Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

• This disclosure relates to welded metals, welded joints, and welded structures.
• Patent Document 1 describes a welding material with a Ni content of 70% as follows: "Ni content is 35 to 70%, and the flux contains TiO 2 , SiO 2 and ZrO 2 in a total amount of 4.0 mass% or more with respect to the total mass of the wire, and further contains Mn oxides in an amount of 0.6 to 1.2 mass% calculated as MnO 2 , and when the contents of TiO 2 , SiO 2 , ZrO 2 and MnO 2 (converted amounts) are [TiO 2 ], [SiO 2 ], [ZrO 2 ] and [MnO 2 ], respectively, the ratio [TiO 2 ]/[ZrO 2 ] is 2.3 to 3.3, the ratio [SiO 2 ]/[ZrO 2 ] is 0.9 to 1.5, and ([TiO 2 ] + [SiO 2 ] + [ZrO 2 ])/[MnO 2 ] is 5-13.
• austenitic welding materials have traditionally been used to obtain weld metals with excellent low-temperature toughness.
• austenitic welding materials have the property of being prone to high-temperature cracking. For this reason, there is a demand for weld metals that suppress the occurrence of high-temperature cracking.
• the objective of this disclosure is to provide a weld metal in which the occurrence of hot cracks is suppressed, a weld joint having the weld metal, and a welded structure having the weld joint.
• the means for solving the problems include the following aspects. ⁇ 1>
• the chemical composition is expressed as mass% relative to the total mass of the weld metal.
• C 0.20-0.80%, Si: 0.03-0.50%, Mn: 5.1 to 20.0%, P: 0 to 0.050%, S: 0 to 0.050%, Cu: 0 to 5.0%, Ni: 6.0 to 20.0%, Cr: 0-10.0%, Mo: 0-10.0%, Nb: 0 to 5.00%, V: 0-5.00%, Ta: 0-5.000%, Hf: 0-5.000%, Ti: 0 to 5.00%, Zr: 0-5.000%, Co: 0 to 1.0%, Pb: 0 to 1.0%, Sn: 0 to 1.0%, W: 0 to 5.0%, Mg: 0 to 0.10%, Al: 0.001-0.100%, Ca: 0-5.00%, B: 0 to 0.500%, REM: 0-0.500%, N: 0 to 0.500%, O: 0.00
• ⁇ 3> The weld metal according to ⁇ 1> or ⁇ 2>, comprising at least two elements selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr, each in the above-mentioned content.
• ⁇ 4> The weld metal according to any one of ⁇ 1> to ⁇ 3>, wherein the fcc content determined by a magnetic induction method is 70 volume% or more.
• ⁇ 5> A welded joint having the weld metal according to any one of ⁇ 1> to ⁇ 4>.
• ⁇ 6> A welded structure having the weld joint according to ⁇ 5>.
• the present disclosure provides a weld metal in which the occurrence of hot cracks is suppressed, a weld joint having the weld metal, and a welded structure having the weld joint.
• FIG. 2 is a schematic cross-sectional view showing a base material having a groove used in the examples.
• FIG. 1 is a schematic cross-sectional view for explaining a test device for a FISCO cracking test.
• FIG. 1 is a schematic cross-sectional view for explaining a test device for a FISCO cracking test.
• FIG. 1 is a schematic cross-sectional view showing a welded joint sample for explaining high-temperature cracking that occurs in a weld metal portion in a FISCO cracking test.
• the weld metal according to an embodiment of the present disclosure has a predetermined chemical composition and contains at least one element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr in the content described below.
• the weld metal according to the present disclosure has the above-described configuration, which suppresses the occurrence of hot cracks. 0060
• austenitic welding materials have been used as welding materials that can produce weld metal with excellent low-temperature toughness, for example, in steels containing 6-9% Ni used for LNG tanks.
• austenitic welding materials have the characteristic of being prone to hot cracking. This is thought to be because austenitic welding materials solidify in the gamma phase (face-centered cubic lattice fcc), causing severe solidification segregation of P, S, C, and Si, etc., which results in a lower melting point of the liquid phase in the (gamma phase + liquid phase) state, and tensile stress due to solidification shrinkage is applied to the liquid phase, causing hot cracking.
