WO2020203336A1

WO2020203336A1 - Solid wire for gas metal arc welding and gas metal arc welding method

Info

Publication number: WO2020203336A1
Application number: PCT/JP2020/012216
Authority: WO
Inventors: 大地泉; 充志 ▲高▼田; 直樹 ▲高▼山; 植田　圭治; 山下　賢; 鵬韓
Original assignee: Ｊｆｅスチール株式会社; 株式会社神戸製鋼所
Priority date: 2019-03-29
Filing date: 2020-03-19
Publication date: 2020-10-08
Also published as: KR20210138102A; TWI744838B; TW202043504A; KR102639546B1; JPWO2020203336A1; JP6978614B2; CN113613827A

Abstract

The present invention provides a solid wire for gas metal arc welding that is suitable as a welding material for a high-Mn steel material, and a gas metal arc welding method using this solid wire. The solid wire has a composition that contains, by mass%, 0.20-0.80% C, 0.15-0.90% Si, 17.0-28.0% Mn, 0.030% or less P, 0.030% or less S, 0.01-10.0% Ni, 0.4-1.9% Cr, 0.0010-0.0050% B, with the remainder being Fe and unavoidable impurities, and in which the SFE, which is defined as SFE (mJm²) = −53 + 6.2Ni + 0.7Cr + 3.2Mn + 9.3Mo), satisfies the range of 17-57 (mJ/m²). This solid wire has superior manufacturability, has superior high-temperature cracking resistance with no generation of cracks during welding and, when used in gas metal arc welding, enables a weld joint portion that has high strength and ductility and superior ultra-low-temperature impact toughness to be easily produced.

Description

Solid wire for gas metal arc welding and gas metal arc welding method

The present invention relates to a solid wire for gas metal arc welding and a gas metal arc welding method, and more particularly to a solid wire for welding high Mn-containing steel materials used in an extremely low temperature environment and a gas metal arc welding method using the same.

In recent years, environmental regulations have become stricter. Since liquefied natural gas (hereinafter, also referred to as LNG) does not contain sulfur, it is said to be a clean fuel that does not generate air pollutants such as sulfide oxides, and its demand is increasing. For transporting or storing LNG, the container (tank) for transporting or storing LNG is required to maintain excellent cryogenic impact toughness at a temperature of -162 ° C or lower, which is the liquefaction temperature of LNG. ..

Since it is necessary to maintain excellent ultra-low temperature impact toughness, aluminum alloys, 9% Ni steel, austenitic stainless steel, etc. have been conventionally used as materials for containers (tanks) and the like.

However, since aluminum alloy has low tensile strength, it is necessary to design a large plate thickness of the structure, and there is a problem that weldability is poor. Further, 9% Ni steel is economically disadvantageous because it is necessary to use an expensive Ni-based material as a welding material. Further, austenitic stainless steel has a problem that it is expensive and the strength of the base material is low.

Due to these problems, as a material for containers (tanks) that transport or store LNG, recently, high Mn-containing steel containing about 10 to 35% of Mn in mass% (hereinafter, also referred to as high Mn steel). Is being considered for application. The high Mn steel is in the austenitic phase even at extremely low temperatures, does not undergo brittle fracture, and has a higher strength than the austenitic stainless steel. Therefore, there has been a demand for the development of a welding material capable of stably welding such a high Mn-containing steel material.

In response to such a request, for example, Patent Document 1 proposes "solid wire for submerged arc welding and gas metal arc welding". The solid wire described in Patent Document 1 is C: 0.15 to 0.8%, Si: 0.5 to 1.5%, Mn: 15 to 32%, Cr: 5.5% or less, Mo: 1.5 to 3%, S in% by weight. : 0.025% or less, P: 0.025% or less, B: 0.01% or less, Ti: 0.05 to 1.2%, N: 0.005 to 0.5%, and the balance is a solid wire having a composition of Fe and unavoidable impurities. .. By welding using the solid wire described in Patent Document 1, it is said that a welded joint portion having an excellent impact toughness with a Charpy impact test absorption energy of 32 J or more at a test temperature of -196 ° C can be secured.

Further, Patent Document 2 proposes "a high-strength welded joint portion having excellent ultra-low temperature impact toughness and a flux cored arc welding wire for this purpose". The flux cored arc welding wire described in Patent Document 2 has a weight% of C: 0.15 to 0.8%, Si: 0.2 to 1.2%, Mn: 15 to 34%, Cr: 6% or less, Mo: 1.5. ~ 4%, S: 0.02% or less, P: 0.02% or less, B: 0.01% or less, Ti: 0.09 to 0.5%, N: 0.001 to 0.3%, TiO ₂ : 4 to 15%, SiO ₂ , ZrO ₂ and Total of one or more selected from Al ₂ O ₃ : 0.01-9%, total of one or more selected from K, Na and Li: 0.5-1.7%, one of F and Ca Above: A wire having a composition containing 0.2 to 1.5%, the balance Fe and other unavoidable impurities. When welded using the flux cored arc welding wire described in Patent Document 2, excellent low-temperature toughness with a Charpy impact test absorption energy of 28 J or more at -196 ° C and high strength with a room temperature tensile strength of 400 MPa or more can be obtained. It is said that the welded joint part to have is effectively obtained, and the wire composition is adjusted to Mo: 1.5% or more, so that the welded joint part having excellent high temperature crack resistance can be secured.

