JPH0985491A - Flux cored wire for ferritic stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a flux cored with for ferritic stainless steel where the oxidation resistance of welding metal is excellent, the cost of welding material can be reduced, and the productivity of wire is improved. SOLUTION: In a flux cored wire of a flux being filled inside a metal skin, the composition of the metal skin and the flux contains, by wire total weight ratio, 0.07 to 2.0% Si, 14.5 to 17.0% Cr, 0.01 to 1.0% Al, 0.05 to 2.0% Ti, 0.02 to 0.1% N, 0.05 to 0.5 F, and the balance Fe with inevitable impurity. The inevitable impurity is restricted as <=0.10% C, <=0.2% Nb, and <=0.5% Mn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for the welding of automobile exhaust system members and the like, and is excellent in the oxidation resistance of the weld metal and at the same time the welding cost can be reduced, and the productivity of the ferrite is improved. A flux-cored wire for stainless steel.

[0002]

2. Description of the Related Art Conventionally, solid wires have been mainly used for welding automobile exhaust system members, but recently, a flux cored wire for ferritic stainless steel having excellent efficiency and good welding workability. The application of is being expanded. Such a flux-cored wire has a problem that a large amount of slag is generated as compared with the conventional solid wire welding. When a flux-cored wire is used for welding an automobile exhaust system member, slag may remain in a pipe or the like to be welded, which causes clogging of the exhaust system member.

In order to solve such a problem, it has been proposed that the amount of slag generated during welding can be suppressed by defining an appropriate amount of chemical components with respect to the total weight of the wire (Japanese Patent Publication No. 30557/1993). ). This is because the content of the slag slag forming agent is limited, and the deterioration of the welding workability caused thereby is improved by defining the content of other metal components to an appropriate amount. Further, the welding cost is reduced due to the improvement in efficiency by using the flux-cored wire. With the reduction in welding cost, there is an increasing demand for cost reduction in welding materials.

[0004]

However, if the Cr content, which is an expensive metal component in the wire, is lowered in order to reduce the cost of the welding material, there is a problem that the oxidation resistance deteriorates. .

On the other hand, the exhaust gas temperature is becoming higher as the engine performance is improved and the exhaust gas purification efficiency is improved. For example, in the exhaust manifold directly below the engine, the temperature is about 850 ° C. in the past, but is now about 950 ° C. as a high temperature. Corresponding to the change in the application temperature of such an automobile exhaust system member to be welded, a better oxidation resistance is required for the weld metal. Therefore, there is a demand for the development of a flux-cored wire that can satisfy the contradictory requirements of reducing the welding material cost and ensuring the welding quality.

The present invention has been made in view of the above problems, and the oxidation resistance of the weld metal is excellent and
An object of the present invention is to provide a flux-cored wire for ferritic stainless steel, which can reduce the cost of welding material and improve the wire productivity.

[0007]

A flux-cored wire for ferritic stainless steel according to the present invention has a metal sheath and a flux containing Si: 0.0 based on the total weight of the wire.
7 to 2.0% by weight, Cr: 14.5 to 17.0% by weight, Al: 0.01 to 1.0% by weight, Ti: 0.05
To 2.0% by weight, N: 0.02 to 0.1% by weight and F: 0.005 to 0.5% by weight, the balance being Fe
And unavoidable impurities, wherein the unavoidable impurities are
C: 0.10 wt% or less, Nb: 0.2 wt% or less, and Mn: 0.5 wt% or less.

The metal skin is preferably made of mild steel.

The slag slag forming agent in the flux is 2.
It is preferably 0% by weight or less.

[0010]

As a result of the inventors' earnest experiments and researches to solve the above-mentioned problems, even if the Cr content contributing to the oxidation resistance is reduced, the content of C, Nb, Al, Ti, N, etc. is contained. It has been found that the oxidation resistance of the weld metal is improved by adjusting the amount appropriately. That is, C and Nb are elements that deteriorate the oxidation resistance, and the oxidation resistance of the weld metal is improved by controlling the content in these wires. Further, by adding Al, Ti and N in combination, the ferrite crystal grains are made finer and the oxidation resistance is improved. Therefore, the Cr content in the wire should be at least 1
Even if it is reduced to 4.5% by weight, the oxidation resistance equal to or higher than the conventional one can be obtained. Further, the inventors of the present application have found that Cr and Nb
It has been found that when the content of such ferrite-forming elements is suppressed, a martensite phase that deteriorates the mechanical performance of the weld metal precipitates in the microstructure of the weld metal. The precipitation of this martensite phase can be prevented by suppressing the content of Mn, which is an austenite forming element.

