TW201002832A - Steel-making method for titanium-containing ultralow carbon steel and method for manufacturing titanium-containing ultralow carbon steel slab - Google Patents

Abstract

After decarburizing molten steel in a vacuum degassing facility or the like, a titanium-containing alloy is added to the ladle and deoxidation is performed, thereby creating a deoxidized molten steel with a composition that satisfies the formula [% Al]≤[% Ti]/10. Next, an alloy for adjusting the inclusion composition, which includes calcium, is added to the molten steel in the ladle, thereby adjusting the inclusion composition in the molten steel to 90% or below for titanium oxide, 5 to 50% for CaO, and 70% or below for Al2O3. Also, by ensuring that, after performing deoxidation, the ladle slag has a T.Fe concentration + MnO concentration of 10% or below by mass, (%CaO)/(%SiO2) of 1 or above, a TiO2 concentration of 1% or above by mass, and an Al2O3 concentration of 10 to 50% by mass, the inclusion composition within the molten steel is optimized and the inclusion amount is reduced, thereby enabling the manufacturing of a titanium-containing ultralow carbon steel that makes it possible to obtain a cold-rolled steel sheet that has excellent surface properties and inner properties, and also prevents clogging of the nozzle due to inclusions.

Description

201002832 VI. Description of the Invention: [Technical Field of the Invention] The present invention relates to a "melt-containing ultralow carbon steel" which is subjected to deoxidation treatment using Ti. Method) and a method for producing a Ti-containing ultra-low carbon steel slab. More particularly, the present invention relates to a Ti-containing ultra-low carbon steel suitable for the manufacture of a cold-rolled steel sheet having excellent surface properties and inner properties, and for obtaining a cast piece thereof. Manufacturing method. [Prior Art] In recent years, in the case of melting extremely low carbon steel for cold-rolled steel sheets such as steel sheets for automobiles, the mainstream is to use A1 to strengthen molten steel so that A1 of 0.005 mass% or more remains in the molten steel. Deoxidation, thereby making the steel clean clean at low cost. In the deoxidation using A1 as described above, the can steel is generally treated by gas bubbling or RH vacuum degassing device (Ruhrstahl-Hausen vacuum degasser), and the generated oxide (deoxidation) is used. Deoxidization products are methods of aggregating and coalescing to achieve flotation and removal. However, in this method, the oxide of A1 (ai2o3) is inevitably left in the cast piece. In particular, since the remaining ai2o3 becomes a cluster-like shape and has a small apparent specific gravity with respect to the molten steel, it is difficult to perform flotation separation. Therefore, it is easy to have a size of several hundred #m or more in the steel. Cluster 098110383 3 201002832 Inclusions. If such inclusions are entrapped to the surface of the cast part during continuous casting, surface defects such as spalling and sliver may occur ( Surface defect), which impairs the surface properties of the cold-rolled steel sheet. Also, the solid phase Al2〇3 formed by the deoxidation of A1 adheres and accumulates during continuous casting (depos The ition is a problem of clogging the nozzle on the inner surface of the immersion nozzle that is injected from the forging groove into the pound mold. A method of suppressing nozzle clogging by injecting Ar gas from an upper nozzle or an impregnation nozzle is generally employed. However, in this method, the blown gas is caught together with AI2O3. In the solidification shell, surface defects such as scale, flaking, and lobes are generated, thereby impairing the surface properties of the cold-rolled steel sheet. As described above, since A1 deoxidized steel has many problems, the A1 is not added recently. The reason for deoxidation by Ti is increased. The reason is as follows. In the case of deoxidized steel, the amount of inclusions is higher than that of A1 deoxidized steel because of its higher limiting oxygen concentration. However, compared with A1 deoxidized steel. It is difficult to form a cluster-like oxide, and an oxide having a size of about 5 to 20 am exists in a state of being dispersed in steel. Therefore, surface defects caused by cluster-like oxide-based inclusions in the Ti-deoxidized steel Less But Cloth, and if the amount of ultra low carbon steel having Ti content of 25 to Τι content is 0.010 mass% or more, the solid-phase Ti oxides in molten steel state. 098110383 Λ 201002832 This 'continuous build-time' Ti oxide adheres and grows (stacks) on the inner surface of the impregnation nozzle in the form of a bare metal, causing nozzle clogging. In order to solve the above-mentioned problem, Japanese Patent Application Laid-Open No. Hei 8-281391 (Patent Document 1) proposes to limit the oxygen content of the molten steel passing through the impregnation nozzle when casting the undepleted Ti deoxidized steel. A method of suppressing adhesion of Ti2〇3 and growing on the inner surface of the impregnation nozzle. However, in the case of Ti deoxidized steel, the limiting oxygen concentration is about 30 mass ppm. Therefore, each nozzle can only cast around fX 80〇 t〇n. Further, as the nozzle clogging is aggravated, it becomes impossible to stably control the level of the bath surface in the mold. For these reasons, the technique of Patent Document 1 is not a fundamental solution to the problem of Ti deoxidized steel. In addition, as a method of casting a very low carbon Ti deoxidized steel without causing clogging of the impregnation nozzle during continuous casting, a method for obtaining a Ti-containing ultra-low-cold steel sheet having excellent surface properties without significantly increasing the number of raw materials is disclosed in Japanese Patent Application. In Japanese Patent Laid-Open No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. 2006-152444 (Patent Document 4). Ca is added to the molten steel (including an alloy containing Ca), and the inclusions are formed into a low melting point composition of ITO oxide-Al2〇3-CaO and/or rare-earth metal (REM) oxide, and A method of casting without injecting Ar gas into the impregnation nozzle during continuous casting. In addition, in the case of the Ti-containing ultra-low carbon steel to which Ca is added, in order to suppress the coarsening of the oxide-based inclusions, it is proposed in Japanese Patent Laid-Open Publication No. Hei. No. 2-26842 (Patent Document 5). Adding 098110383 5 201002832 in the molten steel before Ai, between the oxygen content and the time after adding A1 until the addition of Τι, can be established as 'a °: oxygen content before adding A1 (maSSppm), t: " force A1 After the time until the time of the addition of Τι (4)), the composition of the lost material in the cold-rolled steel sheet is adjusted to _3:1 〇: mass. Pure and / or metal calendar oxide: oxide 1 ~ 90% by mass method. h/〇, Tl [Summary of the invention] (The problem solved by the inventor of the invention) However, the inventors of the present invention found that in the patent document, when Ca is added, the oxide is added, and the oxide inclusions are added. Specifically reoxidizes the oxygen concentration and debris in the steel. Further, since the large-sized oxide is left in the steel after the large-scale production, the cold-rolled steel sheet is pressed into a (four) sub-layer, and there is a problem that the steel sheet is broken. "Inclusions are the starting point for the problem, that is, the convenience of the previous processing time, the method of #^^5 is extended to add Ti, and it is impossible to obtain a group that is difficult to agglomerate. (4) When adding Ca, the amount of steel impurities increases, and the large amount of steel remains after the prayer: and 1 is tied and 'because of the existence of the large oxygen nucleus, =: and will be oxidized during press molding. The object of the present invention is the result of the invention. Ti-containing low-carbon steel which is deoxidized by Ti, and the melting method prevents clogging of the impregnation nozzle (nozzle clogging) due to oxide-based inclusions during continuous casting, and surface properties and endoplasm can be obtained. In the present invention, the cold-rolled steel sheet having excellent surface properties and internal quality is particularly low in surface defects due to oxide-based inclusions or bubbles, and is caused by oxides. Inclusion The breakage has a two-hearted cold-hearted steel plate. (: Further, another object of the present invention is to provide a method for producing a cast piece which is extremely low in Ti-containing which is melted by the above-described melting method. The method of producing a slab of carbon steel can further improve the surface properties and the internal quality of the cold-rolled steel sheet. (Means for Solving the Problem) The present inventors have repeatedly conducted experiments and studies in order to solve the problems of the above-mentioned conventional techniques, and the results have been developed. The following is a method for melting a Ti-containing ultra-low carbon steel and a method for producing a Ti-containing ultra-low carbon steel slab. G [丨] A method for melting a Ti-containing ultra-low carbon steel, the melting thereof containing c: 〇 When 020 mass% or less, Ti: 0.010 mass% or more, and Ca: 0 0005 mass% or more of extremely low carbon Ti deoxidized steel, the molten steel is subjected to decarburization treatment, and then Ti is added to a ladle to perform deoxidation treatment. Thereby, a deoxidized molten steel having an A1 content (% by mass) and a Tl content (% by mass) of S[%Al]g[%Ti]/l〇 is obtained, and thereafter, the deoxidizing melting in the ladle Ca is added to the steel to adjust the inclusion composition in the molten steel to Ti oxide: 90 The amount of % or less, Ca〇: 5 to 5〇% by mass, Al2〇3: 70% by mass or less, and 098110383 7 201002832 In the above-mentioned pouring slag after deoxidizing the molten steel by adding Ti: • Total Fe The total concentration of MnO is 10% by mass or less; • The mass ratio of CaO concentration to Si〇2 concentration (%CaO)/(%SiO2) is 1 or more; • Ti02 concentration is 1% by mass or more; and • A1203 concentration is Further, the above invention [1] is preferably a method of melting a Ti-containing ultra-low carbon steel, characterized in that the melting contains C: 0.020% by mass or less and Ti: 0.010% by mass or more. , Ca: 0.0005 mass% or more of the extremely low carbon Ti deoxidized steel, in the vacuum degassing equipment, decarburization treatment of the steel tapped in the converter or the eiectric furnace, and then Deoxidation treatment is carried out by adding a Ti-containing alloy to the molten steel after the decarburization treatment, thereby obtaining a deoxidized molten steel having a composition of A1 content (% by mass) and a Ti content (% by mass) satisfying [%A1] $ [% Ti]/l0 Then, an alloy for adjusting inclusions containing Ca is added to the deoxidized molten steel, thereby melting the alloy The composition of the inclusions is adjusted to be Ti oxide: 90% by mass or less, CaO: 5 to 50% by mass, Al2〇3: 70% by mass or less, and the above-described addition of the Ti-containing alloy to deoxidize the molten steel In the barrel slag, the total Fe concentration and the MnO concentration are 10% by mass or less. 'The mass ratio of CaO concentration to SiO 2 concentration (%Ca0) / (%SiO 2 ) is 1 or more, the Ti02 concentration is 1% by mass or more, and Al2 The concentration of 〇3 is 10 to 50% by mass. [2] The method for smashing Ti-containing ultra-low carbon steel according to the above [1], which comprises C: 0.020% by mass or less, Ti: 0.010% by mass or more, Ca: 0.0005 mass 0/◦ or more, Si: 0.2% by mass or less, Μη: 2.0% by mass or less, S: 098110383 8 201002832 0.050% by mass or less, P: 0.005 to 0.12% by mass, N: 0.0005 to 0.0040% by mass, the balance of Fe and the inevitable impurities are extremely low Carbon Ti deoxidized steel. [3] The method for melting a Ti-containing ultra-low carbon steel according to the above [1] or [2] further includes Nb: 0.100% by mass or less, B: 0.050% by mass or less, and Mo: 1.0% by mass or less. One or more kinds of extremely low carbon Ti deoxidized steel. [4] The method for melting a Ti-containing ultra-low carbon steel according to any one of the above [1] to [3], wherein, after the decarburization treatment is performed on the molten steel, the Ti is added to perform deoxidation treatment, and the self is added. One or more of Al, Si, and Μn are pre-deoxidized, thereby preliminarily making the dissolved oxygen concentration in the molten steel reach 200 mass ppm or less 0 [5] as in any of [1] to [4] above. The method for melting Ti-containing ultra-low carbon steel, wherein the deoxidation treatment time of the molten steel obtained by adding Ti is set to 5 minutes or longer. [6] A method for producing a Ti-containing ultra-low carbon steel prayer piece, which is continuously cast by using a molten steel melted by the melting method according to any one of [1] to [5] above, thereby producing a casting When the molten steel is injected into the mold from the tank by the impregnation nozzle provided at the bottom of the Aowei groove, the molten steel is not cast into the molten steel flowing down the dipping nozzle. [7] A method for producing a steel sheet containing Ti-very low-carbon steel, which is continuously produced by using a steel-making method prepared by the method of the gluten-free method according to any one of the above [1] to [5] The slab is manufactured, and it is stirred by the electromagnetic force generated by the magnetic field. 098110383 201002832 The molten steel in the mold [8] - the manufacturer of the Ti-containing ultra-low carbon steel slab, the use of the soil as described above

