JPH0698499B2 - Stainless steel welding method and stainless steel welded body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a welding method and a welded body of a ferritic stainless steel having excellent heat resistance against high temperature oxidation and a Ni-containing austenitic stainless steel. is there.

[Conventional technology]

In recent years, ferritic stainless steels containing Al as a heat resistant material are superior to austenitic stainless steels in terms of high-temperature oxidation resistance, and have a strong resistance to stress corrosion cracking, which is a problem with austenitic stainless steels. It has become clear that it exhibits sex, and is drawing attention.
Therefore, this material is being switched and used in recent years for applications where austenitic stainless steel has been used, for example, exhaust gas parts for automobiles, stove parts, heating furnace walls, and the like.

However, when manufacturing a ferritic stainless steel strip containing Al, or when processing the product, when welding with austenitic stainless steel, when the welding part is subjected to processing such as cold rolling or bending, at the welded part. Cracks are likely to occur, and when it is remarkable, it breaks. Conventionally, it has been spliced with austenitic stainless steel by mechanical joining using rivets or the like, but the work efficiency is extremely low compared to welding joining. Further, in the case of manufacturing a steel strip, there is a demerit that the yield is lowered because cold rolling of the rivet portion is impossible.

[Problems to be Solved by the Invention]

The present invention relates to a ferritic stainless steel containing Ni and Ni.
By improving the cracking susceptibility in the weld with austenitic stainless steel containing, the workability of the weld is improved, and also the production of ferritic stainless steel strip containing Al and the ferritic stainless steel and Ni-containing austenite The purpose is to improve workability and yield in the production of welded products with stainless steel.

[Means for Solving the Problems]

The present invention has been completed as a result of various studies on the composition of the filler material and the welded portion for this purpose, and the gist thereof is as follows.

(1) In weight%, ferritic stainless steel containing Cr: 10 to 40%, Al: 3 to 12% and Ni-containing austenitic stainless steel are Ni ≧ 20% as a filler material, and Ni + Mo ≧
A welding method for stainless steel, which comprises using 30% high alloy so that the composition of the welded portion becomes a value within the region ABCDE in Fig. 1.

(2) A base material is a ferritic stainless steel containing Cr: 10 to 40% and Al: 3 to 12% by weight, and a Ni-containing austenitic stainless steel in a weight% basis.
Stainless steel welded body characterized by a value within the area ABCDE in the figure.

[Action]

 The reasons for limiting the present invention will be described in detail below.

In the present invention, the composition of the ferritic stainless steel containing Al is Cr: 10 to 40%, Al: 3 to 12%, and other C, Si, M.
It contains usual constituent elements such as n, and the balance is Fe and unavoidable impurities.

Cr is the most basic element that secures the oxidation resistance or corrosion resistance of stainless steel. In the present invention, if it is less than 10%, these properties are not sufficiently secured, while if it exceeds 40%, the toughness of the hot-rolled steel strip and the cold workability (ductility) are remarkably reduced. Therefore, the Cr component range is
It was set to 10 to 40%.

Al is an element that improves the oxidation resistance of ferritic stainless steel. If it is less than 3%, it is not sufficient to significantly improve the oxidation resistance, and if it exceeds 12%, the toughness of the hot-rolled steel strip is improved. Markedly reduced. Therefore, the Al component range is 3 to 12
%.

Further, in order to further improve the oxidation resistance of this ferritic stainless steel, a small amount of rare earth element (REM) may be contained. The rare earth elements here are lanthanoids such as La, Ce, Pr and Nd. However, if the content is too large, the REM-based oxide becomes coarse and the workability is significantly deteriorated. Therefore, the total content is preferably 0.50% or less. Further, in order to further improve the toughness and cold workability (ductility) of the hot rolled steel strip, one or more elements selected from Ti, Nb, V, Zr, Ta, Hf and B are added. It may be contained. These elements are
Forming nitrides or carbides respectively reduces solid solution C and N and improves workability. However, if the content is too large, the nitride or carbide will become coarse and the workability will be significantly reduced, so 0.50% or less in total is desirable.

In the present invention, the composition of Ni-containing austenitic stainless steel is preferably Cr: 15-30%, Ni: 7-20%. If necessary, Mo may be contained by 3% or less.

