JPH09253886A - Flux cored wire for gas shielded metal arc welding for 690mpa class high tensile steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux cored wire in which excellent bead shape, workability and working efficiency are secured in the all position welding, and the high-temperature strength and low-temperature toughness of a weld zone after the long PWHT are excellent. SOLUTION: The flux has the composition consisting of, by weight, to the total weight of a wire, the slag agent in which 3-6% TiO2 , and 1-4% metal fluoride are essentially contained, and the metal deoxidizing content or alloy content so that the carbon equivalent CeqFCW of the wire expressed by the formula CeqFCW=C+0.08Si+0.07Mn+0.05Ni+0.07Cr+0.15Mo+0.02Cu+0.08Mg is 0.43-0.50%. In addition, 0.01-0.20% Ti, 0.005-0.015% B are contained as the alloy content, and the ratio of Mg to the metal fluoride in the wire satisfies the inequalities 0.4 <= (Mg amount/metal fluoride amount) <= 0.8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to welding of 690 MPa-class high-strength steel, as-welded and after-weld heat treatment (hereinafter, also referred to as PWHT), weld metal performance, particularly both high temperature strength and low temperature toughness. And a flux-cored wire capable of

[0002]

2. Description of the Related Art In recent years, in pressure vessels and penstocks used in petrochemical plants and power generation facilities, it is desired to operate at a higher pressure for the purpose of improving operational efficiency, and steel materials and welds used for structures are required. Of 690 MPa
The application of high-grade high-strength steel is increasing. Conventionally, Mn-Mo steel and Mn-Mo-Ni steel have been used for these steel materials, but the high temperature strength and low temperature toughness after PWHT in the welded part, especially the toughness in the sub-zero region depending on the installation area of the equipment. In consideration of the above, a steel type of a type in which Cr, Ni, Cu of less than 0.5% and a trace amount of Nb or V are added based on low temperature Mn-Ni steel is also used. In the apparatus using these steel materials, as an example of the strength requirement of the welded part, for example, the high temperature strength at 350 ° C. after PWHT for 620 ° C. × 12 hours is 600 MPa and the toughness of the welded part after PWHT is −30 ° C. There are things such as 47 J or more, and it is becoming very strict requirement to cope with the conventional flux-cored wire technology.

On the other hand, as a welding method, the efficiency is higher than that of a welding rod and the shape of the welding bead in the posture welding is good, so that the number of cases of using gas shielded arc welding using flux-cored wire is increasing. ing. In particular, for members used at high temperature and high pressure, the requirements for toughness at low temperatures have also become more sophisticated from the viewpoint of sufficient high temperature strength and at the same time preventing brittle fracture of the welded part, and compatibility of high strength and high toughness is great. It has become a challenge.

In welding such high strength members,
PWHT is generally performed on the welded portion for the purpose of relaxing the residual stress in the welded portion, softening the welded affected portion, and diffusing and releasing hydrogen in the weld metal. However, when this PWHT is exposed to high temperature for a long time, the toughness of the weld metal may deteriorate. In particular, in gas shielded arc welds constructed using flux-cored wire, the oxygen level in the weld metal is higher and the behavior of toughness deterioration due to PWHT is different compared to solid wire, welding rod, and submerged arc welding. It has been demanded to develop a flux-cored wire having an optimum component design, which can obtain good weld metal performance both in the as-welded state and after PWHT.

Regarding the weld metal performance of the flux cored wire for Ni-based low alloy steel after PWHT, for example, a technique relating to a flux cored wire for Mn-Ni-Cu steel-based submerged arc welding is disclosed in JP-A-52-65736. However, with the flux-cored wire of the present invention, it is difficult to perform vertical or upward welding in gas-shield arc welding, and it is not possible to achieve both high temperature strength and low temperature toughness of the welded portion after PWHT.

[0006]

The present invention is based on the above-mentioned 690.
In welding of MPa-class high-strength steel, a flux-cored wire that ensures good bead shape, workability and work efficiency in all-position welding, and has good high-temperature strength and low-temperature toughness of the welded portion after long-time PWHT It is intended to be provided.

