)
θ: Spray angle of powder blast lance (deg)
R: Inner diameter of the vacuum chamber (m) at the surface height of the center of the vacuum chamber
Hlance: Lance height (m), which is the vertical distance from the tip of the powder blasting lance to the center of the vacuum chamber
Y: Bath depth at the center of the bottom of the vacuum chamber (m)
Rn: Horizontal distance from the center of the bottom of the vacuum chamber to the reflux gas injection tuyere (m)
L _H : Bubble arrival distance in the horizontal direction (m)
αn: Vertical distance from the center of the bottom of the vacuum chamber to the reflux gas injection tuyere of the riser (m)
θ ′: Bubble tower spread angle, 12-15 (deg)
Hs: Molten steel height (m) which is the vertical distance between the molten steel in the center of the vacuum chamber and the molten steel in the ladle
Ls: Immersion depth of riser in molten steel (m)
α: Vertical distance from the center tank at the bottom of the vacuum chamber to the tip of the riser (m)
Pa: Atmospheric pressure (kPa)
Pr: Pressure inside the vacuum chamber (kPa)
ρ: Specific gravity of molten steel (g / cm ³ )
g: Gravitational acceleration (g / sec ² )
It is.

  (3) The molten steel desulfurization method according to item 1 or 2, wherein the eccentric lance is reciprocally rotated about the lance center axis as a rotation center when the powdery desulfurization flux is injected.

  (4) The desulfurization method for molten steel according to any one of items 1 to 3, wherein the powdery desulfurization flux contains CaO as a main component and contains 10 to 30% by mass of a Ca-based alloy.

  (5) The desulfurization method for molten steel according to any one of items 1 to 4, wherein the powdery desulfurization flux does not contain fluorite.

(6) a ladle containing molten steel;
A vacuum chamber disposed above the ladle;
An ascending pipe and a descending pipe provided in the lower part of the vacuum chamber and immersed in the molten steel;
A reflux gas blowing tuyere provided in the riser,
The molten steel was arranged inside the vacuum tank while refluxing the reflux gas from the tuyere of the reflux gas, and refluxing the molten steel in the order of the riser pipe, the vacuum tank, the downcomer pipe, and the ladle. In the apparatus for desulfurizing the molten steel by blowing a powdered desulfurization flux from the powder blasting lance to the molten steel surface to be refluxed,
The powder top blowing lance is an eccentric lance in which the center direction of the powder blowing direction is inclined by a lance spray angle with respect to the direction of the lance center axis, and the powdered desulfurized flux is supplied to the reflux gas blowing tuyere Blowing toward the molten steel surface within a distance of 1 m in the horizontal direction from directly above, and extending the center axis of the powder blowing lance and the reflux from the lance hole of the powder blowing lance The distance to the intersection with molten steel is 1.5 to 3.5 m.

(7) The lance spray angle θ is the molten steel desulfurization apparatus according to Item 6, which satisfies the expressions (1) and (2).
tanθ ≦ R / (Hlance-Y) (1)
{Rn + L _H- (αn + Y) × tanθ '} / (Hlance-Y) ≦ tanθ (2)
However,
Bath depth Y = Hs + Ls-α (m)
Molten steel height Hs = (Pa-Pr) / ρg (m)
θ: Spray angle of powder blast lance (deg)
R: Inner diameter of the vacuum chamber (m) at the surface height of the center of the vacuum chamber
Hlance: Lance height (m), which is the vertical distance from the tip of the powder blasting lance to the center of the vacuum chamber
Y: Bath depth at the center of the bottom of the vacuum chamber (m)
Rn: Horizontal distance from the center of the bottom of the vacuum chamber to the reflux gas injection tuyere (m)
L _H : Bubble arrival distance in the horizontal direction (m)
αn: Vertical distance from the center of the bottom of the vacuum chamber to the reflux gas injection tuyere of the riser (m)
θ ′: Bubble tower spread angle, 12-15 (deg)
Hs: Molten steel height (m) which is the vertical distance between the molten steel in the center of the vacuum chamber and the molten steel in the ladle
Ls: Immersion depth of riser in molten steel (m)
α: Vertical distance from the center tank at the bottom of the vacuum chamber to the tip of the riser (m)
Pa: Atmospheric pressure (kPa)
Pr: Pressure inside the vacuum chamber (kPa)
ρ: Specific gravity of molten steel (g / cm ³ )
g: Gravitational acceleration (g / sec ² )
It is.