The molten steel flows to brake. [9] A method for manufacturing a Ti-containing ultra-low carbon steel slab

The molten steel in the mold, and the static magnetic field is applied to the molten steel, and the electromagnetic force stirring casting is used to brake the flow of the molten steel. In the above m and m, as the magnetic field for mixing, it is preferable to move the magnetic field and/or the oscillating magnetic field, and it is more preferable to move the magnetic field. [10] The method for producing a Ti-containing ultra-low carbon steel slab according to any one of the above [7] to [9], wherein the self-feeding groove is moved into the mold through the immersion nozzle provided at the bottom of the feed tank When the molten steel is injected, the molten steel is not cast into the molten steel flowing down in the above-mentioned impregnation nozzle to cast the molten steel. [11] The method for producing a Ti-containing ultra-low carbon steel slab according to any one of the above [6] to [10], wherein the molten steel is continuously cast at a throughput of 4 ton/min or less. [Embodiment] (Main composition of molten steel) The present invention is a method for melting extremely low carbon Ti deoxidized steel, which contains C: 0.020% by mass or less and Ti: 0.1% by mass or more. , Ca : 0.0005 quality 098110383 10 201002832 The amount of ultra-low carbon Ti deoxidized steel is more than 5%, and the decarburization treatment of the molten steel and the deoxidation treatment of Ti are sequentially performed, and then Ca ' is added to the deoxidized molten steel. The inclusions (= oxide-based inclusions, the same below) in the molten steel are adjusted to a predetermined composition. The molten steel to be treated after decarburization is usually tapped from a converter or an electric furnace. The decarburization treatment is preferably carried out in a vacuum degassing apparatus. The T1 deoxidation treatment is also preferably carried out in a vacuum degassing apparatus. The addition of Ca can also be carried out in a vacuum degassing device or in a ladle with Ti deoxidation. As a vacuum degassing apparatus for performing the above-described series of treatments, RH vacuum degassing equipment is particularly desirable, but other vacuum degassing equipment such as a VOD ' Vacuum Oxygen Decarburization apparatus is not allowed. When the amount of C of the ultra-low carbon steel melted in the present invention exceeds 0.020% by mass, the deep drawability of the product cannot be ensured, so that the amount of c is 〇 〇 2 〇 by mass or less. The lower limit of the amount of C is not particularly limited. Further, if the amount of Τι is less than o.oio by mass, the deoxidizing ability of Ti is weak, and the total oxygen concentration is increased, so that the amount of Ti is 0 〇 1 〇 mass% or more. On the other hand, if the amount of right T1 is too large, a large amount of TiN is formed to block the impregnation nozzle, so the amount of Ti is preferably 0.15% by mass or less. In addition, when the amount of Ca is less than 00 〇 5% by mass, the Ca 〇 concentration in the inclusions is less than 5 to 50% by mass. The melting point of the inclusions is improved, and the nozzle is easily blocked. Therefore, the amount of Ca is 0.0005. More than % by mass. On the other hand, when the amount of Q exceeds 0.0050% by mass, the Ca 〇 Moment of the inclusion exceeds % by mass, and the inclusion of 098110383 201002832 easily contains sulfur in a liquid phase. Further, as a result, when the liquid phase inclusions are solidified, CaS' is generated around the inclusions, and the CaS becomes the starting point of the rust of the steel sheet, and the amount of rust of the steel sheet is remarkably increased. Therefore, the amount of Ca is preferably 0.0050% by mass or less. The other steel composition is not particularly limited in terms of the problem to be solved by the present invention in the production of steel or the production of slabs. The preferred composition of the steel sheet will be described later. In the present invention, in a vacuum degassing apparatus such as an RH vacuum degassing apparatus, first, the molten steel is subjected to a decarburization treatment, and then Ti is added to the molten steel after the decarburization treatment to perform a deoxidation treatment (Ti deoxidation treatment) to obtain A1 content (% by mass) ^^] and Ti content (% by mass) [%Ti] satisfying the composition of [〇/〇Α1]$[%Τί]Π〇. Ti is conveniently added in the form of a Ti-containing alloy such as an Fe-Ti alloy. If the deoxidized molten steel is out of the composition range, then A1 deoxidation instead of deoxygenation will generate a large amount of Al2〇3 clusters. Even if Ti-containing arsenic is added and Ti intensity is increased, Α1ζ〇3 cannot be sufficiently reduced, and remains as a cluster-like scum in steel. After that, although the composition of the inclusions was controlled by the addition of Ca, the inclusions formed became CaO.AUO3, which easily became the starting point of the scales, and the inclusions after the reaction of Al2〇3蔟 were huge ca〇.Al2. 〇 3 cool things. Therefore, the deoxidized molten steel must satisfy [%Al]S[%Ti]/l〇. (The composition of the slag after the Ti deoxidation treatment) Then, 'Ca is added to the Ti deoxidized molten steel, and the composition of the 060110383 12 201002832 in the molten steel is adjusted to Ti oxide: 90% by mass or less, Ca〇: 5~ 5〇% by mass, Α1ζ〇3: a low melting point composition of 70% by mass or less. Thereby, it is possible to effectively suppress the adhesion of oxide-based inclusions to the inner surface of the impregnation nozzle during continuous casting, and to prevent clogging of the impregnation nozzle (nozzle clogging). Further, (^ is conveniently added in the form of an alloy for adjusting inclusion composition containing Ca (hereinafter referred to as "Ca-containing flux"). Hereinafter, the Ti deoxidation treatment as described above and the subsequent step are performed. After that

The purpose of the addition and the effect are explained. First, the molten steel is deoxidized by Ti (for example, a Ti-containing alloy such as Fe_Ti alloy), whereby inclusions mainly composed of Ti oxide are formed. The inclusions thus obtained are not formed into a cluster shape when deoxidizing with A1, but are formed in a state of 5 to 2 〇 "granular shape of the crucible" to be dispersed in the steel. If it is in steel When the concentration of A1 is a certain level and the result becomes the same as that of deoxidation, a large Al2〇3蔟 is formed. In this case, even if the alloy concentration is increased after the addition of the alloy, the Ai2〇3襄 has been generated. Also, it will not remain in the steel as a result of the Al2〇3 stealing loss. For the reason, in the present invention, it is necessary to first perform the de-rolling of the Hyun steel by using niobium to form a T1 oxide. The deoxidation of the Ti will produce a mass of 3, which is a size of 5 to 20 (four) and is dispersed in the steel and appears as a granular shape, so that it can be manufactured by the shaft. In the case of extremely low carbon steel, the solidification temperature of steel is 098110383 13 201002832. Continuous casting in the form of metal. Therefore, oxides and base metals adhere to and grow in Immersion of the inner surface of the nozzle causes the nozzle to become clogged. Therefore, in the present invention, after deoxidation using a Ti-containing alloy, Ca is added to the deoxidized steel (for example, a chelating agent). The composition of the oxide-based inclusions in the sturdy steel is changed to a low melting point Ti containing an oxide: 9 〇 mass% or less, CaO: 1 〇 to 5 〇 mass%, and Al2 〇 3: 7 〇 mass% or less. Low-point inclusions of oxides. #, By changing to such recorded points, it is possible to effectively bind the bismuth oxide doped with bare metal and grow on the inner surface of the impregnation nozzle after Tl deoxidation treatment. In the ladle, Ca is added to the Ti deoxidized molten steel, and in the vacuum tank in the vacuum degassing treatment (after deoxidation treatment), Ca is added from the upper portion to the Tl deoxidizing steel, and the method is usually added by the former method. As the Ca-containing flux, for example, one or more of casi, CaNi, CaAl, and CaFe are preferably used, and by appropriately adjusting the amounts of addition, the inclusions having the above composition can be obtained. The reasons for limiting the composition of the inclusions are as follows. When the concentration of the Ti oxide is more than 90% by mass, the melting point of the inclusions cannot be sufficiently lowered, and the inclusions do not form a cluster, but the inclusions adhere to and accumulate on the inner surface of the impregnation nozzle, causing nozzle clogging. The oxide concentration is 90 mass ❶ / 〇 or less, preferably 80 mass % or less. On the other hand, if the concentration of butyl sulfonium oxide is low, the density of A 1203 is increased, so the concentration of Ti oxygen 098110383 14 201002832 of the inclusions is higher. Preferably, it is 20% by mass or more, more preferably 30% by mass or more. The concentration of Ti oxide in the inclusions is determined by an electron micro-analyzer (EPMa, electron pr〇be microanalyser) or an energy dispersive X-ray blanket (EDX). The 'energy dispersive X-ray spectrometer' measures the amount of Ti contained in the depleted matter and calculates it by converting it into Ti2〇3.

