Wire for gas shielded arc welding, and gas shielded arc welding method
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-01-21
- Publication Date
- 2026-08-13
Smart Images
Figure JP2026001802_13082026_PF_FP_ABST
Abstract
Description
Gas shielded arc welding wire and gas shielded arc welding method
[0001] This invention relates to a gas shielded arc welding wire used for welding steel structures in a low-temperature environment of -25°C. Furthermore, this invention relates to a gas shielded arc welding method for steel materials using this gas shielded arc welding wire.
[0002] Gas shielded arc welding is the most widely used welding method among various welding methods, and because it is a highly efficient welding method, it is widely used for welding steel materials in shipbuilding, construction, bridges, automobiles, and other applications. In particular, for welding steel structures such as warehouses used at low temperatures of -25°C, excellent low-temperature toughness of the weld metal is required, and research is being conducted on solid wires used for welding.
[0003] Patent Document 1 discloses a solid wire applicable to carbon steel pipes with a strength of American Petroleum Institute API grade X65 (YS: 450 MPa, 65 kPa) or less. Specifically, according to the technology of Patent Document 1, sufficient strength and good toughness at -5°C can be obtained by adjusting the amount of Si and Mn added to this wire, and the amount of Ti and B added, and by adjusting the amount of oxygen in the weld metal.
[0004] Furthermore, Patent Document 2 discloses a solid wire applicable to all-position circumferential welding of carbon steel pipes. Specifically, Patent Document 2 discloses a solid wire for gas shielded arc welding in which various alloying elements such as Si, Mn, Ti, Ni, and B are added to the wire, resulting in good arc stability, low spatter generation, and consequently, a weld metal with high strength and excellent low-temperature toughness.
[0005] However, the method described in Patent Document 1 cannot ensure excellent low-temperature toughness at -25°C. Furthermore, in the method described in Patent Document 2, although the weldability improves as the proportion of carbon dioxide, the active gas component, increases, when a mixed gas of 30% or more carbon dioxide and the remainder being an inert gas is used to improve welding efficiency, excellent low-temperature toughness at -25°C cannot be ensured.
[0006] Japanese Patent Publication No. 2002-18591 Japanese Patent Publication No. 2023-150153
[0007] As described above, the technologies described in Patent Documents 1 and 2 had the problem of not being able to ensure excellent low-temperature toughness at -25°C.
[0008] The present invention aims to provide a gas-shielded arc welding wire (e.g., a solid wire) that can ensure excellent low-temperature toughness of the weld metal in a low-temperature environment of -25°C, and can also be used with a shielding gas consisting of 100% by volume of carbon dioxide, or a mixed gas consisting of 30% or more by volume of carbon dioxide and the remainder being an inert gas, and a gas-shielded arc welding method using the same. Here, excellent low-temperature toughness of the weld metal means that the absorbed energy in a Charpy impact test of the center of the weld metal is 47 J or more at a test temperature of -25°C. The Charpy impact test can be measured by the method described in the examples below.
[0009] The inventors of the present invention investigated a solid wire capable of ensuring sufficient low-temperature toughness of the weld metal at -25°C in gas shielded arc welding using 100% by volume of carbon dioxide, or a mixed gas of 30% or more by volume of carbon dioxide with the remainder being an inert gas, as the shielding gas.
[0010] As a result, it was found that the amount of oxygen in the weld metal changes depending on the volume percentage of carbon dioxide in the shielding gas. Furthermore, by controlling the content of Al, Ti, and REM, which promote the crystallization of oxides, and Si and Mn, which promote amorphous formation, to the range of the present invention shown in Figure 1 in accordance with the volume percentage of carbon dioxide, it was found that the crystalline phase 7 and amorphous phase 6 of the oxide coexist, as shown in Figure 2. Here, the range of the present invention shown in Figure 1 refers to the shaded area in Figure 1.
[0011] The present invention promotes the formation of an acetal ferrite structure by controlling the appropriate amounts of crystalline phase 7 and amorphous phase 6. If the area falls outside the range 8 of the present invention shown in Figure 1 (i.e., the shaded area in Figure 1), the area percentage of the acetal ferrite structure 9 (see Figure 3) is less than 60 area%, or the acetal ferrite structure 9 is not formed. Figure 3 shows an example of the microstructure of the weld metal of the present invention, and the inventors have found that the desired low-temperature toughness can be obtained when the acetal ferrite structure 9 is 60 area% or more. On the other hand, if the acetal ferrite structure 9 in the weld metal is less than 60 area%, or if the acetal ferrite structure 9 is not formed, the area percentage of the low-toughness grain boundary ferrite structure 10 or bainite structure increases, and as a result, the desired low-temperature toughness cannot be obtained. The area percentage of the acetal ferrite structure can be measured by the method described in the examples below.
[0012] This invention was completed based on the above findings and further investigations.
[0013] The inventors of the present invention investigated a solid wire that can obtain sufficient low-temperature toughness at -25°C in gas shielded arc welding using a shielding gas consisting of 100% by volume of carbon dioxide, or a mixed gas consisting of 30% or more by volume of carbon dioxide and the remainder being an inert gas.
