JPS6327114B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for seam welding stainless steel, and provides a welding method that reduces the occurrence of crevice corrosion in welded parts. Ferritic stainless steel, such as SUS304, which prevents intergranular corrosion at welded parts, has excellent corrosion resistance in environments containing slight chloride ions such as tap water, so it is widely used in various kitchen appliances and hot water equipment. It is being However, when used in hot water equipment, crevice corrosion or stress corrosion cracking accompanying crevice corrosion may occur, particularly in the gaps created by welding, which may lead to water leakage. For this reason, for equipment that has a welded gap structure and is used for applications where crevice corrosion is a concern,
Corrosion prevention methods such as Al sacrificial anodes are generally used, but there are problems such as water becoming cloudy due to the formation of sludge due to the elution of sacrificial anode materials, and piping systems etc. being easily clogged. There is a strong desire to develop a welding method that does not impair the corrosion resistance of stainless steel. It is possible to avoid a gap structure by increasing the gap between gaps to prevent crevice corrosion when using fusion welding such as TIG welding, but this is not possible when using resistance welding such as seam welding. close. Therefore, such applications have resource constraints and are forced to use expensive highly corrosion-resistant stainless steels such as SUS316 and SUS444, which contain Mo.
This results in an increase in manufacturing costs. Moreover, even when these steels are used, crevice corrosion may occur in seam welds, and the current situation is that there are not necessarily sufficient countermeasures. In view of the above circumstances, the present inventors focused on the welding scale that occurs on the inner surface of the gap during seam welding, and in order to clarify the influence of welding scale on crevice corrosion of stainless steel, we investigated its generation state, concentration,
We investigated the relationship between corrosion at the location where it occurs. As a result, we learned that the occurrence of crevice corrosion in weld gaps is largely caused by weld scale that occurs in the gaps. When the boundary between a welded part and a non-welded part is exposed to a corrosive environment, it will corrode preferentially over other parts. That is, if weld scale exists in the gap, crevice corrosion will occur due to this. From this, in order to prevent deterioration of corrosion resistance in the gaps due to seam welding, it is sufficient to weld so that weld scale is generated outside the gaps, and to achieve this,
It has been found that welding can be performed so that the width of the welded or press-welded portion is 90% or more of the width of the welding electrode in contact with the material to be welded. The present invention will be described in detail below with reference to the drawings. When stainless steel plates are seam welded and one of the plates is peeled off along the welded area, a band-shaped scale with a width of about 50 to 100 microns is found near the boundary between the remaining stainless steel plate and the welded area. The situation in which this scale occurs varies depending on the welding conditions, but it is generally classified into three types as shown in FIG.
That is, as shown in Fig. 1A, a band-shaped scale 2 (referred to as type A) separated from the welded part 1, Fig. 1B
A wavy band-like scale 2 (referred to as type B) consisting of repeating semicircular shapes whose legs are in contact with the weld 1 as shown in FIG. Massive scale 2
(referred to as type C). A 0.3 mm thick plate of 18Cr-1Mo-Nb ferritic stainless steel was used as the test material, and resistance seam welding was performed under the following conditions. Welding conditions Electrode width: 4 mm Welding speed: 2 to 3 m/min Pressure force: 250 kg The results are shown in Table 1.

[Table] Corrosion status during immersion.
Width of welded (pressure welded) part
(2)

Claims (1)

[Claims] 1. A stainless steel seam welding method characterized by welding so that the width of the welded or pressure-welded part is 90% or more of the width of the welding electrode in contact with the material to be welded.