JP2003062689A - Filler wire, method for mig welding using it, and welded joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filler wire, a method for MIG welding using the filler, and a welded joint, enabling enhanced fatigue strength of the welded joint compatible with enhanced toughness of the weld metal. SOLUTION: The filler wire for MIG welding of low-alloy steels is a ferrous alloy comprising 0.020 mass% or less carbon, 5.0-16.0 mass% Cr, 5.0-15.0 mass% Ni, 0.01-0.30 mass% rare earth elements, the balance being Fe and inevitable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welded joint suitable for use in large structures such as ships, bridges, storage tanks and construction machines.
The present invention relates to a welding wire and a MIG welding method for manufacturing the welded joint, and more particularly to a welding wire capable of improving the fatigue strength of the welded joint and the toughness of the weld metal, a MIG welding method using the welding wire, and a welded joint.

[0002]

2. Description of the Related Art In ships, bridges, storage tanks, construction machines and the like, there is a demand for high strength steel materials to be used for the purpose of increasing the size and weight thereof. By increasing the strength of the steel material, it is possible to reduce the plate thickness and reduce the weight of the structure. As a material used for these structures, a low alloy steel material in which various alloy elements such as Cr, Ni and Mo are less than 3.0% is used. These low alloy steel materials are welded together to form a structure, but when manufacturing a welded joint of low alloy steel materials, MIG welding (Metal welding) is generally used.
Electrode Inert Gas Arc
Welding) is used.

However, there is a problem that it is difficult to improve the fatigue strength of the welded joint manufactured by this MIG welding in accordance with the increase in strength of the steel material. That is, in order to meet the demand for higher strength of steel materials, when using high-strength low-alloy steel materials, the fatigue strength of high-strength steel is the same as that of the base material. Although it increases with increase, it is said that the fatigue strength of welded joints does not improve even if the material strength increases. The cause of this is that the tensile residual stress generated in the welded part of the welded joint is large.

As a welding method for improving the fatigue strength of this welded joint, conventionally, for example, Japanese Patent Laid-Open No. 11-138290.
The one described in Japanese Patent Publication is known. According to this welding method, the weld metal produced by welding undergoes martensitic transformation in the cooling process after welding so that it is in a state of being expanded at room temperature more than at the start of martensitic transformation. And, as the welding material used in this welding method, the martensitic transformation start temperature is 250 ° C.
An iron alloy whose temperature is lower than 170 ° C. or higher is used. Then, by using such a welding method and welding material, the tensile residual stress generated in the weld metal of the welded joint is reduced, or compressive residual stress is given in place of the tensile residual stress, such as grinding after welding. The effect is that the fatigue strength of the welded joint is improved without performing any special post-treatment.

[0005]

However, in the welding method and welding material disclosed in Japanese Patent Application Laid-Open No. 11-138290, although the fatigue strength of the welded joint is improved, the toughness of the welded portion, particularly the weld metal. There was a problem that the toughness was low. It is considered that this is because the toughness of the weld metal was deteriorated by the alloying elements such as Cr and Ni added to realize the lowering of the transformation temperature of the welding material.

On the other hand, in order to improve the toughness of the weld metal, it is effective to reduce O mixed in the weld metal. That is, when O is mixed in the weld metal, inclusions (oxides) are generated in the weld metal and the toughness of the weld metal is reduced. It has been considered desirable to use MIG welding using an inert gas such as Ar gas as a shielding gas in order to reduce O mixed in the weld metal.

However, in MIG welding, in order to enhance the stability of the arc, it is usual to use O ₂ gas or CO which has the property of supplying O to the molten metal in an inert gas such as Ar gas as a shield gas. _It is necessary to mix _two gases (hereinafter referred to as oxygen supply gas) to form a cathode spot in the arc discharge consisting of an oxide film on the surface of the molten metal.
When an oxygen supply gas is mixed with an inert gas, a deoxidizing element (eg, S in the welding wire used for MIG welding).
Although the oxidation of the weld metal can be prevented by (i, Mn, Al, etc.), it is inevitable that O is mixed in the weld metal. Therefore, inclusions (oxides) are generated in the weld metal, and the toughness of the weld metal deteriorates.

