CN113646456B

CN113646456B - Gap-filling alloy for TIG welding

Info

Publication number: CN113646456B
Application number: CN202080025357.9A
Authority: CN
Inventors: 高田充志; 高山直树; 黑田穰; 石田伦教; 仲道治郎; 植田圭治; 山下贤; 韩鹏
Original assignee: JFE Steel Corp; Kobe Steel Ltd
Current assignee: JFE Steel Corp; Kobe Steel Ltd
Priority date: 2019-03-29
Filing date: 2020-03-19
Publication date: 2023-01-17
Anticipated expiration: 2040-03-19
Also published as: CN113646456A; WO2020203334A1; KR20210143296A; JPWO2020203334A1; JP6978615B2

Abstract

The purpose of the present invention is to provide a shim alloy for TIG welding which is suitable as a welding material for high Mn steel. The interstitial alloy has the following composition: contains, in mass%, C:0.2 to 0.8%, si:0.15 to 0.9%, mn:17.0 to 28.0%, P:0.03% or less, S:0.03% or less, ni:0.01 to 10.0%, cr:0.4 to 4.0%, mo:0.01 to 3.5%, B: less than 0.0010%, N:0.12% or less, and the balance of Fe and inevitable impurities. The filler alloy is excellent in manufacturability, suppresses generation of weld cracks during welding, is excellent in high-temperature crack resistance, can obtain a deposited metal with high strength and excellent cryogenic impact toughness, and can easily produce a TIG welded joint with high strength and excellent cryogenic impact toughness.

Description

Gap-filling alloy for TIG welding

Technical Field

The present invention relates to a gap filler alloy for TIG (Tungsten Inert Gas) welding, and more particularly to a gap filler alloy for high Mn steel welding used in an extremely low temperature environment.

Background

In recent years, regulations on the environment have become more stringent. Since liquefied natural gas (hereinafter, also referred to as LNG) does not contain sulfur, it is called a clean fuel that does not generate air pollutants such as sulfur oxides, and the demand for such a fuel is increasing. In order to transport or store LNG, it is necessary that a container (tank) that transports or stores LNG maintains excellent cryogenic impact toughness at a temperature of-162 ℃.

Further, since it is necessary to maintain excellent cryogenic impact toughness, aluminum alloys, 9-% ni steel, austenitic stainless steel, and the like have been used as materials for containers (cans) and the like.

However, since the aluminum alloy has low tensile strength, the thickness of the structure must be designed to be thick, and weldability is poor. In addition, 9-percent Ni steel requires the use of an expensive Ni-based material as a welding material, and is therefore economically disadvantageous. Further, austenitic stainless steel has problems of being expensive and having low base material strength.

In view of such problems, studies have recently been made to apply steel having a high Mn content (also referred to herein as high Mn steel) containing Mn of about 10 to 35% by mass as a material for a container (tank) for transporting or storing LNG. The high Mn steel has the following characteristics: the steel is in an austenite phase even at extremely low temperatures, does not undergo brittle fracture, and has high strength as compared with austenitic stainless steel. Therefore, it is desired to develop a welding material capable of stably welding such a steel material having a high Mn content.

For such a requirement, for example, patent document 1 proposes "a high-strength welded joint excellent in cryogenic impact toughness and a flux-cored arc welding wire used for the same". The flux-cored arc welding wire described in patent document 1 has a composition as follows: contains C in weight%: 0.15 to 0.8%, si: 0.2E1.2%, mn:15 to 34%, cr:6% or less, mo:1.5 to 4%, S:0.02% or less, P:0.02 percent the following components B:0.01% or less, ti:0.09 to 0.5%, N: 0.001-0.3% of TiO ₂ : 4-15% of SiO ₂ 、ZrO ₂ And Al ₂ O ₃ 1 or more of (a): 0.01 to 9%, 1 or more selected from K, na and Li in total: 0.5 to 1.7%, 1 or more of F and Ca: 0.2 to 1.5%, and the balance of Fe and other inevitable impurities. When welding is performed using the wire for flux cored arc welding described in patent document 1, it is possible to effectively obtain a wire having a test temperature: a welded joint having excellent low-temperature toughness having an absorption energy of 28J or more and high strength having a room-temperature tensile strength of 400MPa or more in a Charpy impact test at-196 ℃, wherein the welding wire composition is adjusted to Mo:1.5% or more, and a welded joint having excellent high-temperature crack resistance can be secured.

