JP7092634B2 - Bond flux for submerged arc welding of duplex stainless steel - Google Patents

Description

The present invention relates to a bond flux for submerged arc welding of duplex stainless steel.

With the development of seawater utilization technology in recent years, duplex stainless steel has been developed as a material for seawater resistant steel, and nowadays, various chemical plant equipment and oil well pipes used in environments containing chloride ions such as seawater. , Used as a material for bulkheads of chemical tankers. Two-phase stainless steel is a stainless steel in which an austenite phase and a ferrite phase are formed in a ratio of approximately 1: 1. The excellent mechanical properties of austenite-based stainless steel and the excellent stress-resistant corrosion resistance of ferrite-based stainless steel. It is a steel that has crackability, is stronger than stainless steel with each single-layer structure, and has excellent pore corrosion resistance.

In parallel with the development of duplex stainless steel sheets, the welding materials used for welding have also been developed. Welded metal parts of duplex stainless steel are often used without heat treatment, and the welding material is such that the same performance (strength, corrosion resistance) as the base duplex stainless steel can be obtained without heat treatment. Is designed to have a higher content of Cr, Ni, etc. than the base metal component.

Research and development of welding materials used for submerged arc welding of duplex stainless steel are also underway. For example, Patent Document 1 discloses a technique for improving welding workability, reducing the amount of oxygen in a weld metal, and improving toughness by combining a welding electrode having a predetermined composition and a welding flux. ing. Further, Patent Document 2 discloses a technique for improving the pitting corrosion resistance of the weld metal by adjusting the composition of the weld metal.

Japanese Unexamined Patent Publication No. 61-014097 Japanese Unexamined Patent Publication No. 61-046391

However, the welding material for duplex stainless steel contains N like the base metal, and when welding, the N causes pore defects and defects (pock marks) occur on the surface of the weld bead. There is. Similarly, N may cause slag seizure, resulting in deterioration of slag peelability. In addition, since the welding wire contains a large amount of alloy components, the viscosity of the molten pool during welding is high, and depending on the balance with the viscosity of the slag, the weld bead tends to become uneven and smooth. It may be lost and there is a risk of slag entrainment. In the past, it was difficult to solve these problems at the same time.

The present invention has been made in view of the above, and an object thereof is that the pock marks on the surface of the weld bead are suppressed at the time of welding, the slag peelability is good, and the appearance of the weld bead is excellent, that is, the weld bead is provided. It is an object of the present invention to provide a bond flux for submerged arc welding of two-phase stainless steel which can obtain a welded metal portion which is smooth and hardly causes slag entrainment.

The present inventors have conducted diligent studies to solve the above problems, and as a result, it has been found that a good weld bead surface, slag peelability, and weld bead appearance can be obtained by adjusting the flux composition to a specific range. We have found and completed the present invention.

That is, in the present invention, CaF ₂ : 25 to 45% by mass, Al _{2O 3} : 25 to 45% by mass, SiO ₂ : 5.0 to 15% by mass, BaCO ₃ : 4.0 to 9.0% by mass, Mn: 3.0% by mass or less, total alkali metal oxide: 3.1 to 9.3% by mass, substantially no lime and magnesium oxide, CaF ₂ , Al ₂ O ₃ , Provided is a bond flux for submerged arc welding of a two-phase stainless steel containing 90% by mass or more of SiO ₂ , BaCO ₃ , Mn, and an alkali metal oxide in total.

One aspect of the bond flux for submerged arc welding of duplex stainless steel of the present invention further contains Cr: 1.0 to 3.0% by mass.

One aspect of the bond flux for submerged arc welding of the two-phase stainless steel of the present invention is ZrO ₂ : 0 to 3.0% by mass, TiO ₂ : 0 to 3.0% by mass, Fe ₂ O ₃ : 0 to 3. Any of 0% by mass, FeS: 0 to 1.0% by mass, B ₂ O ₃ : 0 to 0.1% by mass, Ni: 0 to 1.0% by mass, Mo: 0 to 1.0% by mass. Contains one or more.

According to the bond flux for submerged arc welding of the two-phase stainless steel of the present invention, the pock marks on the surface of the weld bead during welding are suppressed, the slag peelability is good, the weld bead is smooth, and slag entrainment occurs. It is possible to obtain a small number of welded metal parts.

