WO2019132362A1

WO2019132362A1 - Cold-rolled steel sheet for flux-cored wire and method for producing same

Info

Publication number: WO2019132362A1
Application number: PCT/KR2018/016040
Authority: WO
Inventors: 김재익
Original assignee: 주식회사 포스코
Priority date: 2017-12-26
Filing date: 2018-12-17
Publication date: 2019-07-04
Also published as: CN111542634A; KR20190078231A; KR102134310B1

Abstract

A cold-rolled steel sheet for flux-cored wire according to one embodiment of the present invention comprises, in wt%, 0.005-0.08 % carbon (C), 0.05-0.25% manganese (Mn), 0.05% or lower (excluding 0%) silicon (Si), 0.0005-0.01% phosphorus (P), 0.008% or lower (excluding 0%) sulfur (S), 0.001-0.035% aluminum (Al), 0.0005-0.003% nitrogen (N), 0.3-1.7% nickel (Ni), 0.05-0.5% molybdenum (Mo), and the remainder in Fe and unavoidable impurities, and comprises, in surface%, 1-10% cementite, and the remainder in ferrite.

Description

【Specification Tax

Title of the Invention

Cold rolled steel sheet for flux cored wire and manufacturing method thereof

TECHNICAL FIELD

Cold rolled steel sheet for flux cored wire (COLD-ROLLED STEEL SHEET FOR FLUX

CORED WIRE, and MANUFACTURING THE SAME. Specifically, the present invention relates to a cold-rolled steel sheet for a flux cored wire excellent in strength, low temperature toughness, welding workability and workability by adding an appropriate amount of Ni and Mo, and a method for producing the same.

TECHNICAL BACKGROUND OF THE INVENTION

In general, welding is the most efficient welding method, and flux welding (FCW, Flux Cored Welding) is used as welding method. The welding material used in this welding method is a flux cored wire in which a strip (Str ip) drawn from a cold-rolled steel sheet for a welding rod is processed into a U-shape, a flux is added to the processed U- have. In order to secure the weldability, the flux used in this process is prepared by adding an alloy element such as manganese (Mn) in powder form to obtain flux characteristics including an oxidizing agent and the like and using characteristics of the electrode, . That is, the flux component is added for ensuring welding workability, and the alloying element is added in order to secure properties suitable for the intended use of the electrode.

At this time, various kinds of characteristics required for the welding electrode material are secured by changing kinds and addition amounts of the alloy components in the core added in powder form. For example, in order to produce a welded member requiring excellent low-temperature toughness, an alloying element and a flux for improving the low-temperature toughness should be mixed and charged in the processed wire core portion.

On the other hand, low-carbon steels are commonly used as cold-rolled steels for wire used for producing flux cored wires, and stainless steels are also used for some special applications.

Cold rolled steel for welding rod of low carbon steel base has excellent elongation and does not cause tearing of steel during drawing, 2019/132362 1 »(1 ^ 1 {2018/016040

From the molding to the final wire manufacturing, it is applied to various applications because it can be continuously manufactured without a separate heat treatment process.

However, since the above-mentioned cast steel for the carbon steel electrode is a low alloy steel, in order to secure the characteristics of the electrode according to the usage environment of the welding rod, it is a flux component which is filled in the material for the processed electrode rod 5. In addition to the basic flux component, It is necessary to add an alloying element for the purpose. However, since an appropriate level of flux addition is required in order to secure welding workability of a welding rod, there is a limit to increase the amount of the alloy element in the core to a desired level. That is, a large amount of 10 oxidizing agent, a slag forming agent, an arc stabilizer, an alloy component, etc. should be added to the central portion of the steel for the welding rod. In general, it is preferable to fill the wire steel with about 30 to 60% And there is a difference depending on the powder to be filled, but it is known that the weight ratio is about 15 ~ 25%. In such a case, when the content of the alloy element for securing the characteristics of the use of the electrode is increased, the flux component is limited to 15, which makes it difficult to secure stable welding characteristics. In addition, since these alloying elements are added in a high purity powder form, they are not only a cause of cost increase but also cause the segregation of the welded parts due to the high non-cohesion of the added alloying elements, There was also a problem.