On the other hand, when the MIG welding is performed without mixing the oxygen supply gas with the inert gas used as the shield gas, the arc coating becomes unstable because the oxide film serving as the cathode spot is not formed on the molten metal surface. Therefore, the welding work is virtually impossible. Furthermore, in welding in which all-position welding is required, it is inconvenient that the welding operation cannot be performed in a welding position other than downward.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to improve the fatigue strength of welded joints and the toughness of weld metal at the same time.
An object of the present invention is to provide a MIG welding method using this welding wire and a welded joint.

[0010]

In order to solve the above problems, the inventors of the present invention have controlled the martensitic transformation start temperature of the weld metal produced by welding to secure the fatigue strength of the welded joint and shield the welded joint. Adjusting the composition of the welding wire so that MIG welding can be performed without mixing oxygen supply gas into the inert gas, which is earnestly researched on the technology for improving the toughness of the weld metal, and forming the present invention. I arrived.

The structure of the present invention is as follows. (1) A welding wire used for MIG welding of low alloy steel, wherein C is 0.20 mass% or less and Cr is 5.0 to 1
An iron alloy having a composition of 6.0 mass%, Ni of 5.0 to 15.0 mass%, rare earth element of 0.01 to 0.30 mass%, and the balance of Fe and inevitable impurities. Welding wire characterized by. (2) In addition to the composition of the welding wire according to (1), a total of 0.20% by mass or less of C and N and 0.01% by mass or less of O are contained in the welding wire. (3) A welding wire containing Si in an amount of 1.0% by mass or less and Mn in an amount of 2.5% by mass or less in addition to the composition of the welding wire according to (1) or (2). (4) In addition to the composition of the welding wire according to any one of (1) to (3), one or two of Mo is 4.0 mass% or less and Nb is 1.0 mass% or less. A welding wire containing a seed. (5) A welding wire characterized in that the composition of the welding wire according to any one of (1) to (4) is adjusted so as to satisfy the following expression (1).

120 ≦ 719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb <300 (1) Where C, Si, Mn, Cr, Ni, Mo and Nb are contents (mass%) of each element. (6) A MIG welding method characterized by using the welding wire according to any one of (1) to (5) 5 and using an inert gas as a shield gas. (7) The MIG welding method according to (6), wherein the inert gas is Ar gas, He gas, or a mixed gas of Ar and He. (8) A welded joint manufactured by MIG welding using the welding wire according to any one of (1) to (5), the martensitic transformation of a weld metal produced by welding during cooling. A welded joint having a starting temperature of 120 ° C. or higher and 300 ° C. or lower.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Claims
The reason for limiting like the described welding wire is as follows. C: 0.20% by mass or less C is an element that increases the hardness of the martensite of the weld metal, increases the weld hardenability, and lowers the toughness, and is preferably reduced as much as possible. It needs to be less than or equal to mass%. C is preferably 0.12 mass% or less. Cr: 5.0-16.0 mass%, Ni: 5.0-15.
0 mass% Cr and Ni were added in order to lower the martensitic transformation start temperature of the weld metal and improve the fatigue strength of the welded joint. In a practical welded joint, in order to set the martensitic transformation start temperature of the weld metal to 300 ° C. or lower, Cr: 5.0 mass% or more and Ni: 5.0 mass% are required. Even if Cr is less than 5.0% by mass, N
By increasing the content of i, the martensitic transformation start temperature of the weld metal can be set to 300 ° C or lower. However, when the content is less than 5.0 mass%, expensive Ni and welding wire are required in order to set the martensite transformation start temperature of the weld metal to 300 ° C. or lower, which is a condition necessary for ensuring the fatigue strength of the weld metal. It is necessary to contain a large amount of other components that deteriorate the workability during the production of. Therefore, the content of Cr is set to 5.0% by mass or more. The upper limit of the Cr content is set to 16.0% by mass. When it is more than 16.0% by mass, a ferrite structure appears in the structure of the weld metal, which adversely affects the toughness and strength of the weld metal. It is to exert.

