WO2008023863A1

WO2008023863A1 - A ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of nitrogen and inserting method thereof

Info

Publication number: WO2008023863A1
Application number: PCT/KR2006/005406
Authority: WO
Inventors: Ki Kun Hong; Sung Woan Cho; Hee Ho Lee; Dong Sik Kim; Joo Hyun Park
Original assignee: Posco
Priority date: 2006-08-23
Filing date: 2006-12-12
Publication date: 2008-02-28
Also published as: EP2054533A4; JP2010501726A; JP5079005B2; EP2054533A1

Abstract

The present invention relates to an apparatus for inserting ferro-alloy and inserting method without submerging into slag and liquid steel for reducing absorption of oxygen and absorption of nitrogen capable of inserting ferro-alloy by minimizing an incorporation of oxygen and nitrogen in a ladle treatment process of a steelmaking process upon performing a steelmaking operation, comprising: a supplying tube supplied with ferro-alloy from a hopper to insert it to a ladle and subdivided into an upper part, an inclined middle part, a lower part and having a predetermined hollow; a branched and mounted inert gas blocking unit communicated with the middle of the supplying unit and blocking, as first inert gas, air flowed in at the same time when the ferro-alloy is inserted; a branched and mounted inert gas supplying unit communicated with the base end part of the lower part of the supplying tube and blowing a second inert gas on an inserting path of the ferro-alloy; an inert gas injecting unit packing any one of the lower outer sides of the supplying unit relative to axis direction of the lower thereof and injecting a third inert gas toward the end part of the lower part thereof; and a diffusing unit diffusing the third inert gas injected while packing the supplying tube from the gas injecting unit into the end part of the supplying tube.

Description

A FERRO-ALLOY INSERTING APPARATUS WITH REDUCED ABSORPTION OF OXYGEN AND ABSORPTION OF NITROGEN AND INSERTING METHOD THEREOF

Background Art

[ 1 ] 1. Field of the Invention

[2] The present invention relates to an apparatus for inserting ferro-alloy and inserting method thereof reducing absorption of oxygen and absorption of nitrogen, and more specifically, to an apparatus for inserting ferro-alloy and inserting method thereof with reduced absorption of oxygen and absorption of nitrogen, which inserts ferro-alloy by minimizing an incorporation of oxygen and nitrogen in a ladle treatment (LT) process of a steelmaking process, upon performing a stainless steelmaking operation.

[3]

[4] 2. Description of Related Art

[5] In general, in order to refine stainless steel, stainless molten steel is subject to continuous cast of argon oxygen decarburization (AOD) refinement through an electric furnace and then a ladle treatment such as a ladle refining process or a ladle furnace process.

[6] Herein, the molten stainless steel may further be subject to vacuum oxygen decarburization (VOD) refining after the AOD refining.

[7] Prior to performing the continuous cast, in the ladle treatment process in such serial processes, in the ladle treatment process the insertion of ferro-alloy such as Al, Fe-Si, Fe-Cr, Fe-Ni, Ti, and coolant into the molten steel in order to secure the targets of composition and temperature of the molten steel, and a gas agitating refinement in order to make ingredient and temperature uniform and perform floating separation of inclusions are performed at the same time.

[8] Since the insertion of the ferro-alloy is made by making the molten steel covered by slag the naked eye state to expose it in air, the reoxidation of the molten steel and the degradation of the purity of the molten steel due to absorption of nitrogen and absorption of oxygen occur, and nozzle clogging and surface defects during the making steel frequently occur upon casting.

[9] FIG. 1 is a graph showing variations of nitrogen pick-up in molten steel according to analyzed composition by using a conventional ferro-alloy inserting apparatus in ladle.

[10] FIG. 1 shows the absorption of nitrogen concentration before/after the insertion of the ferro-alloy in the ladle for the stainless 409 steel (C: 0.010% or less, N: 0.010%, Cr: 11 to 12%, Ni: 0.5% or less, Si: 0.6% or less, Mn: 0.6% or less) of 90 tons, which is subject to an electric furnace refining and a AOD refining. That is, FlG. 1 shows increase and decrease variations of the difference of nitrogen concentration after the insertion of the ferro-alloy in the ladle and nitrogen concentration before the insertion of the ferro-alloy in the ladle.

[11] FlG. 1 shows that the absorption of nitrogen concentration increases up to between

0 and 28 ppm and the absorption of nitrogen of 9.9ppm in average occurs. This means that oxygen in the molten steel increases. Accordingly, the degradation of continuous casting sequences due to increase of impurities such the oxide of the molten steel and the possibility to generate deviation in quality increases.

[12] Since the steel grades experiencing the VOD process are necessarily subject to the ladle treatment process in order to achieve the targets of temperature and ingredient, the problem of the absorption of oxygen and the absorption of nitrogen caused upon inserting the ferro-alloy in the ladle has seriously an effect on nozzle clogging and surface quality of a product upon casting, by degrading the purity of the molten steel due to reoxidation and absorption of nitrogen.

[13] Although using slag covering molten steel on the upper side of the molten steel in order to minimize the generation of the absorption of nitrogen, as the slag is getting more, it is not evitable to secure the plume eye by gas agitation for inserting the ferroalloy. Thereby, the generation problem of the absorption of nitrogen and the re- oxidation still remains when inserting the ferro-alloy.

[14] That is, the reoxidation products such as high melting point oxides of TiO (melting point: about 1830⁰C), CaO-TiO -based (melting point : about 1930°C), Al O (melting point : about 2020⁰C), etc. among the molten steels by the reoxidation and the nitrides of TiN (melting point: about2930°C) generated by the absorption of nitrogen degrades the purity of the final product upon inserting the ferro-alloy, the nozzle clogging occurs upon casting to degrade continuous-casting productivity, and the surface defect of the steel of a hot rolled coil and a cold rolled coil occurs upon pressing.

[15] In order to solve the problem, an apparatus and a method for preventing absorption of nitrogen and reoxidation upon inserting ferro-alloy into a ladle is disclosed in US Patent No. 5,211,744, entitled "an apparatus and method for inserting ferro-alloy of molten steel into a ladle. However, the cited patent has problems as follows.

[16] First, ferro-alloy is directly inserted into molten steel through an inserting tube by submerging the ferro-alloy inserting hole so that there is almost no reoxidation and absorption of nitrogen. However, it has problems of operation efficiency due to degradation of the ferro-alloy inserting tube and maintenance due to a frequent replacement of the inserting hole.

