JP2024066737A - Solid wire and gas shielded arc welding method - Google Patents

Abstract

The present invention provides a solid wire that can provide a back-shielding surface with excellent appearance and a weld metal with excellent mechanical properties without using a back shielding gas. [Solution] The solid wire is used for welding steel material containing 1% by mass or more and 10% by mass or less of Cr, and contains, in mass % relative to the total mass of the wire, C: 0.05% to 0.15%, Si: 0.8% to 1.7%, Mn: 0.4% to 1.2%, Cr: 7.5% to 13.0%, Mo: 0.70% to 1.5%, Nb: 0.010% to 0.10%, V: 0.10% to 0.50%, N: 0.010% to 0.070%, P: 0.030% or less, S: 0.030% or less, Ni: 0.80% or less, Ti: 0.025% or less, Al: 0.020% or less, Co: 0.70% or less, and the balance being Fe and unavoidable impurities. [Selected Figure] None

Description

The present invention relates to a solid wire and a gas-shielded arc welding method.

In general, steel made by adding Nb, V, etc. to 9Cr-1Mo steel, which contains 8% to 10% by mass of Cr and 0.85% to 1.20% by mass of Mo, is called 9Cr-1Mo-Nb-V steel. Cr-Mo ferritic high-strength heat-resistant steels such as 9Cr-1Mo-Nb-V steel have excellent high-temperature properties and are used in boilers and pressure vessels for thermal and nuclear power plants.

When gas-shielded arc welding steel materials with high Cr content such as those described above to form one-sided butt welded joints, back shielding with inert gas is required for the first layer of welding to prevent poor appearance of the back bead due to the formation of high-melting-point Cr oxides on the back surface. However, continuously flowing back shielding gas from the back side of the steel material increases costs and, when the steel material in question is, for example, pipe material, there are problems in that the work becomes complicated.

Patent Document 1 discloses a welding material that can produce welds with excellent back-sealing and mechanical properties without using back shielding gas. The welding material described in Patent Document 1 has specified contents of C, Cr, Mo, Ni, and Al, and the relationship between the Cr and Mn contents and the Si content, the relationship between the S content and the Mn content, and the total amount of the Al content and the O content are controlled, and the contents of P and S in the impurities are specified.

Japanese Patent Application Laid-Open No. 10-24388

Incidentally, the weld metal of ferritic high-strength heat-resistant steel such as 9Cr-1Mo-Nb-V steel is sometimes subjected to post-weld heat treatment (PWHT) for the purpose of improving toughness, etc. However, the high-temperature transformation temperature (Ac1 transformation point) is not considered in the welding material described in the above-mentioned Patent Document 1, and depending on the PWHT temperature, it may not be possible to ensure the toughness of the weld metal. In addition, there is room for further improvement in the back-strip performance and the mechanical performance of the first layer.

Furthermore, Patent Document 1 does not fully consider the suppression of the formation of δ-ferrite, and in order to form weld metal that is adequate for use in boilers and pressure vessels for thermal and nuclear power plants, it is important to further suppress the formation of δ-ferrite.

The present invention has been made in consideration of the above-mentioned problems, and aims to provide a solid wire and a gas-shielded arc welding method that can be used to weld steel containing 1% to 10% by mass of Cr, and that can produce a back-strip with excellent appearance without using back shielding gas, and can produce a weld metal with excellent mechanical properties.

As a result of intensive research conducted by the inventors to solve the above problems, they discovered that in order to suppress the occurrence of poor formation of the uranami, it is particularly important to control the Si content in the solid wire. Furthermore, they discovered that by controlling the contents of Nb, V, and Co in the solid wire, it is possible to suppress the formation of δ-ferrite and obtain a weld metal with the desired mechanical properties. The present invention was made based on this knowledge.

The above object of the present invention is achieved by the following configuration (1) relating to solid wire.