20 In the case of stainless steel for welding wire, since the amount of alloy element such as chromium (0) existing in the low-carbon steel is basically higher than that of general carbon steel, the addition amount of the core alloy added together with flux can be reduced. Because it is a high-alloy steel, the price of raw material is high and it is applied only to special purpose. In addition, in the case of a steel material for a 25-electrode rod of these stainless steel bases, there is a high possibility that disconnection occurs due to work hardening during wire processing of the electrode. Therefore, there is a problem that a annealing process must be separately performed between manufacturing processes. Respectively.

In cold-rolled steel for welded 30-wire, which requires current processability, especially drawing processability, strength and toughness, the strength 2019/132362 1 »(its 1 ^ 112018/016040

In order to ensure low-temperature toughness, expensive alloying elements are prepared in a high-purity powder form and added together with other flux components added for ensuring weldability to improve strength and low-temperature toughness. In this case, In addition, there is a problem in that the addition conditions of flux components are limited in order to secure the welding stability according to the increase of the input amount, and expensive alloying elements added at this time cause segregation phenomenon in the flux, There was also a problem of deterioration.

For example, as a method for producing a steel sheet for a flux cored wire, a method of producing a welding rod steel excellent in impact toughness and strength characteristics by adding 0, etc. is disclosed. However, since a large amount of expensive alloying elements is added, there is a problem that the manufacturing cost is increased, and the ductility is low, so that it is difficult to secure the drawing processability.

Further, a technique has been proposed in which a deoxidation reaction of a molten metal is promoted by adding a flux or the like to a flux raw material to reduce welding defects. However, in order to obtain sufficient deoxidation effect of molten metal, it is necessary to add many alloying elements to the flux. However, if many alloying elements are added to the flux, the spatter ( _{3? 3} ) There is a problem that the workability of the welding is deteriorated.

Therefore, there is a demand for development of a welded steel strip using a cold-rolled steel sheet for a flux cored wire electrode which is excellent in strength and low temperature toughness in a cryogenic temperature environment, excellent in welding workability and drawability and a manufacturing method thereof It is true.

DISCLOSURE OF THE INVENTION

[Problem to be solved]

A cold-rolled steel sheet for flux cored wire, and a method of manufacturing the same. Specifically, it is intended to provide a cold-rolled steel sheet for a flux cored wire excellent in strength, low temperature toughness, welding workability and workability by adding an appropriate amount of and.

MEANS FOR SOLVING THE PROBLEMS

A cold rolled steel sheet for a flux cored wire according to an embodiment of the present invention 2019/132362 1 »(1 ^ 1 {2018/016040

(0.005% to 0.08%, manganese 0.05% to 0.25%, silicon 0.05% or less (excluding 0%), 0.0005% to 0.01% , 0.001 to 0.035% of aluminum (Si), 0.0005 to 0.003% of nitrogen, 0.3 to 1.7% of nickel, 05 to 0.5% of molybdenum, the balance of ₆ and unavoidable impurities, , 1 to 10% cementite, and the balance ferrite.

The cold-rolled steel sheet for a flux cored wire according to an embodiment of the present invention may have the following formula 1: 0.30 to 1.80.

[Formula 1]

= (35> <[(: +0.8> <[] +34> <[date])> <(1. 1> <[])> <(1.5> <[¾10])

(In the formula 1, [(:], [¾], [Si], [] and] represent the contents of ₀ ,

The cold-rolled steel sheet for a flux cored wire according to an embodiment of the present invention may have an elongation of 40% or more.

The cold-rolled steel sheet for a flux cored wire according to an embodiment of the present invention may have a weld segregation index of less than 0.15%.

A cold rolled steel sheet for a flux cored wire according to an embodiment of the present invention

The impact energy at -401: may be above 501.

The cold-rolled steel sheet for a flux cored wire according to an embodiment of the present invention is characterized in that the yield strength

Or more.

