JPH07268563A - Welding material for high cr ferritic heat resistant steel - Google Patents

Abstract

PURPOSE:To produce a welding material for high Cr ferritic heat resistant steel, capable of providing a weld metal excellent in high temp. creep rupture strength, toughness, and cracking resistance. CONSTITUTION:This welding material has a composition containing, as essential components, <0.05% Ni, 0.03-0.12% C, 0.01-0.3% Si, 0.3-1.5% Mn, 0.03-0.40% V, 0.01-0.15% Nb, 0.01-0.08% N, 8-13% Cr, 0.3-1.6% Mo, and 0.5-3.5% W and also containing at least either of 1.0-5.0% Co and 0.5-4.0% Cu. Further, the contents of Mo, W, Co, and Cu satisfy the relationship in (Mo+W)/(Co+Cu)<=1.5 in this composition.

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, high-efficiency type steel material for energy plants, there has been a strong demand for ferritic heat-resisting steels which have extremely excellent creep strength and are free from the risk of stress corrosion cracking as seen in austenitic stainless steels.
For the purpose of this kind of use, for example, JP-A-60-257.
C, Si, Mn, and C in the welding wire, such as the welding wire for 9Cr-Mo steel disclosed in Japanese Patent No. 991.
0.3 with (Nb + V) by limiting the added amount of r, Mo, Ni
% Welding wires have been proposed. Further, in Japanese Unexamined Patent Publication No. 2-280993, C, Si, Mn, Cr, Ni, Mo, W, V.
A welding material has been proposed in which the amounts of Nb, Al, and N added are limited and Cr _eq : 13% or less.

[0003]

However, these are not intended to significantly improve the creep strength, but they have a drawback that δ ferrite crystallizes in the martensite phase and remarkably lowers the toughness. δ ferrite is a significantly softer phase than martensite in the matrix,
When such a soft second phase is dispersed in a hard matrix, the overall impact properties are significantly reduced. An object of the present invention is to provide a welding material that gives a weld metal excellent in creep rupture strength, toughness, and crack resistance at high temperatures.

[0004]

Means for Solving the Problems The present invention is to solve the above-mentioned problems, and in a weight ratio, Ni: less than 0.05%, C: 0.03 to 0.12%, Si: 0.01
~ 0.3%, Mn: 0.3-1.5%, V: 0.03-
0.40%, Nb: 0.01 to 0.15%, N: 0.0
1 to 0.08%, Cr: 8 to 13%, Mo: 0.3 to
1.6%, W: 0.5 to 3.5% as an essential component, and Co: 1.0 to 5.0%, Cu: 0.5 to
At least one of 4.0%, Mo, W,
Between the Co and Cu contents (Mo + W) / (Co + Cu)
A welding material for high Cr ferritic heat-resistant steel, characterized in that the relationship of ≦ 1.5 is established and the balance consists of Fe and inevitable impurities.

[0005]

The present invention limits the upper limit of the amount of Ni in the welding wire, and the proper amount of C, Si, Mn, V, N in the wire.
By adding b, N, Cr, Mo and W, high temperature creep strength, toughness and crack resistance are ensured, and at least one of Co and Cu is further added.
By maintaining an appropriate content relationship with and W, generation of δ ferrite in the weld metal is suppressed, and further, creep strength and toughness are markedly enhanced. The reasons for limiting the components are shown below.

Ni: Less than 0.05% Ni is an element that improves toughness, but is also an element that reduces high temperature creep strength. In the present invention, the main purpose is to improve high temperature creep strength, and further Si, Mn, Nb, N, Cr, Mo, W, Co and C are used.
Since it is possible to prevent the toughness from decreasing by keeping the added amount of u at an appropriate amount, the Ni content was set to less than 0.05%.

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

Si: 0.01 to 0.3% Si is added as a deoxidizing agent in an amount of 0.01% or more, and is also an element for improving the oxidation resistance. However, if it exceeds 0.3%, the toughness is lowered, so the upper limit is set to 0.
It was set at 3%.

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, the toughness is reduced, and the lower limit is set to 0.
It was set at 3%.

V: 0.03 to 0.40% V is required to be 0.03% at least in order to deposit carbonitrides to secure the strength. On the other hand, when it exceeds 0.40%, the strength is rather lowered. Therefore, the upper limit is set to 0.40%.

Nb: 0.01 to 0.15% Nb is precipitated as a carbonitride similar to V to secure the strength, and is also important as an element for refining the crystal grains to give toughness, so at least 0. 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, and conversely, there arises a problem that the toughness decreases, so 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. The upper limit was set to 13% because δ-ferrite is crystallized and toughness deteriorates significantly.