When the concentration of the inclusion CaO exceeds 50% by mass, the inclusions easily contain sulfur in the liquid phase. As a result, when the liquid phase inclusions are solidified, CaS is generated around the inclusions, and this CaS becomes the starting point of the rust of the steel sheet, and the amount of rust of the steel sheet is remarkably increased. On the other hand, when the Ca 〇 concentration is less than 5% by mass, the melting point of the inclusions cannot be sufficiently lowered, and the inclusions adhere to and accumulate on the inner surface of the impregnation nozzle, causing the nozzle to clog. Therefore, the Ca 〇 concentration is 5 to 5 〇 mass %', preferably 7 to 5 G% by mass, more preferably 15 to 5 G% by mass. The CaO concentration in the sputum was calculated by converting the amount of Ca contained in the inclusions into Ca0 by 纟EPM a or EDX. / The concentration of inclusions Al2〇3 exceeds 7% of the amount of 7Q f, the loss of impurities becomes a high-k point composition', so it is easy to cause nozzle clogging of the impregnation nozzle, and the non-metallic inclusions in the steel sheet are caused by inclusions = 蔟The defects of physical properties increase. Lying / Chen is no problem even if it is low, but in terms of cost, it is advantageous

Hr A1 is coming. The concentration of the secret shot is calculated by taking the amount of A1 contained in the inclusion, and converting it into bismuth may also contain inclusions in addition to the above Ti oxide, Ca 〇, α1λ, 098110383 15 201002832, inevitably mixed in oxidation For example, the material may contain, for example, about 5% by mass or less of MgO and about 2% by mass of Si〇2. The concentration of Mg 或 or the concentration of Si 〇 2 in the inclusions was calculated by measuring the amount of Mg or the amount of Si contained in the inclusions by enthalpy or EDX, and converting them into Mg 〇 or Si 〇 2, respectively. (The composition of the slag after Ti deoxidation treatment) (a. Total Fe concentration and Mn 〇 concentration) The Ca-containing flux is usually applied to the molten steel in the ladle by using a coated iron wire or an injecting lance. Add to. The iron-coated metal wire is a metal wire obtained by coating an alloy powder with a thin steel plate, and the metal wire is supplied to the molten steel. Further, the alloy powder was blown into the molten steel by pouring it by using the method of spraying. When Ca is added to the molten steel, the molten steel is strongly mixed, and the material is present in the steel in the steel, or in the molten steel and the slag.

The oxides such as MnO- and S1〇2 are reacted to re-oxidize the molten steel, and the amount of oxide-based inclusions in the steel making is remarkably increased. Therefore, in the present invention, the total amount of the slag in the washing slag after the T1 degassing treatment of the molten steel (before adding Ca)

The total of the FeaFe) concentration and the Mn0 concentration is 1% by mass or less. Therefore, it can suppress the increase of the oxides in the re-oxidation of the secret steel after the addition of Ca. The cold-rolling =; ^1 secretly rolls her inner body to a full thickness deformation rate. ^^^ can be wrong by the example (10) (four) shot of the fracture part of the board Figure 1 table ^ to achieve the composition of the hair _ specified for the molten steel into the 098110383 16 201002832 Ti deoxidation treatment after the total Fe concentration in the washing tank slag ( Total mass %) and Mn〇 concentration (% by mass) (%T.Fe) + (%MnO) (horizontal axis: mass 0/〇), and the cold rolled steel sheet obtained from the molten steel in the bulging test Relationship between the plate thickness deformation ratio (vertical axis: %) of the fracture portion. In this test, a cast piece containing Ti ultra-low carbon steel was melted in the following manner, and the cast piece obtained by continuous casting was subjected to hot rolling. (hot rolling) and cold rolled steel sheet obtained after cold rolling. For the molten steel (300 ton) charged into the ladle after tapping in the converter, the FeO and MnO in the slag are reduced. Add A1 slag (aluminium dross) as needed. In addition, in order to control the composition of the slag after RH vacuum degassing, add CaO, Al2〇3, Ti〇2 as needed. Furthermore, the Ai slag is a by-product of the surface which is produced when the aluminum is melted, and is often used as an additive in the refining step. Then, in the RH vacuum degassing apparatus, a series of treatments as shown below is performed. First, the molten steel is taken off. Carbon treatment to adjust the composition of the molten steel to C: 0.0007~〇0150% by mass, oxygen concentration: 12〇~7〇〇mass ppm ° and then 'to the molten steel to 0.1~1.2 kg/ molten steel ton (relative to The amount of dissolved oxygen in the molten steel is lowered to 30 to 400 mass ppm, and the concentration of A1 in the molten steel is 0.001 to 0.005 mass%. A Fe-70% by mass Ti alloy of 〇.8~2.0 kg/melt steel ton is added to the molten steel to perform Ti deoxidation treatment. In the Ti deoxidation treatment, the RH vacuum is terminated within 2 to 15 minutes after the addition of the Fe-Ti alloy. Degassing treatment, after the end of the molten steel composition Ti concentration 0.020~0.080% by mass, 098110383 17 201002832 A1 concentration 0.001~0.006% by mass, total oxygen concentration 20~100 mass ppm, full S[%Al]S[%Ti] /l〇. RH vacuum degassing treatment (deoxidation treatment), the slag composition in the pouring tank is CaO Degree: 20 to 60% by mass, Si〇2 concentration: 5 to 20% by mass, Al2〇3 concentration: 10 to 50% by mass, Ti02 concentration: 1 to 10% by mass, Mg〇 concentration to 15% by mass, and total Fe concentration : 1 to 10% by mass, MnO concentration: 〇. 5 to 5 mass%, all satisfying the mass ratio (%CaO) / (%Si02)^1. Further, the composition of the slag was measured by fluorescent X-ray analysis. After the RH vacuum degassing treatment, 20 to 35 mass% of 〇&-60 to 75 mass% Si alloy is supplied to the molten steel in the ladle by the iron-coated metal wire and 0.1 to 0.4 kg/melt steel is added. (Based on the Ca-Si reserve amount) 'The composition of the inclusions in the steelmaking is adjusted to Ti oxide: 30 to 70% by mass, 匸 & 0: 6 to 50% by mass, and Al2 〇 3 : 1 〇 ~ 7〇% by mass. The Ca concentration in the molten steel to be melted is 0.0005 mass% or more. The cast steel produced by the above-described method is continuously cast by a twin-strand continuous casting mold to produce a cast piece. The continuous scale system is not blown into the molten steel flowing down the impregnation nozzle, and the gas such as Ar or A is blown, and the molten steel output (the amount of molten steel per unit time) during casting is 2 to 6 ton. /min. The cast steel chain is hot rolled until the thickness becomes 2 to 4 mm, and further cold rolling is performed until the sheet thickness becomes 〇6 to 1 · 〇 mm, thereby obtaining a cold rolled steel sheet. As shown in Fig. 1, by making the (%T.Fe) + (%Mn〇) in the ladle slag 098110383 18 201002832 10% by mass or less, the thickness of the fracture portion in the bulging test can be changed to 50. %the above. Further, (%T.Fe) + (%MnO) is more preferably 5 f% by weight. The lower limit of (%T.Fe) + (%Mn0) is not particularly limited. Further, in the present invention, the plate thickness deformation ratio of the cold milk steel sheet in the bulging test means that it is obtained by the following method*. Extracted from the cold-rolled steel sheet with a thickness of 0.6 to 1.0 mm, 2 〇〇 mm square square ‘, ',, use oil dust to expand the samples until they break.敎 Breaking (breaking the thickness of the plate) and dividing by the initial thickness, calculate the minimum deformation rate in the thickness direction (4) as the "plate thickness deformation rate". Plate thickness _ rate = high, then For steel sheets with internal defects (in this case, large oxide inclusions) and better internal quality, the plate thickness deformation rate is preferably 5% or more. In order to make the barrel slag (%T) .Fe) + (%Mn〇)g 1% by mass or less (or more suitable value), for example, A1 slag may be added before treatment according to the amount of material flowing out of the converter. ' (b. CaO concentration and Si 〇2 concentration ratio) Further, according to the same viewpoint as described above, the mass ratio (%Ca0)/(%SiO2) of the Ca0 concentration to the si〇2 concentration in the tank slag after Ti deoxidation of the molten steel is 1 or more. Fig. 2 shows the mass ratio (%Ca〇)/(%Si〇^(horizontal axis) in the poured slag after the deoxidation treatment of the molten steel by the method of achieving the composition specified in the present invention, The relationship between the plate thickness deformation rate (vertical axis: %) of the fracture portion in the bulging test of the cold-rolled steel sheet obtained from the molten steel. 098110383 19 201002832 In this test, the following The method comprises the steps of: melting a Ti-containing ultra-low carbon steel, continuously casting the obtained piece to obtain a cast piece, and subjecting the cast piece to hot-rolling and cold-rolling to obtain a cold-rolled steel plate. After being tapped in the converter, the steel is charged into the pouring bucket. Lime is added to the molten steel (300 ton) to adjust the mass ratio (%Ca0)/(%SiO2). In addition, in order to reduce FeO and MnO in the slag, A1 slag is added as needed. The composition of the slag after RH vacuum degassing treatment, adding CaO, AI2O3, Ti〇2 as needed. Then, one series of treatments as described below is carried out in the RH vacuum degassing equipment. First, the molten steel is decarburized. Adjust the composition of the molten steel to C: 0.0007~0.0150% by mass, oxygen concentration: 120~700 mass ppm. Next, add 0.1~1.2 kg/steel ton of A1 to the molten steel to make it in molten steel. The dissolved oxygen concentration is lowered to 30 to 400 mass ppm. At this time, the A1 concentration in the molten steel is 0.001 to 0.005 mass%. Further, 0.8 to 2.0 kg/melt steel ton Fe-70 mass% butadiene alloy is added to the molten steel. Ti deoxidation treatment. In the Ti deoxidation treatment, after adding the Fe-Ti alloy, the RH is terminated within 2 to 15 minutes. After the vacuum degassing treatment, the composition of the molten steel is Ti concentration of 0.020 to 0.080% by mass, A1 concentration of 0.001 to 0.006 mass%, and total oxygen concentration of 20 to 100 mass ppm, which satisfies [% person 1] $ [% Ti]/10 RH Vacuum degassing treatment (deoxidation treatment), the slag composition in the ladle is CaO concentration: 20 to 60% by mass, SiO 2 concentration: 5 to 20% by mass, Al 2 〇 3 concentration: 10 to 50% by mass, Ti02 Concentration: 1 to 1% by mass, MgO concentration: 2 to 15% by mass, total Fe concentration: 1 to 8 mass%, MnO concentration: 0.5 to 4 mass% '098110383 20 201002832 Both satisfy (%T.Fe) + ( %MnO)S 10 Mass 0/〇. After the RH vacuum degassing treatment, 20 to 35 masses are supplied to the molten steel in the ladle by the iron-clad metal wire. / heart - 60 ~ 75 mass alloy and adding 0.1 ~ 0.4 kg / molten steel ton, the composition of the inclusions in the molten steel is adjusted to be oxide: 30 ~ 70% by mass, CaO: 6 ~ 5 〇 mass%, Al2 〇3: ι〇~70% by mass. The Ca concentration in the molten steel to be melted is 〇.〇〇〇5 mass% or more. The cast piece was produced by continuously casting a molten steel melted in the manner described above by a double-strand continuous casting apparatus. The continuous rust system is not blown into the molten steel flowing down the dipping nozzle by blowing a gas such as Ar or N2, and the molten steel output during casting is 2 to 6 ton/min. The cast billet is hot rolled until the sheet thickness becomes 2 to 4 mm, and further cold rolling is performed until the sheet thickness becomes 0.6 to 1_0 mm, thereby obtaining a cold rolled steel sheet. As shown in Fig. 2, the plate thickness deformation rate of the fracture portion in the bulging test can be made higher by making the washing material t (%Ca〇) / (%si〇2) 1 or more. Further, (%CaO) / (%Si〇2) is more preferably 2 or more, and more preferably 2 or more. Further, the upper limit of '(%CaO)/(%Si〇2) is not particularly limited, and is usually at most about 6.0. In order to make (%CaO) / (%Si〇2) 4 or more (or more suitable value) in the ladle slag, for example, lime may be added to the converter tapping stream. (c. Ti02 concentration) In addition, in the present invention, the molten steel is subjected to Ti deoxidation after pouring the slag 098110383 21 201002832, and the reoxidation speed of the Τι is reduced and the cold rolled steel sheet can be added in the bulging. The concentration is 1% by mass or more. If it is small, it can suppress the amount of oxide-based impurities and increase the strength of the plate. The plate thickness deformation rate is more than 5%. The composition of the molten steel into the Ti〇2 concentration (horizontal axis: mass%), the thickness of the fracture portion in the test is shown in Fig. 3, in order to achieve the Τι deoxidation treatment specified in the present invention, in the pouring slag The relationship between the expansion rate (vertical axis: %) of the cold-rolled steel sheet obtained from sHuang steel. In this test, the Ti-containing ultra-low carbon steel was dissolved in the manner shown below to obtain a _ piece by continuous casting, and the cold-rolled steel sheet was obtained after the hot film and cold sheet were taken. After the steel is tapped in the converter, the person is transferred to the steel; in the bright steel in the barrel, t-Fe alloy is added according to the oxygen concentration to adjust the Ti〇2 concentration. In addition, in order to reduce the Fe 〇 and Mn 查 in the material, A1^ is added as needed. In addition, in order to control the composition of the slag after RH vacuum degassing treatment, add as needed