Further, patent document 2 proposes "a welding material for extremely low temperature steel". The "welding material for extremely low temperature steel" described in patent document 2 contains, in mass%, C:0.08% or less, si:2.0% or less, mn:8.0 to 18.0%, ni:12.5 to 20.0%, cr:10.0 to 14.0%, mo:2.0 to 7.0%, N:0.20% or less, S:0.005% or less, and the balance of the welding material is composed of iron and unavoidable impurities; characterized in that REM is contained in a range of 0.001 to 0.1%. In the technique described in patent document 2, not only is the amount of S as an impurity reduced as much as possible, but also a predetermined amount of REM is positively added, so that solidification cracking is suppressed and ductility reduction cracking of the reheated portion is prevented even when welding is performed under severe welding conditions with high welding efficiency. Thus, the "welding material for extremely low temperature steel" described in patent document 2 is a welding material that can obtain good extremely low temperature characteristics of a welded portion and is excellent in ductility reduction cracking resistance of a reheated portion.

Documents of the prior art

Patent literature

Patent document 1: japanese patent application laid-open No. 2017-502842

Patent document 2: japanese patent laid-open publication No. 2013-103233

Disclosure of Invention

However, according to the study of the present inventors, in the technique described in patent document 1, since the wire is a flux-cored wire, the amount of generated fumes increases during welding. Therefore, there is a problem that a welder is exposed to an environment with a large amount of mist, and welding defects such as blowholes and fusion defects are likely to occur, and repair is difficult. It should be noted that according to the study of the present inventors, it was found that if a solid wire (or rod) is used, these problems of smoke can be avoided.

Patent document 2 describes that excellent cryogenic characteristics can be obtained, but does not specifically describe the strength of the welded portion. According to the studies of the present inventors, in the technique described in patent document 2, the strength of the welded portion (deposited metal) obtained is low, and the desired high strength required for the material used in the extremely low temperature environment in recent years cannot be satisfied.

The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide a shim alloy for TIG welding which is suitable as a welding material for high Mn steel materials used in an extremely low temperature environment and which can produce a weld joint having both high strength and excellent extremely low temperature impact toughness. The "filler alloy" as used herein refers to a wire-like or rod-like welding material.

The term "high strength" as used herein means that the yield strength at room temperature (0.2% proof stress) of the deposited metal produced according to the specification of JIS Z3111 is 400MPa or more, and the tensile strength at room temperature is 660MPa or more. The term "excellent cryogenic impact toughness" means the test temperature of a deposited metal produced in accordance with the provisions of JIS Z3111: absorption energy vE of Charpy impact test at-196 DEG C _-196 Is more than 28J.

In order to achieve the above object, the present inventors first conducted extensive studies on a composition capable of securing a desired high strength that a weld metal (deposited metal) can retain as an extremely low temperature application. As a result, they have found that a certain amount or more of C, mn, cr, and Mo needs to be contained to increase the strength of the weld metal (deposited metal). However, particularly in the case where C, mn, cr, and Mo are excessively contained in the shim alloy for TIG welding in which the amount of work is large during wire drawing to increase the strength of the weld metal (deposited metal), there is a problem that cracks and disconnections are likely to occur during wire drawing. In response to such problems, the present inventors have found that wire drawing can be performed by suppressing boron nitride and carbide formed in steel.

