KR102639546B1 - Solid wire for gas metal arc welding and gas metal arc welding method - Google Patents

Abstract

The present invention provides a solid wire for gas metal arc welding suitable as a welding material for high-Mn steel and a gas metal arc welding method using the same. The solid wire has, in mass%, C: 0.20 to 0.80%, Si: 0.15 to 0.90%, Mn: 17.0 to 28.0%, P: 0.030% or less, S: 0.030% or less, Ni: 0.01 to 10.0%, Cr. : 0.4 to 1.9%, B: 0.0010 to 0.0050%, the balance consists of Fe and inevitable impurities, and the SFE defined as SFE (mJ/㎡) = -53 + 6.2Ni + 0.7Cr + 3.2Mn + 9.3Mo is 17. It has a composition that satisfies the range of ∼57 (mJ/㎡). The solid wire of the present invention is excellent in wire manufacturability and has excellent high-temperature crack resistance as no weld cracks occur during welding. When used in gas metal arc welding, welding has high strength, high ductility, and excellent cryogenic impact toughness. The joint part can be easily manufactured.

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. In particular, it relates to a solid wire for welding high Mn-containing steel used in a cryogenic environment and a gas metal arc welding method using the same.

Recently, 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 sulfur oxides, and the demand for it is increasing. For transport or storage of LNG, containers (tanks) for transporting or storing LNG are required to maintain excellent cryogenic impact toughness at a temperature of -162°C or lower, which is the liquefaction temperature of LNG.

In view of the need to maintain excellent cryogenic impact toughness, aluminum alloy, 9% Ni steel, austenitic stainless steel, etc. have conventionally been used as materials for containers (tanks).

However, aluminum alloy has a low tensile strength, so it is necessary to design the thickness of the structure to be large, and it also has the problem of poor weldability. Additionally, 9% Ni steel is economically disadvantageous because it requires the use of expensive Ni-based materials as welding materials. Additionally, austenitic stainless steel has the problem of being expensive and having low base material strength.

Due to these problems, as a material for containers (tanks) for transporting or storing LNG, high-Mn content steel (hereinafter also referred to as high-Mn steel) containing about 10 to 35% Mn in mass% has been applied in recent years. This is being reviewed. High-Mn steel is in an austenitic phase even at extremely low temperatures, does not cause brittle fracture, and has the characteristic of having high strength compared to austenitic stainless steel. Therefore, there has been a demand for the development of a welding material that can stably weld such high-Mn-containing steel materials.

In response to this 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 has, in weight percent, 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: 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 remainder is Fe and inevitable impurities. It is said that by welding using the solid wire described in Patent Document 1, a welded joint having 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.

Additionally, Patent Document 2 proposes “a high-strength weld joint with excellent cryogenic impact toughness and a flux-cored arc welding wire for the same.” The flux-cored arc welding wire described in Patent Document 2 has, in weight percent, C: 0.15 to 0.8%, Si: 0.2 to 1.2%, Mn: 15 to 34%, Cr: 6% or less, and Mo: 1.5 to 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 Al ₂ Total of one or more types selected from O ₃ : 0.01 to 9%, total of one or more types selected from K, Na and Li: 0.5 to 1.7%, one or more types selected from F and Ca: 0.2 to 1.5%, balance Fe and its It is a wire whose composition includes other inevitable impurities. When welded using the flux-cored arc welding wire described in Patent Document 2, a welded joint having 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 is produced. It is said that it can be obtained effectively, and by adjusting the wire composition to Mo: 1.5% or more, a welded joint with excellent high-temperature crack resistance can be secured.

Korean Patent No. 10-1560899 Gazette Japanese Patent Publication No. 2017-502842

However, in the technology described in Patent Document 1, for welded parts welded with a welding heat input of 0.9 kJ/mm, the cryogenic impact toughness satisfies the Charpy impact test absorption energy of 32J or more at a test temperature of -196°C. What we have is just being confirmed. According to the examination by the present inventors, in the technology described in Patent Document 1, it was recognized that there is a risk of brittle fracture occurring in the welded portion in a cryogenic environment when welding is performed under various welding conditions such as those used during pilot welding. That is, in the technology described in Patent Document 1, when welding under various welding conditions such as those used during practical welding, the solute elements are rarefied due to the coarsened dendrite arms of the weld zone, and the stability of austenite decreases. In some cases, there is concern that brittle fracture may occur in the welded joint in a cryogenic environment.

