JP2981167B2 - Stainless steel plate welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding a stainless steel sheet which is excellent in corrosion resistance and effective in improving the surface properties (aesthetic appearance) at a welding margin after welding. A method for obtaining a welded stainless steel sheet exhibiting the above characteristics by selection and proper post-processing after welding is proposed.

[0002]

2. Description of the Related Art Stainless steel sheets are widely used in various applications because of their excellent corrosion resistance. Especially in the case of cold rolled stainless steel sheet,
After being subjected to annealing and pickling treatment, it is subjected to welding and various processes to be used as various products and members.

In the case of a cold-rolled stainless steel sheet, it is used as a product in various applications after performing welding, for example, TIG welding, seam welding, spot welding, and the like. In addition, the same applies hereinafter, including both the “welded metal portion” and the “weld heat affected zone”, and inevitably generates a weld scale (which is distinguished from the annealed oxidation scale). In particular, this weld scale causes a significant deterioration in the aesthetics and corrosion resistance of the product, so that its formation must be prevented or eliminated. Therefore, conventionally, the entire area of the welded portion is sealed and welded with an inert gas to prevent the formation of a surface oxide scale on the welded portion, or is formed by performing pickling or buffing in a later step. A method of removing a welding scale is employed.

[0004]

However, with respect to the above-mentioned measures for preventing and removing the formation of the weld scale, for example, in the case of the method using buffing, the surface is polished and not polished. There is a problem that a difference in gloss occurs. In addition, when pickling is performed, there is a problem that streak-like pickling is generated in a “welded marginal portion” which is an outer region of the welded portion (further outer region of the weld heat affected zone). All of these significantly impair the aesthetic appearance of the stainless steel surface, so that it is necessary to prevent the formation.

[0005] A main object of the present invention is to establish a welding technique for obtaining a stainless steel sheet having excellent surface properties after welding, particularly at a welding margin, without sacrificing the corrosion resistance of the stainless steel at all. Another object of the present invention is to provide a welded stainless cold-rolled steel sheet in which streak-like pickling does not occur at the periphery of the weld during pickling after welding. Another object of the present invention is to propose a new post-treatment method for descaling applied to a welded stainless steel sheet to improve the surface properties after welding. Still another object of the present invention is to propose a method of effectively utilizing a chromium-depleted layer formed immediately below an annealed oxide scale of a stainless steel sheet for welding to improve weldability.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems and achieve the above object, and have obtained the following findings. The stainless steel plate pickled after welding has portions where stains occur when pickling and portions where the stains do not occur.
If you observe these parts carefully, you can see the difference in the form of corrosion.
For example, as shown in FIG. 1, fine pits are formed in the grain on the surface of the stainless steel plate where the stain occurs, and it is found that there is no such pit in the portion where the pickling does not occur. . Irregular reflection of light occurs depending on the presence or absence of pits on the surface of the stainless steel plate, and this is recognized as pickling by a viewer. The difference in the corrosion form is caused by the difference in the scale structure of the weld scale generated by the difference in the stainless steel surface temperature during welding.

[0007] Based on such knowledge, the present inventors have
The mechanism by which pickling occurs during pickling after welding and its prevention method were further studied. As a result, the scale structure itself generated during welding cannot be changed, so the next step, that is, the method of uniformly dissolving and removing the surface during pickling of the welded stainless steel sheet, is more effective in preventing pickling from occurring. We concluded that it was effective.

In general, the annealed oxide scale formed during annealing of a cold-rolled stainless steel sheet deteriorates the corrosion resistance of the product, so that it is subjected to neutral salt electrolysis (or nitric acid electrolysis) or salt bath immersion followed by nitric acid electrolysis or sulfuric acid electrolysis. The chromium-depleted layer formed immediately below the scale is dissolved and removed by performing a nitric hydrofluoric acid immersion treatment.

[0009] On the other hand, the method that the present inventors have found is that a stainless steel sheet annealed after cold rolling is used.
After neutral salt electrolysis (nitric acid electrolysis) or salt bath immersion followed by nitric acid electrolysis or sulfuric acid electrolysis, the conventional nitric hydrofluoric acid immersion treatment is omitted, so that a chromium-depleted layer is actively formed on the stainless steel surface. The first feature is to use the one that has been left. Second, when the welding scale is pickled and dissolved and removed after welding, the residual chromium deficient layer immediately below the welding scale is removed together with the welding scale.

