JPH0375278B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to stainless steel welding materials, and particularly to improvements in welding materials used for welding high-temperature equipment. SUS304 austenitic stainless steel (hereinafter referred to as SUS304 stainless steel) is often used in high-temperature equipment such as fast breeder reactors, chemical plants, or thermal power plants. And these
When manufacturing the above-mentioned high-temperature equipment using SUS304 stainless steel, welding materials made from SUS308 series stainless steel have conventionally been used. By the way, in addition to basic properties such as strength at room temperature and high temperature, the welded parts of high-temperature equipment as mentioned above are required to have creep-related properties such as creep rupture ductility, creep rupture strength, and creep fatigue properties. . On the other hand, when selecting welding materials for the above-mentioned high-temperature equipment, conventionally, strength at room temperature and high temperature, and creep strength have been emphasized, and creep rupture ductility has tended to be sacrificed. For this reason, high-temperature equipment using conventional welding materials made of SUS308 stainless steel has the problem that the creep rupture ductility of the weld metal (welded part) decreases, especially after long-term high-temperature use (550°C x 5000 hours). It was hot. The present invention has been made in view of the above circumstances, and when used for welding high-temperature equipment, particularly high-temperature equipment made of SUS304 stainless steel, the present invention satisfies predetermined appropriate values for the tensile strength of the weld metal at room temperature and high temperature, and An object of the present invention is to provide a stainless steel welding material that can yield a weld metal whose creep rupture ductility does not deteriorate after long-term high-temperature use. That is, the stainless steel welding material according to the present invention is
Creep rupture elongation EL (%) shown by the following formula (1) ≧
10 and is characterized by having the following composition. EL=−60−22Si+12Mn+103P+5.3Ni +25V−20Ti−40Nb+103[O]+0.2λ ……(1) C; 0.02 to 0.07 wt% Si; 0.05 to 0.90 wt% Mn; 1.5 to 3.0 wt% P; 0.01 to 0.04 Weight% S; 0.030% by weight or less Ni; 9.0-11.0% by weight Cr; 18.0-21.0% by weight Mo; 3.0% by weight or less V; 0.15% by weight or less Ti; 0.10% by weight or less B; 0.02% by weight or less O; 0.001- 0.01% by weight N; 0.005 to 0.10% by weight Fe and unavoidable impurities; remainder In formula (1), Si, Mn, P, Ni, V, Ti, Nb,
[O] represents the weight percent of each element, and λ represents the welding heat input (KJ/cm). The composition of the welding material according to the present invention is SUS304
This was obtained by induction from welding test data conducted using stainless steel pieces as the welding base material and SUS308 stainless steel as the welding material. Next, this welding test and induction method will be explained. Welding Test Using various SUS308 stainless steel pieces as welding materials, two SUS304 stainless steel pieces were welded by various welding methods to produce test pieces with a GL of 30 mm and an outer diameter of 6 mm in each case. For each test piece, the tensile strength T ₁ of the weld metal at room temperature, the tensile strength T ₂ of the weld metal at 550°C, and the creep rupture elongation EL of the weld metal after 5000 hours at 550°C were measured using standard methods. Subsequently, the above T ₁ obtained for each specimen and
The correlation diagram shown in FIG. 1 was obtained by plotting the EL value, and the correlation diagram shown in FIG. 2 was obtained by plotting the T ₂ and EL values. In the figure, curve M indicates the average line of these data, and curve U and curve L indicate curve M
The upper limit line and lower limit line drawn based on the above are shown, respectively. However, this correlation diagram was created in order to derive a composition having the characteristics that the present invention is trying to obtain, and from this point of view, it was created using carefully selected data. Therefore, actual data using SUS304 stainless steel as a welding material has even greater variation than this. In addition, in Figures 1 and 2, ○, △,
□, ◇, and ☆ indicate that the test pieces related to the plots were produced by the following welding methods, respectively. ○: GTA (Gas Tungsten Arc welding) △: Covered arc welding □: Submerged arc welding ◇: GMA (Gas Metal Arc welding) ☆: Electron beam welding In addition, ● and ▲ in the figure indicate data related to examples described later. ing. Recursive Method The composition of the welding material according to the present invention was determined from the data shown in FIGS. 1 and 2 as follows. First, the goal that we are trying to achieve with the stainless steel welding material of the present invention is that the weld metal when welding SUS304 stainless steel has an EL≧10% (550℃×5000℃).
time value), T ₁ = 53-62Kgf/mm ² , T ₂ ≦39Kg
It was set to have a characteristic of f/mm ² . 550℃×5000