(8) The molten steel desulfurization apparatus according to 6 or 7, wherein the powder top blowing lance is reciprocally rotatable about the lance center axis when the powdery desulfurization flux is blown.
The present invention is the same as the invention disclosed in Patent Document 2 in that the powder desulfurization flux is blown from the top blowing lance into the molten steel.
(A) The point of promoting the entrainment of powder by blowing desulfurization flux from the eccentric lance toward the molten steel on the riser side,
(B) By reciprocating (swinging) the eccentric lance toward the ascending pipe side, the aggregation of the desulfurizing agent is suppressed and the spray range is expanded, and (c) a desulfurized flux not containing fluorite CaF ₂ It is different from the invention described in Patent Document 2 in terms of controlling the de-S reaction efficiency by adjusting the blending ratio of Ca alloy to 5 to 30%.

  According to the present invention, by using powder blowing in the RH vacuum degassing apparatus which is a secondary refining equipment, a low S steel having an S concentration of 40 ppm or less can be obtained without using fluorite having a large environmental load. It can be produced efficiently and stably with a small amount of desulfurization flux.

FIG. 1 is an explanatory diagram showing a situation in which molten steel is desulfurized using the RH apparatus according to the present invention. FIG. 2 is an explanatory diagram showing plume eyes formed by the reflux gas. The ratio of the powdered desulfurization flux 14 particles to be applied can be increased. FIG. 3 is an explanatory diagram for showing the lance spray angle θ, FIG. 3A shows a preferable value of the upper limit of the lance spray angle θ, and FIG. 3B shows a preferable value of the lower limit of the lance spray angle θ. Indicates. FIG. 4 is an explanatory diagram for illustrating the bubble arrival distance L _H (m) in the horizontal direction. FIG. 5 is an explanatory diagram for illustrating the bubble column spread angle θ ′. FIG. 6A is a top view showing the spraying range of the desulfurization flux when blowing the desulfurization flux without rotating the eccentric lance, and FIG. 6B is the case when blowing the desulfurization flux while rotating the lance. It is a top view which shows the spraying range of a desulfurization flux. FIG. 7 is a graph showing the relationship between the PB basic unit and the change in the desulfurization rate (before ln [S] PB / after [S] PB). FIG. 8 is a graph showing changes in the desulfurization rate due to changes in the Ca alloy concentration in the flux. FIG. 9 is an explanatory diagram showing a situation where the molten steel is refined by the RH apparatus.

  FIG. 1 is an explanatory view showing a situation where the molten steel 2 is desulfurized using the RH apparatus 20 according to the present invention, and FIG. 2 is an explanatory view showing a plume eye formed by the reflux gas 8. In the following description, the same parts as those of the RH device 1 shown in FIG.

  As shown in FIG. 1, in the present invention, the molten steel 2 is desulfurized by the RH-PB method.

  That is, a vacuum tank 4 is disposed above a ladle 3 that accommodates the molten steel 2, and a reflux gas 8 is supplied from a reflux gas blowing tuyere 7 provided in a rising pipe 5 provided in the lower part of the vacuum tank 4. Blow up.

As a result, the molten steel 2 is circulated from the powder top blowing lance 13 disposed inside the vacuum chamber 4 while the molten steel 2 is refluxed in the order of the ascending pipe 5, the vacuum tank 4, the downcomer pipe 6 and the ladle 3. The molten steel 2 is desulfurized by injecting a powdery desulfurization flux 14 into the molten metal surface using, for example, an inert gas such as Ar gas or N ₂ gas as a carrier gas.

  Thus, in the present invention, the addition method in which the desulfurized flux is placed on the molten steel 2 through the alloy addition hole 12 by the RH-PB method (powder blowing method using the powder top blowing lance 13). By blowing the powdery desulfurization flux 14 having a finer particle size, the reaction interface area between the particles of the desulfurization flux 14 and the molten steel 2 can be increased, and the reaction rate can be increased.

