JPH09277084A - Submerged arc welding method for high-chromium ferritic heat resisting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the creep strength and toughness of weld metal by adding Ta, Cu, Co into a welding wire or flux and specifying the relations of the amt. of Mo, W, Ni, Cu and Co. SOLUTION: The wire contg., by weight, 0.03 to 0.12% C, <=0.3% Si, 0.3 to 1.5% Mn, 8 to 13% Cr, 0.01 to 0.15% Nb, 0.03 to 0.40% V and 0.01 to 0.08% N and consisting of the balance Fe with inevitable impurities and the flux contg. 10 to 30% CaF2 , 10 to 40% at least either of Cao or MgO, 10 to 40% Al2 O3 and 5 to 25% SiO2 are used. In accordance with formula 1 when the respective elements are defined as M, 0.3 o 1.6% Mo, 0.5 to 3.5% W, 0.05 to 1.2% Ni, 1.0 to 5.0% at least either of Cu or C and 0.001 to 0.5% Ta are incorporated into the wire and flux and the relation of formula II is established among the amts. of Mo, W, Ni, Cu and Co.

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 latent arc welding method for providing a weld metal having excellent creep characteristics, toughness, and crack resistance at high temperatures. Related to.

[0002]

2. Description of the Related Art As a steel material for high temperature and high efficiency type energy plants, there is a strong demand for a ferritic heat resistant steel having excellent creep strength and less risk of stress corrosion cracking as seen in austenitic stainless steel. The material is starting to be used. As a welding material developed for ferritic heat-resistant steel, for example, Japanese Patent Application Laid-Open No. 60-257
C, Si, Mn, Cr in the welding wire such as the welding wire for 9Cr-Mo steel disclosed in Japanese Patent No. 991.
Limit the amount of Mo and Ni, and further use one of Nb and V or 2
A welding wire has been proposed in which the content of (Nb + V) is 0.3% or less by adding a seed.

Further, in JP-A-2-280993, C, Si, Mn, and C are used as welding materials of 8-12 Cr type.
A welding material has been proposed in which the addition amount of r, Ni, Mo, W, V, Nb, Al, and N is limited and the Cr equivalent is 13% or less. However, these conventional techniques are significantly clearer.
However, δ-ferrite crystallized in the martensite phase during the solidification process of the weld metal may exist in the martensite phase. This crystallized δ-ferrite 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 are significantly reduced. In the case of welding with a large heat input, such as latent arc welding, δ ferrite is particularly likely to be generated, which has the disadvantage of reducing the toughness of the weld metal. The inventors of the present invention have proposed a method for improving these drawbacks in Japanese Patent Application No. 4-95379. However, there is a demand for these welding materials to further improve creep strength while maintaining toughness. It is necessary to improve the deterioration of creep strength in the welding environment, and because the environment in which the welded structure using these welding materials is used tends to have even higher temperatures, it is possible to obtain welding materials with creep properties that can withstand these high temperatures. Development is needed.

[0004]

The object of the present invention is to achieve the toughness of the weld metal by suppressing the formation of δ ferrite crystallized in the martensite of the obtained weld metal in the latent arc welding for welding with a large heat input. In order to improve the creep rupture strength on the long-term side, and further to a higher temperature range (600 to 6 ° C) than the conventional (550 to 600 ° C).
It is also intended to improve the creep rupture strength at 50 ° C.

[0005]