Further, the stability of the arc and the welding workability shown by the generation of spatter can be improved by limiting the addition amounts of Si and fluoride.

Furthermore, when mild steel is used as the metal skin,
Since mild steel has better wire drawability than ferritic stainless steel, the number of wire breakages during the wire drawing process can be reduced and productivity is improved.

The reasons for limiting the composition of the contained components with respect to the total weight of the flux-cored wire in the present invention will be described below.

Cr (chromium): 14.5 to 17.0 weight
Amount% Cr is a main element of ferritic stainless steel and an essential element for forming Cr ₂ O ₃ that contributes to oxidation resistance. However, Al and T described later
The lower limit of the Cr content can be lowered by refining the crystal grains by adding an appropriate amount of i and N and regulating the Nb content. That is, when the Cr content is 14.5% by weight or more, sufficient oxidation resistance can be obtained. On the other hand, Cr
If the addition amount is large, as described above, it causes the material cost to increase. Therefore, the Cr content is 14.5 to 17.0 wt% with respect to the total weight of the wire. Note that Cr is added from either or both of the metal shell and the flux. When added from the flux, metallic Cr or a Cr alloy such as Fe-Cr and N-Cr is used. When added from such a Cr alloy,
The Cr content is the converted value of Cr contained in them. In addition, a mild steel containing no Cr is used as the metal skin,
By adding Cr only from the flux, the cost can be further reduced, and the productivity of the wire can be improved as described above.

C (carbon): 0.10% by weight or less C is mixed as an impurity from the metal shell or flux, but is an element that combines with Cr that contributes to oxidation resistance and reduces the amount of effective Cr. . If the C content exceeds 0.10 wt% with respect to the total weight of the wire, the oxidation resistance deteriorates. Therefore, the C content is 0.1 based on the total weight of the wire.
Restrict to 0% by weight or less. Preferably, the C content is 0.
It is not more than 05% by weight.

Nb (niobium): 0.2% by weight or less Nb is mixed as an impurity from the metal shell or flux, but it destroys the dense network of Cr ₂ O ₃ having the effect of oxidation resistance and resists acid It is an element that significantly deteriorates the chemical conversion property. Particularly in the present invention, the Cr content is 1
It is set to 4.5 to 17.0, and the Cr ₂ O ₃ forming ability is weak, so that the increase in the Nb content that deteriorates the oxidation resistance has a fatal adverse effect on the weld metal. If the Nb content exceeds 0.2% by weight, the effect becomes large. Therefore, the Nb content based on the total weight of the wire is 0.2% by weight.
It is regulated as follows. Preferably, the Nb content is 0.05% by weight or less.

Si (silicon): 0.07 to 2.0 weight
% Si has the effect of reducing the particle size of the droplets. If the Si content is less than 0.07% by weight, the effect is reduced. On the other hand, when the Si content exceeds 2.0% by weight, the amount of spatter generated increases. Therefore, the Si content is 0.07 to 2.0% by weight based on the total weight of the wire. It should be noted that Si is added from either or both of the metal shell and the flux, and when added from the flux, Si alloys such as Fe-Si, Al-Si and Ni-Si are used. When added from such a Si alloy, the Si content is the S content contained in the Si alloy.
The i converted value.

Mn (manganese): 0.5 wt% or less Mn is an element that forms austenite, and as described above, the content of Mn is 0. 0 in a state where the elements that form ferrite such as Cr and Nb are reduced. If it exceeds 5% by weight, the martensite phase precipitates and the mechanical performance of the weld metal deteriorates. Therefore, the Mn content relative to the total weight of the wire is 0.5% by weight or less. It should be noted that Mn is added from either one or both of the metal shell and the flux, and when added from the flux, a metal Mn or Mn alloy such as Fe-Mn is used. Such Mn
When added from the alloy, the Mn content is the Mn conversion value contained in the Mn alloy.