Even if Ni is less than 5.0% by mass, the martensite transformation start temperature of the weld metal is 300 ° C. or less by increasing the content of other elements other than Ni that can lower the martensite transformation start temperature. You can However, if it is less than 5.0% by mass, the martensitic transformation start temperature of the weld metal is set to 300 ° C. or less, and thus it is necessary to contain a large amount of other components that deteriorate the workability during the production of the welding wire. The upper limit of the Ni content is set to 15.0 mass% because it is economically unfavorable to add more than this.

For the above reasons, Cr and Ni are Cr:
5.0 to 16.0 mass% and Ni: 5.0 to 15.0 mass%. Rare earth element: 0.01 to 0.30% by mass The rare earth element has the effect of forming a cathode spot on the surface of the molten metal and stabilizing the arc when MIG welding is performed using an inert gas as a shield gas. Therefore, by containing the rare earth element in the welding wire, it is not necessary to mix the oxygen supply gas into the inert gas that is the shield gas, and it is possible to avoid mixing O in the weld metal, Generation of inclusions (oxides) can be avoided, and deterioration of the toughness of the weld metal can be avoided. Here, the content of the rare earth element is set to 0.01% by mass or more because if it is less than 0.01% by mass, the effect of stabilizing the arc cannot be obtained. In addition, the upper limit of the content of rare earth elements is 0.3
The reason for defining 0 mass% is that if it exceeds 0.30 mass%, inclusions in the weld metal increase and the toughness of the weld metal decreases.

Here, the "rare earth element" is an element having Sc, Y and atomic numbers 57 (La) to 71 (Lu). In the present invention, as the rare earth element, one kind of element may be used, or two or more kinds of elements may be used. The content of the rare earth element is 0.03 to 0.20 from the viewpoint of achieving a high level of both arc stability and weld metal toughness.
It is preferably within the range of mass%. The element used as the rare earth element is preferably La or Ce because it is easily available.

A welding wire according to a second aspect of the present invention contains, in addition to the composition of the welding wire according to the first aspect, C and N in a total amount of 0.20% by mass or less and O in an amount of 0.01% by mass or less. It is characterized by doing. The reason why the compositional components of the welding wire are limited in this way is as follows. C, N: 0.20% by mass or less in total C and N are elements that enhance the strength of the weld metal.
Since excessive addition of C and N lowers the toughness of the weld metal, it is preferable that the content of C and N be reduced as much as possible within a range where the desired strength of the weld metal can be secured. C,
When the total content of N exceeds 0.20 mass%, the toughness of the weld metal decreases. From the viewpoint of increasing the strength of the weld metal, the total content of C and N is preferably 0.01% by mass or more. O: 0.01 mass% or less O is an element that forms inclusions in the weld metal and reduces toughness. If the O content is excessive, the viscosity of the molten metal will be reduced. For this reason, if O is contained excessively, bead drop and bead formation failure may occur especially in all-position welding, and the efficiency of the welding operation decreases. Therefore, the lower the O content, the better, and if it is 0.01% by mass or less,
The toughness of the weld metal does not decrease, it is also advantageous for bead formation, and the efficiency of welding work does not decrease. From the viewpoint of ensuring the toughness of the weld metal, the O content is more preferably 0.005 mass% or less. In addition, "O" refers to the total O here.

In addition to the composition of the welding wire according to claim 1 or 2, the welding wire according to claim 3 of the present invention has Si of 1.0 mass% or less and Mn of 2.5 mass% or less. It is characterized by containing. The reason why the composition components of the welding wire are limited as described above is as follows. Si: 1.0 mass% or less Si is the martensitic transformation start temperature (Ms) of the weld metal.
It has the effect of lowering the point), and it is preferable to add a large amount in order to lower the Ms point. However, when Si is supplied as a deoxidizing agent from the welding material (wire, flux, etc.) to the welding metal, and if the welding metal contains Si in an amount of more than 1.0 mass%, the workability in the production of the welding wire is reduced. To do. In order to secure workability, the Si content is 1.0 mass% or less. Mn: 2.5 mass% or less Mn is supplied as a deoxidizing agent from the welding material to the weld metal, but when Mn is contained in the weld metal in an amount of more than 2.5 mass%, processing in the production of the welding wire. Sex decreases.
Therefore, the Mn content is 2.5 mass% or less.