[0007]

The present invention has been completed as a result of various studies on wire components for the above purpose, and the gist thereof is a gas shield obtained by filling a powder into an outer shell of steel. In the flux-cored wire for arc welding, TiO ₂ : 3.0% by weight based on the total weight of the wire.
To 6.0%, metal fluoride: 1.0 to 2.0%, and a slag agent that is essential and C: 0.15% or less, Si: 0.3 to
1.2%, Mn: 0.5 to 2.5%, Ni: 1.0 to
3.0%, Cr: 0.3% or less, Mo: 0.2% or less,
Cu: 0.5% or less and Mg: 0.4 to 1.2% are essential metal deoxidizing components or alloying components, and the carbon equivalent CeqFCW of the wire represented by the formula (1) is 0.43 to 0. 50%
So that the content of Ti: 0.
01 to 0.20%, B: 0.005 to 0.015%, and the ratio of the amount of Mg in the wire to the amount of metal fluoride is 0.4 ≦ (Mg amount / metal fluoride amount) ≦ It is a flux-cored wire for gas shielded arc welding for 690 MPa class high-strength steel, characterized in that it is 0.8.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the weld portion of the high temperature and high pressure apparatus using 690 MPa class high strength steel is required to have both high temperature strength and low temperature toughness after PWHT. A conventional welded part using a flux-cored wire has a problem that high temperature strength is obtained but toughness is insufficient, or good low temperature toughness is obtained but high temperature strength is insufficient.
The flux-cored wire, which is a component capable of obtaining 90 MPa-class strength, 600 MPa-class strength at 350 ° C., and low-temperature toughness at temperatures below freezing, has not been studied.
The present inventors have obtained the following findings as a result of examining the effects of alloy components and slag composition on weld metal in order to achieve these objects.

High-temperature strength and low-temperature toughness can be achieved by adding Cr, Mo, Cu, Ti, and B to the wire composition based on the Si-Mn-Ni system in small amounts so as to form an appropriate combination component. Is. In order to obtain stable low temperature toughness and ductility at high temperature in all position welding, the viscosity of the slag and weld metal is adjusted by adjusting the composition of the slag agent and the addition amount of Mg in an appropriate amount, It is necessary to reduce non-metallic inclusions that impair toughness.

Based on the above findings, the present invention is effective only by appropriately combining the constituent components of the wire, but the reasons for limiting the constituent amounts of the constituent components of the wire and the individual additive components will be described below. . TiO _2: 3.0~6.0% TiO ₂ constitutes a major component of the slag agent with later metal fluorides as well as a arc stabilizer. At the time of welding, the weld metal is encapsulated and shielded from the atmosphere, and the moderate viscosity affects the shape of the weld bead. Especially, in position welding, the balance with other metal components greatly affects the sagging property of the metal. On the other hand, it also causes the formation of molten or non-molten non-metallic inclusion components, which affects the weld metal performance.
If TiO ₂ is less than 3.0%, the slag is not sufficiently encapsulated and posture welding is difficult. On the other hand, if it exceeds 6.0%, the amount of slag becomes excessive in combination with the metal fluoride, it becomes difficult to hold the weld metal in the posture welding, and a non-melting type non-metal inclusion is formed, so that the weld metal The toughness deteriorates.

Metal Fluoride: 1.0 to 2.0% Fluoride such as CaF ₂ , NaF, MgF ₂ , BaF ₂ and K ₂ ZrF ₆ is a weld metal due to the action of fluorine gas decomposed and produced by the welding arc. It has an effect on deoxidation of slag and has a great influence on basicity and viscosity of slag. Although an appropriate amount of components is determined by the balance with Mg described later, if the metal fluoride content is less than 1.0%, the deoxidation of the weld metal will be insufficient and the toughness of the weld metal will deteriorate. On the other hand, if it exceeds 2.0%, the amount of slag becomes excessive, the arc becomes unstable, and the posture weldability deteriorates.

