JPH07268562A - Coated arc welding rod for high Cr ferritic heat resistant steel - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a covered arc welding rod which has improved creep rupture strength at high temperature and improved toughness when welding high strength heat resistant steel. [Composition] A coated arc welding rod having a good suitability for high Cr ferritic heat-resistant steel, and containing a specific amount of C, Si, Mn, Cr, Mo, V in both or one of the steel core wire and the coating agent.
It contains Nb, W, N, Co, Cu, B and Al, and is further added with an ordinary metal carbonate, metal fluoride, arc stabilizer, slag forming agent and the like and an adhesive. [Effect] It suppresses the formation of δ ferrite in the weld metal and suppresses the decrease in toughness, and significantly increases the creep rupture strength and toughness.

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-Cr ferritic high-strength heat-resistant steel, and more particularly to a covered arc welding rod for obtaining a weld metal having excellent creep characteristics and toughness at high temperatures. Is.

[0002]

2. Description of the Related Art Ferritic heat-resistant steels, which have extremely high creep strength and are less likely to cause 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 steel, for example, JP-A-55-30
Like the Cr-Mo steel coated arc welding rod disclosed in Japanese Patent No. 354 gazette, the addition amount of Ni, Mn, etc. is limited,
A method of containing an austenite phase stabilizing element to reduce the coarse ferrite phase in the weld metal has been proposed. However, when a large amount of Ni is contained, the creep rupture strength for a long time decreases and more than necessary. Since Ni and Mn reduce the crack resistance of the weld metal, it is not possible to obtain the target high performance welded joint.

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 strength at high temperature and long time side is improved. Further, in Japanese Patent Laid-Open No. 2-280993, C, Si, M such as 9 to 12 Cr-based welding materials is used.
A welding material has been proposed in which the addition amount of n, Cr, Ni, Mo, W, V, Nb, Al, and N is limited and Cr _{eq is} 13% or less. However, these techniques do not significantly improve the creep strength, and have the drawback of crystallizing δ ferrite in the martensite phase and significantly reducing it from the viewpoint of toughness. The δ ferrite phase is a phase that is significantly softer than martensite in the matrix, and when such a soft second phase is dispersed in a hard matrix, the overall impact properties deteriorate significantly.

[0004]

The present invention focuses on the above circumstances and reduces the coarse ferrite phase without impairing the high temperature strength, high temperature creep rupture strength, crack resistance, etc., and is comparable to the base metal. An object of the present invention is to provide a covered arc welding rod for high Cr ferritic heat-resistant steel capable of ensuring a weld metal having high strength, toughness, and crack resistance.

[0005]

A feature of the present invention is that in a coated arc welding rod for high Cr ferritic heat-resistant steel, the formation of δ ferrite in the weld metal obtained by welding is suppressed to suppress a decrease in toughness. However, the creep rupture strength has been remarkably increased.

[0006] That is, the gist of the present invention is, in% by weight (hereinafter the same) with respect to the total weight of the coated arc welding rod,
C: 0.01 to 0.11%, Si: 0.3 to 1.3%,
Mn: 1.0 to 1.9%, Cr: 5.9 to 9.5%, M
o: 0.3 to 0.6%, V: 0.10 to 0.40%, N
b: 0.02-0.10%, W: 1.0-1.9%,
N: 0.03 to 0.07% and further Co: 1.
It contains both or one of 0 to 5.0% and Cu: 0.5 to 4.0%, and further B: 0.01 to 0.0 if necessary.
5% and Al: 0.2-1.5%, Ni:
In addition to the content of less than 0.05%, the balance is Fe and inevitable impurities on the steel core wire, and a coating material containing metal carbonate, metal fluoride, arc stabilizer, slag generator, deoxidizer, and adhesive, A coated arc welding rod for high Cr ferritic heat-resistant steel, characterized in that the coating is performed so that the coverage is 25 to 35% by weight based on the total weight of the welding rod.

In the present invention, the above-mentioned C, S
i, Mn, Cr, Mo, V, Nb, W, N, Co, C
Although u, B, and Al are often contained in the steel core wire, even if they are contained in the coating agent, an approximate effect can be obtained. For the steel core wire, in addition to the above components, P: 0.02% or less, S:
0.02% or less, Ti: 0.02% or less, O: 0.05
% Or less, the balance consists of Fe and inevitable impurities.