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

The present invention solves the problems of the prior art described above and provides gas metal arc welding that can produce a welded joint with both high strength and high ductility and excellent cryogenic impact toughness, suitable as a welding material for high-Mn-containing steels used in a cryogenic environment. The purpose is to provide a solid wire for use and a gas metal arc welding method using the same.

In addition, “high strength and high ductility” referred to here means that the room temperature yield strength (0.2% yield strength) of the welded metal (welded metal) manufactured in accordance with the provisions of JIS Z 3111 by gas metal arc welding is 400 MPa or more, and the tensile strength is This means that the height is 660 MPa or more and the total height is 40% or more. In addition, “excellent cryogenic impact toughness” refers to the Charpy impact test absorption energy vE _-196 at a test temperature of -196°C for welded metal (welded metal) produced by gas metal arc welding in accordance with the provisions of JIS Z 3111. This means that it is 28J or more and the brittle fracture ratio is 10% or less.

In order to achieve the above-described object, the present inventors carefully studied the influence of the composition of the solid wire on the cryogenic impact toughness of the deposited metal. As a result, it was recognized that in order to increase the cryogenic impact toughness of the deposited metal and prevent the occurrence of brittle fracture, it was first necessary to sufficiently increase the stability of austenite. And, in relation to the amount of alloy elements contained, the present inventors used the following equation (1)

SFE(mJ/㎡)=-53+6.2Ni+0.7Cr+3.2Mn+9.3Mo… … (One)

(Here, Ni, Cr, Mn, Mo: content of each element (mass%))

It was recognized that the SFE value defined as is effective as an indicator of the stability of austenite.

In addition, the present inventors have found that, if the SFE is a solid wire with a composition that satisfies the range of 17 to 57 (mJ/m2), the austenite formed during welding is stabilized, and a predetermined welding is performed in accordance with the provisions of JIS Z 3111. It was recognized that the welded metal produced under these conditions had both the desired high strength and high ductility and the desired excellent cryogenic impact toughness.

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

In addition, the present inventors believe that since dendrites formed during weld solidification grow while discharging solute elements, a micro region in which the solute elements become rare is formed, and as a result, the stability of austenite decreases, We discussed adjusting the cooling rate during welding. Accordingly, coarsening of the dendrite arm is prevented, the discharge amount of the solute element is reduced, the micro region where the solute element becomes rare is narrowed, and austenite can be stabilized even in the micro region. Accordingly, it was recognized that the cryogenic impact toughness of the deposited metal could be further improved and the occurrence of brittle fracture of the welded joint could be prevented.

The present invention was completed through further investigation based on the above-described recognition. That is, the gist of the present invention is as follows.

(1) In mass%,

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 to 10.0%,

Cr: 0.4 to 1.9%,

B: 0.0010 to 0.0050%

Contains, the balance consists of Fe and inevitable impurities, and the following formula (1)

SFE(mJ/㎡)=-53+6.2Ni+0.7Cr+3.2Mn+9.3Mo… … (One)

(Here, Ni, Cr, Mn, Mo: content of each element (mass%))

A solid wire for gas metal arc welding, characterized in that it has a composition that satisfies the SFE defined as 17 to 57 (mJ/㎡).

(2) In the above (1), the composition is further, in mass%, a total of one or two or more selected from the group consisting of V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less. Solid wire for gas metal arc welding, characterized in that it contains 1.0% or less.