Al (aluminum): 0.01 to 1.
0% by weight Al stabilizes the ferrite structure and, at the same time, has the effect of forming fine grains by combining with N, thereby improving the oxidation resistance. If the Al content is less than 0.01% by weight, the effect is reduced. On the other hand, if the Al content exceeds 1.0% by weight, the effect of refining the crystal grains is lost, and the stability of the arc during welding is reduced, and the amount of spatter is significantly increased. Therefore, the Al content is 0.01 to 1.0% by weight based on the total weight of the wire. It should be noted that Al is added from either or both of the metal shell and the flux. When added from the flux, the metal Al or Fe-Al and Al-
An Al alloy such as Mg is used. When added from such an Al alloy, the Al content is the converted value of Al contained in them.

Ti (titanium): 0.05 to 2.0 weight
% Ti, like Al, has the effect of stabilizing the ferrite structure and by combining with N to make the crystal grains finer, thereby improving the oxidation resistance. If the Ti content is less than 0.05% by weight, the effect is reduced.
On the other hand, as the content of Ti increases, the amount of slag generated also increases, which makes it unsuitable for welding automobile exhaust system members. This is because, as described above, a large amount of the generated slag remains inside the pipe or the like that is the member to be welded and becomes a noise generation source or reduces exhaust efficiency. Therefore, the Ti content is 0.05 to 2.0% by weight based on the total weight of the wire. Note that Ti is added from either or both of the metal shell and the flux. When added from the flux, Ti alloys such as Fe-Ti and Ni-Ti or Ti such as TiN and TiC.
A compound is used. When such a Ti alloy or Ti compound is added, the Ti content is the Ti conversion value contained in them.

N (nitrogen): 0.02 to 0.1% by weight N has an effect of refining crystal grains by combining with Ti or Al as described above. If the N content is less than 0.02% by weight, the effect is reduced. On the other hand, when the amount of N added increases, the welding workability decreases and the amount of spatter generated increases. When a large amount of spatter adheres to the work piece, the appearance of the work piece is significantly impaired. Therefore,
The N content relative to the total weight of the wire is 0.02 to 0.1% by weight. N is added from either or both of the metal shell and the flux, and when added from the flux, TiN, N-Cr and Mn-.
A metal nitride such as N is used. When added from such metal nitrides, N is the N-converted value contained in them.

F (fluorine): 0.005 to 0.5 weight
% F takes in electrons in the welding arc and stabilizes 1
Since it becomes a valent anion, it has the effect of improving the stability and concentration of the arc. F content is 0.005% by weight
If it is less than that, the effect is reduced. On the other hand, if the F content exceeds 0.5% by weight, the stability of the arc is reduced and the amount of spatter is increased. Therefore, the F content relative to the total weight of the wire is 0.005 to 0.5% by weight. In addition, F is LiF, NaF, B contained in the flux.
It is added from metal fluorides such as aF, CaF ₂ and AlF ₃ , and the F content is the F converted value contained in them.

Slag smelting agent: 2.0% by weight or less The slag slagging agent is a component other than the metal powder in the flux. Becomes unsuitable. Therefore, the amount of the slag slag forming agent is 2.0% by weight or less based on the total weight of the wire.

[0024]

EXAMPLES Examples of flux-cored wires for ferritic stainless steel according to the present invention will be specifically described below in comparison with comparative examples.

First, an example in which all the components contained in the wire are within the scope of the present invention is at least 1
A flux-cored wire was produced by using a material whose seed is out of the range of the present invention as a comparative example.

FIG. 1 is a sectional view showing various flux-cored wires used in the present invention. FIG. 1 (a) shows that while filling the inside of a strip-shaped steel outer skin M with a flux F, the steel outer skin M is bent into a tubular shape by abutting both end edges of the steel outer skin M, and then expanded to a predetermined diameter. It is a line. The butt end of this wire is flat,
In (b), the butted end faces are curved. In FIG. 1 (c), the abutting end portion is bent in an L shape to widen the abutting end surface. Further, FIG. 1 (d) shows the inside of a seamless steel outer skin M filled with a flux F.

