The present invention relates to a cold-rolled steel sheet and a manufacturing method for a flux-cored wire.
[2]
BACKGROUND
[3]
For steel strip to be applied to a welding electrode for the flux cored wires (Flux Cored Wire) is, the steel sheet is applied, and flux (Flux) material is developed in combination to be applied to the disk in order to cope with various uses. Special purpose, for example, wear resistance may become high and the development of Mn Steel welding member, a member for extremely low temperature welding is excellent in toughness at cryogenic temperatures, a variety of special-purpose welding member such as anti-vibration performance is superior anti-vibration member made STEEL welding. Accordingly, there is a welding materials developed for progress to meet these special welding steel.
[4]
[5]
In general, the highest productivity welding method of welding an easy welding in various positions has a flux-cored welding (FCW, Flux Cored Welding) method. Weld materials used in the welding method is a flux cored wire, a strip (Strip) drawing a general cold-rolled steel sheet and processed into a U-shape, is to about 5 by weight ratio to the processing U tube 50% of the flux components and after addition of a mixture of alloy elements such as manganese (Mn), nickel (Ni) in the form of a powder is prepared by processing a circular shape. The flux component is added in order to secure the welding operability, the alloying elements are added to ensure the characteristics suitable for intended use of the electrode.
[6]
[7]
At this time, through the core type of the alloy components and the amount change is added in powder form to obtain various properties required for the electrode material. For example, to be charged with a mixture of the alloying element and a flux to improve the low temperature toughness in the processed wire core portion and to produce the weld member that require superior low temperature toughness.
[8]
[9]
On the other hand, cold-rolled steel product for use as a flux cored wire used for the manufacture Dwyer is generally plain carbon steel alloy elements is not added is used a lot, there is a stainless steel is used for some special applications.
[10]
[11]
The steel product for a wire of normal carbon steel base does not cause a tearing phenomenon of the pull-out when the steel material to elongation is excellent, and various because advantage is continuously produced without passing through a separate heat treatment step from FIG lower molding degree of work hardening to a final wire manufacturable It has been applied for the purpose. However, the carbon steel weld steel material is the addition of the flux and the alloy core element filling the internal wirings are needed in order to ensure the electrode characteristics according to the application since the low alloy steel. However, since in order to secure the welding operability by default, requires the addition of an appropriate level of flux, the core sikineunde up to the alloy elements is input to the fact that the limit. That is, a large amount of oxidizing agent in the center portion of the steel wire (Ti, Mn, Zr, Al, etc.), slag forming agents (TiO 2 , SiO 2 , Al 2 O 3 , ZrO 2, MnO, etc.), an arc stabilizer (the K, Na, etc.), alloy components (Si, Mn, Ni, Zr, Cr, etc.) one, approximately yongjeokryang of 30 to 60%, including the flux in the wire of steel, etc. must all be added and that the limit of filling, according to the powder to be filled, but the difference is the weight ratio is about 15 to 25% level, known as a limit. When this increase in the content of the alloying element to ensure the same characteristic when there is a problem that a limited amount of flux components such as difficult to secure a stable welding characteristics. In addition, these alloying elements are also causing the welding the welding portion of the core component segregation during melting operation as added in powder form, a problem that also acts as a weld defect factors.
[12]
[13]
If the welding wire of stainless steel, for there, so basically a lot, the amount of alloying elements in the nickel (Ni) or chromium (Cr), etc. present in the carbon steel component as compared to normal carbon steel, to reduce the amount of the core alloying elements that are added with the flux but that is only applicable to the original material price increases because the special-purpose real high alloy by default. As well as, in the case of these stainless steel welded disk There is another problem of extracting the heat treatment to be carried out separately between the manufacturing process increases the risk caused by work hardening is disconnected when the electrode wire processing served as increase of the manufacturing cost factors.
[14]
[15]
As of workability, in particular the drawing workability and the steel product for welding wire for extremely low temperature required for the low temperature toughness is to prepare a high-priced alloying element as a pure powder form in order to take advantage of the common carbon steel to secure the sheet entrance low temperature toughness after Tube Mill flux other flux While improving the low temperature toughness by charging with ingredients, and in this case the alloy powders to be added, even there is a problem according to a restriction on the addition conditions of the flux component to secure the welding stability in accordance with the high days input Fair as well as highly purified . Further, at this time it is also emerging problem of deteriorating the workability of such split electrode in process step as the expensive alloying elements to the phenomenon that causes a segregation phenomenon in the flux concentration in a portion of the electrode caused to be added.