(1) A solid wire used for welding steel materials containing 1 mass% or more and 10 mass% or less of Cr,
For the total mass of wire,
C: 0.05% by mass or more and 0.15% by mass or less,
Si: 0.8% by mass or more and 1.7% by mass or less,
Mn: 0.4% by mass or more and 1.2% by mass or less,
Cr: 7.5% by mass or more and 13.0% by mass or less,
Mo: 0.70% by mass or more and 1.5% by mass or less,
Nb: 0.010% by mass or more and 0.10% by mass or less,
V: 0.10% by mass or more and 0.50% by mass or less,
N: 0.010% by mass or more and 0.070% by mass or less;
P: 0.030% by mass or less,
S: 0.030% by mass or less,
Ni: 0.80 mass% or less,
Ti: 0.025% by mass or less,
Al: 0.020% by mass or less,
Co: 0.70% by mass or less;
The balance of the solid wire is Fe and unavoidable impurities.

Furthermore, preferred embodiments of the present invention relating to solid wire relate to the following (2) and (3).

(2) Furthermore, with respect to the total mass of the wire,
Zr: 0.10 mass% or less,
The solid wire according to (1), comprising:

(3) Furthermore, with respect to the total mass of the wire,
Cu: 0.50% by mass or less,
The solid wire according to (1) or (2), comprising:

The above object of the present invention is achieved by the following configuration (4) of the gas-shielded arc welding method.

(4) A gas-shielded arc welding method for welding steel containing 1% by mass or more and 10% by mass or less of Cr using a solid wire described in any one of (1) to (3) without using a back shielding gas.

The present invention provides a solid wire that can produce a back-strip with excellent appearance without using back shield gas, and can also produce a weld metal with excellent mechanical properties, as well as a gas-shielded arc welding method that uses this solid wire.

The following is a detailed description of the embodiments for carrying out the present invention. In this specification, solid wire may be simply referred to as "wire." The present invention is not limited to the embodiments described below, and may be modified as desired without departing from the spirit of the present invention.

[Solid wire]
The solid wire according to the present embodiment is used for welding steel materials containing 1% by mass or more and 10% by mass or less of Cr. For example, a combination of 9% Cr steel and 2% Cr steel can be used to form a welded steel material, and the solid wire according to the present embodiment can also be applied to dissimilar material joints. The solid wire according to the present embodiment is particularly preferably used for welding 9Cr-1Mo-Nb-V steel.

Hereinafter, a steel with a Cr content of 8% by mass or more and 10% by mass or less may be referred to as 9% Cr steel. In this embodiment, the shape of the steel material used as the steel material to be welded is not particularly limited, and it can be used, for example, to weld steel plates, steel pipes, etc.

The chemical components contained in the solid wire according to this embodiment are explained in detail below, along with the reasons for their inclusion and the reasons for the numerical limitations.

<C: 0.05% by mass or more and 0.15% by mass or less>
C is an important element that combines with Cr, Mo, V, and Nb to form carbides and ensure the strength of the weld metal. Furthermore, as an austenite-forming element, C contributes to suppressing the formation of δ-ferrite in the weld metal. If the C content relative to the total mass of the wire is less than 0.05 mass%, the desired strength of the weld metal cannot be obtained. Therefore, the C content relative to the total mass of the wire is set to 0.05 mass% or more, preferably 0.06 mass% or more, and more preferably 0.07 mass% or more.
On the other hand, if the C content exceeds 0.15% by mass relative to the total mass of the wire, the solidification temperature of the segregation portion is significantly lowered, and hot cracking is likely to occur. In addition, carbide is excessively precipitated, and the toughness of the weld metal is reduced. Therefore, the C content relative to the total mass of the wire is set to 0.15% by mass or less, preferably 0.14% by mass or less, and more preferably 0.13% by mass or less.

<Si: 0.8 mass% or more and 1.7 mass% or less>
Si has the effect of preferentially forming an oxide film on the uranami surface that has a low melting point and is unlikely to inhibit the solidification of the weld metal, and preventing poor uranami formation due to the oxidation of Cr during welding. If the Si content relative to the total mass of the wire is less than 0.8 mass%, the above effect cannot be sufficiently obtained and the uranami shape deteriorates. Therefore, the Si content relative to the total mass of the wire is set to 0.8 mass% or more, preferably 0.9 mass% or more, and more preferably 1.0 mass% or more.
On the other hand, if the Si content exceeds 1.7 mass% relative to the total mass of the wire, an excessive amount of δ-ferrite is formed in the weld metal, which reduces the toughness of the weld metal. Also, the amount of slag generated in the surface bead increases, which makes slag inclusion more likely to occur. Therefore, the Si content relative to the total mass of the wire is set to 1.7 mass% or less, preferably 1.6 mass% or less, and more preferably 1.5 mass% or less.