[17] Also, corrosion phenomenon due to reaction between inserting refractory tube and slag/liquid steel and erosion phenomenon of refractory tube by melt stirring, may cause to decrease the life of inserting refractory tube. This corrosion and erosion phenomenon also can increase total oxygen content by entrapped refractory particles and reaction in liquid steel. In addition to increasing maintenance expense, difficulties of maintenance can be significantly increased by frequent exchanges and corrosion occurrences of inserting refractory tube. Therefore, the cited U.S. patent has many constraints to apply to an actual operation required for high productivity and quality.

[ 18] Also, Japanese Patent Laid-Open No. 1993-009552, entitled "top blowing lance type ladle refining Apparatus solves the problems of absorption of nitrogen of molten steel and an increase of slag due to reoxidation of molten steel, etc. using a submerging tube. However, since all the operation are performed at a high temperature molten steel above 1550°C, this has effects to prevent the absorption of nitrogen and the re- oxidation, but has problems of a lifetime of a submerging tube, its maintenance. Because corrosion phenomenon due to reaction between inserting refractory tube and slag/liquid steel and erosion phenomenon of refractory tube by melt stirring, may cause to decrease the life of inserting refractory tube same as U.S. patent No. 5,211,744. This corrosion and erosion phenomenon also can increase total oxygen content by entrapped refractory particles and reaction in liquid steel. In addition to increasing maintenance expense, difficulties of maintenance can be significantly increased by frequent exchange and corrosion occurrences of inserting refractory tube.

[19]

[20] SUMMARY OF THE INVENTION

[21] Accordingly, the present invention has been proposed to solve the problems as described above. It is an object of the present invention to provide an apparatus for inserting ferro-alloy and inserting method thereof with reduced absorption of oxygen and absorption of nitrogen, which can reduce absorption of nitrogen of molten steel by minimizing an incorporation of oxygen and nitrogen, and improve the cleanness by restricting reoxidation, upon inserting coolant and various ferro-alloys into molten stainless steel without submerging into slag and liquid steel, in a ladle during the stainless steelmaking process for achieving the targets of temperature and ingredient.

[22] In order to accomplish the objects, there is provided a ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of nitrogen, comprising: a supplying tube supplied with ferro-alloy from a hopper to insert it into a ladle and subdivided into a upper part, an inclined middle part, a lower part and having a predetermined hollow; a branched and mounted inert gas blocking unit communicated with the middle of the supplying unit and blocking, as first inert gas, air flowed in at the same time when the ferro-alloy is inserted; a branched and mounted inert gas supplying unit communicated with the base end part of the lower part of the supplying tube and blowing a second inert gas on an inserting path of the ferro-alloy; an inert gas injecting unit packing any one of the lower outer sides of the supplying unit relative to axis direction of the lower thereof and injecting a third inert gas toward the end part of the lower part thereof; and a diffusing unit diffusing the third inert gas injected while packing the supplying tube from the gas injecting unit into the end part of the supplying tube.

[23] Herein, the supplying tube is subdivided into an upper part supplying tube, a middle part supplying part, and a lower part supplying tube and inclines from its base end part to its end part, the inert gas supplying unit is communicated with the base end part of the lower supplying tube, and the inert gas injecting unit is constituted to pack any one of the regions of the lower part supplying tube.

[24] At this time, the inert gas supplying unit packs any one of the outer side of the lower part supplying tube relative to axis direction of the lower part supplying tube and is a single ring structure that injects the third inert gas into the end part direction by packing the lower part supplying tube, the inert gas injecting unit packs any one of the outer sides of the lower part supplying tube relative to the axis direction of the lower part supplying tube and may be a composite ring structure configured of a first ring structure that uniformly distributes the third inert gas, a second ring structure that packs the lower part supplying tube and injects the third inert gas uniformly distributed in the first ring structure into the end part direction, and a plurality of connectors that communicate the first ring structure with the second ring structure.

[25] In this case, the inert gas injecting unit is formed with predetermined slits in the end part of the lower part supplying tube, wherein the width of the slit is 3.0mm or less, preferably 0.1mm or more to 3.0mm or less.

[26] And, an inner part diffusing angle between the inside of the diffusing unit and the inside of the lower part supplying tube is above 0°to below 90°.

[27] Further, an inserting method of ferro-alloy with reduced absorption of oxygen and absorption of nitrogen receiving molten steel covered by the slag in a ladle installed with porous plug in a bottom part thereof and inserting ferro-alloy stored into a hopper from the upper part of the ladle in the molten steel through the upper part, middle part, and lower supplying tubes, including the steps of: falling the end part of the lower part supplying tube; inserting a first inert gas in the middle supplying tube; inserting a second inert gas into the base end part of the lower part supplying tube; providing a third inert gas injected in a end part direction by packing the outer side of the lower supplying tube; and inserting the ferro-alloy into the upper part, middle part, and lower part supplying tubes in sequence.

[28] Where the falling of the lower part supplying tube without submerging into slag and liquid steel is defined by the following equation 1.

[29] [Equation 1]

[30] y=h_o-x-c

[31] (Where y is a distance[mm] from the inner side of the cover of the ladle to the end part of the lower part supplying part; h is a distance [mm] from the inner side of the cover of the ladle to the bottom part of the ladle; x is a distance [mm] from the bottom part of the ladle to the surface of the molten steel; c is a distance[mm] from the surface of the molten surface to the end part of the lower part supplying tube)

[32] The distance x from the bottom part of the ladle is defined by the following equation 2.

[33] [Equation 2]

[34] w=-51.1*ln(x)+454

[35] (where w is ton of the molten steel)

[36] Also, the end part of the lower part supplying tube can be moved to form 1 to 3m distances with respect to the surface of the molten steel.

[37] At this time, the injection amount per unit time of the second inert gas may be 5 to

50Nm /hr and the injection amount per unit time of the third inert gas may be 10 to 100Nm³/hr.

[38] Advantageous Effects

[39] As described above, the present invention to provide an apparatus for inserting ferro-alloy and inserting method thereof with reduced absorption of oxygen and absorption of nitrogen, which can reduce absorption of nitrogen of molten steel by minimizing an incorporation of oxygen and nitrogen, and improve the cleanliness by restricting reoxidation, upon inserting coolant and various ferro-alloys into molten stainless steel in a ladle during the stainless steelmaking process for achieving the targets of temperature and compositions.