  In the present invention, an eccentric lance 13 in which the center direction of the powder blowing direction is inclined by a predetermined lance spray angle θ with respect to the direction of the lance center axis is used as the powder top blowing lance 13. That is, by using the eccentric lance 13 to decenter the blowing direction of the desulfurization flux 14 toward the hot water surface on the riser pipe 5 side and blowing the powdered desulfurization flux 14, as shown in FIG. On the molten steel 2 surface, the stirring force generated by the spout eye generated on the molten steel 2 surface of the plume eye (surface of the free surface naked hot water 17 excluding the slag 16) 15 generated by the reflux gas 8 on the 5 side Utilizing the flow of the molten steel 2 caused by the bubble breakage of the reflux gas 8, the desulfurization flux 14 is efficiently involved in the refluxing molten steel 2, and the proportion of the particles of the powdered desulfurization flux 14 contributing to the de-S reaction is determined. Can be increased.

FIG. 3 is an explanatory diagram for showing the lance spray angle θ, FIG. 3A shows a preferable value of the upper limit of the lance spray angle θ, and FIG. 3B shows a preferable value of the lower limit of the lance spray angle θ. Indicates. FIG. 4 is an explanatory diagram for showing the bubble arrival distance L _H (m) in the horizontal direction, and FIG. 5 is an explanatory diagram for showing the bubble column spread angle θ ′. A preferred range of the lance spray angle θ will be described with reference to FIGS.

It is desirable that the lance spray angle θ satisfies the expressions (1) and (2).
tanθ ≦ R / (Hlance-Y) (1)
{Rn + L _H- (αn + Y) × tanθ '} / (Hlance-Y) ≦ tanθ (2)
However,
Bath depth Y = Hs + Ls-α (m)
Molten steel height Hs = (Pa-Pr) / ρg (m)
θ: Spray angle of powder blast 13 (deg)
R: Inner diameter (m) of vacuum chamber 4 at the height of the hot water surface at the center of vacuum chamber 4
Hlance: Lance height (m) which is a vertical distance from the tip of the powder top blowing lance 13 to the center of the vacuum chamber 4
Y: Bath depth at the bottom center of vacuum chamber 4 (m)
Rn: Horizontal distance from the center of the bottom of the vacuum chamber 4 to the reflux gas blowing tuyere 7 (m)
L _H : Bubble arrival distance in the horizontal direction (m)
αn: Vertical distance (m) from the center of the bottom of the vacuum chamber 4 to the reflux gas injection tuyere 7 of the riser 5
θ ′: Bubble tower spread angle, 12-15 (deg)
Hs: Molten steel height (m) which is the vertical distance between the molten steel 2 in the center of the vacuum chamber 4 and the molten steel 2 in the ladle 3
Ls: Immersion depth of riser 5 into molten steel 2 (m)
α: Vertical distance from the center tank at the bottom of the vacuum chamber 4 to the tip of the riser 5 (m)
Pa: Atmospheric pressure (kPa)
Pr: Pressure inside the vacuum chamber 4 (kPa)
ρ: Specific gravity of molten steel 2 (g / cm ³ )
g: Gravitational acceleration (g / sec ² )
It is.
As shown in FIG. 3 (a), the upper limit of the lance spray angle θ is such that the side wall of the refractory in the vacuum chamber 4 meets the extension line of the central axis in the spray direction (the limit of landing of the molten steel 2). Point), R / (Hlance-Y) should be set.

On the other hand, as shown in FIG. 3 (b), the lower limit of the lance spray angle θ is {Rn + L _H − (αn + Y) × so that the powder spray range overlaps the estimated region of the rising region of the bubble column. It is desirable to set tanθ ′} / (Hlance-Y).

As shown in FIG. 4, the bubble arrival distance L _H (m) in the horizontal direction is the corrected fluid number Fr, _H , the nozzle diameter d _N (mm), and the gas flow velocity V at the reflux gas blowing tuyere 7. _{From H} (m / sec), L _H (m) = 3.7Fr, _H ^1/3 d _{N =} 3.7 {(ρg / ρL) × (V _H ² / d _N g)} ^1/3 d _N Is exemplified.

In addition, as shown in FIG. 5, the bubble tower spread angle θ ′ is assumed to be formed vertically from the position of the bubble arrival distance L _H (m), and the region has a bubble tower spread angle θ ′ = 12 to 15 Setting as ° is exemplified.