[0014] First, we focused on the composition of the solid wire (i.e., the welding wire) and investigated controlling the proportion of carbon dioxide in the shielding gas after incorporating the deoxidizing elements Si, Mn, Al, Ti, and REM into the composition. As a result, we found that a fine acicular ferrite structure is formed in the weld metal when the value of α in the following equation (1) is between 0.5 and 3.0. α = [Al] × [Ti] × [REM] × 10 ４ / ([Si]×[Mn]×GI / 10 ２ ) ... (1) Here, GI in equation (1) is the volume percentage of carbon dioxide in the shielding gas, and [Al], [Ti], [REM], [Si], and [Mn] are the mass percentages of each element.
[0015] In other words, the gist of this invention is as follows: [1] A gas shielded arc welding wire that uses a shielding gas of 100 volume% carbon dioxide, or a mixed gas consisting of 30 volume% or more carbon dioxide and the remainder being an inert gas, wherein the gas shielded arc welding wire has a chemical composition by mass% containing: C: 0.01 to 0.10%, Si: 0.60 to 1.20%, Mn: 1.40 to 2.40%, P: 0.020% or less, S: 0.020% or less, Cr: 0.05 to 0.60%, Mo: 0.02 to 0.60%, Al: 0.010 to 0.050%, Ti: 0.050 to 0.400%, REM: 0.010 to 0.060%, O: 0.010% or less, N: 0.010% or less, with the remainder being Fe and unavoidable impurities, Furthermore, a gas shielded arc welding wire in which the value of α in the following equation (1) is 0.5 to 3.0: α = [Al] × [Ti] × [REM] × 10 ４ / ([Si]×[Mn]×GI / 10 ２ ) ... (1) Here, in formula (1), [Al], [Ti], [REM], [Si], and [Mn] are the mass %) content of each element, and GI is the volume %) of carbon dioxide in the shielding gas. [2] The chemical composition further contains one or more selected by mass %) from: Cu: 0.60% or less, Ni: 3.00% or less, Nb: 0.05% or less, V: 0.10% or less, B: 0.007% or less, Ca: 0.003% or less, Sn: 0.30% or less, Pb: 0.30% or less, the gas shielded arc welding wire according to [1] above. [3] The gas shielded arc welding wire according to [1] or [2] above, wherein the value of β in the following formula (2) is 0.15 to 0.60. β = [Mo] + 50 × [B] ... (2) Here, [Mo] and [B] in equation (2) are the mass %) of each element, and if the element is not present, the content is set to 0. [4] A gas shielded arc welding method for welding steel materials with positive polarity using a gas shielded arc welding wire described in any one of [1] to [3] above.
[0016] According to the present invention, in gas shielded arc welding using a shielding gas consisting of 100% by volume of carbon dioxide, or a mixed gas consisting of 30% or more by volume of carbon dioxide and the remainder being an inert gas, it is possible to provide a gas shielded arc welding wire and a gas shielded arc welding method using the same that can ensure sufficient low-temperature toughness of the weld metal at -25°C. This will bring about significant industrial benefits.
[0017] Figure 1 is a schematic diagram showing a preferred range of α in equation (1) of the present invention. Figure 2 is a schematic diagram showing differences in the crystalline form of oxides at a specific α. Figure 3 is an example of the microstructure of the weld metal of the present invention. Figure 4 is a schematic cross-sectional view showing an example of groove shape in a gas shielded arc welding method using the welding wire of the present invention. Figure 5 is a schematic cross-sectional view showing an example of the specimen sampling position for a Charpy impact test. Figure 6 is a schematic diagram showing an example of weaving welding.
[0018] One embodiment of the present invention will be described below. The following description illustrates preferred embodiments of the present invention, and the invention is not limited thereto. First, the reasons for limiting the constituent elements of the present invention will be explained.
[0019] In the gas shielded arc welding according to the present invention, considering the ease of welding and economic efficiency, a shielding gas consisting of 100% by volume of carbon dioxide, or a mixed gas consisting of 30% or more by volume of carbon dioxide and the remainder being an inert gas, is used. Preferably, a shielding gas consisting of 50% or more by volume of carbon dioxide and the remainder being an inert gas is used.
[0020] [Welding Wire] Next, we will explain the reasons for the limitations on the welding wire composition. Note that the unit of element content in the chemical composition is "mass percent". Hereafter, unless otherwise specified, it will simply be shown as "%".
[0021] [Basic Chemical Composition] The gas shielded arc welding wire according to the present invention (which may also be simply referred to as "welding wire" in this specification) has the following basic chemical composition: C: 0.01-0.10%, Si: 0.60-1.20%, Mn: 1.40-2.40%, P: 0.020% or less, S: 0.020% or less, Cr: 0.05-0.60%, Mo: 0.02-0.60%, Al: 0.010-0.050%, Ti: 0.050-0.400%, REM: 0.010-0.060%, O: 0.010% or less, N: 0.010% or less, with the remainder being Fe and unavoidable impurities. Furthermore, the value of α in the following formula (1) is 0.5-3.0. α = [Al] × [Ti] × [REM] × 10 ４ / ([Si]×[Mn]×GI / 10 ２ ) ... (1) Here, in equation (1), [Al], [Ti], [REM], [Si], and [Mn] are the mass %) of each element, and GI is the volume %) of carbon dioxide in the shielding gas. The volume %) of carbon dioxide in the shielding gas to be substituted for GI is a value in the range of 30 to 100 volume%.