[40]

Brief Description of the Drawings

[41] FIG. 1 is a graph showing variation of nitrogen in molten steel according to oxide compositionof a surface of molten steel by a conventional ferro-alloy inserting apparatus;

[42] FIG. 2 is a schematic view showing a ferro-alloy inserting apparatus according to the present invention;

[43] FIG. 3 is a partial enlarged view showing "A" part of FIG. 2;

[44] FIG. 4 is a partial enlarged view showing "B" part of FIG. 2;

[45] FIG. 5 is a general acting concept view of a ferro-alloy inserting apparatus according to one embodiment of the present invention; [46] FIG. 6 is a schematic view showing a ferro-alloy inserting apparatus according to this embodiment of the present invention;

[47] FIG. 7 is a partial enlarged view showing "A" part of FIG. 6;

[48] FlG. 8 is a partial enlarged view showing "B " part of FlG. 6;

[49] FlG. 9 is a general acting concept view of a ferro-alloy inserting apparatus according to one embodiment of the present invention; [50] FIG. 10 is a view comparing flow velocity for a circumference of a lower part supplying tube in one embodiment of the present invention and this embodiment of the present invention; [51] FIG. 11 is a schematic view showing a ferro-alloy inserting apparatus with reduced absorption of oxidation and absorption of nitrogen according to the preferred embodiment of the present invention;

[52] FlG. 12 is a partial enlarged view showing "A" part of FlG. 11 ;

[53] FIG. 13a and FIG. 13b are partial enlarged views each showing "B" part of FlG. 11 by applying one embodiment of the present invention and this embodiment of the present invention;

[54] FlG. 14 is a partial cross-sectional view showing a diffusing unit of FlG. 11 ;

[55] FIG. 15 is a general acting concept view showing a ferro-alloy inserting apparatus having a diffusing unit according to the preferred embodiment of the present invention; [56] FlG. 16 is a graph showing variation of nitrogen concentration in molten steel before/after ferro-alloy in a ladle; [57] FIG. 17 is a graph showing variation of oxygen concentration in molten steel before/after ferro-alloy in a ladle; [58] FlG. 18 is a graph showing partial oxygen pressure from a lower part supplying tube to a surface of molten steel upon inserting ferro-alloy into a ladle; [59] FlG. 19 is a graph showing surface defect rate of a stainless hot rolled coil in an example of the prior art and an example of the present invention; [60]

[61] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[62] Hereinafter, an apparatus for inserting ferro-alloy and an inserting method thereof with absorption of oxygen and absorption of nitrogen according to one embodiment of the present invention will be described with reference to the drawings [63] FlG. 2 is a schematic view showing a ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of nitrogen according to one embodiment of the present invention. [64] Referring to FIG. 2, in order to achieve the targets of temperature and ingredient for casting in a ladle refining stand, coolant and ferro-alloy F are weighed and inserted into a ladle 22 in which molten steel M, of which decarburization is completed in a de- carburization vessel such as AOD, VOD and a converter, is dipped.

[65] The ferro-alloy F is stored in a hopper 3 from a ferro-alloy storing hopper 1 by means of a conveyer belt 2, and an opening and closing valve 4 is constituted to control the insertion of the ferro-alloy F into the hopper 3 in which the ferro-alloy F is stored. The ferro-alloy F is inserted from the hopper 3 into the molten steel M through supplying tubes 101, 102 and 103.

[66] The ladle 22 receiving the molten steel M comprises a ladle cover 21 to prevent oxidation by blocking the atmosphere and to enables to insert the ferro-alloy F, and the supplying tube 103 is constituted by penetrating the ladle cover 21.

[67] In one embodiment of the present invention, the supplying tubes 101, 102 and 103 are subdivided into an upper part supplying tube 101, a middle part supplying tube 102 and a lower part supplying tube 103, and the middle part supplying tube 102 may be inclined according to the positions of the hopper 3 and the factory facilities, as shown in the attached drawings.

[68] On any one region of the middle part supplying tube 102, an inert gas blocking unit

123 comprising a first inert gas supplying unit 124, is branched and mounted so that the inserting path of the ferro-alloy F can keep an inert atmosphere by blocking air including oxygen and nitrogen flowed in at the same time when the ferro-alloy F is supplied from the hopper 3.

[69] Referring to FIG. 3, the inert gas blocking unit 123 is branched and mounted to form an angle θ with respect to a base end part of the middle part supplying tube 102 to be above 90° to below 180° so that it is reversely injected to the direction that the insertion of the ferro-alloy F is progressed for an efficient blocking of air to be flowed in.

[70] The ferro-alloy F removes a part of slag S in the upper part of the molten steel to be freely fallen to a place to be plume eye by means of the inert gas such as Ar strongly blown from a porous plug 23 previously installed in the bottom part of the ladle 22.

[71] At this time, the ingredient of the molten steel M is represented by weight % as follows: C: 0 to 0.05%, N: 0 to 0.070%, Si: p to 4%, Ti: 0 to 0.5%, S: below 0.030%, P: below 0.025%, Cr: 11.0 to 30.0%, Ni: 0 to 36%. The molten steel M may be molten steel of stainless steel such as AISI reference stainless 304, 316L, 430, 446 and 447 steel composed of other ingredients. As the molten steel M, other steels suffered from ferro-alloy inserting treatment may be used.

[72] In order to insert the ferro-alloy F into the molten steel M, the insertion hole of the lower part supplying tube 103 falls to the side of the molten steel 31 through a length controlling unit 113 without submerging into slag and liquid steel.

[73] The length controlling unit 113 may usually be a member capable of controlling length, and preferably, it is constituted to raise and fall the end part of the lower part supplying unit 103 positioned right on the ladle 22, that is, only the injection hole.

[74] The supplying tube, more specifically, the end part of the middle part supplying tube 102 and/or the base end part of the lower part supplying tube 103 are communicated with an inert gas supplying unit 133 comprising a second inert gas supplying unit 134 so that an inert gas atmosphere is created up to the end part of the lower part supplying unit 103 when the ferro-alloy F is inserted.

[75] The inert gas supplying unit 133 blows the second inert gas supplied from the second inert gas supplying unit 134 to be jet from the end part of the lower part supplying tube 103 so that the inert atmosphere is created on the path of the lower part supplying tube 103 when the ferro-alloy F is inserted, and the inert atmosphere is kept up to the surface of the molten steel therefrom when the second inert gas is jet from the end part of the lower part supplying tube 103.

[76] The outer side of the lower part supplying tube 103, more specifically, the circumference of the hollow cylindrical lower part supplying tube 103 is provided with a single ring structure 150 forming the same axis with the lower part supplying tube 103 to pack it and comprising a third inert gas supplying unit 154.

[77] Referring to FIG. 4, the single ring structure 150 is supplied with the third inert gas from the third inert gas supplying unit 154 to injected closely to the circumference so that a third inert gas column is formed along with the outer circumference of the lower part supplying unit 103.

[78] The third inert gas supplying unit 154 may be installed in one or two or several depending on facilities.