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

(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 for joining high-Mn-containing steel materials by forming a weld metal by gas metal arc welding using a solid wire,

The solid wire is expressed in mass%,

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 to 10.0%,

Cr: 0.4 to 1.9%,

B: 0.0010 to 0.0050%

Contains, the balance consists of Fe and inevitable impurities, and the following formula (1)

SFE(mJ/㎡)=-53+6.2Ni+0.7Cr+3.2Mn+9.3Mo… … (One)

(Here, Ni, Cr, Mn, Mo: content of each element (mass%))

It has a composition that satisfies the SFE defined as 17 to 57 (mJ/㎡),

The gas metal arc welding is characterized in that the cooling rate CR (°C/s) in the temperature range of 1300 to 1200°C is adjusted to satisfy [SFE+(cooling rate CR) ^1/2 ]: 20 to 70. Metal arc welding method.

(6) The method of (5) above, wherein, in addition to the above composition, the solid wire has, in mass%, one or two selected from the group consisting of V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less. A gas metal arc welding method characterized by containing 1.0% or less in total of more than one species.

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

(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, which is excellent in wire manufacturability and, as a welding material for high-Mn-containing steels, can easily manufacture welded joints with high strength and excellent cryogenic toughness, and the same. It is possible to provide a gas metal arc welding method using gas metal arc welding, which brings remarkable industrial effects.

(Form for carrying out the invention)

The solid wire of the present invention is a solid wire suitable for gas metal arc welding of steel materials containing high Mn. The solid wire of the present invention is a welded metal produced by gas metal arc welding in accordance with JIS Z 3111, and has a 0.2% proof stress at room temperature of 400 MPa or more, a tensile strength of 660 MPa or more, and a total elongation of It has high strength and high ductility of 40% or more, an absorbed energy of 28 J or more in the Charpy impact test at a test temperature of -196°C, and excellent cryogenic toughness with a brittle fracture rate of 10% or less. It has excellent cryogenic toughness due to high strength and high ductility. It is a welding material that can produce welded joints.

The solid wire of the present invention has a basic composition, in mass%, 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, and Ni: 0.01. Contains ∼10.0%, Cr: 0.4∼1.9%, and B: 0.0010∼0.0050%, with the balance consisting of Fe and inevitable impurities, and the following formula (1):

SFE(mJ/㎡)=-53+6.2Ni+0.7Cr+3.2Mn+9.3Mo… … (One)

(Here, Ni, Cr, Mn, Mo: content of each element (mass%))

It has a composition that satisfies the SFE defined as 17 to 57 (mJ/㎡).

First, the reason for the limitation of composition will be explained. In addition, 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 through solid solution strengthening. Additionally, C stabilizes the austenite phase and improves the cryogenic impact toughness of the weld metal. In order to obtain this effect, a content of 0.20% or more is required. However, if the content exceeds 0.80%, carbides precipitate, cryogenic impact toughness decreases, and high-temperature cracking during welding becomes prone to occur. 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 a deoxidizer and 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 sputtering. In order to obtain such an effect, Si must be contained in an amount of 0.15% or more. However, if Si is contained in excess of 0.90%, the cryogenic impact toughness of the weld metal decreases. In addition, it segregates during solidification, creating a liquid phase at the interface of the solidified shell, and reducing high-temperature crack resistance. Therefore, Si was limited to the range of 0.15 to 0.90%. Preferably it is 0.20 to 0.70%.

Mn: 15.0 to 28.0%

Mn is an element that stabilizes the austenite phase at a low cost, and in the present invention, its content is required to be 15.0% or more. If Mn is less than 15.0%, ε-martensite is generated in the Mn-lean portion of the weld metal (deposited metal), and toughness at extremely low temperatures is significantly reduced. On the other hand, even if Mn is contained in excess of 28.0%, not only is the effect of improving cryogenic impact toughness saturated, but excessive Mn segregation occurs during solidification, causing high-temperature cracking. Therefore, Mn was limited to the range of 15.0 to 28.0%. Preferably it is 18.0 to 25.0%.

P: 0.030% or less

P is an element that segregates at grain boundaries, causes high-temperature cracking, and lowers the cryogenic impact toughness of the weld metal. In the present invention, it is desirable to reduce it as much as possible as an impurity element, but it is allowed as long as it is 0.030% or less. can do. Therefore, P was limited to 0.030% or less. Preferably it is 0.02% or less. On the other hand, excessive P reduction causes a sharp increase in refining costs. Therefore, it is desirable to adjust P to 0.003% or more.