As a result of such studies, it has been newly found that defects such as cracks during wire drawing are not generated by adjusting C to 0.2 to 0.8%, si to 0.15 to 0.9%, mn to 17.0 to 28.0%, ni to 0.01 to 10.0%, cr to 0.4 to 4.0%, and Mo to a specific range of 0.01 to 3.5%, and B as an impurity to less than 0.0010%, and Ti, nb, and V as carbide-forming elements to 0.04% or less, respectively, as a composition of a gap filler alloy for TIG welding, and that the gap filler alloy is excellent in manufacturability, and can be manufactured with a room-temperature yield strength (0.2% proof stress) of 400MPa or more, a room-temperature tensile strength of 660MPa or more, and a test temperature: absorption energy vE of Charpy impact test at-196 DEG C _-196 A welded joint having a high strength of 28J or more and excellent in very low temperature impact toughness.

The present invention has been completed based on such findings, and the gist of the present invention is as follows.

(1) A shim alloy for TIG welding having the following composition: contains, in mass%, C:0.2 to 0.8%, si:0.15 to 0.9%, mn:17.0 to 28.0%, P:0.03% or less, S:0.03% or less, ni:0.01 to 10.0%, cr:0.4 to 4.0%, mo:0.01 to 3.5%, B: less than 0.0010% and N:0.12% or less, and the balance of Fe and inevitable impurities.

(2) The shim alloy for TIG welding according to item (1) above, wherein the composition further contains, in mass%, a metal selected from the group consisting of V:0.04% or less, ti:0.04% or less and Nb:0.04% or less of 1 or 2 or more.

(3) The caulking alloy for TIG welding according to the item (1) or (2), wherein the composition further contains, in mass%, a metal selected from the group consisting of Cu:1.0% or less, al:0.1% or less, ca:0.01% or less and REM:0.02% or less of 1 or 2 or more.

The present invention can provide a filler alloy for TIG welding, which is excellent in manufacturability, and further, as a welding material for steel having a high Mn content, can easily produce a welded joint having high strength and excellent cryogenic impact toughness, and has a significant industrial effect.

Detailed Description

The shim alloy for TIG welding of the present invention (hereinafter also referred to as the shim alloy of the present invention) is a shim alloy for TIG welding suitable for steel having a high Mn content. The gap-filling alloy is a welding material as follows: the weld metal produced according to JIS Z3111 can have a high strength at normal temperature of 400MPa or more in 0.2% proof stress and 660MPa or more in tensile strength at normal temperature, and a test temperature: the absorption energy in the Charpy impact test at-196 ℃ is 28J or more, and a TIG welded joint having high strength and excellent cryogenic impact toughness can be produced.

The interstitial alloy of the present invention has the following composition as a basic composition: contains, in mass%, C:0.2 to 0.8%, si:0.15 to 0.9%, mn:17.0 to 28.0%, P:0.03% or less, S:0.03% or less, ni:0.01 to 10.0%, cr:0.4 to 4.0%, mo:0.01 to 3.5%, B: less than 0.0010%, N:0.12% or less, and the balance of Fe and inevitable impurities.

First, the reasons for the limitation of the composition will be explained. In the following compositions, "mass%" is abbreviated as "%".

C：0.2～0.8％

C is an element having an effect of improving the strength of the weld metal by solid solution strengthening. In addition, C stabilizes the austenite phase, improving the very low temperature impact toughness of the weld metal. In order to obtain such an effect, it is necessary to contain 0.2% or more. However, if the content exceeds 0.8%, carbide precipitates, the very low temperature impact toughness is lowered, and high temperature cracking during welding is likely to occur. Therefore, C is limited to the range of 0.2 to 0.8%. Preferably 0.3 to 0.7%, more preferably 0.4 to 0.6%.

Si：0.15～0.9％

Si acts as a deoxidizer, and has the effect of increasing the yield of Mn, increasing the viscosity of the molten metal, and stably maintaining the shape of the flange. In order to obtain such an effect, it is necessary to contain 0.15% or more. However, if Si is contained in excess of 0.9%, the extremely low temperature toughness of the weld metal is lowered. In addition, segregation occurs during solidification, and a liquid phase is formed at the solidification cell interface, thereby reducing the high-temperature cracking resistance. Therefore, si is limited to the range of 0.15 to 0.9%. Preferably 0.2 to 0.7%.