In this example and the comparative example, FIG.
A flux-cored wire having a sectional shape of (b) and a diameter of 1.2 mm was used, and a mild steel or ferritic stainless steel having the chemical composition shown in Table 1 below was used as the metal outer shell. For each example and comparative example, the metal shell symbols used and the content of the chemical components in the wire are shown in Table 2 below.

Next, a weld metal was formed using these wires, and welding workability was evaluated.

FIG. 2 is a schematic sectional view showing a method for forming weld metal. As shown in FIG. 2, a mild steel weld base material 1
Has a V-shaped groove formed by subjecting the surface on which the weld metal is formed to a three-layer buttering treatment with a test wire,
The backing material 2 is disposed below the V-shaped groove. Weld metal 3 was formed in this groove. The welding conditions for forming the weld metal are shown in Table 3 below.

Next, a test piece was sampled from the weld metal thus formed, the oxidation resistance was evaluated, and the microstructure was observed.

FIG. 3 is a schematic cross-sectional view showing a sampling position of the test piece for the oxidation resistance test from the weld metal. In the present example and comparative example, as shown in FIG. 3, the groove angle of this V shape was 45 °, and the groove width of the lower portion where the backing material was arranged was 10 mm. The distance from the tip of the groove to the backing material was 12 mm.

The test piece 4 for the oxidation resistance test is in the shape of a cylinder having a diameter of 10 mm and a length of 15 mm, and the test piece 4 is placed so that the center of the weld metal 3 becomes the center of the circle of the cross section of the test piece. 4 were collected. The surface of the test piece 4 was finished to about # 400. The oxidation resistance test is performed by subjecting the test piece 4 to continuous oxidation treatment for 200 hours in the air at 950 ° C.,
It was evaluated by measuring the weight change before and after the test, and the oxidation weight gain value was 5 mg / cm ² Less than ⊚ (very good), oxidation weight gain value is 5 to 10 mg / cm ² The one
(Good), oxidation weight gain value is 10 mg / cm ² Those which exceeded the above were rated as x (bad).

FIG. 4 is a schematic cross-sectional view showing a sampling position of the test piece for microstructure observation from the weld metal. As shown in FIG. 4, the test piece 5 for microstructure observation is 10 mm ×
A test piece 5 having a rectangular parallelepiped shape of 10 mm × 5 mm was sampled so that the central portion of the weld metal was the center of the rectangular parallelepiped test piece, like the test piece 4 for the oxidation resistance test. The surface of the test piece 5 parallel to the sectional view was used as the microstructure observation surface. The microstructure was obtained by polishing the microstructure observation surface of the test piece 5,
Evaluation was carried out by microscopic examination of the material that had been subjected to etching treatment with aqua regia, and those in which the martensite phase was not confirmed were evaluated as ◯ (good), and those in which the occurrence of the martensite phase was confirmed were evaluated as x (bad).

FIG. 5 is a schematic sectional view showing a test method for welding workability. As shown in FIG. 5, two stainless steel plates 6a and 6b having a thickness of 1.5 mm are arranged so that the ends of the upper steel plate 6a are located at the center of the lower steel plate 6b. The positions were shifted. Then, the wire 7 held by the tip 8 is directed to the end of the steel plate 6a so as to be at a right angle to the steel plate, and lap fillet welding is performed in a state where the distance between the tip of the chip and the steel plate is 15 mm. Welding workability was evaluated for the three points of stability, spatter generation amount, and slag generation amount. The welding conditions for the welding workability test are also shown in Table 3 below.

The evaluation standard of the arc stability was ◯ when the arc stability was good, and x when the arc stability was bad. The evaluation criteria for the amount of spatter generated are that the amount of spatter generated per minute is 3 g or less is ◯ (good), and the amount of spatter generated is 3
Those exceeding g were rated as x (poor). The evaluation criteria of the slag generation amount were as follows: good (good) when the amount of slag generated was 400 mg or less per 300 mm of weld bead length, and bad (bad) when the amount of slag generated was more than 400 mg.