[0022] The reasons for limiting the chemical composition of the welding wire according to the present invention are explained below.
[0023] [C: 0.01-0.10%] Carbon (C) is an element that contributes to improving the strength of the weld metal, and a C content of 0.01% or more is necessary to ensure the strength of the weld metal. On the other hand, if the C content exceeds 0.10%, the weld metal hardens and its toughness decreases. For this reason, the C content is limited to 0.10% or less. The C content is preferably 0.02% or more, and more preferably 0.03% or more. The C content is preferably 0.09% or less, and more preferably 0.08% or less.
[0024] [Si: 0.60-1.20%] Si acts as a deoxidizing element, combining with oxygen introduced into the weld metal to form amorphous oxides. To obtain such an effect, a Si content of 0.60% or more is required. On the other hand, if the Si content exceeds 1.20%, the toughness deteriorates, so the Si content is limited to 1.20% or less. The Si content is preferably 0.63% or more, and more preferably 0.68% or more. The Si content is preferably 1.10% or less, and more preferably 1.00% or less.
[0025] [Mn: 1.40-2.40%] Mn acts as a deoxidizing element, combining with oxygen introduced into the weld metal to form amorphous oxides. To obtain such an effect, a Mn content of 1.40% or more is required. On the other hand, if the Mn content exceeds 2.40%, the strength of the weld metal becomes too high, causing cold cracking. Therefore, the Mn content is limited to 1.40-2.40%. The Mn content is preferably 1.50% or more, and more preferably 1.60% or more. The Mn content is preferably 2.20% or less, and more preferably 2.10% or less.
[0026] [P: 0.020% or less] P is an unavoidable element that is mixed in and reduces the toughness of the weld metal and induces hot cracking, so it is preferable to reduce it as much as possible, but a P content of 0.020% or less is acceptable. For this reason, the P content is limited to 0.020% or less. However, excessive reduction of the P content leads to a surge in refining costs, so it is preferable to adjust the P content to 0.002% or more. The P content is more preferably 0.003% or more, and even more preferably 0.004% or more. The P content is more preferably 0.015% or less, and even more preferably 0.013% or less.
[0027] [S: 0.020% or less] S is an element that inevitably gets mixed in and induces hot cracking, so it is preferable to reduce it as much as possible, but an S content of 0.020% or less is acceptable. For this reason, the S content is limited to 0.020% or less. However, excessive reduction of the S content leads to a surge in refining costs, so it is preferable to adjust the S content to 0.001% or more. The S content is more preferably 0.002% or more, and even more preferably 0.004% or more. The S content is more preferably 0.015% or less, and even more preferably 0.012% or less.
[0028] [Cr: 0.05-0.60%] Cr is an element that improves the strength and toughness of the weld metal and has the effect of suppressing coarse grain boundary ferrite, requiring a Cr content of 0.05% or more. On the other hand, if the Cr content exceeds 0.60%, the strength becomes too high, the weld metal hardens, and the toughness decreases. For this reason, the Cr content is limited to 0.05-0.60%. The Cr content is preferably 0.06% or more, and more preferably 0.08% or more. The Cr content is preferably 0.55% or less, and more preferably 0.50% or less.
[0029] [Mo: 0.02-0.60%] Mo is an element that improves the strength and toughness of weld metal and has the effect of suppressing coarse grain boundary ferrite, requiring a Mo content of 0.02% or more. On the other hand, if the Mo content exceeds 0.60%, the strength becomes too high, the weld metal hardens, and the toughness decreases. For this reason, the Mo content is limited to 0.02-0.60%. The Mo content is preferably 0.03% or more, more preferably 0.05% or more. The Mo content is preferably 0.55% or less, more preferably 0.50% or less.
[0030] [Al: 0.010-0.050%] Al acts as a deoxidizing element, combining with oxygen in the weld metal to form crystalline oxides. To obtain such an effect, an Al content of 0.010% or more is required. On the other hand, if the Al content exceeds 0.050%, the amorphous phase in the oxide disappears, and all of it becomes crystalline oxide, inhibiting the formation of crystalline ferrite. As a result, toughness decreases. For this reason, the Al content is limited to 0.010-0.050%. The Al content is preferably 0.012% or more, and more preferably 0.015% or more. The Al content is preferably 0.045% or less, and more preferably 0.040% or less.
