JPH07164182A - Welding material for high-cr ferritic heat resisting steel - Google Patents

Abstract

PURPOSE:To provide a welding material which yields a weld metal having an excellent creep characteristic at a high temp., toughness and crack resistance as the welding material for high-strength heat resisting steels having high toughness. CONSTITUTION:This welding material contains, by weight %, 0.03 to 0.12% C, 0.02 to 0.3% Si, 0.3 to 1.5% Mn, 0.03 to 0.40% V, 0.01 to 0.15% Nb, 0.01 to 0.08% N, 8 to 13% Cr, 0. 3 to 1.6% Mo and 0. 5 to 3. 5% W and further, at least one of 0.05 to 1.2% Ni and 0.5 to 4.0% Cu are incorporated therein. Further, a relation (Mo+W)/(Ni+Cu)<=1.5 is made to hold among the contents of Mo, W, Ni and Cu at need. The reliability of welded joints is improved if such welding material is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding material for high-strength heat-resistant steel having high toughness, and more specifically to a welding material which gives a weld metal having excellent creep characteristics, toughness, and crack resistance at high temperatures. It is related.

[0002]

2. Description of the Related Art As a high temperature and high efficiency type steel material for energy plants, there has been a strong demand for a ferritic heat resistant steel which has an extremely high creep strength and which is less likely to cause stress corrosion cracking as seen in austenitic stainless steel. Developed for the purpose of this kind of use, for example, 9C disclosed in JP-A-60-257991.
C, S in welding wire such as welding wire for r-Mo steel
The amount of i, Mn, Cr, Mo, and Ni added is limited, and if necessary, one or two of Nb and V are added (Nb
+ V) a welding wire of 0.3% or less is proposed. However, in such a structure, since W is not contained, sufficient creep strength cannot be obtained.

Further, in Japanese Patent Laid-Open No. 2-280993, C, Si, Mn, Cr
A welding material has been proposed in which the addition amounts of Ni, Mo, W, V, Nb, Al, N, and C are limited and Creq: 13% or less. However, even with such a structure, the creep strength is not significantly improved, and the toughness is not sufficient to obtain high toughness because crystallization of δ ferrite in the martensite phase cannot be suppressed.

[0004]

The present invention does not have the above-mentioned problems, and reduces the ferrite phase while securing creep characteristics such as high temperature strength and high temperature creep rupture strength, and further crack resistance. And high C that gives weld metal with excellent toughness
It is an object of the present invention to provide a welding material for ferritic heat resistant steel.

[0005]

The gist of the present invention is that, by weight%, C: 0.03 to 0.12%, Si:
0.02-0.3%, Mn: 0.3-1.5%, V:
0.03 to 0.40%, Nb: 0.01 to 0.15%,
N: 0.01 to 0.08%, Cr: 8 to 13%, Mo:
0.3 to 1.6%, W: 0.5 to 3.5%, Ni: 0.05 to 1.2%, Cu: 0.5 to 4.
At least one of 0%, and if necessary M
Between (o, W, Ni, Cu contents, (Mo + W) / (N
i + Cu) ≦ 1.5, and the balance is Fe and inevitable impurities, which is a welding material for high Cr ferritic heat-resistant steel.

[0006]

The greatest feature of the present invention is that Cu and N are contained in the welding wire.
at least one of i, and Mo, W, N
i and Cu are allowed to coexist in a limited manner in relation to each other, and the generation of δ ferrite in the weld metal obtained by welding is suppressed, and the creep rupture strength and toughness are remarkably enhanced. The reasons for limiting each component of the present invention will be described below.

C: 0.03 to 0.12% C is required to be at least 0.03% to secure hardenability and strength, but the upper limit was made 0.12% from the viewpoint of crack resistance.

Si: 0.02 to 0.3% Si is added as a deoxidizing agent, and is also an element for improving the oxidation resistance. However, if it exceeds 0.3%, the toughness is lowered, so the upper limit was set to 0.3%. The lower limit of 0.02% was set as the amount required for deoxidation.