• gamma phase face-centered cubic lattice fcc
• the inventors have focused on the crystallization of carbides in the liquid phase as a method for increasing the melting point of the liquid phase during solidification.
• the melting point of the liquid phase can be lowered by solidification segregation occurring as the solidification of the weld metal progresses.
• This liquid phase contains concentrated P, S, C, and Si, and by crystallizing carbides in this liquid phase, the C concentration in the liquid phase can be significantly reduced. As a result, the melting point of the liquid phase increases, and it is believed that hot cracking is suppressed.
• the weld metal according to the embodiment of the present disclosure is configured to contain at least one element selected from the group consisting of Ti, Zr, V, Hf, Nb, and Ta, which are elements that easily form carbides, in a predetermined content, respectively.
• the weld metal contains a predetermined amount of at least one element selected from the group consisting of Ti, Zr, V, Hf, Nb, and Ta, the C concentration in the liquid phase decreases due to the crystallization of carbides, and the melting point of the liquid phase increases, suppressing hot cracking.
• the FISCO cracking test specified in JIS Z 3155 (1993) is an example of an indicator of high-temperature cracking, and it is preferable that the cracking rate in the FISCO cracking test for the weld metal according to the embodiment of the present disclosure is 15% or less.
• the chemical composition of the weld metal is: C: 0.20-0.80%, Si: 0.03-0.50%, Mn: 5.1 to 20.0%, P: 0 to 0.050%, S: 0 to 0.050%, Cu: 0 to 5.0%, Ni: 6.0 to 20.0%, Cr: 0-10.0%, Mo: 0-10.0%, Nb: 0 to 5.00%, V: 0-5.00%, Ta: 0-5.000%, Hf: 0-5.000%, Ti: 0 to 5.00%, Zr: 0-5.000%, Co: 0 to 1.0%, Pb: 0 to 1.0%, Sn: 0 to 1.0%, W: 0 to 5.0%, Mg: 0 to 0.10%, Al: 0.001-0.100%, Ca: 0-5.00%, B: 0 to 0.500%, REM: 0-0.500%, N: 0 to 0.500%, O: 0.001 to 0.150%, and the balance: Fe and impurities;
• the alloy further contains at least one element selected
• C is an element that improves the strength of the weld metal and ensures the strength of the weld metal.
• the C content of the weld metal is set to 0.20 to 0.80%.
• the lower limit of the C content of the weld metal may preferably be 0.22%, 0.25%, 0.27%, 0.30%, 0.32%, 0.35%, 0.37%, or 0.40%.
• the upper limit of the C content of the weld metal is preferably 0.75%, 0.70%, 0.65%, 0.60%, 0.55%, or 0.50%.
• Silicon is a deoxidizing element. If the silicon content of the weld metal is too low, the oxygen content of the weld metal increases. On the other hand, Si has a low solid solubility in the austenite phase, and the greater the Si content, the more likely solidification segregation occurs, resulting in hot cracking. Therefore, the Si content in the weld metal is set to 0.03 to 0.50%.
• the lower limit of the Si content in the weld metal is preferably 0.04%, 0.05%, or 0.08%.
• the upper limit of the Si content in the weld metal is preferably 0.48%, 0.45%, 0.40%, 0.35%, 0.30%, or 0.20%.
• Mn is an austenite stabilizing element. If the Mn content in the weld metal is too low, the austenitization of the weld metal is difficult to proceed, and low-temperature toughness is deteriorated. Mn is also an element that functions as a deoxidizer to improve the cleanliness of the weld metal. Mn is also an element that renders S in the weld metal harmless by forming MnS, thereby improving the low-temperature toughness of the weld metal. In addition, Mn has the effect of preventing high-temperature cracking.
• the Mn content of the weld metal is set to 5.1 to 20.0%.
• the lower limit of the Mn content of the weld metal is preferably 5.5%, 5.7%, 6.0%, 7.0%, 8.0%, 9.0%, or 10.0%.