[0031] [Ti: 0.050-0.400%] Ti acts as a deoxidizing element, combining with oxygen in the weld metal to form crystalline oxides. To obtain such an effect, a Ti content of 0.050% or more is required. On the other hand, if the Ti content exceeds 0.400%, the amorphous phase in the oxide disappears, and all of it becomes crystalline oxide, inhibiting the formation of crystalline ferrite. As a result, toughness decreases. For this reason, the Ti content is limited to 0.050-0.400%. The Ti content is preferably 0.080% or more, and more preferably 0.100% or more. The Ti content is preferably 0.350% or less, and more preferably 0.300% or less.
[0032] [REM (Rare Earth Elements): 0.010-0.060%] REM acts as a deoxidizing element, combining with oxygen in the weld metal to form oxides in the crystalline phase. REM is also an effective element for refining inclusions during steelmaking and casting, and for improving the toughness of the weld metal. Furthermore, in positive polarity carbon dioxide shielded arc welding, REM is an essential element for refining droplets and stabilizing their transfer. This refinement and stabilization of droplet transfer suppresses spatter generation and enables stable gas shielded arc welding. To obtain such effects, a REM content of 0.010% or more is required.
[0033] On the other hand, if the REM content exceeds 0.060%, the amorphous phase in the oxide disappears, and the oxide becomes entirely crystalline, inhibiting the formation of crystalline ferrite. As a result, toughness decreases. For this reason, the REM content was limited to 0.010 to 0.060%. The REM content is preferably 0.015% or more, and more preferably 0.020% or more. The REM content is preferably 0.050% or less, and more preferably 0.045% or less.
[0034] Here, REM is a collective term for elements belonging to Group 3 of the periodic table. In this invention, it is preferable to use elements with atomic numbers 57 to 71, and Ce and La are particularly preferred. Ce or La may be included alone or in combination. Therefore, the REM content refers to the total content of these elements.
[0035] [O (Oxygen): 0.010% or less] O (oxygen) is an element that inevitably gets mixed in and reduces the processability of the wire, so it is preferable to reduce it as much as possible, but an O content of 0.010% or less is acceptable. However, excessive reduction of the O content will lead to a rise in refining costs, so it is preferable to adjust the O content to 0.001% or more. The O content is more preferably 0.001% or more, and more preferably 0.002% or more. The O content is preferably 0.008% or less, and even more preferably 0.006% or less.
[0036] [N: 0.010% or less] N is an element that is inevitably mixed in and reduces the toughness of the weld metal, so it is preferable to reduce it as much as possible, but an N content of 0.010% or less is acceptable. However, excessive reduction of the N content leads to a rise in refining costs, so it is preferable to adjust the N content to 0.001% or more. The N content is more preferably 0.002% or more, and more preferably 0.003% or more. The N content is preferably 0.009% or less, and even more preferably 0.008% or less.
[0037] [α: 0.5-3.0] CO in shielding gas ２acts as an active gas and introduces O (oxygen) into the weld metal. This O (oxygen) combines with Si, Mn, Al, Ti, and REM, which are deoxidizing elements contained in the wire, to form oxides. In order to form an acicular ferrite structure from these oxides, it is essential to use oxides containing a crystalline phase and an amorphous phase, and it is necessary to control the content of each deoxidizing element. As shown in Fig. 1, Fig. 2, etc., when the value of α represented by the formula (1) is less than 0.5, it becomes all amorphous phase 6, while when α exceeds 3.0, it becomes all crystalline phase 7 oxides. Therefore, α is limited to 0.5 to 3.0. α is more preferably 0.6 or more, and even more preferably 0.7 or more. α is more preferably 2.8 or less, and even more preferably 2.5 or less. α = [Al] × [Ti] × [REM] × 10 ４ / ([Si] × [Mn] × GI / 10 ２ ) ··· (1) Here, [Al], [Ti], [REM], [Si], and [Mn] in the formula (1) are the contents (mass%) of each element, and GI is the volume% of carbon dioxide gas in the shielding gas.
[0038] [Optional Composition] In addition to the above-described basic chemical composition, the welding wire according to the present invention can contain, as an optional composition, one or more selected from the following: Cu: 0.60% or less, Ni: 3.00% or less, Nb: 0.05% or less, V: 0.1% or less, B: 0.007% or less, Ca: 0.003% or less, Sn: 0.30% or less, Pb: 0.30% or less, as required. By controlling the content of these compositions, more excellent properties can be obtained. Note that Cu, Ni, Nb, V, B, Ca, Sn, and Pb can be contained as required, so the content of each element may be 0%.
[0039] [Cu: 0.60% or less] Cu is an element that increases the strength of the weld metal, and if Cu is included, a content of 0.02% or more is preferable. On the other hand, if Cu is included in a content exceeding 0.60%, red-hot brittleness will be observed in the temperature range around 1100°C, inducing cracking of the weld bead surface. Therefore, if Cu is included, the Cu content is preferably 0.60% or less. Cu may be directly incorporated into the welding wire or incorporated as a Cu plating. The Cu content is more preferably 0.01% or more, and even more preferably 0.05% or more. The Cu content is more preferably 0.50% or less, and even more preferably 0.45% or less.