Means for Solving the Problems The present invention is to solve the above-mentioned problems, and in a weight ratio (hereinafter the same), C: 0.0.
3 to 0.12%, Si: 0.3% or less, Mn: 0.3 to
1.5%, Cr: 8 to 13%, Nb: 0.01 to 0.1
5%, V: 0.03-0.40%, N: 0.01-0.
08%, if necessary, further B: 0.0001
˜0.005%, the balance being Fe and inevitable impurities, CaF ₂ : 10 to 30%, Ca
At least one of O and MgO: 10 to 40%, Al
_When the flux containing ₂ O ₃ : 10 to 40% and SiO ₂ : 5 to 25% and each of the following component elements is M, M = M in wire + 0.7 × M in flux and wire and flux To one or both
o: 0.3 to 1.6%, W: 0.5 to 3.5%, Ni:
0.05 to 1.2%, at least one of Cu and Co: 1.0 to 5.0%, Ta: 0.001 to 0.5%, and Mo, W, Ni, Cu, Co content Is a (Mo + W) / (Ni + Cu + Co) ≤1.8 relationship between the two, and is a latent arc welding method for high Cr ferritic heat-resistant steel.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The feature of the present invention is to add Ta and at least one of Cu and Co into a welding wire or flux, and (Mo + W) / (Ni + Cu + Co) between Mo, W, Ni, Cu and Co. ) Is limited coexistence so that it is 1.8 or less. As a result of conducting a number of research experiments, the present inventors have added Ta and one of Cu and Co to (Mo + W) / (Ni + Cu + C
It has been found that limiting the o) can improve the toughness and creep properties of the weld metal. That is, it was found that the addition of Ta causes the precipitation of Ta carbide, which suppresses the precipitation of Nb carbide, thereby improving the creep strength and toughness of the weld metal. Furthermore, by adding at least one of Cu and Co, the formation of δ-ferrite in the weld metal is suppressed to improve the toughness of the weld metal, and the synergistic effect with Ta described above improves the creep characteristics and toughness. Therefore, it was found that by adding an appropriate amount of B in accordance with the above, the creep characteristics at high temperature are further improved. Addition of B from the flux is also effective, but since it is a small amount of compound, segregation easily occurs, and addition from the wire is more effective.

The reasons for limiting the components of the present invention will be described below starting with the wire. C: 0.03 to 0.12% C
Requires 0.03% or more to secure hardenability and strength, but if it exceeds 0.12%, crack resistance deteriorates. Therefore, C is limited to 0.03 to 0.12%.

Si: 0.3% or less Although Si is added as a deoxidizing agent, it is also an element that improves oxidation resistance. However, if it exceeds 0.3%, toughness deteriorates. Therefore, Si is limited to 0.3% or less.

Mn: 0.3 to 1.5% Mn is a component necessary not only for deoxidation but also for maintaining strength. If it is less than 0.3%, the effect is insufficient, and if it exceeds 1.5%, the toughness deteriorates. Therefore, Mn is 0.3 to
Limit to 1.5%.

Cr: 8 to 13% Cr is a very important element for ensuring the oxidation resistance and the hardenability, and at least 8% is required. If it exceeds 13%, the crack resistance is impaired, and at the same time, δ ferrite is crystallized and the toughness is significantly deteriorated. Therefore, Cr is limited to 8 to 13%.

Nb: 0.01 to 0.15% Similar to V, Nb is precipitated as a carbonitride to secure the strength, and is also important as an element for refining crystal grains to give toughness. If less than 0.01%, the effect is insufficient,
If it exceeds 0.15%, not only the effect is saturated, but also the toughness and weldability are deteriorated. Therefore, Nb is limited to 0.01% to 0.15%.

V: 0.03 to 0.40% V precipitates as carbonitride and is effective in securing strength.
If it is less than 0.03%, the effect is insufficient, while if it exceeds 0.40%, the strength is rather lowered. Therefore, V is limited to 0.03% to 0.40%.

N: 0.01 to 0.08% N contributes significantly to the creep resistance even if it forms a solid solution in the matrix or precipitates as a nitride. If it is less than 0.01%, the effect is insufficient, and if it exceeds 0.08%, a large amount of nitride is precipitated, conversely the toughness deteriorates, and blowholes occur. Therefore, N is limited to 0.01 to 0.08%.

B: 0.0001 to 0.0050% B is added as required, but it improves the tensile strength and creep strength of the weld metal at high temperatures, and maintains the creep strength especially on the long side to prevent deterioration. It is effective for
If less than 0.0001%, the effect is small, and 0.005%
If it exceeds 0%, the crack resistance of the weld metal is significantly deteriorated.
Therefore, B is limited to 0.0001 to 0.0050%.

