Weld metal, welded joint, and welded structure

Abstract

The weld metal comprises the following components in percentage by weight: 0.030 to 1.000 percent of C, 0.03 to 0.50 percent of Si, 4.1 to 30.0 percent of Mn, 0 to 0.050 percent of P, 0 to 0.050 percent of S, 0 to 5.0 percent of Cu, 1.0 to 30.0 percent of Ni, 0 to 20.0 percent of Cr, 0 to 10.0 percent of Mo, 0 to 1.000 percent of Nb, 0 to 1.00 percent of V, 0 to 1.00 percent of Co, 0 to 1.00 percent of Pb, 0 to 1.00 percent of Sn, 0 to 20.0 percent of W, 0 to 5.0 percent of Mg, 0 to 0.100 percent of Al, 0 to 5.0 percent of Ca, 0 to 0.100 percent of Ti, 0 to 0.5000 percent of B, 0 to 0.500 percent of REM, 0 to 0.500 percent of Zr, 0 to 0.5000 percent of N,

Description

Technical Field

[0001] The present disclosure relates to weld metals, weld joints, and welded structures. Background Art

[0002] In recent years, due to the strengthening of carbon dioxide emission restrictions based on the problem of global warming, the demand for hydrogen fuel, which does not emit carbon dioxide compared to oil and coal, and natural gas, which emits less carbon dioxide, has increased. With this, the demand for the construction of liquid hydrogen storage tanks, liquid carbon dioxide storage tanks, and LNG storage tanks used in ships and on the ground has also increased worldwide. For the steel used in liquid hydrogen storage tanks, liquid carbon dioxide storage tanks, and LNG storage tanks, Ni-based low-temperature steel containing 6 to 9% Ni is used to ensure toughness at extremely low temperatures of -196°C.

[0003] In addition, when welding these Ni-based low-temperature steels, the weld metal is formed by welding using an austenitic welding material that can obtain a weld metal with excellent low-temperature toughness. The Ni content of this welding material is mainly designed to be 70%.

[0004] For example, as a welding material with a Ni content of 70%, Patent Document 1 discloses "a flux-cored welding wire with a Ni-based alloy as an outer sheath, wherein the Ni content is 35 to 70%, the flux contains a total amount of 4.0 mass % or more of TiO2, SiO2 and ZrO2 relative to the total mass of the welding wire, and further contains 0.6 to 1.2 mass % of Mn oxide calculated as MnO2, and when the contents of TiO2, SiO2, ZrO2 and MnO2 (converted amounts) are set to [TiO2], [SiO2], [ZrO2] and [MnO2], respectively, in mass %, [TiO2] / [ZrO2] is 2.3 to 3.3, [SiO2] / [ZrO2] is 0.9 to 1.5 and ([TiO2]+[SiO2]+[ZrO2]) / [MnO2] is 5 to 13".

[0005] Patent Document 1: Japanese Patent Application Publication No. 2008-246507 Summary of the invention

[0006] Problems to be solved by the invention

[0007] However, if a large amount of Ni is contained in the weld metal in order to ensure the low-temperature toughness of the weld metal (for example, if a welding material designed to contain 70% Ni is used), the price becomes very high, and therefore, an inexpensive welding material is required.

[0008] Expensive Ni is known as an austenite stabilizing element, but cheap Mn also has the same effect. Therefore, if the Ni content is reduced and the Mn content is increased, a weld metal with low temperature toughness and excellent low temperature toughness can be obtained at a low cost. However, if only the Mn content is increased, the toughness deteriorates and the mechanical properties cannot be ensured.

[0009] Therefore, an object of the present invention is to provide a weld metal which is inexpensive and has excellent low-temperature toughness, a weld joint having the weld metal, and a welded structure having the weld joint.

[0010] Means for solving problems

[0011] Means for solving the problem include the following.

[0012] <1> A weld metal having the chemical composition expressed as mass % relative to the total mass of the weld metal:

[0013] C: 0.030~1.000%,

[0014] Si: 0.03-0.50%,

[0015] Mn: 4.1-30.0%,

[0016] P: 0~0.050%,

[0017] S: 0~0.050%,

[0018] Cu: 0-5.0%,

[0019] Ni: 1.0-30.0%,

[0020] Cr: 0~20.0%,

[0021] Mo: 0-10.0%,

[0022] Nb: 0~1.000%,

[0023] V: 0~1.00%,

[0024] Co: 0-1.00%,

[0025] Pb: 0~1.00%,

[0026] Sn: 0~1.00%,

[0027] W: 0~20.0%,

[0028] Mg: 0-5.0%,

[0029] Al: 0~0.100%,

[0030] Ca: 0-5.0%,

[0031] Ti: 0~0.100%,

[0032] B: 0~0.5000%、

[0033] REM: 0~0.500%、

[0034] Zr: 0~0.500%,

[0035] N: 0~0.5000%、

[0036] O: 0.0010 to 0.1500%, and

[0037] The rest: Fe and impurities,

[0038] The total of the Mn content and the Ni content (Mn+Ni) is 5.0% or more.

[0039] The total of the Nb content, the Ti content, the V content, and the Al content (Nb+Ti+V+Al) is 0.005% or more.

[0040] <2> according to <1> The weld metal described above, wherein the total of the Mn content, the Ni content and the Cr content (Mn+Ni+Cr) is 15.0% or more.

[0041] <3> according to <1> or <2> The weld metal has an fcc ratio of 70% or more determined by a magnetic induction method.

[0042] <4> according to <1> ~ <3> The weld metal described in any one of the above is characterized in that a mass ratio (Ni / Mn) of the Mn content to the Ni content is 0.10 or more.

[0043] <5> according to <4> The weld metal described above, wherein the mass ratio (Ni / Mn) is greater than 1.00.

[0044] <6> according to <1> ~ <5> The weld metal described above has a Ti content of 0.003 to 0.100%.