The method of manufacturing a cold rolled steel sheet for a flux cored wire according to an embodiment of the present invention is a method of manufacturing a cold rolled steel sheet for a flux cored wire, the method comprising the steps of (0 0.005 to 0.08%, manganese 0.05 to 0.25%, silicon 0.05% ), 0.0005 to 0.01% of phosphorus, 0.008% or less of vanadium (excluding 0%), 0.001 to 0.035% of aluminum, 0.0005 to 0.003% of nickel, 0.3 to 1.7% of nickel, molybdenum ₀ ) 0.05 to 0.5%, the remainder

Producing a slab comprising unavoidable impurities; Heating the slab; Hot rolling the heated slab to a final hot rolling temperature of 800 to 900 to obtain a hot rolled steel sheet; Winding the hot-rolled steel sheet in a temperature range of 550 to 700;; Rolling the rolled hot-rolled steel sheet at a reduction ratio of 50 to 85% to obtain a cold-rolled steel sheet; And a cold-rolled steel sheet at 700 to 850 ° (of 2019/132362 1 »(its 1 ^ 112018/016040

And annealing in a temperature range.

The slab may be 0.30 to 1.80 in the formula (1).

[Formula 1]

¾ = (35> <[(:] +0.8 [111] +34> <[hour]) (1. 1> <[])> <(1.5> <[1 \ 10])

(In the formula 1, [F, [Addition], [Time], [Ex.]] And these represent the contents of (: 1, ₁₁ ,

The step of heating the slab may be heated to 1100 to 13001 ° C. And picking up the rolled hot-rolled steel sheet before the hot rolling.

The step of annealing the cold-rolled steel sheet may further include the step of temper rolling the annealed cold-rolled steel sheet.

The flux cored wire according to an embodiment of the present invention may include a shell made of the cold-rolled steel sheet described above and a flux filled in the shell.

【Effects of the Invention】

The cold-rolled steel sheet for a flux cored wire according to an embodiment of the present invention is excellent in strength, low temperature toughness, welding workability and workability.

According to one embodiment of the present invention, it is possible to provide a cold-rolled steel sheet for flux cored wire, which can be welded electronically, for use in the shipbuilding industry, materials industry, construction industry, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a photograph of a cross section of a flux cored wire produced by using a cold-rolled steel sheet of Inventive Example 2 with a scanning electron microscope seed 0.

Fig. 2 is a photograph of a shell portion of a flux cored wire produced by using a cold-rolled steel sheet of Inventive Example 2 with a scanning electron microscope 0. Fig.

Fig. 3 is a scanning electron microscope (cross-sectional photograph) of a cross-section of a flux cored wire produced using the cold-rolled steel sheet of Comparative Example 5. Fig.

4 is a photograph of a shell portion of a flux cored wire produced by using the cold-rolled steel sheet of Comparative Example 5 with a scanning electron microscope (table ratio).

DETAILED DESCRIPTION OF THE INVENTION 0 2019/132362 1 »(: 1 ^ 1 {2018/016040

The terms first, second and third, etc. are used to describe various portions, components, regions, layers and / or sections, but are not limited thereto. These terms are only used to distinguish any moiety, element, region, layer or section from another moiety, moiety, region, layer or section. Thus, the first portion, the fifth component, the region, the layer or the section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms used herein include singular 10 forms unless the phrases expressly have the opposite meaning. Means that a particular feature, region, integer, step, operation, element and / or component is specified and that the presence or absence of other features, regions, integers, steps, operations, elements, and / It does not exclude addition.

When referring to a portion as being "above" or "on" another portion, it may be directly on or over another portion, or it may be accompanied by another portion. In contrast, If you mention that "just above", there is no other part in it.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Normally used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as an ideal or highly formal occasion, unless defined otherwise.

Further, unless otherwise stated,% means weight%, and cut is 25 0.0001 wt%.

In the embodiment of the present invention, the term further includes an additional element, which means that the additional element is replaced by an additional amount of the additional element. Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms, 2019/132362 1 »(: 1 ^ 1 {2018/016040

The present invention is not limited to the embodiment described.

The cold rolled steel sheet for a flux cored wire according to an embodiment of the present invention may contain carbon (0.0000 to 0.08%, manganese 0.05 to 0.25%, silicon 0.05% or less (excluding 0%), 0.001 to 0.03%, nickel (0.0005 to 0.003%, nickel 0.3 to 1.7%, molybdenum ₀ ) 0.05 to 0.005% (excluding 0%), aluminum 0.5%, rest

Contains inevitable impurities, and contains, by area%, 1 to 10% cementite and the remainder ferrite.

The reasons for limiting the components of the cold-rolled steel sheet will be described below.