S: 0.030% or less

S exists as sulfide-based inclusions MnS in weld metal (deposited metal). Since MnS becomes the origin of fracture, it reduces cryogenic toughness. Therefore, S was limited to 0.030% or less. Preferably it is 0.02% or less. On the other hand, excessive S reduction causes a sharp increase in refining costs. Therefore, it is desirable to adjust S to 0.001% or more.

Ni: 0.01 to 10.0%

Ni is an element that strengthens austenite grain boundaries and segregates at grain boundaries to improve cryogenic impact toughness. Additionally, Ni improves the mobility of dislocations. In order to obtain this effect, Ni must 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 cryogenic impact toughness of the weld metal (deposited metal) is improved. However, Ni is an expensive element, and its content exceeding 10.0% becomes economically disadvantageous. Therefore, Ni was limited to 0.01 to 10.0%. Preferably it is 1.0 to 8.0%, more preferably 2.0 to 7.0%.

Cr: 0.4 to 1.9%

Cr has the effect of stabilizing the austenite phase at extremely low temperatures, improving grain boundary strength, and improving the cryogenic impact toughness of the weld metal. Additionally, Cr also has the effect of improving the strength of the weld metal. Additionally, Cr increases the liquidus line of molten metal and acts effectively to suppress the occurrence of high-temperature cracks. Additionally, Cr also effectively increases the corrosion resistance of the weld metal. In order to obtain this effect, Cr needs to be contained at 0.4% or more. If Cr is less than 0.4%, the above effect cannot be secured. On the other hand, if the content exceeds 1.9%, Cr carbides are generated at the austenite grain boundaries when the cooling rate is slow, resulting in a decrease in cryogenic impact toughness. Additionally, the production of Cr carbide reduces processability during wire drawing. Therefore, Cr was limited to the range of 0.4 to 1.9%. Preferably, it is 0.5 to 1.8%.

B: 0.0010% to 0.0050%

By segregating at austenite grain boundaries, B has the effect of improving the grain boundary strength and improving the cryogenic impact toughness of the weld metal. In addition, along with the improvement of grain boundary strength, it also has the effect of preventing breakage during wire drawing. To obtain this effect, B needs to be contained at 0.0010% or more. If B is less than 0.0010%, the above effect cannot be secured. On the other hand, if it contains more than 0.0050%, it combines with N mixed as an inevitable impurity, forms boron nitride at the austenite grain boundaries, and reduces the grain boundary strength. Due to this decrease in grain boundary strength, during wire drawing, the austenite grain boundary becomes the origin of fracture and causes breakage, which reduces wire drawing processability and lowers manufacturability of the wire. 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 used as basic components.

In order to improve the cryogenic impact toughness of weld metal (deposited 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/㎡)=-53+6.2Ni+0.7Cr+3.2Mn+9.3Mo… … (One)

(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 as satisfies 17 to 57 (mJ/㎡). SFE is a value adopted as an index of macroscopic austenite stability in the present invention, and is defined by equation (1) based on the respective contents of Ni, Cr, Mn, and Mo. If SFE is less than 17 (mJ/m2), the stability of austenite is low and the desired cryogenic impact toughness cannot be satisfied. On the other hand, if SFE exceeds 57 (mJ/m2), the work hardening ability during the tensile test decreases, and the desired tensile strength cannot be satisfied. For this reason, the SFE defined by equation (1) was limited to the range of 17 to 57 (mJ/m2). Preferably it is 20 to 55 (mJ/m2). In addition, when the element described in equation (1) is not contained, the content of the element is set to 0 and the value SFE in equation (1) is calculated.

In the solid wire of the present invention, in addition to the basic components described above, additionally, if necessary, as an optional component, one or two or more types selected from V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less. A total of 1.0% or less and/or Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.01% or less, REM: 0.02% or less, and/or Mo: 3.5%. You can select and include the following.

