KR101858984B1 - Manufacturing method of steel palte having excellent electro gas arc welding property and steel palte having excellent electro gas arc welding property thereby - Google Patents

Abstract

The present invention relates to a method to manufacture a thick steel plate with an excellent electro gas arc welding property, and a thick steel plate with an excellent electro gas arc welding property manufactured thereby. According to the present invention, a slab is re-heated in a heating furnace and then is rolled and cooled, and comprises: 0.14 to 0.15 weight percent of C; 0.13 to 0.17 weight percent of Si; 0.84 to 0.88 weight percent of Mn; 0.019 to 0.025 weight percent of P; greater than 0 and not greater than 0.008 weight percent of S; 0.02 to 0.03 weight percent of T-Al; and the balance of Fe and other unavoidable impurities, wherein at least one among Cr, Ni, Mo, Cu, Ti, V, and Nb is included by greater than zero and not greater than 0.015 weight percent, but is not intentionally added. Accordingly, provided are effects of largely reducing manufacturing costs, providing excellent tensile strength of a weld part, providing a good bending characteristic to lower impact toughness in a welding metal and a fusion line without using yield behavior, and providing a good mechanical property of a heat affected zone (HAZ) due to a low carbon equivalent chemical composition.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing a steel sheet having excellent electrogas weldability and a steel sheet having excellent electro-gas weldability, which is produced by the method. [0002]

The present invention relates to a method of manufacturing a steel sheet having excellent electrogas weldability and a steel sheet excellent in electrogas weldability produced by the method. More particularly, the present invention relates to a steel sheet having excellent weldability, such as Cr, Ni, Mo, Cu, Ti, V, The present invention relates to a method for producing a post-steel sheet excellent in electromagnet weldability and excellent resistance to electrosurgical gas welding, and an excellent post welded steel sheet produced by the method.

Steel structures used in fields such as ships, buildings, and civil engineering are generally completed with structures required by welding. Therefore, in order to ensure the safety of these structures, the toughness of the base metal and the toughness of the welded portion of the steel sheet to be used must be excellent. In recent years, the ship or steel structure has become larger, and the strength of the steel sheet used therefor has actively progressed.

In the case of the steel plate, the welding method of the high-efficiency substitution heat should be applied. Accordingly, the SEGARC (Simple Electro Gas Arc) welding is known as the welding method for the high-efficiency substitution heat.

SEGARC welding is a method in which a copper shoe (water-cooled copper backing material), which is moved upward with the welding point, is provided on the front surface to prevent molten metal and slag from leaking, It is a welding technique applied to a kind of electrogas welding which supplies a protective gas such as carbon dioxide from a porter.

SEGARC welding (a) is a welding technique with a higher welding rate than SMAW (Shielded Metal Arc Welding, b) and FCAW (Flux Cored Arc Welding, c) Tandem, B) technique is selectively applied, and the heat input is high.

On the other hand, although not shown in detail, both the molten base metal (BM) and the weld metal produced from the welding material (the portion which is dissolved in the welding process and solidify again) Welding metal (WM), which is solidified due to mixing of the base metal and the weld metal, is also present together.

On both sides of the weld metal, there is a heat affected zone (HAZ) in which the structure and properties of the base material are altered by heat affected by the heat applied during welding, and the base material exists on both sides of the weld metal.

The boundary between the weld metal and the heat affected zone is generally referred to as the fusion line (FL). Since the heat affected zone around the fusion line is quenched after being heated to a high temperature especially near the melting point, .

Here, the grain size of the welded heat affected zone increases when the heat input at the time of welding increases, so that the toughness remarkably decreases. Therefore, many alternatives have been proposed for reducing the toughness of the heat affected zone accompanying such large heat welding.