0: 0.005 to 0.08 wt%

Carbon (0) is an element that is added to improve the strength of steel and is added to make the weld heat affected zone have similar properties to the base metal. When the content of 0 is too small, the above-mentioned effect is insufficient. On the other hand, when the content of 0 is too high, problems such as high strength or work hardening and disconnection in the drawing process may occur. In addition, low-temperature cracking of the welded joint occurs or the impact toughness is reduced, and a large number of heat treatments are performed due to high hardness, which is disadvantageous in that it can be processed into an intended final product. Therefore, the content of O may be 0.005 to 0.08% by weight. More specifically, it may be 0.008 to 0.05% by weight for improving the properties of the weld heat affected zone.

此: 0.05 to 0.25 wt%

In the case of manganese (), it enhances the strength of steel as a solid solution strengthening element and improves hot workability. However, in the case of excessive addition, a large amount of manganese-sulfide may form, which may inhibit ductility and processability of the steel. If the content is too low, it becomes a cause of generation of a brittle brittleness and it may be difficult to contribute to the stabilization of austenite. On the other hand, when the content is too large, the ductility is lowered and the center segregation is generated, which may lead to breakage in the drawing process in the electrode manufacturing process. Therefore, the content may be 0.05 to 0.25% by weight. More specifically, the content thereof may be 0.07 to 0.23% by weight.

: Not more than 0.05% by weight Silicon (Si) bonds with oxygen to form an oxide layer on the surface of a steel sheet to deteriorate surface characteristics and deteriorate corrosion resistance, as well as promoting hard phase transformation in the weld metal, thereby deteriorating low-temperature impact properties . Therefore, the Si content is limited to 0.05 wt% or less. More specifically, the Si content may be 0.001 to 0.03% by weight.

P: 0.0005 to 0.01 wt%

If the content of P is too small, it may be difficult to maintain a certain level of rigidity. If the content of P is too large, The P content can be 0.0005 to 0.01% by weight, more specifically, the P content can be 0.001 to 0.009% by weight.

S: not more than 0.008% by weight

Sulfur (S) is combined with manganese in the steel to form nonmetallic inclusions and is a factor of red shortness, so it is desirable to reduce the content as much as possible. The S content may be 0.008% by weight or less, more specifically, the S content may be 0.0005 to 0.007% by weight.

A1: 0.001 to 0.035 wt%

Aluminum (A1) is an element to be added for the purpose of preventing material deterioration due to deoxidizing agent and aging in aluminum killed steel, and is an element favorable for securing ductility. Such effect is more remarkable than at extremely low temperature. When the A1 content is too small, the above-mentioned effect is insufficient. On the other hand, when the content of Al is too large, surface inclusions such as Al ₂ O ₃ (Al ₂ O ₃₎ abruptly increase, which deteriorates the surface properties of the hot rolled steel and deteriorates workability. In addition, The Al content may be 0.001 to 0.035% by weight, more specifically, the A1 content may be 0.005 to 0.033%. Weight%.

N: 0.0005 to 0.003 wt% 2019/132362 1 »(: 1 ^ 1 {2018/016040

Nitrogen) is an element that is effective for strengthening the material while it exists in the solid state in the steel. If N is too small, it may become difficult to secure the target rigidity. On the other hand, if the content of N is too large, the aging property is not only deteriorated but also the burden of denitrification in the steel making step is increased, which may deteriorate the steel making workability. Accordingly, the N content may be 0.0005 to 0.003% by weight. More specifically, the N content may be 0.001 to 0.0027% by weight.

: 0.3 to 1.7 wt%

Nickel () is an austenite stabilizing element and is an effective element for improving ductility by improving ductility, and is a necessary element for improving low temperature impact properties by forming a stable structure even at a very low temperature. Is too small, it is difficult to obtain such an effect and stable operation of the flux composition may be difficult. On the other hand, if the content is too high, the drawing processability may be lowered due to the increase of the strength, and surface defects may be caused. Therefore, the content may be 0.3 to 1.7% by weight, and more specifically 0.5 to 1.5% by weight.

0.05 to 0.5 wt%

Molybdenum ₀ ) is an advantageous element in terms of securing the strength of the welded joint by increasing the incombustibility.

