JPH1085943A - Corrosion resistant welding method for stainless steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve corrosion resistance in a weld zone by r specifying the maximum thickness of the welded metal part formed in a welded stainless steel plate a prescribed value or above. SOLUTION: The welded metal part 3 and a pressed part 4 in the outside of it are formed in the seam welded position of two stainless steel plates 1, 2, and further gaps 5 are formed in the outside of them. When the maximum thickness of the welded metal part 3 is 80% or above of the plate thickness and also the interval of the gap in the place 50μm away from the position wherein the gaps 5 begin to open is 4μmor above, excellent corrosion resistance is obtained. The ferritic stainless steel containing Cr, Mo, and the contents satisfies Cr+3Mo>=24 is used as the stainless steel plate used in a superposing resistance welding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion prevention welding method for a stainless steel sheet, and more particularly to a resistance welding method for obtaining a ferritic stainless steel welding steel sheet having excellent corrosion resistance. The present invention provides a welding method for obtaining a so-called effective anticorrosion welded plate, which is effective for preventing crevice corrosion which is likely to occur at the time.

[0002]

2. Description of the Related Art Generally, stainless steel, especially ferritic stainless steel, is preferred as a material for various water heaters because of its low cost and good corrosion resistance in hot water. It should be noted that when using these materials, structural gaps are inevitably generated during welding, and if such gaps are present in the welded area, chlorine ions present in tap water will be concentrated. Crevice corrosion may occur, or in the presence of residual stress, stress corrosion cracking may occur, resulting in a water leakage accident.

[0003] Conventionally, as a method for solving the above-mentioned corrosion problems caused by tap water for stainless steel welded plates,
There was a method of applying a sacrificial anode technology using Al or Zn to prevent corrosion. However, this conventional technique has a problem that clogging is caused by a precipitate of hydroxide eluted from the sacrificial anode, and that the precipitate must be frequently cleaned.

[0004] In addition, there is a method of improving the corrosion resistance of a welded portion by performing a welding method for preventing generation of a gap (see Japanese Patent Application Laid-Open No. 63-27114). However, also in this case, for example, in the case of resistance welding such as seam welding, the generation of a gap cannot be avoided due to the characteristics of this welding, and therefore, a large amount of Cr or Mo, which is an element that improves corrosion resistance, is added. Even when corrosion-resistant stainless steel was used, there was a concern that crevice corrosion would still occur.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is a method developed for the purpose of solving the problems. In particular, the method is inevitably generated during resistance welding such as seam welding. An object of the present invention is to provide a welding method for effectively preventing corrosion of a weld plate gap.

[0006]

In order to achieve the above object, the inventors of the present invention have made the thickness of a weld metal formed when two stainless steel plates are resistance-welded, and spread the solidified shrinkage outside the weld metal. Focusing on the clearance between two stainless steel plates, the relationship between these and the corrosion resistance was examined. As a result, it was found that when the maximum thickness of the weld metal portion was set to 80% or more of the plate thickness and the gap between the positions 50 μm away from the position where the clearance was generated was set to 4 μm or more, corrosion by tap water did not occur.

That is, according to the present invention, first, when two stainless steel plates are overlapped and resistance-welded, the maximum thickness of the weld metal portion formed on the stainless steel weld plate is set to the plate thickness.
This is a corrosion protection welding method for stainless steel sheets characterized by being 80% or more. Further, in the above-described anticorrosion welding method of the present invention, in addition to the above conditions, in resistance welding, a clearance interval at a position 50 μm away from a position where a clearance starts to be formed between two stainless steel plates is set to 4 μm or more. It is a feature.

[0008] In addition, the anticorrosion welding method of the present invention provides a stainless steel sheet to be subjected to lap resistance welding, which contains Cr and Mo, and whose content (wt%) satisfies Cr + 3Mo ≧ 24. It is characterized by using a material based on stainless steel (SUS444).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an experiment which led to the development of the method of the present invention will be described below together with the results. The test materials No. 1 and No. 2 used in this experiment are both ferritic stainless steels (SUS444), and their chemical components are shown in Table 1. The thickness of the stainless steel plate subjected to welding is 0.3 mm. In addition, seam welding was performed under the following conditions. Seam welding conditions; Current: 5400A, 6600A, Pressure: 2.5kg, Electrode width: 5m
m, welding speed: 3m / min

[0010]

[Table 1]

FIG. 1 shows a cross section of the seam welding plate. As shown in the figure, two stainless steel plates 1
, 2 are formed with a weld metal part 3 at the seam welding position and a press contact part 4 on the outside thereof, and further with a gap 5 on the outside thereof.
Is formed. Therefore, for this welded plate, the maximum thickness of the weld metal portion and the distance between the gap 5 at a position 50 μm away from the position where the gap 5 starts to open were measured.