  In the present invention, the distance from the lance hole 18 at the tip of the powder top blowing lance 13 to the molten metal surface 19 of the molten steel 2 to be refluxed (that is, from the lance hole 18 at the tip of the powder top blowing lance 13 to the powder The distance L) between the extension of the central axis of the blowing lance 13 and the molten steel surface 19 of the molten steel 2 to be refluxed is set to 1.5 to 3.5 m. If the distance L is less than 1.5 m, the powder top blowing lance 13 is melted, while if it exceeds 3.5 m, the CaO particles of the desulfurization flux 14 blown in the vacuum chamber 4 are exhausted from the vacuum chamber 4. It is because it is attracted | sucked by 11 and dissipates and removal S efficiency cannot be improved.

Here, the fluctuating height H _steel of the molten metal surface 19 is a case where the pressure outside the vacuum chamber 4 is Pa, the pressure inside the vacuum chamber 4 is P, the density of the molten steel 2 is ρ, and the gravitational acceleration is g. Since H _steel = (Pa−P) / ρg, the distance L = the set height of the powder blowing lance 13 −H _steel = the set height of the powder blowing lance 13− (Pa−P) / ρg Asking.

  In the present invention, the powdered desulfurization flux 14 is further blown toward the molten steel 2 surface, which is located within 1 m from the position directly above the reflux gas blowing tuyere 7 in the horizontal direction. Thereby, the removal S efficiency can be increased.

In addition, it is preferable that the particle size of the desulfurization flux 14 is 10 ^{< -5} > -10 ^<-2> m. When the particle size of the desulfurization flux 14 is less than 10 ⁻⁵ m, the CaO particles of the desulfurization flux 14 blown in the vacuum chamber 3 are sucked into the exhaust system 11 of the vacuum chamber 3 and dissipated, thereby improving the deS-efficiency. On the other hand, when it is more than 10 ⁻² m, the reaction efficiency is lowered, and a low S steel having an S concentration of 50 ppm or less cannot be stably melted.

  Thus, according to the present invention, the de-S reaction efficiency in the RH-PB method can be increased, and the amount of low S steel 1 having an S concentration of 50 ppm or less is reduced without using fluorite having a large environmental load. The amount of desulfurization flux 14 used can be efficiently and stably melted.

  6A is a top view showing a spray range of the desulfurization flux 14 when the desulfurization flux 14 is blown without rotating the eccentric lance 13, and FIG. 6B is a desulfurization while rotating the eccentric lance 13. It is a top view which shows the spraying range of the desulfurization flux 14 in the case of blowing the flux 14. FIG.

  As shown in FIG. 6 (a) and FIG. 6 (b), the difference in the spraying range of the desulfurization flux 14 is shown in the present invention. It is desirable to reciprocate as the center of rotation. That is, during the powder blowing by the RH-PB method, the blowing direction of the desulfurization flux 14 is decentered by the eccentric lance 13 toward the hot water surface on the rising pipe 5 side as shown in FIG. As shown in FIG. 6B, the eccentric lance 13 is reciprocated (swinged) around its central axis as a rotation center, whereby the desulfurization flux 14 is attached to the molten steel 2 (the desulfurization flux 14 is deposited on the molten steel 2). Change the blowing position).

  Thereby, aggregation of the blown desulfurization flux 14 can be suppressed, and the spraying range of the desulfurization flux 14 can be expanded. In addition, the desulfurization reaction interfacial area between the molten steel 2 and the desulfurization flux 14 can be increased. In the present invention, these combine to accelerate the reaction of the desulfurization flux 14 and improve the desulfurization rate.

  It is desirable to reciprocate the eccentric lance 13 by 5 to 180 degrees at a central angle θ in the horizontal plane. When the rotation angle of the eccentric lance 1 is less than 5 deg, it is impossible to suppress the aggregation of the blown desulfurization flux 9 and to expand the spray range of the desulfurization flux 9, while the rotation angle of the eccentric lance 1 exceeds 180 deg. It is because it deviates from the area | region where the molten steel flow velocity is quick.