• the upper limit of the Mn content of the weld metal is preferably 19.0%, 18.0%, 17.0%, 15.0%, or 14.5%.
• 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.
• S is an impurity element that promotes hot cracking or reduces toughness, so it is preferable to reduce the S content of the weld metal as much as possible. Therefore, the lower limit of the S content of the weld metal is set to 0%. However, from the viewpoint of reducing the desulfurization cost, the S content of the weld metal should be 0.003% or more. On the other hand, if the S content of the weld metal is 0.050% or less, the adverse effect of S on toughness falls within an allowable range. Therefore, the S content of the weld metal is set to 0 to 0.050%. In order to effectively suppress hot cracking or 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.
• Cu is a precipitation strengthening element and may be contained in the weld metal to improve the strength of the weld metal.
• Cu is also an austenite stabilizing element and may be contained in the weld metal to improve the low temperature toughness of the weld metal.
• the Cu content in the weld metal is set to 0 to 5.0%.
• the lower limit of the Cu content in the weld metal is preferably 0.3%, 0.5%, or 0.7%.
• the upper limit of the Cu content in the weld metal is preferably 4.5%, 4.0%, or 3.5%.
• Ni is an austenite stabilizing element. If the Ni content in the weld metal is too low, the austenitization of the weld metal becomes difficult to proceed, and the low-temperature toughness deteriorates. On the other hand, increasing the Ni content of the weld metal increases the cost of the weld metal. Therefore, the Ni content of the weld metal is set to 6.0 to 20.0%.
• the lower limit of the Ni content of the weld metal is preferably 6.5%, 7.0%, 7.5%, or 8.0%.
• the upper limit of the Ni content in the weld metal is preferably 19.0%, 17.0%, 15.0%, or 13.0%.
• Cr is an austenite stabilizing element and may be contained in the weld metal to improve the low-temperature toughness of the weld metal.
• the Cr content of the weld metal is set to 0 to 10.0%.
• the lower limit of the Cr content of the weld metal is preferably 1.0%, 2.0%, or 3.0%.
• the upper limit of the Cr content of the weld metal is preferably 9.0%, 8.0%, or 7.0%.
• Mo is a precipitation strengthening element and may be contained in the weld metal to improve the strength of the weld metal.
• Mo content in the weld metal is set to 0 to 10.0%.
• the lower limit of the Mo content in the weld metal is preferably 1.0%, 2.0%, or 3.0%.
• the upper limit of the Mo content in the weld metal is preferably 9.0%, 8.0%, or 7.0%.
• 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.
• the Nb content in the weld metal is set to 0 to 5.00%.
• the lower limit of the Nb content of the weld metal is preferably 0.01%, 0.05%, 0.10%, 0.15%, or 0.20%.
• the upper limit of the Nb content of the weld metal is preferably 4.50%, 4.00%, 3.50%, 3.00%, or 2.50%.
• the lower limit of the Nb content in the weld metal is preferably within the range described below.
• 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.
• the V content of the weld metal is set to 0 to 5.00%.
• the lower limit of the V content of the weld metal is preferably 0.01%, 0.05%, 0.10%, 0.15%, or 0.20%.
• the upper limit of the V content of the weld metal is preferably 4.50%, 4.00%, 3.50%, or 3.00%.
• the lower limit of the V content in the weld metal is preferably in the range described below.
• Ta 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.
• the Ta content of the weld metal is set to 0 to 5.000%.
• the lower limit of the Ta content in the weld metal is preferably 0.001%, 0.003%, 0.005%, 0.010%, 0.020%, 0.030%, or 0.050%.
• the upper limit of the Ta content in the weld metal is preferably 4.500%, 4.000%, 3.500%, 3.000%, 2.000%, 1.000%, 0.500%, 0.200%, or 0.100%.
• the lower limit of the Ta content in the weld metal is preferably in the range described below.
• Hf Hf 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.
• the Hf content of the weld metal is set to 0 to 5.000%.
• the lower limit of the Hf content in the weld metal is preferably 0.001%, 0.002%, 0.005%, 0.010%, 0.020%, 0.030%, or 0.040%.