Next, the reasons for limiting the flux components will be described. CaF _2: 10~30% CaF ₂ increases the basicity of the slag, the effect of improving significantly reduced toughness for O in the weld metal. In addition, the melting point of the slag is lowered, the penetration is made shallow, the releasability of the slag is improved, and the bead shape and appearance are improved. 1
If it is less than 0%, its effect is small, and if it exceeds 30%, the fluidity of the slag becomes excessive and the bead shape and appearance deteriorate.
Thus limiting the CaF ₂ 10 to 30%.

At least one of CaO and MgO: 1
0-40% CaO and MgO are both strongly basic components and CaF ₂
It is also effective for reducing O in the weld metal. In addition, Ca
O and MgO are components with high fire resistance, and C with a low melting point.
It is effective for adjusting the melting characteristics of the flux containing aF ₂ and adjusting the bead shape. If it is less than 10%, the effect is insufficient, and if it exceeds 40%, the flux is difficult to melt, the bead surface loses smoothness, and welding defects such as undercut occur. Therefore, the total amount of at least one of CaO and MgO is limited to 10 to 40%.

Al ₂ O ₃ : 10 to 40% Al ₂ O ₃ has a high melting point and is effective in adjusting the fluidity of the slag and adjusting the bead shape. This effect is particularly important when it is used for multi-pass welding, and the bead-to-beads are well fitted to each other, and defects such as slag entrainment and undercut are prevented. If it is less than 10%, there is no effect, and if it exceeds 40%, slag entrainment and undercut tend to occur. Therefore, Al ₂ O ₃ is limited to 10 to 40%.

SiO ₂ : 5 to 25% SiO ₂ is effective for adjusting the viscosity of the slag and improving the bead appearance, but if it is less than 5%, the effect is small and 25
If it exceeds%, the viscosity increases and slag entrapment occurs. Therefore, SiO ₂ is limited to 5 to 25%.

The raw materials can be added as a single substance together with a compound containing the above-mentioned components, ore, molten flux or the like. For example, as raw materials used, CaF ₂ is fluorite, molten flux, etc., CaO is carbonated lime, molten flux, etc., MgO is magnesia clinker, molten flux, etc., and Al ₂ O ₃ is alumina, molten flux, etc. In addition to the essential components, a metal powder, an alloy powder, a deoxidizing agent, and the like can be blended in order to adjust components that are oxidized and consumed.

Further, the reasons for limiting the components added in the combination of the wire and the flux will be described. Here, each component element described below is a quantity according to the following formula (1), where M is this. This is because, even if the same amount is added, the yield to the weld metal is different between in the wire and in the flux, and in the flux it is about 70% of the yield in the wire. M = M in wire + 0.7 × M in flux ... (1)

Mo: 0.3 to 1.6% Mo is an element that remarkably enhances the high temperature strength by solid solution strengthening, and is added for the purpose of raising the operating temperature and pressure. W
Coexistence is effective for improving the high-temperature strength, particularly the creep rupture strength on the high-temperature long-time side. If it is less than 0.3%, its effect is small, and if it exceeds 1.6%, δ ferrite is crystallized and the toughness deteriorates. Therefore, Mo is 0.3
% To 1.6%.

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. Particularly, the effect of improving the creep rupture strength on the high temperature and long time side is extremely large. If it is less than 0.5%, the effect cannot be exhibited in the coexistence with Mo, and if it exceeds 3.5%, δ ferrite is crystallized to reduce the toughness of the weld metal. Therefore, W is 0.5 to 3.
Limit to 5%.

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. Is an essential element for. 0.0
If it is less than 5%, its effect is small, and if it exceeds 1.2%, the high temperature creep property is deteriorated. Therefore, Ni is 0.05
Limit to ~ 1.2%.