V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less, total of 1 or 2 or more selected from the group consisting of 1.0% or less

V, Ti, and Nb are all elements that form carbides and contribute to improving the strength of the weld metal, and can be selected as needed and contain one or two or more types in a total amount of 1.0% or less.

V: 0.5% or less

V is a carbide forming element and contributes to improving the strength of the weld metal by precipitating fine carbides. In order to obtain this effect, it is preferable to contain 0.001% or more. On the other hand, if it contains more than 0.5%, the carbide becomes coarse and becomes the origin of cracks during wire drawing of solid wire, which reduces wire drawing processability and lowers manufacturability of the wire. Therefore, when containing it, it is preferable to limit V to 0.5% or less.

Ti: 0.5% or less

Ti is a carbide forming element and contributes to improving the strength of the weld metal by precipitating fine carbides. Additionally, Ti causes carbides to precipitate at the interface of the solidification cell of the weld metal, contributing to suppressing the occurrence of high-temperature cracks. In order to obtain this effect, it is preferable to contain 0.001% or more. However, if Ti: contains more than 0.5%, carbides become coarse and become the origin of cracks during wire drawing of solid wire, which reduces wire drawing processability and lowers manufacturability of the wire. Additionally, if Ti is contained in excess of 0.5%, carbides become coarse, refinement of crystal grains is suppressed, and cryogenic impact toughness deteriorates. Therefore, when containing Ti, it is preferable to limit it to 0.5% or less.

Nb: 0.5% or less

Nb is a carbide forming element that precipitates carbide and contributes to improving the strength of the weld metal. In addition, Nb precipitates carbides at the interface of the solidification cell of the weld metal, contributing to suppressing the occurrence of high-temperature cracks. In order to obtain this effect, it is preferable to contain 0.001% or more. However, if Nb is contained in excess of 0.5%, carbides become coarse and become the origin of cracks during wire drawing of solid wire, which reduces wire drawing performance and lowers manufacturability of the wire. Additionally, if Nb is contained in excess of 0.5%, carbides become coarse, refinement of crystal grains is suppressed, and cryogenic impact toughness also decreases. Therefore, when containing it, it is preferable to limit Nb to 0.5% or less.

Additionally, if V, Ti, and Nb are contained in large amounts exceeding 1.0% in total, the manufacturability and cryogenic impact toughness of the wire deteriorate. Therefore, when containing it, it is preferable to limit V, Ti, and Nb to 1.0% or less in total.

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

Cu is an element that contributes to austenite stabilization, Al is an element that improves welding workability, and Ca and REM are elements that contribute to improved processability, and can be selected as needed and contained in one or two or more types.

Cu: 1.0% or less

Cu is an element that stabilizes the austenite phase, and stabilizes the austenite phase even at extremely low temperatures, improving the cryogenic impact toughness of the weld metal (deposited metal). In order to obtain this effect, it is preferable to contain 0.01% or more. However, if it is contained in a large amount exceeding 1.0%, hot ductility decreases and the manufacturability of the wire decreases. Therefore, when containing it, it is preferable to limit Cu to 1.0% or less.

Al: 0.10% or less

Al acts as a deoxidizer and has an important effect of increasing the viscosity of the molten metal, stably maintaining the bead shape, and reducing the occurrence of sputtering. Additionally, Al increases the liquidus temperature of the molten metal and contributes to suppressing the occurrence of high-temperature cracks in the weld metal. Since this effect becomes noticeable when it contains 0.005% or more, it is preferable to contain 0.005% or more. However, if it contains more than 0.10%, the viscosity of the molten metal becomes too high, and conversely, defects such as increased sputtering, poor fusion due to the beads not expanding, and the like increase. Therefore, when containing Al, it is preferable to limit it 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 sulfide CaS with a high melting point. Since CaS has a higher melting point than MnS, it does not advance in the rolling direction during hot processing of solid wire and maintains its spherical shape, which is advantageous in improving the workability of solid wire. This effect becomes noticeable when the content is 0.001% or more. On the other hand, if it contains more than 0.01%, the arc will be disturbed during welding, making stable welding difficult. Therefore, when containing it, it is preferable to limit Ca to 0.01% or less.