Mn：17.0～28.0％

Mn is an element that stabilizes the austenite phase at low cost, and is required to be contained in 17.0% or more in the present invention. If Mn is less than 17.0%, a ferrite phase is formed in the weld metal, and the toughness at extremely low temperatures is significantly reduced. On the other hand, if Mn exceeds 28.0%, mn segregation occurs excessively at the time of solidification, and hot cracking is induced. Therefore, mn is limited to the range of 17.0 to 28.0%. Preferably 18.0 to 26.0%.

P: less than 0.03%

P is an element which causes segregation in grain boundaries and induces hot cracking, and is preferably as small as possible in the present invention, but if 0.03% or less, it is allowable. Therefore, P is limited to 0.03% or less. Preferably 0.02% or less. On the other hand, excessive reduction leads to an increase in refining cost. Therefore, P is preferably adjusted to 0.003% or more.

S: less than 0.03%

S is present as a sulfide-based inclusion MnS in the weld metal. MnS is a starting point for fracture generation, thus reducing the very low temperature impact toughness. Therefore, S is limited to 0.03% or less. Preferably 0.02% or less. On the other hand, excessive reduction leads to an increase in refining cost. Therefore, S is preferably adjusted to 0.001% or more.

Ni：0.01～10.0％

Ni strengthens the elements of austenite grain boundaries, generates segregation in the grain boundaries and improves the extremely low temperature impact toughness. In order to obtain such an effect, the content of the compound is required to be 0.01% or more. Further, since Ni also has an effect of stabilizing the austenite phase, if the content is further increased, the austenite phase is stabilized, and the very low temperature impact toughness of the weld metal is improved. However, ni is an expensive element, and the inclusion of more than 10.0% is economically disadvantageous. Therefore, ni is limited to 0.01 to 10.0%. Preferably 0.05 to 9.0%, more preferably 1.0 to 8.0%.

Cr：0.4～4.0％

Cr acts as an element stabilizing the austenite phase at extremely low temperatures, and improves the extremely low temperature impact toughness of the weld metal. In addition, cr also has the effect of improving the strength of the weld metal. In addition, cr effectively increases the liquidus line of the molten metal and suppresses the occurrence of high-temperature cracks. Further, cr effectively improves the corrosion resistance of the weld metal. In order to obtain such an effect, it is necessary to contain 0.4% or more. If Cr is less than 0.4%, the above-described effects cannot be ensured. On the other hand, if it exceeds 4.0%, cr carbide is formed, resulting in a decrease in very low temperature impact toughness. Further, the formation of Cr carbide deteriorates the workability of the interstitial alloy during wire drawing. Therefore, cr is limited to the range of 0.4 to 4.0%. Preferably 0.8 to 3.0%.

Mo：0.01～3.5％

Mo is an element for strengthening austenite grain boundaries, generates segregation in the grain boundaries, and improves the extremely low temperature impact toughness of the weld metal. Such an effect becomes remarkable when 0.01% or more is contained. If the content exceeds 0.01%, the strength of the weld metal is also improved by solid solution strengthening. On the other hand, if it exceeds 3.5%, the carbide precipitates to lower hot workability, and cracks are induced during the drawing of the interstitial alloy to lower the productivity. Therefore, mo is limited to the range of 0.01 to 3.5%. Preferably 0.1 to 3.2%, more preferably 1.0 to 3.0%.

B: less than 0.0010%

B mixed as an impurity into steel segregates at austenite grain boundaries. When B is mixed at 0.0010% or more, boron nitride is formed at austenite grain boundaries, and the grain boundary strength is reduced. Due to this decrease in grain boundary strength, austenite grain boundaries become a starting point for fracture during the wire drawing of the interstitial alloy, and therefore, wire breakage occurs, which reduces wire drawing workability and decreases the manufacturability of the interstitial alloy. The formation of boron nitride can be suppressed by limiting B to less than 0.0010%, and thus B is limited to less than 0.0010%. Preferably 0.0009% or less, more preferably 0.0008% or less.

