KR20180074860A - Welded joint with excellent ultra-low temperature toughness and strength - Google Patents

Abstract

The present invention relates to a welded joint part with excellent ultra-low temperature toughness and strength. According to the present invention, a welded joint part acquired by welding nickel steel comprises any one composition selected from (1) a first composition including: 0.1 to 0.5 weight percent of C; 0.1 to 2.0 weight percent of Si; 18 to 26.0 weight percent of Mn; 9 weight percent or less of Ni (excluding 0 weight percent); and the remainder being Fe and unavoidable impurities, and (2) a second composition including: 0.1 to 0.5 weight percent of C; 0.1 to 2.0 weight percent of Si; 0.5 to 12.0 weight percent of Mn; 20 to 30 weight percent of Ni; and the remainder being Fe and unavoidable impurities. According to the present invention, provided is a welded joint part applicable to nickel steel (nickel content: 4.8 to 9.2 weight percent), and providing an yield strength of 360 MPa or more and, at the same time, providing impact toughness of 27 J or more at an ultra-low temperature (-196°C).

Description

[0001] WELDED JOINT WITH EXCELLENT ULTRA-LOW TEMPERATURE TOUGHNESS AND STRENGTH [0002]

The present invention relates to a welded joint having excellent cryogenic toughness and strength, and more particularly, to a welded joint having an impact toughness of 27J or more at a cryogenic temperature (-196 ° C) and being applicable to nickel steel (nickel content: 4.8 to 9.2 wt% And a weld joint having a yield strength of 360 MPa or more.

Conventionally, nickel steel containing nickel (Ni) of 4.8 to 9.2% by weight is a cryogenic steel material having impact toughness of 27J or more at -110 to -196 ° C. It is a steel material that is actually used for transporting liquefied LNG and liquefied CO ₂ , It is utilized as a material to be produced.

In the case of manufacturing a welded structure using nickel steel having an impact toughness of 27 J or more in the cryogenic region as described above, it is necessary to secure the welded portion showing the same level of impact resistance at the cryogenic temperature in order to secure the stability of the welded structure. It is necessary to provide a weld joint having a room temperature yield strength of 360 MPa or more.

As a means for solving this problem, Inconel or Hastelloy series welding materials are widely used. For example, molybdenum (Mo), tungsten (W), and tungsten (W) may be added together with Ni in an amount of 60 wt% or more in case of a Hastelloy based welding material, And the like.

For example, Patent Document 1 discloses a method of flux cored arc welding a 9% Ni steel base material by using Inconel-based and Hastelloy-based welding materials.

However, the above-described welding material is extremely expensive because it contains a very high content of expensive Ni. In some cases, the welding material is used in an amount of 1 to 3% of the total weight in order to fabricate the LNG tank for the actual transportation, and therefore, the cost of the welding material is more than 10% of the manufacturing cost of the actual structure.

Therefore, if nickel steel is welded with an inexpensive material other than the expensive Inconel and Hastelloy series welding materials, cost competitiveness will arise in the production of actual structures. In other words, it is possible to reduce the manufacturing cost of the structure by 5% or more simply by lowering the cost of the welding material.

Therefore, by controlling the composition and content of alloying elements, it is possible to develop a low-cost material compared to existing materials such as Inconel and Hastelloy, and to apply this to nickel steel, which is excellent in cryogenic toughness and yield strength. Development is necessary.

Korean Patent Publication No. 2001-0063589

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a welded joint having excellent cryogenic toughness and yield strength by controlling the composition and content of welded joints obtained by welding nickel steel.

In order to solve the above problems, the present invention provides a welded joint obtained by welding nickel steel, wherein the welded joint comprises (1) 0.1 to 0.5% by weight of carbon (C) A first composition comprising 18 to 26.0 wt.% Mn, 9 wt.% Ni (excluding 0 wt.%), Residual Fe and other unavoidable impurities; And (2) 0.1 to 0.5 wt% of carbon (C), 0.1 to 2.0 wt% of silicon (Si), 0.5 to 12.0 wt% of manganese (Mn), 20 to 30 wt% of nickel And a second composition including other unavoidable impurities, which is excellent in cryogenic toughness and strength.

The welding part is composed of 0.1 to 3.0% by weight of chromium (Cr), 0.1 to 6.0% by weight of molybdenum (Mo), 0.1 to 4.0% by weight of tungsten (W) And sulfur (S): not more than 0.01% (excluding 0% by weight).

The nickel steel may include 4.8-9.2 wt% nickel.

