Solid wire for gas shielded arc welding

Abstract

To provide a solid wire for gas shielded arc welding that excels in the workability of welding, the strength of weld metal, and low-temperature toughness in the all-attitude circumferential welding of carbon steel pipes.SOLUTION: A solid wire for gas shielded arc welding comprises a steel wire that contains, in mass% based on the total wire mass, C: 0.01-0.12%, Si: 0.2-0.7%, Mn: 1.0-1.9%, Ti: 0.01-0.15%, Ni: 0.7-1.2%, B: 0.0010-0.0050%, S: 0.005-0.02%, P: 0.015% or less, Mo: 0.1% or less, Cr: 0.1% or less, Al: 0.1% or less, Nb: 0.01% or less, Cu: 0.4% or less, V: 0.01% or less, with the balance being Fe and impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solid wire for gas-shielded arc welding, which has good arc stability in all-position girth welding of carbon steel pipes, produces little spatter, provides a good bead shape, is free of welding defects, and produces a weld metal with excellent strength and low-temperature toughness. [Background technology]

[0002] Gas-shielded arc welding is widely used in various fields. For example, in recent years, the development of natural gas and oil fields on the seabed has progressed, and the construction of pipelines to transport the produced fluids has increased. For this reason, gas-shielded arc welding, which allows for highly efficient welding and aims to reduce costs, is being used in welding carbon steel pipes.

[0003] Pipelines are laid on land, under the sea, in cold regions, and other locations, and therefore require extremely high reliability due to the harsh operating environments, and high quality is also required in welds. Regarding the welding of carbon steel pipes that make up such pipelines, for example, Patent Document 1 discloses a solid wire that can be used for carbon steel pipes having a strength of API X65 or less, and that achieves sufficient strength and good toughness by adjusting the amounts of Si and Mn and Ti and B added to the wire and adjusting the oxygen content in the weld metal. Patent Document 2 discloses a solid wire that can be used for carbon steel pipes having a strength of API X60 or less, and that achieves sufficient strength and good toughness by adjusting the amounts of Si and Mn and Ni added to the wire and adjusting the oxygen content in the weld metal. Patent Document 3 discloses a welding wire that can be used for high-tensile steel pipes, and that has Cr and Mo as essential additive elements to ensure strength, and that achieves good low-temperature toughness by adjusting the amounts of Si and Mn and Ti, B, and Ni added.

[0004] In recent years, in order to improve transportation efficiency in high-pressure operation, the expansion of the use of high-tensile steel and the increase in diameter of pipelines have been considered. As a result, pipeline welds are required to have better mechanical properties, particularly excellent low-temperature toughness. The solid wire described in Patent Document 1 has a base metal strength of API X65 or lower and a toughness of 0°C, which results in a problem of insufficient low-temperature toughness at -40°C. The solid wire described in Patent Document 2 has a base metal strength of API X60 or lower and a toughness of -5°C, which results in a problem of insufficient low-temperature toughness at -40°C. Furthermore, the solid wire described in Patent Document 3 adds Mo and Cr to the base metal to ensure weld metal strength so that it can be used with high-strength materials such as API X70 and X80. However, the ranges of Ti, Ni, and B are inappropriate, which results in insufficient low-temperature toughness at temperatures above -40°C. Furthermore, although the low-temperature toughness of the weld metal is described at -60°C, there is a problem of large variations in toughness, which results in insufficient low-temperature toughness being consistently achieved. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-18591 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-18592 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-148389 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to provide a solid wire for gas-shielded arc welding which has good arc stability in all-position circumferential welding of carbon steel pipes, generates little spatter, provides a good bead shape, is free from welding defects, and produces a weld metal with excellent strength and low-temperature toughness. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors have conducted detailed studies on the chemical composition of a solid wire for gas-shielded arc welding that provides good arc stability, a small amount of spatter, a good bead shape, prevents welding defects, and produces a weld metal having strength and excellent low-temperature toughness in all-position circumferential welding of carbon steel pipes using gas-shielded arc welding.