[0045] <7> according to <1> ~ <6> The weld metal described above has a C content of 0.110 to 1.000%.

[0046] <8> A welding joint having <1> ~ <7> The weld metal of any one of the above.

[0047] <9> A welded structure having <8> The welded joint.

[0048] Effects of the Invention

[0049] According to the present disclosure, it is possible to provide a weld metal that is inexpensive and has excellent low-temperature toughness, a weld joint having the weld metal, and a welded structure having the weld joint. DETAILED DESCRIPTION

[0050] An embodiment as an example of the present disclosure will be described.

[0051] It should be noted that in this specification, for a numerical range expressed by "to", when the numerical values ​​recorded before and after the "to" are not marked with "exceeding" and "below", it means a range including these numerical values ​​as the lower limit and the upper limit. In addition, a numerical range in which the numerical values ​​recorded before and after the "to" are marked with "exceeding" or "below" means a range not including these numerical values ​​as the lower limit or the upper limit.

[0052] In the numerical ranges described in the step-wise manner in this specification, the upper limit of a numerical range in a certain step-wise manner may be replaced by the upper limit of a numerical range described in other step-wise manners, or by the value shown in the embodiments. In addition, the lower limit of a numerical range in a certain step-wise manner may be replaced by the lower limit of a numerical range described in other step-wise manners, or by the value shown in the embodiments.

[0053] In addition, regarding the content, "%" means "mass %".

[0054] As content (%), "0 to" means that the component is an optional component and may not be contained.

[0055] <Weld Metal>

[0056] The chemical composition of the weld metal disclosed in the present invention is a predetermined composition.

[0057] The weld metal of the present disclosure can be obtained at low cost and with excellent low-temperature toughness by the above-mentioned configuration.

[0058] Furthermore, the weld metal of the present disclosure was discovered through the following insights.

[0059] The inventors have studied a technique for obtaining a weld metal capable of improving the low-temperature toughness of the weld metal even when the Ni content is reduced and the Mn content is increased. As a result, they have obtained the following findings.

[0060] In order to ensure low temperature toughness, it is preferred that the structure of the weld metal be made into an austenite single phase. Ni and Mn are both austenite stabilizing elements. However, if Ni is excessively reduced or Mn is increased, the stacking fault energy becomes lower and the toughness deteriorates. Therefore, by controlling the content of Ni and Mn, the reduction of the stacking fault energy is prevented. Therefore, even if the Ni content in the entire weld metal is reduced and the Mn content is increased, a weld metal with excellent low temperature toughness is obtained.

[0061] From the above findings, it was found that the weld metal of the present disclosure is inexpensive and has excellent low-temperature toughness.

[0062] Hereinafter, the reasons for limiting the requirements (including the requirements of the optional requirements) constituting the weld metal of the present disclosure will be described in detail.

[0063] (Chemical composition of weld metal)

[0064] The chemical composition of the weld metal will be described in detail below.

[0065] In the description of the chemical composition of the weld metal, “%” means “mass % relative to the total mass of the weld metal” unless otherwise specified.

[0066] The chemical composition of the weld metal is:

[0067] C: 0.030~1.000%,

[0068] Si: 0.03-0.50%,

[0069] Mn: 4.1-30.0%,

[0070] P: 0~0.050%,

[0071] S: 0~0.050%,

[0072] Cu: 0-5.0%,

[0073] Ni: 1.0-30.0%,

[0074] Cr: 0~20.0%,

[0075] Mo: 0-10.0%,

[0076] Nb: 0~1.000%,

[0077] V: 0~1.00%,

[0078] Co: 0-1.00%,

[0079] Pb: 0~1.00%,

[0080] Sn: 0~1.00%,

[0081] W: 0~20.0%,

[0082] Mg: 0-5.0%,

[0083] Al: 0~0.100%,

[0084] Ca: 0-5.0%,

[0085] Ti: 0~0.100%,

[0086] B: 0~0.5000%、

[0087] REM: 0~0.500%、

[0088] Zr: 0~0.500%,

[0089] N: 0~0.5000%、

[0090] O: 0.0010 to 0.1500%, and

[0091] The rest: Fe and impurities,

[0092] The total of the Mn content and the Ni content (Mn+Ni) is 5.0% or more.

[0093] The total of the Nb content, the Ti content, the V content, and the above-mentioned Al content (Nb+Ti+V+Al) is 0.005% or more.

[0094] (C: 0.030~1.000%)

[0095] C is an element that increases the strength of the weld metal and is an element for ensuring the strength of the weld metal.

[0096] On the other hand, if the C content of the weld metal is excessive, the influence of deterioration of toughness due to increase in strength of the weld metal is large, and the low-temperature toughness of the weld metal decreases.

[0097] Therefore, the C content of the weld metal is set to 0.030 to 1.000%.

[0098] The lower limit of the C content in the weld metal may also be preferably set to 0.050%, 0.100%, 0.110%, 0.120%, 0.140%, 0.150%, 0.200%, or 0.250%.

[0099] The upper limit of the C content of the weld metal is preferably 0.900%, 0.800%, 0.700%, 0.600%, 0.550%, 0.500%, 0.450%, or 0.400%.

[0100] (Si: 0.03-0.50%)

[0101] Si is a deoxidizing element. If the Si content of the weld metal is too low, the P content of the weld metal increases.

[0102] On the other hand, Si has a low solid solubility in the austenite phase, and the more Si is contained, the more brittle phases such as intermetallic compounds and δ-ferrite are generated at high temperatures, and the high-temperature ductility deteriorates.

[0103] Therefore, the Si content of the weld metal is set to 0.03 to 0.50%.

[0104] The lower limit of the Si content in the weld metal is preferably 0.04%, 0.05%, or 0.08%.

[0105] The upper limit of the Si content of the weld metal is preferably 0.48%, 0.45%, 0.40%, 0.35%, 0.30%, or 0.20%.