Further, in the welding wire according to claim 4 of the present invention, in addition to the composition of the welding wire according to any one of claims 1 to 3, Mo is 4.0% by mass or less and Nb is not more than Nb. Of 1.0% by mass or less is contained. In this welding wire, M
Although o can be 4.0 mass% or less, Mo can be added for the purpose of improving the corrosion resistance of the weld metal, but when it is contained in excess of 4.0 mass%, it is processed in the production of the welding wire. This is because the sex is reduced.

Further, Nb is set to 1.0% by mass or less, because Nb has an action of lowering the martensitic transformation start temperature (Ms point), and it is preferable to add a large amount thereof in order to lower the Ms point. However, if it is contained in an amount of more than 1.0% by mass, the workability in the production of the welding wire deteriorates. The welding wire according to claim 5 of the present invention is that the composition of the welding wire according to any one of claims 1 to 4 is adjusted so as to satisfy the following expression (1). It has a feature.

120 ≦ 719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb <300 (1) where C, Si, Mn, Cr, Ni, Mo and Nb are contents (mass%) of each element.

This welding wire is composed of C, Si, Mn, C
By adjusting the contents of r, Ni, Mo, and Nb so as to satisfy the expression (1), residual stress in the compressive direction near the weld toe is introduced, and the fatigue of the welded joint is reduced. Strength is further improved. M according to claim 6 of the present invention
The IG welding method is characterized by using the welding wire according to any one of claims 1 to 5 and using an inert gas as a shield gas.

According to this MIG welding method, since the arc stabilizing effect of the rare earth element can be utilized by using the welding wire according to any one of claims 1 to 5, the shielding gas is mixed with the oxygen supply gas. Inert gas that does not contain oxidizing supply gas can be used as the shielding gas, and inclusions (oxides) are not generated in the weld metal, and a welded joint with high toughness of the weld metal can be manufactured. You can

The MIG welding method according to claim 7 of the present invention is characterized in that the inert gas according to claim 6 is Ar gas, He gas, or a mixed gas of Ar and He. Since Ar gas, He gas, or mixed gas of Ar and He is inexpensive, it is economically preferable to use these gases as the inert gas. When a mixed gas of Ar and He is used as the inert gas, the mixing ratio thereof is He: 20 to Ar: 80 to 30% by volume from the viewpoint of ensuring the directivity of the arc and the penetration depth. 70
It is preferably within the range of volume%.

The welded joint according to claim 8 of the present invention is a welded joint manufactured by MIG welding using the welding wire according to any one of claims 1 to 5, It is characterized in that the martensitic transformation start temperature of the weld metal produced by welding during cooling is 120 ° C or higher and 300 ° C or lower. By setting the martensitic transformation start temperature during cooling of the weld metal to 120 ° C. or higher and 300 ° C. or lower, the expansion amount of the weld metal due to the martensitic transformation can be increased, and the state where the expansion amount is large is around room temperature. Thus, at the end of the cooling process of the weld metal, the weld metal is in a more expanded state than at the start of the martensitic transformation. Therefore, compressive residual stress is introduced by the expansion, and the tensile residual stress generated in the cooling process of the weld metal is reduced, which improves the fatigue strength of the welded joint after welding. Therefore, by adjusting the contents of C, Cr, Ni, Si, Mn, Mo, and Nb in the welding wire so that the martensitic transformation start temperature of the weld metal is 120 ° C. or higher and 300 ° C. or lower, after welding The fatigue strength of the welded joint can be improved. The martensitic transformation start temperature of the weld metal depends on the chemical composition of the material to be welded and the chemical composition of the welding wire, but the present invention is intended for the case of a low alloy steel material, so the welding wire The martensitic transformation start temperature of the weld metal is adjusted to 120 ° C by adjusting the chemical composition of the welding wire so that the martensitic transformation start temperature of is not less than 120 ° C and not more than 300 ° C.
It is possible to set the temperature to 300 ° C. or lower. Also, MI
In G welding, by using the welding wire according to any one of claims 1 to 5, the arc stabilizing effect of the rare earth element can be utilized, so that it is not necessary to mix the oxygen supply gas with the shielding gas, and the shielding gas As an inert gas that does not contain an oxidizing supply gas, it is possible to produce a welded joint with high toughness of the weld metal without the formation of inclusions (oxides) in the weld metal.