Korean Registered Patent No. 10-1560899 Special Table 2017-502842

However, in the technique described in Patent Document 1, for a welded portion welded at a welding heat input amount of 0.9 kJ / mm, a Charpy impact test at a test temperature of -196 ° C. An extremely low temperature impact that satisfies an absorbed energy of 32 J or more. It has only been confirmed to have toughness. According to the study by the present inventors, in the technique described in Patent Document 1, brittle fracture occurs in the welded portion in an extremely low temperature environment when welding is performed under various welding conditions as in the case of actual welding. I found that there was a risk. This is because, in the technique described in Patent Document 1, when welding is performed under various welding conditions as in the case of actual welding, the solute element is diluted by the coarsened dendrite arm of the welded portion, and the stability of austenite is improved. In such a case, there is a concern that brittle fracture may occur in the welded joint portion in an extremely low temperature environment.

Further, in the technique described in Patent Document 2, since it is a flux cored wire, there is a problem that the amount of fume generated during welding increases and the welder is exposed to an environment with a large amount of fume. According to the study by the present inventors, this problem can be avoided by using a solid wire instead of the flux cored wire and increasing the manufacturability of the solid wire by using a composition in which the content of carbide-forming elements and B is reduced. I found out that I can do it.

The present invention solves the above-mentioned problems of the prior art and has both high strength and high ductility suitable as a welding material for high Mn-containing steel materials used in an extremely low temperature environment and excellent extremely low temperature impact toughness. It is an object of the present invention to provide a solid wire for gas metal arc welding capable of producing a welded joint portion and a gas metal arc welding method using the solid wire.

The term "high strength and high ductility" as used herein means that the normal temperature yield strength (0.2% proof stress) of the weld metal (welded metal) manufactured in accordance with the provisions of JIS Z 3111 by gas metal arc welding is 400 MPa or more. It is assumed that the tensile strength is 660 MPa or more and the total elongation is 40% or more. "Excellent ultra-low temperature impact toughness" means the Charpy impact test absorption energy of a weld metal (welded metal) manufactured in accordance with JIS Z 3111 by gas metal arc welding at a test temperature of -196 ° C. It is assumed that vE _-196 is 28J or more and the brittle fracture surface ratio is 10% or less.

In order to achieve the above object, the present inventors have diligently studied the influence of the composition of the solid wire on the cryogenic impact toughness of the weld metal. As a result, it was found that in order to enhance the ultra-low temperature impact toughness of the weld metal and prevent the occurrence of brittle fracture, it is first necessary to sufficiently increase the stability of austenite. Then, in relation to the amount of alloying elements contained, the present inventors have the following equation (1) SFE (mJ / m ² ) = −53 ＋ 6.2Ni ＋ 0.7Cr ＋ 3.2Mn ＋ 9.3Mo …… (1)
(Here, Ni, Cr, Mn, Mo: content of each element (mass%))
It was found that the SFE value defined in is effective as an index of the stability of austenite.
Then, the present inventors, if the above-mentioned SFE is a solid wire having a composition satisfying the range of 17 to 57 (mJ / m ² ), the austenite formed at the time of welding is stabilized, and it is specified in JIS Z 3111. It has been found that the weld metal produced under predetermined welding conditions in accordance with the above is a weld metal having both desired high strength and high ductility and desired excellent ultra-low temperature impact toughness.

Further, the composition of the solid wire is adjusted so that C is 0.20 to 0.80%, Si is 0.15 to 0.90%, Mn is 15.0 to 28.0%, Ni is 0.01 to 10.0%, and Cr is 0.4 to 1.9. By adjusting% and B to a specific range of 0.0010 to 0.0050% and adjusting each of the carbide-forming elements V, Ti, and Nb to a specific range of 0.5% or less, defects such as cracks during wire drawing can occur. It was found that the solid wire has excellent manufacturability.

In addition, the present inventors have decided that dendrites formed during welding solidification grow while discharging solute elements, so that microscopic regions where solute elements are diluted are formed, and therefore the stability of austenite is lowered. I came up with the idea of adjusting the cooling rate during welding. As a result, it is possible to prevent the dendrite arm from becoming coarse, reduce the discharge amount of the solute element, narrow the micro region where the solute element becomes diluted, and stabilize austenite even in the micro region. As a result, it was found that the ultra-low temperature impact toughness of the weld metal can be further improved and the occurrence of brittle fracture of the welded joint can be prevented.

The present invention has been completed by further studying based on the above findings. That is, the gist of the present invention is as follows.