<Mn: 0.4 mass% or more and 1.2 mass% or less>
Mn functions as a deoxidizer for the weld metal, and is an element that has the effect of improving the strength and toughness of the weld metal. Mn is also an austenite-forming element, and contributes to suppressing the formation of δ-ferrite in the weld metal. If the Mn content relative to the total mass of the wire is less than 0.4 mass%, it causes insufficient deoxidation and is unable to fully suppress the residual δ-ferrite in the weld metal, resulting in a decrease in the toughness of the weld metal. Therefore, the Mn content relative to the total mass of the wire is set to 0.4 mass% or more, preferably 0.5 mass% or more, and more preferably 0.6 mass% or more.
On the other hand, if the Mn content exceeds 1.2 mass% relative to the total mass of the wire, the high-temperature strength of the weld metal deteriorates. In addition, the solidification temperature of the segregation part decreases, and the transformation point decreases, making PWHT at high temperatures difficult. Furthermore, Mn generates a complex oxide together with Cr, causing poor formation of the uranami. Therefore, the Mn content relative to the total mass of the wire is set to 1.2 mass% or less, preferably 1.1 mass% or less, and more preferably 1.0 mass% or less.

<Cr: 7.5 mass% or more and 13.0 mass% or less>
Cr is a main element of high Cr content welded steel material in which good uranami formation is difficult in welding using the solid wire according to this embodiment, and is an essential element for ensuring oxidation resistance at high temperatures and high-temperature strength of the weld metal. If the Cr content relative to the total mass of the wire is less than 7.5 mass%, the oxidation resistance and high-temperature strength of the weld metal become insufficient. Therefore, the Cr content relative to the total mass of the wire is set to 7.5 mass% or more, preferably 7.8 mass% or more, and more preferably 8.0 mass% or more.
On the other hand, if the Cr content exceeds 13.0% by mass relative to the total mass of the wire, even if the Si content is controlled as described above, an oxide film that inhibits uniform solidification of the high melting point weld metal is formed on the back surface. In addition, since Cr is a ferrite forming element, it causes δ ferrite to remain, which deteriorates the toughness and creep performance of the weld metal. Therefore, the Cr content relative to the total mass of the wire is set to 13.0% by mass or less, preferably 12.5% by mass or less, and more preferably 12.0% by mass or less.

<Mo: 0.70 mass% or more and 1.5 mass% or less>
Mo is a solid solution strengthening element and also has the effect of increasing high-temperature strength by precipitation of carbides. If the Mo content relative to the total mass of the wire is less than 0.70 mass%, the high-temperature strength of the weld metal becomes insufficient. Therefore, the Mo content relative to the total mass of the wire is set to 0.70 mass% or more, preferably 0.75 mass% or more, and more preferably 0.80 mass% or more.
On the other hand, if the Mo content exceeds 1.5 mass% relative to the total mass of the wire, residual δ ferrite is caused, and the toughness and creep performance of the weld metal deteriorates. Therefore, the Mo content relative to the total mass of the wire is set to 1.5 mass% or less, preferably 1.3 mass% or less, and more preferably 1.2 mass% or less.

<Nb: 0.010 mass% or more and 0.10 mass% or less>
Nb is an element that has the effect of improving the strength of the weld metal by solid solution strengthening and precipitating as nitrides. If the Nb content relative to the total mass of the wire is less than 0.010 mass%, the effect of improving the strength of the weld metal cannot be sufficiently obtained. Therefore, the Nb content relative to the total mass of the wire is set to 0.010 mass% or more, preferably 0.013 mass% or more, and more preferably 0.015 mass% or more.
On the other hand, if the Nb content exceeds 0.10% relative to the total mass of the wire, residual δ ferrite is caused, and the toughness of the weld metal is significantly deteriorated. Therefore, the Nb content relative to the total mass of the wire is set to 0.10% by mass or less, preferably 0.09% by mass or less, and more preferably 0.08% by mass or less.