With respect to the shape of the welded joint to which the present invention can be applied, any joint shape used in ships such as load non-transmission type cross welded joints, butt joints, marine structures, penstocks, bridges, storage tanks, construction machines, etc. It may be. The welding device used for MIG welding may be either an automatic welding machine or a semi-automatic welding machine. Further, the welding posture can be applied to all the postures of downward, vertical upward, vertical downward, upward and lateral.

[0027]

EXAMPLES In order to verify the effects of the present invention, the following was performed. A steel plate to be welded having the chemical composition shown in Table 1,
MIG using welding wire having chemical composition shown in Table 2
Joining was performed by welding to produce a load non-transmission type cross weld joint 4 shown in FIG. This load non-transmission type cross weld joint 4 is
The main plate 1 is formed by joining two sub-plates 2 so as to be orthogonal to the main plate 1 at fillet welds 3 by the MIG welding method. The plate thickness of each of the steel plates A and B to be welded shown in Table 1 is 16 mm, and the width of the parallel portion of the cross weld joint 4 is 40 mm.
mm, and the length of the main plate 1 is 600 mm.

[0028]

[Table 1]

[0029]

[Table 2]

In the chemical composition of the welding wire shown in Table 2, all of the welding wires A, B and C are examples satisfying the requirements described in claims 1 to 5, and the welding wire D,
Both E and F are comparative examples that do not satisfy the requirements described in claim 1. The shielding gas in MIG welding is
A mixed gas of Ar and He having the compositions shown in Table 3 was used, and O ₂ gas was added to some shield gases for comparison. The shield gas added with this O ₂ gas does not meet the requirement described in claim 6.

The welding conditions are 250 A for current and 30 for voltage.
V, welding speed was 20 cm / min, and preheating was not performed. Then, a fatigue test piece was sampled from the load non-transmission type cross welded joint 4 produced by welding, and a fatigue test was performed by repeatedly applying a load in the longitudinal direction of the main plate 1 using a hydraulic servo type fatigue tester. The fatigue strength was measured. The amplitude frequency in this fatigue test was 3 to 8 Hz.

Further, in order to confirm the toughness of the weld metal, J
A Charpy impact test based on IS Z 3111 was carried out to measure the absorbed energy vE ₀ at 0 ° C. Table 3 shows the test results of the fatigue test and the impact test.

[0033]

[Table 3]

Referring to Table 3, with regard to the welded joints 1 to 5 using the welding wires A, B and C satisfying the requirements of claims 1 to 5 as the welding wire, the fatigue strength at 2,000,000 cycles is 1.
90 MPa-240 MPa, weld metal toughness of 6
It was 0J to 83J, and excellent characteristics were obtained. Above all,
Welded joint 1 using a mixed gas of Ar and He as a shield gas satisfying the requirements described in claims 6 and 7.
In 3 and 5, the fatigue strength of 2 million times is 230 MPa to 24
It was 0 Mpa and the toughness of the weld metal was 80 J to 83 J, and more excellent properties were obtained. In addition, welded joints 1-5
In any of the above, the martensitic transformation start temperature (Ms point) of the weld metal is 135 ° C to 167 ° C, and the martensite transformation start temperature of the weld metal, which is the requirement described in claim 8, is 120 ° C or higher and 300 ° C or higher. It meets the requirement of ℃ or less.