(1) By mass%
C: 0.20 to 0.80%,
Si: 0.15 to 0.90%,
Mn: 15.0-28.0%,
P: 0.030% or less,
S: 0.030% or less,
Ni: 0.01-10.0%,
Cr: 0.4-1.9%,
B: 0.0010-0.0050%
Containing the balance Fe and unavoidable impurities, and the following equation (1) SFE (mJ / m ² ) =-53 + 6.2Ni + 0.7Cr + 3.2Mn + 9.3Mo …… (1)
(Here, Ni, Cr, Mn, Mo: content of each element (mass%))
A solid wire for gas metal arc welding, characterized in that the SFE defined in is having a composition satisfying 17 to 57 (mJ / m ² ).

(2) In the above (1), the composition is a total of one or more selected from V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less in mass%. A solid wire for gas metal arc welding characterized by a content of 1.0% or less.

(3) In the above (1) or (2), the composition is further selected from Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.01% or less, and REM: 0.02% or less in mass%. A solid wire for gas metal arc welding, which comprises one or more of the above.

(4) The solid wire for gas metal arc welding according to any one of (1) to (3) above, wherein the composition further contains Mo: 3.5% or less in mass%.

(5) A gas metal arc welding method in which a steel material containing high Mn is joined by forming a weld metal by gas metal arc welding using a solid wire.
The solid wire is by mass%
C: 0.20 to 0.80%,
Si: 0.15 to 0.90%,
Mn: 15.0-28.0%,
P: 0.030% or less,
S: 0.030% or less,
Ni: 0.01-10.0%,
Cr: 0.4-1.9%,
B: 0.0010-0.0050%
Containing the balance Fe and unavoidable impurities, and the following equation (1) SFE (mJ / m ² ) =-53 + 6.2Ni + 0.7Cr + 3.2Mn + 9.3Mo …… (1)
(Here, Ni, Cr, Mn, Mo: content of each element (mass%))
SFE defined in has a composition satisfying 17 to 57 (mJ / m ² ).
The gas metal arc welding is characterized by adjusting the cooling rate CR (° C / s) in the temperature range of 1300 to 1200 ° C so as to satisfy [SFE + (cooling rate CR) ^1/2 ]: 20 to 70. Gas metal arc welding method.

(6) In the above (5), in addition to the composition, the solid wire is further selected from V: 0.5% or less, Ti: 0.5% or less, Nb: 0.5% or less in mass%. Alternatively, a gas metal arc welding method characterized in that two or more types are contained in a total of 1.0% or less.

(7) In the above (5) or (6), in addition to the composition, the solid wire further has Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.01% or less and REM: 0.02 in mass%. % A gas metal arc welding method characterized by containing one or more selected from less than or equal to.

(8) The gas metal arc welding method according to any one of (5) to (7) above, wherein the solid wire further contains Mo: 3.5% or less in mass% in addition to the composition.

According to the present invention, a solid wire for gas metal arc welding and a solid wire for gas metal arc welding, which is excellent in wire manufacturability and can easily manufacture a welded joint portion having high strength and excellent ultra-low temperature toughness as a welding material for steel materials containing high Mn. It is possible to provide a gas metal arc welding method using it, which is extremely effective in industry.

The solid wire of the present invention is a solid wire suitable for gas metal arc welding of high Mn-containing steel materials. In the solid wire of the present invention, a weld metal (welded metal) produced in accordance with JIS Z3111 by gas metal arc welding is 400 MPa or more at 0.2% toughness at room temperature, 660 MPa or more in tensile strength, and 40% or more in total elongation. High strength and high ductility, and excellent ultra-low temperature toughness with test temperature: -196 ° C, Charpy impact test absorption energy of 28J or more, brittle fracture surface ratio of 10% or less. It is a welding material capable of producing a welded joint portion having high strength and high ductility and excellent ultra-low temperature toughness.

The solid wire of the present invention has a basic composition of C: 0.20 to 0.80%, Si: 0.15 to 0.90%, Mn: 15.0 to 28.0%, P: 0.030% or less, S: 0.030% or less, Ni: 0.01. It contains ~ 10.0%, Cr: 0.4 ~ 1.9%, B: 0.0010 ~ 0.0050%, consists of the balance Fe and unavoidable impurities, and has the following equation (1) SFE (mJ / m ² ) =-53 + 6.2Ni + 0.7Cr + 3 .2Mn + 9.3Mo …… (1)
(Here, Ni, Cr, Mn, Mo: content of each element (mass%))
It has a composition in which the SFE defined in is satisfied with 17 to 57 (mJ / m ² ).

First, the reason for limiting the composition will be explained. Hereinafter, "mass%" in the composition is simply described as "%".

C: 0.20 to 0.80%
C is an element that has the effect of increasing the strength of the weld metal by strengthening the solid solution. C also stabilizes the austenite phase and improves the cryogenic impact toughness of the weld metal. In order to obtain such an effect, a content of 0.20% or more is required. However, if it is contained in excess of 0.80%, carbides are precipitated, the cryogenic impact toughness is lowered, and high temperature cracking is likely to occur during welding. Therefore, C was limited to the range of 0.20 to 0.80%. Preferably, it is 0.30 to 0.70%.