Mn: 0.3-1.5% Mn is a component required not only for deoxidation but also for strength retention. The upper limit is set to 1.5% because if it exceeds this, it is not preferable from the viewpoint of toughness, and the lower limit is set to 0.3% as the amount required for deoxidation.

V: 0.03 to 0.40% V is required to be at least 0.03% in order to deposit carbonitrides to secure the strength, but on the other hand, if it exceeds 0.40%, the strength is rather lowered. Therefore, the upper limit was made 0.40%.

Nb: 0.01 to 0.15% Like V, Nb is precipitated as a carbonitride to secure the strength, and is also important as an element which gives the toughness by refining the crystal grains. 01% is required, but 0.15
If it exceeds%, not only the effect is saturated but also the weldability is deteriorated. Therefore, the upper limit was made 0.15%.

N: 0.01 to 0.08% N, even if it forms a solid solution in the matrix or precipitates as a nitride, contributes as a remarkable creep resistance, so at least 0.01%.
Need. If it exceeds 0.08%, a large amount of nitride precipitates, which causes problems such as deterioration of toughness. Therefore, the upper limit was set to 0.08%.

Cr: 8 to 13% Since Cr is a very important element for ensuring the oxidation resistance and hardenability, at least 8% is necessary, but if it exceeds 13%, the crack resistance is impaired and at the same time δ Since ferrite is crystallized and toughness is significantly deteriorated, the upper limit was made 13%.

Mo: 0.3-1.6% Since Mo is an element that remarkably enhances high temperature strength by solid solution strengthening, it is added for the purpose of raising the working temperature and pressure, but when added in a large amount, weldability is obtained. And δ-ferrite is crystallized, resulting in a decrease in toughness. Therefore, the upper limit of the addition range is set to 1.6%. On the other hand, when coexisting with W, 0.3% or more is effective in improving the high temperature strength, particularly the creep rupture strength on the high temperature long time side, so the lower limit was made 0.3%.

W: 0.5 to 3.5% W is the most excellent element as a solid solution strengthening element that contributes to the creep strength of the ferritic weld metal. In particular, the effect of improving the creep rupture strength at high temperature for a long time is extremely large. However, if it is less than 0.5%, the effect cannot be exhibited in the coexistence with Mo, so the lower limit was set to 0.5%. However, excessive addition causes δ-ferrite to be crystallized to lower the toughness of the weld metal and deteriorate the welding workability, so the upper limit was made 3.5%.

Ni: 0.05 to 1.2% Ni is an element that suppresses the formation of ferrite and is effective in reducing embrittlement during use, and is used for a long time at high temperature such as the welding material of the present invention. Is an effective element against. In the present invention, Ni or Cu is an essential element,
In case of less than 0.05%, the effect cannot be obtained. On the other hand, if it exceeds 1.2%, the high temperature creep property is deteriorated, so the upper limit was made 1.2%.

Cu: 0.5 to 4.0% Like Ni, Cu is an important element that cancels out the problem of crystallization of δ-ferrite caused by the addition of Mo and W, and at least 0 is required to obtain the effect. It is preferable to add 0.5% or more. However, if added excessively, the Ac ₁ point is lowered, so that there is a drawback that high temperature tempering becomes impossible and the structure cannot be stabilized, so the upper limit was made 4.0%.

The types of elements contained in the welding material of the present invention and the optimum contents thereof are as described above, and the object of the present invention can be achieved as long as the above requirements are satisfied, but the functions of each element are comprehensively evaluated. Considering this, in order to more effectively increase the high temperature creep rupture strength of the weld metal while ensuring a predetermined level of toughness, it is optimal to satisfy the following formula. If this ratio exceeds the upper limit, the creep strength will decrease, and at the same time, the formation of δ-ferrite will be remarkable and the toughness will also deteriorate. (Mo + W) / (Ni + Cu) ≦ 1.5

According to the construction of the present invention, the welding method applied is most preferably TIG welding. However, it is not limited to TIG welding, and for example, Ar--CO ₂ or A
Good performance is also obtained in MIG welding using r-O ₂ as a shielding gas. The shield gas composition is also applicable to gas shield arc welding in which Ar is mixed with He.

