JP7743349B2 - Solid wire for gas shielded arc welding - Google Patents

Description

The present invention relates to a solid wire for gas-shielded arc welding, which provides good arc stability in all-position circumferential welding of carbon steel pipes, minimizes spatter generation, produces a good bead shape, is free of welding defects, and produces weld metal with excellent strength and low-temperature toughness.

Gas-shielded arc welding is widely used in a variety of fields. For example, in recent years, the development of offshore natural gas and oil fields has progressed, leading to an increase in the construction of pipelines to transport the produced fluids. For this reason, gas-shielded arc welding, which allows for highly efficient construction and aims to reduce costs, is being used to weld carbon steel pipes.

Pipelines are laid on land, under the sea, in cold regions, and other locations. Because they are used in harsh environments, they require extremely high reliability, and high-quality welds. Regarding the welding of carbon steel pipes that make up such pipelines, for example, Patent Document 1 discloses a solid wire suitable for carbon steel pipes with strengths of API X65 or less. By adjusting the amounts of Si and Mn, Ti, and B in the wire and adjusting the amount of oxygen in the weld metal, sufficient strength and good toughness can be achieved. Patent Document 2 discloses a solid wire suitable for carbon steel pipes with strengths of API X60 or less. By adjusting the amounts of Si, Mn, and Ni in the wire and adjusting the amount of oxygen in the weld metal, sufficient strength and good toughness can be achieved. Patent Document 3 discloses a welding wire suitable for high-tensile steel pipes. From the perspective of ensuring strength, Cr and Mo are essential additive elements, and by adjusting the amounts of Si and Mn, Ti, B, and Ni, the solid wire exhibits good low-temperature toughness.

In recent years, efforts have been made to expand the use of high-tensile steel and increase the diameter of pipelines to improve transportation efficiency during high-pressure operation. This has led to demands for pipeline welds with better mechanical properties than ever before, 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, resulting in an inability to achieve 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, resulting in an inability to achieve 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, preventing consistent low-temperature toughness at temperatures above -40°C. Furthermore, while low-temperature toughness at -60°C is described for the weld metal, there is a problem with significant variation in toughness, making it difficult to consistently achieve low-temperature toughness.

Japanese Patent Application Laid-Open No. 2002-18591 Japanese Patent Application Laid-Open No. 2002-18592 Japanese Patent Application Laid-Open No. 2004-148389

The present invention was made to solve the above problems, and aims to provide a solid wire for gas-shielded arc welding that provides good arc stability in all-position circumferential welding of carbon steel pipes, minimizes spatter generation, produces a good bead shape, is free of welding defects, and produces weld metal with excellent strength and low-temperature toughness.

In order to solve the above-mentioned problems, the inventors conducted detailed research into the chemical composition of a solid wire for gas-shielded arc welding that provides good arc stability, low spatter generation, a good bead shape, prevents welding defects, and produces weld metal with excellent strength and low-temperature toughness when performing all-position circumferential gas-shielded arc welding of carbon steel pipes.

The gist of the present invention resides in a solid wire for gas-shielded arc welding, characterized in that it comprises a steel wire containing, 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: over 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, and the balance being Fe and impurities.

The solid wire for gas-shielded arc welding to which the present invention is applied provides good arc stability in all-position circumferential welding of carbon steel pipes, reduces spatter generation, produces a good bead shape, is free of welding defects, and produces weld metal with excellent strength and low-temperature toughness.

FIG. 1 is a diagram showing the groove shape of a test piece when conducting welding workability and weld metal tests.

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

[C: 0.01-0.12%]
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%.

[Si: 0.2 to 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 be insufficiently deoxidized, resulting in a decrease in the low-temperature toughness of the weld metal. 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%.

[Mn: 1.0 to 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, increasing the strength of the weld metal and decreasing the low-temperature toughness. Therefore, the Mn content is set to 1.0 to 1.9%.

[Ti: 0.01 to 0.15%]
Ti has the effect of deoxidizing and forming fine Ti oxides in the weld metal, which act as nuclei for the formation of acicular ferrite, thereby improving toughness. 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 exceeds 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%.

[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, the Ni content is set to 0.7% to 1.2%.

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

[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%.

[P: 0.015% or less]
P is one of the main elements that cause hot cracking in weld metal, and is an impurity contained in trace amounts in raw materials. If P is contained in excess, hot cracking will occur. Therefore, the P content is set to 0.015% or less.

[Mo: 0.1% or less]
Mo may be added because it has the effect of increasing 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.

[Cr: 0.1% or less]
Cr 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 arc will become unstable. Therefore, the Cr content is set to 0.1% or less.

[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 Al is added in excess, the amount of spatter generated increases. Therefore, the Al content is set to 0.1% or less.

[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.

[Cu: 0.4% or less]
In gas-shielded arc welding solid wires, copper plating is often applied 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, if the Cu content is excessive, hot cracking occurs. Therefore, the Cu content is set to 0.4% or less.