Si: 0.15 to 0.90%
Si acts as an antacid, has the effect of increasing the yield of Mn, increasing the viscosity of the molten metal, stably maintaining the bead shape, and reducing the occurrence of spatter. In order to obtain such an effect, Si needs to have a content of 0.15% or more. However, if Si is contained in excess of 0.90%, the cryogenic impact toughness of the weld metal is reduced. In addition, segregation occurs during solidification to form a liquid phase at the interface of the solidified cell, which reduces high temperature crack resistance. Therefore, Si was limited to the range of 0.15 to 0.90%. It is preferably 0.20 to 0.70%.

Mn: 15.0-28.0%
Mn is an element that stabilizes the austenite phase at low cost, and the content of Mn is required to be 15.0% or more in the present invention. When Mn is less than 15.0%, ε-martensite is formed in the Mn-lean part in the weld metal (welded metal), and the toughness at extremely low temperatures is significantly reduced. On the other hand, even if Mn is contained in excess of 28.0%, not only the effect of improving cryogenic impact toughness is saturated, but also excessive Mn segregation occurs during solidification, which induces high temperature cracking. Therefore, Mn was limited to the range of 15.0 to 28.0%. It is preferably 18.0 to 25.0%.

P: 0.030% or less P is an element that segregates at grain boundaries, induces high-temperature cracking, and lowers the cryogenic impact toughness of the weld metal. In the present invention, it is preferable to reduce it as an impurity element as much as possible. , 0.030% or less is acceptable. Therefore, P was limited to 0.030% or less. It is preferably 0.02% or less. On the other hand, excessive P reduction causes a rise in refining cost. Therefore, P is preferably adjusted to 0.003% or more.

S: 0.030% or less S exists as a sulfide-based inclusion MnS in the weld metal (welded metal). Since MnS is the starting point of fracture, it reduces cryogenic toughness. Therefore, S was limited to 0.030% or less. It is preferably 0.02% or less. On the other hand, excessive S reduction causes a rise in refining cost. Therefore, it is preferable to adjust S to 0.001% or more.

Ni: 0.01-10.0%
Ni is an element that strengthens austenite grain boundaries and segregates at grain boundaries to improve cryogenic impact toughness. In addition, Ni improves the mobility of dislocations. In order to obtain such an effect, Ni needs to be contained in an amount of 0.01% or more. In addition, Ni also has the effect of stabilizing the austenite phase, so if the content is further increased, the austenite phase is stabilized and the ultra-low temperature impact toughness of the weld metal (welded metal) is improved. However, Ni is an expensive element, and a content of more than 10.0% is economically disadvantageous. Therefore, Ni was limited to 0.01 to 10.0%. It is preferably 1.0 to 8.0%, more preferably 2.0 to 7.0%.

Cr: 0.4-1.9%
Cr has the effect of stabilizing the austenite phase at extremely low temperatures, improving the grain boundary strength, and improving the cryogenic impact toughness of the weld metal. Cr also has the effect of improving the strength of the weld metal. In addition, Cr works effectively to increase the liquidus line of the molten metal and suppress the occurrence of high temperature cracking. Furthermore, Cr also works effectively to enhance the corrosion resistance of the weld metal. In order to obtain such an effect, Cr must be contained in an amount of 0.4% or more. If Cr is less than 0.4%, the above effect cannot be ensured. On the other hand, if it is contained in excess of 1.9%, Cr carbides are formed at the austenite grain boundaries when the cooling rate is slow, resulting in a decrease in cryogenic impact toughness. Further, due to the formation of Cr carbide, the workability at the time of wire drawing is lowered. Therefore, Cr was limited to the range of 0.4 to 1.9%. It is preferably 0.5 to 1.8%.

B: 0.0010% -0.0050%
B has the effect of improving the grain boundary strength and improving the cryogenic impact toughness of the weld metal by segregating at the austenite grain boundaries. Further, as the grain boundary strength is improved, it also has an effect of preventing breakage during wire drawing. In order to obtain such an effect, B needs to have a content of 0.0010% or more. If B is less than 0.0010%, the above effect cannot be ensured. On the other hand, if it is contained in excess of 0.0050%, it binds to N mixed as an unavoidable impurity to form boron nitride at the austenite grain boundary, which lowers the grain boundary strength. Due to this decrease in grain boundary strength, the austenite grain boundary becomes the starting point of fracture occurrence during wire drawing, causing disconnection, reducing wire drawing workability, and reducing wire manufacturability. Therefore, B was limited to the range of 0.0010 to 0.0050%. Preferably, it is 0.0011 to 0.0030%.