<V: 0.10 mass% or more and 0.50 mass% or less>
V is an element that precipitates in the weld metal as a carbonitride and has the effect of improving the strength of the weld metal. If the V content relative to the total mass of the wire is less than 0.10 mass%, the effect of improving the strength of the weld metal cannot be sufficiently obtained. Therefore, the V content relative to the total mass of the wire is set to 0.10 mass% or more, preferably 0.13 mass% or more, and more preferably 0.15 mass% or more.
On the other hand, if the V content exceeds 0.50 mass% relative to the total mass of the wire, residual δ ferrite is caused and the toughness of the weld metal is deteriorated. Therefore, the V content relative to the total mass of the wire is set to 0.50 mass% or less, preferably 0.40 mass% or less, and more preferably 0.30 mass% or less.

<N: 0.010 mass% or more and 0.070 mass% or less>
N is an element that contributes to solid solution strengthening and stabilization of strength by precipitating as nitrides. It is also an austenite forming element and has the effect of suppressing δ-ferrite in the weld metal. If the N content relative to the total mass of the wire is less than 0.010 mass%, the above effect cannot be sufficiently obtained, the strength is reduced, and δ-ferrite is generated. Therefore, the N content relative to the total mass of the wire is set to 0.010 mass% or more, preferably 0.015 mass% or more, and more preferably 0.020 mass% or more.
On the other hand, if the N content with respect to the total mass of the wire exceeds 0.070 mass%, blowholes occur. Therefore, the N content with respect to the total mass of the wire is set to 0.070 mass% or less, preferably 0.065 mass% or less, and more preferably 0.060 mass% or less.

<P: 0.030 mass% or less>
P is an impurity element and a component that increases hot cracking susceptibility. If the P content with respect to the total mass of the wire exceeds 0.030 mass%, there is a concern that hot cracking may occur. Therefore, the P content with respect to the total mass of the wire is set to 0.030 mass% or less, preferably 0.020 mass% or less, and more preferably 0.015 mass% or less.

<S: 0.030 mass% or less>
S has the effect of affecting convection in the molten pool, increasing the penetration depth, improving the stability of the arc, and forming a good backside wave. In this embodiment, the lower limit of the S content is not particularly limited and may be 0 mass %, but when S is contained in the wire for the purpose of further improving the backside wave formation ability, the S content relative to the total mass of the wire is preferably 0.003 mass % or more, and more preferably 0.005 mass % or more.
On the other hand, if the S content exceeds 0.030% by mass relative to the total mass of the wire, there is a concern that hot cracks may occur. Therefore, the S content relative to the total mass of the wire is set to 0.030% by mass or less, preferably 0.025% by mass or less, and more preferably 0.020% by mass or less.

<Ni: 0.80 mass% or less>
Ni, like Mn, is an austenite-forming element and contributes to suppressing the formation of δ-ferrite in the weld metal. In the present embodiment, the lower limit of the Ni content is not particularly limited and may be 0 mass%, but when Ni is contained in the wire for the purpose of suppressing the formation of δ-ferrite in the weld metal, the Ni content relative to the total mass of the wire is preferably 0.05 mass% or more, and more preferably 0.10 mass% or more.
On the other hand, if the Ni content exceeds 0.80 mass% relative to the total mass of the wire, the high-temperature strength of the weld metal deteriorates. Also, the transformation point decreases, making PWHT at high temperatures difficult. Therefore, the Ni content relative to the total mass of the wire is set to 0.80 mass% or less, preferably 0.60 mass% or less, and more preferably 0.50 mass% or less.

<Ti: 0.025 mass% or less>
Ti forms an oxide film that inhibits uniform solidification of the weld metal, and deteriorates the formation of a good back bead shape. If the Ti content exceeds 0.025 mass% relative to the total mass of the wire, the back bead shape deteriorates. Therefore, the Ti content relative to the total mass of the wire is set to 0.025 mass% or less, preferably 0.018 mass% or less, and more preferably 0.015 mass% or less.