[16]
[17]
Accordingly, a situation where the development of a superior low-temperature steel product for welding wire having a toughness and welding operability is desired to be preferably applied in cryogenic environments. For example, the extremely low temperature in a suitable flux cored wire by more than 40% elongation of the material in order to secure the properties of the cold-rolled steel sheet for, weld segregation index less than 0.15%, which measures the impact energy value at -40 ℃ securing at least 50J the review is being conducted for.
[18]
[19]
For example, in Patent Document 1 a A method of manufacturing a flux-cored wire steel sheet, Cr, Mo, Ti, etc. in steel containing Mn 1.4 ~ 2.4%, Si 0.2 ~ 0.4%, Ni 2.8 ~ 6.4% adding a method of the impact toughness and strength of manufacturing the electrode for superior steel disclosed by. However, Patent Document 1 is, because a lot of the addition of expensive alloying elements, there is a problem in that manufacturing cost is increased, there is also a difficult problem to secure the drawing workability by the addition of alloying elements, a high strength, but can be secured, the flexible lower.
[20]
[21]
Further, in Patent Document 2, and by the addition of Ti, Mg, etc. in the flux material discloses a technique for reducing welding defects to facilitate deoxygenation reaction of the molten metal. However, many alloys it is necessary to add an element, thus when the addition of many alloying elements to the flux of fine particles during welding going out around the spatter (spatter) developing the flux more in order to obtain sufficient deoxidizing effect of the molten metal the welding operability such as occurring, there is a problem to be lowered.
[22]
[23]
Therefore, the it is possible to obtain an excellent low-temperature toughness of the weld in a cryogenic environment for, the welding workability and drawing workability is excellent flux cored welding utilizing the cold-rolled steel sheet for the wire strips and development of a method of manufacturing the same situation that is desired.
[24]
[25]
[Patent Document]
[26]
[Patent Document 1] Korea Patent Laid-open No. 2006-107910 No.
[27]
(Patent Document 2) Japanese Unexamined Patent Publication Sho No. 60-46896
[28]
Detailed Description of the Invention
SUMMARY
[29]
One aspect of the present invention is to provide a low-temperature toughness, welding operability and workability is excellent flux cored wire for cold-rolled steel sheet and a method of manufacturing the same.
[30]
[31]
On the other hand, object of the present invention is not limited to the above-described information. An object of the present invention will be understood from the overall context of the present specification, Those having ordinary skill in the art will not have any difficulty to understanding an additional object of the present invention.
[32]
Problem solving means
[33]
In one embodiment of the present invention weight%, C: 0.005 ~ 0.10%, Mn: 0.05 ~ 0.25%, Si: 0.05% or less (0 except percent), P: 0.0005 ~ 0.01% , S: less than 0.008% ( 0% is excluded), Al: 0.005 ~ 0.06% , N: 0.0005 ~ 0.003%, Ni: 0.8 ~ 1.7%, Cr: 0.1 ~ 0.5%, remainder Fe and unavoidable W contained impurities, defined by the following relation 1 N is 0.10 ~ 0.75 provides the flux cored wire for cold-rolled steel sheet.
[34]
Equation 1: W N = (C × 31 + 0.5 × Mn + 20 × Al) × (Ni) × (0.6 × Cr)
[35]
(Where, the unit being in each element content in the above relational expression 1 is% by weight.)
[36]
[37]
To another embodiment of the present invention weight%, C: 0.005 ~ 0.10%, Mn: 0.05 ~ 0.25%, Si: 0.05% or less (0 except percent), P: 0.0005 ~ 0.01% , S: less than 0.008% ( 0% is excluded), Al: 0.005 ~ 0.06% , N: 0.0005 ~ 0.003%, Ni: 0.8 ~ 1.7%, Cr: 0.1 ~ 0.5%, remainder Fe and unavoidable W contained impurities, defined by the following relation 1 N steps of: heating the slab to 0.10 ~ 0.75 1100 ~ 1300 ℃; Phase is finished the heated slab hot rolling temperature to obtain a hot rolled steel sheet by hot rolling such that the 880 ~ 950 ℃; Step for winding the hot-rolled steel sheet in a temperature range of 550 ~ 700 ℃; To obtain a cold-rolled steel sheet to the take-up the hot-rolled steel sheet cold-rolled to a reduction ratio of 50 to 85% step; And it provides a process for the production of cold-rolled steel sheet for use in a flux cored wire comprises continuous annealing the cold-rolled steel sheet in a temperature range of 700 ~ 850 ℃.