[0008] The gist of the present invention is that a solid wire for gas shielded arc welding contains, in mass % relative to the total mass of the wire, C: 0.01 to 0.12%, Si: 0.2 to 0.7%, Mn: 1.0 to 1.9%, Ti: 0.01 to 0.15%, Ni: 0. Over 9% ~1.2%, B: 0.0010~0.0050%, S: 0.005~0.02%, P: 0.015% or less, Mo: 0.1% or less, Cr: 0.1% or less, Al: 0.1% or less 、 The solid wire for gas-shielded arc welding includes a steel wire containing 0.01% or less of Nb, 0.4% or less of Cu, 0.01% or less of V, and the balance being Fe and impurities. [Effects of the Invention]

[0009] According to the solid wire for gas-shielded arc welding to which the present invention is applied, it is possible to provide a solid wire for gas-shielded arc welding which has good arc stability in all-position girth welding of carbon steel pipes, generates little spatter, obtains a good bead shape, is free from welding defects, and produces a weld metal with excellent strength and low-temperature toughness. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the groove shape of a test piece when conducting a welding workability test and a weld metal test. DETAILED DESCRIPTION OF THE INVENTION

[0011] The solid wire for gas-shielded arc welding of the present invention is made possible by the synergistic effects of each component composition, both alone and in combination, and the reasons for limiting each component composition are described below. The content of each component composition is expressed as mass% relative to the total mass of the solid wire, and the mass% is simply expressed as %.

[0012] [C: 0.01 to 0.12%] C is an element necessary for improving the strength of the weld metal. If the C content is less than 0.01%, sufficient weld metal strength cannot be obtained, and the arc becomes unstable, resulting in increased spatter generation. On the other hand, if the C content exceeds 0.12%, the strength of the weld metal becomes excessively high and low-temperature toughness decreases. Furthermore, if the C content exceeds 0.12%, the cracking sensitivity increases, making weld cracks more likely to occur. Therefore, the C content is set to 0.01 to 0.12%.

[0013] [Si: 0.2-0.7%] Si is added to deoxidize the weld metal and ensure its strength. If the Si content is less than 0.2%, the weld metal will not be sufficiently deoxidized, and the low-temperature toughness of the weld metal will decrease. On the other hand, if the Si content exceeds 0.7%, excessive Si will be retained in the weld metal, increasing the strength of the weld metal and decreasing the low-temperature toughness. Furthermore, if the Si content exceeds 0.7%, the amount of slag generated during welding will increase, causing slag inclusion. Therefore, the Si content is set to 0.2 to 0.7%.

[0014] [Mn: 1.0-1.9%] Mn has the effect of improving the strength and low-temperature toughness of the weld metal. If the Mn content is less than 1.0%, the strength and low-temperature toughness of the weld metal will decrease. On the other hand, if the Mn content exceeds 1.9%, Mn will be excessively retained in the weld metal, which will increase the strength of the weld metal and decrease the low-temperature toughness. Therefore, the Mn content is set to 1.0 to 1.9%.

[0015] [Ti: 0.01~0.15%] Ti has the effect of improving toughness by forming fine Ti oxides in the deoxidizing and weld metal, which act as nuclei for the formation of acicular ferrite. If Ti is less than 0.01%, the formation of acicular ferrite in the weld metal is not promoted, resulting in a decrease in low-temperature toughness. On the other hand, if Ti is more than 0.15%, precipitates such as TiC are formed in the weld metal, which increases the strength of the weld metal excessively and decreases low-temperature toughness. Therefore, the Ti content is set to 0.01 to 0.15%.

[0016] [Ni: 0.7~1.2%] Ni has the effect of improving the low-temperature toughness of the weld metal. If Ni is less than 0.7%, the low-temperature toughness of the weld metal decreases. On the other hand, if Ni exceeds 1.2%, the strength of the weld metal becomes excessively high, the low-temperature toughness decreases, and hot cracking occurs. Therefore, Ni is set to 0.7% to 1.2%.

[0017] [B: 0.001 to 0.0050%] Addition of trace amounts of B has the effect of refining the structure of the weld metal and improving its toughness. If the B content is less than 0.001%, low-temperature toughness decreases. On the other hand, if the B content exceeds 0.0050%, the strength of the weld metal becomes excessively high and hot cracking occurs. Therefore, the B content is set to 0.001 to 0.0050%.

[0018] [S:0.005~0.02%] S changes the flow of molten metal, resulting in a flat bead shape and a good bead shape. If the S content is less than 0.005%, the bead will be convex and the bead shape will be poor. On the other hand, if the S content exceeds 0.02%, hot cracking will occur. Therefore, the S content is set to 0.005 to 0.02%.

[0019] [P:0.015% or less] P is one of the main elements that causes hot cracking in weld metal, and is an impurity contained in trace amounts in raw materials. If excessive P is added, hot cracking will occur. Therefore, the P content should be 0.015% or less.

[0020] [Mo: 0.1% or less] Mo may be added because it has the effect of improving the hardenability of the weld metal and improving its strength, but if added in excess, it reduces the low-temperature toughness of the weld metal and causes the bead to have a convex shape. Therefore, the Mo content is set to 0.1% or less.

[0021] [Cr:0.1% or less] Cr may be added because it has the effect of improving the strength of the weld metal, but if it is added in excess, the low-temperature toughness of the weld metal will decrease and the arc will become unstable. Therefore, the Cr content should be 0.1% or less.