In the solid wire of the present invention, the above-mentioned components are the basic components.
In order to improve the cryogenic impact toughness of the weld metal (welded metal), it is necessary to increase the stability of austenite and suppress the occurrence of brittle fracture of the weld metal. Therefore, in the solid wire of the present invention, the following equation (1) SFE (mJ / m ² ) = −53 ＋ 6.2Ni ＋ 0.7Cr ＋ 3.2Mn ＋ 9.3Mo …… (1)
(Here, Ni, Cr, Mn, Mo: content of each element (mass%))
The content of each component is adjusted within the content range of each component described above so that the SFE (Stacking Fault Energy) defined in the above satisfies 17 to 57 (mJ / m ² ). SFE is a value adopted as an index of macroscopic austenite stability in the present invention, and is defined by Eq. (1) from each content of Ni, Cr, Mn, and Mo. If the SFE is less than 17 (mJ / m ² ), the stability of austenite is low and the desired cryogenic impact toughness cannot be satisfied. On the other hand, if SFE exceeds 57 (mJ / m ² ), the work hardening ability at the time of the tensile test is lowered, and the desired tensile strength cannot be satisfied. Therefore, the SFE defined by Eq. (1) is limited to the range of 17 to 57 (mJ / m ² ). It is preferably 20 to 55 (mJ / m ² ). If the element described in the formula (1) is not contained, the content of the element is assumed to be zero and the value SFE of the formula (1) is calculated.

In the solid wire of the present invention, in addition to the above-mentioned basic components, if necessary, one selected from V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less as optional components. Or two or more types in total 1.0% or less, and / or one or two or more types selected from Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.01% or less and REM: 0.02% or less. , And / or Mo: 3.5% or less can be selected and contained.

V: 0.5% or less, Ti: 0.5% or less and Nb: 0.5% or less and one or more selected from 1.0% or less in total V, Ti and Nb form carbides and are welded. It is an element that contributes to the improvement of the strength of the metal, and can be selected as necessary and contains 1 type or 2 or more types in a total of 1.0% or less.

V: 0.5% or less V is a carbide-forming element, which precipitates fine carbides and contributes to the improvement of the strength of the weld metal. In order to obtain such an effect, it is preferably contained in an amount of 0.001% or more. On the other hand, if the content exceeds 0.5%, the carbide becomes coarse and becomes a cracking starting point during wire drawing of the solid wire, the wire drawing workability is lowered, and the wire manufacturability is lowered. Therefore, when it is contained, it is preferable to limit V to 0.5% or less.

Ti: 0.5% or less Ti is a carbide-forming element, which precipitates fine carbides and contributes to the improvement of the strength of the weld metal. In addition, Ti deposits carbides at the interface of the solidified cell of the weld metal and contributes to suppressing the occurrence of high temperature cracks. In order to obtain such an effect, it is preferably contained in an amount of 0.001% or more. However, if it is contained in excess of Ti: 0.5%, the carbide becomes coarse and becomes a starting point of cracking during wire drawing of the solid wire, which lowers the wire drawing workability and lowers the wire manufacturability. Further, when Ti is contained in an amount of more than 0.5%, carbides are coarsened, fineness of crystal grains is suppressed, and cryogenic impact toughness is lowered. Therefore, when it is contained, Ti is preferably limited to 0.5% or less.

Nb: 0.5% or less Nb is a carbide-forming element, which is an element that precipitates carbides and contributes to the improvement of the strength of the weld metal. In addition, Nb precipitates carbides at the interface of the solidified cell of the weld metal and contributes to suppressing the occurrence of high-temperature cracks. In order to obtain such an effect, it is preferably contained in an amount of 0.001% or more. However, if Nb is contained in an amount of more than 0.5%, the carbide becomes coarse and becomes a cracking starting point at the time of wire drawing of the solid wire, the wire drawing workability is lowered, and the wire manufacturability is lowered. Further, when Nb is contained in an amount of more than 0.5%, carbides are coarsened, fineness of crystal grains is suppressed, and cryogenic impact toughness is also lowered. Therefore, when it is contained, it is preferable to limit Nb to 0.5% or less.

If V, Ti, and Nb are contained in a large amount exceeding 1.0% in total, the wire manufacturability and cryogenic impact toughness will decrease. Therefore, when contained, it is preferable to limit V, Ti, and Nb to 1.0% or less in total.

One or more selected from Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.01% or less and REM: 0.02% or less Cu is an element that contributes to austenite stabilization, and Al is welded. It is an element that improves workability, and Ca and REM are elements that contribute to the improvement of workability, and can be selected and contained in one or more types 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 cryogenic impact toughness of the weld metal (welded metal). In order to obtain such an effect, it is preferably contained in an amount of 0.01% or more. However, if it is contained in a large amount exceeding 1.0%, the hot ductility is lowered and the manufacturability of the wire is lowered. Therefore, when it is contained, it is preferable to limit Cu to 1.0% or less.