The creep rupture elongation EL over time was set at 10% or more because this is the range that most of the data input in Figures 1 and 2 satisfies, and some data below 10% are within the range. This is because I thought that even if it did, I would be able to obtain a value that was close to that. If the above-mentioned EL setting value is increased to 15% or 20%, even better creep ductility can be obtained, but various conditions become stricter, and there are very few products that can satisfy these conditions. It has no choice but to be limited to a narrow range. By the way, when considering obtaining a value of 10% or more as EL at 550℃ x 5000 hours on the correlation diagram in Figure 1, if the average line M is used as a guide, the weld metal should be 53 to 62 kgf/mm ² . It can be considered that it is sufficient to have T ₁ . Here, 35Kgf/mm ² is the minimum tensile strength of the base material SUS304 stainless steel. Also, when considering the average line M on the correlation diagram in Figure 2 as a guide, if T ₂ is 39Kgf/mm ² or less,
It can be seen that an EL value of 10% or more (550°C x 5000 hours) is obtained, and a weld metal with extremely excellent creep ductility can be obtained especially if T ₂ is set to 35 Kgf/mm ² or less. On the other hand, in FIGS. 1 and 2, the lower limit line L
When considering creep rupture elongation EL of 10% or more using as a guideline, the regulatory conditions regarding T ₁ and T ₂ are even stricter than when using the average line M. Also, using the upper limit line L as a guide, creep rupture elongation EL
When considering that the tensile strength is 10% or more, the values of the tensile strengths T ₁ and T ₂ become large. In the present invention, T ₁ ,
10 by keeping T ₂ as low as possible.
% or more, the average line M was used as a guideline. Next, by performing multiple regression analysis, we found that 550
The influence of welding wire chemical composition on creep rupture elongation EL after 5000 hours at °C was determined. According to the results, the creep rupture elongation EL (%) after 550°C x 5000 hours is given by the following equation (1). EL=-60-22Si+12Mn+103P+5.3Ni +25V-20Ti-40Nb+103[O]+0.2λ...(1) Here, Si, Mn, P, Ni, V, Ti, Nb,
[O] represents the weight percent of each element, and λ represents the welding heat input (KJ/cm). In addition to these elements, C, S, Cr, Mo, B, Cu, Co, Al, N
Multiple regression analysis was also conducted for EL (%), but the t value, which is one of the parameters used to see the influence on EL (%), was low and the contribution rate was low, so it was deleted. As mentioned above, five different welding methods are used: GTA, coated arc, submerged arc, GMA, and electron beam welding.
The formula includes chemical component factors (such as the amount of O) and thermal factors (heat input λ) that affect EL (%) due to differences in welding methods, so differences in welding methods do not really matter. Must not be. Therefore, the above formula (1) is
It is considered that this method can be applied to all conventional welding methods. From the above, the creep ductility aimed at in the present invention,
That is, a weld metal having a creep rupture elongation EL of 10% or more at 550°C x 5000 hours can be obtained by determining the amount of each component element that can satisfy EL≧10 in equation (1). The composition of the welding material of the present invention described above was obtained in this manner, and as shown in the results of the examples described later, according to the welding material that conforms to the composition range of the present invention, the composition of the welding material of the present invention is 550℃
Creep rupture elongation over time of 10% or more can be obtained, and at the same time, tensile strength at room temperature and high temperature can be satisfied within the appropriate range. In this case, S,
The reason for placing upper limits on V, Ti, Nb, and B is that adding too much of these components will impair the creep rupture elongation of the weld metal. Further, upper and lower limits were set for O and N in consideration of weldability. Although the amounts of O and N are not regulated in conventional SUS308 welding materials, too much of these can cause welding defects called blowholes.
Therefore, the welding material of the present invention in which the amounts of O and N are regulated as described above can be expected to improve weldability. In addition, the chemical composition of the welding wire according to the present invention described above and the mechanical properties of the weld metal based on the chemical composition of the welding wire according to the present invention are
The results are summarized in a table (the chemical components and mechanical properties of Examples described below are also listed). FN, which is listed as one of the mechanical properties of weld metal in the same table, is
δ ferrite amount (ferrite number according to Daylong phase diagram). Regarding FN, 0.5FN or more is necessary to reduce cracking susceptibility during welding, but if it is too large, δ ferrite will transform into σ phase due to long-term heating, reducing creep ductility. From this point of view, it is desirable to set it to 0.5 to 10FN as described in the table. For reference, the chemical composition of SUS308 welding material is shown in Table 2.

