JP3266344B2 - How to prevent oxidation in stainless steel welding. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to welding of stainless steel, particularly to TIG welding, which is one type of arc welding.
In particular, the present invention relates to a welding method capable of preventing oxidation which causes discoloration.

[0002]

2. Description of the Related Art Conventionally, methods for welding stainless steel include TIG welding, covered arc welding, MIG welding, and MA welding.
There are G welding, carbon dioxide arc welding, self-shielding arc welding, and the like, and particularly TIG welding is widely used.

[0003] In this TIG welding, argon gas or a mixture of helium, oxygen and hydrogen in argon gas is discharged from a welding nozzle as a shielding gas to protect the molten metal from the atmosphere and to form a good weld. It has been practically used without any problem in mechanical strength.

[0004] However, this TIG welding has a disadvantage that the welded portion and its peripheral portion are discolored by oxidation, and the discolored portion is liable to generate rust. In particular, stainless steel products are commercialized in a welded state, so the commercial value decreases if the discolored portion has the above-mentioned discolored portion.
Post-processing is performed by a method such as buffing or silver powder spraying, which has a problem that there are many steps in the operation.

As a means for preventing discoloration in TIG welding, a method of applying an antioxidant to the surface of the base material before welding is also practiced. However, although it has a certain effect, it takes time and effort to apply. It is difficult to apply the antioxidant so that it conforms to the range in which the antioxidant is applied, and it is impossible to supply the antioxidant afterwards, so the absolute amount of the antioxidant is often insufficient. It cannot be said that there are many problems.

[0006] Further, in any stainless steel welding method other than TIG welding, there is no problem in the mechanical strength of the welded portion. However, similar to TIG welding, there is a problem of discoloration due to oxidation of the welded portion and its surroundings. They have drawbacks such as defects in appearance and rust. In particular, in recent years, automation and robotization of stainless steel welding have been advanced, and there is a strong demand for the appearance of an antioxidant technology that can easily cope with such automation.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the occurrence of discolored portions due to oxidation in conventional arc welding of stainless steel as described above. It is an object of the present invention to provide a new and very useful anti-oxidation method for welding stainless steel, which prevents the welding method itself from oxidizing the weld bead and its peripheral portion and does not generate discolored portions without application. .

[0008]

In order to achieve the above object, the present inventors have made intensive studies and found that the welding nozzle has a double structure.
From the inner nozzle, a normal shield gas flows out to form a good weld bead, and from the outer nozzle, a mixture of a normal shield gas containing a boron compound having a specific chemical structural formula as an antioxidant. It has been found that by causing the gas to flow out, it is possible to extremely effectively prevent the generation of a discolored portion due to oxidation of the welded portion and the vicinity of the welded portion.

That is, in the present invention, a double nozzle is used as a welding nozzle, a normal shield gas flows out from an inner nozzle, and a normal shield gas flows from an outer nozzle into a general shield gas represented by the following general formula (1) or (2). A method of preventing oxidation in stainless steel welding, characterized by flowing out a mixed gas containing one or more selected from the group of boron compounds represented by the formula (1). General formula

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(Wherein R1, R2 and R3 in the general formula are O
Cn Hm or Cn Hm, where n is an integer of 0 to 6,
m represents an integer of 1 to 12. )

The present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic explanatory view showing one embodiment of the method of the present invention, in which only a nozzle portion is shown in an enlarged sectional view.
Like the nozzle portion in this figure, the present invention uses a double nozzle in which a double tip member (S) is mechanically connected to a normal welding nozzle (N), for example.

The inner nozzle (i) in this double nozzle
Is provided with an electrode (e) at the center thereof, and a shielding gas (g) supplied from a gas cylinder (b) as shown by an arrow (a) in the figure passes around the electrode (e). Flows out from the tip of the inner nozzle (i) and shields the base material (M). Examples of the type of the shielding gas (g) flowing out from the inner nozzle (i) include a known shielding gas such as argon gas, or a gas obtained by mixing helium, oxygen, hydrogen, etc. with argon gas, for welding stainless steel. , Which are effective for forming a suitable weld bead.

On the other hand, from the outer nozzle (z) of the double nozzle, a mixed gas (t) containing the above-mentioned ordinary shielding gas containing a special gas having an antioxidant property is passed through a path (p) from the arrow (FIG. It is guided and discharged as in (b). The present invention uses this mixed gas (t) for the outer nozzle (z).
The most characteristic feature is to prevent the weld and its surroundings from being oxidized and to prevent the occurrence of discolored portions.