If it is included, it may be difficult to obtain such an effect. If the amount of 1? ₀ gauge is too much, the formation amount of molybdenum carbide increases to cause brittleness, which may cause deterioration of workability. Therefore, the content of? ₀ may be 0.05 to 0.5 wt%. And the ¾ content may be 0.1 to 0.45% by weight.

The remainder of the present invention is iron. However, the impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated in a conventional manufacturing process, so that this can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

In addition, the cold-rolled steel sheet according to an embodiment of the present invention has a microstructure in an area percent of 1 to 10% of cementite and the remainder ferrite. When the fraction of cementite is too small, the precipitation of carbide is not promoted. Accordingly, 2019/132362 1 »(: 1 ^ 1 {2018/016040

It serves as a factor indicating deformation aging defects by the elements of employment. On the other hand, when the cementite fraction is too high, not only cracking occurs in the drawing process but also corrosion resistance is deteriorated. Therefore, the fraction of the cementite may be in the range of 1 to 10 area square. More specifically, the fraction of the cementite may be 1.3 to 7.5% by area. The remainder is ferrite.

On the other hand, the cold-rolled steel sheet of the present invention not only satisfies the above-mentioned alloy composition, but also has a thickness of 0.30 to 1.80 in the following formula 1.

[Formula 1]

= (35> <[(:] + 0.8> <[111] +34> <[city]) (1. 1> <[])> <(1.5> <¾0]

(In the formula 1, [0], [], [], [] and [¾] represent the contents of X,, Si and ¾ / [ ₀ ], respectively.

I is designed considering the correlation of each element on welding workability and drawability. When ¾ is too small, the transformation from a normal-temperature structure to a hard phase is advantageous in terms of workability, but in order to secure strength and low-temperature toughness, welding workability deteriorates as the amount of alloy element added as a composition in flux increases . On the other hand, if is too large, there may be a problem that the fracture of the welded member occurs at the tube and pull out due to an increase in the fraction of the light metamorphic structure. Therefore, the range of 0.30 to 1.80 can be satisfied. More specifically, it can be 0.33 to 1.70. The cold-rolled steel sheet according to one embodiment of the present invention is excellent in elongation. Specifically, the elongation may be 40% or more. By satisfying such physical properties, it can be preferably applied to a material for a flux cored wire electrode. If the elongation is too low, the reduction rate of the cross-section may be lowered during drawing of the welding wire, which may result in deterioration of the torsional strength and cracking such as tearing during processing. More specifically, the elongation may be 40 to 50%.

In addition, the cold-rolled steel sheet according to the embodiment of the present invention is excellent in the weld segregation index. The weld segregation index means the segregation index of the welded portion welded with the flux cored wire manufactured using the cold-rolled steel sheet according to an embodiment of the present invention. The segregation index of the weld is calculated from the total area of the weld 2019/132362 1 »(: 1 ^ 1 {2018/016040

And the area occupied by the segregation portion. Specifically, the weld segregation index may be 0.15% or less. May more specifically the weld segregation index of 0.01 and the number of days 0.13¾ _».

Further, the cold-rolled steel sheet according to an embodiment of the present invention may have a low impact energy at low temperature of -40 ° (:) _. Specifically, the low-temperature impact energy at 40 _° (: may be less than 501). The welded portion or the like may cause cracks due to low-temperature shock or the like in a low-temperature environment, which may cause problems in the safety of the welded structure.

Further, the cold-rolled steel sheet according to an embodiment of the present invention is excellent in yield strength of a welded portion. The yield strength of a weld means the yield strength of a weld welded with a flux cored wire manufactured using a cold rolled steel sheet according to an embodiment of the present invention. The yield strength of welds is required to be maintained at an appropriate level irrespective of the base material, and high strength characteristics of 500 ¾ or more should be ensured in terms of securing the stability of welds when applied as structural members.