CaO, Al2〇3, Ti02. Then, a series of treatments as shown below were carried out in the RH vacuum degassing apparatus. First, the molten steel is subjected to decarburization treatment, and the composition of the molten steel is adjusted to C: 0.0007 to 0.0150% by mass, and the oxygen concentration is 120 to 700 mass ppm. Next, A1 of 0.1 to 1.2 kg/bright steel ton was added to the steelmaking to reduce the dissolved oxygen concentration in the molten steel to 30 to 400 mass ppm. At this time, the A1 concentration in the molten steel is 0.001 to 0.005 mass%. Further, Fe-70 mass% butadiene alloy of 〇8 to 2.0 kg/steel steel ton was added to the molten steel to carry out Ti deoxidation treatment. In the Ti deoxidation treatment, the Fe-Ti alloy is added, and the RH vacuum degassing treatment is completed in 2 to 15 minutes 098110383 22 201002832. After the completion, the Ti composition of the molten steel is 0.020 to 0.080% by mass, and the concentration of 1 is 0.001 to 0.006. Mass %, total oxygen concentration 20 to 100 mass ppm, satisfying [%Al]S[%Ti]/10. RH Vacuum degassing treatment (deoxidation treatment) The composition of the slag in the washing tub is CaO concentration: 20 to 60% by mass, SiO 2 concentration: 5 to 20% by mass, Al 2 〇 3 concentration: 10 to 50% by mass, 1^ 02 concentration: 1 to 10% by mass, MgO concentration: 2 to 15% by mass, total Fe concentration: 1 to 8% by mass, ]^11〇 concentration: 0.5 to 4% by mass, ( 'all satisfy the mass ratio (%Ca0) /(%Si02)g 1, (%T.Fe) + (%MnO)S 10% by mass. After the RH vacuum degassing treatment, the iron-coated metal wire is supplied to the molten steel in the ladle 20~ 35 mass% Ca-60~75 mass ° / 〇Si alloy and adding 0.1~0.4 kg / molten steel ton, the composition of the inclusions in the molten steel is adjusted to Ti oxide: 30~70% by mass, CaO: 6~50 Mass %, Al2〇3: 10 to 70% by mass. The Ca concentration in the molten steel to be melted is 0.0005 mass% I- or more. It is melted by the double-strand continuous casting apparatus in the manner described above. The molten steel is continuously cast to produce a cast piece. The continuous casting is not performed by blowing a gas such as Ar or N2 into the molten steel flowing down the impregnation nozzle, and the molten steel output during casting is 2 to 6 Ton/min. The cast steel is hot rolled until the sheet thickness becomes 2 to 4 mm, and further cold rolling is performed until the sheet thickness becomes 0.6 to 1.0 mm, thereby obtaining a cold rolled steel sheet. As shown in Fig. 3, When the TiO2 concentration in the slag is 1% by mass, 098110383 23 201002832 or more, the plate thickness deformation rate of the fracture portion in the bulging test can be 50% or more. Further, the TiO 2 concentration is more preferably 2% by mass or more. Further, the upper limit of the TiO 2 concentration is not particularly limited, and is usually up to about 10%. In order to make the TiO 2 concentration in the ladle slag 1% by mass or more, for example, it may be added according to the oxygen concentration. Further, in the present invention, the concentration of A1203 in the poured slag after the Ti deoxidation treatment on the molten steel is 10 to 50% by mass. Fig. 4 shows that the present invention is achieved. After the Ti deoxidation treatment of the molten steel in the form of composition, the ai2o3 concentration (horizontal axis: mass%) in the poured slag, and the thickness of the fracture portion of the cold rolled steel sheet obtained from the molten steel in the bulging test The relationship between the deformation rate (vertical axis: %). In this test, The Ti-containing ultra-low carbon steel is melted in the following manner, and the cast piece is continuously cast to obtain a cast piece, and the cast piece is subjected to hot rolling and cold rolling to obtain a cold-rolled steel sheet. Add A1 slag to the molten steel (300 ton) in the ladle to adjust the concentration of Al2〇3. In addition, in order to reduce FeO and MnO in the slag, add A1 slag as needed. In addition, to control RH vacuum degassing After the slag composition, 'CaO, AI2O3, Ti〇2 are added as needed. Then, a series of treatments as shown below were carried out in the RH vacuum degassing apparatus. First, the molten steel is subjected to decarburization treatment, and the composition of the molten steel is adjusted to C: 0.0007 to 0.0150% by mass, and the oxygen concentration is 120 to 700 mass ppm. 098110383 24 201002832 Next, add 0.1 to 1.2 kg/melt ton of A1 to the molten steel to reduce the dissolved oxygen concentration in the molten steel to 30 to 400 mass ppm. At this time, the A1 concentration in the molten steel is 0.001 to 0.005 mass%. Further, a Fe-70 mass% butyl alloy of 0.8 to 2.0 kg/melt steel ton was added to the molten steel to carry out Ti deoxidation treatment. In the Ti deoxidation treatment, after the Fe-Ti alloy is added, the RH vacuum degassing treatment is completed within 2 to 15 minutes, and after completion, the Ti composition of the molten steel is 0.020 to 0.080% by mass, and the A1 concentration is 0.001 to 0.006 mass%. The oxygen concentration of 20~10〇11^35??111' satisfies [% person 1]$[%1^]/10. 101 CaO concentration in the slag composition of the ladle after vacuum degassing treatment (deoxidation treatment): 20 to 60% by mass, Si〇2 concentration: 5 to 20 masses 0/〇, Ti02 concentration: 1 to 10% by mass, MgO concentration: 2 to 15% by mass, total Fe concentration: 1 to 8 mass%, MnO concentration: 0.5 to 4% by mass, both satisfying the mass ratio (〇/〇CaO)/(%SiO 2 ) 2 1 and (%T.Fe) + (%MnO)S 10% by mass. After the RH vacuum degassing treatment, '20 to 35 mass% Ca-60 to 75 mass% Si alloy is supplied to the molten steel in the ladle by the iron-coated metal wire and 0.1 to 0.4 kg/melt steel ton' will be added. The composition of the inclusions in the molten steel was adjusted to Ti oxide: 30 to 70% by mass, CaO: 6 to 50% by mass, and Al2〇3: 1 to 70% by mass. The Ca concentration in the molten steel to be melted is 0.0005 mass% or more. The molten steel which was melted as described above was continuously cast by a double-strand continuous casting apparatus to produce a cast piece. The continuous casting is carried out by blowing a gas such as Ar or N2 into the molten steel flowing down the impregnation nozzle, and the molten steel output at the time of casting 098110383 25 201002832 is 2 to 6 ton/min. The cast steel slab is hot rolled until the thickness becomes 2 to 4 mm. Further cold rolling is performed until the thickness of the steel sheet becomes 0.6 to 1.0 mm, whereby a cold rolled steel sheet is obtained. As shown in Fig. 4, by making the concentration of the barium 2〇3 in the ladle slag to be more than 10% by mass, the melting point of the material collapse is lowered, so that the absorption capacity of the oxide-based inclusions is increased. It can reduce the amount of oxide inclusions. In addition, by making the arsenal of 5% by mass or less, it is possible to suppress the mass % of Al 2 〇 3 in the oxide-based swarf, and it is possible to prevent the oxide-based inclusions from becoming coarse, and, for example, The plate thickness deformation ratio of the fracture portion in the test was such that the concentration of _3 in the barrel material was 10 to 50% by mass, and for example, the amount of addition of the A1 slag was adjusted. (Pre-deoxidation implementation and Ti deoxidation treatment time) In the present invention, it is preferred to add one selected from the group consisting of Al, Si, and Mn in the deoxidation of the molten steel after the decarburization treatment. Two or more kinds of pre-deoxidation are performed, and the dissolved oxygen concentration in the molten steel is previously set to 200 mass PP m or less. By this treatment, the amount of formation of oxide-based inclusions can be reduced, and the thickness deformation rate of the fracture portion in the test can be further improved in the vacuum degassing treatment. .溶 The dissolved oxygen concentration (white dots, black dots) in the molten steel before the T1 deoxidation treatment and the Ti dehydrated milk treatment day (horizontal axis: minutes), and the cold steel plate obtained from the molten steel The relationship between the plate thickness deformation rate of the fracture part in the expansion 4 ^ Φ 4 test. 098110383 26 201002832