The welding material used for the welding of the nickel steel may include 0.2 to 0.6% by weight of carbon (C), 0.1 to 2.0% by weight of silicon (Si), 25.0 to 35.0% by weight of manganese (Mn) By weight or less of nickel (Ni), 12% by weight or less of Fe, residual Fe and other unavoidable impurities, or 0.2 to 0.6% by weight of carbon (C), 0.1 to 2.0% (Ni): 25.0 to 40.0% by weight, residual Fe, and other unavoidable impurities.

The welding material may further include at least one selected from the group consisting of Cr: 0.01 to 3 wt%, molybdenum (Mo): 0.1 to 6.0 wt%, and tungsten (W): 0.1 to 4.0 wt%.

According to the present invention, it is possible to provide a weld joint which exhibits impact toughness of 27J or more at a cryogenic temperature (-196 DEG C) and at the same time a yield strength of 360 MPa or more by controlling the composition and content of the welded joint obtained by welding nickel steel .

Accordingly, the weld joint according to the present invention is effectively applicable to welding structures for cryogenic temperatures such as liquefied LNG and liquefied CO ₂ carrier vessels and land tank.

In addition, since the welding material used for obtaining the welded joint according to the present invention contains a significantly lower amount of nickel than the conventional Inconel and Hastelloy based welding materials, it is possible to secure price competitiveness.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

 The inventors of the present invention have conducted extensive studies to secure the cryogenic toughness and strength in the welding process of nickel steel. As a result, the present inventors have found that the composition of the welded joints can be improved by using carbon (C), silicon (Si), manganese (Mn) It was confirmed that when the content of iron (Fe) and other unavoidable impurities were appropriately controlled, impact toughness of 27 J or more at a cryogenic temperature (-196 ° C) and a welded joint exhibiting a yield strength of 360 MPa or more were obtained, .

Specifically, the weld joint having excellent cryogenic toughness and strength of the present invention is composed of (1) 0.1 to 0.5% by weight of carbon (C), 0.1 to 2.0% by weight of silicon (Si) and 18.0 to 26.0% of manganese %, Nickel (Ni): not more than 9.0 wt% (excluding 0 wt%), residual Fe and other unavoidable impurities; And (2) 0.1 to 0.5% by weight of carbon (C), 0.1 to 2.0% by weight of silicon (Si), 0.5 to 12.0% by weight of manganese (Mn), 20.0 to 30.0% And a second composition including other inevitable impurities.

First, the reason why each component constituting the welded joint of the present invention is added and the reasons for limiting the content range of the welded joint are described in detail.

Carbon (C): 0.1 - 0.5 wt%

Carbon is the most powerful austenite-forming element that can ensure weld strength and cryogenic toughness. If the content of carbon is less than 0.1 wt%, it is impossible to secure high-temperature strength. On the other hand, when the content of carbon exceeds 0.5 wt%, the process compound is excessively formed during welding, thereby promoting high-temperature cracking and welding fume and spatter. Therefore, in the present invention, the carbon content is limited to 0.1 to 0.5 wt%.

silicon( Si ): 0.1 ~ 2.0 wt%

Silicon is added to maximize complex deoxidation effect with manganese at the time of welding, and it is preferable to contain at least 0.1%. On the other hand, when the content of silicon exceeds 2.0% by weight, the process compound is excessively precipitated and the crack resistance is lowered. Therefore, in the present invention, the content of silicon is limited to 0.1 to 2.0 wt%.

Mn (Mn): 18.0-26. 0 wt% (First composition), 0.5 to 12. 0 wt% (Second composition)

Since manganese reacts with oxygen and sulfur during welding to perform deoxidation and desulfurization, 0.5% or more of manganese should be added. The weld joint according to the present invention is composed of the first composition and the second composition according to the contents of manganese and nickel.

First, in the case of the first composition, the content of nickel as the austenite stabilizing element is 9.0% by weight or less (excluding 0% by weight), and at this time, the content of manganese is 18.0% by weight or more for increasing the austenite stabilization degree . However, when the content of manganese exceeds 26.0% by weight, the content of manganese contained in the first composition is limited to 18.0 to 26.0% by weight in the present invention because of cost and difficulty in producing the welding material.

In the case of the second composition, when the content of Ni as the austenite stabilizing element is 20.0 wt% or more, the addition amount of manganese should be adjusted to a range not exceeding 12.0 wt% to improve the strength of the welded joint And the austenite stabilization degree can be increased. Therefore, in the present invention, the content of manganese contained in the second composition is limited to 0.5 to 12.0 wt%.