N: less than 0.12%

N is an element that is inevitably mixed, but as with C, it can contribute effectively to the improvement of the strength of the weld metal, and also stabilize the austenite phase and stably improve the very low temperature impact toughness. Such an effect becomes remarkable when 0.003% or more is contained, and therefore 0.003% or more is preferably contained. However, if the content exceeds 0.12%, nitrides are formed, and the very low temperature impact toughness is lowered. Therefore, N is limited to 0.12% or less. Preferably 0.10% or less, more preferably 0.08% or less.

The interstitial alloy of the present invention contains the above-mentioned components as essential components, and in the present invention, the above-mentioned essential components may optionally contain, as required, a component selected from the group consisting of V:0.04% or less, ti:0.04% or less and Nb:0.04% or more of 1 or 2 of the following, and/or, selected from Cu:1.0% or less, al:0.1% or less, ca:0.01% or less and REM:0.02% or less of 1 or 2 or more of them as optional components. These optional components will be described below.

Is selected from V:0.04% or less, ti:0.04% or less and Nb: less than 0.04% of 1 or more than 2

V, ti and Nb are elements that promote the formation of carbide and contribute to the improvement of the strength of the weld metal, and may be contained in 1 or 2 or more species as needed.

V: less than 0.04%

V is a carbide-forming element, and precipitates fine carbides, contributing to improvement in the strength of the weld metal. In order to obtain such an effect, it is preferable to contain 0.001% or more. On the other hand, if it exceeds 0.04%, the carbide becomes coarse, which becomes a starting point of crack generation at the time of drawing of the interstitial alloy, and the drawability is lowered, and the manufacturability of the interstitial alloy is lowered. Therefore, when contained, V is limited to 0.04% or less.

Ti: less than 0.04%

Ti is a carbide-forming element, and precipitates fine carbides, contributing to improvement in the strength of the weld metal. Ti also precipitates carbide at the solidification cell interface of the weld metal, and contributes to suppression of the occurrence of high-temperature cracks. In order to obtain such an effect, it is preferable to contain 0.001% or more. However, if Ti is contained: if the content exceeds 0.04%, the carbide becomes coarse, and becomes a starting point of crack generation during the wire drawing of the interstitial alloy, which reduces the wire drawing workability and the productivity of the interstitial alloy. Therefore, when it is contained, ti is limited to 0.04% or less.

Nb: less than 0.04%

Nb is a carbide-forming element, and is an element that precipitates carbides and contributes to the improvement of the strength of the weld metal. Nb also precipitates carbide at the solidification cell interface of the weld metal, and contributes to suppression of occurrence of high-temperature cracks. In order to obtain such an effect, it is preferable to contain 0.001% or more. However, if Nb exceeds 0.04%, carbides coarsen, become starting points for crack generation during wire drawing of the interstitial alloy, and reduce wire drawing workability and manufacturability of the interstitial alloy. Therefore, nb is limited to 0.04% or less when contained.

Is selected from Cu:1.0% or less, al:0.1% or less, ca:0.01% or less and REM:0.02% or less of 1 or 2 or more

Cu is an element contributing to the stabilization of austenite, al is an element contributing to the improvement of welding workability, and Ca and REM are elements contributing to the improvement of workability, and 1 or 2 or more species may be selectively contained as necessary.

Cu:1.0% or less

Cu is an element that stabilizes the austenite phase, stabilizes the austenite phase even at extremely low temperatures, and improves the extremely low temperature impact toughness of the weld metal. In order to obtain such an effect, the content is preferably 0.01% or more. However, if the content exceeds 1.0%, the hot ductility is lowered, and the manufacturability of the interstitial alloy is lowered. Therefore, when contained, cu is limited to 1.0% or less.

Al: less than 0.1%

Al plays an important role as a deoxidizer, increases the viscosity of molten metal, and stably maintains the shape of the flange. In addition, al increases the liquidus temperature of the molten metal, and contributes to suppression of high-temperature cracking of the weld metal. Such an effect becomes remarkable when 0.005% or more is contained, and therefore 0.005% or more is preferably contained. However, if the content exceeds 0.1%, the viscosity of the molten metal becomes too high, and conversely, defects such as poor fusion due to no diffusion of the flange increase. Therefore, when contained, al is limited to a range of 0.1% or less. Preferably 0.005 to 0.06%.