[0106] (Mn: 4.1~30.0%)

[0107] Mn is an austenite stabilizing element. If the Mn content of the weld metal is too low, the austenitization of the weld metal becomes difficult to progress, and the low-temperature toughness deteriorates. In addition, Mn is an element that functions as a deoxidizer to improve the cleanliness of the weld metal. In addition, Mn is an element that detoxifies S in the weld metal by forming MnS and improves the low-temperature toughness of the weld metal. In addition, Mn also has the effect of preventing high-temperature cracking.

[0108] On the other hand, if the Mn content of the weld metal is excessive, micro segregation is likely to occur in the weld metal, causing significant embrittlement in the segregated portion. In addition, if Mn is excessively added, the stacking fault energy decreases, and the toughness deteriorates.

[0109] Therefore, the Mn content of the weld metal is set to 4.1 to 30.0%.

[0110] The lower limit of the Mn content of the weld metal is preferably 4.2%, 4.5%, 5.0%, 7.0%, 9.0%, or 10.0%.

[0111] The upper limit of the Mn content of the weld metal is preferably 28.0%, 25.0%, 23.0%, 20.0%, 18.0%, 15.0%, or 14.5%.

[0112] (P: 0~0.050%)

[0113] P is an impurity element that reduces toughness, so the P content of the weld metal is preferably as low as possible. Therefore, the lower limit of the P content of the weld metal is set to 0%. However, from the perspective of reducing the cost of P removal, the P content of the weld metal is preferably 0.003% or more.

[0114] On the other hand, when the P content of the weld metal is 0.050% or less, the adverse effect of P on toughness is within the allowable range.

[0115] Therefore, the P content of the weld metal is set to 0 to 0.050%.

[0116] In order to effectively suppress a decrease in toughness, the P content of the weld metal is preferably 0.040% or less, 0.030% or less, 0.020% or less, 0.015% or less, or 0.010% or less.

[0117] (S: 0~0.050%)

[0118] S is an impurity element and reduces toughness, so the S content of the weld metal is preferably as low as possible. Therefore, the lower limit of the S content of the weld metal is set to 0%. However, from the perspective of reducing the cost of desulfurization, the S content of the weld metal is preferably 0.003% or more.

[0119] On the other hand, when the S content of the weld metal is 0.050% or less, the adverse effect of S on toughness is within the allowable range.

[0120] Therefore, the S content of the weld metal is set to 0 to 0.050%.

[0121] In order to effectively suppress a decrease in toughness, the S content of the weld metal is preferably 0.040% or less, 0.030% or less, 0.020% or less, 0.015% or less, or 0.010% or less.

[0122] (Cu: 0-5.0%)

[0123] Cu is a precipitation strengthening element and may be contained in the weld metal in order to improve the strength of the weld metal. In addition, Cu is an austenite stabilizing element and may be contained in the weld metal in order to improve the low temperature toughness of the weld metal.

[0124] On the other hand, if the Cu content of the weld metal is excessive, the above-mentioned effect is saturated.

[0125] Therefore, the Cu content of the weld metal is set to 0 to 5.0%.

[0126] The lower limit of the Cu content of the weld metal is preferably 0.3%, 0.5%, or 0.7%.

[0127] The upper limit of the Cu content of the weld metal is preferably 4.5%, 4.0%, or 3.5%.

[0128] (Ni: 1.0~30.0%)

[0129] Ni is an austenite stabilizing element. If the Ni content of the weld metal is too low, austenitization of the weld metal becomes difficult to progress, and low-temperature toughness deteriorates.

[0130] On the other hand, if the Ni content of the weld metal is increased, the cost of the weld metal increases.

[0131] Therefore, the Ni content of the weld metal is set to 1.0 to 30.0%.

[0132] The lower limit of the Ni content in the weld metal is preferably 2.0%, 3.0%, 3.2%, 3.7%, 5.0%, or 7.0%.

[0133] The upper limit of the Ni content of the weld metal is preferably 28.0%, 25.0%, 23.0%, 20.0%, 18.0%, or 15.0%.

[0134] (Cr: 0~20.0%)

[0135] Cr is an austenite stabilizing element and may be contained in the weld metal in order to improve the low-temperature toughness of the weld metal.

[0136] On the other hand, if the Cr content of the weld metal is excessive, the amount of low melting point compounds in the molten metal increases, and the solid-liquid coexistence temperature range of the molten metal becomes wider, so that high temperature cracking becomes more likely to occur.

[0137] Therefore, the Cr content of the weld metal is set to 0 to 20.0%.

[0138] The lower limit of the Cr content in the weld metal is preferably 1.0%, 2.0%, or 3.0%.

[0139] The upper limit of the Cr content of the weld metal is preferably 18.0%, 15.8%, 15.3%, 15.0%, 13.3%, 13.0%, 10.0%, 9.0%, 8.0%, or 7.0%.

[0140] (Mo: 0~10.0%)

[0141] Mo is a precipitation strengthening element and may be contained in the weld metal in order to increase the strength of the weld metal.

[0142] On the other hand, if the Mo content of the weld metal is excessive, the strength of the weld metal becomes excessive and the low-temperature toughness decreases.

[0143] Therefore, the Mo content of the weld metal is set to 0 to 10.0%.

[0144] The lower limit of the Mo content in the weld metal is preferably 1.0%, 2.0%, or 3.0%.

[0145] The upper limit of the Mo content in the weld metal is preferably 9.0%, 8.0%, or 7.0%.

[0146] (Nb: 0~1.000%)

[0147] Nb is an element that forms carbides in the weld metal and increases the strength of the weld metal, and therefore may be contained in the weld metal.

[0148] On the other hand, if the Nb content of the weld metal is excessive, high-temperature cracking of the weld metal may occur.

[0149] Therefore, the Nb content of the weld metal is set to 0 to 1.000%.

[0150] The lower limit of the Nb content of the weld metal is preferably 0.010%, 0.050%, 0.100%, 0.150%, or 0.200%.