[79] In the lower part of the single ring structure 150, that is, in the side of the end part of the lower part supplying tube 103 a predetermined slit 151 is formed so that the third inert gas is injected through it. The slit 151 may be a point slit and preferably, a line slit 151 so that the third inert gas is uniformly injected over the whole circumference of the lower part supplying tube 103.

[80] Also, preferably, the third inert gas column is progressed in a direction to the end part of the lower part supplying tube 103 along with the outer circumference of the lower part supplying tube 103 and is extended from the end part to the molten steel M so that it keeps the progressing path of the ferro-alloy F the inert atmosphere, together with the first inert gas and the second inert gas ejected from the inner side of the end part of the lower pat supplying tube 103.

[81] In order that the third inert gas is injected while keeping the inject shape up to the surface of the molten steel M, it is preferable that the slit 151 is below 3.0mm in width.

[82] When the width of the slit 151 exceeds 3.0mm, the flow velocity becomes slow by means of a continuous theorem so that the third inert gas can be dispersed before arriving on the surface of the molten steel M. [83] When the width of the slit 151 is below 0.1mm, it causes a problem that the sufficient amount of flow is not able to be dispersed or the clogging by means of CaO powder, etc., injected after the completion of the ladle treatment is happened. Therefore, the most preferable width of the slit 151 is 0.1mm or more to 3.0mm or less.

[84] FlG. 5 is a general acting concept view of a ferro-alloy inserting apparatus according to one embodiment of the present invention.

[85] Referring to FIG. 5, the ferro-alloy F is entered in the upper part supplying tube 101 to be inserted into the molten steel M through the middle part supplying tube 102 and the lower part supplying tube 103.

[86] When the ferro-alloy F passes through the middle part supplying tube 102, the first inert gas is injected by means of the inert gas blocking unit 123 to block the air entered in simultaneously with the ferro-alloy F (IGl).

[87] The first inert gas may be 8 group gases such as nitrogen or Ar, and more preferably, Ar in consideration of possibility of absorption of nitrogen and manufacturing cost. Also, in the case of austenitic steel grades, nitrogen may be used.

[88] When the ferro-alloy F passes through the lower part supplying tube 103, the second inert gas supplied through the inert gas supplying unit 133 keeps the inserting path of the ferro-alloy F from the base end part of the lower part supplying tube 103 to the surface of the molten steel M the inert atmosphere (IG2).

[89] The second inert gas may be 8 group gases, and more preferably, Ar. In the case that steel grade is 300 series austenite, nitrogen may be also used.

[90] Also, the third inert gas is dispersed from the outer side of the end part of the lower part supplying tube 103 through the single ring structure 150 to prevent the dispersion of the second inert gas, keeping the inserting path of the ferro-alloy F the inert atmosphere (IG3).

[91] The third inert gas may be 8 group gases, and more preferably, Ar. Also, since the third inert gas allows the flow (IG2) of the second inert gas ejected from the inner side of the lower part supplying tube 103 to be kept in the outer side thereof, it is preferable that the flow velocity of the third inert gas is faster than that of the second inert gas or the injecting pressure of the third inert gas is greater than that of the second inert gas.

[92] FlG. 6 is a schematic view showing a ferro-alloy injecting apparatus according to this embodiment of the present invention.

[93] Referring to FIG. 6, in order to achieve the targets of temperature and ingredient for casting in a ladle refining stand, coolant and ferro-alloy F are weighed and inserted into a ladle 22 in which molten steel M, of which decarburization is completed in a de- carburization vessel such as AOD, VOD and a converter, is dipped.

[94] The ferro-alloy F is stored in a hopper 3 from a ferro-alloy storing hopper 1 by means of a conveyer belt 2, and an opening and closing valve 4 is constituted to control the insertion of the ferro-alloy F into the hopper 3 in which the ferro-alloy F is stored. The ferro-alloy F is inserted from the hopper 3 into the molten steel M through supplying tubes 301, 302 and 303.

[95] The ladle 22 receiving the molten steel M comprises a ladle cover 21 to prevent oxidation by blocking the atmosphere and to enables to insert the ferro-alloy F, and the supplying tube 303 without submerging into slag is constituted by penetrating the ladle cover 21.

[96] In one embodiment of the present invention, the supplying tubes 301, 302 and 303 are subdivided into an upper part supplying tube 301, a middle part supplying tube 302 and a lower part supplying tube 303, and the middle part supplying tube 302 may be inclined according to the positions of the hopper 3 and the factory facilities, as shown in the attached drawings.

[97] On any one region of the middle part supplying tube 302, an inert gas blocking unit

323 comprising a first inert gas supplying unit 324, is branched and mounted so that the inserting path of the ferro-alloy F can keep an inert atmosphere by blocking air including oxygen and nitrogen flowed in at the same time when the ferro-alloy F is supplied from the hopper 3.

[98] Referring to FIG. 7, the inert gas blocking unit 123 is branched and mounted to form an angle θ with respect to a base end part of the middle part supplying tube 302 to be above 90° to below 180° so that it is reversely injected to the direction that the insertion of the ferro-alloy F is progressed for an efficient blocking of air to be flowed in.

[99] The ferro-alloy F removes a part of slag S in the upper part of the molten steel to be freely fallen to a place to be plume eye by means of the inert gas such as Ar strongly blown from a porous plug 23 previously installed in the bottom part of the ladle 22.

[100] At this time, the ingredient of the molten steel M is represented by weight % as follows: C: 0 to 0.05%, N: 0 to 0.070%, Si: p to 4%, Ti: 0 to 0.5%, S: below 0.030%, P: below 0.025%, Cr: 11.0 to 30.0%, Ni: 0 to 36%. The molten steel M may be molten steel of stainless steel such as AISI reference stainless 304, 316L, 430, 446 and 447 steel composed of other ingredients. As the molten steel M, other steels suffered from ferro-alloy inserting treatment may be used.

[101] In order to insert the ferro-alloy F into the molten steel M, the insertion hole of the lower part supplying tube 303 falls to the side of the molten steel 31 through a length controlling unit 313.

[ 102] The length controlling unit 313 may usually be a member capable of controlling length, and preferably, it is constituted to raise and fall the end part of the lower part supplying unit 303 positioned right on the ladle 22, that is, only the injection hole.

[103] The supplying tube, more specifically, the end part of the middle part supplying tube 302 and/or the base end part of the lower part supplying tube 303 are communicated with an inert gas supplying unit 333 comprising a second inert gas supplying unit 334 so that an inert gas atmosphere is created up to the end part of the lower part supplying unit 303 when the ferro-alloy F is inserted.