[0008]

The most important feature of the present invention is that, in place of Ni, which is effective for improving toughness, in the steel core wire or the coating agent, Co and / or Cu is added to secure the toughness of the weld metal while maintaining the creep strength. Has been improved. It is well known that Ni is an element effective for improving toughness, but
On the other hand, recent studies have revealed that carbides and oxides are promoted to agglomerate to lower the creep strength at high temperature for a long time.

As a result of various researches conducted by the present inventors, by adding at least one of Co and Cu in an appropriate amount, the structure is transformed in the δ phase during cooling of the heat treatment without increasing the Cr equivalent. I found that I had enough time to do it. Therefore, the generation of δ-ferrite is suppressed like Ni and a uniform tempered martensite structure is generated without deteriorating the creep property at high temperature for a long time, so that the toughness can be improved. That is, both or one of Co and Cu is added instead of Ni, and the range is 1.0 to 5.0% for Co and 0.5 to 4.0 for Cu.
By limiting the content to%, it is possible to suppress the formation of δ ferrite in the weld metal obtained by welding and to improve the creep rupture strength while ensuring the toughness.

It has also been found that the addition of B further deteriorates the toughness but further improves the creep strength. Addition of B from the coating agent is also effective, but since it is contained in a small amount, segregation occurs and the effect is unstable compared to addition from the steel core wire. Therefore, the addition of B is limited only to the steel core wire. In addition, it was also found that the addition of Al reduces the amount of oxygen in the weld metal, and that fixing C by promoting the precipitation of fine carbide improves the crack resistance of the weld metal. The range is Al: 0.2 to 1.5%
The crack resistance of the weld metal is improved by limiting to The reasons for limiting each component of the present invention will be described below.

C: 0.01 to 0.11%, C is required to be 0.01% or more to secure hardenability and strength, but the upper limit was made 0.11% from the viewpoint of crack resistance.

Si: 0.3 to 1.3% Si is added as a deoxidizing material, but it is also necessary from the viewpoint of ensuring welding workability. If it is less than 0.3%, porosity is likely to occur in the weld metal due to insufficient deoxidation, while if it exceeds 1.3%, toughness is deteriorated, so the upper limit is 1.3.
Defined as%.

Mn: 1.0 to 1.9% Mn is a component necessary not only for deoxidizing but also for maintaining strength. The upper limit is set to 1.9% because if it exceeds this, it is not preferable from the viewpoint of toughness, and the lower limit is set to 1.0% as the amount required for deoxidation.

Cr: 5.9 to 9.5% Since Cr is a very important element for ensuring the oxidation resistance and hardenability, a minimum of 5.9% is required, but 9.5%.
If it exceeds, the crack resistance is impaired and, at the same time, δ ferrite is crystallized to significantly reduce the toughness, so the upper limit was made 9.5%.

Mo: 0.3 to 0.6% Mo is an element that remarkably enhances the high temperature strength by solid solution strengthening. It is added for the purpose of improving the high temperature resistance property against the increase of operating temperature and pressure, but a large amount is added. In that case, the weldability is impaired and δ-ferrite is crystallized, resulting in a decrease in toughness. Therefore, the upper limit of the addition range is set to 0.6%. On the other hand, coexistence with W is effective in improving the high temperature strength, especially the creep rupture strength on the high temperature long time side.
Since it is 3% or more, the lower limit was made 0.3%.

V: 0.10 to 0.40% V is required to be precipitated as carbonitride to secure the strength, and at least 0.10% is necessary. On the other hand, when it exceeds 0.40%, the strength is rather lowered. Therefore, the upper limit was made 0.40%.

Nb: 0.02 to 0.10% Nb is precipitated as a carbonitride similar to V to secure strength, and is also important as an element for refining crystal grains to enhance toughness, so that Nb is at least 0. 02% is required. But 0.
If it exceeds 10%, not only the effect is saturated but also the weldability is deteriorated, so the upper limit was made 0.10%.

W: 1.0 to 1.9% 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 1.0%, the effect cannot be exhibited in the coexistence with Mo, so the lower limit was set to 1.0%.
However, if added excessively, the δ ferrite phase is crystallized to lower the toughness of the weld metal and deteriorate the welding workability, so the upper limit was made 1.9%.