That is, according to the present invention, the content of manganese is limited to 18.0 to 26.0 wt% in the case of the first composition in which the content of nickel is 9.0 wt% or less (excluding 0 wt%) and the content of nickel is 20 wt% 2, the content of manganese is limited to 0.5 to 12.0% by weight.

nickel( Ni ): 9.0 wt% or less ( 0 wt% is excluded) (first composition) , 20 ~ 30 wt% (Second composition)

Nickel is a strong austenite forming element. As described above, the weld joint according to the present invention is composed of the first composition and the second composition according to the contents of manganese and nickel.

First, in the case of the first composition, when nickel is added together with 18.0% by weight or more of manganese, the austenite stability can be increased even if the content of nickel is adjusted to 9.0% by weight or less, Deterioration can be prevented, and price competitiveness can be ensured. Therefore, in the present invention, the content of nickel contained in the first composition is limited to 9 wt% or less (excluding 0 wt%).

In the case of the second composition, a complete austenite structure was formed, and the content of nickel was adjusted to 20.0 wt% or more in order to secure cryogenic toughness. However, when the content of nickel exceeds 30.0% by weight, the strength of the welded portion is lowered and the cost is raised. Therefore, the content is limited to 30.0% by weight or less. In this case, the content of Mn is limited to a range not exceeding 12%.

That is, according to the present invention, in the case of the first composition having a manganese content of 18.0 wt% or more, the content of nickel is limited to 9.0 wt% or less (excluding 0 wt%) and the content of manganese is 12.0 wt% 2, the content of nickel is limited to 20.0 to 30.0% by weight.

On the other hand, the weld joint having excellent cryogenic toughness and strength according to the present invention includes the balance of iron (Fe) and unavoidable impurities in addition to the above-mentioned component composition. However, the impurities can not be excluded because they are inevitably incorporated from the raw material or the surrounding environment in an unintended state during the ordinary steel making process. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of steel making.

In addition, the weld joint according to the present invention may include 0.1 to 3.0% by weight of chromium (Cr), 0.1 to 6.0% by weight of molybdenum (Mo), 0.1 to 4.0% by weight of tungsten (W) % Or less (excluding 0%) and sulfur (S): 0.01% or less (excluding 0% by weight). Hereinafter, the reasons for limiting the content of these components will be described.

chrome( Cr ): 0.1 ~ 3.0 wt%

Chromium is a ferrite-forming element, but may contain 0.1 wt% or more of chromium to ensure corrosion characteristics. However, if the content of chromium exceeds 3.0% by weight, toughness of the welded joint may be deteriorated due to formation of excess ferrite and chromium carbide. Therefore, the content of chromium is preferably 0.1 to 3.0% by weight.

molybdenum( Mo ): 0.1 ~ 6.0 wt%

Molybdenum is an element that increases the strength by fine precipitation of molybdenum-based carbides, and 0.1 wt% or more can be added to improve the strength. However, such precipitates may cause a decrease in impact toughness at low temperatures and high temperatures, and when the content of the molybdenum exceeds 6.0 wt%, ductility may decrease. Accordingly, the content of the molybdenum is preferably 0.1 to 6.0 wt%.

Tungsten (W): 0.1 ~ 4.0 wt%

Tungsten is an element which precipitates tungsten in a similar manner to molybdenum and increases strength at room temperature and high temperature. In order to improve the strength at high temperature and oxidation resistance, 0.1 wt% or more of tungsten may be added. However, such a precipitate may cause a decrease in impact toughness at low temperature and high temperature, and if the content of tungsten exceeds 4.0 wt%, ductility may be deteriorated. Accordingly, the content of tungsten is preferably 0.1 to 4.0% by weight.

(P): 0.01% or less (Excluding 0%)

Phosphorus is an impurity which is inevitably contained in the welded joint, and it is preferable that the phosphorus is not included as much as possible, since a low melting point compound is easily formed even by adding a trace amount thereof to lower the melting point of the material and increase the susceptibility to cracking at high temperature. When it is inevitably included, it is preferable that the content is not more than 0.01% by weight.

Sulfur (S): 0.01% or less (Excluding 0%)

Sulfur is an impurity inevitably contained in the welded joint, and it is preferable that sulfur is not included as much as possible because a low melting point compound is easily formed even by adding a trace amount to lower the melting point of the material and increase the susceptibility to cracking at high temperature. When it is inevitably included, it is preferable that the content is not more than 0.01% by weight.