[0022] [Al: 0.1% or less] Al may be added because it has the effect of improving the low-temperature toughness of the weld metal through its deoxidizing effect, but if it is added in excess, the strength of the weld metal increases and the low-temperature toughness decreases. Also, if excessive Al is added, the amount of spatter generated increases. Therefore, the Al content is set to 0.1% or less.

[0023] [Nb:0.01% or less] Nb may be added because it has the effect of improving the strength of the weld metal, but if added in excess, the low-temperature toughness of the weld metal will decrease and the amount of spatter will increase. Therefore, the Nb content is set to 0.01% or less.

[0024] [Cu:0.4% or less] Copper plating is often applied to solid wire for gas shielded arc welding to stabilize wire feedability and current conduction. Therefore, when copper plating is applied, the solid wire contains a certain amount of Cu. On the other hand, excessive Cu content can cause hot cracking. Therefore, the Cu content is set to 0.4% or less.

[0025] [V:0.01% or less] V may be added because it has the effect of improving the strength of the weld metal, but if added in excess, the strength of the weld metal increases and the low-temperature toughness decreases. Therefore, the V content is set to 0.01% or less.

[0026] Other components that may be added include Zr and Ca. From the viewpoint of the strength of the weld metal, Zr is preferably 0.01% or less. From the viewpoint of arc stability, Ca is preferably 0.01% or less.

[0027] The balance of the present invention is Fe and impurities. The impurities are components contained in raw materials or components mixed in during the manufacturing process, but are not intentionally contained in the solid wire.

[0028] The diameter of the solid wire for gas-shielded arc welding of the present invention is not particularly limited, but is, for example, 0.9 to 2.0 mm.

[0029] The shielding gas used during welding may be a known shielding gas, for example, a mixed gas of Ar-5 to 20% by volume of CO2 is preferably used to reduce the amount of oxygen in the weld metal. [Example]

[0030] The effects of the present invention will be specifically explained below with reference to examples.

[0031] The raw steel was vacuum melted, forged, rolled, drawn, annealed, and the wire surface was copper-plated as needed, then finish-drawn to a product diameter of 1.0 mm and wound into a 20 kg spool to be used as a prototype. The chemical composition of the prototype solid wire is shown in Table 1.

[0032] [Table 1]

[0033] Using the prototype solid wires shown in Table 1, the welding workability of all-position girth welding of carbon steel pipes and the mechanical properties of the weld metal were evaluated.

[0034] Welding workability and weld metal tests were carried out using steel pipes specified in API X80 having the groove shape shown in Figure 1, under the welding conditions shown in Table 2, after automatic welding of the steel pipes.

[0035] [Table 2]

[0036] The welding workability was evaluated by visually inspecting the arc stability, spatter generation, and bead shape during automatic welding of steel pipes using the following methods. The presence or absence of weld cracks was also evaluated using the following methods.

[0037] (Arc stability) It is preferable that there is little fluctuation in the length of the arc generated between the wire tip and the steel pipe during welding. When there is little fluctuation in the arc length, it is considered stable, and when there is a lot of fluctuation, it is considered unstable. Arc stability was judged visually during automatic welding of steel pipes.

[0038] (Spatter occurrence status) It is preferable that the amount of spatter generated during welding is small. When the amount of spatter generated during welding was small, it was rated as good, and when the amount of spatter generated was large, it was rated as poor. The spatter generation status was judged visually during automatic welding of the steel pipe.

[0039] (Bead shape) It is preferable that the weld metal bead height is flat and the bead width is uniform. A bead shape in which the weld metal bead height is flat and the bead width is uniform was rated as good, while a bead shape in which the weld metal bead is high and convex and the bead width is uneven was rated as poor. The bead shape was judged visually during automatic welding of the steel pipe.

[0040] (weld cracks) If even one hot crack was found on the bead surface during automatic welding of the steel pipe, it was marked as "present." The presence or absence of hot cracks was determined visually after each welding pass.

[0041] The weld metal tests were carried out by taking tensile test pieces and impact test pieces from the center of the weld metal after automatic welding of the steel pipe. In addition, before taking each test piece, an X-ray examination was carried out on the weld metal to check for the presence of welding defects.

[0042] (welding defects) X-ray examination was conducted in accordance with JIS Z3104 to check for the presence or absence of welding defects such as slag inclusions.

[0043] (mechanical properties) Tensile test (A0 type) and impact test (V-notch test piece) specimens were taken from the center of the weld metal in the thickness direction, and mechanical tests were carried out.

[0044] In the tensile test, a tensile strength of 700 to 800 MPa was considered good.

