JP2551512B2 - Welding material for high Cr ferritic heat resistant steel - Google Patents

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 extremely excellent creep strength and is less likely to cause stress corrosion cracking as seen in austenitic stainless steel.

For the purpose of this kind of use, for example, 9Cr-M disclosed in JP-A-60-257991.
C, S in the welding wire, like the welding wire for o type steel
i, Mn, Cr, Mo, Ni addition amount is limited, and further N
0.3% by adding 1 or 2 of b and V (Nb + V)
% Welding wires have been proposed. Further, in JP-A-2-280993, C, Si, Mn, Cr, Ni, Mo, W
Limit the amount of V, Nb, Al, N, C added, and Creq: 1
Welding materials of 3 or less have been proposed.

[0004]

However, these are not intended to significantly improve the creep strength, but they have a drawback that δ ferrite is precipitated in the martensite phase and remarkably lowers the toughness. δ ferrite is a phase that is significantly softer than martensite in the matrix,
When such a soft second phase is dispersed in a hard matrix, the overall impact properties are significantly reduced.

[0005]

The gist of the present invention is, by weight ratio, C: 0.03 to 0.12%, Si: 0.3% or less,
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%, Ni: 0.05 to 1.2%, M
o: 0.3 to 1.6%, W: 0.5 to 3.5%, Cu:
0.5 to 4.0% as an essential component, and further M
(Mo + W) / (Ni
+ Cu) ≦ 1.5, and the balance is Fe and inevitable impurities, which is a welding material for high Cr ferritic heat resistant steels.

[0006]

In the present invention, Cu is added to the welding wire and M
O, W, and Ni were allowed to coexist in a limited manner in relation to each other, and the formation of δ ferrite in the weld metal obtained by welding was suppressed, and the creep rupture strength and toughness were remarkably enhanced. The reasons for limiting each component will be described below.

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

Si: 0.3% or less Although Si is added as a deoxidizing material, it is also an element that improves oxidation resistance. However, if it exceeds 0.3%, toughness is deteriorated, so the upper limit was set to 0.3%.

Mn: 0.3 to 1.5% Mn is a component necessary not only for deoxidation but also for maintaining strength. The upper limit is set to 1.5% because if it exceeds this, toughness is reduced, 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 0.03% at least in order to precipitate carbonitride to secure the strength. 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% 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% Since N contributes as a remarkable creep resistance even if it forms a solid solution in the matrix or precipitates as a nitride, a minimum of 0.01% is required. 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. Since δ ferrite is precipitated and the toughness deteriorates significantly, the upper limit was made 13%.

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 temperatures such as the welding material of the present invention. , Which is an essential element for
If it is less than 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 is 1.
It was set to 2%.

Mo: 0.3-1.6% Mo is an element that remarkably enhances the high temperature strength by solid solution strengthening, so it is added for the purpose of raising the operating temperature and pressure, but if a large amount is added, the weldability is improved. Since it causes damage and precipitates δ ferrite, the toughness is lowered. Therefore, the upper limit is set to 1.6%. On the other hand, in the coexistence with W, it is 0.3% or more that is effective in improving the high temperature strength, especially the creep rupture strength on the high temperature long time side, so the lower limit is 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 less than 0.5%, the effect cannot be exhibited in the coexistence with Mo, so the lower limit was set to 0.5%. In addition, δ ferrite is precipitated by excessive addition,
The toughness of the weld metal is lowered and the welding workability is also deteriorated, so the upper limit was made 3.5%.

Cu: 0.5 to 4.0% Like Ni, Cu is an important element that cancels out the problem of precipitation of δ-ferrite caused by addition of Mo and W, and a minimum of 0.5% is required. To do. However, excessive addition lowers the A _c1 point, making high temperature tempering impossible,
It has a drawback that the stabilization treatment of the tissue cannot be performed.
As described above, Cu is an element that gives the effect of conflicting with Mo and W, like Ni, and an appropriate addition range in this alloy system is (Mo + W) / (Ni + Cu) ≦ 1.5.

[0018]

[Example] ASTM standard A387 Gr having a thickness of 20 mm
22, 9Cr-1Mo steel, 9Cr-1Mo-Nb-V-
W steel, 9Cr-0.5Mo-Nb-V-W steel, 12Cr
Grooves (thickness T = 20 mm, groove angle θ = 20 °, root gap L = 12 mm) as shown in FIG. 1 were formed using -0.5Mo-Nb-V-W steel. TIG welding was performed under the welding conditions shown in Table 3 using a welding wire having the composition shown below and a wire diameter of 1.6 mmφ.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

After the post-heat treatment at 740 ° C. for 4 hours, the obtained weld metal was subjected to a creep rupture test at a stress of 20 kgf / mm ² at 600 ° C. and a ² mmV notch impact test at a test temperature of 0 ° C.

Table 2 shows the test results. Wire TGS
-1 to 9 all satisfy the requirements of the present invention,
The weld metal structure was a martensite single-phase structure with no precipitation of δ ferrite, and it was possible to obtain a weld metal having good toughness and creep rupture properties after post heat treatment and excellent weldability.

The wires TG-10 to 16 are comparative examples.
The wire TG-10 is an example of a 2 (1/4)% Cr-1% Mo-based wire used for ordinary heat resistant steel,
The wire TG-11 is a heat exchanger wire having further improved high-temperature corrosion resistance, but all have significantly lower creep rupture strength than the wire of the present invention. TG-12 is 9Cr
This is an example of a -1Mo-Nb-V-W type wire, but since the amount of C is remarkably higher than that of the wire of the present invention, cracking occurs during welding, and crack resistance and impact value decrease. TG-13
Had an N content exceeding the upper limit, and had poor toughness as well as generation of broholes in the weld metal. TG-14
Has low C and N and no Ni and Cu, so that δ ferrite is generated and the toughness is lowered. TG-15 is 9Cr-0.5
The Mo-Nb-V-W system contains Mo, W, Ni, and Cu, but (Mo + W) / (Ni + Cu) is outside the conditions of the present invention, the creep rupture strength is low, and δ ferrite is generated, resulting in toughness. Low. TG-16 is 12Cr-0.5Mo-
In the Nb-V-W system, Mo, W, Ni,
Although it contains Cu, (Mo + W) / (Ni + Cu) is out of the condition of the present invention, the creep rupture strength is low, and δ
Ferrite is generated and toughness is reduced.

[0025]

EFFECTS OF THE INVENTION The welding material of the present invention has a conventional content of 9-12% 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. By using the welding material of 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 significantly improved.

[Brief description of drawings]

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

[Explanation of symbols]

 1 Material to be welded 2 Backing material

Claims (1)

(57) [Claims] 1. By weight ratio, C: 0.03 to 0.12%, Si: 0.3% or less, Mn: 0.3 to 1.5%, V: 0.03 to 0.40%, Nb: 0.01 to 0.15%, N: 0.01 to 0.08%, Cr: 8 to 13%, Ni: 0.05 to 1.2%, Mo: 0.3 to 1.6% , W: 0.5 to 3.5%, Cu: 0.5 to 4.0% as an essential component, and (Mo + W) / between the addition amounts of Mo, W, Ni, and Cu.
A welding material for high Cr ferritic heat-resistant steel, characterized in that the relationship of (Ni + Cu) ≦ 1.5 is established and the balance is Fe and inevitable impurities.