Meanwhile, the welded joint according to the present invention is obtained by welding nickel steel, and the nickel steel may be a cryogenic steel containing 4.8 to 9.2 wt% nickel.

The welding material used for the welding of the nickel steel may contain 0.2 to 0.6% by weight of carbon (C), 0.1 to 2.0% by weight of silicon (Si), 25.0 to 35.0% by weight of manganese (Mn) (C): 0.2 to 0.6 wt%, silicon (Si): 0.1 to 2.0 wt%, manganese (Mn): 0.5 to 14 wt%, and the balance of Fe and other unavoidable impurities. (Ni): 25.0 to 40.0 wt.% Or less, residual Fe and other unavoidable impurities. The welding material may include 0.01 to 3 wt% of chromium (Cr), 0.1 to 6.0 wt% of molybdenum (Mo) And tungsten (W): 0.1 to 4.0% by weight.

The component content of the above-mentioned welding material is a numerical value obtained as a result of repeated intensive studies for obtaining the composition of the welded joint to be obtained in the present invention. When the content of each alloy component is out of the above range, the desired component composition and content It is difficult to obtain a welded joint.

That is, according to the present invention, welded joints having desired component compositions and contents can be obtained by welding nickel steel containing nickel of 4.8 to 9.2% by weight by using a welding material having the above composition and content, The weld joint is preferable because it exhibits an impact toughness of 27 J or more at a cryogenic temperature (-196 DEG C) and can exhibit a yield strength of 360 MPa or more.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these embodiments.

Example  1 to 16 and Comparative Example  1 to 30

First, nickel steel (base material) having a thickness of 20 mm, which satisfies the composition and content ranges shown in Table 1, was prepared.

Base material Alloy component (% by weight) Guaranteed temperature C Ni Si Mn P S 9% Ni steel 0.045 9.07 0.196 0.648 0.005 0.003 -196 ° C 5% Ni steel 0.035 4.99 0.194 0.663 0.005 0.003 -110 ° C

Then, flux cored wires (welding materials) 1 to 23 having a diameter of 1.2 mm which satisfied the composition and content ranges shown in Table 2 were prepared. In this case, the unit of the numerical values shown in the following table is% by weight.

No C Si Mn Cr Ni Mo W One 0.51 0.9 0.9 - 35 - - 2 0.3 0.7 9 2 28 - - 3 0.3 1.8 6 One 35 - - 4 0.2 0.8 6 - 34 2 One 5 0.6 0.9 8 - 39 - - 6 0.6 0.9 6 - 32 One One 7 0.3 0.7 30 2.5 4.5 2.5 0 8 0.2 0.6 31 0.05 9 1.5 0 9 0.08 0.4 One - 31 - - 10 0.05 2.2 0.9 - 35 - - 11 0.05 0.9 0.9 - 43 - - 12 0.8 2.5 9 - 28 - - 13 1.2 0.9 8 14 34 2 - 14 0.8 0.8 10 5 35 10 5 15 0.9 1.3 35 - 40 4 One 16 1.5 0.7 10 - 45 One 0.5 17 1.3 0.3 3 - 48 One - 18 0.6 0.4 15 0.05 0 1.5 0 19 0.1 0.7 30 2 5 2 4.5 20 0.6 0.6 19 2 0 1.5 2.5 21 0.3 0.2 20 0.02 5.5 1.5 1.5 22 0.3 0.6 20 6.5 5.5 2.5 0 23 0.6 0.6 20 1.9 0 2 0

Then, each of the prepared base materials (nickel steel) was subjected to flux cored arc welding (FCAW) using the respective welding materials. At this time, the butt welding was carried out at a heat input of 1.5 kJ / mm using a protective gas having a weight ratio of Ar: CO ₂ of 8: 2. The above FCAW current was 180 to 220 A, the voltage was 25 to 28 V, the welding speed was 20 to 35 cm / min, the protective gas was 100% CO ₂ , the polarity DC +, and the interlayer temperature was 150 ° C. or less.

The composition and content of the welded joint obtained according to the combination of the base material and the welding material are shown in Table 3 below.

<Evaluation method>

1. Cryogenic impact toughness (CVN @ -196 ℃, J)

The cryogenic impact toughness of the weld joints obtained according to Examples 1 to 16 and Comparative Examples 1 to 30 was measured by using a Charpy impact test (CVN) at -196 ° C using a KS standard (KS B ISO 9016) VWT 0 / And the results are shown in Table 3 below.