The solution in the molten steel before Ti deoxidation treatment (white dots in the figure) is the sub-pore concentration: 50~ period _ The test example of the deoxidation before the oxygen treatment, Μ nnmm Φ ^ wm and more than 200 ~500 mass

Ppm (Time Black) The county is expected to reduce the test case as follows. Continuous casting (4) - including Tl very low carbon steel

The cast piece is subjected to hot rolling and cold rolling, and then rolled. After the tapping in the converter, the person is left to the left of the _. (4) Add and adjust the concentration of Al2〇3. Further, in order to reduce the amount of A1, it is necessary to add A1 slag. In addition, in order to control the composition of the sputum after the vacuum degassing treatment, Ca 〇, A (four), and now are added as needed. Then, the series treatment as shown below was carried out in the RH vacuum degassing apparatus. First, decarburization treatment is performed on the molten steel, and the composition of the molten steel is adjusted to C. 0.0GG7 to G.G15G mass%, oxygen concentration: m~weight brain s ppm. Next, in the case of pre-deoxidation, A1 of 2 kg/melt ton was added to the steel to reduce the dissolved oxygen concentration in the molten steel to 5 〇 2 〇〇 mass ppm. At this time, the A1 concentration in the steelmaking is o.ooi~〇 〇〇5 mass%. Then, a Fe-70% by mass Ti alloy of 0.8 to 2.0 kg/melt steel ton was added to the molten steel to carry out Ti deoxidation treatment. In the Ti deoxidation treatment, after the Fe-Ti alloy is added, the RH vacuum degassing treatment is completed within 2 to 15 minutes, and after completion, the Ti composition of the molten steel is 0.020 to 0.080% by mass, and the A1 concentration is 0.001 to 0.006 mass%. The oxygen concentration is 20 to 100 mass ppm, which satisfies [%A1]S [%Ti]/10. 098110383 27 201002832 RH vacuum degassing treatment (deoxidation treatment), the composition of the slag in the washing tank is CaO concentration: 20~60% by mass, SiO2 concentration: 5~20% by mass, Al2〇3 concentration: 10~50% by mass Ding 102 concentration: 1 to 10% by mass, MgO concentration: 2 to 15% by mass, total Fe concentration: mass%, MnO concentration: 0.5 to 4% by mass, all satisfying mass ratio (%ca〇)/(%Si02) 2 : l, (%T.Fe) + (%ΜηΟ) $ 1〇% by mass. After RH vacuum degassing treatment, 20~35 mass% Ca-60~75 mass% Si alloy is supplied to the molten steel in the washing tub by the iron-coated metal wire and added 〇.1 to 0.4 kg/melting steel ton' will melt The composition of the inclusions in the steel is adjusted to Ti oxide: 30 to 70% by mass, 〇 & 0: 6 to 50% by mass, and ar : 1203: 10 to 7 % by mass. The Ca concentration in the molten steel and molten steel is 0.0005 mass% or more. The cast steel obtained by the above-described method is continuously cast by a double-strand continuous casting apparatus to produce a cast piece. This continuous casting is carried out by blowing a gas such as Ar or N2 into the molten steel flowing down the impregnation nozzle, and the yield of the molten steel at the time of the binding is 2 to 6 ton/min. The cast billet is hot rolled until the sheet thickness becomes 2 to 4 mm, and further cold rolling is performed until the sheet thickness becomes 0.6 to 1. mm, thereby obtaining a cold rolled steel sheet. As shown in Fig. 5, by pre-deoxidizing the Ti before the deoxidation treatment, the dissolved oxygen concentration in the niobium steel is 200 mass ppm or less, thereby suppressing the formation of oxide-based inclusions, and further improving the swelling test. Break through 1 deformation rate. Conversely, excess pre-deoxidation will increase the nozzle blockage-risk, so the degree of pre-deoxidation and pre-deoxidation is preferably selected according to the requirements of the suppression of the inclusions 098110383 28 201002832. Further, as shown in Fig. 5, the Ti deoxidation treatment time (RH treatment time after the addition of the alloy is preferably) is preferably 5 minutes or more 'by thereby obtaining an appropriate effect of the present invention' and the cold rolled steel sheet can be expanded. The plate thickness deformation rate of the fracture portion in the test was raised to the required level. Further, the upper limit of the Ti deoxidation treatment time is not particularly limited, and is usually about 5 minutes or less from the viewpoint of operational efficiency. 〇 (Manufacturing method of Ti-containing ultra-low carbon steel tantalum sheet) Hereinafter, a method of producing a Ti-containing ultra-low-pollution steel sheet by continuously tempering the molten steel melted by the method of the present invention will be described. In the continuous casting, when the molten steel is injected into the mold, the oxide-based inclusions contained in the molten steel are infiltrated into the deep portion of the unsolidified layer of the cast piece by the downflow and are caught by the solidified shell. In addition, in order to prevent oxide inclusions and the like from adhering to the impregnation nozzle and to blow the human/(four) ship gas to the dipping, the gas of the ship gas is bubbled in the process of floating in the _, due to the mold (10)_bath The chaos of the dazzling steel near the surface is captured by the solidified shell. These oxide-based inclusions or bubbles trapped in the cast piece cause surface defects in the steel sheet. Further, in many cases, oxidized (tetra) inclusions adhere to the bubbles of the inert gas, and the oxide-based inclusions are caught by the solidified shell together with the bubbles of the inert gas. In view of the above problems, the slab manufacturing method of several forms as described below is effective. That is, in the manufacturing method of the first Ti-containing ultra-low carbon steel slab, in the continuation casting device, Yulian 098110383 29 201002832, the molten steel is injected into the mold from the feeding tank through the immersion nozzle provided at the bottom of the feeding tank. At this time, the molten steel is not blown into the molten steel flowing down the dipping nozzle (inert gas such as Ar or non-oxidizing gas such as N2). By melting the molten steel by the method of the present invention described above, nozzle clogging can be prevented without blowing a gas into the molten steel flowing down the dipping nozzle. Further, by not blowing the gas, it is possible to suppress the occurrence of bubble defects in the cast piece due to the entrapment of the gas, and it is possible to significantly reduce surface defects such as peeling, cracking, and scale of the cold-rolled steel sheet or the gold-plated steel sheet as the final product. Further, in the method for producing a Ti-containing ultra-low carbon steel slab, it is preferred to carry out casting at a throughput of 4 ton/min or less. Fig. 6 is a graph showing the thickness deformation rate of the fracture portion of the cold-rolled steel sheet in the bulging test of the continuous casting yield (horizontal axis: ton/min) and the cold-rolled steel sheet obtained by using the steel sheet obtained by the continuous casting ( Vertical axis: %) relationship. In this test, a Ti-containing ultra-low carbon steel was melted in the following manner, and it was continuously cast to obtain a cast piece, and the cast piece was subjected to hot rolling and cold rolling to obtain a cold rolled steel sheet. After the steel was tapped from the converter, A1 was added to the steel (300 ton) which was charged into the washing tub, and the concentration of Al2〇3 was adjusted. Further, in order to reduce FeO and MnO in the slag, A1 slag is added as needed. Further, in order to control the composition of the crush after the RH vacuum degassing treatment, CaO, Al2〇3, and Ti02 are added as needed. Then, a series of treatments as shown below were carried out in the RH vacuum degassing apparatus. First, the molten steel is subjected to decarburization treatment, and the composition of the molten steel is adjusted to C: 0.0007 to 0.0150% by mass, and the oxygen concentration is 120 to 700 mass ppm. 098110383 30 201002832 Next, 0.1 to 1.2 kg/mel of molten steel ton is added to the molten steel to reduce the dissolved oxygen concentration in the molten steel to 30 to 400 mass ppm. At this time, the A1 concentration in the molten steel is o.ooi to 0.005 mass%. Further, a Fe-70% by mass Ti alloy of 0·8 to 2.0 kg/melt steel ton was added to the molten steel to carry out Ti deoxidation treatment. After the addition of the Fe-Ti alloy in the Ti deoxidation treatment, the RH vacuum degassing treatment is completed within 2 to 15 minutes, and after completion, the composition of the molten steel is Ti concentration of 0.020 〇.〇80% by mass, and the A1 concentration is 0.001 〜0 〇 〇6 mass%, total oxygen concentration 20~1〇〇mass ppm ' satisfies [〇/〇Α1]$ [〇/. Ding Wei] / 1〇. The composition of the slag in the ladle after RH vacuum degassing (deoxidation treatment) is Ca 〇 concentration: 20 〜 6 〇 mass. /〇, Si02 concentration: 5 to 20% by mass, a12〇3 concentration: 1〇~50 mass. /0, TiO2 concentration: 1 to 10% by mass, Mg 〇 concentration: 2 to 15% by mass, total Fe concentration: 1 to 8% by mass, MnO concentration: 〇. 5 to 4 mass 〇 / 〇, both satisfying the mass ratio (%<^0)/(./(^02)21, (%1^) + (%_〇)$1〇% by mass. After RH vacuum degassing treatment, the wire is wrapped by a coated iron wire. 20~35 mass% Ca-60~75 mass% Si alloy is supplied into the molten steel, and 〇1~0.4 kg/melting steel ton is added to adjust the composition of the inclusions in the molten steel to Ti oxide: 30~70 mass %, CaO: 6 to 50 mass%, /0, Al2〇3:1〇~7〇% by mass. The Ca concentration in the molten steel to be melted is 0.0005 mass% or more. By the double-strand continuous casting apparatus The molten steel obtained by the above-described method is continuously cast to produce a cast piece. The continuous casting is not performed by blowing a gas such as Ar or N2 into the molten steel flowing down the dipping nozzle, and casting 098110383 31 201002832 The steel output of the time is 2~6 _min. The heat of the cast is changed until the thickness becomes 2~4 mm, and the cold is further carried out until the plate is turned into 仏^~丨力mm, from The cold-rolled steel sheet was obtained. As shown in Fig. 6, the scale formation of the oxide-based inclusions was reduced by the scale production of 4 ton/min or less, and as a result, the cold-rolled steel sheet was subjected to the bulging test. The plate thickness deformation rate of the fracture portion is improved. Further, as a method for manufacturing the second T1 ultra-low carbon steel scale, it is preferable to carry out (1) using an electromagnetic force generated by a moving magnetic field and/or an oscillating magnetic field. Steel '(ii) either or both of the two operations of applying a static magnetic field to the molten steel in the mold to brake the flow. With such a manufacturing method, solidification can be achieved without flotation separation in pure The amount of oxide-based inclusions captured by the shell is reduced, and as a result, the plate thickness deformation rate of the fracture portion of the cold-rolled steel sheet in the bulging test is further improved. Further, by performing both (i) and (ii) above, In the above method (i) applying a moving magnetic field (AC magnetic field), an AC moving magnetic field applying device is provided, and the molten steel in the mold is rotated in the horizontal direction by the electromagnetic force of the magnetic field applying device. Grant The scales are scaled on one side. This prevents the oxide-based impurities from being trapped by the solidified shell, so that a clean cast piece with less oxide-based inclusions can be obtained. A non-moving oscillating magnetic field is applied as a six-flow magnetic field to stir. The method of melting the steel in the mold is also effective. In addition, a method of imparting an oscillating magnetic field (moving an oscillating magnetic field) accompanying the movement in the horizontal direction, 09SU0383 32 201002832 (9) In the method of applying a static magnetic field, the method is surrounded by the impregnation A static magnetic field applying means is provided at a position where the molten steel is discharged from the spout hole of the mouth, and a static magnetic field is applied by the static magnetic field applying means to reduce the flow velocity of the discharge flow. Thereby, it is possible to promote the floating of the oxide-based inclusions and suppress the solidified shell from capturing the inclusions of the present system, and obtain a clean cast having less oxide-based impurities.