[38]
Equation 1: W N = (C × 31 + 0.5 × Mn + 20 × Al) × (Ni) × (0.6 × Cr)
[39]
(Where, the unit being in each element content in the above relational expression 1 is% by weight.)
[40]
[41]
In addition, solving means of the above-described problems is, it is not enumerate all features of the present invention. The various features and advantages and effects thereof of the present invention can be understood in more detail with reference to specific embodiments below.
[42]
Effects of the Invention
[43]
According to an aspect of the invention, low temperature toughness, welding operability and workability is excellent flux cored wire by providing a cold-rolled steel sheet shipbuilding industry, materials industry, building industry electronic three welding is possible flux cored wire-welding electrode used in for It can provide the pulpit.
[44]
Brief Description of the Drawings
[45]
1 is a picture of observing the microstructure of an invention example 2, the present invention embodiment, (a) is a picture of observing the flux cored wire produced by using the invention example 2, (b) it is the outer covering of the (a) a photograph enlarged portion.
[46]
2 is a picture of observing the microstructure of the examples Comparative Example 5 present invention, (a) is a picture of observing the flux cored wire produced by using the invention example 2, (b) it is the outer covering of the (a) a photograph enlarged portion.
[47]
Best Mode for Carrying Out the Invention
[48]
Hereinafter, the preferred embodiments of the present invention. However, embodiments of the present invention can be modified in many different forms and is not limited to the embodiments and the scope of the present invention described below. In addition, embodiments of the present invention is provided in order to explain more fully the present invention to those having ordinary skill in the art.
[49]
[50]
It will now be described in detail with respect to a flux cored wire for cold-rolled steel sheet of the present invention.
[51]
[52]
Flux cored cold-rolled steel sheet for the wire of the present invention in weight%, C: 0.005 ~ 0.10% , Mn: 0.05 ~ 0.25%, Si: 0.05% or less (0% excluded), P: 0.0005 ~ 0.01% , S: 0.008% or less (0% excluded), Al: 0.005 ~ 0.06% , N: 0.0005 ~ 0.003%, Ni: 0.8 ~ 1.7%, Cr: 0.1 ~ 0.5%, remainder Fe and unavoidable inclusion of impurities, and the relational expression 1 W defined by N is characterized in that 0.10 ~ 0.75.
[53]
[54]
First, a detailed description of the alloy composition of the present invention. Units or less for each element content refers to a weight% unless otherwise specified.
[55]
[56]
C: 0.005~0.10%
[57]
Carbon (C) is generally an element to be added to improve the strength of steel, and is an element to be added in order to have similar properties to the welding heat affected portion base material. If the C content is less than 0.005%, it is insufficient that the aforementioned effect. If, on the other hand, C content exceeds 0.10%, there may occur problems such as breakage during drawing process that occurs due to the high strength or strain hardening. In addition, there is a disadvantage that not only causes the low-temperature welding cracks or joints decreases the impact toughness due to high hardness can be processed into the final product desired be carried out a plurality of heat treatment. Therefore, C content may be 0.005 ~ 0.10% is desirable, and more preferably for a welding heat affected portion improved properties from 0.01 to 0.06%.
[58]
[59]
Mn: 0.05 ~ 0.25%
[60]
In the case of manganese (Mn) as a solid solution strengthening element to increase the strength of the steel and serves to improve the hot workability. However, excessive addition of manganese has a large amount of - it is possible to form a sulfide (MnS) precipitates inhibit the river ductility and formability. When the amount of Mn is less than 0.05% had become red-short occurrence factor is hard to contribute to the stabilization of austenite. On the other hand, when the Mn content exceeds 0.25%, the so flexible can decrease, and serves as a factor for generating center segregation result in disconnection during the drawing operation in the electrode manufacturing process, Mn amount is preferably 0.05 to 0.25%, and , it may be more preferably 0.06 ~ 0.24%.