2. Yield strength (MPa)

The yield strengths of the weld joints obtained according to Examples 1 to 16 and Comparative Examples 1 to 30 were measured by a tensile test method using an universal testing machine. The results are shown in Table 3 below.

Base material welding
material C Si Mn Cr Ni Mo W CVN @ -196 ° C
(J) surrender
burglar
(MPa) Example 1 5% Ni steel One 0.368 0.688 0.83 - 26.0 - - 50.4 371.5 Example 2 5% Ni steel 2 0.221 0.548 6.50 1.40 21.1 - - 63.7 416.3 Example 3 5% Ni steel 3 0.221 1.318 4.40 0.70 26.0 - - 29.4 432.4 Example 4 5% Ni steel 4 0.151 0.618 4.40 - 25.3 1.72 0.80 37.1 515.2 Example 5 5% Ni steel 5 0.431 0.688 5.80 - 28.8 - - 28.7 449.7 Example 6 5% Ni steel 6 0.431 0.688 4.40 - 23.9 0.82 0.92 53.9 572.7 Example 7 5% Ni steel 7 0.221 0.548 21.20 1.75 4.6 1.75 - 32.1 482.0 Example 8 5% Ni steel 8 0.151 0.478 21.90 0.04 7.8 1.25 - 29.5 455.5 Example 9 9% Ni steel One 0.380 0.760 0.78 - 26.5 - - 57.6 362.1 Example 10 9% Ni steel 2 0.210 0.570 4.72 1.50 23.4 72.8 398.2 Example 11 9% Ni steel 3 0.220 1.420 3.27 0.80 28.2 33.6 413.6 Example 12 9% Ni steel 4 0.154 0.720 3.27 28.4 1.62 0.84 42.4 492.8 Example 13 9% Ni steel 5 0.420 0.710 4.25 29.3 32.8 430.1 Example 14 9% Ni steel 6 0.450 0.710 3.27 25.1 0.75 0.62 61.6 547.8 Example 15 9% Ni steel 7 0.224 0.548 21.20 1.75 5.9 2.01 - 28.0 570.2 Example 16 9% Ni steel 8 0.154 0.478 21.90 0.04 9.0 1.23 - 31.2 435.7 Comparative Example 1 5% Ni steel 9 0.067 0.338 0.90 - 23.2 - - 72.1 339.3 Comparative Example 2 5% Ni steel 10 0.046 1.598 0.83 - 26.0 - - 60.9 320.9 Comparative Example 3 5% Ni steel 11 0.046 0.688 0.83 - 31.6 - - 65.8 295.6 Comparative Example 4 5% Ni steel 12 0.571 1.808 6.50 - 21.1 - - 25.2 489.9 Comparative Example 5 5% Ni steel 13 0.851 0.688 5.80 9.80 25.3 1.40 - 13.3 659.0 Comparative Example 6 5% Ni steel 14 0.571 0.618 7.20 3.50 26.0 7.00 4.05 16.1 571.6 Comparative Example 7 5% Ni steel 15 0.641 0.968 24.70 - 29.5 2.80 0.70 10.5 568.1 Comparative Example 8 5% Ni steel 16 1.061 0.548 7.20 - 33.0 0.70 0.35 21.7 627.9 Comparative Example 9 5% Ni steel 17 0.921 0.268 2.30 - 35.1 0.70 - 23.1 599.2 Comparative Example 10 5% Ni steel 18 0.431 0.338 10.70 0.04 1.5 1.05 - 21.7 491.6 Comparative Example 11 5% Ni steel 19 0.081 0.548 21.20 1.40 5.0 1.40 3.65 18.9 600.9 Comparative Example 12 5% Ni steel 20 0.431 0.478 13.50 1.40 1.5 1.05 2.03 20.3 553.1 Comparative Example 13 5% Ni steel 21 0.221 0.198 14.20 0.01 5.3 1.05 1.22 22.4 515.9 Comparative Example 14 5% Ni steel 22 0.221 0.478 14.20 4.55 5.3 1.75 - 9.8 652.9 Comparative Example 15 5% Ni steel 23 0.431 0.478 14.20 1.33 1.5 1.40 - 16.8 553.0 Comparative Example 16 9% Ni steel 9 0.070 0.350 0.80 - 24.4 - - 82.4 324.5 Comparative Example 17 9% Ni steel 10 0.060 1.580 0.75 - 26.2 - - 69.6 306.9 Comparative Example 18 9% Ni steel 11 0.049 0.720 0.76 - 32.9 - - 75.2 282.7 Comparative Example 19 9% Ni steel 12 0.580 1.820 4.92 - 23.0 - - 26.5 468.6 Comparative Example 20 9% Ni steel 13 0.870 0.710 4.35 10.10 26.7 1.30 - 15.2 630.3 Comparative Example 21 9% Ni steel 14 0.540 0.650 5.73 3.50 29.0 7.50 3.52 18.4 546.7 Comparative Example 22 9% Ni steel 15 0.620 1.100 17.62 - 30.1 1.40 0.72 12.0 543.4 Comparative Example 23 9% Ni steel 16 1,000 0.650 5.43 - 34.1 0.80 0.45 24.8 600.6 Comparative Example 24 9% Ni steel 17 0.910 0.280 1.80 - 36.5 0.78 - 26.4 573.1 Comparative Example 25 9% Ni steel 18 0.434 0.338 10.70 0.04 2.7 1.05 - 24.8 470.2 Comparative Example 26 9% Ni steel 19 0.084 0.548 21.20 1.40 6.2 1.40 3.65 21.6 574.8 Comparative Example 27 9% Ni steel 20 0.434 0.478 13.50 1.40 2.7 1.05 2.03 23.2 362.1 Comparative Example 28 9% Ni steel 21 0.224 0.198 14.20 0.01 6.6 1.05 1.22 26.5 493.5 Comparative Example 29 9% Ni steel 22 0.224 0.478 14.20 4.55 6.6 1.75 - 11.2 624.5 Comparative Example 30 9% Ni steel 23 0.434 0.478 14.20 1.33 2.7 1.40 - 19.2 528.9