[104] The inert gas supplying unit 333 blows the second inert gas supplied from the second inert gas supplying unit 334 to be jet from the end part of the lower part supplying tube 303 so that the inert atmosphere is created on the path of the lower part supplying tube 303 when the ferro-alloy F is inserted, and the inert atmosphere is kept up to the surface of the molten steel therefrom when the second inert gas is jet from the end part of the lower part supplying tube 303.

[105] The outer side of the lower part supplying tube 303, in more detail, the circumference of the hollow cylindrical lower part supplying tube 303 is provided with a composite ring structure 350 forming the same axis with the lower part supplying tube 303 to pack it and comprising a third inert gas supplying unit 354.

[106] Referring to FIG. 8, the composite ring structure 350 is supplied with the third inert gas from the third inert gas supplying unit 354 to injected closely to the circumference so that a third inert gas column is formed along with the outer circumference of the lower part supplying unit 103.

[107] The third inert gas supplying unit 354 may be installed in one or more depending on facilities.

[108] The composite ring structure 350 comprises a first ring structure 355 uniformly distributing the third inert gas to the circumference of the lower part supplying tube 303, and a second ring structure 353 communicated with the first ring structure by means of several connectors 352.

[109] In the first ring structure 355 packing the circumference of the lower part supplying tube 303, the third inert gas supplied from the third inert gas supplying unit 354 is uniformly distributed in a circumferential direction of the lower part supplying tube 303. To this end, the opposite side to the side connected with the third inert gas supplying unit 354 may have a non-communicated shape.

[110] The third inert gas almost uniformly distributed in the first ring structure 355 along the circumference of the lower part supplying tube 303 is supplied to the second ring structure 353 through several connectors 352 constituted to be uniform to the first ring structure 355.

[Ill] In the lower part of the second ring structure 353 of the composite ring structure

350, that is, in the side of the end part of the lower part supplying tub 303 a predetermined slit 351 is formed so that the third inert gas is injected through it. The slit 351 may be a point slit and preferably, a line slit 351 so that the third inert gas is uniformly injected over the whole circumference of the lower part supplying tube 303. [112] Also, preferably, the third inert gas column is progressed in a direction to the end part of the lower part supplying tube 303 along with the outer circumference of the lower part supplying tube 303 and is extended from the end part to the molten steel M so that it keeps the progressing path of the ferro-alloy F the inert atmosphere, together with the first inert gas and the second inert gas ejected from the inner side of the end part of the lower pat supplying tube 303.

[113] In order that the third inert gas is injected while keeping the inject shape up to the surface of the molten steel M, it is preferable that the slit 351 is below 3.0mm in width.

[114] When the width of the slit 351 exceeds 3.0mm, the flow velocity becomes slow by means of a continuous theorem so that the third inert gas can be dispersed before arriving on the surface of the molten steel M.

[115] When the width of the slit 351 is below 0. lmm, it causes a problem that the sufficient amount of flow is not able to be dispersed or the flow velocity is excessively quick so that the clogging of the flow of the third inert gas is happened. Therefore, the more preferable width of the slit 351 is 0.1mm or more to 3.0mm or less.

[116] FIG. 9 is a general acting concept view of a ferro-alloy inserting apparatus according to one embodiment of the present invention.

[117] Referring to FIG. 9, the ferro-alloy F is entered in the upper part supplying tube 301 to be inserted into the molten steel M through the middle part supplying tube 302 and the lower part supplying tube 303.

[118] When the ferro-alloy F passes through the middle part supplying tube 302, the first inert gas dispersed by means of the inert gas blocking unit 323 blocks the air flowed in simultaneously with the ferro-alloy F (IGl).

[119] The first inert gas may be 8 group gases such as nitrogen or Ar, and more preferably, Ar in consideration of possibility of absorption of nitrogen and manufacturing cost. Also, in the case of austenitic steel grade, nitrogen may be used.

[120] When the ferro-alloy F passes through the lower part supplying tube 303, the second inert gas supplied through the inert gas supplying unit 333 keeps the inserting path of the ferro-alloy F from the base end part of the lower part supplying tube 303 to the surface of the molten steel M the inert atmosphere (IG2).

[121] The second inert gas may be 8 group gases, and more preferably, Ar. In the case that steel grade is 300 series austenite, N may be also used.

[122] Also, the third inert gas is dispersed from the outer side of the end part of the lower part supplying tube 103 through the composite ring structure 350 to prevent the dispersion of the second inert gas, keeping the inserting path of the ferro-alloy F the inert atmosphere (IG3).

[123] The third inert gas may be 8 group gases, and preferably, Ar. Also, since the third inert gas allows the flow (IG2) of the second inert gas ejected from the inner side of the lower part supplying tube 303 to be kept in the outer side thereof, it is preferable that the flow velocity of the third inert gas is faster than that of the second inert gas or the injecting pressure of the third inert gas is greater than that of the second inert gas.

[124] FlG. 10 is a view comparing flow velocity for a circumference of a lower part supplying tube in one embodiment of the present invention and this embodiment of the present invention.

[125] As in (a), the flow velocity is significantly reduced as progressing from the side (0) installed with the third inert gas supplying unit 154 to the side (180) opposite thereto, relative to the circumference of the lower part supplying tube 103. This is because the third inert gas is injected as it is without distributing the third inert gas supplied by using the single ring structure 150 to the circumferential direction.

[126] However, in this embodiment of the present invention, as in (b), the flow velocity can be even further reduced as progressing from the side (0) installed with the third inert gas supplying unit 354 to the side (180) opposite thereto, relative to the circumference of the lower part supplying tube 303. In the composite ring structure 350 of this embodiment unlike the single ring structure 150 of the one embodiment, the uniform distribution of the third inert gas to the circumferential direction is achieved.

[127] The flow velocity in the (b) case is uniform as a whole, as compared with the (a) case that the non-uniform region of the flow velocity is 50% with respect to the whole region.

[128] The composite ring structure 350 can includes a plurality of ring structures within the technical scope disclosed in the present invention, depending on the precision of the distribution of the flow velocity required for the process. That is, the composite ring structure having natural number of ring structures such as a third ring structure, a fourth ring structure, or the like can be adopted, in addition to the composite ring structure 350 configured of the first ring structure 355 and the second ring structure 353.

[129] The third inert gas supplying unit can also be communicated with the composite structures 350 of more than two as in the technical scope so that the amount of flow is uniformly distributed to the circumferential direction as described above. However, there may be the non-uniformity of the flow velocity even in this case.

[130] Hereinafter, an apparatus for inserting ferro-alloy according to the preferred embodiment of the present invention will be described with reference to the attached drawings.

[131] FIG. 11 is a schematic view showing a ferro-alloy inserting apparatus with reduced absorption of oxidation and absorption of nitrogen according to the preferred embodiment of the present invention.