At least one of Cu and Co: 1.0
~ 5.0% Like Ni, Ni and Cu are important elements that offset the problem of δ-ferrite crystallization caused by the addition of Mo and W, and require at least 1.0%. But 5.
If it exceeds 0%, the A _C1 point is lowered, and high temperature tempering becomes impossible, so that the structure cannot be stabilized. Therefore, one or both of Cu and Co are limited to 1.0 to 5.0%.

Ta: 0.001 to 0.5% Ta is an effective component for increasing high temperature strength and creep rupture strength. It precipitates as Ta carbide at grain boundaries, and has a great effect of improving creep rupture strength especially at high temperature and long time. It also has the effect of suppressing the precipitation of Nb carbide and improving the toughness of the weld metal. If it is less than 0.001%, the effect is small, and if it exceeds 0.5%, the effect is not only saturated, but the toughness is rather deteriorated. Therefore, Ta is 0.
It is limited to 001 to 0.5%.

(Mo + W) / (Ni + Cu + Co) ≦ 1.8 (Mo + W) / (Ni + Cu + Co) is very important in balancing the high temperature strength and toughness in this alloy system. Mo and W are effective elements for improving the high temperature strength of the weld metal, but they crystallize δ ferrite and deteriorate the toughness. Ni, Cu and Co are elements that suppress the formation of ferrite and improve toughness. High temperature strength and good toughness of the weld metal can be obtained by the coexistence effect of these elements. When (Mo + W) / (Ni + Cu + Co) exceeds 1.8, δ ferrite crystallizes and the toughness deteriorates. Therefore, it is limited to (Mo + W) / (Ni + Cu + Co) ≦ 1.8.

[0027]

EXAMPLES The effects of the welding method of the present invention will be described below with reference to examples. The wire used in the experiment was melted in a vacuum melting furnace, forged, rolled and drawn to have a diameter of 4.0 mm. The composition of the wires is shown in Table 1. W1 to W6 are wires that meet the conditions of the present invention, and W7 to W12 are comparative wires.

[0028]

[Table 1]

The bond flux used in the experiment was prepared by mixing ore powder, a composite compound, etc., which are used as usual flux raw materials, stirring, granulating with water glass, and firing at 400 ° C. for about 2 hours. The composition of the flux is shown in Table 2. F1 to F5 are the fluxes conforming to the conditions of the present invention, and F6 to F10 are the comparative examples.

[0030]

[Table 2]

The wire shown in Table 1 and the flux shown in Table 2 were combined and the test base metal shown in Table 3 was used to form a groove (thickness: 20 mm, groove angle: 30 °, rule: (T gap: 15 mm) was formed and the latent arc welding was performed under the welding conditions shown in Table 4. In the figure, 1 is a material to be welded and 2 is a backing material. The obtained weld metal was post-heat treated at 740 ° C. for 2 hours and then subjected to a creep rupture test at 600 ° C. and a stress of 200 N / mm ^{2 and} a ² mmV notch impact test at a test temperature of 0 ° C. Tables 5 to 8 show the combinations of the wire and the flux and the accuracy test results. Regarding the welding workability test, the judgment was made after each pass welding. Regarding the welding crack test, after forming the groove shown in FIG. 2 on the steel plate of B-1 shown in Table 3 and performing 1-pass latent arc welding under the welding conditions shown in Table 4, the presence or absence of cracks was checked by color check. It was judged.

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

[0035]

[Table 6]

[0036]

[Table 7]

[0037]

[Table 8]

No. 1 of the present invention example. 1 to No. No. 13 had excellent welding workability and weld metal. On the other hand, N of the comparative example
o. 14 is C, Cr, N deficiency in the wire, Mo, W deficiency due to the combination of the wire and the flux, Cu or C
o is insufficient and Ni is excessive. No. 15 is deficient in C, Cr and N in the wire, deficient in Cu or Co and Ta due to the combination of the wire and flux, and excessive in Ni.

No. 16 is Nb shortage and S in the wire
i, N, B excess, Mo and Ta deficiency and W excess due to combination of wire and flux, (Mo + W) / (Ni
+ Cu + Co) exceeds 1.8. In addition, No. 1
7 is excessive C, Si, Cr in the wire, lack of Ni due to the combination of wire and flux, Cu or Co, Ta
Insufficiency, (Mo + W) / (Ni + Cu + Co) exceeds 1.8.