As shown in Table 1, when the weld joint obtained according to Examples 1 to 16 of the present invention shows a cryogenic impact strength of 27 J or more at a target temperature (-196 ° C), a yield strength of 360 MPa or more can be obtained can confirm.

On the other hand, in the case of weld joint provided according to Comparative Examples 1 to 9, 11, 16 to 24 and 26 in which the carbon content is out of the range of 0.1 to 0.5 wt%, impact toughness at -196 캜 is less than 27J, , It was impossible to apply it to a cryogenic material for manufacturing a carrier such as liquefied LNG and liquefied CO ₂ or a land tank.

Further, in the case of the weld joint provided according to Comparative Examples 10 and 25 including 10.7 wt% of manganese and 1.5 wt% of nickel and Comparative Examples 12 to 15 and 27 to 30 containing manganese content of 13 to 17 wt% It can be seen that the impact toughness is poor, and therefore, these are also not applicable as cryogenic materials.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Should be construed as being included in the scope of the present invention.

Claims (5)

A welded joint obtained by welding nickel steel,
The welded joint is composed of (1) 0.1 to 0.5% by weight of carbon (C), 0.1 to 2.0% by weight of silicon (Si), 18.0 to 26.0% by weight of manganese (Mn) (Excluding 0% by weight), residual Fe and other unavoidable impurities; And (2) 0.1 to 0.5% by weight of carbon (C), 0.1 to 2.0% by weight of silicon (Si), 0.5 to 12.0% by weight of manganese (Mn), 20.0 to 30.0% And a second composition including other unavoidable impurities, wherein the cryogenic toughness and strength are excellent. The method according to claim 1,
The welding part is composed of 0.1 to 3.0% by weight of chromium (Cr), 0.1 to 6.0% by weight of molybdenum (Mo), 0.1 to 4.0% by weight of tungsten (W) ) And sulfur (S): not more than 0.01% (excluding 0% by weight). The method according to claim 1,
Wherein the nickel steel comprises 4.8 to 9.2% by weight of nickel and has excellent cryogenic toughness and strength. The method according to claim 1,
The welding material used for the welding of the nickel steel may include 0.2 to 0.6% by weight of carbon (C), 0.1 to 2.0% by weight of silicon (Si), 25.0 to 35.0% by weight of manganese (Mn) By weight or less of nickel (Ni), 12% by weight or less of Fe, residual Fe and other unavoidable impurities, or 0.2-0.6% by weight of carbon (C), 0.1-2.0% (Ni): 25.0 to 40.0% by weight, and residual Fe and other unavoidable impurities. 5. The method of claim 4,
Wherein the welding material further comprises at least one selected from the group consisting of Cr: 0.01 to 3.0 wt%, molybdenum (Mo): 0.1 to 6.0 wt%, tungsten (W): 0.1 to 4.0 wt% Excellent welding strength.