A method of manufacturing a cold rolled steel sheet for a flux cored wire according to an embodiment of the present invention comprises the steps of: (1) forming a carbon steel sheet having a carbon content of 0.005 to 0.08%, manganese (0.05 to 0.25% ), of (I ³⁾ 0.0005 naeja 0.01%, sulfur (except幻0.008% or less (0%), Al (g) 0.001 to 0.035%, nitrogen: air) from 0.0005 to 0.003%, Ni (), 0.3 to 1.7%, 0.05 to 0.5% molybdenum (¾), the balance Fe and unavoidable impurities; Heating the slab; Hot-rolling the heated slab to obtain a hot-rolled steel sheet; Winding a hot-rolled steel sheet; A step of cold-rolling the wound hot-rolled steel sheet to obtain a cold-rolled steel sheet; And annealing the cold-rolled steel sheet.

Hereinafter, each step will be described in detail.

First, a slab is manufactured. In the steelmaking step

¾ is controlled to an appropriate amount. The molten steel whose composition is adjusted in the steelmaking process is made into a slab through continuous casting.

Since each composition of the slab is described in detail in the cold-rolled steel sheet for flux cored wire described above, a duplicate description will be omitted. The foregoing formula 1 can be equally satisfied within the alloy component of the slab. Flux cored 2019/132362 1 »(: 1 ^ 1 {2018/016040

Since the alloy component does not substantially change during the manufacturing process of the cold-rolled steel sheet for wire, the alloy component of the slab and the cold-rolled steel sheet for the finally-produced flux cored wire can be the same.

Next, the slab is heated. This is to smoothly perform the subsequent hot rolling process and homogenize the slabs. Specifically, the slab can be heated to 1100 to 1300 °. If the slab heating temperature is too low, there is a problem that the load increases rapidly during the subsequent hot rolling, while if it is too high, the energy cost increases and the amount of surface scale increases, leading to loss of material. The slab heating temperature may be 1150 to 12501 :.

Next, the hot slab is hot-rolled to produce a hot-rolled steel sheet. At this time, the finish rolling temperature of the hot rolling may be 800 to 9001 :. When the finishing rolling temperature is too low, the hot rolling is completed in the low temperature region, so that the solidification of the crystal grains proceeds rapidly, which may lead to deterioration of the hot rolling property and the workability. On the other hand, if the finishing rolling temperature is too high, the peelability of the surface scale is deteriorated, the hot rolling is not uniformly performed throughout the thickness, the grain refinement becomes insufficient, and the impact toughness due to grain boundary coarsening may be reduced . More specifically, the finish rolling temperature may be 810 to 8901.

Next, the hot-rolled steel sheet is wound. At this time, the coiling temperature may be 550 to 700.. The cooling of the hot-rolled steel sheet before the rolling after hot rolling is performed by a run-

1 &_lt; / _RTI > _11-0111 ; ₃₁₃₁₆ ). When the coiling temperature is too low, the generation behavior of the low-temperature precipitates differs due to the non-uniformity in the width direction during cooling and holding, resulting in a material variation, which adversely affects the workability. On the other hand, when the coiling temperature is too high, there arises a problem that the surface material softens and the toughness deteriorate as the texture of the final product coarsens. More specifically, the coiling temperature may be 610 to 690.

The method may further include the step of pickling the hot rolled steel sheet wound before cold-rolling the wound hot-rolled steel sheet after winding the hot-rolled steel sheet.

Next, the rolled hot-rolled steel sheet is cold-rolled to produce a cold-rolled steel sheet. this 2019/132362 1 »(: 1 ^ 1 {2018/016040

, The reduction rate may be 50 to 85%. If the rolling reduction rate is too low, it is difficult to obtain a uniform material such as localized tissue growth due to low recrystallization driving force. In addition, considering the thickness of the final product, it is necessary to reduce the thickness of the hot- There is a problem that makes it significantly worse. On the other hand, if the reduction rate is too high, the material will harden and cause cracks during drawing, and there is a problem in that the rolling workability is lowered due to the load of the rolling mill, so that the rolling reduction can be 50 to 85%. More specifically from 65 to 80%.

Next, the cold-rolled steel sheet is annealed. The desired strength and workability can be secured by performing annealing from a state where the strength is increased by the deformation introduced in the cold rolling. At this time, the annealing temperature may be 700 to 8501 :. If the annealing temperature is too low, the deformation formed by the cold rolling is not sufficiently removed, resulting in a problem that the workability is significantly lowered. On the other hand, if the annealing temperature is too high, problems such as plate breakage may occur in the annealing line. More specifically, the annealing temperature may be from 730 to 845 DEG C. Annealing can proceed continuously without winding the cold-rolled steel sheet.