<Al: 0.020 mass% or less>
Al, together with Si, is an element that preferentially forms an oxide film on the uranami surface that has a low melting point and does not inhibit the solidification of the weld metal, but has a high slag generating ability, so there is a concern that slag inclusion may occur. In addition, Al is a ferrite generating element, and excessive δ ferrite is generated in the weld metal, which reduces the toughness of the weld metal. Furthermore, Al preferentially forms nitrides over Nb and V, and therefore inhibits the generation of Nb and V nitrides that have the effect of ensuring high-temperature strength, resulting in a decrease in high-temperature strength. Therefore, the Al content of the wire is set to 0.020 mass% or less, preferably 0.015 mass% or less, and more preferably 0.012 mass% or less.

<Co: 0.70 mass% or less>
Co is an austenite-forming element like Ni and Mn, and contributes to suppressing the formation of δ-ferrite in the weld metal, and the desired mechanical performance of the weld metal can be obtained by including Co in the wire. In this embodiment, the lower limit of the Co content is not particularly limited and may be 0 mass%, but when Co is included in the wire for the purpose of suppressing the formation of δ-ferrite in the weld metal, the Co content relative to the total mass of the wire is preferably 0.005 mass%, more preferably 0.05 mass% or more, even more preferably 0.10 mass% or more, and particularly preferably 0.15 mass% or more.
On the other hand, if the Co content exceeds 0.70% by mass relative to the total mass of the wire, the transformation point decreases, making it difficult to perform PWHT at high temperatures. Therefore, the Co content relative to the total mass of the wire is set to 0.70% by mass or less, preferably 0.60% by mass or less, and more preferably 0.50% by mass or less.

In addition to the above components, the solid wire according to this embodiment may contain either Zr or Cu or both within the ranges shown below. The contents of other components that the wire may further contain and the reasons for limiting them are explained below.

<Zr: 0.10 mass% or less>
Zr, together with Si, is an element that preferentially forms an oxide film on the uranami surface that does not easily inhibit the solidification of the weld metal, so it is preferable to include Zr in the solid wire according to the present embodiment as necessary. If Zr is included in the wire in the range of 0.10 mass% or less, poor uranami formation due to oxidation of Cr during welding can be prevented without reducing toughness due to excessive generation of δ ferrite. Therefore, when Zr is included in the solid wire according to the present embodiment, the Zr content relative to the total mass of the wire is 0.10 mass% or less, preferably 0.08 mass% or less, and more preferably 0.07 mass% or less.
On the other hand, when Zr is contained in the wire in order to obtain the above-mentioned effect, the Zr content relative to the total mass of the wire is preferably 0.005 mass % or more, and more preferably 0.010 mass % or more.

<Cu: 0.50 mass% or less>
Since Cu is an austenite forming element like Ni and Mn, and contributes to suppressing the formation of δ-ferrite in the weld metal, it is preferable to contain Cu in the solid wire according to the present embodiment as necessary. When Cu is contained in the wire in the range of 0.50 mass% or less, it is possible to obtain a weld metal having the desired mechanical performance without deteriorating the high-temperature strength of the weld metal. Therefore, when Cu is contained in the solid wire according to the present embodiment, the Cu content relative to the total mass of the wire is preferably 0.50 mass% or less, more preferably 0.40 mass% or less, and even more preferably 0.30 mass% or less.
On the other hand, when Cu is contained in the wire to obtain the above-mentioned effect, the Cu content relative to the total mass of the wire is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and even more preferably 0.10 mass% or more. Note that the wire of this embodiment may be Cu-plated, and the Cu content includes the copper plating.

<Balance: Fe and inevitable impurities>
The balance of the solid wire according to the present embodiment is Fe and inevitable impurities. The inevitable impurities refer to elements that are not intentionally added to the wire, and examples of elements other than those mentioned above include B, Sn, As, Sb, etc. The total content of impurities in the solid wire is preferably 0.10 mass% or less, and more preferably 0.05 mass% or less.