[0045] For impact testing, a Charpy impact test (vE-40) was conducted at -40°C, and a specimen with an average absorbed energy of 160J or more after three repeated tests was deemed good. A Charpy impact test (vE-60) was also conducted at -60°C, and a specimen with an average absorbed energy of 130J or more after three repeated tests was deemed good.

[0046] These results are summarized in Table 3. If all evaluation items were good or better, the overall evaluation was marked with a circle, and if even one item was not good, it was marked with an X.

[0047] [Table 3]

[0048] In Table 3, wires W1 to W11 are examples of the present invention, and wires W12 to W26 are comparative examples. The wires W1 to W11, which are examples of the present invention, contained appropriate amounts of C, Si, Mn, Ti, Ni, B, S, P, Mo, Cr, Al, Nb, Cu, and V in total mass of the solid wire for gas-shielded arc welding. Therefore, in these examples of the present invention, the arc was stable, spatter generation was good, the bead shape was good, there were no welding defects, and no weld cracks occurred. Furthermore, in these examples of the present invention, the mechanical properties of the weld metal, such as tensile strength and absorbed energy, were good, and the absorbed energy was particularly good.

[0049] The wire W12 in the comparative examples had a low carbon content, resulting in low tensile strength of the weld metal, unstable arc, and a large amount of spatter, resulting in poor results. The wire also had a low nickel content, resulting in low absorbed energy at -40°C and -60°C. Furthermore, the wire had a low sulfur content, resulting in a convex bead, resulting in a poor bead shape.

[0050] Wire symbol W13 has a high carbon content, so the tensile strength of the weld metal is high, the absorbed energy at -40°C and -60°C is low, and high-temperature cracking occurs.

[0051] Wire symbol W14 has a low Si content, so the absorbed energy of the weld metal at -40℃ and -60℃ was low. Also, because it has a high B content, the tensile strength of the weld metal was high, and hot cracking occurred.

[0052] Wire W15 has a high Si content, which results in high tensile strength of the weld metal, low absorbed energy at -40℃ and -60℃, and slag inclusion in the weld. Furthermore, the high S content caused high-temperature cracking.

[0053] Wire symbol W16 had a low Mn content, so the tensile strength of the weld metal was low, and the absorbed energy at -40°C and -60°C was also low. In addition, because it had a high P content, hot cracking occurred.

[0054] Wire symbol W17 has a high Mn content, so the tensile strength of the weld metal was high and the absorbed energy at -40°C and -60°C was low. Also, because it has a high Cu content, hot cracking occurred.

[0055] Wire symbol W18 has a low Ti content, so the absorbed energy of the weld metal at -40°C and -60°C was low.

[0056] Wire symbol W19 has a high Ti content, so the tensile strength of the weld metal was high and the absorbed energy at -40°C and -60°C was low.

[0057] Wire symbol W20 has a high Ni content, so the tensile strength of the weld metal is high, the absorbed energy at -40℃ and -60℃ is low, and high-temperature cracking occurred.

[0058] Wire symbol W21 has a low B content, so the absorbed energy of the weld metal at -40°C and -60°C was low.

[0059] Wire symbol W22 contains a lot of Mo, so the absorbed energy of the weld metal at -40℃ and -60℃ was low.

[0060] Wire symbol W23 contains a lot of Cr, so the absorbed energy of the weld metal at -40℃ and -60℃ was low, resulting in an unstable arc.

[0061] Wire symbol W24 has a high Al content, so the tensile strength of the weld metal is high, the absorbed energy at -40℃ and -60℃ is low, and the amount of spatter generated is large, resulting in a poor result.

[0062] Wire symbol W25 contains a lot of Nb, so the absorbed energy of the weld metal at -40℃ and -60℃ is low, and there is a lot of spatter generated, resulting in a poor result.

[0063] Wire symbol W26 has a high V content, so the tensile strength of the weld metal is high and the absorbed energy at -40℃ and -60℃ is low.

Claims

[Claim 1] A solid wire for gas shielded arc welding used for all-position circumferential welding of steel pipes, In mass % relative to the total mass of the wire, C: 0.01-0.12%, Si: 0.2-0.7%, Mn: 1.0 to 1.9%, Ti: 0.01 to 0.15%, Ni: more than 0.9% to 1.2%; B: 0.0010 to 0.0050%, S: 0.005 to 0.02%; P: 0.015% or less, Mo: 0.1% or less, Cr: 0.1% or less, Al: 0.1% or less, Nb: 0.01% or less, Cu: 0.4% or less, V: 0.01% or less, A solid wire for gas-shielded arc welding comprising a steel wire with the balance being Fe and impurities.

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