JPH07155988A - Coated arc electrode for high-cr ferritic heat resisting steel - Google Patents

Abstract

PURPOSE:To improve the creep rupture strength and toughness of weld metal by coating a steel core wire with a specific amt. of a coating material specified in the contents of C, Si, Mn, V, Nb, N, Cr, Ni, Mo, W, Co and Ta. CONSTITUTION:The components of the coating material are specified, by the total weight of a welding electrode, to 0.01 to 0.12% C, 0.3 to 2.4% Si, 0.3 to 1.9% Mn, 0.03 to 0.40% V, 0.01 to 0.15% Nb, 0.01 to 0.08% N, 5.8 to 13% Cr, 0.05 to 1.2% Ni, 0.3 to 1.6% Mo, 0.5 to 3.5% W, 1.0 to 5.0% Co and 0.01 to 3.0% Ta. Further, an arc stabilizer, slag forming agent and binder are incorporated therein. The outer periphery of the steel core wire is so coated with the coating material that the weight thereof attains 22 to 40%. The formation of a delta ferrite phase of the weld metal is suppressed if this welding electrode is used.

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

[0002]

2. Description of the Related Art Ferritic heat-resistant steels, which have extremely high creep strength and are less susceptible to stress corrosion cracking as seen in austenitic stainless steels, have begun to be used as high-temperature, high-efficiency steel materials for energy plants.
As a welding material for this kind of heat-resistant steel, for example, Japanese Patent Laid-Open No.
As in the coated arc welding rod for Cr-Mo steel disclosed in Japanese Patent No. 30354, the addition amount of Ni, Mn and the like is limited, an austenite phase stabilizing element is contained, and a coarse ferrite phase in the weld metal is contained. Although it has been proposed to reduce the amount, when a large amount of Ni is contained, the creep rupture strength decreases, and when a large amount of Ni or Mn is contained, the crack resistance of the weld metal decreases. Therefore, the target high performance welded joint cannot be obtained.

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 JP-A-2-280993, C, Si, Mn, C as in the case of 9-12 Cr-based welding materials is used.
A welding material has been proposed in which the added amounts of r, Ni, Mo, W, V, Nb, Al, N, and C are limited and Creq: 13% or less. However, these materials 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 toughness aspect. 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]

SUMMARY OF THE INVENTION The object of the present invention is to pay attention to the above-mentioned circumstances, in consideration of high temperature strength and high temperature creep strength,
Further, the coarse ferrite phase is reduced without impairing the crack resistance and the like, and the strength, toughness and crack resistance comparable to those of the base material are ensured.

[0005]

The gist of the present invention is that the weight ratio to the total weight of the welding rod is C: 0.01-.
0.12%, Si: 0.3 to 2.4%, Mn: 0.3 to
1.9%, V: 0.03 to 0.40%, Nb: 0.01
.About.0.15%, N: 0.01 to 0.08%, Cr: 5.
8 to 13.0%, Ni: 0.05 to 1.2%, Mo:
0.3-1.6%, W: 0.5-3.5%, Co: 1.
0 to 5.0%, Ta: 0.01 to 3.0%, and a coating agent containing an arc stabilizer, a slag forming agent, and a binder in an amount of 22 to 40% by weight based on the total weight of the welding rod. %, High Cr content is obtained by coating the outer circumference of the steel core wire
It is a coated arc welding rod for ferritic heat resistant steel.

[0006]

The greatest feature of the present invention is that in a coated arc welding rod for high Cr ferritic heat-resistant steel, toughness deterioration is suppressed by suppressing the formation of δ ferrite phase in the weld metal, and creep rupture strength and toughness are remarkably improved. It is in a raised position.

The steel core wire used in the present invention is the above-mentioned C,
Si, Mn, V, Nb, N, Cr, Ni, Mo, W, C
The chemical ratio other than o and Ta is P: 0.02% or less, S: 0.02% or less, Ti: 0.01% or less, O:
0.05% or less, the balance being Fe and unavoidable impurities. The reason for limiting the components in the present invention will be described in detail below.

C: 0.01 to 0.12% C is required to be 0.01% or more to secure hardenability and strength, but the upper limit is 0.12% from the viewpoint of crack resistance.

Si: 0.3 to 2.4% 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%, pores are easily generated in the weld metal due to insufficient deoxidation, while if it exceeds 2.4%, toughness is deteriorated, so the upper limit is 2.4.
Defined as%.

Mn: 0.3 to 1.9% Mn is a component required not only for deoxidation but also for maintaining strength. The upper limit is set to 1.9% because if it exceeds this, it is not preferable in terms 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% for precipitating as carbonitride to secure the strength, but if it exceeds 0.40%, the strength rather decreases. Therefore, the upper limit was made 0.40%.

Nb: 0.01 to 0.15% 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. 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: 5.8 to 13.0% Since Cr is a very important element for ensuring oxidation resistance and hardenability, at least 5.8% is required, but 13.0%
If it exceeds, the crack resistance is impaired, and at the same time, δ ferrite is crystallized and the toughness is significantly deteriorated, so the upper limit was made 13.0%.

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 1.2.
%.

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 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, the excessive addition causes the δ ferrite phase to crystallize and the toughness of the weld metal to deteriorate, and the welding workability to deteriorate, so the upper limit was made 3.5%.