N: 0.03 to 0.07% N is required to be at least 0.03% because it significantly contributes to creep resistance even if it forms a solid solution in the matrix or precipitates as a nitride. On the other hand, if it exceeds 0.07%, a large amount of nitride precipitates, which causes problems such as deterioration of toughness, so the upper limit was set to 0.07%.

Co and / or Cu are necessary for the following reasons.

Co: 1.0 to 5.0% Co is an important element that cancels out the problem of crystallization of δ ferrite caused by the addition of Mo and W, and is required to be 1.0% or more. However, if added excessively, the A _C1 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 is 5.0%.
I decided.

Cu: 0.5 to 4.0% Like Co, Cu is an element that offsets the problem of crystallization of δ ferrite generated by Mo and W, and 0.5%.
You need more than that. However, if added excessively, high temperature tempering becomes impossible and the stabilization treatment of the structure cannot be performed, so the upper limit was made 4.0%.

Ni: Less than 0.05% Ni lowers the high temperature creep property, so the lower the better, the better.

Further, B and Al, which are optionally added, are added for the following reason.

B: 0.01 to 0.05% B has a function of synergistically increasing the effect of adding Mo and W, but if it is less than 0.01%, the effect is not effectively exhibited. On the other hand, if it exceeds 0.05%, the toughness of the weld metal decreases and the welding workability also decreases.

Al: 0.2 to 1.5% Al is effective in reducing oxygen in the deposited metal and improving the crack resistance of the deposited metal by fixing carbon by promoting the precipitation of fine carbide. If it is less than 0.2%, the effect is insufficient. On the other hand, if it exceeds 1.5%, the arc becomes unstable, the amount of spatter increases, and the welding workability deteriorates.

In the present invention, it is necessary to adjust the above components as a whole welding rod. In this case, the amount of each component of the entire welding rod is the following coverage A (%), taking carbon as an example.
In consideration of, the amount is represented by the following formula.

[C of welding rod] (%) = [C in core wire] ×
(100-A) / 100 + [C in coating agent] × A / 10
0

The coated arc welding rod of the present invention contains, in addition to the above-mentioned components, metal carbonate, metal fluoride, arc stabilizer, and slag-forming agent in the coating material such as lime, fluorite, alumina, iron powder,
Add alkaline components, rutile, etc. The range of the coating agent weight% (coverage ratio) based on the total weight of the coated arc welding rod is 2
It should be 5 to 35%. If it is less than 25%, the function as a protective cylinder becomes insufficient and spatter increases, or the bead appearance deteriorates due to insufficient amount of slag produced. On the other hand, if it exceeds 35%, the amount of slag becomes too large and defects such as slag entrainment are likely to occur, and when it is applied to a welded joint having a narrow groove width, it becomes difficult to carry. Further, as the binder, water glass mainly containing sodium silicate and potassium silicate is used. The coated arc welding rod of the present invention is coated and coated by a usual welding rod coating machine,
It is manufactured by baking at 300 to 550 ° C. to remove water.

[0030]

EXAMPLES Examples of the present invention will be described below. In this example, a coverage of 30 was applied to the outer circumference of the steel core wire (4.0 mm diameter) of Table 1 containing the elements specified according to the present invention.
A coating agent having the composition shown in Table 2 was applied so that the content of the coating arc was 100% to produce a coated arc welding rod. Using each of the obtained coated arc welding rods, the ASTM standard A38 with a thickness of 20 mm was used as the base metal for the test.
7 Gr22, 9Cr-1Mo steel, 9Cr-1Mo-N
b-V-W steel, 9Cr-0.5Mo-Nb-V-W steel,
A groove of 12Cr-Nb-V-W steel as shown in FIG. 1 (thickness T of welded material T = 20 mm, groove angle θ = 20 °, root gap L = 12 mm using backing material 2) is used. Formed,
Arc welding was performed. The welding conditions are welding current 16
0A, welding heat input 20kJ / cm, preheating / pass temperature 15
Welded joints were manufactured in a downward posture at 0 to 200 ° C. After the post-heat treatment of the obtained weld metal at 760 ° C. for 5 hours,
A creep rupture test at a stress of 630 ° C. and 250 N / mm ^{2 and} a ² mmV notch impact test at a test temperature of 0 ° C. were performed.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

Table 3 shows the results of the creep rupture test in terms of rupture time (hr), and the results of the impact test are vE0 ° C (J).
Indicate. All of TW-1 to TW-10 satisfy all the requirements of the present invention, the weld metal structure is a martensite single phase structure without crystallization of the δ ferrite phase, and the toughness and creep rupture properties after post heat treatment are A weld metal having good and excellent weldability could be obtained.