[0010] That is, a stainless steel sheet having a chromium-deficient layer which has no problem in weldability is used as a raw material, which is welded, and the chromium-depleted layer is removed together with the welding scale during pickling after the welding. Upon removal, even at the weld marginal area, which is the main cause of the above-described acidic stain, no pits are observed in the grains in this area, as shown in FIG. 2, and therefore, no acid wash is observed. I discovered that.

[0011] The idea is that the stainless steel plate for welding is always welded, and after the welding, pickling is always performed to remove the weld scale, so the chromium-depleted layer must be removed at this stage. If carried out, it is possible to prevent the deterioration of the corrosion resistance of the final product, and it is possible to obtain a welded stainless steel product without generating the pickling stain observed in the above-mentioned welding marginal area. is there. In this sense, in the welding method of the present invention, the stainless steel sheet used as a material may be subjected to a weak nitric hydrofluoric acid treatment after annealing to leave a thin chromium-depleted layer on the surface of the stainless steel sheet. Good.

The gist of the present invention described above is as follows. (1) A method for welding stainless steel sheets, wherein a material for welding stainless steel sheets whose surface is covered with a chromium-deficient layer is used for welding. (2) As a material for welding stainless steel plates, use a material in which only the chromium-deficient layer remains by removing the annealed oxide scale on the surface of the steel plate.After welding, dissolve and remove the chromium-depleted layer together with the welding scale. Characteristic welding method of stainless steel plate. In each of the above inventions, the thickness of the chromium-deficient layer is desirably 0.5 μm to 30 μm.
The invention is also a particularly advantageous method for welding austenitic stainless steel.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, when a stainless steel sheet for welding used as a raw material is pickled after annealing a cold-rolled steel strip, only the annealed oxidized scale on the surface is removed to ensure weldability. The chromium-depleted layer immediately below the annealed oxide scale is left exposed on the surface, and the stainless steel is welded using such a welding material, so that pickling after welding can be performed without impairing corrosion resistance. An object of the present invention is to prevent pickling during treatment.

[0014] In the present invention, the above-mentioned material has a chromium-deficient layer having a thickness of 0.5 to 30 µm on the surface of a cold-rolled stainless steel sheet.
Use those within the range. The reason is that in the process of removing the scale (pickling) after welding the cold-rolled stainless steel sheet, if the chromium-depleted layer has a thickness of 0.5 μm or less, some pickling will occur. On the other hand, if the thickness of the chromium deficient layer is 30 μm or more, the chromium deficient layer remains after the dissolution removal treatment after welding, and the corrosion resistance is significantly deteriorated. From this, the thickness of the chromium deficient layer remaining on the material surface is 0.5-30 μm,
Preferably it is in the range of 1 to 10 μm, more preferably 1 to 5 μm.

Next, on the surface of the stainless steel material for welding,
Various methods can be applied as a method for leaving a chromium-deficient layer having a predetermined thickness. For example, by annealing a cold-rolled stainless steel sheet in a combustion gas atmosphere, a chromium-depleted layer is formed immediately below the scale, and then subjected to a neutral salt electrolytic treatment or a salt bath immersion treatment, and if necessary, nitric acid electrolytic treatment or sulfuric acid treatment. The post treatment is stopped by performing the electrolytic treatment. That is, a method of omitting the pickling step that is usually performed thereafter. After annealing in a combustion gas atmosphere, a method in which only the scale is positively removed (by shot blast or the like) may be used.
In any case, any method can be used as long as a chromium-deficient layer having a predetermined thickness is left on the surface of the stainless steel sheet and a stainless steel sheet whose surface is covered with the chromium-depleted layer can be obtained. Good.

Further, as a method for dissolving and removing the weld scale together with the residual chromium-deficient layer immediately below the weld scale,
Nitric hydrofluoric acid, sulfuric hydrofluoric acid, aqua regia, etc. are applied.

As the welding means for the stainless steel material for welding, resistance welding such as spot welding and seam welding and arc welding such as MIG welding and TIG welding are advantageously applicable.

