JP2543801B2 - Coated arc welding rod 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 coated arc welding rod for high-Cr ferritic high-strength heat-resistant steel, and more specifically, a coating for obtaining weld metal having excellent creep characteristics, toughness, and crack resistance at high temperatures. It relates to an arc welding rod.

[0002]

2. Description of the Related Art Ferritic heat-resistant steels having excellent creep strength and less fear of stress corrosion cracking as seen in austenitic stainless steels have begun to be used as high-temperature type energy plant steel materials. As a welding material for heat-resistant steel, for example, JP-A-55-303
Like the coated arc welding rod for Cr-Mo steel disclosed in Japanese Patent Publication No. 54, the addition amount of Ni, Mn, etc. is limited, and the austenite phase stabilizing element is contained to reduce the coarse ferrite phase in the weld metal. However, when a large amount of Ni is contained, the creep rupture strength decreases for a long time, and when a large amount of Ni or Mn is contained, the crack resistance of the weld metal is As a result, it is impossible to obtain the target high-performance weld metal.

Further, in JP-A-62-220300, in welding 9% Cr-based steel, a proper amount of W is added to the welding rod and W is allowed to coexist for a limited period of time in relation to the amount of Mo, whereby the weld metal is The coarsening of the carbide that precipitates on V ₄
By suppressing the precipitation of C ₃ and NbC for a long time, and further maintaining the precipitation balance of Mo ₂ C and W ₂ C within an appropriate range, the creep rupture strength at high temperature and long time side is improved. Furthermore, JP-A-2-280993
In the gazette, C, S, etc. like 9-12% Cr-based welding materials are used.
i, Mn, Cr, Ni, Mo, W, V, Nb, Al, N
A welding material has been proposed in which the addition amount is limited and Creq is 13 or less. However, these materials do not improve the creep rupture strength to a large extent, and have a drawback in that the δ ferrite phase is precipitated in the martensite phase and remarkably lowered in terms of toughness. The δ ferrite phase 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.

[0004]

DISCLOSURE OF THE INVENTION The present invention does not have the above-mentioned problems and reduces the coarse ferrite phase without impairing the high temperature strength, high temperature creep rupture strength, crack resistance, etc. It is an object of the present invention to provide a coated arc welding rod for high Cr ferritic heat-resistant steel capable of ensuring a weld metal having strength, toughness, and crack resistance comparable to those of.

[0005]

The gist of claim 1 of the present invention is that the total weight of the coated arc welding rod is Fe.
As elements other than C, 0.01 to 0.12 by weight ratio
%, Si: 0.3 to 2.4%, Mn: 0.3 to 1.9
%, V: 0.03 to 0.40%, Nb: 0.01 to 0.
15%, N: 0.01 to 0.08%, Cr: 5.8 to 1
3%, Ni: 0.05 to 1.2%, Mo: 0.3 to 1.
6%, W: 0.5-3.5%, and further Co:
Contains 1.0 to 5.0% and / or Cu: 0.5 to 4.0%, and also contains a coating agent containing an arc stabilizer other than the above, a slag generator, and a binder. A coated arc welding rod for high Cr ferritic heat resistant steel, characterized in that

Further, the gist of claim 2 of the present invention is that in claim 1, the relationship of (Mo + W) / (Co + Cu) ≦ 2.5 is established between Co and Cu and Mo and W. It is a coated arc welding rod for high Cr ferritic heat-resistant steel, characterized in that it is contained as described above. The greatest feature of the present invention is that in a coated arc welding rod for high Cr ferritic heat-resistant steel, it suppresses the formation of δ ferrite in the weld metal obtained by welding, suppresses the reduction in toughness, and significantly increases creep rupture strength and toughness. It is in the place where it raised to.

The reasons for limiting the components of the present invention will be described below. In the present invention, the aforementioned C, Si, M
n, V, Nb, N, Cr, Ni, Mo, W, Co, Cu
In many cases, it is contained in the steel core wire, but if it is contained in the steel core wire, the coating agent, the slag generator, the arc stabilizer, etc., an approximate effect can be obtained. For the steel core wire, in addition to the above components, P: 0.02 wt% or less, Ti: 0.01 wt% or less,
O: 0.05 wt% or less may be contained, and the balance is Fe and inevitable impurities.

[0008]

The reason for limiting the components in the present invention will be described in detail below. C: 0.01 to 0.12% by weight C is required to be 0.01% by weight or more to secure hardenability and strength, but the upper limit is 0.12% by weight from the viewpoint of crack resistance.
And

Si: 0.3 to 2.4 wt% Si is added as a deoxidizer, but it is also necessary from the viewpoint of ensuring welding workability. If it is less than 0.3% by weight, pores are easily generated in the weld metal due to insufficient deoxidation, while if it exceeds 2.4% by weight, toughness is deteriorated, so the upper limit was set to 2.4% by weight.