Ca: less than 0.01%

Ca combines with S in the molten metal to form high melting sulfide CaS. CaS has a higher melting point than MnS, and therefore, maintains a spherical shape without developing in the rolling direction during hot working of the interstitial alloy, and contributes to improvement of workability of the interstitial alloy. Such an effect becomes remarkable when 0.001% or more is contained. On the other hand, if it exceeds 0.01%, the amount of slag generated during welding increases, causing slag inclusion. Therefore, ca is limited to 0.01% or less when contained.

REM: less than 0.02%

REM is a strong deoxidizer and exists as REM oxide in the weld metal. REM oxide serves as a nucleation site during solidification, thereby refining crystal grains and contributing to improvement in strength of the weld metal. Such an effect becomes remarkable when 0.001% or more is contained. On the other hand, if the content exceeds 0.02%, the amount of slag generated increases, causing slag inclusion. Therefore, when contained, REM is limited to 0.02% or less.

The remainder excluding the above components is composed of Fe and inevitable impurities.

Next, a method for producing the interstitial alloy of the present invention will be explained.

The filler alloy of the present invention can be produced by any commonly used method for producing a filler alloy, without any particular limitation, except that the molten steel having the above composition is used and the annealing temperature is set to 900 to 1200 ℃. For example, the following steps are sequentially performed: a casting step of melting the molten steel having the above composition in a conventional melting furnace such as an electric furnace or a vacuum melting furnace, and casting the molten steel in a mold having a predetermined shape or the like to obtain a steel ingot; a heating step of heating the obtained steel ingot to a predetermined temperature; and a hot rolling step of hot rolling the heated steel slab to obtain a steel slab (rod-like) having a predetermined shape; the filler alloy of the present invention can be produced by performing a cold rolling step to the obtained steel billet (rod) and performing cold rolling (cold wire drawing) a plurality of times and annealing as necessary to produce a filler alloy of a desired size.

The present invention will be further described below with reference to examples.

Examples

Molten steel having a composition shown in table 1 was melted in a vacuum melting furnace and cast to obtain a steel ingot of 1000kg. Heating the obtained steel ingot to 1200 ℃, hot rolling, cold rolling, and annealing (900-1200 ℃) as required to obtain the steel ingot

A shim alloy (welding rod) for TIG welding having a length of 1000 mm.

When producing a filler alloy, the productivity of each filler alloy was evaluated by measuring the rolling load (wire drawing load), observing cracks, observing the cross section of the filler alloy, and the like. The following was evaluated as "poor": the rolling (wire drawing) process was judged to be impossible due to a high rolling load (wire drawing load), and the occurrence of cracks was confirmed, and the subsequent process could not be continued due to the cracks. In addition, the evaluation was "good".

Then, a high Mn steel sheet for extremely low temperature (sheet thickness: 12 mm) was prepared as a test sheet, and a 45 DEG V groove was formed by butt joint in accordance with JIS Z3111, and TIG welding was performed to obtain a deposited metal in the groove. The steel sheet used as the test sheet was a high Mn steel sheet for very low temperature having a composition consisting of 0.5% by mass of C-0.4% by mass of Si-25% by mass of Mn-3% by mass of Cr-the remainder of Fe.

In the TIG welding, each filler metal (2.0 mm in diameter) produced from molten steel having a composition shown in table 1 was used as a welding material, and the welding material was turned in a downward posture without preheating, under a condition of current: 200A (DCEN), voltage: 12V, welding speed: 8 cm/min, interstitial alloy feed rate: 10 g/min, weld pass interval: 100-150 ℃, protective gas: ar is used. The electrode being a pure tungsten rod

The obtained deposited metal was observed with an optical microscope to determine the presence or absence of weld cracking. The weld crack was a high-temperature crack, and when the occurrence of the crack was confirmed, the high-temperature crack resistance was reduced, and the evaluation was "poor". When no crack was observed, the high temperature cracking resistance was excellent and the evaluation was "good".