REM: 0.02% or less

REM is a strong deoxidizing agent, and exists in the form of REM oxide in weld metal (deposited metal). REM oxide serves as a nucleation site during solidification, thereby refining crystal grains and contributing to improving the strength of the weld metal (deposited metal). This effect becomes noticeable when the content is 0.001% or more. However, if it contains more than 0.02%, the stability of the arc decreases. Therefore, when containing it, it is preferable to limit REM to 0.02% or less.

Mo: 3.5% or less

Mo is an element that improves strength through solid solution strengthening, and it is preferable to contain 0.5% or more to obtain this effect. On the other hand, if it contains more than 3.5%, carbides precipitate, hot workability decreases, and wire manufacturability, such as wire drawing, decreases. Therefore, when it is contained, it is preferable to limit Mo to 3.5% or less.

The remainder other than the above components consists of Fe and inevitable impurities.

Next, the manufacturing method of the solid wire of the present invention will be described.

For the production of the solid wire of the present invention, there is no need to specifically limit the production method other than using molten steel having the above-mentioned composition, and all commercial methods for producing solid wire for welding can be applied. For example, molten steel having the above-mentioned composition is melted in a commercial furnace such as an electric furnace or vacuum melting furnace, cast into a mold of a predetermined shape, etc., a casting process to obtain a steel ingot, and the obtained steel ingot is heated to a predetermined temperature. A heating process and a hot rolling process of performing hot rolling on the heated steel ingot to obtain a steel material (rod shape) of a predetermined shape are sequentially performed, and then the obtained steel material (rod shape) is cold rolled (cold drawn) multiple times. The solid wire of the present invention can be manufactured by performing annealing at an annealing temperature of 1000 to 1200°C as needed and performing a cold rolling process to obtain a wire of the desired size.

Next, a gas metal arc welding method using the solid wire of the present invention having the above-described composition will be described.

In the above welding method, a high-Mn-containing steel material is joined by forming a weld metal by gas metal arc welding using the solid wire of the present invention having the above-mentioned composition as a welding material. Gas metal arc welding is also called “gas shielded arc welding” and generally includes “solid electrode type (consumable electrode type)” using a welding material (filler metal) as an electrode and a non-consumable electrode such as tungsten. It can be broadly divided into the “non-consumable electrode type” used. The solid wire of the present invention is preferably used for positive electrode gas metal arc welding from the viewpoint of achieving excellent cryogenic impact toughness with high strength and high ductility.

All commercially available welding conditions such as welding posture, preheating, welding heat input (current, voltage, welding speed), and shielding gas can be applied.

The high-Mn-containing steel material that is gas metal arc welded using the solid wire of the present invention contains a high content of Mn as an alloy element. The lower limit of the Mn content is not particularly limited, but is, for example, 10 mass% or more, preferably 15 mass% or more, and more preferably 20 mass% or more. The upper limit of the Mn content is not particularly limited, but is, for example, 35 mass% or less, preferably 30 mass% or less, and more preferably 27 mass% or less. If the Mn content of the high-Mn-containing steel is within the above range, gas metal arc welding using the solid wire of the present invention as a welding material has excellent high-temperature crack resistance and weld bead appearance, resulting in the desired high strength, high ductility, and excellent cryogenic impact. Weld metal (deposited metal) and welded joints that have both toughness can be stably obtained.

In the above-mentioned high-Mn-containing steel, the composition of alloy elements other than Mn, the size and shape of the steel, etc. are not particularly limited, and any suitable for the desired application can be adopted, but the desired high strength, high ductility, and excellent cryogenic impact toughness are achieved. From the viewpoint of achieving this, 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 manufacturing products including weld metal requiring high strength, high ductility, and excellent cryogenic impact toughness, for example, and preferably high Mn. It can be used in the manufacture of containers for transporting or storing LNG from containing steel materials.