In the test example of the above (i), the "application of a moving magnetic field" (black dot) is the test example of the above (9). As shown in FIG. 6, in the case of performing the operation of braking (4) or braking the flow of the Hyungang by applying a magnetic field in the above (i) or (9) in the mold, the bulging is performed as compared with the case where the magnetic field is not applied. The plate thickness deformation rate of the fracture portion in the test was further improved. In the case of both of the above (1) and (11), the moving magnetic field and/or the oscillating magnetic field is preferably applied to the upper portion of the relatively static magnetic field, and is preferably applied to the bath surface of the secret furnace. The following method is also effective in the production method of 4 ton/min in the second second Ti-containing ultra-low carbon steel slab. (Other components of the molten steel) Next, it is corrected by the condition of d r t as described above by the extremely low Ti content of the invention. (1) Compared with the content of the main reduction of the outside, the month, the middle, and the above are not so much from the viewpoint of further promoting the effect of improving the above-mentioned table and the quality of the internal quality, as it is more enjoyable. The preferred steel composition is exemplified by the viewpoint of the advantages of the political fruit. 098110383 33 201002832

Sl A is set to 0, 5 mass ° Λ below. When the amount of Si is more than 0.5% by mass, the material properties of the steel sheet are deteriorated, and when used as a plated steel sheet, the bismuth & alpha & double-face properties are deteriorated due to deterioration of electrical bond properties. In the case where these characteristics are emphasized, it is more preferable to make the amount of Si to be 0.2% by mass or less. Furthermore, the mass ratio (%Si)/(%Ti) 2 50 of the right S1 and the butyl sulphide is such that the formation of Si 〇 2 ′ in the inclusion is also enhanced as the characteristics of the shixi deoxidized steel, so it is preferably (%Si). /(%Ti)<5〇.

The lower limit of Si 1 is not particularly limited.