[0040] [Ni: 3.00% or less] Ni is an element that increases the strength of the weld metal without reducing its toughness, and if Ni is included, a content of 0.02% or more is preferable. On the other hand, if the Ni content exceeds 3.00%, the strength of the weld metal becomes too high and cold cracking occurs. Therefore, if Ni is included, the Ni content is preferably 3.00% or less. The Ni content is more preferably 0.02% or more, and even more preferably 0.05% or more. The Ni content is more preferably 2.80% or less, and even more preferably 2.70% or less.
[0041] [Nb: 0.05% or less] Nb is an element that precipitates fine carbides and increases the strength of the weld metal, and if Nb is included, a content of 0.01% or more is preferable. On the other hand, if Nb is included in a content exceeding 0.05%, the toughness of the weld metal decreases. Therefore, if Nb is included, the Nb content is preferably 0.05% or less. The Nb content is more preferably 0.01% or more, and even more preferably 0.02% or more. The Nb content is more preferably 0.04% or less.
[0042] [V: 0.10% or less] V is an element that precipitates fine carbides and increases the strength of the weld metal. When V is contained, it is preferably contained at 0.01% or more. On the other hand, when V is contained in excess of 0.10%, the toughness of the weld metal is decreased. Therefore, when V is contained, the V content is preferably 0.10% or less. The V content is more preferably 0.01% or more, and even more preferably 0.02% or more. The V content is more preferably 0.05% or less, and even more preferably 0.04% or less.
[0043] [B: 0.007% or less] B is an element that improves the hardenability of the weld metal and has the effect of suppressing the formation of grain boundary ferrite by segregating at the austenite grain boundary. In order to obtain such an effect, when B is contained, B is preferably contained at 0.001% or more. On the other hand, when B is contained in excess of 0.007%, hard martensite is formed in the weld metal. Therefore, when B is contained, the B content is preferably 0.007% or less. The B content is more preferably 0.001% or more, and even more preferably 0.002% or more. The B content is more preferably 0.006% or less, and even more preferably 0.005% or less.
[0044] [Ca: 0.003% or less] When Ca is contained, it combines with S in the welding wire to form spherical CaS, improving the wire drawing property of the welding wire. In order to obtain such an effect, when Ca is contained, Ca is preferably contained at 0.001% or more. On the other hand, when Ca is contained at 0.003% or more, it segregates at the grain boundary and causes embrittlement. Therefore, when Ca is contained, the Ca content is preferably 0.003% or less. The Ca content is more preferably 0.001% or more, and more preferably 0.002% or less.
[0045] [Sn: 0.30% or less] Sn has the effect of improving the corrosion resistance of the weld metal, and if Sn is included, a content of 0.01% or more is preferable. On the other hand, if Sn is included in amounts exceeding 0.30%, it induces hot cracking. Therefore, if Sn is included, the Sn content is preferably 0.30% or less. The Sn content is more preferably 0.01% or more, and even more preferably 0.02% or more. The Sn content is more preferably 0.25% or less, and even more preferably 0.20% or less.
[0046] [Pb: 0.30% or less] Pb has the effect of improving the machinability of weld metal, and if Pb is included, a content of 0.01% or more is preferable. On the other hand, if Pb is included in amounts exceeding 0.30%, it induces hot cracking. Therefore, if Pb is included, the Pb content is preferably 0.30% or less. The Pb content is more preferably 0.01% or more, and even more preferably 0.02% or more. The Pb content is more preferably 0.25% or less, and even more preferably 0.20% or less.
[0047] Furthermore, in order to improve the toughness of the weld metal, it is useful to suppress coarse grain boundary ferrite and improve the area ratio of the acicular ferrite structure. To suppress grain boundary ferrite, it is preferable to include Mo and B, which have a high suppressive effect, and it is preferable to set the value of β, expressed in the following formula (2), to 0.15 or higher. On the other hand, if β exceeds 0.60, the hardenability becomes too high and the toughness deteriorates, so it is preferable to set the value of β to 0.60 or lower. More preferably β is 0.18 or higher, and even more preferably 0.20 or higher. More preferably β is 0.55 or lower, and even more preferably 0.50 or lower. β = [Mo] + 50 × [B] ... (2) Here, [Mo] and [B] in formula (2) are the content (mass%) of each element, and if the element is not contained, the content is set to 0.
[0048] [Remainder Composition] The remainder of the chemical composition other than that described above consists of Fe and unavoidable impurities. Examples of unavoidable impurities include H, Mg, Zn, Re, Co, As, Sb, and Bi, and their total content is acceptable as long as it is 0.1000% or less. In addition, other elements may be included as long as they satisfy the basic composition and selective composition described above, and such embodiments are also included within the technical scope of the present invention.
[0049] [Method for Manufacturing Welding Wire] Next, the method for manufacturing the welding wire of the present invention will be described.
[0050] First, molten steel having the above-mentioned chemical composition is produced using a converter or electric furnace, etc. The method for producing this molten steel is not limited to any particular technology, but uses conventionally known technologies.