[ 132] Referring to FIG. 11 , in order to achieve the targets of temperature and ingredient for casting in a ladle refining stand, coolant and ferro-alloy F are weighed and inserted into a ladle 22 in which molten steel M, of which decarburization is completed in a de- carburization vessel such as AOD, VOD and a converter, is dipped.

[133] The ferro-alloy F is stored in a hopper 3 from a ferro-alloy storing hopper 1 by means of a conveyer belt 2, and an opening and closing valve 4 is constituted to control the insertion of the ferro-alloy F into the hopper 3 in which the ferro-alloy F is stored. The ferro-alloy F is inserted from the hopper 3 into the molten steel M through supplying tubes 501, 502 and 503.

[134] The ladle 22 receiving the molten steel M comprises a ladle cover 21 to prevent oxidation by blocking the atmosphere and to enables to insert the ferro-alloy F, and the supplying tube 503 without submerging into slag is constituted by penetrating the ladle cover 21.

[135] In a preferred embodiment of the present invention, the supplying tubes 501, 502 and 503 are subdivided into an upper part supplying tube 501, a middle part supplying tube 502 and a lower part supplying tube 503, and the middle part supplying tube 502 may be inclined according to the positions of the hopper 3 and the factory facilities, as shown in the attached drawings.

[136] On any one region of the middle part supplying tube 502, an inert gas blocking unit

523 comprising a first inert gas supplying unit 524, is branched and mounted so that the inserting path of the ferro-alloy F can keep an inert atmosphere by blocking air including oxygen and nitrogen flowed in at the same time when the ferro-alloy F is supplied from the hopper 3.

[137] Referring to FIG. 12, the inert gas blocking unit 523 is branched and mounted to form an angle θ with respect to a base end part of the middle part supplying tube 502 to be above 90° to below 180° so that it is reversely injected to the direction that the insertion of the ferro-alloy F is progressed for an efficient blocking of air to be flowed in.

[138] The ferro-alloy F removes a part of slag S in the upper part of the molten steel to be freely fallen to a place to be plume eye by means of the inert gas such as Ar strongly blown from a porous plug 23 previously installed in the bottom part of the ladle 22.

[139] At this time, the ingredient of the molten steel M is represented by weight % as follows: C: 0 to 0.05%, N: 0 to 0.070%, Si: p to 4%, Ti: 0 to 0.5%, S: below 0.030%, P: below 0.025%, Cr: 11.0 to 30.0%, Ni: 0 to 36%. The molten steel M may be molten steel of stainless steel such as AISI reference stainless 304, 316L, 430, 446 and 447 steel composed of other ingredients. As the molten steel M, other steels suffered from ferro-alloy inserting treatment may be used.

[140] In order to insert the ferro-alloy F into the molten steel M, the insertion hole of the lower part supplying tube 503 without submerging into slag and liquid steel falls to the side of the molten steel 31 through a length controlling unit 513.

[141] The length controlling unit 513 without submerging into slag and liquid steel may usually be a member capable of controlling length, and preferably, it is constituted to raise and fall the end part of the lower part supplying unit 503 positioned right on the ladle 22, that is, only the injection hole.

[142] The supplying tube, more specifically, the end part of the middle part supplying tube 502 and/or the base end part of the lower part supplying tube 503 are communicated with an inert gas supplying unit 533 comprising a second inert gas supplying unit 534 so that an inert gas atmosphere is created up to the end part of the lower part supplying unit 503 when the ferro-alloy F is inserted.

[143] The inert gas supplying unit 533 blows the second inert gas supplied from the second inert gas supplying unit 534 to be jet from the end part of the lower part supplying tube 503 so that the inert atmosphere is created on the path of the lower part supplying tube 503 when the ferro-alloy F is inserted, and the inert atmosphere is kept up to the surface of the molten steel therefrom when the second inert gas is jet from the end part of the lower part supplying tube 503.

[144] The outer side of the lower part supplying tube 503, more specifically, the circumference of the hollow cylindrical lower part supplying tube 503 is provided with a single ring structure 550 forming the same axis with the lower part supplying tube 503 to pack it and comprising a third inert gas supplying unit 554.

[145] This inert gas injecting unit 550 is injected into the end part of the lower part supplying tube 503, that is, into the surface direction of the molten steel M by packing the lower part supplying tube 503 with the third inert gas supplied from the third inert gas supplying unit 554.

[146] The third inert gas supplying unit 554 may be installed in one or two or several depending on facilities.

[147] Referring to FIG. 13a and FIG. 13b, the inert gas injecting unit 550 may be a single ring structure 550 or a composite ring structure 550 as in the one embodiment and this embodiment as described above.

[148] However, as described with reference to FIG. 10 in the above embodiment, it is preferable that the inert gas injecting unit 550 is the composite ring structure 550'.

[149] The third inert gas injected from the inert gas injecting unit 550 is diffused from the end part of the lower part supplying tube 503 by means of the diffusing unit 570.

[150] The diffusing unit 570 has a shape that is extended integrally and outwardly from the end part of the lower part supplying tube 503. Also, the third inert gas is extended outwardly accordingly. That is, the third inert gas reaches the surface of the molten steel M in the outwardly diffused shape by means of the diffusing unit 570. At this time, the third inert gas can secure a wider naked eye diameter by the diffused area. [151] Referring to FIG. 14, the diffusing angle θ from the inner side of the lower part supplying tube 503 is above 0°to below 90°.

[ 152] More preferably, the shape of the inner 7side and outer side of the lower part supplying tube 503 becomes the range of the diffusing angle or more to 15 or less so that it conforms to the diffusing angle θ described above.

[153] FIG. 15 is a general acting concept view showing a ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of oxygen according to the preferred embodiment of the present invention.

[154] Referring first to FIG. 15, the ferro-alloy F is entered in the upper part supplying tube 501 to be inserted into the molten steel M through the middle part supplying tube 502 and the lower part supplying tube 503.

[155] Before the ferro-alloy F is inserted through the upper part supplying tube 501, the lower part supplying tube 503 falls to the side of the molten steel M by the length controlling unit (513 in FIG. 2).

[156] The end part of the lower part supplying tube 503 falls at a predetermined distance from the surface of the molten steel. The fall of the lower part supplying tube 503 uses the following equation 1 in order to be fallen to an always constant height from the surface of the molten steel M depending on the amount of the molten steel M varied according to the process.