1A and 1B are schematic views showing the shape and size of a base material in a groove filling test, where FIG. 1A is a perspective view of the base material, FIG. 1B is a front view, and FIG. 1C is a top view. FIG. 2 is a schematic diagram showing an outline of the evaluation of the pock mark. 3A and 3B are schematic views showing an outline of evaluation of weld bead smoothness, FIG. 3A is a top view of a base metal and a welded metal, and FIG. 3B is a sectional view taken along line BB of FIG. 3A. 4A and 4B are schematic views showing an outline of evaluation of slag entrainment, in which FIG. 4A is a front view before removing the excess and smoothing the surface, and FIG. 4B is a front view after removing the excess and smoothing the surface. c) is a top view of the base metal and the weld metal.

Hereinafter, the present invention will be described in detail with reference to embodiments. Hereinafter,% means mass% unless otherwise specified. Further, "-" means that the value is equal to or more than the lower limit value and is equal to or less than the upper limit value.
Further, the content of each component in the flux means the content per total mass of the flux including water glass.

<Bond flux for submerged arc welding of duplex stainless steel>
The bond flux for submerged arc welding of the two-phase stainless steel of the present embodiment (hereinafter, also referred to as bond flux or simply flux) is CaF ₂ : 25 to 45% by mass, Al ₂ O ₃ : 25 to 45% by mass, SiO. ₂ : 5.0 to 15% by mass, BaCO ₃ : 4.0 to 9.0% by mass, Mn: 3.0% by mass or less, and total of alkali metal oxides: 3.1 to 9.3% by mass. It contains and is substantially free of lime and magnesium oxide. Hereinafter, the reason for limiting the numerical value of the content of each component will be described.

(CaF ₂ )
CaF ₂ in the flux has the effect of stabilizing the arc and increasing the viscosity of the slag to improve the bead shape, but when the CaF ₂ content in the flux is less than 25% by mass, these effects are exhibited. I can't get enough. Therefore, in this embodiment, the CaF ₂ content in the flux is set to 25% by mass or more. On the other hand, when the CaF ₂ content in the flux exceeds 45% by mass, the arc becomes unstable and the fluidity of the slag deteriorates, so that slag entrainment occurs. Therefore, in this embodiment, the CaF ₂ content in the flux is set to 45% by mass or less.
The CaF ₂ content in the flux is preferably 35% by mass or more. Further, the CaF ₂ content in the flux is preferably 40% by mass or less. In such a case, since the bead shape is particularly stable and smoothed, a particularly good bead appearance can be obtained.

(Al ₂ O ₃ )
Al ₂ O ₃ in the flux acts as a slag forming agent, is an effective component for increasing the solidification temperature and viscosity of the molten slag, and has an effect of improving the peelability of the slag. It also has the effect of adjusting the fluidity of the slag and adjusting the shape of the weld bead. If the Al ₂ O ₃ content in the flux is less than 25% by mass, this effect cannot be sufficiently obtained, and the uneven state of the bead becomes remarkable. Therefore, in the present embodiment, the Al ₂ O ₃ content in the flux is set to 25% by mass or more. On the other hand, when the Al ₂ O ₃ content in the flux exceeds 45% by mass, the viscosity of the slag becomes too high and the fluidity deteriorates, so that slag entrainment occurs. In addition, the wave of the bead becomes rough and the number of pock marks generated increases. Therefore, in the present embodiment, the Al ₂ O ₃ content in the flux is set to 45% by mass or less.
The Al ₂ O ₃ content in the flux is preferably 32% by mass or more. Further, the Al ₂ O ₃ content in the flux is preferably 38% by mass or less. In such a case, since the bead shape is particularly stable and smoothed, a particularly good bead appearance can be obtained.

(SiO ₂ )
The flux of the present embodiment contains SiO ₂ derived from minerals, water glass and the like. SiO ₂ in the flux has the effect of raising the solidification temperature of the molten slag, increasing the holding power of the bead, and stabilizing the bead shape. If the SiO ₂ content in the flux is less than 5.0% by mass, the bead shape becomes unstable due to insufficient bead holding power of the molten slag. Therefore, in the present embodiment, the SiO ₂ content in the flux is set to 5.0% by mass or more. On the other hand, when the SiO ₂ content exceeds 15% by mass, the viscosity of the molten slag becomes too high, the peelability of the slag deteriorates, and slag entrainment occurs. Therefore, in the present embodiment, the SiO ₂ content in the flux is set to 15% by mass or less.
The SiO ₂ content in the flux is preferably 10% by mass or more. Further, the SiO ₂ content in the flux is preferably 14% by mass or less. In such a case, the slag peeling property is particularly improved, a particularly good slag peeling property is obtained, and the bead shape is particularly stable and smoothed, so that a particularly good bead appearance can be obtained.