[0051] Next, the obtained molten steel is used to manufacture steel materials (e.g., billets) by continuous casting or ingot forming. After heating these steel materials, they are subjected to hot rolling and then dry cold rolling (i.e., wire drawing) to produce steel wires. The steel wires have a wire diameter of φ: 0.8 to 1.6 mm. The operating conditions for hot rolling and cold rolling are not limited to specific conditions, but are acceptable as long as they produce steel wires of the desired dimensions and shape.
[0052] Furthermore, the steel wire undergoes the processes of annealing, pickling, copper plating, wire drawing, and lubricant application in sequence as needed to produce the predetermined product, i.e., welding wire. In this invention, it is not always necessary to copper plate the steel wire; welding wire with lubricant applied to the surface of the steel wire can be used without any problems.
[0053] Furthermore, in order to ensure stable adhesion of lubricant to the surface of the steel wire and improve the stability of power supply, it is preferable to set the flatness of the steel wire to 1.0005 or more and less than 1.0100. This flatness can be calculated as "flatness = actual surface area / theoretical surface area". The flatness of the steel wire can be maintained within the range of 1.0005 or more and less than 1.0100 by strictly controlling the dies used in the wire drawing process.
[0054] When copper plating is applied to the surface of steel wire, applying a copper plating thickness of 0.2 μm or more can prevent arc instability caused by poor power supply to the welding wire. Furthermore, a copper plating thickness of 0.4 μm or more is even more preferable, as it significantly enhances the effect of preventing power supply failure. This thicker copper plating also reduces wear on the power supply tip.
[0055] However, if the Cu content of the welding wire, including the Cu content in the steel wire, exceeds 0.60%, the toughness of the weld metal decreases significantly. Therefore, it is preferable to keep the Cu content of the welding wire (i.e., the sum of the Cu content of the steel wire and the Cu content of the copper plating) below 0.60%.
[0056] To improve the feeding of the welding wire, lubricating oil may be applied to the surface of the welding wire (i.e., the surface of the steel wire or the copper-plated surface). The amount of lubricating oil applied is preferably in the range of 0.35 to 1.70 g per 10 kg of welding wire.
[0057] Furthermore, various impurities adhere to the surface of the welding wire during the manufacturing process. In particular, suppressing the amount of solid impurities to 0.01 g or less per 10 kg of welding wire further improves the stability of power supply.
[0058] [Gas Shielded Arc Welding Method] The gas shielded arc welding method of the present invention is a method of welding steel materials using the welding wire manufactured as described above, using the shielding gas described later, and with positive polarity. As described above, during the welding, the value of α in equation (1) is controlled to satisfy conditions of 0.5 to 3.0.
[0059] [Shielding Gas] As the shielding gas, a shielding gas consisting of 100% by volume of carbon dioxide, or a mixed gas consisting of 30% or more by volume of carbon dioxide and the remainder being an inert gas, is used. If the carbon dioxide content is less than 30% by volume, welding workability is poor, and the amount of oxygen introduced into the weld metal is small, resulting in insufficient oxide formation for acicular ferrite formation. As described above, preferably, a shielding gas consisting of 50% or more by volume of carbon dioxide and the remainder being an inert gas is used.
[0060] Furthermore, gas shielded arc welding can be performed without any problems even when carbon dioxide is used alone as a shielding gas (i.e., a carbon dioxide mixture ratio of 100% by volume).
[0061] The remaining inert gas is preferably Ar or He gas, or a mixture thereof.
[0062] The preferred flow rate of the shielding gas is 10 to 50 L / min.
[0063] [Wire Polarity] In this invention, it is preferable to set the wire polarity to negative, i.e., positive, when performing gas shielded arc welding. The welding wire of this invention contains REM, and by setting the wire polarity to positive, spray transfer is performed more effectively, and the arc becomes stable, enabling deep penetration welding. Note that a positive wire polarity is equivalent to a negative wire polarity or a positive base metal polarity.
[0064] [Other Welding Conditions] Other main welding conditions are as follows: ・Welding current I: 150 to 400 A ・Welding voltage V: 20 to 45 V (Note that the voltage increases with the current) ・Welding speed S: 10 to 80 cm / min ・Wire protrusion length L: 15 to 40 mm ・Wire diameter φ: 0.8 to 1.6 mm ・Welding heat input Q: 5 to 100 kJ / cm It is preferable to control the welding conditions within the above range.
[0065] Gas shielded arc welding can be performed without problems under these welding conditions. In particular, when the thickness of the base material (steel) exceeds 15 mm, it is preferable to perform multi-layer welding. The number of layers depends on conditions such as the plate thickness, but it is preferable to have up to 10 layers on each side (i.e., 10 layers or less). Also, the number of passes is preferably in the range of 1 to 4 passes per layer.
[0066] In addition to the V-groove shown in Figure 4, other groove shapes such as L-grooves, X-grooves, K-grooves, and I-grooves are also acceptable. For V-grooves and X-grooves, the preferred groove angle θ is 0 to 60°, while for I-grooves, there is no groove angle.
[0067] If the thickness of the base material (steel) exceeds 30 mm, the groove shape may be an X groove and double-sided welding may be performed.