  Further, the rotational speed of the reciprocating rotation of the eccentric lance 13 is preferably 1 to 20 (deg / sec). When the rotational speed is less than 1 (deg / sec), the change in the powder injection direction becomes small, and it is impossible to suppress the aggregation of the blown desulfurization flux 9, and the rotation speed exceeds 20 (deg / sec). In this case, the effect of the spray range expansion effect due to rotation is reduced. However, even when blowing at a rotational speed of more than 20 (deg / sec), it is possible to obtain a desulfurization promoting effect by the rotation of the lance.

  FIG. 7 is a graph showing the relationship between the PB basic unit and the change in the desulfurization rate (before ln [S] PB / after [S] PB). In the graph of FIG. 7, “normal PB” indicates a conventional method using a normal lance instead of an eccentric lance, and “rising pipe direction PB” indicates the method of the present invention using an eccentric lance, and “rising pipe swing”. “PB” indicates the method of the present invention in which the eccentric lance is reciprocated.

  As shown in the graph of FIG. 7, the blowing amount of the desulfurization flux 14 can be reduced by about 10% by blowing the desulfurization flux 14 toward the hot water surface on the ascending pipe 5 side using the eccentric lance 13. Further, the blowing amount of the desulfurization flux 14 can be reduced by about 20% by blowing the desulfurization flux 14 while reciprocating the eccentric lance 13 around the lance center axis.

  Such a reduction in the blowing amount of the desulfurization flux 14 can reduce the environmental load by reducing the generation amount of steelmaking slag, reduce the cost required for the desulfurization flux 14, and increase the heating cost by reducing the temperature drop of the molten steel 2. (Al addition amount) can be reduced.

  Furthermore, in this invention, it is desirable for the powdery desulfurization flux 14 to contain CaO as a main component and to contain 10 to 30% by mass of a Ca-based alloy. The Ca concentration in the molten steel at the time of blowing can be adjusted by mixing the Ca-based alloy with the desulfurization flux 14 mainly composed of CaO and controlling the concentration of the Ca alloy in the desulfurization flux 14 to 10% by mass or more. As a result, the [Ca] concentration supplied to the molten steel 2 at the time of blowing can be increased to decrease the equilibrium S concentration, and the de-S rate can be improved as a condition for the de-S reaction to proceed easily. It can proceed efficiently.

Examples of the Ca-based alloy include Ca—Si, Ca—Al, and CaC ₂ . The mass ratio of CaO in the desulfurization flux 14 is, for example, 90% or more.

  FIG. 8 is a graph showing changes in the desulfurization rate due to changes in the Ca alloy concentration in the flux. In the graph of FIG. 8, “rising pipe direction PB” indicates the method of the present invention using an eccentric lance, and “Ca alloy concentration change in flux” means desulfurization flux with a changed concentration of Ca alloy contained in the eccentric lance. The method of the present invention blown from is shown.

  As shown in the graph of FIG. 8, the desulfurization efficiency can be further increased by blowing a desulfurization flux having a changed Ca alloy concentration from an eccentric lance.

  As described above, the desulfurization flux 14 used in the present invention is a low-S steel having an S concentration of 40 ppm or less using the powder blowing in the RH apparatus 20 without containing fluorite. The desulfurization flux 14 may contain fluorite as long as it can be efficiently and stably melted in the amount used, but the amount of environmental load is small and does not substantially cause a problem.

  In this way, according to the present invention, the S concentration is obtained by utilizing the powder blowing in the RH apparatus 20 as the secondary refining equipment, that is, by using the RH-PB method without using fluorite having a large environmental load. Can be efficiently and stably melted with a smaller amount of the desulfurization flux 14 used.

  Steel discharge temperature: 1600-1700 ° C., Steel output C concentration: 0.01-0.20 mass%, S concentration after decarburization: 0.0010-0.0050 mass% 1 to 3, CaO is added over the alloy addition hole 12 to adjust the basicity of the slag, and then the CaO-based desulfurization flux 14 powder is molten from the eccentric lance 13 to the molten steel. By blowing into 2, desulfurization treatment by RH-PB method was performed.

  Further, as a conventional example, CaO is added to the above molten steel using the RH apparatus 1 shown in FIG. Was blown into the molten steel 2 through the eccentric lance 13 to perform a desulfurization treatment by the RH-PB method.