[157] [Equation 1]

[158] y=(h +x)-c

[159] where y is a distancefmm] from the inner side of the cover 21 of the ladle to the end part of the lower part supplying part 503; h is a distance [mm] from the inner side of the cover 21 of the ladle to the leading end part of the ladle, wherein it is fixed value; x is a distance [mm] from the leading end part of the ladle 22 to the surface of the molten steel wherein it is a variable varied according the amount of the molten steel M; c is a distance[mm] from the surface of the molten surface to the end part of the lower part supplying tube 503.

[160] At this time, x is obtained by the following equation 2.

[161] [Equation 2]

[162] w=-51.1*ln(x)+454

[163] (where w is the amount of the molten steel of a ton unit )

[164] Generally, if the end part of the lower part supplying part 503 is arranged at 3m or more distance from the surface of the molten steel M, the fallen distance of the ferroalloy F inserted becomes long to generate a great quantity of splash. If arranged below Im, since it is closed to the molten steel M to cause the melting loss of the lower part supplying tube 503, etc. Therefore, it is preferable that the distance from the end part of the lower part supplying tube 503 to the surface of the molten steel M is 1 to 3m. [165] However, the distance from the end part of the lower part supplying tube 503 to the surface of the molten steel M can be varied depending on the steel grade of the molten steel M used.

[166] The end part of the lower part supplying tube 503 is spaced and moved at a constant distance from the surface of the molten steel M by the length controlling unit 513 and then the first inert gas is inserted into the middle part supplying tube 502.

[167] When the ferro-alloy F passes through the middle part supplying tube 502, the first inert gas is injected by means of the inert gas blocking unit 523 to block the air entered in the middle part supplying tube 502 simultaneously with the ferro-alloy F (IGl).

[168] The first inert gas may be 8 group gases such as nitrogen or Ar, and more preferably, Ar in consideration of possibility of absorption of nitrogen and manufacturing cost. Also, in the case of austenitic steel grades, nitrogen may be used.

[169] When the ferro-alloy F passes through the lower part supplying tube 503, the second inert gas supplied through the inert gas supplying unit 533 keeps the inert atmosphere from the base end part of the lower part supplying tube 503 to the surface of the molten steel M. At this time, the ferro-alloy F can be inserted in a state securing a wider naked eye area that is arrived at the surface of the molten steel M through the diffusing part 570 (IG2).

[170] The second inert gas may be 8 group gases, and more preferably, Ar. In the case that steel grade is 300 series austenite, nitrogen may be also used.

[171] Also, in the outer side of the end part of the lower part supplying tube 503, the third inert gas passing through the inert gas injecting unit 550 is injected in an outwardly diffused shape through the diffusing part 570 to prevent the dispersion of the second inert gas so that the inserting path of the ferro-alloy keeps in the inert atmosphere (IG3).

[172] The third inert gas may be 8 group gases, and more preferably, Ar. Also, since the third inert gas allows the flow (IG2) of the second inert gas ejected from the inner side of the lower part supplying tube 503 to be kept in the outer side thereof, it is preferable that the flow velocity of the third inert gas is faster than that of the second inert gas or the injecting pressure of the third inert gas is greater than that of the second inert gas.

[173] At this time, it is preferable that the injection amount per unit time of the second inert gas may be 5 to 50Nm³/hr. If the injection amount is below 5Nm³/hr, the sufficient inert atmosphere is not formed to generate absorption of oxygen and absorption of nitrogen by oxygen and nitrogen in air and if the injection amount exceeds 50Nm /hr, the column of the third inert gas is destroyed to disperse the second inert gas due to side diffusion or to increase process cost due to the supply of the second inert gas more than necessary.

[ 174] Further, it is preferable that the injection amount per unit time of the third inert gas may be 10 to 100Nm /hr. If the injection amount is below 10Nm /hr, the dispersion due to the side diffusion of the second inert gas is generated to deteriorate the inert atmosphere and if the injection amount exceeds 100Nm³/hr,the third inert gas more than necessary is supplied. Therefore, it is preferable that the injection amount is controlled 100Nm³/hr or less.

[175] After the inert atmosphere is created on the inserting path of the ferro-alloy F by using the fist inert gas, the second inert gas, and the third inert gas, the fourth inert gas is blown using the porous plug 23 communicated with the inert gas supplying pipe 24 in the bottom part of the ladle 22.

[176] The fourth inert gas is lifted from the bottom part of the ladle 22 to the upper surface of the molten steel in a bubble form to generate the naked eye by the bubble.

[177] If the plume eye is generated by the bubble of the fourth inert gas to arrive at a steady state stabled to a degree, that is, if it is confirmed that the generation degree of the plume eye is continuous, the opening and closing valve 4 is opened so that the ferro-alloy F received in the storing hopper 3 is inserted.

[178] As described above, since an area A of the inert atmosphere generated by the flow of the second inert gas and the third inert gas is sufficient to unfold the naked eye generated in the surface of the molten steel M, the ferro-alloy F can be inserted from the hopper to the molten steel M at the inert atmosphere, thereby minimizing absorption of oxygen and absorption of nitrogen.

[179] Hereinafter, the stainless 409 steel and 336L steel molten in an electric furnace of

90 tons will be described by way of an example.

[180] Table 1 shows data comparing the variations of oxygen and nitrogen in the molten steel by the conventional ferro-alloy inserting method with the variations of nitrogen and oxygen in the molten steel, upon inserting stainless 409 steel and 436L steel into the ladle using the ferro-alloy inserting apparatus shown in FIG. 2 in the ladle treatment stand after flowing out the stainless 409 steel and 436L steel from the AOD decarburization vessel. At this time, the insertion amount of the ferro-alloy into the ladle is in the range of 0.5 to 2 ton/heat.

[181] Table 1

[182] [183] As shown in table 1 and FlG. 16, the increase amount of nitrogen (ΔN) is from 8 ppm up to 18 ppm under the condition that the partial oxygen pressure in the atmosphere state is 0.185atm (steel numbers: 1 to 4) in the case of the conventional example, however, the increase amount(ΔN) of nitrogen is significantly reduced to 7 to 24 ppm in the case (steel numbers: 5 to 9) of the present invention, excepting steel number 8.

[184] In other words, as shown in FlG. 16, in the case of the steel numbers 1 to 4 of the conventional example, each of the nitrogen concentration in the molten steel before and after the ferro-alloy inserting treatment in the ladle is varied from 58 to 6ppm, from 75 to 7 ppm, from 80 to 4 ppm, from 79 to 7 ppm. As a result, it can be appreciated that the nitrogen concentration after the ferro-alloy inserting treatment is significantly increased to 13 ppm in average more than that before the ferro-alloy inserting treatment. This means that the absorption of nitrogen of the molten steel from the atmosphere is generated during the ferro-alloy insertion. [ 185] However, each of the nitrogen concentration in the molten steel before and after the ferro-alloy treatment in the case (steel numbers: 5 to 9) of the prevent invention is significantly reduced to 2 ppm in average such as from 68 to 2 ppm, from 53 to 4 ppm, from 73 to 5 ppm, from 70 to 2 ppm, and from 67 to 68 ppm.