Mn: 0.3 to 1.9 wt% Mn is a component necessary not only for deoxidation but also for maintaining strength. The upper limit is set to 1.9% by weight, because if it exceeds this, it is not preferable from the viewpoint of toughness, and the lower limit is set to 0.3% by weight as an amount necessary for deoxidation. V: 0.03 to 0.40 wt% V is required to be at least 0.03 wt% in order to precipitate as carbonitride to secure the strength. On the other hand, if it exceeds 0.40 wt%, the strength is rather increased. The upper limit is 0.40
It was set to% by weight.

Nb: 0.01 to 0.15% by weight Nb is precipitated as a carbonitride similar to V to secure strength, and is also important as an element for refining the crystal grain to enhance toughness, so that it is at least 0. 0.01 wt% is required, but
If it exceeds 15% by weight, not only the effect is saturated but also the weldability is deteriorated, so the upper limit was made 0.15% by weight.

N: 0.01 to 0.08% by weight N contributes to the remarkable creep resistance even if it forms a solid solution in the matrix or precipitates as a nitride, so at least 0.01% by weight.
Need. On the other hand, if it exceeds 0.08% by weight, a large amount of nitride is precipitated, and conversely, there arises a problem that the toughness is lowered.

Cr: 5.8 to 13% by weight Since Cr is a very important element for ensuring the oxidation resistance and hardenability, a minimum amount of 5.8% by weight is required.
If it exceeds 5% by weight, cracking resistance is impaired and δ-ferrite is precipitated at the same time, and the toughness is remarkably reduced, so the upper limit was made 13% by weight. Ni: 0.05 to 1.2 wt% Ni is an element that suppresses the formation of δ ferrite and is effective in reducing embrittlement during use, and is an essential element for applications that are used at high temperatures for a long time. However, if less than 0.05% by weight, the effect cannot be obtained. On the other hand, if it exceeds 1.2% by weight, the high temperature creep property is deteriorated, so the upper limit was made 1.2% by weight.

Mo: 0.3 to 1.6% by weight Mo is an element that remarkably enhances high temperature strength by solid solution strengthening. It is added for the purpose of improving resistance to operating temperature and pressure rise, but when a large amount is added. Weldability is impaired, and δ
Since ferrite is precipitated, the toughness is lowered. Therefore, the upper limit of the addition range is set to 1.6% by weight. on the other hand,
In the coexistence with W, 0.3% by weight is effective for improving high temperature strength, especially creep rupture strength at high temperature and long time.
Therefore, the lower limit is set to 0.3% by weight.

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

Co: 1.0 to 5.0% by weight Co is an important element that offsets the problem of precipitation of δ-ferrite caused by the addition of Mo and W, and at least 1.0
Requires more than weight percent. However, if added excessively, Ac
_{Since 1} point is lowered, there is a drawback that high temperature tempering is impossible and the structure cannot be stabilized, so the upper limit was set to 5.0% by weight.

Cu: 0.5 to 4.0% by weight Cu is an element that cancels the problem of precipitation of δ-ferrite caused by Mo and W, like Co, and is at least 0.
5 wt% or more is required. However, if added in excess,
Since high temperature tempering is impossible and the structure cannot be stabilized, the upper limit was set to 4.0% by weight.

The types and optimum contents of the elements contained in the coated arc welding rod of the present invention 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 integrated. In view of the above, it is optimal to satisfy the following formula in order to secure the toughness at a predetermined level and further effectively increase the high temperature creep rupture strength of the weld metal. (Mo + W) / (Co + Cu) ≦ 2.5 The coated arc welding rod of the present invention includes, for example, a steel core wire containing the above-mentioned elements, an arc stabilizer, an iron powder, an alkaline component, a slag forming agent such as rutile, and silicic acid. Manufactured by coating a coating material obtained by kneading with a binder such as water glass containing soda and potassium silicate with a conventional welding rod coating machine and then firing at 300 to 550 ° C to remove water. To do.

[0019]

Embodiments of the present invention will be described below. In this example, as shown in Table 1, a coating material having the composition shown in Table 2 was formed so that the outer circumference of the steel core wire (4.0 mm diameter) containing the element defined according to the present invention had a coverage rate of 30%. Was applied to produce a large number of coated arc welding rods (13 rods). Using each of the obtained welding rods, ASTM standard A387 Gr22, 9Cr-1Mo steel having a thickness of 20 mm as a test base metal,
9Cr-1Mo-Nb-V-W steel, 9Cr-0.5Mo
-Nb-V-W steel, 12Cr-0.5Mo-Nb-V-
The W steel was formed with a groove (thickness T = 20 mm, groove angle θ = 20 °, root gap L = 12 mm) as shown in FIG. 1, and arc welding was performed. The welding conditions are welding current 120 amperes, welding heat input 20 kJ / cm, preheating / pass temperature 150 to 200 ° C., and downward arc welding. Weld metal obtained by this arc welding was performed at 740 ° C for 4
After post-heat treatment for 600 hours, 600 ℃, 220N / mm ²
Rupture test at various stresses and 2 at test temperature 0 ° C
A mmV notch impact test was conducted.