[0151] The upper limit of the Nb content of the weld metal is preferably 0.950%, 0.900%, 0.850%, or 0.800%.

[0152] (V: 0~1.00%)

[0153] V is an element that forms carbonitrides in the weld metal and increases the strength of the weld metal, and therefore may be contained in the weld metal.

[0154] On the other hand, if the V content of the weld metal is excessive, high-temperature cracking of the weld metal may occur.

[0155] Therefore, the V content of the weld metal is set to 0 to 1.00%.

[0156] The lower limit of the V content in the weld metal is preferably 0.01%, 0.05%, 0.10%, 0.15%, or 0.20%.

[0157] The upper limit of the V content of the weld metal is preferably 0.95%, 0.90%, 0.85%, or 0.80%.

[0158] (Co: 0~1.00%)

[0159] Co is an element that increases the strength of the weld metal by solid solution strengthening, and therefore may be contained in the weld metal.

[0160] On the other hand, if the Co content of the weld metal is excessive, the ductility of the weld metal decreases and the toughness cannot be ensured.

[0161] Therefore, the Co content of the weld metal is set to 0 to 1.00%.

[0162] The lower limit of the Co content in the weld metal is preferably 0.01%, 0.05%, 0.10%, 0.15%, or 0.20%.

[0163] The upper limit of the Co content in the weld metal is preferably 0.95%, 0.90%, 0.85%, or 0.80%.

[0164] (Pb: 0~1.00%)

[0165] Pb has the effect of improving the seam formability between the steel material as the base material and the weld metal and improving the machinability of the weld metal, and therefore may be contained in the weld metal.

[0166] On the other hand, if the Pb content of the weld metal is excessive, high-temperature cracking occurs.

[0167] Therefore, the Pb content of the weld metal is set to 0 to 1.00%.

[0168] The lower limit of the Pb content in the weld metal is preferably 0.01%, 0.05%, 0.10%, 0.15%, or 0.20%.

[0169] The upper limit of the Pb content in the weld metal is preferably 0.95%, 0.90%, 0.85%, or 0.80%.

[0170] (Sn: 0~1.00%)

[0171] Sn is an element that improves the corrosion resistance of the weld metal, and therefore may be contained in the weld metal.

[0172] On the other hand, if the Sn content of the weld metal is excessive, cracks may occur in the weld metal.

[0173] Therefore, the Sn content of the weld metal is set to 0 to 1.00%.

[0174] The lower limit of the Sn content in the weld metal is preferably 0.01%, 0.05%, 0.10%, 0.15%, or 0.20%.

[0175] The upper limit of the Sn content in the weld metal is preferably 0.95%, 0.90%, 0.85%, or 0.80%.

[0176] (W: 0~20.0%)

[0177] W is a solid solution strengthening element and may be contained in the weld metal in order to improve the strength.

[0178] On the other hand, if the W content of the weld metal is excessive, the strength of the weld metal may become excessive, resulting in a decrease in toughness.

[0179] Therefore, the W content of the weld metal is set to 0 to 20.0%.

[0180] The lower limit of the W content in the weld metal is preferably 0.5%, 1.0%, or 2.0%.

[0181] The upper limit of the W content of the weld metal is preferably 19.0%, 18.0%, 17.0%, 16.0%, or 15.0%.

[0182] (Mg: 0-5.0%)

[0183] Mg is a deoxidizing element and has the effect of reducing oxygen and improving toughness, so it may be contained in the weld metal.

[0184] On the other hand, if the Mg content of the weld metal is excessive, the arc becomes unstable during welding work for obtaining the weld metal, spatter and porosity increase, and welding workability deteriorates.

[0185] Therefore, the Mg content of the weld metal is set to 0 to 5.0%.

[0186] The lower limit of the Mg content of the weld metal is preferably 0.02%, 0.05%, 0.1%, or 0.2%.

[0187] The upper limit of the Mg content of the weld metal is preferably 4.8%, 4.5%, 4.3%, or 4.0%.

[0188] (Al: 0~0.100%)

[0189] Al is a deoxidizing element and may be contained in the weld metal in order to suppress welding defects and improve the cleanliness of the weld metal.

[0190] On the other hand, if the Al content in the weld metal is excessive, Al may form nitrides or oxides in the weld metal, thereby possibly reducing the low-temperature toughness of the weld metal.

[0191] Therefore, the Al content of the weld metal is set to 0 to 0.100%.

[0192] The lower limit of the Al content in the weld metal is preferably 0.010%, 0.020%, or 0.030%.

[0193] The upper limit of the Al content in the weld metal is preferably 0.090%, 0.080%, or 0.070%.

[0194] (Ca: 0-5.0%)

[0195] Ca has the effect of changing the structure of sulfides in the weld metal and reducing the size of sulfides and oxides in the weld metal, and is therefore effective in improving the ductility and toughness of the weld metal. Therefore, Ca may be contained in the weld metal.

[0196] On the other hand, if the Ca content of the weld metal is excessive, coarsening of sulfides and oxides may occur, which may lead to deterioration of the low-temperature toughness of the weld metal.

[0197] Therefore, the Ca content of the weld metal is set to 0 to 5.0%.

[0198] The lower limit of the Ca content in the weld metal is preferably 0.01%, 0.02%, or 0.03%.

[0199] The upper limit of the Ca content in the weld metal is preferably 4.8%, 4.5%, 4.3%, or 4.0%.

[0200] (Ti: 0~0.100%)

[0201] Ti is a deoxidizing element and may be contained in the weld metal in order to suppress welding defects and improve the cleanliness of the weld metal.

[0202] On the other hand, if the Ti content of the weld metal is excessive, carbides may be generated in the weld metal, thereby deteriorating the toughness of the weld metal.

[0203] Therefore, the Ti content of the weld metal is set to 0 to 0.100%.

[0204] The lower limit of the Ti content in the weld metal is preferably 0.003%, 0.010%, 0.020%, or 0.030%.