  Conditions for this desulfurization treatment (molten steel treatment amount, reflux amount, flux blowing basic unit, lance powder blowing direction, test conditions, lance eccentric angle) and determination results (initial S concentration, end point S concentration, desulfurization rate / Table 1 shows the flux blowing basic unit and Ca-based alloy blending ratio.

  Test No. 1 in Table 1 In 1-4, the desulfurization flux 14 in which the mixing ratio of the Ca-based alloy is 30 mass% is an eccentricity in which the distance from the lance hole 18 at the tip to the intersection of the extension of the lance central axis and the molten steel 2 to be returned is set to 2 m While the eccentric lance 13 is reciprocatingly rotated at a central angle of 40 ° centered on the center axis of the lance from the lance 13 and blown at a spray angle θ of 5 °, the desulfurized flux 14 is horizontal from directly above the reflux gas blowing tuyere 7. It was blown toward the hot water surface existing within a distance of 1 m in the direction.

  Test No. 5 to 9, the desulfurization flux 14 having a Ca-based alloy blending ratio of 10% by mass is eccentrically set to a distance of 2 m from the lance hole 18 at the tip to the intersection of the extension of the lance central axis and the molten steel 2 to be refluxed. While the eccentric lance 13 is reciprocatingly rotated at a central angle of 40 ° centered on the center axis of the lance from the lance 13 and blown at a spray angle θ of 5 °, the desulfurized flux 14 is horizontal from directly above the reflux gas blowing tuyere 7. It was blown toward the hot water surface existing within a distance of 1 m in the direction.

  Test No. 10-14, the desulfurization flux 14 with a Ca-based alloy blending ratio of 10% by mass is eccentrically set to a distance of 2 m from the lance hole 18 at the tip to the intersection of the lance center axis extension and the molten steel 2 to be refluxed. The lance 13 was blown at a spray angle θ7 °, and the desulfurized flux 14 was blown toward the hot water surface existing within a range of 1 m in the horizontal direction from directly above the reflux gas blowing tuyere 7.

  Test No. In Nos. 15 to 19, the desulfurization flux 14 having a Ca-based alloy blending ratio of 10% by mass is eccentrically set to a distance of 2 m from the lance hole 18 at the tip to the intersection of the extension of the lance central axis and the molten steel 2 to be refluxed. The lance 13 was blown at a spray angle θ of 5 °, and the desulfurized flux 14 was blown toward the hot water surface existing within a range of 1 m in the horizontal direction from directly above the reflux gas blowing tuyere 7.

  Test No. 20 to 24, the desulfurization flux 14 with a Ca-based alloy blending ratio of 10% by mass is eccentrically set to a distance of 2 m from the tip lance hole 18 to the intersection of the lance central axis extension and the molten steel 2 to be refluxed. The lance 13 was blown at a spray angle θ3 °, and the desulfurization flux 14 was blown toward the hot water surface existing within 1 m in the horizontal direction from directly above the reflux gas blowing tuyere 7.

In Test Nos. 1 to 24,
The inner diameter R of the vacuum chamber 4 at the hot water level at the center of the vacuum chamber 4: 1.574 (m),
Lance height Hlance: 2.5 (m), which is the vertical distance from the tip of the powder top blowing lance 13 to the center of the vacuum chamber 4
Horizontal distance Rn: 0.44 (m) from the bottom center of the vacuum chamber 4 to the tuyere 7
Horizontal bubble arrival distance L _H : 0.06m),
Vertical distance αn: 1.22 (m) from the center of the bottom of the vacuum chamber 4 to the reflux gas injection tuyere 7 of the riser 5
Bubble tower spread angle θ ': 15 (deg),
The immersion depth Ls of the riser pipe 5 into the molten steel 2 is 0.5 (m),
Atmospheric pressure Pa: 101.325 (kPa),
Vacuum pressure in vacuum chamber 4 Pr: 5 (kPa),
Molten steel height, which is the vertical distance between the molten steel 2 in the center of the vacuum chamber 4 and the molten steel 2 in the ladle 3, is 1.40 (m) (when the pressure Pr in the chamber is 5 (kPa))
Vertical distance α from the bottom central tank of the vacuum chamber 4 to the tip of the rising pipe 5: 1.62 (m),
Specific gravity ρ of molten steel 2: 7 (g / cm ³ ),
Gravitational acceleration g: 9.80665 (g / sec ² ). Therefore, the bath depth Y at the center of the bottom of the vacuum chamber 4 was 0.28 (m). Therefore, for example, when the spray angle θ is 3 ° and the bubble column spread angle θ ′ is 12 °, the equation (1) is satisfied but the equation (2) is not satisfied.