In the gas metal arc welding method using a solid wire of the present invention, in cooling during welding, the cooling rate CR (°C/s) in the temperature range of 1300 to 1200°C at the weld bead (weld zone) is [SFE+(cooling rate) CR) ^1/2 ]: Adjust the welding heat input to satisfy 20 to 70. As a result, austenite is stabilized and the occurrence of brittle fracture in the weld metal (deposited metal) can be suppressed, and as a result, a weld metal (deposited metal) with high strength, high ductility and excellent cryogenic impact toughness can be obtained. there is.

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 a 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, so when solidification occurs in the dendrite arm portion, The discharge amount of the solute element increases, the area where the solute element is rare expands, and the stability of the microscopic austenite cannot be secured.

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 a CR (°C/s) such that [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. In addition, “SFE” referred to here is an index of the stability of macroscopic austenite and is defined by the above-mentioned equation (1).

In welding, generally, each time one pass of welding is performed, the formed weld bead (weld zone) is cooled to a predetermined temperature and solidified, and then the subsequent work, such as welding in the next pass or any post-heat treatment, etc. Do. When multiple passes of welding are performed and the cooling process in the temperature range of 1300 to 1200°C is performed multiple times, each pass must satisfy [SFE+(cooling rate CR) ^1/2 ]: 20 to 70 in all cooling processes. Adjust the welding heat input in .

In the welding method of the present invention, the formed weld bead (weld zone) is cooled by leaving it standing in the air to cool, so by adjusting the amount of welding heat input in each pass, cooling is achieved in the temperature range of 1300 to 1200°C. Speed CR (℃/s) can be controlled. Specifically, the welding heat input amount equivalent to the cooling rate applied to the above equation may be obtained in advance from preliminary experiments or the Inagaki formula, and welding may be performed using that heat input amount.

Hereinafter, the present invention will be further explained based on examples.

Example

Molten steel with the composition shown in Table 1 was melted in a vacuum melting furnace and casted to obtain 100 kg of steel ingots. The obtained steel ingot was heated to 1200°C, hot rolled, and then cold rolled to obtain a 1.2 mm phi solid wire for gas metal arc welding. During wire manufacturing, rolling load (drawing load) was measured and cracks were observed to evaluate the manufacturability of each solid wire. When the rolling load (drawing load) is high and rolling (drawing) processing is judged to be impossible, when the occurrence of cracks is confirmed, or when the process cannot proceed further due to the cracks that have occurred, it is classified as “defect”. ” was evaluated. Other than that, it was evaluated as “good.”

Next, as a test plate, a high-Mn steel plate for cryogenic use (plate thickness: 6 to 40 mm) was prepared, butted in accordance with JIS Z 3111 to form a 45° V-shaped groove, and the composition shown in Table 1. A solid wire manufactured from molten steel was used as a welding material, and gas metal arc welding was performed in a positive electrode manner to obtain deposited metal within the improvement. The steel plate used as a test plate was a high-Mn steel plate for cryogenic use with a composition consisting of 0.5%C-0.4%Si-25%Mn-3%Cr-balance Fe in mass%.

In the above welding, each solid wire (diameter 1.2 mm) manufactured from molten steel with the composition shown in Table 1 is used as an electrode, without preheating, in a downward position, temperature between passes: 100 to 150 ° C., shield gas: 80% Ar + 20. It was carried out using %CO ₂ . The temperature history during welding was measured using a thermocouple, and the cooling rate in the temperature range of 1300 to 1200°C was calculated.

After welding, the deposited metal was observed under an optical microscope to determine the presence or absence of weld cracks. Welding cracks are high-temperature cracks, and when cracking was confirmed, the high-temperature cracking resistance was said to be low and it was evaluated as “defective.” In cases where cracking was not confirmed, it was evaluated as “good” because it had excellent high-temperature cracking resistance.

Additionally, the appearance of the weld bead was observed with the naked eye to determine the appearance of the weld bead. When undercuts, overlaps, and pits were confirmed, the weld bead appearance was considered to be poor and was evaluated as “defective.” In cases where these were not confirmed, the weld bead appearance was evaluated as "good".

From the obtained welded metal, in accordance with the provisions of JIS Z 3111, weld metal tensile test pieces (parallel part diameter 6 mmϕ) and weld metal Charpy impact test pieces (V notch) were taken, and tensile tests and impact tests were performed. did. Additionally, for steel sheets with a thickness of less than 10 mm, Charpy impact test pieces (V notches) of 5 mm subsize were taken and impact tests were performed.