[0205] The upper limit of the Ti content in the weld metal is preferably 0.090%, 0.080%, or 0.070%.

[0206] (B: 0~0.5000%)

[0207] B is an austenite stabilizing element and an interstitial solid solution strengthening element, and may be contained in the weld metal in order to improve the low-temperature toughness and strength of the weld metal.

[0208] On the other hand, if the B content of the weld metal is excessive, M 23 (C, B) 6, which causes the deterioration of toughness.

[0209] Therefore, the B content of the weld metal is set to 0 to 0.5000%.

[0210] The lower limit of the B content in the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%.

[0211] The upper limit of the B content of the weld metal is preferably 0.4800%, 0.4500%, 0.4300%, or 0.4000%.

[0212] (REM: 0~0.500%)

[0213] REM is an element for stabilizing the arc during welding work to obtain the weld metal, and therefore may be contained in the weld metal.

[0214] On the other hand, if the REM content of the weld metal is excessive, spatter may become severe during welding work for obtaining the weld metal, and welding workability may be deteriorated.

[0215] Therefore, the REM content of the weld metal is set to 0 to 0.500%.

[0216] The lower limit of the REM content of the weld metal is preferably 0.001%, 0.002%, or 0.005%.

[0217] The upper limit of the REM content of the weld metal is preferably 0.480%, 0.450%, 0.430%, or 0.400%.

[0218] (Zr: 0~0.500%)

[0219] Zr can stabilize the weld bead shape during welding work for obtaining the weld metal, and therefore may be contained in the weld metal.

[0220] On the other hand, if the Zr content of the weld metal is excessive, the oxygen content of the weld metal increases, which may deteriorate the low-temperature toughness.

[0221] Therefore, the Zr content of the weld metal is set to 0 to 0.500%.

[0222] The lower limit of the Zr content in the weld metal is preferably 0.001%, 0.002%, or 0.005%.

[0223] The upper limit of the Zr content in the weld metal is preferably 0.480%, 0.450%, 0.430%, or 0.400%.

[0224] (N: 0~0.5000%)

[0225] N is an austenite stabilizing element and an interstitial solid solution strengthening element, and may be contained in the weld metal in order to improve the low-temperature toughness and strength of the weld metal.

[0226] On the other hand, if the N content of the weld metal is excessive, the occurrence of melting increases, which becomes a cause of welding defects.

[0227] Therefore, the N content of the weld metal is set to 0 to 0.5000%.

[0228] The lower limit of the N content of the weld metal is preferably 0.0010%, 0.0100%, or 0.0500%.

[0229] The upper limit of the N content of the weld metal is preferably 0.4500%, 0.4000%, or 0.3500%.

[0230] (O: 0.0010~0.1500%)

[0231] O is contained in the weld metal as an impurity. However, if the content of O becomes excessive, toughness and ductility will deteriorate, so the upper limit of the content of O in the weld metal is made 0.1500% or less.

[0232] On the other hand, an extreme decrease in the O content leads to an increase in manufacturing cost, so the lower limit of the O content in the weld metal is made 0.0010% or less.

[0233] The lower limit of the O content in the weld metal is preferably 0.0020% or 0.0030%.

[0234] The upper limit of the O content in the weld metal is preferably 0.1300% or 0.1000%.

[0235] (Remainder: Fe and impurities)

[0236] The remaining components in the chemical composition of the weld metal are Fe and impurities.

[0237] Impurities refer to components that are mixed into weld metal due to raw materials such as ore and scrap iron or various factors in the manufacturing process when weld metal is manufactured industrially, and are permitted within a range that does not adversely affect the properties of the weld metal.

[0238] (Total of Mn content and Ni content (Mn+Ni))

[0239] Mn and Ni are austenite stabilizing elements, respectively, and improve the low temperature toughness of the weld metal. On the other hand, Ni is an expensive metal, so in order to suppress the cost of the weld metal and improve the low temperature toughness of the weld metal, the Mn content and the Ni content in the weld metal are respectively within the above ranges, and the total of the Mn content and the Ni content (Mn+Ni) is set to 5.0% or more.

[0240] The total content of Mn and Ni in the weld metal (Mn+Ni) is preferably 5.2% or more, 6.2% or more, 6.7% or more, 7.0% or more, 10.0% or more, or 15.0% or more.

[0241] In addition, if Mn is excessively increased, the stacking fault energy becomes low and the toughness deteriorates. Therefore, from the viewpoint of suppressing the cost of the weld metal and improving the low temperature toughness of the weld metal, it is preferred that the Mn content and the Ni content in the weld metal satisfy the above ranges respectively, and the total of the Mn content and the Ni content (Mn+Ni) is set to 37.0% or less.

[0242] The total of the Mn content and the Ni content (Mn+Ni) in the weld metal is more preferably 35.0% or less, 32.0% or less, or 30.0% or less.

[0243] (Total of Mn content, Ni content and Cr content (Mn+Ni+Cr))

[0244] Mn, Ni and Cr are austenite stabilizing elements, respectively, and improve the low temperature toughness of the weld metal. On the other hand, Ni is an expensive metal, so in order to suppress the cost of the weld metal and improve the low temperature toughness of the weld metal, it is preferred that the Mn content, Ni content and Cr content in the weld metal respectively meet the above ranges, and the total of the Mn content, Ni content and Cr content (Mn+Ni+Cr) is set to 15.0% or more.

[0245] The total of the Mn content, the Ni content and the Cr content (Mn+Ni+Cr) in the weld metal is more preferably 17.0% or more, 19.0% or more, 20.0% or more, 22.0% or more, 24.0% or more, 26.0% or more, 28.0% or more, or 30.0% or more.