[0018]

EXAMPLE In this example, SUS304 stainless steel plate was used as a stainless steel material for welding (chemical composition is shown in Table 1).
The stainless steel cold-rolled sheet was annealed in a butane combustion atmosphere (oxygen concentration: 5%) (final sheet temperature: 1100 ° C.), water-cooled, and a 50 × 200 × 1 t (mm) sample was prepared. Thereafter, the sample was subjected to descaling treatment (that is, treatment for leaving a chromium-deficient layer) under various conditions shown in Table 2 and used.

Then, the above sample was subjected to TIG welding.
(Condition: 50 A, Ar 7 L / min. 300 mm / min). Further, thereafter, pickling was performed to dissolve and remove the weld scale of the welded plate. Then, pickling was observed for the material after the treatment.

In this observation of pickling, each sample was measured for 2
It was immersed in a solution of N-HNO ₃ (2 mol / L) + 1N-HF (1 mol / L) + 10Fe (g / L) (25 ° C.) for 30 minutes, and the degree of pickling was visually observed. -The descaling conditions in the table were as follows. Salt bath: Alkaline molten salt of NaOH 80%, NaNO ₃ 10% (the remainder is impurities such as water). Immersion in 450 ° C for 10 seconds. Neutral salt electrolysis: Na ₂ SO ₄ 180g / L aqueous solution at 80 ° C, id 0.0
Electrolysis was performed at +10 s−10 s + 10 s at 6 A / cm ² . Nitric acid electrolysis: 60 ℃ in 2N HNO ₃ aqueous solution, id 0.05A / cm ²
-10 s +10 s was electrolyzed. Sulfuric acid electrolysis: H ₂ SO ₄ 0.7 M / L, temperature 25 ° C, current density 5
Electrolysis was performed at 0 mA / cm ² electrolysis time of −15 s and +15 s. Nitric hydrofluoric acid immersion: 0.8N HNO ₃ 0.4N HF.30g / L 60 in Fe aqueous solution
Soaked at ℃.

The results are shown in Table 2 and FIGS. 3 and 4. In the method of the present invention (FIG. 4), no pickling was observed at all, whereas the conventional method was as shown in FIG. At the same time, pickling stains were apparently generated at the weld margins. In particular, as shown in the table, this is remarkable when a material having a chromium-deficient layer thickness of more than 0.5 μm is used as a welding material.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

As described above, according to the welding method of the present invention, the use of a material having a chromium-depleted layer remaining on the surface thereof as a material for a stainless steel plate for welding completely eliminates the occurrence of pickling by welding. Can be prevented. That is,
In the case of welding, by removing the welding scale generated on the surface by the subsequent pickling with an oxidizing solution together with the chromium-depleted layer that existed before welding, deterioration of corrosion resistance is prevented and acid during pickling is prevented. Since the occurrence of washing is completely prevented, the surface properties (aesthetic appearance) of the stainless steel sheet after welding are significantly improved as compared with the conventional material.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view schematically showing a structure of a welding frontier part after welding a conventional stainless steel plate.

FIG. 2 is an explanatory view schematically showing a structure of a welding frontier part after welding of the stainless steel sheet of the present invention.

FIG. 3 is a photograph of a metal surface structure showing the results of a bead-on TP pickling test showing the appearance of pickling of a conventional stainless steel plate.

FIG. 4 is a photograph of a metal surface structure showing the results of a bead-on TP pickling test showing the appearance of pickling of the stainless steel sheet of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Hayakawa 4-2 Kojima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nippon Yakin Kogyo Co., Ltd. (72) Inventor Takahiro Takai 4 Kojima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 2 Nippon Yakin Kogyo Co., Ltd. Research and Development Division Technology Research Laboratory (56) References JP-A-6-648 (JP, A) JP-A-2-200394 (JP, A) JP-A-2-224873 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C25F 1/06

Claims (4)

(57) [Claims] 1. A method for welding a stainless steel sheet, comprising using a material having a chromium-deficient layer remaining on the surface of the steel sheet as a material for welding a stainless steel sheet, and welding the material. 2. A material for welding a stainless steel sheet, in which an annealed oxide scale on a steel sheet surface is removed to leave only a chromium-deficient layer, and in a post-weld post-treatment, the chromium-depleted layer is removed together with the welding scale. A method for welding stainless steel sheets, characterized by dissolving and removing. 3. The chromium-depleted layer has a thickness of 0.5 μm to 30 μm.
The welding method according to claim 1, wherein the thickness is μm. 4. The welding method according to claim 1, wherein the stainless steel sheet is an austenitic stainless steel sheet.