JPH0212670B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for welding high purity ferritic stainless steel containing 10 to 20 wt% Cr. In recent years, austenitic stainless steels such as SUS304 and SUS316 have low resistance to stress corrosion cracking, so stainless steels containing 10 to 20 wt% of Cr and C and N have been developed to prevent stress corrosion cracking. High-purity ferrite stainless steel with reduced ferrite content is attracting attention. These high-purity ferrite stainless steels (hereinafter referred to as the “main steel materials”),
For example, the recently developed 18Cr−2Mo steel and 19Cr−
2Mo steel has better corrosion resistance and workability than SUS304.
It has properties similar to SUS316 and high resistance to stress corrosion cracking, and is being applied to various uses such as chemical equipment, either alone or as a plywood of clad steel plates. When using this steel material as a welded structure, when welding this steel material in one-sided butt multilayer welding, conventionally TIG
Full-thickness welding by welding, or
The method used was full-thickness welding using TIG welding using an austenitic stainless steel welding rod such as the D316L welding rod. However, in the former method, the entire structure of the weld metal becomes a ferrite phase, and the parts that come into contact with the atmosphere (hereinafter referred to as atmosphere contact parts), which can cause stress corrosion cracking, are highly susceptible to stress corrosion cracking. Although it had resistance, the crystal grains of the weld metal became coarse and the toughness value decreased. In addition, although the latter method satisfies the mechanical properties of the welded part, it does not solve the problem of stress corrosion cracking due to the austenite phase remaining in the atmosphere contact part, which limits the application of this steel material to welded structures. There were times when it happened. An object of the present invention is to provide a welding method that can satisfy both good mechanical properties and stress corrosion cracking resistance of the welded part when the present steel material is used as a welded structure. According to the research of the present inventors, when performing one-sided butt multilayer welding of this steel material, it is possible to weld the first layer to the third layer or more using a welding rod having the same composition as the steel material. The crystal grains of the weld metal become coarser, making welding defects such as cracks more likely to occur.Therefore, co-metal welding must be performed only on the first layer or up to the second layer, and on the second or third layer. The layer to the final layer can be welded using an austenitic stainless steel welding rod or an Inconel welding rod, and if the first layer side of the welded part is the side that comes into contact with the atmosphere, stress corrosion resistance can be achieved. It was found that both crackability and mechanical properties were satisfied. The present invention is based on these findings, and the main point is that when welding this steel material in one-sided butt multilayer, the first layer or up to the second layer is welded together using a welding rod with the same composition as the steel material, and the second layer or The third layer to the final layer are welded using an austenitic stainless steel welding rod or an Inconel welding rod. In the present invention, since the above-mentioned steel materials are butt welded on one side, the groove is shaped so that one side can be welded prior to welding, so that the first layer side is the atmosphere contact side. Welding of each layer in the present invention can be done by following normal welding methods, but for co-metal welding with this steel material, we aim for welding current of 90 to 140 A, welding voltage of 10 to 15 V, and welding heat input of 20 KJ/cm or less. It is preferable to carry out the In addition, when welding a clad steel plate in which this steel material is used as a plywood on a base material such as carbon steel or low alloy steel, the groove shape is formed so that the steel material as a plywood is on the first layer side in the same manner as above. , butt welding on one side is sufficient. In this case, welding from the second or third layer to the final layer after co-metal welding with the main steel material is performed using an austenitic stainless steel welding rod or an Inconel welding rod, as well as carbon steel that is the clad base material, low alloy welding, etc. Welding rods having the same composition as steel etc. can also be used. Austenitic stainless steel welding rods
Includes welding rods such as D316L, D308L, and D309L, and Inconel welding rods include ER NiCr according to AWS standards.
-3, etc., and all of these can be preferably used in the present invention. According to the present invention as described above, co-metal welding with the main steel material is performed only in the first layer or up to the second layer, so that the weld metal structure becomes a ferrite phase and coarsening of crystal grains is avoided. and also the second
from the layer to the final layer (from the third layer to the final layer if co-metal welding is performed up to the second layer) using an austenitic stainless steel welding rod or an Inconel welding rod (if this steel material is used as plywood for clad steel sheets) (including a welding rod having the same composition as the base material of the clad steel plate), the mechanical properties of the weld metal are improved. Therefore, if welding is carried out with the initial layer side facing the atmosphere contact side, the entire atmosphere contact area of the weld will be in the ferrite phase, which will have high resistance to stress corrosion cracking, and the crystal grains will Since they are fine, they have good toughness and mechanical strength. The invention will be explained in more detail below with reference to examples. Example 1 This steel material has a chemical composition shown in Table 1 and has a thickness of 75 mm.
Butt welding was performed using 19Cr-2Mo steel with a 60° V-shaped groove.