  On the other hand, test no. In Nos. 25 to 28, the desulfurization flux 10 having a Ca-based alloy blending ratio of 10% by mass is set to a lance 9 in which the distance from the tip lance hole to the intersection of the extension of the lance central axis and the refluxed molten steel 2 is set to 2 m. The air was blown in the direction of the center axis of the lance (vertically downward).

  As shown in Table 1, test no. 1 to 24 are end point S concentration: 6 to 18 ppm, desulfurization rate / flux injection basic unit: 7.6 to 20.6% · ton / kg, and the RH-PB method has a large environmental load. It can be seen that a low S steel having an S concentration of 40 ppm or less could be efficiently and stably produced with a smaller amount of desulfurization flux 14 used.

  In particular, test no. 15-19 and Test No. 5 to 9, the amount of the desulfurization flux 14 used can be further reduced by reciprocating the eccentric lance 13 with the lance center axis as the center of rotation. 5-9 and test no. By comparing 1 to 4, the eccentric lance 13 is reciprocated around the center axis of the lance and the Ca alloy blending ratio in the desulfurized flux 14 is increased, thereby further reducing the amount of desulfurized flux 14 used. I understand.

  For this reason, according to this invention, the molten steel for pipe materials which requires sour resistance and HIC resistance including an oil well pipe and a line pipe can be provided at low cost, for example.

  On the other hand, test No. which is a conventional example. 25 to 28, the end point S concentration was 11 to 14 ppm, and a low S steel having an S concentration of 40 ppm or less could be produced, but the de-S ratio / flux blowing basic unit was 3.7 to 5.5% · ton. The amount of desulfurization flux 10 used cannot be reduced and the manufacturing cost is increased.

DESCRIPTION OF SYMBOLS 1 Conventional RH apparatus 2 Molten steel 3 Ladle 4 Vacuum tank 5 Rising pipe 6 Lowering pipe 7 Reflux gas blowing tuyere 8 Recirculation gas 9 Powder blowing lance 10, 14 Desulfurization flux 11 Exhaust system 12 Alloy addition hole 13 Powder Top blowing lance (eccentric lance)
15 Plume eye 16 Slag 17 Bare hot water 18 Lance hole 19 Hot water surface 20 RH device according to the present invention

Claims (8)