Tensile test pieces (parallel portion diameter) obtained by collecting deposited metal from the obtained deposited metal in accordance with the regulations of JIS Z3111

) And a charpy impact test piece (V-notch) of the deposited metal, and a tensile test and an impact test were performed.

The tensile test was performed on 3 test pieces each at room temperature, and the average value of the obtained values (0.2% proof stress and tensile strength) was used as the tensile characteristic of the deposited metal using the interstitial alloy. In addition, charpy impact test was performed on 3 test pieces each, and the test temperature: absorption energy vE at-196 deg.C _-196 The average value is used as the ultralow temperature impact toughness of the deposited metal using the interstitial alloy.

The results obtained are shown in table 2.

[ Table 1]

[ Table 2]

* ) Cannot measure

* Star) according to JIS Z3111

Underlined indicates that

Examples of the present invention are: the rolling load during wire drawing is not high, cracks are not generated, and the interstitial alloy has excellent manufacturability. Further, no weld cracking (hot cracking) occurs during welding, and the high-temperature cracking resistance is also excellent. Further, a welding material (filler alloy) for TIG welding that can obtain a deposited metal having the following characteristics: a yield strength (0.2% proof stress) at room temperature of 400MPa or more, a tensile strength at room temperature of 660MPa or more, and a test temperature: absorption energy vE of Charpy impact test at-196 DEG C _-196 High strength of 28J or more and excellent cryogenic temperature toughness.

On the other hand, in comparative examples outside the scope of the present invention, the productivity of the caulking alloy is lowered, or weld cracking (hot cracking) occurs to lower the hot cracking resistance, or the 0.2% proof stress at normal temperature is less than 400MPa, or the tensile strength at normal temperature is less than 660MPa, or the test temperature: absorption energy vE of Charpy impact test at-196 DEG C _-196 Less than 28J, a deposited metal having both high strength and excellent cryogenic impact toughness cannot be obtained.

Further, since the B content of interstitial alloy nos. 15 and 16 (comparative examples) is out of the range of the present invention, the Cr content of interstitial alloy No.17 (comparative example) is out of the range of the present invention, and the N content of interstitial alloy No.18 (comparative example) is out of the range of the present invention, the wire drawability is lowered, and wire drawing to a desired diameter is impossible.

In addition, the P content of interstitial alloy No.19 (comparative example), the C content of interstitial alloy No.20 (comparative example), the Mn content of interstitial alloy No.21 (comparative example), and the Si content of interstitial alloy No.22 (comparative example) were out of the ranges of the present invention, respectively, and therefore weld cracks were generated and the high temperature cracking resistance was lowered.

In addition, the S content of interstitial alloy No.23 (comparative example) is out of the range of the present invention, and therefore the very low temperature impact toughness is lowered.

Further, since the Ni content of interstitial alloy No.24 (comparative example) and the Mo content of interstitial alloy No.25 (comparative example) are respectively lower than the ranges of the present invention, the austenite grain boundary is weak and the very low temperature impact toughness is lowered.

Further, since the C content of interstitial alloy No.26 (comparative example) and the Cr content of interstitial alloy No.27 (comparative example) are respectively lower than the ranges of the present invention, the strength is lowered, and the desired high strength cannot be secured.

Claims

1. A TIG welding method using a caulking alloy for TIG welding having a composition comprising: contains, in mass%, C:0.2 to 0.8%, si:0.15 to 0.9%, mn:17.0 to 28.0%, P:0.03% or less, S:0.03% or less, ni:0.01 to 10.0%, cr:0.4 to 4.0%, mo:0.01 to 3.5%, B: less than 0.0010%, N: 0.003-0.12% and V:0.001 to 0.04%, and the balance of Fe and unavoidable impurities.

2. A TIG welding method according to claim 1, wherein the composition further contains, in mass%, a component selected from the group consisting of Ti:0.04% or less and Nb:0.04% or less of 1 or 2.

3. TIG welding method according to claim 1 or 2, wherein the composition further contains, in mass%, a metal selected from Cu:1.0% or less, al:0.1% or less, ca:0.01% or less and REM:0.02% or less of 1 or 2 or more.