Next, in order to evaluate the corrosion resistance of these welded metal plates, test pieces shown in FIG.
The crevice corrosion initiation potential was measured in 80 ° C. hot water containing 200 ppm of Cl ⁻ . In this evaluation test, when stainless steel is generally immersed in tap water, the natural potential is about 0.1 V
_Since it rises to _SCE , the crevice corrosion potential is 0.1
Those with _VSCE or more were judged to have corrosion resistance. The results are shown in FIGS.

[0013] From these results, if the maximum thickness of the weld metal portion is 80% or more of the plate thickness, and if the gap between the locations 50 µm away from the position where the gap begins to open is 4 µm or more, crevice corrosion The generated potential was 0.1 V _SCE or more, and it was found that the film had good corrosion resistance. However, it was also found that the component composition of the test material was required to be a stainless steel whose Cr and Mo content (wt%) satisfied the formula of Cr + 3Mo ≧ 24.

In short, the present invention has been developed based on the above findings, and it has been found that when such anti-corrosion welding is performed, a welded plate of ferritic stainless steel does not corrode even in hot water at 80 ° C. .

[0015]

Next, an embodiment of the present invention will be described. Table 2
Ferritic stainless steel with the composition shown in the table: Thickness 0.3
Using two mm, a solar water heater heat collecting plate was prepared. The welding conditions at this time were the same as above, with a current value of 5000A and
7000A. Corrosion test, cut a test piece comprising a weld line as shown in FIG. 5, 200 ppm of Cl ^- was carried out one month immersion in hot water of containing 80 ° C.. The results are shown in Table 2. As is clear from the results shown in Table 2,
The maximum thickness of the weld metal part 3 generated inside the welded section cross section is 80% or more of the plate thickness, the gap between the places 50 μm away from the position where the gap starts to open is 4 μm or more, and C
Specimen No. with r and Mo content (wt%) satisfying Cr + 3Mo ≧ 24
In Example 3 of the present invention, crevice corrosion did not occur at all, and it was recognized that the sample had good corrosion resistance. In contrast, the plate thickness is 80%
Comparative example in which the clearance is less than 4 μm.
In 4), the weld plate penetrated due to crevice corrosion.

[0016]

[Table 2]

[0017]

As described above, when corrosion-resistant welding is performed on a stainless steel plate according to the present invention, the corrosion resistance of the welded portion of a solar water heater or the like can be greatly improved, and the reliability of the water heater can be improved. Can be.

[0018]

[Brief description of the drawings]

FIG. 1 is a cross section of a resistance welded portion, showing the shape of a weld metal portion and a gap.

FIG. 2 is a view schematically showing a test piece for evaluating the corrosion resistance of a resistance weld.

FIG. 3 is a graph showing a relationship between a maximum thickness of a weld metal portion and a clearance interval with respect to corrosion resistance of a resistance weld portion.

FIG. 4 is a graph showing a relationship between a maximum thickness of a weld metal portion and a clearance interval with respect to corrosion resistance of a resistance weld portion.

FIG. 5 is a schematic diagram of a corrosion test piece.

[Explanation of symbols]

 1, 2 stainless steel plate, 3 weld metal part, 4 press contact part, 5 clearance

Claims (3)

[Claims] 1. A stainless steel sheet wherein the maximum thickness of a weld metal portion formed on the stainless steel welded plate is set to 80% or more of the plate thickness when two stainless steel plates are overlapped and resistance-welded. Corrosion-proof welding method. 2. The anticorrosion welding method according to claim 1, wherein in the resistance welding, a clearance interval at a position 50 μm away from a position where a clearance starts to form between two stainless steel plates is 4 μm or more. 3. A stainless steel sheet to be subjected to lap resistance welding, containing Cr and Mo and its content (wt%).
3. A ferritic stainless steel having a component composition satisfying Cr + 3Mo.gtoreq.24.
Anticorrosion welding method described in 1.