[0246] On the other hand, if the Mn content is not excessive, the stacking fault energy will not be too low, and the toughness can be ensured. In addition, if the Cr content is not excessive, the amount of low melting point compounds in the molten metal can be reduced, and the solid-liquid coexistence temperature range of the molten metal can be suppressed from widening, and the generation of high temperature cracks can be suppressed. Therefore, from the viewpoint of suppressing the cost of the weld metal, improving the low temperature toughness of the weld metal, reducing the amount of low melting point compounds generated in the molten metal, and suppressing the generation of high temperature cracks, it is preferred that the Mn content, Ni content, and Cr content in the weld metal respectively meet the above ranges, and the total of the Mn content, Ni content, and Cr content (Mn+Ni+Cr) is set to 47.0% or less.

[0247] The total of the Mn content, the Ni content, and the Cr content (Mn+Ni+Cr) in the weld metal is more preferably 45.0% or less, 42.0% or less, or 40.0% or less.

[0248] (Mass ratio of Mn content to Ni content (Ni / Mn))

[0249] Mn and Ni are austenite stabilizing elements, respectively, and improve the low temperature toughness of the weld metal. On the other hand, Ni is an expensive metal, and if Mn is excessively increased, the stacking fault energy decreases, and the toughness deteriorates.

[0250] Therefore, from the viewpoint of suppressing the cost of the weld metal and improving the low-temperature toughness of the weld metal, the mass ratio (Ni / Mn) of the Mn content to the Ni content in the weld metal is preferably set to 0.10 or more.

[0251] The lower limit of the mass ratio of the Mn content to the Ni content (Ni / Mn) in the weld metal is more preferably 0.20, 0.30, 0.50, 0.70, 0.73, 1.00, 1.10, or 1.20.

[0252] The upper limit of the mass ratio of the Mn content to the Ni content in the weld metal (Ni / Mn) is preferably 10.00, 8.00, or 5.00.

[0253] (Total of Nb content, Ti content, V content and Al content (Nb+Ti+V+Al))

[0254] Nb, Ti, V and Al are elements that improve the strength of the weld metal by precipitation strengthening, so the weld metal contains one or more of them, and the total amount (Nb+Ti+V+Al) is set to 0.005% or more.

[0255] The lower limit of the total amount of Nb, Ti, V, and Al (Nb+Ti+V+Al) in the weld metal is preferably 0.010%, 0.020%, 0.050%, 0.100%, 0.300%, or 0.500%.

[0256] On the other hand, the upper limit of the total amount of Nb, Ti, V and Al (Nb+Ti+V+Al) in the weld metal is not particularly limited, but is preferably 2.000%, 1.800%, 1.500% or 1.300% in order to prevent deterioration of toughness due to excessive precipitation.

[0257] (fcc ratio obtained by magnetic induction method)

[0258] In order to improve the low temperature toughness of the weld metal, it is preferred to increase the proportion of austenite in the structure of the weld metal. Therefore, it is preferred to set the fcc ratio in the weld metal to 70% or more. The fcc ratio is more preferably 80% or more, or 90% or more, and may also be 100%. It should be noted that the remainder of the structure is bcc.

[0259] The fcc ratio in the structure of the weld metal can be obtained by the following method.

[0260] A sample was collected from the weld metal, and the bcc ratio (%) was measured on the sample surface by magnetic induction method using FERITSCOPE (registered trademark) FMP30 (manufactured by Fischer Instruments Co., Ltd.) and the probe of the measuring instrument was a probe (FGAB 1.3-Fe) manufactured by Fischer Instruments Co., Ltd., and the arithmetic mean of the measured bcc ratios was calculated. Using the obtained average value of the bcc ratio, the fcc ratio (%) in the structure of the weld metal was calculated by the following formula.

[0261] fcc ratio = 100 - bcc ratio

[0262] (tensile strength)

[0263] The tensile strength of the weld metal is preferably set to, for example, 590 to 1200 MPa. The tensile strength can be measured by performing a tensile test on the weld metal in accordance with JIS Z3111:2005.

[0264] <Welded joints and welded structures>

[0265] Next, the welded joint and welded structure of the present disclosure will be described.

[0266] The welded joint of the present disclosure has the weld metal of the present disclosure. For example, the welded joint of the present disclosure includes a steel material as a base material and a weld portion composed of the weld metal and a weld heat-affected zone.

[0267] Furthermore, the welded structure of the present disclosure has the welded joint of the present disclosure.

[0268] The welded joint of the present disclosure has the weld metal of the present disclosure and is therefore inexpensive and excellent in low-temperature toughness.

[0269] Here, a method for manufacturing a welded joint according to the present disclosure will be described.

[0270] It should be noted that the manufacturing method described below is an example, and the method for manufacturing the welded joint of the present disclosure is not limited to the following method.

[0271] The welded joint of the present disclosure can be manufactured by welding using a steel material that is a base material of the welding material.

[0272] For example, the method for manufacturing a welded joint disclosed herein can be obtained by gas-shielded arc welding a steel material using a flux-cored welding wire. In this case, the chemical composition of the weld metal includes components derived from the flux-cored welding wire as a welding material and the steel material as a base material.

[0273] In addition, the manufacturing method of the welded joint disclosed in the present invention can be obtained by performing submerged arc welding using a solid welding wire and a flux. For example, in submerged arc welding, the following general submerged arc welding equipment can be applied: a granular flux is pre-spread on a welding wire, a solid welding wire is fed therein, and welding is performed in the flux by arc heat generated by an arc between the solid welding wire and a steel material. In this case, the chemical composition of the weld metal includes components derived from the solid welding wire and the flux as welding materials, and the steel material as a base material.

[0274] In addition, the manufacturing method of the welded joint disclosed in the present invention is obtained by welding methods such as coated arc welding, simplified gas shielded arc welding, electroslag welding, TIG welding, and gas shielded welding using a solid wire. In this case, the chemical composition of the weld metal includes components derived from the welding material and the steel material as the base material.

[0275] The base material of the welded joint disclosed herein, that is, the steel material (welded material) used in the above-mentioned method for manufacturing the welded joint is not particularly limited in type, but for example, Ni-based low-temperature steel containing 6 to 9% Ni and having a plate thickness of 20 mm or more can be preferably used.