The amount of Mn is preferably 2.0% by mass or less. If the amount of Μη exceeds 2.0% by weight, the material is easily hardened. The amount of Μη is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 0.5% by mass or less. Further, if the mass ratio (%Mn)/(%Ti)g 100 of Μη to Ti is MnO in the inclusions, the characteristics of the manganese-deoxidized steel are also enhanced, so it is preferably (%Mn)/(0/ 〇Ti)< 100. The lower limit of the amount of Μη is not particularly limited. The amount of S is preferably 0.050% by mass or less. When the amount of s exceeds 0.050% by mass, the amount of CaS or REM sulfide in the molten steel increases, and the thin steel sheet as a product is liable to rust. The amount of S is preferably 0.030% by mass or less. The lower limit of the amount of S is not particularly limited. The amount of P is preferably from 0.005 to 0.12% by mass. If a large amount of p is contained, the amount of segregation at the grain boundary is increased to cause grain boundary embrittlement. In particular, the secondary steel sheet as a product is deteriorated in secondary work embrittlement resistance, so that it is desirable to reduce p as much as possible. The amount of p is preferably 098110383 34 201002832 is 〇.〇5〇 mass% or less. However, even if the amount of p is less than 〇.〇〇5 mass%, the material is not expected to be further improved, but the melting cost is increased. On the other hand, it is acceptable as long as the amount of P is 0.12% by mass or less. The amount of N is preferably from 0 to 0005 to 0.0040% by mass. N is the same as c. In order to improve the deep drawability of the steel sheet as a product, it is desirable to reduce n as much as possible, but even if the content is less than 〇〇〇〇5 mass%, the material cannot be expected to be further improved. The melt is made up. In terms of 邛, if the amount of N exceeds 〇 〇 4 〇 mass%, then the material of the thin steel plate is temporarily reduced. Among them, the strength, sometimes the s L machine 驷 plate to the upper limit 〇 〇 2 () 〇 mass% or so a use of such steel is not a big problem. In addition, it is also possible to add one or more of the elements listed below, depending on the purpose. .wb : 质景〇 / ,,,__ 下···Know: Deep pullability of the south thin steel plate • Β : 0.050 质金〇〇下.··Improve the secondary processing brittleness of the thin steel plate •Mo : 1.0 f #〇/oiv , The following... Increase the tensile strength of the steel sheet. Sb : 0.0200 〇乂 〇 / 〇 M... Prevent nitriding when the billet is heated • Ce : 0.0050 詈 / 0 / 卞 0 乂...to lower the melting point of the inclusions, thereby stably suppressing the mouthpiece blocking. La : 0.0050 Quality. /, 、, 〇^下... Reduces the melting point of the inclusions, thereby suppressing nozzle clogging more stably, and if necessary, makeup & illusion T will select from Nl, Cu, Cr, etc. 0/. The following 笳 <dry within the order to add. Add these elements to 098110383 35 201002832 to improve the corrosion resistance of the steel plate. It is also possible to appropriately add an alloying element other than the above, which is about 1% in total. The remainder is Fe and unavoidable impurities. [Examples] [Inventive Example 1] For a molten steel (300 ton) charged into a ladle after tapping in a converter, 400 g of A1 was added to reduce FeO and MnO in the slag, and CaO is added to control the composition of the slag after vacuum degassing. Then, a series of treatments as shown below were carried out in the RH vacuum degassing apparatus. First, 'the carbon steel is decarburized, and the composition of the molten steel is adjusted to C: 0.0010% by mass, Si: 0.01% by mass, Μη: 0.15 mass%, p: 0.015 mass%, S: 0.005 mass%, and oxygen concentration. : 500 mass ppm (the remainder is Fe and unavoidable impurities, the same in the following composition after decarburization), and the steelmaking temperature is adjusted to 1000. Then, A1' of 0.5 kg/bright steel ton was added to the molten steel to reduce the dissolved oxygen concentration in the molten steel to 12 〇 mass ppm. At this time, the A1 concentration in the molten steel was 〇 2% by mass. Further, '1 〇 kg / Hyun Steel ton's Fe-7 〇 mass 0 / 〇 Ti human gold was added to the Hyun Steel for 7 minutes of Ti deoxidation treatment. After the Ti deoxidation treatment φ 'table ~ ι T, after adding the Fe-Ti alloy, the vacuum degassing treatment is completed within 7 minutes, and the Ti coating degree in the molten steel in the cascading pouring bucket is 040.040% by mass, A1 concentration is a large mass%, and the concentration of Si〇2 after the treatment (deoxidation treatment): the total oxygen is 30 mass ppm. Further, the composition of the slag in the ladle of the vacuum degassing system is CaO concentration: 35 mass 0/098110383 36 201002832 15 mass%, Α12〇3 concentration: 35 mass%, Ti02 concentration: 3 mass%, MgO concentration: 7 mass %, total Fe concentration: 2% by mass, MnO concentration: 2% by mass (other unavoidable oxide: 1% by mass). After the vacuum degassing treatment is completed, 0.3 kg / molten steel ton of 30% by mass of Ca-70% by mass of Si alloy is added to the molten steel in the washing tub by the iron-clad metal wire to the inclusions in the molten steel. The composition is controlled. The Ca concentration in the molten steel to be melted was o.ooio mass%. The cast steel melted in the manner described above was continuously cast by a double-strand continuous casting apparatus to produce a cast piece. The morphology and composition of the inclusions in the feed tank at the time of casting were examined, and as a result, spherical inclusions of 70% by mass of Ti203-15 mass% CaCM5 mass% 八1203 were obtained. The continuous casting was carried out by blowing a gas such as Ar or N2 into the molten steel flowing down the impregnation nozzle, and the molten steel output at the time of casting was 3.8 ton/min. Further, there is almost no deposit on the inner surface of the impregnation nozzle after casting. w The cast billet is hot rolled until the sheet thickness becomes 3.5 mm, and further cold rolled until the sheet thickness becomes 〇.8 mm, and then continuous annealing is performed under annealing conditions of 780 ° C x 45 seconds (c〇ntinu 〇us. On the annealed sheet obtained in this way, 'only 2/1〇〇〇m non-Meng's inclusion properties and bubble defects were confirmed. Further, the cold-rolled steel sheet was broken in the bulging test. The plate thickness deformation rate of the part is 5 %, which is good. [Inventive Example 2] For the molten steel (3〇〇t〇n) which is charged into the ladle after tapping in the converter, the material is broken 098110383 37 201002832 In the reduction of FeO and MnO, 500 kg of A1 slag was added, and CaO and TiO2 were added to control the composition of the slag after the vacuum degassing treatment. Then, a series of treatments as shown below were carried out in the RH vacuum degassing apparatus. First, the molten steel is subjected to decarburization treatment, and the composition of the molten steel is adjusted to (:: 0.0015 mass%, 31:0.01 mass%, ]\411: 0.10 mass%, ?··0.012 mass%, S: 0.006 mass %, oxygen concentration: 450 mass ppm, and adjust the temperature of the molten steel to 1600 ° C. Then Add 0.4 kg / A1 of molten steel to the molten steel to reduce the dissolved oxygen concentration in the molten steel to 150 mass ppm. At this time, the A1 concentration in the molten steel is 0.002% by mass. Further, 1.2 is added to the molten steel. Kg / molten steel ton Fe-70% by mass Ti alloy, 6 minutes of Ti deoxidation treatment. In the Ti deoxidation treatment, after the addition of Fe-Ti alloy, the vacuum degassing treatment is completed within 6 minutes, and the Ti concentration of the molten steel at the end It is 0.045% by mass, the concentration of octa 1 is 0.002% by mass, and the total oxygen concentration is 30 mass ppm. Further, the composition of the slag in the washing tub after vacuum degassing treatment (deoxidation treatment) is CaO concentration: 30% by mass, SiO 2 concentration: 17% by mass, Al2〇3 concentration: 40% by mass, Ti02 concentration: 2% by mass, MgO concentration: 8% by mass, total Fe concentration: 1% by mass, MnO concentration: 2% by mass. After the vacuum degassing treatment is completed, borrowing Adding 0.25 kg/melting steel 30% by mass of Ca-70% by mass 81 alloy to the molten steel in the ladle by the iron-coated metal wire to control the composition of the inclusions in the molten steel. The Ca concentration in the steel is 0.0005 mass%. By the double-strand continuous casting device pair The molten steel of 098110383 38 201002832 is melted in the manner as described above for continuous casting, so that the potential and the inclusions of the skin are in the J state and composition, and the mass in the rice cooker during the casting is checked from the ball of 〇3; 7〇 mass% Ti2〇3_12 mass break nozzle 0 German steel ^ A _. Continuous casting system is not immersed when the amount of dissolution _ output is 4.Gt. The gas is replaced by a gas such as N2, and is transferred to .^u., and the molten steel is stirred in the mold by electromagnetic stirring with a moving magnetic field. Almost on the surface. (4) In addition, after the shouting nozzle, the cast steel Zhao is hot-rolled until the thickness becomes 35, and further cold is performed until the thickness becomes 0.8 mm, and then, at 78 (rcx 45 second shirt) Under the conditions of the 崎 敎 敎 敎 ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( The rate is 55%, which is good. [Inventive Example 3] For the steel (3 〇〇 (10) which is poured into the washing tub after tapping in the converter, 3 〇〇 is added to reduce Fe 〇 and Mn ( in (4) Kg ai collapse, and add Ca〇 to control the composition of the slag after vacuum degassing. Then 'in the RH vacuum degassing equipment, one of the series of treatments shown below. First, decarburization of molten steel' The composition of the molten steel was adjusted to C: 0.0015 mass%, 8 丨: 0.01 mass%, theory: 0.12 mass%, !: 0.015 mass%, s: 〇.006 mass%, oxygen concentration: 4 〇〇 mass ppm, The temperature of the molten steel was adjusted to 1600 ° C. Then, 〇.4 kg / 098110 was added to the molten steel. 383 39 201002832 A1 of molten steel ton reduces the dissolved oxygen concentration in Hyun Steel to 100 mass ppm. At this time, the A1 concentration in the molten steel is 0.002% by mass. Further, 1.1 kg/sol of molten steel is added to the molten steel. - 70 mass% 11 alloy, and subjected to Ti deoxidation treatment for 5 minutes. In the Ti deoxidation treatment, the vacuum degassing treatment was completed in 5 minutes after the addition of the Fe-Ti alloy, and the Ti concentration of the molten steel at the end was 0.042% by mass, eight. 1 concentration is 0.002 mass%, total oxygen concentration is 30 mass ppm. Further, the composition of the slag in the ladle after vacuum degassing treatment (deoxidation treatment) is CaO concentration: 42% by mass, SiO 2 concentration: 13% by mass, Al2 〇3 concentration: 30% by mass, TiO2 concentration: 4% by mass, MgO concentration: 6% by mass, total Fe concentration: 1% by mass, MnO concentration: 2% by mass (other unavoidable oxide: 2% by mass). Vacuum After the degassing treatment is completed, the composition of the inclusions in the molten steel is controlled by adding 0.27 kg/melting steel 30 mass% Ca-70 mass% Si alloy to the molten steel in the ladle by the iron-coated metal wire. The Ca concentration in the molten steel to be melted is 0.0006 mass%. The strand continuous casting apparatus continuously casts the molten steel melted in the manner described above to produce a cast piece. The morphology and composition of the inclusions in the feed tank during the casting were examined, and the result was 72% by mass. -12% by mass of CaO-16% by mass of spherical inclusions of Al2〇3. Continuous casting is carried out by blowing a gas such as Ar or N2 into the molten steel flowing down the impregnation nozzle, and the amount of molten steel produced during casting is obtained. It is 4.0 ton/min. Further, a static magnetic field of a direct current magnetic field is applied to the molten steel in the mold to brake the flow of the molten steel. Further, there is almost no deposit on the inner surface of the impregnation nozzle after casting. 098110383 40 201002832 The cast steel is heat-dried until the thickness of the plate becomes 3.5 _ until a step is cold-rolled until the plate thickness becomes progressive and U.8mm is taken as the soil, and continuous annealing is performed under the annealing condition of the second. On such a square 8〇CX45 board, only about 2 of her _m ^ shank is the defect of annealing. Further, the non-metal-physical property and the bubble property are further deteriorated, and the cold-rolled steel sheet has a enthalpy ratio of 55%.板 之 之 板 板 板 [ [ 发明 发明 发明 发明 发明 发明 发明 [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ The form and composition of ^ are the same as in Invention Example 1). In the continuous casting apparatus, a static magnetic field applying means is provided at a position below the lower end of the discharge port of the dipping nozzle. Further, the shape of the discharge hole of the impregnation nozzle is a square of gas and a width of 80 mm. The Ar gas in the impregnation nozzle is blown into the flow rate. The magnetic field applied by the static magnetic field application device is strong.