[Gas shielded arc welding method]
The gas-shielded arc welding method according to the present embodiment is a welding method for welding steel materials containing 1% by mass or more and 10% by mass or less of Cr using the above-mentioned solid wire without using back shield gas. As described above, when the Cr content of the steel materials to be welded is, for example, 8% by mass to 10% by mass, if a conventional solid wire is used for welding, the back wave is easily oxidized, and the shape and appearance of the back wave deteriorate. However, by using the solid wire according to the present embodiment as at least the first layer of welding, a back wave having excellent back wave performance and mechanical performance can be formed not only for steel materials with a high Cr content in which the back wave is particularly easily oxidized, but also for steel materials containing 1% by mass to 10% by mass or less of Cr, without using back shield gas.

In the gas-shielded arc welding method according to this embodiment, the type of welding is not particularly limited, and in addition to TIG (Tungsten Inert Gas) welding, MAG (Metal Active Gas) welding and MIG (Metal Inert Gas) welding can be used.

<Type and flow rate of shielding gas>
The shielding gas used on the front side during welding with the solid wire according to this embodiment is not particularly limited, but may be, for example, Ar gas, carbon dioxide gas, a mixed gas of Ar gas and carbon dioxide gas, or a mixed gas of Ar gas and oxygen gas. The flow rate of the gas is also not particularly limited, but may be, for example, 15 to 50 L/min.

<Welding position, wire diameter>
In addition, the welding position using the solid wire according to the present embodiment is not particularly limited, and welding can be performed in various welding positions. Furthermore, the wire diameter (diameter) of the solid wire according to the present embodiment is not particularly limited, but it can be applied to a wire having a diameter specified in a welding material standard such as AWS or JIS.

The effects of the present invention will be specifically explained below using examples of the present invention and comparative examples, but the present invention is not limited to these.

[Solid wire manufacturing]
Solid wires were prepared so that the wires contained various amounts of the components. The amounts (mass%) of the chemical components per total mass of the wires are shown in Table 1 below. The remainder of the wires, excluding the chemical components shown in Table 1 below, is Fe and unavoidable impurities.

[Gas shielded arc welding (for back wave evaluation)]
Welding was carried out to evaluate the reverse side of the welded joint. Specifically, a pair of steel plates having a plate thickness of 19 mm, a steel type of ASTM A387 Grade 91 Class 2, and a groove angle of 70° were prepared, and a first layer was formed by TIG welding. The welding conditions are as follows.

<Welding conditions>
Welding method: TIG welding Wire diameter: 2.4 mm
Root gap: 2-3mm
Welding current: 90-110A
Arc voltage: 10-14V
Preheat: 150-300℃
Shielding gas type and flow rate: 100% Ar, 15 liters/min. Back shielding gas: None. Welding position: Downward.

[Uranami evaluation test]
<Evaluation items>
For the weld metal obtained using each solid wire, the back side of the weld (appearance of the back wave) was visually observed, and the cross-sectional macro of the weld metal was visually observed to evaluate the back wave. For the appearance of the back wave, the degree of oxidation, the presence or absence of burn-through, and the presence or absence of a concave bead were observed. For the cross-sectional macro, the height of the back wave, the depth of the depression in the back wave, and the shape of the boundary between the base metal and the back wave were observed. The measurement results and evaluation results for each evaluation item are shown in Table 2 below.

<Evaluation method and criteria>
(Exterior of Uranami)
Regarding the appearance of the back wave, those that had a uniform width, no meandering or unevenness, no discoloration or unevenness due to oxidation, and no burn-through or concave beads were confirmed were rated as good. On the other hand, those that had an uneven width and severe unevenness, those that had discoloration or unevenness due to oxidation, or those that had burn-through or concave beads were rated as failing, and the appearance of those that were judged to be failing was recorded in the measurement results column.

(Height of back wave)
In the cross-sectional macro observation, the height of the back wave was measured. In this example, a back wave height of 0.5 mm or more was considered to be acceptable, and a back wave height of less than 0.5 mm was considered to be unacceptable. The height of the back wave was recorded in the measurement result column.