The step of annealing the cold-rolled steel sheet may further include the step of temper rolling the annealed cold-rolled steel sheet. Temper rolling can be rolled to a rolling reduction of 10% or less. After annealing the hot-rolled steel sheet, the hot-rolled steel sheet can be used for producing the flux cored wire.

The flux cored wire according to an embodiment of the present invention includes a shell made of the cold-rolled steel sheet described above and a flux filled in the shell. The effect of the flux cored wire according to an embodiment of the present invention is an effect expressed by the cold rolled steel sheet regardless of the type of the filled flux. Thus, the flux can be used without limitation to the general flux used in the flux cored wire field. Since the flux is widely known, detailed description thereof will be omitted.

Hereinafter, preferred embodiments and comparative examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the present invention is not limited to the following examples. 2019/132362 1 »(: 1 1 ^ 18/016040

Example

Slabs were prepared. The slabs were heated to 12301 ° C., and hot rolling, coiling, cold rolling and annealing were performed under the manufacturing conditions summarized in Table 2 below. The type and fraction of microstructure, elongation, ductility and drawability of the cold-rolled steel sheet were measured and are shown in Table 3 below.

In case of cold rolled and hot rolled, there is no rolling load and when there is no defect such as heat buckle (◦) in continuous annealing, "◦" is indicated. In case of rolling load or defect such as plate breakage in continuous annealing, X ".

The drawing processability is indicated as "poor" when a machining defect such as tearing occurs in the drawing process of the flux cored wire, and "good" if the machining defect does not occur.

This strip was machined into a U-shape to fill the flux component, and then a urethane welder having a diameter of 3.1 占 was manufactured. The welded material thus prepared was pulled out to produce a flux cored wire having a diameter of 1.2 占 and subjected to a low-temperature impact test and a tensile test, and the results are shown in Table 3 below.

The weld seam indices of the welded parts welded with flux cored wire were measured, and the results are shown in Table 3 below. At this time, the welded member was drawn with a wire having a diameter of 1.2 占 and the welded member manufactured under the conditions of a voltage of 29 volts, a current of 150 to 18, and a welding speed of 40 占.

Figs. 1 to 4 are cross-sectional photographs of flux cored wires produced using cold-rolled steel sheets of Inventive Example 2 and Comparative Example 5, respectively.

As shown in Fig. 1 and Fig. 2, in the case of Inventive Example 2, it can be confirmed that the outer skin is relatively homogeneous, and thus it can be seen that good drawing workability can be ensured.

On the other hand, in the case of Comparative Example 5 of FIG. 3 and FIG. 4, 2019/132362 1 »(: 1 ^ 1 {2018/016040

It is possible to confirm that it is difficult to ensure good drawing processability.

[Table 1]

[Table 2]

2019/132362 1 »(: 1/10 公 018/016040

[Table 3]

2019/132362 1 »(: 1 ^ 1 {2018/016040

As you can see from the above Table 1 to Table 3, the alloy composition, to match all of the microstructural characteristics and the manufacturing conditions Examples 1 to 9 as well as the tongpan having good, the material of the cold-rolled steel sheet for use in a flux cored wire for aiming The elongation of 40% or more as a standard was satisfied. In addition, the segregation index of the wire made of the welded member is less than 0.15%, so that tearing and cracking of the welded portion do not occur during the secondary processing, and excellent workability can be ensured. In addition, the impact energy at -401: was 501 or more, and the yield strength of the welded member was 500Wa or more, so that excellent strength and low temperature toughness were secured.

On the other hand, Comparative Examples 1 to 3 satisfied the alloy composition shown in the present invention but did not satisfy the microstructural characteristics and manufacturing conditions, and the rolling ductility (Comparative Examples 1 to 3) and the annealing throughput (Comparative Example 4 ), And it is confirmed that the elongation rate is lower than the target, the impact energy value at -40 ° (: is less than -501, or the yield strength of the welded member is less than 500¾0½, or the drawing processability is poor. Can not be obtained.