Al: 0.10% or less Al acts as an antacid, increases the viscosity of the molten metal, stably maintains the bead shape, and has an important effect of reducing the occurrence of spatter. In addition, Al raises the liquidus temperature of the molten metal and contributes to suppressing the occurrence of high-temperature cracking of the weld metal. Since such an effect becomes remarkable when the content is 0.005% or more, it is preferable to contain 0.005% or more. However, if it is contained in excess of 0.10%, the viscosity of the molten metal becomes too high, and conversely, defects such as increased spatter and bead do not spread and fusion failure increase. Therefore, when it is contained, it is preferable to limit Al to 0.10% or less. More preferably, it is 0.005 to 0.04%.

Ca: 0.01% or less Ca combines with S in the molten metal to form a high melting point sulfide CaS. Since CaS has a higher melting point than MnS, it maintains a spherical shape without advancing in the rolling direction during hot working of solid wire, which is advantageous for improving workability of solid wire. Such an effect becomes remarkable when the content is 0.001% or more. On the other hand, if the content exceeds 0.01%, the arc is disturbed during welding, which makes stable welding difficult. Therefore, when it is contained, it is preferable to limit Ca to 0.01% or less.

REM: 0.02% or less REM is a strong deoxidizer and exists in the form of REM oxide in weld metals (welded metals). The REM oxide acts as a nucleation site during solidification, thereby refining the crystal grains and contributing to the improvement of the strength of the weld metal (welded metal). Such an effect becomes remarkable when the content is 0.001% or more. However, if it is contained in excess of 0.02%, the stability of the arc will decrease. Therefore, when it is contained, it is preferable to limit the REM to 0.02% or less.

Mo: 3.5% or less Mo is an element that improves the strength by strengthening the solid solution, and it is desirable to contain 0.5% or more in order to obtain such an effect. On the other hand, if it is contained in excess of 3.5%, carbides are precipitated, the hot workability is lowered, and the manufacturability of the wire such as wire drawing is lowered. Therefore, when it is contained, it is preferable to limit Mo to 3.5% or less.

The rest other than the above components consist of Fe and unavoidable impurities.

Next, a method for manufacturing the solid wire of the present invention will be described.
The production of the solid wire of the present invention does not need to be particularly limited in the production method except that the molten steel having the above composition is used, and any of the conventional solid wire production methods for welding can be applied. For example, a casting step of melting molten steel having the above composition in a regular melting furnace such as an electric furnace or a vacuum melting furnace and casting it into a mold having a predetermined shape to obtain a steel ingot, and a obtained steel ingot. A heating step of heating the steel to a predetermined temperature and a hot rolling step of hot rolling the heated steel ingot to obtain a steel material (rod shape) having a predetermined shape are sequentially performed, and then the obtained steel material is obtained. By cold-rolling (rod-shaped) multiple times (cold wire drawing) and, if necessary, annealing to a quenching temperature of 1000 to 1200 ° C., a cold rolling process is performed to obtain a wire of the desired size. , The solid wire of the present invention can be manufactured.

Next, a gas metal arc welding method using the solid wire of the present invention having the above composition will be described.
In the welding method, a steel material containing high Mn is joined by forming a weld metal by gas metal arc welding using the solid wire of the present invention having the above composition as a welding material. Gas metal arc welding is also called "gas shielded arc welding", and is generally called "melting electrode type (consumable electrode type)" that uses a welding material (additive material) as an electrode and "non-consumable electrode type" that uses a non-consumable electrode such as tungsten. It can be roughly divided into "consumable electrode type". The solid wire of the present invention is preferably used for electrodeposition type gas metal arc welding from the viewpoint of achieving high strength and high ductility and excellent cryogenic impact toughness.
Welding conditions such as welding posture, preheating, welding heat input (current, voltage, welding speed), shield gas, etc. can be applied to any of the usual welding conditions.

The high Mn-containing steel material that is gas metal arc welded using the solid wire of the present invention contains Mn as an alloying element in a high content. The lower limit of the Mn content is not particularly limited, but is, for example, 10% by mass or more, preferably 15% by mass or more, and more preferably 20% by mass or more. The upper limit of the Mn content is not particularly limited, but is, for example, 35% by mass or less, preferably 30% by mass or less, and more preferably 27% by mass or less. When the Mn content of the high Mn-containing steel material is within the above range, gas metal arc welding using the solid wire of the present invention as a welding material is excellent in high temperature crack resistance and weld bead appearance, and desired high strength and high strength. Welded metal (welded metal) and welded joints that have both ductility and excellent ultra-low temperature impact toughness can be stably obtained.
In the high Mn-containing steel material, the composition of alloying elements other than Mn, the size and shape of the steel material, and the like are not particularly limited, and those suitable for the desired application can be adopted, but the desired high strength and high ductility and From the viewpoint of achieving excellent ultra-low temperature impact toughness, when the high Mn-containing steel material is a steel plate, the plate thickness is preferably 6 mm or more, more preferably 10 mm or more, preferably 40 mm or less, and more preferably 30 mm or less.