(BaCO ₃ )
BaCO ₃ has effects such as improvement of bead shape and stabilization of arc during welding, but the effects cannot be obtained when the addition amount is less than 4.0% by mass. Therefore, in the present embodiment, the content of BaCO ₃ in the flux is set to 4.0% by mass or more. Further, if it is added in an amount of more than 9.0% by mass, the bead shape is deteriorated and slag entrainment occurs. Therefore, in the present embodiment, the content of BaCO ₃ in the flux is set to 9.0% by mass or less.
The BaCO ₃ content in the flux is preferably 5.2% by mass or more. The BaCO ₃ content in the flux is preferably 7.5% by mass or less, and more preferably 6.5% by mass or less. In such a case, the bead shape is particularly stable and smooth, and slag entrainment is particularly suppressed.

(Mn)
Mn has an action of adjusting the amount of ferrite in the weld metal and contributes to the improvement of the toughness of the weld metal. From the viewpoint of improving toughness, Mn is preferably contained in an amount of 1.0% by mass or more, and more preferably 1.2% by mass or more. On the other hand, excessive addition of Mn causes slag seizure and causes deterioration of slag peelability. Therefore, the content of Mn in the flux is limited to 3.0% by mass or less. Mn is more preferably limited to 2.3% by mass or less, further preferably 1.8% by mass or less, and particularly preferably 1.5% by mass or less.

(Alkali metal oxide)
The flux of the present embodiment contains an alkali metal oxide due to water glass. Here, the alkali metal oxide specifically means Na ₂ O, K ₂ O, and Li ₂ O. The alkali metal oxide has the effect of improving the arc stability, increasing the concentration of the arc, and preventing slag entrainment in the weld metal. If the total content of these in the flux is less than 3.1% by mass, this effect cannot be sufficiently obtained. Therefore, in the present embodiment, the total content of the alkali metal oxides in the flux is 3.1% by mass or more. On the other hand, when the content of the alkali metal oxide in the flux exceeds 9.3% by mass in total, the peelability of the slag deteriorates. Therefore, in the present embodiment, the total content of the alkali metal oxides in the flux is set to 9.3% by mass or less.
The total content of the alkali metal oxides in the flux is preferably 4.1% by mass or more, more preferably 5.2% by mass or more, and further preferably 5.7% by mass or more. .. The total content of the alkali metal oxides is preferably 8.3% by mass or less, and more preferably 7.3% by mass or less. In such a case, the peelability of the slag is particularly good.
In the flux of the present embodiment, the alkali metal oxide may contain either Na ₂ O, K ₂ O, or Li ₂ O, but it is preferable that all of them are contained.

(Lime and magnesium oxide)
When lime and magnesium oxide are substantially contained in the flux, the peelability of the slag is significantly reduced. Therefore, the flux of this embodiment is substantially free of lime and magnesium oxide.
Here, substantially not contained means that the flux is not intentionally added as a component, and lime and magnesium oxide to the extent that they are mixed as impurities are acceptable. Specifically, the contents of lime and magnesium oxide in the flux of the present embodiment are each regulated to 0.5% by mass or less. The contents of lime and magnesium oxide are preferably regulated to 0.1% by mass or less, and more preferably to 0.05% by mass or less.
Further, lime is CaO, CaCO ₃ and Ca (OH) ₂ , and magnesium oxide is MgO.

Here, CaF ₂ , Al ₂ O ₃ , SiO ₂ , BaCO ₃ , alkali metal oxide, and Mn described above are preferably 90% by mass or more, and preferably 95% by mass or more in total. Is more preferable, and 97% by mass or more is particularly preferable.