In the conventional case, most of the steel sheets are rolled by TMCP (Thermo Mechanical Control Process) and water cooled to produce a steel sheet satisfying EGW (Electro Gas Welding) -60 ° C characteristics. Such a manufacturing method of the steel sheet is disclosed in Korean Patent No. 10-1193799 and Japanese Patent Application Laid-Open No. 2000-0042183, for example.

However, the above-mentioned Japanese Patent Registration No. 10-1193799 has a high carbon content, so that deformation occurs during quenching and the impact toughness of the weld heat affected zone is relatively low, so that the SEGARC welding characteristic may be deteriorated.

Also, in the case of the steel for heat welding of large quantity such as the one disclosed in Japanese Patent Laid-Open No. 2000-0042183, since it corresponds to the steel plate after the water-cooling type, it is necessary to provide an accelerated cooling facility.

However, the conventional steel sheet has a problem that a high cost of alloying elements such as Cr, Ni, Mo, Cu, Ti, V, and Nb is added,

An object of the present invention is to provide a method of manufacturing a steel sheet having excellent electrogas weldability and excellent resistance to electrosurgical welding with excellent resistance to abrasion without the intentional addition of expensive alloying elements such as Cr, Ni, Mo, Cu, Ti, V and Nb And a finished steel sheet produced by this manufacturing method and having excellent electrogas weldability.

In order to accomplish the above object, the present invention provides a method of manufacturing a slab, comprising the steps of: heating a slab in a heating furnace to reheat, rolling the slab to produce a rolled steel sheet, and cooling the rolled steel sheet 0.14 to 0.15% of Si, 0.13 to 0.17% of Si, 0.84 to 0.88% of Mn, 0.019 to 0.025% of P, 0 to 0.008% of S and less than 0.008% of T, To 0.03% and the balance of Fe and other unavoidable impurities, and at least one of Cr, Ni, Mo, Cu, Ti, V and Nb is contained in an amount of 0 to 0.015% And a manufacturing method thereof.

In the present invention, the slab is made of Ceq (1) = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / Ce + Ce (1) + Ce + Ce + Ce + Ce + Ce + Ce in Ce + Ce + Ce + ), Ceq (2) and Ceq (3) can satisfy the range of 0.29 to 0.31.

In the present invention, the slab may satisfy Ceq (4) in the range of 0.31 to 0.35 at Ceq (4) = C + Mn / 6 + Cr / 5 + Mo / 5 + V / 3 + Nb / 4 + 0.0001 / S .

In the present invention, the slab is made of Ceq (1) = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / Ce + Ce (1) + Ce + Ce + Ce + Ce + Ce + Ce in Ce + Ce + Ce + ), Ceq (2) and Ceq (3) satisfy the range of 0.29 to 0.31 and Ceq (4) = C + Mn / 6 + Cr / 5 + Mo / 5 + V / 3 + Nb / 4 + Ceq (4) in the range of 0.31 to 0.35 can be satisfied.

In the present invention, the rolling step may be completed by rolling the slab heated at 1,050 to 1,150 ° C in the range of Ar3 temperature + 20 to + 60 ° C calculated by Equation 1 below.

[Equation 1]

Ar3 (占 폚) = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo

In the present invention, the rolling step can be rolled under conditions of a cumulative rolling reduction of 80% or more so as to have a thickness in the target range of 20t to 40t.

In the present invention, the slab is made of Ceq (1) = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / Ce + Ce (1) + Ce + Ce + Ce + Ce + Ce + Ce in Ce + Ce + Ce + ), Ceq (2) and Ceq (3) satisfy the range of 0.29 to 0.31 and Ceq (4) = C + Mn / 6 + Cr / 5 + Mo / 5 + V / 3 + Nb / 4 + And Ceq (4) satisfies the range of 0.31 to 0.35. In the rolling step, the slabs heated at 1,050 to 1,150 DEG C are rolled in the range of Ar3 temperature + 20 to +60 DEG C calculated by Equation (1) It can be rolled under conditions of a cumulative rolling reduction of 80% or more so as to have a thickness of 40 t target range.