Welding rods TW-11 to TW-20 show comparative examples. 1. The welding rod TW-11 is used for ordinary heat resistant steel. It is an example of a 25% Cr-1% Mo-based welding rod, and the welding rod TW-12 is a welding rod for a heat exchanger with further improved high-temperature corrosion resistance, but both are remarkably better than the welding rod of the present invention. Low creep rupture strength.

The welding rod TW-13 is 9Cr-1Mo-Nb.
This is an example of a -V-W type welding rod, but since the amount of C is remarkably higher than that of the welding rod of the present invention, cracking occurred during welding, and crack resistance and impact value decreased. In the welding rod TW-14, the N content exceeded the upper limit thereof, and blow holes were generated in the weld metal and the toughness was poor. Welding rod TW-
In No. 15, the amount of Mo and the amount of W exceeded the upper limits of the range of the present invention, and the creep rupture strength and toughness were lowered.

The welding rod TW-16 is 9Cr-0.5Mo-
Creep rupture strength is low because the amounts of Co and Cu are deviated in the Nb-V-W system. Welding rod TW-17 is 12Cr-0.5
In the Mo-Nb-V-W system, the amount of Nb is below the lower limit,
The creep rupture strength was low and δ ferrite was generated, resulting in a decrease in toughness.

The welding rod TW-18 is 9Cr-0.5Mo-.
In the Nb-V-W system, when the V content exceeded the upper limit, δ ferrite was formed and the toughness was lowered. In the welding rod TW-19, the toughness was low when the Ni content exceeded the upper limit, and cracking occurred when the Al content exceeded the upper limit. The welding rod TW-20 has a B content exceeding the upper limit, so that the creep rupture strength is low and δ ferrite is formed and the toughness is low.

[0039]

The welding material according to the present invention has a conventional content of 9% to 12% C.
Compared with the coated arc welding rod for r steel, the creep strength at high temperature is remarkably increased, and it has excellent characteristics such as toughness and weldability. For example, as shown in Tables 1 to 3, those satisfying the requirements of the present invention are superior in not only high temperature creep characteristics but also toughness and weldability to those not satisfying the requirements of the present invention (comparative examples). Is clear. Used in various power generation boilers, chemical pressure vessels, etc. 9
By using the welding material according to the present invention when welding .about.12% Cr steel, 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 Welding material 2 Backing material θ: Groove angle T: Thickness L: Root gap

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Tanaka 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Corporate Technology Development Division

Claims (3)

[Claims] 1. A weight% based on the total weight of the coated arc welding rod.
C: 0.01 to 0.11% Si: 0.3 to 1.3% Mn: 1.0 to 1.9% Cr: 5.9 to 9.5% Mo: 0.3 to 0. 6% V: 0.10 to 0.40% Nb: 0.02 to 0.10% W: 1.0 to 1.9% N: 0.03 to 0.07%, and further Co: 1.0 to 5.0% and Cu: 0.5 to 4.0%, or both are contained, Ni: less than 0.05%, and the balance is a steel core wire consisting of Fe and unavoidable impurities. , A metal carbonate, a metal fluoride, an arc stabilizer, a slag forming agent, a deoxidizer, and an adhesive, and the coating rate is 25 to 35 with respect to the total weight of the welding rod.
A coated arc welding rod for high Cr ferritic heat-resistant steel, which is coated so as to have a weight percentage. 2. The high Cr ferrite according to claim 1, wherein the steel core wire contains B: 0.01 to 0.05% in weight% with respect to the total weight of the coated arc welding rod. Coated arc welding rod for heat resistant steels. 3. The steel core wire according to claim 1, wherein the steel core wire contains Al: 0.2 to 1.5% by weight based on the total weight of the coated arc welding rod. Coated arc welding rod for Cr ferritic heat resistant steel.