[0068] At least one layer of the weld metal in the above multilayer structure may be weaving welded. Here, weaving weld refers to a welding technique in which the torch 11 used in gas metal arc welding is moved left and right relative to the weld line (i.e., the center position in the groove width direction) while advancing in the welding direction (in Figure 6, the direction perpendicular to the plane of the paper), as shown in Figure 6 for example. The weaving width W for each layer is the root gap G for the first layer, and the distance W between the intersection points of the weld metal surface of the previous layer and both walls of the groove for other layers. The weaving width W refers to the length in the groove width direction of the range in which the torch 11 is moved left and right.
[0069] [Steel Material] This invention relates to steel used in low-temperature environments such as cold storage warehouses at -25°C (JIS G3106:2017) TS level 490-590 MPa (N / mm²). ２ This invention relates to a gas shielded arc welding wire used for welding steel materials of the following class. The thickness of the steel material is preferably in the range of 6 to 100 mm. The thickness is more preferably 9 mm or more.
[0070] The chemical composition of the above base material (steel) contains, for example, C: 0.03 to 0.15%, Si: 0.50% or less, Mn: 0.50 to 2.50%, P: 0.015% or less, and S: 0.010% or less. Furthermore, it is preferable that it also contains Al: 0% to 0.060%, N: 0.001 to 0.010%, and O (oxygen): 0.010% or less. Here, "%" in relation to chemical composition means "mass%". The same applies hereafter unless otherwise specified.
[0071] The chemical composition of the above-mentioned base material preferably further contains one or more elements selected from the following constituent elements, as needed. When these elements are included, one or more elements selected from Cu: 2.00% or less, Ni: 2.00% or less, Cr: 1.00% or less, Mo: 1.00% or less, V: 1.00% or less, Nb: 0.10% or less, Ti: 0.005 to 0.100%, Ca: 0.020% or less, Mg: 0.020% or less, B: 0.0100% or less, and REM: 0.025% or less. Note that Cu, Ni, Cr, Mo, V, Nb, Ti, Ca, Mg, B, and REM can be included as needed, so the content of each element may be 0%.
[0072] Furthermore, the remaining chemical composition of the base material, other than the chemical composition described above, consists of Fe and unavoidable impurities. Examples of these unavoidable impurity elements include Zn, Sn, Sb, As, Pb, and Bi, and their total content is acceptable if it is 0.10% or less.
[0073] The present invention will be described below based on examples. However, the following examples are merely illustrative and intended to provide a more detailed explanation of the present invention, and do not limit the scope of the rights of the present invention.
[0074] In this example, 32 mm thick steel plates with the chemical compositions (steel symbols A, B, C, D) shown in Table 1 were used as the steel material. Elements not listed in Table 1 are Fe and unavoidable impurities. The chemical composition of the steel material was kept within the numerical range described above. Two of these thick steel plates 1 were joined together as shown in Figure 4, with a groove angle θ: 30° and a gap G: 7 mm (V-groove 2). A backing plate 3 with the same chemical composition as the steel material was used on the groove bottom surface, and the two plates were butted together in accordance with JIS Z 3111:2005. Next, the two thick steel plates 1 were joined by gas shielded arc welding under the following welding conditions to create a welded joint.
[0075] The welding wires were prepared by melting steel ingots with the chemical compositions shown in Table 2 (wires No. 1 to 16) and drawing them into wires with a diameter of φ1.2 mm. Elements not listed in Table 2 are Fe and unavoidable impurities, which constitute the remaining chemical composition.
[0076] In each welding test, the steel material used, welding wire, wire polarity, and CO2 in the shielding gas were all considered. ２ The volume percentages are shown in Table 3. All wire polarity was set to negative (positive polarity). Since the steel plate thickness used in this embodiment was 32 mm, multi-layer welding was performed, resulting in eight layers of weld metal. The number of welding passes was one or two for each layer. Here, all eight layers were weaving welded, and the weaving was performed under the welding conditions shown in Table 4. Specifically, the welding current, welding voltage, welding speed, and weaving width W for each layer were as shown in Table 4. Also, as shown in Table 3, the shielding gas was CO. ２ Gas: 20-100% by volume was used, and the gas flow rate was in the range of 10-30 L / min.
[0077] As shown in Figure 5, three Charpy impact test specimens 5 with a v-notch were taken from the center of the weld metal 4 and the center of the base metal 1 in the thickness direction, and the welded joint was evaluated. The evaluation temperature for the Charpy impact test was -25°C. The average value of the absorbed energy of the three Charpy impact test specimens was taken as the absorbed energy of the welded joint. The Charpy impact test was performed in accordance with JIS Z2242:2018.
[0078] Furthermore, for the obtained welded joint, three test specimens were taken from the center of the weld metal 4 and the center of the base metal 1 in the thickness direction for microstructural observation. The microstructural observation surface of each test specimen was etched with nital, and the etched microstructure was observed with an optical microscope (100x magnification). The microstructure images were processed, and the area percentage of the acicular ferrite structure of the three test specimens was measured. The average value was taken as the acicular ferrite area percentage (%) of the welded joint. Note that, unlike the coarse ferrite structure formed at the prior austenite grain boundaries, the fine ferrite structure formed within the grains was identified as the acicular ferrite structure.