[Equation 1]

Ar3 (占 폚) = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo

The present invention provides a backsheet excellent in electro-gas weldability, which is manufactured in one embodiment of the method for manufacturing a backsheet having excellent electro-gas weldability according to the present invention.

The present invention can reduce the manufacturing cost by minimizing the addition of alloying elements and manufacturing a steel sheet excellent in electro-gas weldability without intentionally adding expensive alloying elements such as Cr, Ni, Mo, Cu, Ti, V, and Nb .

The present invention relates to a weld metal having excellent tensile strength of a welded portion and having good bending properties and having a low impact toughness in a weld metal (WM), a fusion line (hereinafter referred to as FL) and a low carbon equivalent chemical The mechanical properties of the weld heat affected zone (HAZ) are advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall view showing a step of a method of manufacturing a steel sheet having excellent electrogas weldability according to the present invention; FIG.
Figs. 2 and 3 are SEM photographs of Example 1 and Example 2 of the present invention. Fig.
Figs. 4 and 5 are photographs of the welding portions of Examples 1 and 2, which are welded under the welding conditions shown in Table 4 in the method of manufacturing a steel sheet having excellent electrogas weldability according to the present invention.
FIG. 6 is a graph showing tensile test results of welded joints in Examples 1 and 2 in a method of manufacturing a steel sheet with excellent electro-gas weldability according to the present invention. FIG.
FIG. 7 is a graph showing the relationship between the distance from the FL to the fusing line (FL), which is the boundary between the welded joint and the weld heat affected zone (HAZ) in the method of manufacturing the steel sheet excellent in electro- A graph showing the Vickers hardness value (HV).
8 is a scanning electron micrograph showing the grain boundaries of WM and HAZ in the vicinity of FL in Example 1 in the method of manufacturing a steel sheet having excellent electrogas weldability according to the present invention.
Figs. 9 to 11 are views showing a first point A on the FL line in Fig. 8, a second point B spaced by 2 mm from the welding heat affected zone HAZ in FL, And an enlarged photograph of the third spot (C) spaced apart.
12 is a photograph of a scanning electron microscope taken at a point D in Fig.
13 is a scanning electron micrograph showing the grain boundaries of WM and HAZ in the vicinity of FL in Example 2 in the method of manufacturing a steel sheet with excellent electromagnet weldability according to the present invention.
Figs. 14 to 16 are diagrams showing the relationship between the first point E on the FL line in Fig. 13, the second point F spaced by 2 mm from the welding heat affected zone HAZ in FL, And an enlarged photograph of a third spot (G) spaced apart.

Hereinafter, the present invention will be described in more detail.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to the detailed description of the present invention, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

FIG. 1 is an overall schematic view of a method for manufacturing a steel sheet for a low-resistance, high-strength line pipe according to the present invention.

1, there are shown a heating step (S100) for reheating the slab in a heating furnace, a rolling step (S200) for rolling the slab to produce a steel sheet after the slab is rolled, and a steel sheet after cooling the steel sheet produced in the rolling step (S200) And a cooling step S300.

The slab is composed of 0.14 to 0.15% of C, 0.13 to 0.17% of Si, 0.84 to 0.88% of Mn, 0.019 to 0.025% of P, 0.008 to less than 0.008% of S, 0.02 to 0.03% of T- And at least one of Cr, Ni, Mo, Cu, Ti, V, and Nb is contained in an amount of more than 0 to 0.015%.

C (carbon) is the most effective element to improve the strength of steel, but when added in too much amount, it may deteriorate weldability, formability and toughness. If the content of carbon is less than 0.14 wt%, it is difficult to obtain the desired strength because the content of carbon is too low, so that the desired strength can be obtained by additionally including a high-priced alloy element. However, when the content is more than 0.15% by weight, the content of carbon is too high to cause a problem of deterioration in weldability, formability and toughness as described above. Therefore, the content thereof is preferably limited to a range of 0.14 to 0.15% by weight .