[61]
[62]
Si: 0.05% or less (excluding 0%)
[63]
Since silicon (Si) is not only act as a break to form an oxide layer on the surface of the steel sheet by combination with oxygen deterioration of surface properties and fell corrosion resistance factors promote hard phase transformation in the weld metal acts as a factor to degrade the low-temperature impact properties It defines the amount to 0.05% or less. The amount of the Si is advantageously more preferably not more than 0.04%.
[64]
[65]
P: 0.0005~0.01%
[66]
Phosphorus (P) is to, while present in the employed elements in steel keeping the rigidity of a certain level as an element which causes a solid-solution strengthening to improve the strength and hardness preferably added 0.0005% or more, however, in a case where the content exceeds 0.01%, the causing the casting center segregation during the ductility is reduced, it is possible to make the wire inferior processability. Therefore, P content is preferably of 0.0005 ~ 0.01%, and may be more preferably from 0.001 to 0.009%.
[67]
[68]
S: less than 0.008% (excluding 0%)
[69]
Sulfur (S) content is preferably lower as possible, so that a factor of forming the non-metallic inclusions combined with Mn in steel brittle and glowing (red shortness). Further, when the S content is high, so the problem of lowering the toughness of the base metal of the steel sheet S content is preferably not more than 0.008%, and preferably less than 0.0075%.
[70]
[71]
Al: 0.005~0.06%
[72]
Aluminum (Al) is an element advantageous for securing a flexible element to be added in order to prevent the material deterioration due to aging at a deoxidizer and an aluminum killed steel, an effect that is significantly greater than when the extremely low temperature. If the Al content is less than 0.005%, it is insufficient that the aforementioned effect. If, on the other hand the Al content exceeds 0.06%, the aluminum-oxide (Al 2 O 3 ) and the surface inclusions is increasing by locally to deteriorate the surface properties of the hot rolled material and grain boundaries as well as the HAZ be workability is lowered as and ferrite are formed to be reduced in mechanical properties, may cause a problem that the weld bead (bead) shaped deteriorate after welding. Therefore, Al content is preferably 0.005 ~ 0.06%, and may be more preferably 0.007 ~ 0.050%.
[73]
[74]
N: 0.0005~0.003%
[75]
Nitrogen (N) is an element effective for strengthening as present in a solid solution state within the steel, the addition of more than 0.0005% is required to secure the target stiffness. On the other hand, if the N content exceeds 0.003%, the aging property by increasing the pressure as rapidly worse, not according to the denitrification step in steel production there is a problem in that the steel-making workability deteriorate. Therefore, N content is preferably 0.0005% to 0.003%, and may be more preferably 0.008 ~ 0.0029%.
[76]
[77]
Ni: 0.8 ~ 1.7%
[78]
Nickel (Ni) is as an element necessary for the low temperature improved impact properties to form a stable organization in improving the ductility as well as effective for improving drawing formability extremely low temperature, on the other to obtain the same effect at least 0.8% in order for stable operation of the flux composition the addition is necessary. On the other hand, if the Ni content is more than 1.7%, the workability may become inferior by the drawing in strength, can lead to surface defects. Further, Ni is an expensive element, so there is a problem in that production cost rises. Therefore, the Ni content is preferably 0.8 ~ 1.7%, may be more preferably 0.085 ~ 1.65%.
[79]
[80]
Cr: 0.1~0.5%
[81]
Chromium (Cr) is more than 0.1%, the addition is preferable in order to ensure the same effect as this element contributing to improving the corrosion resistance and also operates as to form a stable nokcheung as a favorable element to the portion welded joint strength. On the other hand, if in the Cr amount exceeds 0.5% chromium carbide can cause a formed brittle and Thus it is a problem to process should not, Cr content, it is preferable to satisfy the range from 0.1 to 0.5%, more preferably 0.13 ~ may be 0.45%.
[82]
[83]
The remaining components of the invention are iron (Fe). However, in the conventional manufacturing process it is not intended from the raw material or the environment, because impurities may be unavoidably incorporated, it is impossible to exclude them. These impurities are, because you know if anyone skilled in the normal manufacturing process does not specifically mention that all the contents herein.