C: 0.15% or less In the flux-cored wire for 690 MPa class steel according to the present invention, the wire component of the alloy or metal deoxidizer having a balance that optimizes the high temperature strength and the low temperature toughness of the weld metal is CeqFCW described later. However, the upper limit or the appropriate component range must be limited for each component. C not only strengthens the weld metal by solid solution, but also affects the toughness of the weld metal by the optimum balance amount. Also PW
When HT is performed, Cr, Mn, Cr, Mo, Nb, V
The toughness is deteriorated by the interaction with a component that easily forms a carbide with the above. When the amount of C in the wire exceeds 0.15%, the low temperature toughness deteriorates, and more spatter is generated during welding, and the welding workability also deteriorates. Also,
The lower limit of C is not particularly limited as long as the below-mentioned CeqFCW is secured, and it may be a value of an ordinary steel shell component.

Si: 0.3 to 1.2% Si is a component for deoxidizing the weld metal and strengthening the solid solution. If Si is less than 0.3%, the strength of the weld metal cannot be secured. On the other hand, if it is less than 0.3%, deoxidation of the weld metal becomes insufficient, sufficient high temperature strength and low temperature toughness cannot be secured, and the arc becomes unstable, and further SiO ₂ produced as a deoxidation product. Since the amount is insufficient, the balance of slag viscosity is lost and good welding workability cannot be obtained. If it exceeds 1.2%, the low temperature toughness of the weld metal deteriorates.

Mn: 0.5 to 2.5% Mn also acts as a deoxidizing agent for the weld metal and a solid solution strengthening agent like Si. If it is less than 0.5%, the low temperature toughness deteriorates due to insufficient deoxidation. On the other hand, if it exceeds 2.5%, the strength of the weld metal increases and the low temperature toughness deteriorates due to PWHT. Ni: 1.0 to 3.0% Ni improves the strength of the weld metal by solid solution strengthening, and significantly improves the corrosion resistance and the low temperature toughness. Also Ni
Has a lower degree of embrittlement on the low temperature toughness due to PWHT than other alloy components. In the present invention, the effect of improving high temperature strength and low temperature toughness can be obtained by adding 1.0% or more in terms of balance with other components, but if 3.0% or more is added, the strength becomes excessive and high temperature during welding. Cracks easily occur.

Cr: 0.3% or less, Mo: 0.2% or less Cr and Mo, like Mn, are components that increase the high temperature strength of the weld metal. However, if added too much, PWH
Since the weld metal becomes brittle due to T, in the present invention, Cr: 0.3% or less and Mo: depending on the balance with other alloying agents.
It is necessary to limit it to 0.2% or less. Cu: 0.5% or less Cu exhibits the strength of the weld metal and, at the same time, is added together with Ni to improve the corrosion resistance. In addition, by applying Cu plating to the surface of the wire, the electric conductivity and the feedability of the wire are stabilized. The appropriate amount of Cu added to the wire is determined by the balance with other components.
If it exceeds 5%, hot cracking occurs.

Mg: 0.4-1.2% Mg reacts in a high temperature welding arc and acts as a strong deoxidizer. In the wire of the present invention,
Since the viscosity of the molten metal and MgO generated by the deoxidation reaction have a great influence on the slag composition and the viscosity of the slag,
As will be described later, it is necessary to add an appropriate amount depending on the balance with the metal fluoride. In order to obtain the effect of deoxidation, it is necessary to add 0.4 or more. On the other hand, if it exceeds 1.2%, the viscosity of the slag becomes excessive and the workability in posture welding deteriorates.

Ti: 0.01 to 0.20% When Ti is added in a small amount, the crystal grains become fine, and when added in an amount of 0.01% or more, the low temperature toughness is improved. But,
If added over 0.20%, the strength becomes excessive and conversely the toughness deteriorates. Since the above components from C to Ti mainly act as a metal deoxidizing agent or an alloying agent, they are added to the steel shell or the filling flux in the form of a simple metal or an alloy.

B: 0.005 to 0.015% B improves the hardenability of the weld metal by adding a trace amount, and improves the strength and low temperature toughness of the weld metal. 0.005
If it is less than 0.1%, there is no effect, and if it exceeds 0.015%, the strength becomes excessive and the toughness deteriorates. Since the effect of B can be exhibited by any one of a simple metal, an alloy and addition by oxidation, the form of addition to the flux is arbitrary.