The present inventors, in order to clarify the effect of the weld composition and structure and filler metal composition on the workability of the weld, Cr: 2
Ferritic stainless steel containing 0%, Al: 5% and Cr: 1
Submerged arc welding experiments of austenitic stainless steel containing 8% and Ni: 8% and repeated bending tests of welds were carried out. Ni of the composition of the filler metal used in the welding
10 to 70%, Mo was changed to 0 to 20%, and the rest was changed to Cr and Fe. FIG. 1 shows the results of the composition of the weld zone, the amount of ferrite, and the presence or absence of cracks in the weld zone during cold rolling. The numbers in the figure represent the ferrite content (%) of the welded part, and ○ and ●.
Indicates the presence of cracks in the weld and the occurrence of cracks in cold rolling. From this figure, the composition of the welded portion is shown in the area AB in Fig. 1.
It was found that if the value in the CDE, that is, the amount of ferrite in the portion is 20% or less, the workability of the welded portion is significantly improved. In the figure, the coordinates of point C (45, 20, 35) are Cr + 3Al is 4
It shows that the composition is 5%, Ni + Mo is 20%, and Fe is 35%.
The mechanism of this workability improvement has not been clarified yet, but it is presumed as follows. The structure of the welded portion can change from the austenite single phase to the austenite + ferrite two phase to the ferrite single phase depending on the composition of the filler material. The ferrite phase here indicates both the δ-ferrite phase and the martensite phase. When the structure of the welded part contains a lot of ferrite phase and exceeds 20% in quantity, the solid solution hardening due to Al becomes extremely large due to the high solid solubility of Al in the ferrite phase, and the ductility decreases remarkably. Conceivable. Also,
Although Mo itself is a ferrite-forming element, it is presumed that the presence of Mo in the austenite phase lowers the solid solubility of Al and has the effect of promoting crystallization and precipitation of Al-based compounds. Further, it has been found that a filler metal having a composition of less than 20% Ni and less than 30% Ni + Mo cannot be used in order to make the component composition of the welded portion within the range ABCDE in FIG.
Therefore, the composition of the filler metal is Ni ≧ 20%, and Ni + Mo ≧
30%.

〔Example〕

Base material shown in Table 1 and filler material (wire) shown in Table 2
Was used to conduct submerged arc welding, and the composition, ferrite content, and workability of the welded portion were investigated. The composition of the welded portion was measured by quantitative line analysis with an X-ray microanalyzer at the center of the cross section of the molten metal. The amount of ferrite in the welded portion was measured by a ferrite indicator in the central portion of the cross section of the molten metal. The bendability of the weldability is 100 m.
A repeated bending test was performed using a jig having m with a maximum tension of 8.5 kg / mm ^2, and the number of times until breakage was evaluated. The evaluation results are shown in Table 3.

The weldability of the method according to the present invention is greatly improved in workability as shown in Table 3, and the production of the ferritic stainless steel strip containing Al and the production of the ferritic stainless steel and the Ni-containing austenitic stainless steel. It can be seen that no problems such as cracks occur in the welded part during the processing of welded products.

[Effects of the Invention] As is clear from the above, if the ferritic stainless steel containing Al and the austenitic stainless steel containing Ni are welded according to the method of the present invention, the welded portion is processed by cold rolling or bending. It is possible to prevent cracks and fractures in the welded portion when performing the welding, and to greatly improve workability and yield.

[Brief description of drawings]

FIG. 1 is a (Cr + 3Al)-(Ni + Mo) -Fe pseudo-ternary alloy composition diagram. The numbers in the figure are the amount of ferrite in the welded part (%)
Represents The circles and circles show no cracking and cracking in the welded portion during cold rolling.

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Claims (2)

[Claims] 1. A ferritic stainless steel containing Cr: 10 to 40% and Al: 3 to 12% by weight and a Ni-containing austenitic stainless steel as a filler, Ni ≧ 20%, and Ni.
The composition of the weld zone is the first using a high alloy with + Mo ≧ 30%.
Welding method for stainless steel, characterized in that welding is performed so that the value is within the area ABCDE in the figure. 2. The base material in weight% Cr: 10-40%, Al: 3-1
A ferritic stainless steel containing 2% and a Ni-containing austenitic stainless steel, wherein the composition of the welded portion is a value within the region ABCDE in Fig. 1;