In Comparative Examples 4 to 8, the manufacturing conditions satisfied in the present invention were satisfied, but the alloy composition and the microstructure properties were not satisfied. In Comparative Example 9, the alloy composition and the manufacturing conditions were not all satisfied. In Comparative Examples 4 to 9, it was found that the target elongation percentage, segregation index and impact energy of the welded portion, the yield strength of the welded portion, and the like were not satisfied. Further, tearing or cracking occurred in the drawing process. In particular, Comparative Example 10 satisfied all of the other alloy composition and manufacturing conditions, but was not included, 2019/132362 1 »(: 1 ^ 1 {2018/016040

Segregation index and yield strength of welded joints are low, and low temperature impact energy value is low.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. It will be understood that the invention may be practiced otherwise than as described. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims

2019/132362 1 »(: 1 ^ 1 {2018/016040

Claims:

[Claim 1]

By weight%, carbon (0.005 to 0.08%, manganese 01, ₁₁₎ 0.05 to 0.2¾, silicon () (excluding 0%), 0.05% or less, of (I ^3), 0.0005 to 0.01%, sulfur比) less than 0.008% ( 0.001 to 0.035% of aluminum (excluding 0%), 0.0005 to 0.003% of nitrogen, 0.3 to 1.7% of nickel, 0.05 to 0.5% of molybdenum (¾)

Including unavoidable impurities,

A cold rolled steel sheet for a flux cored wire, comprising, by area%, 1 to 10% of cementite and gypsumite.

[Claim 2]

The method according to claim 1,

A cold rolled steel sheet for an in-flux cored wire of the following formula 1: 0.30 to 1.80.

[Formula 1]

¾ = (35> <[(:] + 0.8> <[111] +34> <[hour])> <(1. 1> <[])> <(1.5> <[] \ 10]

(In the formula 1, [0],], [hour], [], and [¾! Which indicates the content of each of 0, during, and 1 _«0).

[Claim 3]

The method according to claim 1,

Wherein the cold-rolled steel sheet has an elongation of 40% or more.

[4]

The method according to claim 1,

The cold-rolled steel sheet has a weld segregation index of less than 0.15%.

[Claim 5]

The method according to claim 1,

Wherein the cold-rolled steel sheet has an impact energy at -401: 1 or higher.

[Claim 6] 2019/132362 1 »(: 1 ^ 1 {2018/016040

The method according to claim 1,

Wherein the cold-rolled steel sheet has a yield strength of 500Wa or higher.

[7]

(Excluding 0.005% to 0.08%, manganese 0.05% to 0.25%, silicon 0.05% or less (excluding 0%), phosphorus (0.0005% to 0.01% 0.001 to 0.035% of aluminum (Si), 0.0005 to 0.003% of nitrogen (N), and 0.3 to 1 of nickel (Ni).

7%, molybdenum < RTI ID = _0.0 > ₀ )

Producing a slab comprising unavoidable impurities;

Heating the slab;

Hot rolling the heated slab to a final hot rolling temperature of 800 to 900 to obtain a hot rolled steel sheet;

Winding the hot rolled steel sheet in a temperature range of 550 to 7001:

Cold rolling the rolled hot-rolled steel sheet at a reduction ratio of 50 to 85% to obtain a cold-rolled steel sheet; And

And annealing the cold-rolled steel sheet at a temperature in the range of 700 to 8501. The method of manufacturing a cold-rolled steel sheet for a flux cored wire according to claim 1,

[8]

8. The method of claim 7,

Wherein the slab is W _{A7 of 0.30} to 1.80, which is defined by the following formula (1).

[Formula 1]

1 = (35 < ([(+

8><[¾111]+34> hour]) (1. 1><[])><(1.5><[] \ 10]

Content.

9]

8. The method of claim 7,

Wherein the heating of the slab is performed at a temperature of 1100 to 13001 ° C.

Claim 10 2019/132362 1 »(: 1 ^ 1 {2018/016040

8. The method of claim 7,

The method of manufacturing a cold-rolled steel sheet for a flux cored wire according to claim 1, further comprising pickling the rolled hot-rolled steel sheet before cold-rolling.

Claim 11

8. The method of claim 7,

Further comprising the step of temper rolling the annealed cold rolled steel sheet after the step of annealing the cold rolled steel sheet.

Claim 12

A shell made of the cold-rolled steel sheet described in the paragraph 11

Wherein the flux cored wire comprises a flux filled in the shell.