• the upper limit of the Hf content in the weld metal is preferably 4.500%, 4.000%, 3.500%, 3.000%, 2.000%, 1.000%, 0.500%, 0.200%, or 0.100%.
• the lower limit of the Hf content in the weld metal is preferably within the range described below.
• 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.
• the Ti content of the weld metal is set to 0 to 5.00%.
• the lower limit of the Ti content in the weld metal is preferably 0.003%, 0.01%, 0.02%, or 0.03%.
• the upper limit of the Ti content in the weld metal is preferably 4.50%, 4.00%, 3.50%, or 3.00%, 2.00%, or 1.50%.
• the lower limit of the Ti content in the weld metal is preferably in the range described below.
• Zr 0-5.000%
• Zr content of the weld metal is set to 0 to 5.000%.
• the lower limit of the Zr content of the weld metal is preferably 0.003%, 0.01%, 0.02%, or 0.03%.
• the upper limit of the Zr content of the weld metal is preferably 4.50%, 4.00%, 3.50%, or 3.00%, 2.00%, 1.50%, or 1.00%.
• the lower limit of the Zr content in the weld metal is preferably in the range described below.
• Co (Co: 0-1.0%) Co is an element that increases the strength of the weld metal through solid solution strengthening, and therefore may be contained in the weld metal.
• the Co content of the weld metal is set to 0 to 1.0%.
• the lower limit of the Co content in the weld metal is preferably 0.01%, 0.05%, 0.1%, 0.15%, or 0.2%.
• the upper limit of the Co content of the weld metal is preferably 0.95%, 0.9%, 0.85%, or 0.8%.
• Pb 0-1.0%)
• Pb has the effect of improving the toe formability between the base steel material and the weld metal and improving the machinability of the weld metal, and therefore may be contained in the weld metal.
• the Pb content in the weld metal is set to 0 to 1.0%.
• the lower limit of the Pb content of the weld metal is preferably 0.01%, 0.05%, 0.1%, 0.15%, or 0.2%.
• the upper limit of the Pb content of the weld metal is preferably 0.95%, 0.9%, 0.85%, or 0.8%.
• Sn is an element that improves the corrosion resistance of the weld metal and may be contained in the weld metal.
• the Sn content of the weld metal is set to 0 to 1.0%.
• the lower limit of the Sn content in the weld metal is preferably 0.01%, 0.05%, 0.1%, 0.15%, or 0.2%.
• the upper limit of the Sn content of the weld metal is preferably 0.95%, 0.9%, 0.85%, or 0.8%.
• W is a solid solution strengthening element and may be contained in the weld metal to improve strength.
• the W content of the weld metal is set to 0 to 5.0%.
• the lower limit of the W content of the weld metal is preferably 0.1%, 0.2%, 0.5%, 0.8%, or 1.0%.
• the upper limit of the W content of the weld metal is preferably 4.8%, 4.5%, 4.3%, or 4.0%.
• Mg is a deoxidizing element and is effective in reducing oxygen and improving toughness, and therefore may be contained in the weld metal.
• the Mg content in the weld metal is set to 0 to 0.10%.
• the lower limit of the Mg content in the weld metal is preferably 0.005%, 0.01%, 0.02%, 0.03%, or 0.04%.
• the upper limit of the Mg content of the weld metal is preferably 0.09%, 0.08%, 0.07%, or 0.06%.
• Al is a deoxidizing element and is contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal.
• Al content in the weld metal is set to 0.001 to 0.100%.
• the lower limit of the Al content in the weld metal is preferably 0.003%, 0.005%, 0.010%, 0.020%, or 0.030%.
• the upper limit of the Al content of the weld metal is preferably 0.090%, 0.080%, or 0.070%.
• Ca (Ca: 0-5.00%) Ca has the effect of changing the structure of sulfides in the weld metal and of 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, so Ca may be contained in the weld metal.
• the Ca content in the weld metal is set to 0 to 5.00%.
• the lower limit of the Ca content in the weld metal is preferably 0.01%, 0.02%, or 0.03%.