Mo: 0.3 to 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 operating temperature and pressure, but when a large amount is added, weldability is improved. In addition, the δ-ferrite is crystallized, resulting in a decrease in toughness. Therefore, the upper limit is set to 1.6%. On the other hand, the coexistence with W has the effect of improving the high temperature strength of 0.3% or more, 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%. Further, the excessive addition causes the δ ferrite to crystallize, the toughness of the weld metal is lowered, and the welding workability is also deteriorated, so the upper limit is 3.
It was set to 5%.

Co: 1.0 to 5.0%, Cu: 0.5 to
At least one of 4.0% Co and Cu are important elements that offset the problem of crystallization of δ ferrite due to the addition of Mo and W, and Co is 1.0
%, Cu needs to be 0.5% or more. However, excessive addition lowers the A _C1 point, making high temperature tempering impossible and stabilizing treatment of the structure impossible. Therefore, the upper limit of Co is 5.0% and the upper limit of Cu is 4.
It was set to 0%. As described above, Co and Cu are elements that have the effect of conflicting with Mo and W, and the appropriate addition range in the present alloy system is (Mo + W) / (Co + Cu) ≦ 1.5.
When it exceeds 1.5, the effect of suppressing δ ferrite by Co and Cu cannot be obtained, and the creep strength and toughness are deteriorated.

[0017]

[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
-0.5Mo-Nb-V-W steel groove as shown in FIG. 1 (thickness T of welded material 1 = 20 mm, groove angle θ = 20)
°, using a backing material 2 to form a root gap L = 12 mm), using a welding wire having a composition of the composition shown in Table 1 and a wire diameter of 1.6 mm, the combination with the base material shown in Table 2 and Table 3
TIG welding was performed under the welding conditions shown in.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[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 ² mmV at a test temperature of 0 ° C.
A notch impact test was conducted. Table 2 shows the test results.
Wires TGCC-1 to 9 all satisfy the requirements of the present invention, the weld metal structure is a martensite single phase structure without crystallization of δ ferrite, and the toughness and creep rupture properties after post heat treatment are good, Moreover, an excellent weld metal could be obtained.

Wires TGCC-10 to 19 represent comparative examples. The wire TGCC-10 is an example of a 2 1/4% Cr-1% Mo-based wire that is used for ordinary heat resistant steel, and the wire TGCC-11 is a heat exchanger wire with further improved high temperature corrosion resistance. However, since N is low and W is not contained, the creep rupture strength is significantly lower than that of the wire of the present invention. TGCC-12 is 9Cr-1Mo
This is an example of a -Nb-V-W type wire, but since the amount of C is significantly higher than that of the wire of the present invention, cracking occurs during welding, and crack resistance and impact value are lowered.

In TGCC-13, the N content exceeds the upper limit, and blow holes were generated in the weld metal and the toughness was poor. TGCC-14 has low C and N, and C
Since there is no o or Cu, δ ferrite is generated and the toughness is lowered.

TGCC-15 is 9Cr-0.5Mo-N
Although it contains Mo, W, Ni, and Co in the bVW system,
(Mo + W) / (Cu + Co) is outside the conditions of the present invention, the creep rupture strength is low, and δ ferrite is generated, and the toughness is low. TGCC-16 is 12Cr-0.5Mo
-Nb-V-W system, Mo, W, like TGCC-15
Although it contains Co, (Mo + W) / (Cu + Co) is out of the condition of the present invention, the creep rupture strength is low, and δ ferrite is generated, and the toughness is lowered.

TGCC-17 is 9Cr-0.5Mo-N
Although it contains Mo, W, Ni, and Cu in the bVW system,
(Mo + W) / (Cu + Co) is outside the conditions of the present invention, the creep rupture strength is low, and δ ferrite is generated, and the toughness is low. TGCC-18 is 12Cr-0.5Mo
-Nb-V-W system, Mo, W, like TGCC-17
Although it contains Cu, (Mo + W) / (Cu + Co) is out of the conditions of the present invention, the creep rupture strength is low, and δ ferrite is generated, and the toughness is lowered.

TGCC-19 is 9Cr-1Mo-Nb-
The V-W system also contains Mo, W, Co, and Cu, but
(Mo + W) / (Cu + Co) is outside the conditions of the present invention. Therefore, the creep rupture strength is low and δ ferrite is generated, and the toughness is lowered.

[0027]

The welding material according to the present invention has a conventional content of 9% to 12% C.
Compared with welding wire for r steel, the creep strength at high temperature is remarkably increased, and it is also excellent in 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 greatly 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)

[Claims] 1. By weight ratio, Ni: less than 0.05%, and C: 0.03 to 0.12% Si: 0.01 to 0.3% 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% Mo: 0.3 to 1.6% W: 0.0. 5 to 3.5% as an essential component, and at least one of Co: 1.0 to 5.0% and Cu: 0.5 to 4.0%, and Mo, W, Co, A welding material for high Cr ferritic heat-resistant steel, characterized in that a relationship of (Mo + W) / (Co + Cu) ≦ 1.5 is established between Cu contents, and the balance is Fe and inevitable impurities.