In Table 2, the results of the creep rupture test are shown by the breaking time (h), and the results of the impact test are shown by vE0 ° C. (J). All of the welding rods SW-1 to SW-13 satisfy all the requirements of the present invention, the weld metal structure is a martensite single-phase structure without precipitation of δ ferrite, and the toughness and creep rupture properties after the post heat treatment. Was good. Welding rods SW-14 to SW-23 show comparative examples. Welding rod S
W-14 is used for ordinary heat resistant steel 21 /
It is an example of a 4% Cr-1% Mo-based welding rod, and a welding rod SW-
No. 15 is a welding rod for heat exchangers having further improved high temperature corrosion resistance, but all have significantly lower creep rupture strength than the welding rod of the present invention. Welding rod SW-16 is 9Cr-1
This is an example of a Mo-Nb-V-W-based welding rod, but since the C content is significantly higher than that of the welding rod of the present invention, cracking occurs during welding, and the crack resistance and impact value are reduced. Welding rod S
W-17 had an N content exceeding the upper limit of the range of the present invention, and had poor toughness as well as generation of broholes in the weld metal. Welding rod SW-18 has no Co or Cu, so δ
Ferrite is generated and toughness is reduced. Welding rod SW-
No. 19 is a 9Cr-0.5Mo-Nb-V-W system in which the V content exceeds the upper limit of the range of the present invention, and the creep rupture strength is low. Welding rod SW-20 is 12Cr-0.5Mo-Nb-
In the V-W system, the amount of Nb is below the lower limit of the range of the present invention,
Creep rupture strength is low, δ ferrite is generated, and toughness is reduced. Welding rod SW-21 is 9Cr-0.5Mo
In the -Nb-V-W system, the amount of W is out of the range of the present invention, and δ
Ferrite is generated and toughness is reduced. Welding rod SW-
No. 22 is a 9Cr-0.5Mo-Nb-V-W system, the amount of Mo is outside the range of the present invention, and the creep rupture strength is low. The welding rod SW-23 is 9Cr-0.5Mo-Nb-VWW system, and the amounts of Co and Cu are out of the range of the present invention, the creep rupture strength is low, δ ferrite is generated, and the toughness is low.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

EFFECTS OF THE INVENTION The coated arc welding rod of the present invention has the conventional 9-
Compared to the 12% Cr steel coated arc welding rod, the creep rupture strength at high temperature is remarkably enhanced, and the toughness and weldability are also excellent. For example, Table 1 and Table 2
As shown in, it is clear that those satisfying the requirements of the present invention are excellent not only in high temperature creep properties but also in toughness and weldability as compared with those not satisfying the requirements of the present invention (comparative examples). It is a covered arc welding rod having high suitability when welding high Cr ferritic heat resistant steel such as 9 to 12% Cr steel used for power generation boilers, chemical pressure vessels and the like.

[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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-266199 (JP, A) JP-A-59-101298 (JP, A) JP-A-49-34439 (JP, A) JP-B-49- 24334 (JP, B1)

Claims (2)

(57) [Claims] 1. A weight ratio of elements other than Fe to the total weight of the coated arc welding rod, C: 0.01 to 0.12%, Si: 0.3 to 2.4%, Mn: 0.3. -1.9%, V: 0.03-0.40%, Nb: 0.01-0.15%, N: 0.01-0.08%, Cr: 5.8-13%, Ni: 0.05 to 1.2%, Mo: 0.3 to 1.6%, W: 0.5 to 3.5%, further Co: 1.0 to 5.0% and Cu: 0. A coating for high Cr ferritic heat-resistant steel, characterized by containing 5 to 4.0% of both or one of them, and additionally containing a coating agent containing an arc stabilizer, a slag forming agent, and a binder other than the above. Arc welding rod. 2. C: 0.01 to 0.12%, Si: 0.3 to 2.4%, Mn: 0.3 by weight ratio as an element other than Fe relative to the total weight of the coated arc welding rod. -1.9%, V: 0.03-0.40%, Nb: 0.01-0.15%, N: 0.01-0.08%, Cr: 5.8-13%, Ni: 0.05 to 1.2%, Mo: 0.3 to 1.6%, W: 0.5 to 3.5%, further Co: 1.0 to 5.0% and Cu: 0. 5 to 4.0% of both or one of them is contained within the range where the relation of (Mo + W) / (Co + Cu) ≦ 2.5 is satisfied in relation to Mo and W, and other arc stabilizers other than the above. A coated arc welding rod for high-Cr ferritic heat-resistant steel, which contains a coating material containing a slag-forming agent and a binder.