(Cr)
The flux of the present embodiment may further contain Cr in addition to the above components. Cr has an action of forming a weld metal composition into a two-phase structure, and by adding Cr so that the content of Cr in the flux is 1.0% by mass or more and 3.0% by mass or less, the weld metal can be made of Improves strength, toughness, and corrosion resistance.
The Cr content in the flux is more preferably 1.5% by mass or more. Further, the Cr content is more preferably 2.5% by mass or less, and further preferably 2.0% by mass or less. In such a case, the strength, toughness, and corrosion resistance of the weld metal are particularly excellent.

(Remaining)
The flux of the present embodiment has ZrO ₂ : 0 to 3.0% by mass, TiO ₂ : 0 to 3.0% by mass, Fe _{2O 3} : 0 to 3.0% by mass, and FeS: 0-1 by mass as the balance. .0 mass%, B ₂ O ₃ : 0 to 0.1 mass%, Ni: 0 to 1.0 mass%, Mo: 0 to 1.0 mass%, any one or more of the present embodiments. It can also be contained within a range that does not impair the effect of the flux. Further, the flux of the present embodiment may contain P, S, water and the like as unavoidable impurities. It is practical that the amount of unavoidable impurities is 1.0% by mass or less.

<Welding wire>
The flux of this embodiment is used for submerged arc welding in combination with a welding wire. The welding wire is not particularly limited as long as it is a wire that can be used for welding duplex stainless steel, and for example, a welding wire having the following composition can be used.
That is, for example, by mass% with respect to the total mass of the welded wire.
C: 0.03% by mass or less (not including 0% by mass),
Si: 0.90% by mass or less (not including 0% by mass),
Mn: 0.50 to 2.00 mass%,
P: 0.03% by mass or less (not including 0% by mass),
S: 0.03% by mass or less (not including 0% by mass),
Cu: 0.75% by mass or less (not including 0% by mass),
Ni: 7.5 to 9.5% by mass,
Cr: 21.5 to 23.5% by mass,
Mo: 2.5 to 3.5% by mass,
N: 0.08 to 0.20% by mass,
Inevitable impurities: 0.5% by mass or less (not including 0% by mass)
Fe: Welding wire containing the balance can be used.
More specifically, for example, a wire whose component system is equivalent to AWS A5.9 ER2209 can be used.

The flux according to the embodiment of the present invention does not depend on the power polarity (AC, DCEP) of welding and can be preferably used.

Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.

Using the submerged arc welding wire having a diameter of 4.0 mm having the component composition shown in Table 1 and the submerged arc welding flux of Examples 1 to 24 having the component composition shown in Table 2, the base material 1 is shown in Table 3. Using SUS329J3L having the composition and the shape and dimensions shown in FIG. 1, a groove filling test was performed under the welding conditions shown in Table 4, and the pock mark and welding workability (slag peelability, weld bead smoothness, slag entrainment) were performed. ) Was evaluated.
The balance in the component compositions shown in Tables 1 and 3 is Fe and unavoidable impurities. Further, the balance in the component composition shown in Table 2 is an unavoidable impurity.

The details of the pock mark and the evaluation method of welding workability (slag peeling property, weld bead smoothness, slag entrainment) will be described below.

<Evaluation of Pockmark>
As shown in FIG. 2, on the surface of the obtained weld metal 3, the number of pock marks 4 having a diameter of 1 mm or more in the central portion 300 mm (evaluation target region α) excluding 25 mm each of the start portion and the end portion. , Those with 4 or less pock marks 4 are evaluated as particularly good (◎), those with 5 or more and 10 or less are evaluated as good (○), and those with 11 or more are evaluated as defective (△). Those with a rating of ◎ or ○ were considered acceptable.

<Slag peelability>
With respect to the obtained weld metal, the degree of slag peeling when hitting with a slag hammer was determined, and the slag completely peeled off over the entire length of the weld bead by hitting with a slag hammer 10 times or less is particularly good ( ◎) Although some slag remains at the time of welding beads after hitting 10 times or less with a slag hammer, it is good that all slag can be removed by hitting 11 times or more and less than 20 times. (○), those for which it was difficult to remove slag with a slag hammer were evaluated as defective (Δ), and those with an evaluation of ◎ or ○ were evaluated as acceptable.

<Welded bead smoothness>
As shown in FIG. 3A, in the obtained weld metal 3, the position where the unevenness variation of the bead surface is maximum in the central portion 300 mm (evaluation target region α) excluding 25 mm each of the start portion and the end portion. The difference in height between the concave portion and the convex portion (A in FIG. 3B) is particularly good (⊚), that is more than 2 mm and 4 mm or less is good (◯), and is more than 4 mm. Was evaluated as defective (△), and those with an evaluation of ◎ or ○ were regarded as acceptable.