[0276] Example

[0277] Next, the feasibility and effects of the present disclosure are further described in detail through the present disclosure examples and comparative examples, but the following embodiments do not limit the present disclosure, and design changes based on the above and the following gist are included in the technical scope of the present disclosure.

[0278] The weld metal is obtained by the method described below using shielded metal arc welding (SMAW) using a coated electrode, gas metal arc welding (GMAW) using a flux-cored wire, and submerged arc welding (SAW) using a solid wire and flux.

[0279] <1. SMAW (SmAW) using coated electrodes>

[0280] (Manufacture of coated welding rods)

[0281] The coated welding electrode is manufactured by the method described below.

[0282] First, a flux having the composition shown in Table 2-C was applied to a core having the chemical composition shown in Table 2-A and Table 2-B, and the flux was fired at a temperature range of 300 to 500°C for 1 to 3 hours to produce a coated electrode. The obtained coated electrode had a final electrode diameter of φ6.0 mm and an average thickness of the flux of 1.0 mm. The structures of these coated electrodes (Nos. 1 to 3, 15, A1, A4) are shown in Tables 2-A to 2-C.

[0283] The units of the contents of the chemical components of the welding core shown in Table 2-A and Table 2-B are "mass % relative to the total mass of the welding core". In addition, the units of the contents of the components (oxides, fluorides and metal carbonates) of the flux shown in Table 2-C are "mass % relative to the total mass of the flux".

[0284] "TiO2" shown in Table 2-C represents the total of TiO2 conversion values ​​of Ti oxide, "SiO2" represents the total of SiO2 conversion values ​​of Si oxide, "Al2O3" represents the total of Al2O3 conversion values ​​of Al oxide, "MgO" represents the total of MgO conversion values ​​of Mg oxide, "Na2O" represents the total of Na2O conversion values ​​of Na oxide, and "K2O" represents the total of K2O conversion values ​​of K oxide.

[0285] The remainder of the core weld shown in Table 2-A and Table 2-B (that is, components other than the components shown in the tables) is iron and impurities.

[0286] In Table 2-A to Table 2-C, blank columns in the table concerning the chemical composition of the solder core and the content of the components of the flux mean that the content of the components is less than the effective digit. These components may be inevitably mixed or generated at a content less than the effective digit.

[0287] (Manufacture of welded joints)

[0288] Using the obtained coated electrodes (Nos. 1 to 3, 15, A1, A4), coated arc welding was performed by vertical welding to produce welded joints with weld metal. As the steel plate to be welded, 9% Ni steel (steel plate in accordance with JIS G3127: 2013SL9N590) with a plate thickness of 50 mm was used. The welding current during welding was all set to AC, and the welding conditions were set to the conditions of "coated arc welding (SMAW)" described in Table 5.

[0289] The chemical compositions of the weld metals in the produced welded joints are shown in Tables 1-A to 1-C (Nos. 1 to 3, 15, A1, A4). In Tables 1-A to 1-C, numerical values ​​outside the range specified in the present disclosure are underlined.

[0290] <2. Gas shielded arc welding (GMAW) using flux-cored wire>

[0291] (Manufacturing of flux-cored welding wire)

[0292] The flux-cored welding wire is produced by the method described below.

[0293] First, a steel strip is conveyed in the longitudinal direction while being formed using a forming roll to obtain a U-shaped open tube. Flux is supplied into the open tube through the opening of the open tube, and the opposite edges of the opening of the open tube are butt-welded to obtain a seamless steel tube. The seamless steel tube is drawn to obtain a flux-cored wire without a slit-like gap.

[0294] In this way, a flux-cored welding wire having a final wire diameter of φ1.2 mm was produced by trial.

[0295] It should be noted that during the drawing process of these flux-cored welding wires, the flux-cored welding wires were annealed at a temperature range of 650 to 950°C for more than 4 hours. After the trial production, a lubricant was applied to the surface of the welding wire. The composition (chemical composition of the entire welding wire, composition of the flux) of these flux-cored welding wires (No. 4 to 9, A2) is shown in Table 3-A to Table 3-C.

[0296] The units of the contents of the chemical components of the entire welding wire and the contents of the components of the flux (oxides and fluorides) shown in Tables 3-A to 3-C are "mass % relative to the total mass of the flux-cored welding wire." In the table, "the chemical components of the entire welding wire" refer to "the chemical components of the welding wire excluding oxides and fluorides."

[0297] The remainder of the chemical composition of the entire welding wire shown in Table 3-A and Table 3-B (that is, components other than the components shown in the tables) is iron and impurities.

[0298] Each element contained in the flux-cored welding wire shown in Table 3-A and Table 3-B is in the form of a steel sheath or metal powder.

[0299] In Table 3-A to Table 3-C, blank columns in the table related to the chemical composition of the entire welding wire and the content of the components of the flux mean that the content of the components is less than the effective number. These components may inevitably be mixed or generated at a content less than the effective number.

[0300] (Manufacture of welded joints)

[0301] Using the obtained flux-cored wire (No. 4 to 9, A2), a welded joint with weld metal was manufactured by gas shielded arc welding by vertical upward welding. As the steel plate to be welded, a 9% Ni steel with a plate thickness of 50 mm (steel plate in accordance with JIS G3127SL9N590) was used. The type of welding gas during welding was set to Ar-20% CO2 gas. The welding current during welding was all set to direct current, and the polarity of the welding wire was all set to positive. The welding conditions were set to the conditions of "flux-cored wire (GMAW)" recorded in Table 5.

[0302] The chemical components of the weld metals in the manufactured welded joints are shown in Tables 1-A to 1-C (Nos. 4 to 9, A2). In Tables 1-A to 1-C, numerical values ​​outside the range specified in the present disclosure are underlined.

[0303] <3. Submerged Arc Welding (SAW) using solid wire and flux>

[0304] (Manufacturing of solid welding wire)

[0305] The solid welding wire is produced by the method described below.