Further, in the present invention, C, Si, Mn, Ni,
Regarding Cr, Mo, Cu and Mg, it is necessary that the carbon equivalent CeqFCW represented by the formula (1) is 0.43 to 0.50%. When CeqFCW is less than 0.43%, the tensile strength of the weld metal after PWHT is 690MP at room temperature.
a and high temperature tensile strength at 350 ° C. of 600 MPa or more cannot be obtained. Further, if it exceeds 0.50%, the strength becomes excessive and the low temperature toughness deteriorates.

The present invention further sets the ratio of the amount of Mg to the amount of metal fluoride within a certain range in order to improve the hot ductility, the low temperature toughness of the weld metal after PWHT, and the welding workability in posture welding. Keeping it is one of its characteristics. Generally, in a welding position such as vertical or upward welding in which the weld metal is liable to sag, it is necessary for the slag to hold the weld metal due to interfacial tension. However, as in the present invention, TiO ₂ and metal fluoride are the main components. The slag-based flux-cored wire is characterized in that the viscosity of the slag is relatively low due to the addition of fluoride.

As a deoxidizing agent, Mg undergoes a rapid oxidation reaction in the tip of the wire or in the droplets in an arc atmosphere to become MgO.
When a large amount of Mg is added, this MgO forms a solid solution in the molten slag, so that the viscosity of the slag is increased and the welding workability is improved. The relationship between the Mg amount / fluoride amount and the sagging property of the metal in vertical welding is shown in FIG. 1. By setting the Mg amount / fluoride amount to 0.4 or more, the sagging property of the metal is improved. However, if the amount of Mg / fluoride is too large, the viscosity of the slag becomes too large, and the amount of spatter increases, which makes stable welding impossible. Therefore, the amount of Mg / fluoride must be 0.8 or less. There is. When Mg is added from the flux, it may be added as a simple substance of metal Mg or as an alloy with another metal element.

Further, although it is usual that Nb and V are inevitably present in the wire as impurities of TiO ₂ which is a slag agent and fluoride, these Nb and V easily form a carbide by PWHT, Deteriorates the low temperature toughness after PWHT. In the flux-cored wire of the present invention, these N
Although b and V are not specified, it is preferable that both are limited to 0.015% or less.

The flux-cored wire of the present invention includes
In addition to the above components, addition of iron powder, a small amount of arc stabilizer, a small amount of slag agent, etc. does not affect the effect. Further, the filling rate of the flux may be in the range of 8 to 25% which is applied to a normal flux-cored wire, but is preferably 12% or more from the viewpoint of arc stability. Further applied to the shielding gases CO _2, Ar and CO ₂ and a small amount of O ₂ added ones such conventional MA gas mixture further to these gases
Any shielding gas specified for G welding can be used.

[0024]

Next, the present invention will be described more specifically with reference to examples. Using a jacket made of mild steel pipe, after filling the hollow part of the jacket with flux, wire drawing and finishing to 1.2 mmφ were performed to prepare a flux-cored wire. Fluoride is CaF ₂ ,
MgF ₂ and K ₂ ZrF ₆ were compounded in a fixed ratio of 1: 2: 1. In addition, all the flux filling rates were 16%.
The composition of the wire is shown in Table 1. In Table 1, No. 1-6
Is an example of the present invention, and No. 7 to 26 are comparative examples. Using the above wire, vertical welding was performed under the conditions shown in Table 2, and the welding workability was evaluated by observing the arc state and measuring the upper limit voltage that causes metal dripping. FIG. 2 is a schematic diagram showing a welding work test method, in which reference numeral 1 is a test piece and 2 is a welding torch. Welding was performed under the conditions shown in Table 3 and a weld metal performance test was carried out except for those having particularly poor welding workability. FIG. 3 is a sectional view showing a groove shape in a weld metal test. After welding, the test piece had a P of 620 ° C for 12 hours.
After performing WHT, JIS Z
3111 A1 tensile test piece and JIS G056
7 II-10 type high temperature tensile test was sampled and the tensile test of the deposited metal was carried out. A 2 mmV notch Charpy impact test at −30 ° C. was performed using a JIS Z31114 test piece. The tensile test was conducted at room temperature and 350
It was carried out at two temperatures of ° C.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