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 at least 1.0.
Need more than%. 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 set to 5.0%.

Ta: 0.01 to 3.0% Ta is a component that remarkably enhances the high temperature strength and the creep rupture strength, and TaC is precipitated, and the effect of improving the creep rupture strength particularly at a high temperature and a long time is extremely large. But 0.
If it is less than 01%, the effect cannot be obtained, while if it exceeds 3.0%, the toughness deteriorates remarkably, so the upper limit was set to 3.0%.

The coated arc welding rod of the present invention comprises, for example, a steel core wire containing the above-mentioned elements, an arc stabilizer, an iron powder, an alkali component, a slag forming agent such as rutile, and also sodium silicate and potassium silicate. A coating material obtained by kneading with a binder such as water glass is coated and coated by an ordinary welding rod coating machine, and then baked at 300 to 550 ° C. to remove water. The appropriate amount of coating material is 22 to 40% by weight with respect to the total weight of the welding rod. If it is less than this, the shielding effect becomes insufficient and it causes deterioration of the material. It becomes uneconomical and uneconomical.

[0021]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples. A coating agent was applied to the outer circumference of a steel core wire (4.0 mm diameter) containing the elements specified in the present invention so that the coverage rate was 30%, and a coated arc welding rod having the composition shown in Table 1 was produced. did. Using each of the obtained welding rods, ASTM standard A387 Gr22, 9Cr-1Mo steel with a thickness of 20 mm,
9Cr-1Mo-Nb-V-W steel, 9Cr-0.5Mo
-Nb-V-W steel and 12Cr-Nb-V-W steel are groove (thickness T = 20 mm, groove angle θ = 20 as shown in FIG.
And a root gap L = 12 mm) were formed, and the results shown in Table 2 were obtained. The welding conditions are welding current 170 A, welding heat input 20 kJ / cm, preheating / pass temperature 150 to 20.
A welded joint was prepared in a downward posture at 0 ° C. After the post-heat treatment of the obtained weld metal at 740 ° C. for 4 hours, 600
A creep rupture test at a temperature of 220 ° C. and a stress of 220 N / mm ^{2 and} a ² mmV notch impact test at a test temperature of 0 ° C. were performed.

[0022]

[Table 1]

[0023]

[Table 2]

All of AS-1 to AS-13 satisfy all the requirements of the present invention, and the weld metal structure is a martensite single phase structure without crystallization of δ ferrite phase, and the toughness and creep after the post heat treatment. It was possible to obtain a weld metal having good fracture properties and excellent weldability.

Welding rods AS-14 to AS-23 show comparative examples. The welding rod AS-14 is an example of a 2 1/4% Cr-1% Mo welding rod which is used for ordinary heat resistant steel,
The welding rod AS-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.

The welding rod AS-16 is 9Cr-1Mo-Nb.
This is an example of a -VW type welding rod, but the amount of C is significantly higher than that of the welding rod of the present invention, so cracking occurs during welding, and the crack resistance and impact value are reduced. Welding rod AS-17 is M
When o and N exceed the upper limit, blowholes are generated in the weld metal and a δ ferrite phase is generated,
The toughness was poor. Since the V content of the welding rod AS-18 is below the lower limit and there is no Nb, the crack resistance is deteriorated, and the crystal grains become coarse due to the formation of the δ ferrite phase, and the toughness is reduced.

The welding rod AS-19 is 9Cr-0.5Mo-
Creep rupture strength was low when the V amount exceeded the upper limit in the Nb-V-W system, and cracks occurred because the C amount exceeded the upper limit. Welding rod AS-20 is 12Cr-0.5Mo
In the -Nb-V-W system, the Mn content exceeds the upper limit and the toughness is reduced.

The welding rod AS-21 is 9Cr-0.5Mo-
Nb-V-W type has low Mo content and low creep rupture strength. Welding rod AS-22 is also 9Cr-0.5Mo-Nb-V
In the -W system, the amount of W exceeds the upper limit, and since there is no Co, a δ ferrite phase occurs and the toughness decreases. Welding rod A
S-23 is also Ta in 9Cr-0.5Mo-Nb-VW system.
Since the Co content is less than the lower limit, the creep rupture strength is low and the δ ferrite phase is generated, resulting in low toughness.

[0029]

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 and 2, 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). Clearly, 9-12% used in various power generation boilers, chemical pressure vessels, etc.
It is a highly suitable welding rod when welding high Cr ferritic heat resistant steel such as Cr steel.

[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

Claims (1)

[Claims] 1. A weight ratio of C: 0.01 to 0.12% Si: 0.3 to 2.4% Mn: 0.3 to 1.9% V: 0.0. 03-0.40% Nb: 0.01-0.15% N: 0.01-0.08% Cr: 5.8-13.0% Ni: 0.05-1.2% Mo: 0. 3 to 1.6% W: 0.5 to 3.5% Co: 1.0 to 5.0% Ta: 0.01 to 3.0%, and further contains an arc stabilizer, a slag forming agent, and a viscous agent. A coated arc welding rod for high Cr ferritic heat-resistant steel, characterized in that the coating material containing a binder is coated on the outer circumference of the steel core wire so as to be 22 to 40% by weight with respect to the total weight of the welding rod.