The special gas having an antioxidant property contained in the mixed gas (t) is one or two selected from the group of boron compounds represented by the following general formula (1) or (2). It is one that has vaporized more than seeds.

[0014]

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[0015]

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In the above general formulas (1) and (2), R
1, R2 and R3 each represent OCn Hm or Cn Hm, where n is an integer of 0 to 6 and m is an integer of 1 to 12, and is usually various oxyalkyl groups, oxyphenyl groups,
Or various alkyl groups or phenyl groups, wherein n is 0 and m
Is 1 means a hydroxy group or a hydrogen group. If the above n and m are integers exceeding a predetermined value, the boiling point of the boron compound becomes too high and gasification becomes difficult.

Specific examples of the boron compound represented by the above general formula 1 or 2 include trimethyl borate, triethyl borate, triisopropyl borate,
Tributyl borate, triphenyl borate, trimethyl boron, triethyl boron, triphenyl boron, trimethoxy boroxine, triethoxy boroxine, trimethyl boroxine, triethyl boroxine and the like can be mentioned.

In the present invention, one or more selected from the group of various boron compounds as described above are contained in a normal shielding gas and discharged from the outer nozzle (z) as a mixed gas. As the normal shielding gas, similarly to the shielding gas (g) flowing out from the inner nozzle (i), a known shielding gas such as argon gas or a gas obtained by mixing helium, oxygen, hydrogen or the like with argon gas is used. You can do it.

The amount of the boron compound contained in the ordinary shielding gas is desirably 10 mg / liter or more in terms of the concentration of the boron compound with respect to the shielding gas.
Even if the content is less than this, the effect is recognized but it cannot be said to be complete, and post-treatment is required. There is no particular problem even if the content is large, but the effect is the same if the content is too large, and it is usually useless to contain 150 mg / liter or more.

The method for obtaining the mixed gas (t) is as follows.
There are various means. For example, as shown in FIG. 1, one or more liquids (L) of the boron compound are stored in a mixing tank (k), and a gas cylinder of a usual shielding gas (L) is stored. As shown in the arrow (c) in the figure from b), it is appropriate to introduce a shielding gas into the liquid (L) and to eject and pass the shielding gas to contain a boron compound in the shielding gas. In this case, the content can be determined by adjusting the temperature of the liquid (L).

As another mixing means, one or more of the above-mentioned boron compounds are gasified in advance and separately stored in a gas tank, and directly mixed with a normal shield gas by a pipe and a valve capable of adjusting a flow rate. 1, and a method in which the shielding gas is introduced into the upper gas instead of into the liquid to mix the liquid (L) while being vaporized by heating.

In the double nozzle according to the present invention, the inner diameter of the outlet of the inner nozzle (i) depends on the thickness of the electrode rod, but is naturally larger than the diameter of the electrode rod. Of the range. The inner diameter of the outlet of the outer nozzle (z) is naturally larger than the outer diameter of the inner nozzle (i), and it is usually desirable that the inner diameter of the outlet is 2 mm or more larger than the outer diameter of the inner nozzle (i).

[0023]

The present invention is as described above, in which the normal shielding gas flows out from the inner nozzle to form a weld bead in a good condition, while the outer nozzle has an antioxidant property. Because the boron compound of a special chemical structure having it flows out in a state mixed with ordinary shielding gas,
This has the effect of preventing discoloration of the welded portion and its surroundings due to oxidation, and as described in the effect section described below, exhibits extremely usefulness in workability, efficiency, automation, and the like.

[0024]

EXAMPLE The following experiment was conducted using the apparatus as shown in FIG. Welding machine… Daihen Electrocompa 200S Welding torch… Daihen Co., Ltd. AW-26 type Double nozzle structure… Mechanically connected to the above welding torch Inner nozzle outlet inner diameter… 8 mm Inner nozzle outlet Outer diameter of ... 12 mm Inner diameter of outer nozzle outlet ... 15 mm

Welding conditions Welding current: 70 A Electrode: Tungsten rod containing 2% thorium (diameter 1.6 mm) Welding speed: 150 mm / min Arc length: 2 mm Projection length: 5 mm Filler rod: None

The welding method is a butt welding with a groove of 0 mm.
SUS304 stainless steel plate with a thickness of 2 mm was used as a welding base material, and argon gas alone (except for experiment number 14 only) was used as a shielding gas from the inner nozzle at 3 liters / hour.
Per minute.