[84]
[85]
On the other hand, cold-rolled steel sheet of the present invention is to be defined by the W 1 to, not only the alloy composition satisfy the aforementioned relational expression FC is preferably 0.10 ~ 0.75. However, in relation to a unit of each element content it is weight%.
[86]
[87]
Equation 1: W N = (C × 31 + 0.5 × Mn + 20 × Al) × (Ni) × (0.6 × Cr)
[88]
[89]
The relational expression 1 is designed in consideration of the relationship of the elements on the welding workability and the drawing processability. W N when a is less than 0.10, there is a problem that at room temperature tissue is the welding operability deteriorates as the light in the write amount of transformation processability aspects of onto the glass, however, in order to secure the low temperature toughness, increasing the amount of alloy added to the alloying elements of the flux . On the other hand, W N when the 0.75 exceeded, it is a problem that manufacturing cost increases with increasing fraction of the mild microstructure with much addition of expensive alloying elements not only be a problem with the breaking of Tube Mill and drawn during welding member occurs , W N is preferable to satisfy the range of 0.10 ~ 0.75, and may be 0.11 ~ 0.73 and more preferably.
[90]
[91]
On the other hand, cold-rolled steel sheet of the present invention with the area%, cementite: it is preferable to have a fine structure consisting of 1 to 6% and the balance ferrite. If the case, the fraction of the cementite low as less than 1% is, and in accordance with not promote the precipitation of the carbide acts as a factor that represents the strain aging defect by the steel employed elements, while the cementite fraction exceeds 6%, the there is a problem, as well as the risk of cracking when the drawing process is also degraded corrosion resistance fraction of the cementite is preferably in the range of 1 to 6%, and may be more preferably 1.3 ~ 5.8%.
[92]
[93]
Cold-rolled steel sheet according to the present invention may be at an elongation of 40%. By satisfying such properties it can be applied preferably as a material for the flux cored wires. If the elongation is less than 40% may cause a deterioration lowered a reduction of area during the drawing process of the welding wire and the Tube Mill workability problem that a crack, such as during processing tearing occurs.
[94]
[95]
Further, the cold-rolled steel sheet is produced according to the invention the weld segregation index of more than 0.15%, the low temperature impact energy at -40 ℃ be at least 50J. More specifically means a segregation factor of the welding welds in the flux cored wire produced by using the cold-rolled steel sheet according to the present invention, the weld segregation index of the area of ​​the side seokbu occupied by the additive element in the entire area of ​​the weld ratio is displayed. When segregation occurs in the weld zone is the concentration of stress to the side during processing seokbu it acts as breaking factor. In order to prevent the tearing of the weld zone during secondary processing segregation after welding of the welded part is preferably a segregation index less than or equal to 0.15%, can be not more than more preferably 0.125%. As in the conventional flux cored wire is added an element such as nickel (Ni) as an alloying element in the flux rather than the base material in order to secure the low temperature toughness, but a problem of segregation index of the weld rise occurs, the cold-rolled steel sheet according to the invention a it may be secured to these factors significantly reduce the segregation of the weld segregation index to less than 0.15% when it uses. In addition, it is necessary that the impact energy in the impact test for evaluating the low-temperature stability of the electrode to obtain more than 50J in the experimental temperature -40 ℃. Impact energy value obtained by the impact test at -40 ℃ is the welded part, such as in a low temperature environment falls below 50J is a factor that causes cracks due to low temperature shock can cause problems in the safety of welded structures, so it is necessary to secure more than 50J. Low-temperature impact energy at the -40 ℃ is more preferably not less than 55J.
[96]
[97]
It will be described in detail below, the method of manufacturing a cold-rolled steel sheet for use in a flux cored wire of the present invention.
[98]
[99]
Method of manufacturing a cold-rolled steel sheet for use in a flux cored wire of the present invention includes the steps of heating a slab which satisfies the above-described alloy composition to 1100 ~ 1300 ℃; Phase is finished the heated slab hot rolling temperature to obtain a hot rolled steel sheet by hot rolling such that the 880 ~ 950 ℃; Step for winding the hot-rolled steel sheet in a temperature range of 550 ~ 700 ℃; To obtain a cold-rolled steel sheet to the take-up the hot-rolled steel sheet cold-rolled to a reduction ratio of 50 to 85% step; And a step of continuous annealing the cold-rolled steel sheet in a temperature range of 700 ~ 850 ℃.