The gas metal arc welding method using the solid wire of the present invention is not particularly limited, but is preferably used, for example, for manufacturing a product provided with a weld metal that requires high strength and high ductility and excellent ultra-low temperature impact toughness. It can be used for manufacturing containers for transporting or storing LNG from steel materials containing high Mn.

In the gas metal arc welding method using the solid wire of the present invention, the cooling rate CR (° C / s) in the temperature range of 1300 to 1200 ° C. in the weld bead (welded portion) is [SFE + (cooling rate CR) in the cooling during welding. ) ^1/2 ]: Adjust the welding heat input so as to satisfy 20 to 70. As a result, austenite is stabilized and the occurrence of brittle fracture in the weld metal (welded metal) can be suppressed, resulting in a weld metal (welded metal) having high strength and high ductility and excellent ultra-low temperature impact toughness. be able to.
The lower limit of [SFE + CR ^1/2 ] is 20, and is not particularly limited, but is preferably 25 or more, and more preferably 30 or more. At CR (° C / s) where [SFE + (cooling rate CR) ^1/2 ] is less than 20, cooling is slow and coarsening of the dendrite arm cannot be prevented. Therefore, in the dendrite arm part, solute elements during solidification The discharge amount increases, the region where the solute element is diluted expands, and microscopic austenite stability cannot be ensured.
The upper limit of [SFE + CR ^1/2 ] is 70, and is not particularly limited, but is preferably 65 or less, and more preferably 60 or less. At CR (° C / s) where [SFE + (cooling rate CR) ^1/2 ] exceeds 70, the work hardening ability during the tensile test decreases, and the desired tensile strength cannot be satisfied. The "SFE" referred to here is defined by the above equation (1) as an index of the stability of macroscopic austenite.

In welding, generally, every time one pass is welded, the formed weld bead (welded portion) is cooled to a predetermined temperature and solidified, and then subsequent operations such as welding of the next pass and optional post-heat treatment are performed. I do. When welding multiple passes and undergoing multiple cooling processes in the temperature range of 1300 to 1200 ° C, [SFE + (cooling rate CR) ^1/2 ]: 20 to 70 should be satisfied in all the cooling processes. , Adjust the welding heat input in each pass.
In the welding method of the present invention, the formed weld bead (welded portion) is cooled by allowing it to stand in the air and allowed to cool. Therefore, by adjusting the amount of heat input to the weld in each pass, the temperature is 1300 to 1200 ° C. The cooling rate CR (° C / s) in the range can be controlled. Specifically, the welding heat input amount so as to have a cooling rate applicable to the above formula may be obtained in advance from a preliminary experiment or Inagaki's formula, and welding may be performed with that heat input amount.

Hereinafter, the present invention will be further described based on Examples.

The molten steel having the composition shown in Table 1 was melted and cast in a vacuum melting furnace to obtain 100 kg of steel ingot. The obtained ingot was heated to 1200 ° C., then hot-rolled, and then cold-rolled to obtain a 1.2 mmφ solid wire for gas metal arc welding. When manufacturing the wire, the rolling load (drawing load) was measured and cracks were observed to evaluate the manufacturability of each solid wire. If it is determined that rolling (drawing) processing is impossible due to a high rolling load (drawing load), cracks are found, or the cracks that have occurred cause further steps to proceed. When it became impossible to do so, it was evaluated as "defective". Other than that, it was evaluated as "good".

Next, as a test plate, a high-Mn steel plate for ultra-low temperature (plate thickness: 6 to 40 mm) was prepared, and butt-welded to form a 45 ° V-shaped groove in accordance with JIS Z 3111, and the composition shown in Table 1 was formed. A welded metal was obtained in the groove by performing welded gas metal arc welding using a solid wire manufactured from the molten steel of No. 1 as a welding material. The steel sheet used as the test plate was a high Mn steel sheet for cryogenic temperature having a composition of 0.5% C-0.4% Si-25% Mn-3% Cr-residue Fe in mass%.
In the welding, each solid wire (1.2 mm in diameter) manufactured from molten steel having the composition shown in Table 1 was used as an electrode, with no preheating, in a downward posture, inter-pass temperature: 100 to 150 ° C., shield gas: 80% Ar + 20. Conducted as% CO ₂ . The temperature history at the time of welding was actually measured using a thermocouple, and the cooling rate in the temperature range of 1300 to 1200 ° C. was calculated.

After welding, the weld metal was observed with an optical microscope to determine the presence or absence of welding cracks. Weld cracks are high-temperature cracks, and when cracks are observed, they are evaluated as "defective" because the high-temperature crack resistance is reduced. When no cracking was observed, it was evaluated as "good" because of its excellent high temperature cracking resistance.

In addition, the appearance of the weld bead was visually observed to determine the appearance of the weld bead. When undercuts, overlaps, and pits were observed, the appearance of the weld bead was evaluated as "defective". When these were not observed, the appearance of the weld bead was evaluated as "good".