[Table] The first layer was 1.6mmφ YUS190L alloy TIG welded. At that time, the welding current was 120A, and the welding voltage was
The welding heat input was 12.5V and 19.1KJ/cm. 1.6mmφ D316ULC from 2nd layer to 5th layer (final layer)
TIG welding was performed using a welding rod. The welding current at that time was 110 to 140A, and the welding voltage was 12 to 14V. Table 2 shows the mechanical properties of the obtained weld, FIG. 1 shows the hardness distribution measurement results, and FIG. 2 shows a photograph of the cross-sectional structure. In Figure 1, A indicates the weld and B indicates the base metal.The measurement position was approximately 1 mm deep from the surface of the final layer, and the weld was measured at 2 mm intervals, and the base metal was measured at 1 mm intervals. did. These test results show that the properties of the welded part are good.

[Table] * 5mm sub-size example 2 19Cr-12mm plate with the chemical composition shown in Table 1
2Mo steel was welded with a rectangular groove by the welding method according to the present invention and the welding method using a full-thickness alloy welding method, and the hardness, impact properties, and stress corrosion cracking resistance of the welds were compared. As for the welding conditions, in the case of the method of the present invention, the first layer is welded with a welding current of 120A and the welding voltage is 12V, and the second to eighth layers are welded with a D316L welding rod at a current of 160~
190A, voltage 13-14.5V. In addition, for full-layer mutual metal welding, the current from the first layer to the 8th layer (final layer) is 120~
I did it at 190A and a voltage of 12-14.5V. (1) Comparison of hardness and toughness values of welded parts Figures 3 and 4 show cross-sectional microstructure photographs and hardness distributions of welded parts obtained by the welding method according to the present invention and the method using full-thickness alloy welding, respectively. As shown in the figure. In FIG. 3, a shows the case where the method of the present invention is used, and b shows the case where the full thickness alloy welding is used. Further, FIG. 4 shows the results obtained by the same measurement method as in FIG. 1, and in the figure, the ○ mark indicates the method of the present invention, and the △ mark indicates the case of full-thickness alloy welding. An impact test was also conducted using an impact test piece having a notch in the weld heat affected zone. The results are shown in FIG. Fifth
In the figure, the hatched area between the dashed-dotted lines shows the results for the welded part obtained by the method of the present invention, and the hatched area between the solid lines shows the results for the welded part obtained by full-thickness alloy welding. These results showed that the crystals in the welded area formed by full-thickness alloy welding were significantly coarsened, and the impact properties were extremely degraded. (2) Comparison of stress corrosion cracking resistance of welded parts
In accordance with the 42% Magnesium Chloride Corrosion Test Method, we conducted an evaluation test for stress corrosion cracking resistance of plate specimens taken from the first layer weld obtained by the welding method of the present invention and the alloy weld of SUS316L. I went. The test pieces obtained by the welding method according to the present invention had a thickness of 2 mm except for the welded portion of the first layer, and after U-bending, the test pieces were immersed in a boiling 42% magnesium chloride solution. The results are shown in Table 3.

[Table] ○: No cracking ●: Cracking From these results, the properties of the welded part obtained by the welding method of the present invention are superior to those obtained by the conventional welding method in terms of mechanical properties and resistance to corrosion cracking. It turns out that it is also excellent. Example 3 Using 19Cr-2Mo steel (YUS190L) with a plate thickness of 8 mm, a container having a tower diameter of 1 m, a body height of 2 m, and having 10% dish-shaped mirrors on the top and bottom was manufactured by the method of the present invention. Table 4 shows the welding conditions at that time.

[Table] The longitudinal weld line of the body of this container was taken at the same time as welding and used as a welded test piece with the main body, and various tests were conducted. The results are shown in Table 5. From Table 5, it can be seen that in the welded structures obtained by applying the method of the present invention, Example 1
It was also confirmed that the characteristics shown in Example 2 could be fully exhibited.

[Table] * 5mm sub size

[Brief explanation of drawings]

FIG. 1 is a hardness distribution diagram according to Example 1. FIG. 2 is a photograph of the cross-sectional structure of the welded part welded in Example 1. FIG. 3 is a photograph of the cross-sectional structure of the welded part welded in Example 2. FIG. 4 is a hardness distribution diagram according to Example 2. FIG. 5 is a diagram showing the results of an impact test in Example 2.

Claims (1)

[Claims] 1 In a method of butt multilayer welding of high-purity ferrite stainless steel containing 10 to 20 wt% Cr, one side butt welding is performed, and the first layer or up to the second layer is welded together using a welding rod with the same composition as the stainless steel. A method for welding high-purity ferritic stainless steel, the method comprising welding the second or third layer to the final layer using an austenitic stainless steel welding rod or an Inconel welding rod.