For continuous casting of molten steel, it is 0~10 NL/min, and the degree (DC static magnetic field) changes within the range of (U~〇·3 Tesla, to 4 5~ 6.〇t〇n The casting speed of /min is cast and the steel has a width of mm and a thickness of 250 mm. After the cast slab is hot-rolled and cold-rolled to form a thin steel sheet, the ruthenium steel sheet is subjected to hot-dip galvanizing. In the galvanized steel sheet, the surface defects of the inclusion property and the bubble property are extremely small, and it can be confirmed that the steel surface can be cleaned by the addition of a static magnetic field during casting. 098110383 41 201002832 [Inventive Example 5] The continuous restraining device performs continuous casting on the dissolution of the same conditions as the invention. Thus, (4) and composition and invention examples (4) of the inclusions in the casting casting are produced. In the continuous build-up, an AC shift field application device is placed at a distance of 2 m from the mold bath surface of the mold (4). In addition, the material of the spit out of the hole, the square of the horizontal. When the molten steel is connected, the flow rate of the Ar gas in the impregnation nozzle is 0 to 10 NL/mmM, and the magnetic field strength (AC moving magnetic field) applied by the AC moving magnetic field applying device is (10) 5 to 〇 2 The range of the drawing is changed, and the cleaning speed of 5 6G tC>n/min is made of a copper billet having a width of 1200 to 1500 mm and a thickness of 250 mm. After the casting is reduced, the shape of the steel sheet is determined by the praying. The surface of the steel sheet is very small, and the surface defects of the invisible steel sheet are extremely small. When an alternating magnetic field is applied, the steel which is clean on both the surface and the inside can be fabricated. [Invention 6] It is prepared to use Nb = 0.01 〇 mass based on the invention of Invention Example 1. /〇, B==〇〇溶1〇% by mass of molten steel, and a molten steel containing Μ〇==〇〇ι〇〇% by mass, and the conditions of the same were adjusted to the same conditions as in Invention Example 1 to produce an annealed sheet. 098110383 42 201002832 A, B In the annealed sheet, only 0.2/1000 m of non-metallic inclusion properties and bubble defects were confirmed. Further, the plate thickness deformation ratio of the fracture portion of the cold-rolled steel sheet in the bulging test was 50%, which was good. Comparative Example 1] For the molten steel (300 ton) charged into the drum after tapping in the converter, 100 kg of A1 slag was added to reduce FeO and MnO in the slag. Then, the RH vacuum degassing device was used. Perform one of the series of treatments as shown below. First, the molten steel is decarburized and will The composition of the molten steel is adjusted to 0: 0.0010% by mass, 3:1: 0.01% by mass, ]\/[11: 0.15 mass%, ?: 0.015 mass%, S: 0_005 mass%, oxygen concentration: 500 mass ppm, And adjust the temperature of the molten steel to 1600 ° C. Then, add 0.3 kg / molten steel ton A1 to the molten steel, so that the dissolved oxygen concentration in the molten steel is reduced to 220 mass ppm. At this time, the A1 concentration in the molten steel is 0.002% by mass. Further, 1.2 kg/melt ton of Fe-70% by mass Ti alloy was added to the molten steel, and Ti deoxidation treatment was performed for 7 minutes. In the Ti deoxidation treatment, the Fe-Ti alloy was added within 7 minutes after the addition of the Fe-Ti alloy. At the end of the vacuum degassing treatment, the Ti concentration of the molten steel is 0.035 mass%, the A1 concentration is 0.001 mass%, and the total oxygen concentration is 40 mass ppm. Further, the material in the ladle after vacuum degassing treatment (deoxidation treatment) The slag composition CaO concentration: 23% by mass, SiO 2 concentration: 27% by mass 'Al2〇3 concentration: 20% by mass, Ti02 concentration: 0.8% by mass, MgO concentration: 9% by mass, total Fe concentration: 8% by mass, MnO concentration : 6 mass% (other unavoidable oxides: 6.2 mass%). 098110383 43 201002832 After the vacuum defluorination treatment is completed, a 0.2 kg/melt steel 30 mass 〇/oCa_7 〇 mass 〇/〇si alloy is added to the molten steel in the ladle by the iron-coated metal wire, and the inclusions in the molten steel are added. The composition is controlled to produce a cast piece by continuously casting a molten steel melted in the manner described above by means of a continuous casting device of a double-twist steel. The morphology and composition of the inclusions in the feed tank during the casting were examined as a result of a spherical inclusion of 70% by mass of 1^203-15 mass% CaO-15 mass ° / 〇Al2〇3. The continuous casting was carried out by blowing a gas such as Ar or N2 into the molten steel flowing down the impregnation nozzle, and the yield of the molten steel at the time of casting was 4.8 ton/min. Further, there is almost no deposit on the inner surface of the impregnation nozzle after casting. The cast billet was hot rolled until the sheet thickness became 3.5 mm, and further cold rolling was performed until the sheet thickness became 〇.8 mm, and then continuous annealing was performed under annealing conditions of 780 ° C x 45 seconds. On the annealed sheets obtained in such a manner, only defects of 0.5/1000 m of non-metallic inclusion properties and bubbles were confirmed. Further, the plate thickness deformation rate of the fracture portion of the cold-rolled steel sheet in the bulging test was 25%, which was not preferable. [Comparative Example 2] An annealed sheet was produced under substantially the same conditions as in Comparative Example 2, wherein the time of A1 deoxidation (500 mass ppm - 220 mass ppm) before Ti deoxidation treatment was set to 120 seconds with reference to the technique of Patent Document 5. A0/t= 4.2). The plate thickness deformation ratio of the fracture portion in the bulging test of the obtained annealed sheet in this manner was 30%, which was improved as compared with Comparative Example 1, but still did not reach the level of the object of the present application 098110383 44 201002832. Furthermore, it was confirmed that the non-metallic inclusions and bubble defects of 0.4/looo m were defective. (Industrial Applicability) According to the method for making a Ti-containing ultra-low carbon steel according to the present invention, the composition of the oxide-based inclusions in the molten steel can be optimized, and the amount of inclusions can be reduced. Therefore, it can prevent clogging of the impregnation nozzle due to oxide-based inclusions during continuous casting (nozzle clogging), and can be used to form a cold-rolled steel sheet, especially from oxide-based impurities and bubbles. The resulting surface defects are higher than y' and have a high resistance to cold-rolled steel sheets resulting from the press fracture of oxide-based inclusions. In addition, according to the manufacturing method of the Τι extremely low carbon steel flakes of this meal, by optimizing the continuous casting conditions, the Ti-containing ultra-low carbon steel, which can be made by the method of the above-mentioned Wei method, can be used to improve the cold rolling. The surface properties of the steel sheet and the cast of the endogenous material.

[Simple description of the drawing] Fig. 1 shows the total Fe concentration and MnO concentration in the washing tank after deoxidation treatment of molten steel i^Tl: (%TFe) + (%Mn〇) (horizontal sleeve: mass%) And a graph showing the relationship between the thickness deformation rate (vertical axis: %) of the fracture portion of the cold-rolled steel sheet in the % test. Fig. 2 Silk (4) Close the CaO concentration in the fine material after the Ti-simplification treatment and the mass of the Si02 Han & (%Ca〇)/(%si(6) (horizontal sleeve), and the cold-rolled steel plate (4) (4) Wipe, crack Plate thickness deformation rate (vertical axis: %) of 098110383 45 201002832 Relational chart. Fig. 3 shows the Ti02 concentration (horizontal axis: mass%) in the ladle slag after Ti deoxidation treatment on molten steel, and cold The graph of the relationship between the plate thickness deformation rate (vertical axis: %) of the fracture portion of the rolled steel sheet in the bulging test. Fig. 4 is a graph showing the Al2〇3 concentration in the tank slag after the Ti deoxidation treatment of the molten steel ( The horizontal axis: mass %), and the relationship between the thickness deformation rate (vertical axis: %) of the fracture portion of the cold-forward L steel plate in the bulging test. Fig. 5 shows the dissolution in the molten steel before the Ti deoxidation treatment. Graph of the relationship between the oxygen concentration (white dots, black dots) and the Ti deoxidation treatment time (horizontal axis: minutes) and the thickness deformation rate (vertical axis: %) of the fracture portion of the cold rolled steel sheet in the bulging test Fig. 6 is a view showing a test example (black dot, black square) for applying a magnetic field to molten steel in a mold, and a test case in which no magnetic field is applied. (White dot) A graph showing the relationship between the yield of continuous casting (horizontal axis: ton/min) and the thickness deformation rate (vertical axis: %) of the fracture portion of the cold-rolled steel sheet in the bulging test. 098110383 46

Claims (1)

201002832 VII. Patent application scope: 1. A method for melting Ti-containing ultra-low carbon steel, which is contained in a melting system containing C: 0.020 mass% or less, Ti: 0.010 mass% or more, and Ca: 0.0005 mass% or more. In the case of carbon Ti deoxidized steel, the molten steel is subjected to decarburization treatment, and then Ti is added to the ladle to perform deoxidation treatment, thereby obtaining A1 content (% by mass) and Ti content (% by mass) satisfying [%A1] S [% A deoxidized molten steel having a composition of Ti]/10, after which Ca is added to the deoxidized steel in the washing tub, thereby adjusting the composition of the inclusions in the molten steel to Ti oxide: 90% by mass or less, CaO: 5 to 50% by mass, Al2〇3: 70% by mass or less, and the above-described state of the poured slag after deoxidizing the molten steel by adding Ti as described above: • The total Fe concentration and the MnO concentration are 10 masses. % or less; • Mass ratio of CaO concentration to SiO 2 concentration (%CaO) / (%Si02) is 1 or more; • Ti02 concentration is 1% by mass or more; and • A1203 concentration is 10 to 50% by mass. 2. For the method of melting Ti-containing ultra-low carbon steel according to item 1 of the patent application, the system melts extremely low carbon Ti deoxidized steel having the following composition: C: 0.020% by mass or less, Ti: 0.010% by mass or more, Ca: 0.0005 mass% or more, Si: 0.2 mass% or less, Μη: 2.0 mass% or less, S: 0.050 mass% or less, P: 0.005 to 0.12 mass%, :^: 0.0005 to 0.0040 mass%, and the remaining Fe and Inevitable impurities. 098110383 47 201002832 3. For the fusion method of Ti-containing ultra-low carbon steel according to item 2 of the patent application scope, in addition to the composition of the second item of the patent application scope, further containing Nb: 0.100% by mass or less, B: 0.050 mass % or less, and Mo: 1.0% by mass or less. 4. The method for melting Ti-containing ultra-low carbon steel according to any one of claims 1 to 3, wherein after the decarburization treatment of the molten steel, the addition of Ti to perform deoxidation treatment, addition to Al Further, one or two or more selected from the group consisting of Si and Μη are pre-deoxidized, whereby the dissolved oxygen concentration in the molten steel is previously 200 ppm by mass or less. 5. The method for melting Ti-containing ultra-low carbon steel according to any one of claims 1 to 3, wherein the deoxidation treatment time of the molten steel obtained by adding Ti is set to 5 minutes or longer. 6. A method for producing a Ti-containing ultra-low carbon steel slab, which is a continuous casting of a molten steel melted by the melting method according to any one of claims 1 to 5, thereby producing a slab When the molten steel is injected into the mold from the feed tank by the dipping nozzle provided at the bottom of the feed tank, the molten steel is not cast into the molten steel flowing down the dipping nozzle. 7. A method for producing a Ti-containing ultra-low carbon steel slab, which is a continuous casting of a molten steel melted by the melting method according to any one of claims 1 to 5, thereby producing a slab Among them, 098110383 48 201002832 stirs the molten steel in the mold by the electromagnetic force brought by the magnetic field. 8. A method for producing a Ti-containing ultra-low carbon steel slab, which is obtained by continuously casting a molten steel melted by the melting method according to any one of claims 1 to 5, thereby producing a slab A static magnetic field is applied to the molten steel in the mold to brake the flow of the molten steel. A method for producing a Ti-containing ultra-low carbon steel slab, which is a continuous casting of a molten steel melted by the melting method according to any one of claims 1 to 5, thereby producing a slab Among them, the molten steel in the mold is stirred by the electromagnetic force by the magnetic field, and a static magnetic field is applied to the molten steel to brake the flow of the molten steel. 10. The method for manufacturing a Ti-containing ultra-low carbon steel slab according to Item 7 of the patent application, wherein when the molten steel is injected into the mold from the feeding tank through the immersion nozzle provided at the bottom of the feeding tank, The molten steel which is blown down in the above-mentioned impregnation nozzle is blown with gas to cast molten steel. 11. The method for manufacturing a Ti-containing ultra-low carbon steel slab according to Item 8 of the patent application, wherein when the molten steel is injected into the mold from the feeding tank through the immersion nozzle provided at the bottom of the feeding tank, The molten steel which is blown down in the above-mentioned impregnation nozzle is blown with gas to cast molten steel. 12. The method for manufacturing a Ti-containing ultra-low carbon steel slab according to Item 9 of the patent application, wherein 098110383 49 201002832 when molten steel is injected into the mold from the feeding tank through the surface of the impregnation nozzle provided at the bottom of the feeding tank, The molten steel is not cast into the molten steel flowing down in the above-mentioned impregnation nozzle. 13. The method for producing a Ti-containing ultra-low carbon steel slab according to item 6 of the patent application, wherein the sinter steel is continuously cast at a throughput of 4 ton/min or less. 098110383 50