• the upper limit of the Ca content in the weld metal is preferably 4.8%, 4.5%, 4.3%, 4.0%, 3.0%, 2.0%, 1.0%, or 0.5%.
• B is an austenite stabilizing element and an interstitial solid solution strengthening element, and may be contained in the weld metal to improve the low temperature toughness and strength of the weld metal.
• M 23 (C, B) 6 precipitates, causing a deterioration in toughness. Therefore, the B content of the weld metal is set to 0 to 0.5000%.
• the lower limit of the B content of the weld metal is preferably 0.0005%, 0.001%, or 0.002%.
• the upper limit of the B content of the weld metal is preferably 0.480%, 0.450%, 0.430%, 0.400%, 0.300%, 0.200%, 0.100%, or 0.050%.
• REM 0-0.500%
• REM is an element that stabilizes the arc during welding work to obtain the weld metal, and therefore may be contained in the weld metal.
• the REM content of the weld metal is set to 0 to 0.500%.
• the lower limit of the REM content of the weld metal is preferably 0.001%, 0.002%, or 0.005%.
• the upper limit for the REM content of the weld metal is preferably 0.480%, 0.450%, 0.430%, 0.400%, 0.300%, 0.200%, 0.100%, or 0.050%.
• N is an austenite stabilizing element and an interstitial solid solution strengthening element, and may be contained in the weld metal to improve the low temperature toughness and strength of the weld metal.
• the N content of the weld metal is set to 0 to 0.500%.
• the lower limit of the N content of the weld metal is preferably 0.001%, 0.005%, 0.010%, 0.020%, or 0.050%.
• the upper limit of the N content of the weld metal is preferably 0.450%, 0.400%, or 0.350%, 0.300%, 0.200%, or 0.100%.
• O is contained in the weld metal as an impurity.
• the upper limit of the O content in the weld metal is set to 0.150% or less.
• the lower limit of the O content in the weld metal is set to 0.001% or less.
• the lower limit of the O content in the weld metal is preferably 0.002% or 0.003%.
• the upper limit of the O content in the weld metal is preferably 0.130% or 0.100%.
• the remaining components in the chemical composition of the weld metal are Fe and impurities.
• impurities refers to components that are mixed in due to raw materials such as ores or scraps, or various factors in the manufacturing process, when industrially producing weld metal, and are acceptable within a range that does not adversely affect the properties of the weld metal.
• the weld metal contains at least one element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr (hereinafter simply referred to as the "specific element") in the following content:
• the specific element By containing the specific element in the following content, carbides can be crystallized in the liquid phase to reduce the C concentration in the liquid phase, and high-temperature cracking can be suppressed.
• Nb More than 1.00%
• V More than 1.00%
• Ta More than 0.001%
• Hf More than 0.001%
• Ti More than 0.10%
• Zr More than 0.500%
• the lower limit of the Nb content in the weld metal is more than 1.00%.
• the lower limit of the Nb content in the weld metal is preferably 1.10%, 1.20%, 1.30%, or 1.50%.
• the lower limit of the V content in the weld metal is more than 1.00%.
• the lower limit of the V content in the weld metal is preferably 1.10%, 1.20%, 1.30%, 1.50%, 1.80%, or 2.00%.
• the lower limit of the Ta content in the weld metal is 0.001% or more.
• the lower limit of the Ta content in the weld metal is preferably 0.002%, 0.005%, 0.010%, 0.030%, 0.050%, or 0.060%.
• the lower limit of the Hf content in the weld metal is 0.001% or more.
• the lower limit of the Hf content in the weld metal is preferably 0.002%, 0.005%, 0.010%, 0.030%, 0.040%, 0.050%, or 0.060%.
• the lower limit of the Ti content in the weld metal is more than 0.10%.
• the lower limit of the Ti content in the weld metal is preferably 0.11%, 0.13%, 0.20%, 0.30%, 0.50%, 0.80%, or 1.00%.
• the lower limit of the Zr content in the weld metal is more than 0.500%.
• the lower limit of the Zr content in the weld metal is preferably 0.510%, 0.530%, 0.550%, 0.600%, or 0.630%.