<Slag involvement>
As shown in FIG. 4 (b), the obtained weld metal 3 is smoothed by removing the surplus portion to the same height as the surface of the base metal 1 as shown in FIG. 4 (b). An X-ray transmission test was carried out in the central part 300 mm (evaluation target area α) excluding 25 mm each of the start part and the end part, and the number of detected shadows with a diameter of 1 mm or more was 0, which is particularly good. (◎) One or two pieces were evaluated as good (◯), three or more pieces were evaluated as defective (Δ), and those with an evaluation of ◎ or ○ were regarded as acceptable.

The results of the above evaluation are shown in Table 5.

Examples 1 to 12 passed all the evaluations of the number of pock marks, the slag peelability, the smoothness of the weld bead, and the slag entrainment because the chemical components in the flux were appropriately regulated.

In Example 13, since the content of CaF ₂ in the flux was less than the lower limit of the range specified in the present invention, the smoothness of the weld bead surface was deteriorated.
In Example 14, since the content of CaF ₂ in the flux exceeds the upper limit of the range specified in the present invention, the number of slag entrainment occurrences has increased.
In Example 15, since the content of Al ₂ O ₃ in the flux was less than the lower limit of the range specified in the present invention, the smoothness and slag peeling property of the weld bead surface were deteriorated.
In Example 16, since the content of Al ₂ O ₃ in the flux exceeded the upper limit of the range specified in the present invention, the number of pock marks and the number of slag entrainment occurred increased.
In Example 17, since the content of SiO ₂ in the flux was less than the lower limit of the range specified in the present invention, the smoothness of the weld bead surface was deteriorated.
In Example 18, since the content of SiO ₂ in the flux exceeds the upper limit of the range specified in the present invention, the number of slag entrainment occurrences increases and the slag peelability deteriorates.
In Example 19, since the content of BaCO ₃ in the flux was less than the lower limit of the range specified in the present invention, the smoothness of the weld bead surface was deteriorated.
In Example 20, since the content of BaCO ₃ in the flux exceeds the upper limit of the range specified in the present invention, the number of slag entanglements increases and the smoothness of the weld bead surface deteriorates.
In Example 21, since the total content of Na ₂ O, K ₂ O, and Li ₂ O in the flux was less than the lower limit of the range specified in the present invention, the number of slag entrainment occurrences increased.
In Example 22, the total content of Na ₂ O, K ₂ O, and Li ₂ O in the flux exceeded the upper limit of the range specified in the present invention, so that the slag peelability was deteriorated.
In Example 23, the content of Mn in the flux exceeded the upper limit of the range specified in the present invention, so that the slag peelability was deteriorated.
In Example 24, since at least one of lime and magnesium oxide was contained in the flux, the slag exfoliation property was deteriorated.

1 Base material 2 Groove 3 Welded metal 4 Pock mark 5 Crater 6 Slag entrainment α Evaluation target area

Claims (2)

CaF ₂ : 25-45% by mass,
Al ₂ O ₃ : 25-45% by mass,
SiO ₂ : 5.0 to 15% by mass,
BaCO ₃ : 4.0-9.0 mass%,
Mn: 3.0% by mass or less ,
Total alkali metal oxides: 3.1-9.3% by mass , and
Cr: 1.0 to 3.0% by mass,
Contains,
Lime and magnesium oxide : 0.1% by mass or less, respectively
Regulated by
A bond flux for submerged arc welding of a two-phase stainless steel containing 95 % by mass or more of the total of the CaF ₂ , the Al ₂ O ₃ , the SiO ₂ , the BaCO ₃ , the Mn, and the alkali metal oxide. ZrO ₂ : 0 to 3.0% by mass,
TiO ₂ : 0 to 3.0% by mass,
Fe ₂ O ₃ : 0 to 3.0% by mass,
FeS: 0 to 1.0% by mass,
B ₂ O ₃ : 0 to 0.1% by mass,
Ni: 0 to 1.0% by mass,
Mo: 0 to 1.0% by mass,
The bond flux for submerged arc welding of duplex stainless steel according to claim 1, which contains any one or more of them.

Images