The tensile test was conducted 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 taken as the tensile properties of the welded metal using the solid wire. In addition, the Charpy impact test was performed on three test pieces each, and the absorbed energy vE _-196 at the test temperature: -196°C was determined, and the average value was taken as the cryogenic impact toughness of the deposited metal using the solid wire. Additionally, for the Charpy impact test piece (V notch) of 5 mm subsize, the obtained absorbed energy was multiplied by 1.5 times and the cryogenic impact toughness was evaluated. In addition, the brittle fracture ratio was determined visually.

The obtained results are shown in Table 2.

All of the examples of the present invention had excellent wire manufacturability, excellent high-temperature crack resistance due to no occurrence of weld cracks (high-temperature cracks) during welding, and a good weld bead appearance. In addition, the yield strength (0.2% proof stress) at room temperature is 400 MPa or more, the tensile strength is 660 MPa or more, and the total elongation is 40% or more, showing high strength and high ductility. Additionally, test temperature: Charpy at -196°C. It was a welding material (solid wire) capable of obtaining welded metal with excellent cryogenic impact toughness, with an absorbed energy vE _-196 of 28 J or more in the impact test and a brittle fracture ratio of 10% or less.

On the other hand, in comparative examples outside the scope of the present invention, the manufacturability of the wire is poor, weld cracks (high-temperature cracks) occur and the high-temperature cracking resistance is reduced, the appearance of the weld bead is poor, or the 0.2% proof strength is less than 400 MPa, tensile strength is less than 660 MPa, total elongation is less than 40%, absorbed energy vE _-196 is less than 28 J, or brittle fracture ratio is more than 10%, and the desired high-strength high lead A deposited metal that had both high performance and excellent cryogenic impact toughness was not obtained.

Claims (8)

In mass%,
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 to 10.0%,
Cr: 0.4 to 1.9% and
B: 0.0010 to 0.0050%
Contains, the balance consists of Fe and inevitable impurities, and also,
A solid wire for gas metal arc welding, characterized in that it has a composition that satisfies the SFE of 17 to 55, as defined by the formula (1) below.
SFE=-53+6.2Ni+0.7Cr+3.2Mn+9.3Mo... … (One)
Here, Ni, Cr, Mn, Mo: content (mass%) of each element, and Mo is 0. According to paragraph 1,
A gas characterized in that the composition further contains, in mass%, a total of 1.0% or less of one or two or more selected from the group consisting of V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less. Solid wire for metal arc welding. According to claim 1 or 2,
The composition further contains, in mass%, one or two or more selected from among Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.01% or less, and REM: 0.02% or less. Solid wire for gas metal arc welding. A gas metal arc welding method for joining high-Mn-containing steel materials by forming a weld metal by gas metal arc welding using a solid wire,
The solid wire is expressed in mass%,
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 to 10.0%,
Cr: 0.4 to 1.9% and
B: 0.0010 to 0.0050%
Contains, the balance consists of Fe and inevitable impurities, and the following formula (1)
SFE=-53+6.2Ni+0.7Cr+3.2Mn+9.3Mo... … (One)
(Here, Ni, Cr, Mn, Mo: content (mass%) of each element, Mo is 0)
It has a composition that satisfies the SFE defined as 17 to 55,
The gas metal arc welding is characterized in that the cooling rate CR (°C/s) in the temperature range of 1300 to 1200°C is adjusted to satisfy [SFE+(cooling rate CR) ^1/2 ]: 20 to 70. Metal arc welding method. According to paragraph 4,
In addition to the composition, the solid wire further contains, in mass%, a total of 1.0% or less of one or two or more types selected from the group consisting of V: 0.5% or less, Ti: 0.5% or less, and Nb: 0.5% or less. A gas metal arc welding method characterized in that. According to clause 4 or 5,
In addition to the above composition, the solid wire further contains, in mass%, one or two 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. A gas metal arc welding method characterized in that. delete delete