• the weld metal preferably contains at least one of Ta and Hf in the following content:
• Ta and Hf which are considered to have a higher carbide forming ability, the formation of carbides is promoted, and as a result, hot cracking can be further suppressed.
• the specific elements i.e., elements selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr
• the inclusion of two or more specific elements promotes the formation of carbides more than the addition of only one of the specific elements at the above content.
• the inclusion of two or more specific elements is thought to lower the activity of the carbide (increase the activity of the carbide-forming element), promoting the reaction.
• Mn and Ni are austenite stabilizing elements that improve the low-temperature toughness of the weld metal.
• Ni is an expensive metal
• the Mn content and Ni content in the weld metal each satisfy the above-mentioned range, and that the sum of the Mn content and Ni content (Mn+Ni) is 11.5% or more, and more preferably 12.0% or more, 13.0% or more, or 15.0% or more.
• the Mn content and the Ni content in the weld metal each satisfy the above-mentioned ranges, and that the sum of the Mn content and the Ni content (Mn + Ni) is 37.0% or less.
• the total content of Mn and Ni in the weld metal (Mn+Ni) is more preferably 35.0% or less, 32.0% or less, or 30.0% or less.
• Mn, Ni, and Cr are each an austenite stabilizing element and improve the low-temperature toughness of the weld metal.
• Ni is an expensive metal, so in order to improve the low-temperature toughness of the weld metal while suppressing the cost of the weld metal, it is preferable that the Mn content, Ni content, and Cr content in the weld metal each satisfy the above-mentioned ranges, and that the total of the Mn content, Ni content, and Cr content (Mn+Ni+Cr) be 15.0% or more.
• the total of the Mn content, Ni content and 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.
• the Mn content is not excessive, the stacking fault energy does not become too low and toughness can be ensured. Furthermore, since 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 prevented from widening, so that the occurrence of hot cracks can be suppressed.
• the Mn content, Ni content, and Cr content in the weld metal each satisfy the above-mentioned range, and the total of the Mn content, Ni content, and Cr content (Mn + Ni + Cr) is 47.0% or less.
• the total content of Mn, Ni and Cr (Mn+Ni+Cr) in the weld metal is more preferably 45.0% or less, 42.0% or less, or 40.0% or less.
• Mn and Ni are each an austenite stabilizing element and improve the low temperature toughness of the weld metal.
• Ni is an expensive metal, and if Mn is excessively increased, the stacking fault energy decreases and the toughness deteriorates. Therefore, from the viewpoint of improving the low-temperature toughness of the weld metal while suppressing the cost of the weld metal, it is preferable that the mass ratio of the Mn content to the Ni content (Ni/Mn) in the weld metal be 0.33 or more.
• the lower limit of the mass ratio (Ni/Mn) of the Mn content to the Ni content in the weld metal is more preferably 0.50, 0.70, 1.00, 1.10, or 1.20.
• the upper limit of the mass ratio (Ni/Mn) of the Mn content to the Ni content in the weld metal is preferably 3.80, 3.50, 3.30, or 3.00.
• the fcc content in the weld metal is 70 volume % or more.
• the fcc content is more preferably 80 volume % or more, or 90 volume % or more, and may be 100 volume %.
• the remainder of the structure is bcc.
• the tensile strength of the weld metal is preferably, for example, 590 to 1200 MPa.
• the tensile strength can be measured by conducting a tensile test on the weld metal in accordance with JIS Z3111:2005.
• the weld joint according to the present disclosure includes the weld metal according to the present disclosure.
• the weld joint according to the present disclosure includes a steel material serving as a base material, and a welded portion including a weld metal and a weld heat affected zone.
• a welded structure according to the present disclosure has the welded joint according to the present disclosure.
• the welded joint according to the present disclosure contains the weld metal according to the present disclosure, and is therefore inexpensive and has excellent low-temperature toughness.
• the welded joint according to the present disclosure can be manufactured by welding the base steel material with a welding material.
• the method of manufacturing a welded joint according to the present disclosure is obtained by gas-shielded arc welding of steel material using a flux-cored wire.
• the chemical components of the weld metal include components derived from the flux-cored wire, which is the welding material, and the steel material, which is the base material.