Further, the productivity evaluation standard is that in the wire drawing step in which the diameter of the finished wire is 1.2 mm, the wire is not broken even once with respect to 100 kg of wire, and the wire is broken (excellent). Those that occurred once were evaluated as Δ (good).
The results of these evaluations are shown in Table 4 below.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

As shown in Tables 2 and 4, for the examples in which all the components contained in the wire are within the scope of the present invention, the oxidation resistance and welding workability are good, and martensite is also confirmed. There wasn't. In addition, in Example No. 3 using a metal shell made of mild steel (metal shell symbol a). Regarding 1 to 4, 6 and 8 to 9, the wire productivity was extremely excellent.

On the other hand, in Comparative Example No. In No. 15, the C content exceeded the upper limit of the range of the present invention, so the oxidation resistance was lowered.
Comparative Example No. In both 16 and 17, since the Si content was out of the range of the present invention, a large amount of spatter was generated. Comparative Example No. In No. 18, since the Mn content exceeds the upper limit of the range of the present invention, a large amount of martensite was generated.
Also, in Comparative Example No. In No. 19, the Cr content was less than the lower limit of the range of the present invention, so the oxidation resistance was lowered.

Comparative Example No. With respect to Nos. 20, 22 and 25, the content of Al, Ti or N was less than the lower limit of the range of the present invention, so that the effect of refining the ferrite crystal grains was decreased and the oxidation resistance was decreased. Comparative Example No. 21 is Al
Since the content exceeds the upper limit of the range of the present invention, the oxidation resistance is lowered, the arc becomes unstable, and a large amount of spatter is generated.

Comparative Example No. In No. 23, since the Ti content exceeds the upper limit of the range of the present invention, the slag increased. Comparative Example No. In No. 24, since the Nb content exceeds the upper limit of the range of the present invention, the oxidation resistance is lowered. Comparative Example No. In No. 26, the N content exceeded the upper limit of the range of the present invention, so the amount of spatter generated increased and the arc became unstable.

Comparative Example No. In Nos. 27 and 28, since the F content is out of the range of the present invention, the arc becomes unstable and No. For No. 28, the amount of spatter generated also increased. Also, in all of the comparative examples, those using the metal shell made of mild steel have excellent wire productivity, and those using the stainless steel metal shell (metal shell symbols b and c) are wire drawn. A wire break occurred in the process.

[0046]

As described in detail above, according to the present invention,
C, Nb, A while reducing the Cr content in the wire
By properly limiting the l, Ti and N contents,
It is possible to obtain a flux-cored wire for stainless steel which has excellent oxidation resistance of the weld metal and can reduce the cost of the welding material. Further, by adding Cr from the flux and using a metal shell made of mild steel, the cost is further reduced and the productivity of the wire is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing various flux-cored wires used in the present invention.

FIG. 2 is a schematic cross-sectional view showing a method for forming weld metal.

FIG. 3 is a schematic cross-sectional view showing a sampling position from a weld metal of a test piece for an oxidation resistance test.

FIG. 4 is a schematic cross-sectional view showing a sampling position of a test piece for microstructure observation from a weld metal.

FIG. 5 is a schematic cross-sectional view showing a welding workability test method.

[Explanation of symbols]

 1; Weld base material 2; Backing material 3; Weld metal 4, 5; Test pieces 6a, 6b; Steel plate 7; Wire 8; Chip M; Steel outer shell F; Flux

Claims (3)

[Claims] 1. A flux-cored wire in which a metal shell is filled with a flux, wherein Si: 0.07 to 2.0% by weight and Cr: 14. 5 to 17.0% by weight,
Al: 0.01 to 1.0% by weight, Ti: 0.05 to 2.0% by weight, N: 0.02 to 0.1% by weight and F:
0.005 to 0.5% by weight, with the balance being Fe and inevitable impurities, the inevitable impurities being C:
0.10 wt% or less, Nb: 0.2 wt% or less and M
n: A flux-cored wire for ferritic stainless steel, which is regulated to 0.5% by weight or less. 2. The flux-cored wire for ferritic stainless steel according to claim 1, wherein the metal skin is made of mild steel. 3. The slag slag forming agent in the flux is 2.
The flux-cored wire for ferritic stainless steel according to claim 1 or 2, which is 0% by weight or less.