Si (silicon) is an element essential for deoxidation of steel, and is an element effective for increasing the strength. It is preferable to limit the content to a range of 0.13 to 0.17% by weight for securing a desired target strength and weldability.

The Mn (manganese) has an effect of increasing the strength at the time of heat treatment, and is also an essential element added to compensate the strength due to the limited amount of carbon added. However, when the amount of manganese is too low, the effect of improving the sintering property is hardly obtained. When the amount exceeds manganese, manganese (MnS), which is a nonmetallic inclusion, is formed to lower the weldability and patience structure. Do.

Al (aluminum) is an element that acts as a deoxidizer for removing oxygen by reacting with oxygen present in molten steel. When the amount is too large, however, a large amount of oxide inclusions is formed to deteriorate the impact toughness of the material. Is preferably limited to 0.02 to 0.03% by weight.

The P (phosphorous) is inevitably contained in steel production, and it is preferable to control it as low as possible because it induces brittleness as an element easily segregated at the center of the slab during solidification, and theoretically the content of phosphorus can be limited to 0 wt% It is inevitable to add inevitably to the manufacturing process. Therefore, it is important to manage the upper limit, and the content of phosphorus is preferably limited to 0.019 to 0.025% by weight.

S (sulfur) is an element which is inevitably contained in the production of steel and exists in the form of manganese sulfide (MnS) because it has good affinity with manganese (Mn), and is not squeezed during rolling and is elongated. Further, since it causes red embrittlement, it is preferable to suppress the content to the maximum. In theory, it is possible to limit the content of sulfur to 0% by weight, but it is inevitably added to the manufacturing process inevitably. Therefore, it is important to control the upper limit, and it is preferable to limit the upper limit of the sulfur content to more than 0 to 0.008% by weight, that is, 80 ppm or less.

In addition, the slab can be made of Ceq (1) = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / ) / 15 + (Cr + Mo + V) / 5, Ceq (3) = C + Mn / 6 + Cu / 40 + Ni / 20 + Cr / Ceq (2) and Ceq (3) satisfy the range of 0.29 to 0.31.

Ceq (4) satisfies the range of 0.31 to 0.35 at Ceq (4) = C + Mn / 6 + Cr / 5 + Mo / 5 + V / 3 + Nb / 4 + 0.0001 / S.

The slabs satisfy Ceq (1), Ceq (2) and Ceq (3) in the range of 0.29 to 0.31 and Ceq (4) in the range of 0.31 to 0.35.

The slab is manufactured to a thickness of 220 to 260 t through a continuous casting process.

In the heating step (S100), the slabs having a thickness of 220 to 260t are reheated in the heating furnace by continuous casting to heat the slabs at 1,050 to 1,150 ° C.

In the rolling step (S200), the slabs heated at 1,050 to 1,150 占 폚 are subjected to rolling down in the range of Ar3 temperature + 20 to + 60 占 폚 as calculated by Equation (1) below, And rolling at a rate of 80% or more.

[Equation 1]

Ar3 (占 폚) = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo

In the cooling step S300, the steel sheet having the thickness within the target range of 20 t to 40 t rolled in the range of Ar 3 temperature + 20 to + 60 ° C is cooled to room temperature in the rolling step (S200).

The following Tables 1 and 2 show the composition ratios of the steel sheet and the comparative example (IACS) of Examples 1 and 2 of the present invention, and the compositions of Table 1 and Table 2 below and the balance Fe and other unavoidable impurities . Example 1 of the present invention is a post-steel plate having a thickness of 30t, and Example 2 of the present invention is a post-steel plate having a thickness of 40t.