The molten steel is blown upward from a reflux gas blowing tuyere provided in a riser pipe provided at a lower portion of a vacuum chamber disposed above a ladle containing molten steel, the riser pipe, the riser pipe, While refluxing the vacuum tank, the downcomer provided in the lower part of the vacuum tank and the ladle in this order, from the powder top blowing lance placed inside the vacuum tank, In the method of desulfurizing the molten steel by blowing desulfurization flux,
As the powder top blowing lance, an eccentric lance in which the center direction of the powder blowing direction is inclined with respect to the direction of the lance central axis with respect to the lance spray angle,
The distance from the lance hole of the powder blowing lance to the intersection of the extension of the central axis of the powder blowing lance and the refluxed molten steel is 1.5 to 3.5 m,
A method for desulfurizing molten steel, in which the powdery desulfurization flux is blown toward the molten metal surface located within a distance of 1 m in the horizontal direction from immediately above the reflux gas blowing tuyere. The said lance spray angle (theta) is a desulfurization method of the molten steel of Claim 1 which satisfy | fills Formula (1) and Formula (2).
tanθ ≦ R / (Hlance-Y) (1)
{Rn + LH- (αn + Y) × tanθ '} / (Hlance-Y) ≦ tanθ (2)
However,
Bath depth Y = Hs + Ls-α (m)
Molten steel height Hs = (Pa-Pr) / ρg (m)
θ: Spray angle of powder blast lance (deg)
R: Inner diameter of the vacuum chamber (m) at the surface height of the center of the vacuum chamber
Hlance: Lance height (m), which is the vertical distance from the tip of the powder blasting lance to the center of the vacuum chamber
Y: Bath depth at the center of the bottom of the vacuum chamber (m)
Rn: Horizontal distance from the center of the bottom of the vacuum chamber to the reflux gas injection tuyere (m)
L _H : Bubble arrival distance in the horizontal direction (m)
αn: Vertical distance from the center of the bottom of the vacuum chamber to the reflux gas injection tuyere of the riser (m)
θ ′: Bubble tower spread angle, 12-15 (deg)
Hs: Molten steel height (m) which is the vertical distance between the molten steel in the center of the vacuum chamber and the molten steel in the ladle
Ls: Immersion depth of riser in molten steel (m)
α: Vertical distance from the center tank at the bottom of the vacuum chamber to the tip of the riser (m)
Pa: Atmospheric pressure (kPa)
Pr: Pressure inside the vacuum chamber (kPa)
ρ: Specific gravity of molten steel (g / cm ³ )
g: Gravitational acceleration (g / sec ² )
It is.   The molten steel desulfurization method according to claim 1 or 2, wherein the eccentric lance is reciprocally rotated about the center axis of the lance when the powdery desulfurization flux is blown.   The method for desulfurizing molten steel according to any one of claims 1 to 3, wherein the powdery desulfurization flux contains CaO as a main component and contains 10 to 30% by mass of a Ca-based alloy.   The method for desulfurizing molten steel according to claim 1, wherein the powdery desulfurization flux does not contain fluorite. A ladle containing molten steel;
A vacuum chamber disposed above the ladle;
An ascending pipe and a descending pipe provided in the lower part of the vacuum chamber and immersed in the molten steel;
A reflux gas blowing tuyere provided in the riser,
The molten steel was arranged inside the vacuum tank while refluxing the reflux gas from the tuyere of the reflux gas, and refluxing the molten steel in the order of the riser pipe, the vacuum tank, the downcomer pipe, and the ladle. In the apparatus for desulfurizing the molten steel by blowing a powdered desulfurization flux from the powder blasting lance to the molten steel surface to be refluxed,
The powder top blowing lance is an eccentric lance in which the center direction of the powder blowing direction is inclined by a lance spray angle with respect to the direction of the lance center axis, and the powdered desulfurized flux is supplied to the reflux gas blowing tuyere Blowing toward the molten steel surface within a distance of 1 m in the horizontal direction from directly above, and extending the center axis of the powder blowing lance and the reflux from the lance hole of the powder blowing lance The distance to the intersection with molten steel is 1.5 to 3.5 m. The molten steel desulfurization apparatus according to claim 6, wherein the lance spray angle θ satisfies the expressions (1) and (2).
tanθ ≦ R / (Hlance-Y) (1)
{Rn + L _H- (αn + Y) × tanθ '} / (Hlance-Y) ≦ tanθ (2)
However,
Bath depth Y = Hs + Ls-α (m)
Molten steel height Hs = (Pa-Pr) / ρg (m)
θ: Spray angle of powder blast lance (deg)
R: Inner diameter of the vacuum chamber (m) at the surface height of the center of the vacuum chamber
Hlance: Lance height (m), which is the vertical distance from the tip of the powder blasting lance to the center of the vacuum chamber
Y: Bath depth at the center of the bottom of the vacuum chamber (m)
Rn: Horizontal distance from the center of the bottom of the vacuum chamber to the reflux gas injection tuyere (m)
L _H : Bubble arrival distance in the horizontal direction (m)
αn: Vertical distance from the center of the bottom of the vacuum chamber to the reflux gas injection tuyere of the riser (m)
θ ′: Bubble tower spread angle, 12-15 (deg)
Hs: Molten steel height (m) which is the vertical distance between the molten steel in the center of the vacuum chamber and the molten steel in the ladle
Ls: Immersion depth of riser in molten steel (m)
α: Vertical distance from the center tank at the bottom of the vacuum chamber to the tip of the riser (m)
Pa: Atmospheric pressure (kPa)
Pr: Pressure inside the vacuum chamber (kPa)
ρ: Specific gravity of molten steel (g / cm ³ )
g: Gravitational acceleration (g / sec ² )
It is.   The molten steel desulfurization apparatus according to claim 6 or 7, wherein the powder top blowing lance is reciprocally rotatable around the center axis of the lance when the powdery desulfurization flux is blown.