(Depth of the recess)
The presence or absence of dents was observed near the width direction end of the back side, and the depth of dents was measured for those that had dents. In this example, those that did not have dents with a depth of 0.5 mm or more on the back side of the base material were considered to have passed, and those that had dents of 0.5 mm or more were considered to have failed, and the depth of the dents was recorded in the measurement results column.

(Shape of the boundary between the base material and the back wave)
The shape of the boundary between the base material and the back wave was observed in the cross section macro, and those with a gentle convex shape from the base material to the back wave were judged as good (passed), and those with a sudden convex shape at the boundary between the base material and the back wave were judged as bad (failed), and "good" or "bad" was entered in the measurement results column. Note that for those where burn-through occurred, there was a tendency for the back wave to suddenly rise convex at the boundary between the base material and the back wave.

(Overall rating of the back waves)
In assessing the back side of the wave, a wave that passed all of the above items was given a rating of "A", and a wave that failed one or more items was given a rating of "C", and the evaluation results were recorded in the back side evaluation result column.

[Gas shielded arc welding (for weld metal evaluation)]
Welding was carried out to evaluate the weld metal. Specifically, the groove angle of SM490A steel material described in JIS G3106:2020, which has a plate thickness of 12 mm, was processed to 45°, and the inside of the groove and the backing metal were buttered in two or more layers using the prepared solid wire, and then the weld metal was formed by multi-layer welding using TIG welding with a root spacing of 6.5 mm. The welding conditions are shown below.

<Welding conditions>
Welding method: TIG welding Wire diameter: 1.2 mm
Welding current: 160-180A
Arc voltage: 10-16V
Shielding gas type and flow rate: 100% Ar, 25 liters/min. Welding position: Downward PWHT temperature and time: 760°C, 2 hours

[Mechanical performance evaluation test of weld metal]
<Evaluation items>
For the weld metal obtained using each solid wire, the Ac1 transformation point was measured to evaluate the PWHT temperature setting tolerance, and the area ratio of δ-ferrite was measured. In addition, a tensile test and a Charpy impact test were performed to evaluate the mechanical performance. The measurement results and evaluation results for each evaluation item are shown in Table 2 below. Note that, for some test pieces with poor back-beam, the mechanical performance evaluation test of the weld metal was not performed.

<Evaluation method and criteria>
(Measurement of Ac1 transformation point)
A round bar-shaped test piece having a diameter of 8 mm and a length of 12 mm was taken from the obtained weld metal before PWHT, and the Ac1 transformation point was measured by measuring the volume change of the test piece during heating by a high-frequency induction heating method.
In addition, when PWHT is performed at a temperature higher than the Ac1 transformation point, the weld metal undergoes reverse transformation to become a structure containing high-strength, low-toughness fresh martensite, and the performance of the welded joint deteriorates, so a higher Ac1 transformation point allows for a larger margin in the temperature setting of the PWHT. Therefore, as the evaluation criteria, those with an Ac1 transformation point of 800°C or higher were rated "A" (excellent), those with an Ac1 transformation point of 780°C or higher and less than 800°C were rated "B" (good), and those with an Ac1 transformation point of less than 780°C were rated "C" (poor).

(Measurement of δ-ferrite area ratio)
A 12 mm square test piece including the final pass original part of the cross section perpendicular to the welding direction was taken from the obtained weld metal before PWHT, and the microstructure of the final pass original part was observed by appropriately polishing and corroding it, and the area ratio of δ-ferrite was measured in a field of view of 100 times. The point counting method was used to measure the area ratio, and the area ratio was calculated from 600 or more lattice points per field of view.
In addition, δ-ferrite is a material that does not transform into austenite during welding and remains, and since it adversely affects strength and toughness and deteriorates the performance of the welded joint, the smaller the area ratio, the better. Therefore, as the evaluation criteria, an area ratio of δ-ferrite of less than 5% was rated as "A" (excellent), an area ratio of 5% or more but less than 10% was rated as "B" (good), and an area ratio of 10% or more was rated as "C" (bad).