Table 4 shows the test results. Here, the results of the impact test were shown as an average of three test pieces. As is clear from Table 4, No. 3 with TiO ₂ less than 3%. 7. Conversely, TiO ₂
No. over 6% No. 8 and No. 8 containing more than 2% of fluoride. With regard to the wire No. 10, the amount of slag is improper, the arc is unstable, and the amount of spatter is large.
The posture was difficult. Moreover, No. with Si less than 0.3%. Also for No. 12, it was difficult to perform stable vertical welding because the viscosity of the slag was insufficient. Further, in No. 3 containing more than 0.5% Cu. In No. 20, vertical cracks, which are considered to be high temperature cracks, occurred at the center of the weld bead.

No. 3 with C exceeding 0.15%. 11, Si
Is over 1.2%. No. 13, Ni containing more than 3.0%. 17, No. 17 with Mg exceeding 1.2%. In all of the wires of No. 22, the CeqFCW exceeded 0.50% and the strength of the weld metal was excessive, and good low temperature toughness was not obtained. Further, the Ti content of Ti exceeding 0.20%. Nos. 24 and B exceeding 0.015%. With respect to the wire No. 26, the strength of the weld metal was too high and good toughness was not obtained.

On the other hand, No. 3 having Mn of less than 0.5%. 1
No. 4 and Ni with less than 1.0%. 16 is Ce
Although qFCW was also less than 0.43, the strength of the weld metal of each wire was less than 690 MPa. Mn is 2.5
%, Which exceeds%. No. 15 with Cr exceeding 0.3%.
18, No. 18 with Mo exceeding 0.2%. In the wire No. 19, insufficient toughness due to PWHT embrittlement was observed. Ti is 0.
No. less than 01%. Nos. 23 and B of less than 0.005%. In No. 25, good toughness was not obtained.

No. 1 containing less than 1.0% of fluoride. 9, M
No. in which g is less than 0.4%. In No. 21, in each case, a low impact value starting from non-metallic inclusions, which is considered to be due to insufficient deoxidation of the weld metal, was observed, and good toughness was not obtained on average. In comparison with the above comparative example, N which is an example of the present invention
o. 1 to No. The wire of No. 6 has good values for both high temperature strength and low temperature toughness.

[0032]

[Table 4]

[0033]

As described above in detail, the sixth aspect of the present invention
The flux-cored wire for gas shielded arc welding for 90 MPa class high-strength steel enables to obtain a well-balanced weld metal in terms of room temperature strength, high temperature strength and low temperature toughness after PWHT.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between the amount of Mg / amount of fluoride in a wire and a limit voltage in upward welding.

FIG. 2 is a schematic diagram showing a welding workability test method,

FIG. 3 is a sectional view showing a groove shape in a weld metal test.

[Explanation of symbols]

 1 Test piece 2 Welding torch

Claims (1)

[Claims] 1. A flux-cored wire for gas shielded arc welding, comprising a steel shell filled with powder, wherein TiO _{2 is} 3.0 to 6.0% by weight with respect to the total weight of the wire. Compound: 1.0 to 2.0% essential slag agent and C: 0.15% or less Si: 0.3 to 1.2% Mn: 0.5 to 2.5% Ni: 1.0 to 3.0% Cr: 0.3% or less Mo: 0.2% or less Cu: 0.5% or less Mg: 0.4 to 1.2% are essential metal deoxidizing components or alloy components as described below (1 )
The carbon equivalent CeqFCW of the wire represented by the formula is 0.43
To 0.50%, and further contains Ti: 0.01 to 0.20% B: 0.005 to 0.015% as an alloy component, and further contains Mg in the wire and metal fluoride. A flux-cored wire for gas shielded arc welding of 690 MPa class high-strength steel, characterized in that the ratio with the amount is 0.4 ≦ (Mg amount / metal fluoride amount) ≦ 0.8. CeqFCW = C + 0.08Si + 0.07Mn + 0.05Ni + 0.07Cr + 0.15Mo + 0.02Cu + 0.08Mg (1) (however, each component is% by weight)