C (wt%) Si (wt%) Mn (wt%) P (wt%) S (wt%) T-Al (wt%) Example 1 0.15 0.15 0.87 0.019 0.004 0.02 Example 2 0.14 0.15 0.86 0.020 0.004 0.03

V (wt%) N (wt%) Cu (wt%) Ti (wt%) Ni (wt%) Nb (wt%) Mo (wt%) Cr (wt%) Example 1 0.01 0.0025 0.01 0.001 0.01 0.001 0.001 0.02 Example 2 0.01 0.0031 0.01 0.001 0.01 0.001 0.003 0.03

Table 3 below shows Ceq (1), Ceq (2), Ceq (3), Ceq (4) and Ar3 temperatures of Example 1 and Example 2.

Ceq (1) Ceq (2) Ceq (3) Ceq (4) Ar3 temperature (占 폚) Example 1 0.31 0.30 0.30 0.33 792.77 Example 2 0.30 0.29 0.29 0.32 796.52

Table 4 below shows the tensile test results of Example 1, Example 2 and Comparative Example (IACS) of the present invention.

Direction Position YS (N / mm ²⁾ TS (N / mm ² ) Bending
Test EL. (%) Example 1 T Flat 278 433 Crack Free 32 Example 2 T Flat 270 439 Crack Free 31 Comparative Example
(IACS) T Flat 235 400 to 520 Crack ≤ 3mm 22

Table 5 below shows the CVN impact test results of Example 1, Example 2 and Comparative Example (IACS) of the present invention.

Direction Position Test Temp (° C) Each value (J) Average (J) Example 1 L Face vE 0 C 123 195 265 194 Example 2 L Face vE 0 C 123 195 265 212 Comparative Example
(IACS) L Face vE 0 C 70% of 34 27

2 and 3 are SEM micrographs of Example 1 and Example 2 of the present invention, and the microstructure of Examples 1 and 2 can be confirmed.

Referring to FIGS. 2 and 3, it can be confirmed that Examples 1 and 2 of the present invention have a ferrite and a pearlite structure together.

Table 6 below shows the welding test conditions for evaluating the weldability in Examples 1 and 2 of the present invention.

Welding Process Single Pole SEGARC Groove and Position Single V - 3G (Vertical-Up) Root gap (mm) 10 Angle (°) 30 Consumables A5.26 / EG72T (EG-3, D = 1.6) Plate Example 1 Example 2 Heat Input (kJ / cm) 250 340

Figs. 4 and 5 are photographs of the welding portions of the first and second embodiments, which are welded under the welding conditions shown in Table 4. Fig.

Referring to FIGS. 4 and 5, it can be seen that the shape of the back bead is slightly different due to the difference in welding conditions considering the discharge of the welding slag.

6 is a graph showing the tensile test results of the welding joints in Examples 1 and 2. Fig.

Table 7 below shows the tensile test results of the welding joints in Examples 1 and 2.

Specimen TS (N / mm ² ) Fractured Position Bending Test Example 1 Full Thickness 452, 452 Base Metal Crack Free Example 2 Full Thickness 449, 450 Base Metal Crack Free Comparative Example
(IACS) Max. Bead Width + 2T 400 ≤ Base Metal Crack ≤ 3mm

In Examples 1 and 2 of the present invention, it was confirmed that the tensile strength of the welded joint exceeded the standard of the comparative example (IACS) and satisfactory bending properties were obtained.

7 is a graph showing the Vickers hardness value (HV) at each distance point spaced apart from the FL on the basis of a fusion line (FL) which is the boundary between the welded joint and the weld heat affected zone (HAZ). In FIG. 7, it is confirmed that the positive (+) direction is the weld heat affected zone (HAZ) with respect to FL, and the negative (-) direction is the weld zone or weld metal.

Table 8 below shows the results of the CVN impact test on the welded joints. In Table 8, the first point is the position on the FL line, the second point is the point where the weld heat affected zone (HAZ) , And the third point is the point at which the point is separated by 5 mm from the FL to the weld heat affected zone (HAZ).