[100]
[101]
First, heating the slab to 1100 ~ 1300 ℃. This is to perform the subsequent hot rolling process smoothly, and the process for homogenizing the slab. The slabs from problems that the heating temperature is subsequently increased rapidly load during hot rolling of less than 1100 ℃, and the other hand, if it exceeds 1300 ℃ as well as energy costs increase, the amount of the surface scale may increase to lead to loss of material have. Thus, the slab heating temperature is preferably in the 1100 ~ 1300 ℃, it may be more preferably 1150 ~ 1280 ℃.
[102]
[103]
Wherein the finish hot rolling, the slab heating temperature, hot-rolled so that the 880 ~ 950 ℃ to obtain a hot-rolled steel sheet. If the finish rolling temperature is lower than 880 ℃ has been honrip the grain upset proceeds rapidly as the hot rolling is finished at a low temperature area, results in a reduction in the hot rolling resistance and workability. On the other hand, if the finish rolling temperature exceeds 950 ℃ has become a grain size not support a uniform hot-rolled made insufficient throughout the thickness can receive a reduction in the impact toughness due to coarsening of crystal grains. Therefore, the finishing hot rolling temperature is preferably in the 880 ~ 950 ℃, it may be more preferably 885 ~ 940 ℃.
[104]
[105]
The hot-rolled steel sheet is wound at a temperature of 550 ~ 700 ℃. At this time, the cooling of the winding former hot rolled steel sheet after hot rolling is run-it can be carried out at a table (ROT, Run-out-table) - out. If the coiling temperature is less than 550 ℃ there gives an adverse effect on formability by causing the material to create a difference image shows a variation of the behavior of the low temperature the precipitate by the temperature unevenness in the width direction during cooling and keeping. On the other hand, if the coiling temperature exceeds 700 ℃ there arises a problem of deteriorating the surface material and the softened jogwanseong as the dialog is in the final product tissue bath. Therefore, the winding temperature is preferably in the 550 ~ 700 ℃, may be more preferably 555 ~ 690 ℃.
[106]
[107]
Cold-rolling the hot-rolled steel sheet to a take-up reduction ratio of 50 to 85% to obtain a cold-rolled steel sheet. Rolling reduction is less than 50%, it not only difficult to ensure a uniform material such as a low recrystallization driving force localized tissue growth occurs, in consideration of the thickness of the finished product should work by lowering the thickness of the hot-rolled steel sheet hot-rolling workability there is a significantly worse problems. On the other hand, if the reduction ratio exceeds 85%, the material is a hardened, as well as the risk of cracking during drawing, there is a problem of lowering the cold-rolling workability of a mill load. Therefore, the reduction rate is preferably 50 to 85%, and may be more preferably from 65 to 80%.
[108]
[109]
At this time, it may further comprise the step of pickling the hot-rolled steel sheet before cold rolling the winding.
[110]
[111]
And continuous annealing the cold-rolled steel sheet to ensure the workability and stiffness. From the state in which the intensity increases by a variation introduced in the cold rolling, to secure the strength and workability of the target by performing a stress-relief annealing. The continuous annealing can be carried out at a temperature range of 700 ~ 850 ℃. The annealing temperature lower than 700 ℃ there is significantly less workability problem according to a modification is not removed sufficiently formed by cold rolling. In contrast, the annealing temperature is more than 850 ℃ may cause problem in tongpan to continuous annealing in accordance with the high-temperature annealing. Therefore, the continuous annealing temperature is preferably in the 700 ~ 850 ℃, may be more preferably 730 ~ 845 ℃.
[112]
[113]
Next, the continuous annealing the cold-rolled steel sheet may further include a step of skin-pass rolling, it can be used after the temper rolling, the welding wire manufacturing.
[114]
Mode for the Invention
[115]
The present invention the following examples will be described in detail. However, the following examples are to be noted in that not intended to limit the may make the scope of the present invention to be described in more detail by illustrating the invention. The scope of the present invention is because it is determined by what is a reasonable inference from this information and set forth in the claims.