On the other hand, in the welded joint 6 using the welding wire D which does not satisfy the requirements of claim 1 as the welding wire, the Cr content is as small as 4.4% by mass, and the martensitic transformation of the weld metal starts. The temperature is as high as 393 ° C. If the martensitic transformation start temperature is high, the fatigue strength of the welded joint does not improve, and the fatigue strength at 2,000,000 cycles is as low as 90 MPa. Further, in the welded joint 7 using the welding wire E that does not satisfy the requirement of claim 1 as the welding wire, the content of Cr is as large as 18.2% by mass, and the martensitic transformation start temperature of the weld metal is −. It is extremely low at 55 ° C. When the martensitic transformation start temperature is low, the fatigue strength of the welded joint is not improved, so the fatigue strength at 2,000,000 cycles is as small as 100 MPa. Further, in the welded joint 8 using the welding wire F that does not satisfy the requirements of claim 1 as the welding wire, the content of C is as large as 0.45% by mass, so that the martensitic transformation start temperature of the welding metal is It is extremely low at -247 ° C. If the martensitic transformation start temperature is low, the fatigue strength of the welded joint does not improve, and if the content of C is high, the toughness of the weld metal decreases, so the fatigue strength at 2 million cycles is as low as 90 MPa, and the weld metal Has a very low toughness of 8J.

[0036]

As described above, according to the welding wire, the MIG welding method using the welding wire, and the weld joint according to the present invention, the martensitic transformation start temperature of the weld metal produced by welding is controlled. As a result, MIG welding can be performed without mixing the oxygen supply gas into the inert gas that is the shield gas while ensuring the fatigue strength of the welded joint, thereby improving the toughness of the weld metal.

[Brief description of drawings]

FIG. 1 is a view showing a load non-transmission type cross weld joint in which a sub plate is welded to a main plate according to an embodiment of the present invention.

[Explanation of symbols]

1 main plate 2 Secondary plate 3 fillet welds 4 Non-transmission type cross welded joint

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koichi Yasuda             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. (72) Inventor Shinichi Amano             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. F-term (reference) 4E001 AA03 BB08 CA07 DD02 DD03

Claims (8)

[Claims] 1. A welding wire used for MIG welding of low alloy steel, wherein C is 0.20% by mass or less, Cr is 5.0 to 16.0% by mass, and Ni is 5.0 to 15.0. A welding wire comprising an iron alloy having a composition of mass% and 0.01 to 0.30 mass% of a rare earth element, and the balance being Fe and inevitable impurities. 2. In addition to the composition of the welding wire according to claim 1, a total of C and N is 0.20 mass% or less and O is 0.0.
A welding wire containing 1 mass% or less. 3. A welding wire containing 1.0 mass% or less of Si and 2.5 mass% or less of Mn in addition to the composition of the welding wire according to claim 1 or 2. 4. In addition to the composition of the welding wire according to claim 1, one or more of 4.0 mass% or less of Mo and 1.0 mass% or less of Nb. A welding wire containing a seed. 5. A welding wire, wherein the composition of the welding wire according to any one of claims 1 to 4 is adjusted so as to satisfy the following formula (1). 120 ≦ 719-795C-35.55Si-13.25Mn-23.7Cr-26.5Ni-23.7Mo-11.85Nb <300 (1) Here, C, Si, Mn, Cr, Ni, Mo , Nb are the contents (mass%) of each element. 6. A MIG welding method, wherein the welding wire according to claim 1 is used, and an inert gas is used as a shield gas. 7. The MIG welding method according to claim 6, wherein the inert gas is Ar gas, He gas, or A gas.
A MIG welding method, which is a mixed gas of r and He. 8. A welded joint manufactured by MIG welding using the welding wire according to claim 1, wherein the martensitic transformation of the weld metal produced by welding during cooling. A welded joint having a starting temperature of 120 ° C. or higher and 300 ° C. or lower.