[ 186] As a result, it can be appreciated that the absorption of nitrogen of the molten steel from the atmosphere is significantly reduced during the ferro-alloy insertion.

[187] Meanwhile, reviewing the variation of oxygen, as shown in table 1 and in FlG. 17, the increase amount of oxygen is from 0 ppm up to 37 ppm under the condition that the oxygen partial pressure in the atmosphere state is 0.185atm (steel numbers: 1 to 4) in the case of the conventional example, however, oxygen is significantly reduced to 7 to 24 ppm in the case (steel numbers: 5 to 9) of the present invention, excepting steel number 8.

[188] That is, as can be appreciated from the FlG. 17, in the case of the steel numbers 1 to

4 of the conventional example, each of the oxygen concentration before and after treating the ferro-alloy in the ladle is varied from 73 to lOppm, from 91 to lppm, from 91 to 10 ppm, from 92 to 10 ppm. As a result, it can be appreciated that the oxygen concentration after the ferro-alloy inserting treatment is significantly increased to 18.5 ppm in average more than that before the ferro-alloy inserting treatment. This means that the reoxidation of the molten steel is generated during the ferro-alloy insertion.

[ 189] However, each of the oxygen concentration of the molten steel before and after the ferro-alloy treatment in the case (steel numbers: 5 to 9) of the prevent invention is varied from 91 to 0 ppm, from 75 to 1 ppm, from 86 to 6 ppm, from 92 to 110 ppm, and from 97 to 90 ppm. As a result, it can be appreciated that the oxygen is reduced to 10.8 ppm in average.

[190] That is, this means that the reoxidation of the molten steel is significantly reduced in the case of the present invention, upon inserting the ferro-alloy.

[191] This reason is well shown in FlG. 18. FlG. 18 shows the variation of the oxygen concentration over time upon inserting the ferro-alloy. The variations of nitrogen and oxygen is measured with a measuring unit 203 by collecting gas on any one point on the path from a gas inhaler 201 to the surface of the molten steel M via the lower part supplying tube 53 and measuring it with a partial pressure measuring sensor 202.

[192] As shown in FlG. 18, in the case of the conventional example the ferro-alloy insertion is made in the conventional example under the condition that the partial oxygen pressure between the inserting tube and the surface of the molten steel is about 0.185 atm (18.5%), that is, the condition that the atmosphere oxidation is easy.

[193] However, in the case of the present invention, since the ferro-ally insertion is made under the condition that the oxygen partial pressure is about 0.02 to 0.0002 atm (2 to 0.02%), that is, the condition that the oxygen partial pressure is low, it can be es timated that the reoxidation of the molten steel is less generated.

[194] FlG. 19 is a view showing a comparison example of defect rate of oxide (making steel) inclusions on a surface of a stainless hot rolled coil experiencing the ladle treatment processes of the conventional example and the present inventive example.

[195] As shown in FlG. 19, the making steel defect rate is 3.4% in average such as 4.8,

1.5, 3.9, 3.3% in the case of steel numbers 1 to 4 in the conventional example, respectively; however, the making steel defect rate is significantly reduced to 1.7% in average such as 1.5, 0.87, 1.3, 3.7, and 1.3% in the case of steel numbers 5 to 9, respectively.

[196] The result is because the cleanness of the molten steel is improved. Therefore, it can be appreciated that the surface quality of a product is significantly improved.

[197] Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes might be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

[198]

Claims

[1] A ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of nitrogen, comprising: a supplying tube supplied with ferro-alloy from a hopper to insert it into a ladle without submerging into slag and liquid steel, and subdivided into a upper part, an inclined middle part, a lower part and having a predetermined hollow; a branched and mounted inert gas blocking unit communicated with the middle part of the supplying tube and blocking, as first inert gas, air flowed in at the same time when the ferro-alloy is inserted; a branched and mounted inert gas supplying unit communicated with the base end part of the lower part of the supplying tube and blowing a second inert gas on an inserting path of the ferro-alloy; an inert gas injecting unit packing any one of the lower part outer sides of the supplying tube relative to axis direction of the lower part thereof and injecting a third inert gas toward the end part of the lower part thereof; and a diffusing unit diffusing the third inert gas injected while packing the supplying tube from the inert gas injecting unit into the end part of the supplying tube.

[2] The ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of nitrogen as claimed in claim 1, wherein the inert gas injecting unit is a composite ring structure configured of a first ring structure that uniformly distributes the third inert gas, a second ring structure that packs the lower part supplying tube and injects the third inert gas uniformly distributed in the first ring structure into the end part direction, and a plurality of connectors that communicate the first ring structure with the second ring structure.

[3] The ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of nitrogen as claimed in claim 2, wherein the inert gas injecting unit is formed with predetermined slits in the end part of the lower part supplying tube.

[4] The ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of nitrogen as claimed in claim 3, wherein the width of the slit is 3.0mm or less.

[5] The ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of nitrogen as claimed in claim 4, wherein the width of the slit is 0.1mm or more to 3.0mm or less.

[6] The ferro-alloy inserting apparatus with reduced absorption of oxygen and absorption of nitrogen as claimed in claim 1, wherein an inner part diffusing angle between the inside of the diffusing unit and the inside of the lower part supplying tube is above 0°to below 90°. [7] An inserting method of ferro-alloy with reduced absorption of oxygen and absorption of nitrogen receiving molten steel covered by the slag in a ladle installed with porous plug in a bottom part thereof and inserting ferro-alloy stored into a hopper from the upper part of the ladle in the molten steel through the upper part, middle part, and lower part supplying tubes, including the steps of: falling the end part of the lower part supplying tube; inserting a first inert gas in the middle part supplying tube; inserting a second inert gas into the base end part of the lower part supplying tube; providing a third inert gas injected in a end part direction by packing the outer side of the lower part supplying tube; and inserting the ferro-alloy into the upper part, middle part, and lower part supplying tubes in sequence. [8] The inserting method of ferro-alloy with reduced absorption of oxygen and absorption of nitrogen as claimed in claim 7, wherein the injection amount per unit time of the second inert gas is 5 to 50Nm /hi. [9] The inserting method of ferro-alloy with reduced absorption of oxygen and absorption of nitrogen as claimed in claim 7, wherein the injection amount per unit time of the third inert gas is 10 to 100Nm /hr.