[0306] First, steel having the chemical composition shown in Table 4-A and Table 4-B was melted and then forged. Then, the steel was processed into a rod shape by rolling, and the rod-shaped steel was drawn to obtain a solid welding wire. In this way, solid welding wires (Nos. 10 to 14, 16 to 17, A3, and A5) with a final wire diameter of φ2.4 mm were trial-produced.

[0307] It should be noted that the chemical composition of the obtained solid wire was analyzed and the results showed that the solid wire had the chemical composition shown in Table 4-A and Table 4-B. After the trial production, a lubricant was applied to the surface of the wire.

[0308] The units of the contents of the chemical components of the welding wires shown in Table 4-A and Table 4-B are "mass % relative to the total mass of the solid welding wire."

[0309] The remainder of the welding wire shown in Table 4-A and Table 4-B (that is, components other than the components shown in the tables) is iron and impurities.

[0310] In Table 4-A and Table 4-B, blank columns in the table related to the content of chemical components of welding wires mean that the content of the chemical components is less than the effective digit. These chemical components may inevitably be mixed or generated at a content less than the effective digit.

[0311] (Manufacture of welded joints)

[0312] The obtained solid welding wires (Nos. 10 to 14, 16 to 17, A3, and A5) were used to perform submerged arc welding downward to produce welded joints having weld metal. Specifically, submerged arc welding was performed using the solid welding wires in combination with NITTETSU FLUX 10H manufactured by NIPPONSTEEL WELDING & ENGINEERING Co., Ltd. as a submerged arc welding flux.

[0313] As the steel plate to be welded, a 9% Ni steel (steel plate in accordance with JIS G 3127SL9N590) with a plate thickness of 40 mm was used. The welding current during welding was all set to direct current, and the polarity of the welding wire was all set to positive. The welding conditions were set to the "submerged arc welding (SAW)" conditions described in Table 5.

[0314] The chemical compositions of the weld metals in the produced welded joints are shown in Tables 1-A to 1-C (Nos. 10 to 14, 16 to 17, A3, A5). In Tables 1-A to 1-C, numerical values ​​outside the range specified in the present disclosure are underlined.

[0315] <Evaluation Test>

[0316] (Evaluation of Low Temperature Toughness)

[0317] Three impact test specimens (V-notch test specimens with a notch depth of 2 mm) were collected from the center in the plate thickness direction of the weld metals (Nos. 1 to 17, A1 to A5) obtained in the disclosed examples and comparative examples.

[0318] The three impact test pieces were subjected to a Charpy impact test at -196°C in accordance with JIS Z2242:2005.

[0319] Then, the average value of the Charpy absorbed energy at -196°C of the three impact test pieces was set as "excellent" when it was 34 J or more, "acceptable" when it was 27 J or more and less than 34 J, and "unacceptable" when it was less than 27 J.

[0320]

[0321]

[0322]

[0323]

[0324]

[0325]

[0326]

[0327]

[0328]

[0329]

[0330]

[0331] Table 5

[0332]

[0333] Table 6

[0334] serial number distinguish Low temperature toughness 1 This disclosure example qualified 2 This disclosure example excellent 3 This disclosure example qualified 4 This disclosure example qualified 5 This disclosure example excellent 6 This disclosure example qualified 7 This disclosure example excellent 8 This disclosure example qualified 9 This disclosure example excellent 10 This disclosure example excellent 11 This disclosure example excellent 12 This disclosure example qualified 13 This disclosure example qualified 14 This disclosure example excellent 15 This disclosure example excellent 16 This disclosure example qualified 17 This disclosure example qualified A1 Comparative Example Failure A2 Comparative Example Failure A3 Comparative Example Failure A4 Comparative Example Failure A5 Comparative Example Failure

[0335] It was found that the weld metal of the disclosed example was excellent in low temperature toughness.

[0336] On the other hand, since the comparative examples did not satisfy any of the requirements specified in the present disclosure, the low-temperature toughness was unacceptable.

Claims

1. A weld metal having the chemical composition, expressed in mass % relative to the total mass of the weld metal, of: C：0.030～1.000％、 Si: 0.03-0.50%, Mn: 4.1-30.0%, P：0～0.050％、 S：0～0.050％、 Cu: 0-5.0%, Ni: 1.0-30.0%, Cr：0～20.0％、 Mo: 0-10.0%, Nb: 0~1.000%, V：0～1.00％、 Co: 0-1.00%, Pb: 0~1.00%, Sn: 0~1.00%, W：0～20.0％、 Mg: 0-5.0%, Al：0～0.100％、 Ca: 0-5.0%, Ti: 0~0.100%, B：0～0.5000％、 REM: 0~0.500%、 Zr：0～0.500％、 N：0～0.5000％、 O: 0.0010 to 0.1500%, and The rest: Fe and impurities, and the total of the Mn content and the Ni content (Mn+Ni) is 5.0% or more, The total of the Nb content, the Ti content, the V content, and the Al content (Nb+Ti+V+Al) is 0.005% or more.

2. The weld metal according to claim 1, wherein: The total of the Mn content, the Ni content, and the Cr content (Mn+Ni+Cr) is 15.0% or more.

3. The weld metal according to claim 1 or claim 2, wherein: The fcc ratio determined by the magnetic induction method is 70% or more.

4. The weld metal according to any one of claims 1 to 3, wherein The mass ratio of the Mn content to the Ni content (Ni / Mn) is 0.10 or more.

5. The weld metal according to claim 4, wherein: The mass ratio (Ni / Mn) is 1.00 or more.

6. The weld metal according to any one of claims 1 to 5, wherein The content of Ti is Ti: 0.003-0.100%.

7. The weld metal according to any one of claims 1 to 6, wherein The C content is C: 0.110-1.000%.

8. A welded joint comprising the weld metal according to any one of claims 1 to 7.

9. A welded structure comprising the welded joint according to claim 8.

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