(Tensile test)
A tensile test piece having a diameter of 6 mm and a gauge length of 24 mm was taken from the center of the plate thickness of the obtained weld metal parallel to the weld line direction, and the room temperature tensile strength (TS: Tensile Strength) of the weld metal was measured in accordance with the tensile test method for metallic materials described in JIS Z 2241:2011.
The evaluation criteria were as follows: a tensile test result of 720 MPa or more was rated as "A" (excellent), a tensile test result of 620 MPa or more but less than 720 MPa was rated as "B" (good), and a tensile test result of less than 620 MPa was rated as "C" (poor).

(Charpy impact test)
A 2 mm V-notch Charpy impact test piece was taken perpendicular to the weld line direction from the center of the plate thickness of the obtained weld metal, and the Charpy impact value at 20° C. was measured in accordance with the Charpy impact test method for metallic materials described in JIS Z 2242:2005.
The evaluation criteria for toughness based on Charpy impact value were as follows: a Charpy impact value of 60 (J/ ^cm2 ) or more, calculated by dividing the absorbed energy measurement result in a Charpy impact test at 20°C by the original cross-sectional area of the notch, was rated as "A"(excellent); a value of 34 (J/ ^cm2 ) or more and less than 60 (J/ ^cm2 ) was rated as "B"(good); and a value less than 34 (J/ ^cm2 ) was rated as "C" (poor).

[Evaluation results]
As shown in Tables 1 and 2 above, in the invention examples No. A1 to A7, although steel plates with a high Cr content, which is generally difficult to form a good uranami, were welded together, the chemical composition of the solid wire used was within the numerical range specified in the present invention. Therefore, it was possible to obtain a uranami with excellent appearance and a weld metal with excellent mechanical performance without using back shielding gas. In welding of steel plates with a Cr content of 8% by mass to 10% by mass, the poor appearance of the uranami bead is caused by the high Cr content of the steel plate and the welding material, so the solid wire according to this embodiment can be applied in the same way when the Cr content of the welded steel material is 1% by mass or more and less than 8% by mass. In other words, when the Cr content of the welded steel material is 1% by mass or more and 10% by mass or less, by using the solid wire according to the present invention, a good weld metal can be obtained without using a back shielding gas.

On the other hand, in Comparative Examples B1 to B7, the Si content in the solid wire was less than the lower limit specified in the present invention, and in Comparative Examples B5 to B7, the Ti content in the solid wire exceeded the upper limit specified in the present invention. Therefore, the evaluation result of the back wave was poor. In Comparative Example B8, the Si content in the solid wire exceeded the upper limit specified in the present invention, so the area ratio of δ ferrite increased. In Comparative Examples B9 and B10, the Si content in the solid wire exceeded the upper limit specified in the present invention, so the area ratio of δ ferrite increased and the evaluation result of the toughness was poor.

Claims (5)

A solid wire used for welding a steel material containing 1 mass% or more and 10 mass% or less of Cr,
For the total mass of wire,
C: 0.05% by mass or more and 0.15% by mass or less,
Si: 0.8% by mass or more and 1.7% by mass or less,
Mn: 0.4% by mass or more and 1.2% by mass or less,
Cr: 7.5% by mass or more and 13.0% by mass or less,
Mo: 0.70% by mass or more and 1.5% by mass or less,
Nb: 0.010% by mass or more and 0.10% by mass or less,
V: 0.10% by mass or more and 0.50% by mass or less,
N: 0.010% by mass or more and 0.070% by mass or less;
P: 0.030% by mass or less,
S: 0.030% by mass or less,
Ni: 0.80 mass% or less,
Ti: 0.025% by mass or less,
Al: 0.020% by mass or less,
Co: 0.70% by mass or less;
The balance of the solid wire is Fe and unavoidable impurities. Furthermore, for the total mass of the wire,
Zr: 0.10 mass% or less,
2. The solid wire according to claim 1, comprising: Furthermore, for the total mass of the wire,
Cu: 0.50% by mass or less,
3. The solid wire according to claim 1, further comprising: A gas-shielded arc welding method for welding steel containing 1% by mass or more and 10% by mass or less of Cr using the solid wire described in claim 1 or 2 without using back shielding gas. A gas-shielded arc welding method comprising welding a steel material containing 1 mass % or more and 10 mass % or less of Cr using the solid wire according to claim 3 without using a back shielding gas.