From the obtained weld metal, a tensile test piece of weld metal (parallel part diameter 6 mmφ) and a Charpy impact test piece of weld metal (V notch) are collected in accordance with JIS Z 3111, and the tensile test and impact are performed. The test was carried out. For steel sheets with a thickness of less than 10 mm, a 5 mm sub-sized Charpy impact test piece (V notch) was sampled and an impact test was carried out.
The tensile test was carried out at room temperature with three test pieces each, and the average value of the obtained values (0.2% proof stress, tensile strength, total elongation) was calculated as the tensile characteristics of the weld metal using the solid wire. And said. In addition, the Charpy impact test was carried out with three test pieces each, and the absorbed energy vE _-196 at the test temperature: -196 ° C was determined, and the average value was calculated as the ultra-low temperature impact of the weld metal using the solid wire. It was made tough. For the 5 mm sub-sized Charpy impact test piece (V notch), the value obtained by multiplying the obtained absorbed energy by 1.5 times was evaluated as the cryogenic impact toughness. The brittle fracture surface ratio was visually determined.
The results obtained are shown in Table 2.

In each of the examples of the present invention, the wire manufacturability was excellent, welding cracks (high temperature cracks) did not occur during welding, the high temperature crack resistance was excellent, and the appearance of the weld bead was also good. Furthermore, the yield strength (0.2% proof stress) at room temperature is 400 MPa or more, the tensile strength is 660 MPa or more, the total elongation is 40% or more, and it has high strength and high ductility. Furthermore, the absorption of the Charpy impact test at the test temperature: -196 ° C. It was a welding material (solid wire) capable of obtaining a welded metal having excellent ultra-low temperature impact toughness with an energy vE _-196 of 28 J or more and a brittle fracture surface ratio of 10% or less.

On the other hand, in the comparative example outside the scope of the present invention, the wire manufacturability is inferior, the weld crack (high temperature crack) occurs and the high temperature crack resistance is lowered, the weld bead appearance is inferior, or at room temperature. 0.2% toughness less than 400MPa, tensile strength less than 660MPa, total elongation less than 40%, absorbed energy vE _-196 less than 28J, brittle fracture surface ratio more than 10%, , A weld metal having both desired high strength and high ductility and excellent ultra-low temperature impact toughness has not been obtained.

Claims

By mass%
C: 0.20 to 0.80%,
Si: 0.15 to 0.90%,
Mn: 15.0-28.0%,
P: 0.030% or less,
S: 0.030% or less,
Ni: 0.01-10.0%,
Cr: 0.4 to 1.9% and B: 0.0010 to 0.0050%
Containing, remaining Fe and unavoidable impurities, and
A solid wire for gas metal arc welding, wherein the SFE defined by the following equation (1) has a composition satisfying 17 to 57 (mJ / m 2 ).
Note SFE (mJ / m 2 ) =-53 + 6.2Ni + 0.7Cr + 3.2Mn + 9.3Mo …… (1)
Here, Ni, Cr, Mn, Mo: content of each element (mass%)
The composition is further characterized in that, in mass%, one or more selected from V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less are contained in a total of 1.0% or less. The solid wire for gas metal arc welding according to claim 1.
The composition further contains one or more selected from Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.01% or less, and REM: 0.02% or less in mass%. The solid wire for gas metal arc welding according to claim 1 or 2.
The solid wire for gas metal arc welding according to any one of claims 1 to 3, wherein the composition further contains Mo: 3.5% or less in mass%.
A gas metal arc welding method in which high Mn-containing steel materials are joined by forming weld metal by gas metal arc welding using solid wires.
The solid wire is by mass%
C: 0.20 to 0.80%,
Si: 0.15 to 0.90%,
Mn: 15.0-28.0%,
P: 0.030% or less,
S: 0.030% or less,
Ni: 0.01-10.0%,
Cr: 0.4 to 1.9% and B: 0.0010 to 0.0050%
Containing the balance Fe and unavoidable impurities, and the following equation (1) SFE (mJ / m 2 ) =-53 + 6.2Ni + 0.7Cr + 3.2Mn + 9.3Mo …… (1)
(Here, Ni, Cr, Mn, Mo: content of each element (mass%))
SFE defined in has a composition satisfying 17 to 57 (mJ / m 2 ).
The gas metal arc welding is characterized by adjusting the cooling rate CR (° C / s) in the temperature range of 1300 to 1200 ° C so as to satisfy [SFE + (cooling rate CR) 1/2 ]: 20 to 70. Gas metal arc welding method.
In addition to the composition, the solid wire is 1.0% in total of one or more selected from V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less in mass%. The gas metal arc welding method according to claim 5, wherein the gas metal arc welding method contains the following.
In addition to the composition, the solid wire is one or two selected from Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.01% or less, and REM: 0.02% or less in mass%. The gas metal arc welding method according to claim 5 or 6, which comprises the above.
The gas metal arc welding method according to any one of claims 5 to 7, wherein the solid wire further contains Mo: 3.5% or less in mass% in addition to the composition.