Plate Location One 2 3 Avg. Req. CVN 0 ° C, vE Avg. ≥34J Example 1 WM 100 97 100 99 FL (first point) 93 125 85 101 FL + 2mm
(Second point) 140 82 114 112 FL + 5mm
(Third point) 261 273 271 268 Example 2 WM 79 61 50 63 FL (first point) 35 177 40 84 FL + 2mm
(Second point) 177 255 170 201 FL + 5mm
(Third point) 83 256 254 198

In the first and second embodiments according to the present invention, it is confirmed that the precondition satisfies the standard.

8 is an electron micrograph showing the grain boundaries of WM and HAZ in the vicinity of FL in Example 1. Fig.

Figs. 9 to 11 are views showing a first point A on the FL line in Fig. 8, a second point B spaced by 2 mm from the welding heat affected zone HAZ in FL, And a third spot (C) spaced apart from each other.

Referring to FIGS. 8 to 11, it is confirmed that when the heat input is small, the development of WM and HAZ intergranular ferrite near the FL is the same and the structure of Bu + Pearlite + MA is at the second point (B).

FIG. 12 is a micrograph of the electron microscope taken at point D in FIG. 10, and FIG. 12 shows the microstructure of pearlite-removed MA.

13 is a scanning electron micrograph showing the grain boundaries of WM and HAZ in the vicinity of FL in Example 2. Fig.

Figs. 14 to 16 are diagrams showing the relationship between the first point E on the FL line in Fig. 13, the second point F spaced by 2 mm from the welding heat affected zone HAZ in FL, And a third point G spaced apart from each other.

13 to 16, the toughness at the second point 2 mm away from the weld heat affected zone (HAZ) is excellent and the Large Bu + Pearlite + (RA) structure is obtained when the heat input amount is large due to the increase in thickness of the thick plate .

The present invention can minimize the addition of alloying elements and can produce a post-steel sheet excellent in electro-gas weldability without adding expensive alloying elements such as Cr, Ni, Mo, Cu, Ti, V and Nb, .

The present invention relates to a weld metal having excellent tensile strength of a welded portion and having good bending properties and having a low impact toughness in a weld metal (WM), a fusion line (hereinafter referred to as FL) and a low carbon equivalent chemical The mechanical properties of the weld heat affected zone (HAZ) are advantageous.

It will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the present invention.

S100: heating step (S100) S200: rolling step (S200)
S300: Cooling step (S300)

Claims (8)

A heating step of reheating the slab in a heating furnace;
A rolling step of rolling the slab to produce a steel sheet after rolling; And
And a cooling step of cooling the steel sheet after it is manufactured in the rolling step,
Wherein the slab comprises 0.14 to 0.15% of C, 0.13 to 0.17% of Si, 0.84 to 0.88% of Mn, 0.019 to 0.025% of P, 0.008 to less than 0.008% of S and 0.02 to 0.03% of T- And Cr, Ni, Mo, Cu, Ti, V, and Nb are each contained in an amount of more than 0 and not more than 0.015% Lt; / RTI &
Ceq (1) = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / Ceq (1), Ceq (2) and Ceq (2) in the (Cr + Mo + V) / 5 and Ceq (3) = C + Mn / 6 + Cu / , Ceq (3) satisfies the range of 0.29 to 0.31 and Ceq (4) at Ceq (4) = C + Mn / 6 + Cr / 5 + Mo / 5 + V / 3 + Nb / 4 + 0.0001 / 0.31 to 0.35,
The rolling step is a rolling step in which the slabs heated at 1,050 to 1,150 캜 are rolled in the range of Ar 3 temperature + 20 to + 60 ° C calculated by Equation 1 below and a cumulative rolling reduction of 80% or more Wherein the rolled steel sheet is rolled under the following conditions.
[Equation 1]
Ar3 (占 폚) = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo delete delete delete delete delete delete The backsheet according to claim 1, wherein the backsheet has excellent electrogas weldability.

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