【table】

【table】

[Table] Examples of the present invention will be described below. Example 1 A welding material having the composition shown in the Example 1 column of Table 1 was produced by a standard method, and processed into a welding wire. Next, using this welding wire, weld a SUS304 stainless steel piece using the GTA welding method so that GL = 30
mm, and a test piece with an outer diameter of 6 mm was prepared. Regarding this test piece, the tensile strength of the weld metal at room temperature T ₁ ,
The tensile strength T ₂ of the weld metal at 550°C and the creep rupture elongation EL of the weld metal after 5000 hours at 550°C were measured by standard methods. The results are listed in Table 1, and in Figures 1 and 2.
It was shown in As is clear from these results, according to the welding material of this example, a weld metal having desired creep ductility and predetermined tensile strength can be obtained. Example 2 A welding material having the composition shown in the Example 2 column of Table 1 was produced by a standard method, and processed into a welding wire. Using this welding wire, a test piece similar to that in Example 1 was prepared by covered arc welding, and the same test as in Example 1 was conducted using this test piece. The results are listed in Table 1 and indicated by ▲ in FIGS. 1 and 2. As is clear from these results, even when using the welding material of this example, a weld metal having the desired creep ductility and predetermined tensile strength can be obtained. As detailed above, according to the stainless steel welding material of the present invention, when used for welding high-temperature equipment, especially high-temperature equipment made of SUS304 stainless steel, the tensile strength of the weld metal at room temperature and high temperature can be maintained at a predetermined appropriate value. It is possible to obtain a weld metal that satisfies the above requirements and whose creep rupture ductility does not deteriorate after long-term use at high temperatures, and other remarkable effects can be achieved.

[Brief explanation of drawings]

Figure 1 is a diagram showing the correlation between the tensile strength of the weld metal at room temperature and the creep rupture elongation at 550°C x 5000 hours for test pieces made of SUS304 stainless steel pieces welded by various welding methods.
The figure shows the tensile strength of weld metal at 550℃ and 550℃
It is a figure showing the correlation with creep rupture elongation at ×5000 hours.

Claims (1)

[Claims] 1 Creep rupture elongation EL expressed by the following formula (1)
A stainless steel welding material that satisfies (%)≧10 and has the following composition. EL=−60−22Si+12Mn+103P+5.3Ni +25V−20Ti−40Nb+103[O]+0.2λ ……(1) C; 0.02 to 0.07 wt% Si; 0.05 to 0.90 wt% Mn; 1.5 to 3.0 wt% P; 0.01 to 0.04 Weight% S; 0.030% by weight or less Ni; 9.0-11.0% by weight Cr; 18.0-21.0% by weight Mo; 3.0% by weight or less V; 0.15% by weight or less Ti; 0.10% by weight or less B; 0.02% by weight or less O; 0.001- 0.01% by weight N; 0.005 to 0.10% by weight Fe and unavoidable impurities; remainder In formula (1), Si, Mn, P, Ni, V, Ti, Nb,
[O] represents the weight percent of each element, and λ represents the welding heat input (KJ/cm).