On the other hand, from the outer nozzle, various boron compounds and other compounds shown in the column of "Antioxidant compound" in Table 1 were also added to the argon gas as a shielding gas in the column of "Content" in Table 1. The mixed gas contained at the indicated compounding concentration was discharged at a rate of 7 liter / min, and each welding experiment was performed. Table 1 shows the types and contents of the antioxidant compounds and the evaluation of the experimental results.

[0028]

[Table 1]

In Table 1, Experiment No. 1 is a blank test, Experiment No. 7 is a comparative example of a boron compound having too many carbon atoms, and Experiment Nos. 8 and 9 use silanes known as deoxidizing elements for steel. Comparative Example, furthermore, Experiment No. 1
Reference numeral 4 is a comparative example in which a boron compound was mixed into the inner nozzle and only argon gas was allowed to flow out from the outer nozzle. Therefore, the examples of the present invention correspond to Experiment Nos. 2 to 6 and Experiment No. 1
The numbers are 0 to 13, and Experiment Nos. 10 to 13 show the case where the content of the same boron compound is changed and Experiment No. 10 is slightly too small and Experiment No. 13 is considerably large.

In each of the evaluation columns in Table 1, Δ,
Although Δ and X are shown, Δ indicates a good state, Δ indicates a slightly bad state, and × indicates a bad state corresponding to each column. They are assessing what they are doing.

From the results shown in Table 1, it can be seen that in Examples of the present invention, in most cases, there was no discoloration due to oxidation and the color was close to the base color, and only Experiment No. 10 having a small boron compound content was slightly worse. is there. In comparison, Experiment No. 1 containing no boron compound, Experiment Nos. 8 and 9 using an antioxidant compound other than the boron compound, and further containing the boron compound in the gas from the inner nozzle and the outer nozzle Experiment number 1 in which only shielding gas was discharged
In 4, and the like, the welded part and its surroundings turned brown or blue or the like.

[0032]

The effects of the present invention are listed below in a bulleted form. (1) In the welding of stainless steel, the occurrence of discolored portions due to oxidation at and around the welded portion can be almost completely prevented. (2) Therefore, no rust is generated, and it is not necessary to correct the discolored portion by post-processing. Even if the product is manufactured in a welded state, its commercial value does not decrease at all.

(3) Since the welding method itself has an antioxidant function rather than a method of pretreating the welding base metal, the antioxidant may be insufficient, or the antioxidant range may shift. There is no failure and necessary and sufficient oxidation protection can be achieved. (4) Since there is no pre-treatment step or post-treatment step, it has extremely high efficiency, efficiency and labor saving. (5) Therefore, it has an advantage that it can easily cope with robotization and automation of welding, and meets the demands of the industry. As described above, the present invention has an extremely excellent effect, and exhibits extremely high utility in the welding technology of stainless steel.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an embodiment of an apparatus for carrying out the method of the present invention, in which only a nozzle portion is shown in an enlarged sectional view.

[Explanation of symbols]

 (N) Welding nozzle (S) Double tip member (M) Base material (i) Inner nozzle (e) Electrode (b) Gas cylinder (g) Shielding gas (z) Outer nozzle (t) Mixed gas (p) Path (k) Mixing tank (L) Boron compound liquid

Continuation of the front page (56) References JP-A-49-123452 (JP, A) JP-B-50-15454 (JP, B1) JP-B-50-31107 (JP, B2) JP-B-63-60095 (JP, B2) , B2) JP 58-55868 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 9/16 B23K 9/23

Claims (1)

(57) [Claims] 1. A double nozzle is used as a welding nozzle, and a normal shielding gas is discharged from an inner nozzle.
A mixture gas containing one or more selected from the group of boron compounds represented by the following general formula (1) or (2) is discharged from the outer nozzle into a normal shielding gas. To prevent oxidation in stainless steel welding. General formula Embedded image (However, R1, R2 and R3 in the general formula are OCn Hm
Or Cn Hm, wherein n is an integer of 0 to 6, and m is 1 to
Represents an integer of 12. )