[0079] As shown in Tables 2 and 3, the examples of the present invention (joints No. 1 to 12, 20) show that the chemical composition of the welding wire and α in formula (1) are within the scope of the present invention, resulting in good toughness of the weld metal with an absorbed energy of 47 J or more at the evaluation temperature of -25°C in the Charpy impact test.
[0080] In the example of the present invention, joints No. 11 and 12 satisfy the range of welding wire composition and the range of α in equation (1). However, as shown in Table 2, β in equation (2) is 0.14 and 0.73, respectively, which falls outside the above-mentioned range of β (i.e., 0.15 to 0.60), resulting in absorbed energies of 54 J and 49 J, respectively.
[0081] In the examples of the present invention (joints No. 1 to 12, 20), the microstructure of the weld metal all had an area ratio of 70% or more of acicular ferrite structure.
[0082] On the other hand, in comparative examples that fell outside the scope of the present invention, the results were as shown in Tables 2 and 3. In joint No. 13, the Cr in the welding wire composition fell outside the lower limit of the present invention, and the area ratio of the acicular ferrite structure decreased due to the formation of coarse grain boundary ferrite. As a result, the absorbed energy was 32 J, and good toughness could not be obtained.
[0083] In joint No. 14, the Si content of the welding wire composition fell outside the lower limit of the present invention range, resulting in the formation of amorphous oxides and thus the absence of acetal ferrite. Consequently, the absorbed energy was 38 J, and good toughness could not be obtained.
[0084] Furthermore, in joint No. 15, the Al content of the welding wire composition fell outside the upper limit of the present invention range and also outside the upper limit of equation (1) α, thus inhibiting acicular ferrite formation. As a result, the absorbed energy was 11 J, and good toughness could not be obtained.
[0085] Furthermore, the welding wire composition for joints No. 16 to 18 satisfies the scope of the present invention. However, because it falls outside the range of α in equation (1), an appropriate area % of acicular ferrite was not formed. As a result, the absorbed energies were 12 J, 20 J, and 18 J, respectively, and good toughness could not be obtained.
[0086] Furthermore, in joint No. 19, the carbon dioxide content in the shielding gas was less than 20% and 30% by volume, and α in equation (1) fell outside the upper limit of the present invention range, resulting in the absence of an acicular ferrite structure. Consequently, the absorbed energy was 15 J, and good toughness could not be obtained.
[0087]
[0088]
[0089]
[0090]
[0091] 1 Base material (steel) 2 V-groove 3 Backing plate 4 Weld metal 5 Charpy impact test specimen 6 Amorphous phase 7 Crystalline phase 8 Scope of the present invention in formula (1) 9 Asymmetric ferrite structure 10 Grain boundary ferrite structure 11 Torch a Notch position t Plate thickness θ Groove angle G Gap α Numerical value in formula (1) and slope of the line in Figure 1 W Weaving width
Claims
1. A gas shielded arc welding wire that uses a shielding gas of 100% by volume of carbon dioxide, or a mixed gas consisting of 30% or more by volume of carbon dioxide and the remainder being an inert gas, wherein the gas shielded arc welding wire has a chemical composition by mass% containing: C: 0.01 to 0.10%, Si: 0.60 to 1.20%, Mn: 1.40 to 2.40%, P: 0.020% or less, S: 0.020% or less, Cr: 0.05 to 0.60%, Mo: 0.02 to 0.60%, Al: 0.010 to 0.050%, Ti: 0.050 to 0.400%, REM: 0.010 to 0.060%, O: 0.010% or less, N: 0.010% or less, with the remainder being Fe and unavoidable impurities. Furthermore, a gas shielded arc welding wire in which the value of α in the following equation (1) is 0.5 to 3.0: α = [Al] × [Ti] × [REM] × 10 ４ / ([Si]×[Mn]×GI / 10 ２ ) ... (1) Here, in equation (1), [Al], [Ti], [REM], [Si], and [Mn] are the mass %) of each element, and GI is the volume %) of carbon dioxide in the shielding gas.
2. The gas shielded arc welding wire according to claim 1, wherein the chemical composition further contains one or more selected from by mass percent: Cu: 0.60% or less, Ni: 3.00% or less, Nb: 0.05% or less, V: 0.10% or less, B: 0.007% or less, Ca: 0.003% or less, Sn: 0.30% or less, Pb: 0.30% or less.
3. A gas shielded arc welding wire according to claim 1 or 2, wherein the value of β in the following equation (2) is 0.15 to 0.60: β = [Mo] + 50 × [B] ... (2) Here, [Mo] and [B] in equation (2) are the mass %) of each element, and if the element is not contained, the content is set to 0.
4. A gas shielded arc welding method for welding steel materials with positive polarity using a gas shielded arc welding wire according to any one of claims 1 to 3.