[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.

Other elements such as Zr and Ca may be added. Zr is preferably 0.01% or less from the perspective of weld metal strength. Ca is preferably 0.01% or less from the perspective of arc stability.

The balance of this invention is Fe and impurities. Impurities are components contained in raw materials or components mixed in during the manufacturing process, but are not intentionally included in the solid wire.

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.

The shielding gas used during welding can be any known shielding gas. For example, it is preferable to use a mixed gas of Ar-5 to 20% by volume of _CO2 in order to reduce the amount of oxygen in the weld metal.

The effects of the present invention will be specifically explained below using examples.

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

The experimental solid wires shown in Table 1 were used to evaluate the welding workability and mechanical performance of the weld metal in all-position girth welding of carbon steel pipes.

Weldability and weld metal tests were conducted after automatic welding of steel pipes specified in API X80 with the groove shape shown in Figure 1 under the welding conditions shown in Table 2.

The welding workability was evaluated by visually inspecting the arc stability, spatter generation, and bead shape during automatic steel pipe welding using the methods described below. The presence or absence of weld cracks was also examined using the methods described below.

(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.

(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.

(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.

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

Weld metal testing was performed by taking tensile test pieces and impact test pieces from the center of the weld metal after the steel pipe was automatically welded. In addition, before taking each test piece, an X-ray examination was performed on the weld metal to check for the presence of weld defects.

(Welding defects)
An X-ray transmission test was carried out in accordance with JIS Z3104 to check for the presence or absence of welding defects such as slag inclusion.

(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 plate thickness direction, and mechanical tests were carried out.

The tensile test evaluation showed that a tensile strength of 700 to 800 MPa was considered good.

A Charpy impact test (vE-40) was conducted at -40°C for impact evaluation, with a rating of good if the average absorbed energy of three repeated tests was 160J or more. A Charpy impact test (vE-60) was also conducted at -60°C, with a rating of good if the average absorbed energy of three repeated tests was 130J or more.

These results are summarized in Table 3. If all evaluation items were good or better, the overall evaluation was marked with a ○; if even one item was not good, an × was marked.

In Table 3, wire symbols W1 to W11 are examples of the present invention, while wire symbols W12 to W26 are comparative examples. The wire symbols W1 to W11, which are examples of the present invention, had appropriate amounts of C, Si, Mn, Ti, Ni, B, S, P, Mo, Cr, Al, Nb, Cu, and V in total mass of solid wire for gas-shielded arc welding. As a result, these examples of the present invention had stable arcs, good spatter generation, good bead shapes, no weld defects, and no weld cracks. Furthermore, these examples of the present invention had good mechanical properties, such as tensile strength and absorbed energy, of the weld metal, with the absorbed energy being particularly good.

In the comparative example, wire symbol W12 had a low carbon content, resulting in low tensile strength of the weld metal, unstable arcs, and a large amount of spatter, resulting in a poor result. Also, because of the low nickel content, the weld metal had low absorbed energy at -40°C and -60°C. Furthermore, because of the low sulfur content, the bead was convex, resulting in a poor bead shape.

Wire symbol W13 has a high carbon content, which means the weld metal has high tensile strength, low absorbed energy at -40°C and -60°C, and hot cracking occurred.

Wire symbol W14 has a low Si content, so the absorbed energy of the weld metal at -40°C and -60°C was low. Also, because it has a high B content, the tensile strength of the weld metal was high, resulting in hot cracking.

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

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. Also, because it had a high P content, hot cracking occurred.

Wire symbol W17 has a high Mn content, which means the weld metal has high tensile strength and low absorbed energy at -40°C and -60°C. Also, because it has a high Cu content, high-temperature cracking occurred.

Wire symbol W18 has a low Ti content, so the weld metal had low absorbed energy at -40°C and -60°C.

Wire symbol W19 has a high Ti content, which means the weld metal has high tensile strength and low absorbed energy at -40°C and -60°C.

Wire symbol W20 has a high Ni content, which means the weld metal has high tensile strength, low absorbed energy at -40°C and -60°C, and hot cracking occurred.

Wire symbol W21 has a low B content, so the weld metal had low absorbed energy at -40°C and -60°C.

Wire symbol W22 contains a high amount of Mo, so the absorbed energy of the weld metal at -40°C and -60°C was low.

Wire symbol W23 contains a high amount of Cr, so the weld metal absorbed less energy at -40°C and -60°C, resulting in an unstable arc.

Wire symbol W24 contains a high amount of Al, resulting in high tensile strength of the weld metal, low absorbed energy at -40°C and -60°C, and a large amount of spatter, resulting in a defective weld.

Wire symbol W25 contains a high amount of Nb, so the weld metal absorbed low energy at -40°C and -60°C, resulting in a large amount of spatter and a poor result.

Wire symbol W26 contains a high amount of V, which means the weld metal has high tensile strength and low absorbed energy at -40°C and -60°C.

Claims (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.