20 mm thick ASTM standard A387 G
r22, 9Cr-1Mo steel, 9Cr-1Mo-Nb-V
-W steel, 9Cr-0.5Nb-V-W steel, 12Cr-N
Grooves as shown in the sectional view of FIG. 1 for b-V-W steel (thickness T of welded material 1 = 20 mm, groove angle θ = 20 °, root gap L = 12 mm when backing material 2 is used) Forming a welding wire having a composition of the composition shown in Table 1 and a wire diameter of 1.6 mm, Table 3
TIG welding was carried out under the welding conditions shown in. The wire is a steel ingot obtained by melting and is forged, hot rolled, drawn, annealed, plated, drawn and wound, and finished to a diameter of 1.6 mm.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

After the post-heat treatment of the obtained weld metal at 740 ° C. for 4 hours, a creep rupture test at a stress of 20 kgf / mm ² at 600 ° C. and ² mmV at a test temperature of 0 ° C.
A notch impact test was conducted. Table 2 shows the test results and the weldability investigation results. Wires TGS-1 to TGS-1
1 all satisfy all the requirements of the present invention, the weld metal structure is a martensite single-phase structure without crystallization of δ ferrite, good toughness and creep rupture properties after post heat treatment, and weldability It was possible to obtain an excellent weld metal.

Wires TGS-12 to TGS-18 represent comparative examples. The wire TGS-12 is an example of a 2 1/4% Cr-1% Mo-based wire used for ordinary heat resistant steel, and the wire TGS-13 is a heat exchanger wire with further improved high temperature corrosion resistance. However, in both cases, the creep rupture strength is significantly lower than that of the wire of the present invention. TGS-1
No. 4 is an example of 9Cr-1Mo-Nb-VW type wire, but the amount of C is significantly higher than that of the wire of the present invention, so cracking occurs during welding, and crack resistance and impact value are lowered. .

TGS-15 has N content and (Mo + W) / (N
i + Cu) exceeds the upper limit, blowholes are generated in the weld metal, the toughness is poor, and the creep rupture strength is also low. Since TGS-16 has low C and N and does not have Ni and Cu, δ ferrite is generated and the toughness is lowered.

TGS-17 is 9Cr-0.5Mo-Nb
Although it contains Mo, W, Ni, and Cu in the -V-W system, W is out of the conditions of the present invention, so that creep rupture strength is low and δ ferrite is generated, resulting in low toughness. 12Cr- for TGS-18
M in 0.5Mo-Nb-V-W system like TGS-16
Although it contains o, W, Ni, and Cu, Mo is out of the condition of the present invention, so that the creep rupture strength is low and δ ferrite is generated, and the toughness is lowered.

[0028]

The welding material according to the present invention has a conventional content of 9% to 12% C.
Compared with welding wire for r steel, it has significantly higher creep strength at high temperature and has excellent characteristics such as toughness and weldability. As shown in Tables 1 and 2, those having a welding wire composition satisfying the requirements of the present invention have not only high temperature creep properties but also toughness and weldability as compared with those not satisfying the requirements of the present invention (Comparative Examples). It is clear that it is excellent. By using the welding material according to the present invention when welding 9 to 12% Cr steel used for various power generation boilers, chemical pressure vessels, etc., the reliability of the welded joint can be greatly improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a groove shape of a welded portion used in an example.

Claims (2)

[Claims] 1. By weight%, C: 0.03-0.12% Si: 0.02-0.3% Mn: 0.3-1.5% V: 0.03-0.40% Nb : 0.01 to 0.15% N: 0.01 to 0.08% Cr: 8 to 13% Mo: 0.3 to 1.6% W: 0.5 to 3.5% , Ni: 0.05 to 1.2% Cu: 0.5 to 4.0%, at least one of which is composed of Fe and inevitable impurities, and the balance is composed of high Cr ferritic heat resistant steel welding. material. 2. The high Cr ferritic heat-resistant steel according to claim 1, wherein the relationship of (Mo + W) / (Ni + Cu) ≦ 1.5 is established among the contents of Mo, W, Ni and Cu. Welding material.