[116]
[117]
(Example)
[118]
To prepare a cold-rolled steel sheet according to the manufacturing conditions described in the after heating the slab having the composition components shown in Table 1 to 1250 ℃, Table 2 below. The microstructure of the cold-rolled steel sheet was observed to have the ferrite structure. To measures the type of tissue and fine fraction, elongation, tongpan properties and drawing workability with respect to the cold-rolled steel sheet are shown in Table 3 below. The tongpan castle no rolling load during cold and hot rolling, if defects such as during continuous annealing heat buckle (Heat buckle) does not occur was indicated by "○", the rolling load is generated or occurrence of defects, such as during continuous annealing heat buckle when expressed as "×". If the pull-out section when the machining deteriorated workability of the flux cored wire during the drawing process and breakage occurs as a reduction rate 61% "bad", the machining deteriorated not occur was indicated as "good".

WE Claims

[Claim 1]
By weight%, C: 0.005 ~ 0.10% , Mn: 0.05 ~ 0.25%, Si: 0.05% or less (0% excluded), P: 0.0005 ~ 0.01% , S: ( excluding 0%) 0.008%, Al : 0.005 ~ 0.06%, N: 0.0005 ~ 0.003%, Ni: 0.8 ~ 1.7%, Cr: 0.1 ~ 0.5%, remainder Fe and unavoidable W contained impurities, defined by the following relation 1 N 0.10 ~ 0.75 of the flux cored wire for cold-rolled steel sheet. Equation 1: W N = (C × 31 + 0.5 × Mn + 20 × Al) × (Ni) × (0.6 × Cr) (however, the unit being in each element content in the above relational expression 1 is% by weight.)
[Claim 2]
The method according to claim 1, wherein the cold-rolled steel sheet in area%, cementite: 1-6% and a flux cored wire for cold-rolled steel sheet having a microstructure consisting of ferrite balance.
[Claim 3]
The method according to claim 1, wherein the cold-rolled steel sheet has an elongation of 40% or more flux-cored wire for cold-rolled steel sheet.
[Claim 4]
The method according to claim 1, wherein the cold-rolled steel sheet is welded portion segregation index 0.15% lower than the flux cored wire for cold-rolled steel sheet.
[Claim 5]
The method according to claim 1, wherein the cold-rolled steel sheet is less than the impact energy of 50J at -40 ℃ the flux cored wire for cold-rolled steel sheet.
[Claim 6]
By weight%, C: 0.005 ~ 0.10% , Mn: 0.05 ~ 0.25%, Si: 0.05% or less (0% excluded), P: 0.0005 ~ 0.01% , S: ( excluding 0%) 0.008%, Al : 0.005 ~ 0.06%, N: 0.0005 ~ 0.003%, Ni: 0.8 ~ 1.7%, Cr: 0.1 ~ 0.5%, remainder Fe and unavoidable W contained impurities, defined by the following relation 1 N of 0.10 ~ 0.75 slab the step of heating to 1100 ~ 1300 ℃; Phase is finished the heated slab hot rolling temperature to obtain a hot rolled steel sheet by hot rolling such that the 880 ~ 950 ℃; Step for winding the hot-rolled steel sheet in a temperature range of 550 ~ 700 ℃; To obtain a cold-rolled steel sheet to the take-up the hot-rolled steel sheet cold-rolled to a reduction ratio of 50 to 85% step; And a method of producing a cold-rolled steel sheet for use in a flux cored wire comprises continuous annealing the cold-rolled steel sheet in a temperature range of 700 ~ 850 ℃. Equation 1: W N = (C × 31 + 0.5 × Mn + 20 × Al) × (Ni) × (0.6 × Cr) (however, the unit being in each element content in the above relational expression 1 is% by weight.)
[Claim 7]
The method according to claim 6, the method of producing a cold-rolled steel sheet for use in a flux cored wire further comprising the step of pickling the rolled hot-rolled steel sheet before the cold rolling.
[Claim 8]
The method according to claim 6, the method of producing a cold-rolled steel sheet for use in a flux cored wire further comprising the step of temper rolling the continuous annealing the cold-rolled steel sheet.