• the manufacturing method of the welded joint according to the present disclosure is obtained by submerged arc welding using a solid wire and flux.
• a solid wire and flux For example, in submerged arc welding, granular flux is spread on the weld line in advance, a solid wire is fed into it, and welding is performed by the arc heat generated from the arc between the solid wire and the steel material in the flux.
• the chemical components of the weld metal include components derived from the solid wire and flux, which are the welding materials, and the steel material, which is the base material.
• the manufacturing method of the welded joint according to the present disclosure can be obtained by a welding method such as, for example, shielded metal arc welding, simple electrogas arc welding, electroslag welding, TIG welding, and gas shielded welding using a solid wire.
• a welding method such as, for example, shielded metal arc welding, simple electrogas arc welding, electroslag welding, TIG welding, and gas shielded welding using a solid wire.
• the chemical components of the weld metal include components derived from the welding material and the base steel material.
• the base material of the welded joint according to the present disclosure i.e., the type of steel material (welded material) used in the manufacturing method of the welded joint described above, is not particularly limited, but for example, Ni-based low-temperature steel containing 6-9% Ni with a plate thickness of 20 mm or more can be suitably used.
• SAW submerged arc welding
• SMAW shielded metal arc welding
• FCAW gas arc welding using filler metal (Tungsten Inert Gas: TIG ) to obtain the weld metal.
• Submerged arc welding (SAW) using solid wire and flux> Solid wire manufacturing
• the solid wire was manufactured by the method described below. First, the steel was melted and then forged, then rolled into a rod shape, and the rod shape was drawn to obtain a solid wire. In this way, a solid wire with a final wire diameter of ⁇ 2.4 mm was produced. After the production, a lubricant was applied to the wire surface.
• the obtained solid wire was used to perform submerged arc welding to produce a welded joint having a weld metal.
• the solid wire was used in combination with NITTETSU FLUX 10H manufactured by Nippon Steel & Sumitomo Metals Co., Ltd., which is a flux for submerged arc welding, to perform submerged arc welding.
• a steel plate (20 mmt x 120 mmw x 300 mml) having the composition shown in Table 1 was used as the steel plate (base material) to be welded.
• a groove was formed in the base materials 2A and 2B up to half the plate thickness so that the groove angle was 90°.
• the base materials 2A and 2B were butted together with the gap between them adjusted to 1 mm. Single bead welding was performed on these base materials 2A and 2B.
• the welding conditions were the conditions for "submerged arc welding (SAW)" shown in Table 2. In this way, a welded joint having a weld metal was produced.
• the chemical composition of the weld metal was controlled by adjusting the composition of the solid wire.
• the chemical compositions of the weld metal in the produced welded joints are shown in Tables 3-1 to 3-4 (Nos. 1 to 8, 33, 34, and 39).
• Shielded metal arc welding (SMAW) using a shielded metal arc welding electrode> (Manufacture of covered electrodes)
• the covered electrode was manufactured by the method described below. First, a core wire was coated with flux and baked for 1 to 3 hours at a temperature range of 300 to 500° C. to produce a prototype covered metal arc welding rod. The final welding rod diameter of the obtained covered metal arc welding rod was ⁇ 6.0 mm, and the average thickness of the flux was 1.0 mm.
• the resulting covered metal arc welding rod was used to produce a welded joint having a weld metal by covered metal arc welding.
• a steel plate (base material) to be welded a steel plate (20 mmt x 120 mmw x 300 mml) having the composition shown in Table 1 was used.
• a groove was formed in the base materials 2A and 2B up to half the plate thickness so that the groove angle was 90°.
• the base materials 2A and 2B were butted together with the gap between them adjusted to 1 mm.
• Single bead welding was performed on these base materials 2A and 2B.
• the welding conditions were the conditions for "sheathed metal arc welding (SMAW)" shown in Table 2.
• FCAW Flux-cored wire arc welding
• FCAW Manufacturing of flux-cored wire
• the flux-cored wire was produced by the method described below. First, a steel strip was fed in the longitudinal direction and formed into a U-shaped open tube using a forming roll. Flux was supplied into the open tube through the opening of the open tube, and the opposing edges of the opening of the open tube were butt-welded to obtain a seamless tube. This seamless tube was drawn to obtain a flux-cored wire without slit-like gaps. In this manner, a flux-cored wire having a final wire diameter of ⁇ 1.2 mm was produced. During the drawing process, the flux-cored wires were annealed for 4 hours or more within a temperature range of 650 to 950° C. After the prototypes were made, a lubricant was applied to the wire surface.
• the obtained flux-cored wire was used to produce a welded joint having a weld metal by gas-shielded arc welding.
• a steel plate (base material) to be welded a steel plate (20 mmt x 120 mmw x 300 mml) having the composition shown in Table 1 was used.
• a groove was formed in the base materials 2A and 2B up to half the plate thickness so that the groove angle was 90°.
• the base materials 2A and 2B were butted together with the gap between them adjusted to 1 mm.
• Single bead welding was performed on these base materials 2A and 2B.
• the welding conditions were the conditions for "flux-cored wire (FCAW)" shown in Table 2.
• the obtained filler metal (solid wire) was used for welding by gas tungsten arc welding to produce a welded joint having a weld metal.
• a groove was formed in the base materials 2A and 2B up to half the plate thickness so that the groove angle was 90°.
• the base materials 2A and 2B were butted together with the gap between them adjusted to 1 mm. Single bead welding was performed on these base materials 2A and 2B.
• the welding conditions were the conditions for "tungsten arc welding (TIG)" shown in Table 2.
• the unit of the contents of the chemical components of the weld metal shown in Tables 3-1 to 3-4 is "mass % relative to the total mass of the weld metal.”
• the balance of the weld metals shown in Tables 3-1 to 3-4 i.e., components other than those shown in the tables) is iron and impurities.
• the blanks in the tables for the contents of chemical components in the weld metal mean that the contents of the chemical components are less than the significant digits. These chemical components may be unavoidably mixed or generated in amounts less than the significant digits.
• the fcc content in the structure of the weld metal was determined by the following method. First, a sample was taken from the weld metal. The sample was taken from the center of the weld metal so that the base metal was not included. The bcc content (volume%) was measured on the surface of the sample by a magnetic induction method using a FERITSCOPE (registered trademark) FMP30 (manufactured by Fisher Instruments, Inc.) and a Fisher Instruments probe (FGAB 1.3-Fe) as the probe of the measuring instrument.
• FERITSCOPE registered trademark
• FMP30 manufactured by Fisher Instruments, Inc.
• FGAB 1.3-Fe Fisher Instruments probe
• the probe of the FERITSCOPE was placed on the center of the surface cut perpendicular to the longitudinal direction of the weld bead, and on a surface as flat as possible.
• the probe diameter was 7 mm.
• the arithmetic average value of the measured bcc contents was calculated, and the fcc content (volume %) in the structure of the weld metal was calculated using the obtained average bcc content value according to the following formula.
• fcc content rate 100-bcc content rate
• FISCO Cracking Evaluation Method The hot cracking resistance was evaluated for cracking (hot cracking) occurring when solidifying from the liquid phase by carrying out a FISCO cracking test (JIS Z 3155 (1993): "C-type jig restraint butt weld cracking test method" (Method of FISCO test).
• FISCO cracking test JIS Z 3155 (1993): "C-type jig restraint butt weld cracking test method" (Method of FISCO test).
• FISCO cracking test first, two steel plates 10A (base material) were butted together and placed on the rough surface 122 of a C-type jig 12 as shown in FIG. 2A, and the ends of each were fixed with fixing bolts 14. The two steel plates 10A were placed so that the butted parts were located on the non-rough surface part 124 in the center of the rough surface 122.
• the length of cracks occurring in the weld metal portion was measured.
• the weld length was L (mm)
• the total crack length of L was Lc (mm)
• the crack rate R (%) was calculated using the following formula.
• a crack rate R ⁇ 15% was judged as pass, and a crack rate R>15% was judged as fail.
• R Lc/L ⁇ 100(%)

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