No. 18 is Mn in the wire, lack of V, excess Ta due to the combination of wire and flux, (Mo
+ W) / (Ni + Cu + Co) exceeds 1.8,
No. In No. 19, Nb and N in the wire are excessive, W is insufficient due to the combination of the wire and the flux, and Ni is excessive. In addition, No. 20 is excessive Mn, V, B in the wire, Mo, Ta due to the combination of the wire and the flux.
Too many.

No. No. 21 had excess CaF ₂ and insufficient Al ₂ O ₃ in the flux. No. 22 has excess CaF ₂ in the flux, lack of Al ₂ O ₃ , and lack of Ta due to the combination of wire and flux. In addition, No. 23 is CaO and MgO in the flux
Is excessive and the SiO _{2 is} insufficient, and Mo is excessive due to the combination of the wire and the flux. 24 is CaF ₂ deficiency and excess SiO _{2 in the} flux, Mo and W excess due to the combination of wire and flux, (M
o + W) / (Ni + Cu + Co) exceeds 1.8.

No. 25 is CaO and Mg in flux
The sum of O is insufficient, Al ₂ O _{3 is} excessive, Mo is excessive due to the combination of wire and flux, and the sum of Cu and Co is excessive. In No. 26, the amount of CaF ₂ in the flux is excessive and the sum of CaO and MgO is insufficient, and the amount of Cu and Co due to the combination of the wire and the flux is excessive. In addition, No. In No. 27, the sum of Cu and Co due to the combination of the wire and the flux is excessive.

No. No. 28 has an excessive sum of Cu and Co due to the combination of wire and flux.
29 is insufficient C, Cr, N in the wire, C in the flux
The amount of aF _{2 is} excessive and the amount of Al ₂ O _{3 is} insufficient, the combination of Mo and Cu and Co due to the combination of the wire and the flux, the amount of Ta is insufficient, and the amount of Ni is excessive. In addition, No. 30 is Mn, V, B excess in the wire, CaF ₂ deficiency in the flux and SiO ₂ excess, Mo and Ta excess due to the combination of the wire and the flux, (Mo + W) / (Ni + Cu + C)
o) exceeds 1.8. In these comparative examples, problems such as poor welding workability, deterioration of mechanical properties, and generation of cracks and blowholes were recognized for each of the above reasons.

[0044]

According to the present invention, the high-temperature creep strength and toughness of the weld metal are remarkably enhanced as compared with the conventional 9-12% Cr steel submerged arc welding material. The characteristics are also excellent. As shown in the examples, those in which the combination of welding materials satisfies the requirements of the present invention, not only the high temperature characteristics of the weld metal, toughness, but also the weldability, as compared with those not satisfying the requirements of the present invention (comparative examples), It is clear that it has excellent crack resistance. By using the welding material according to 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 diagram showing a groove shape of a weld used in an example.

FIG. 2 is a diagram showing a groove shape for a welding crack test.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C22C 38/26 C22C 38/26 38/32 38/32 (72) Inventor Yu Morimoto Futtsu, Chiba Prefecture Shintomi 20-1 Nippon Steel Co., Ltd. Technology Development Division

Claims (2)

[Claims] 1. By weight ratio, C: 0.03 to 0.12%, Si: 0.3% or less, Mn: 0.3 to 1.5%, Cr: 8 to 13%, Nb: 0. 01~0.15%, V: 0.03~0.40%, N: contains 0.01 to 0.08 percent, the balance being a wire consisting of Fe and unavoidable impurities, CaF _2: 10 to 30 %, At least one of CaO and MgO: 10 to 40%, Al ₂ O ₃ : 10 to 40%, SiO ₂ : 5 to 25%, and M, where each of the following component elements is M: Mo + 0.3 to 1.6%, W: 0.5 to 3.5%, Ni: 0.05 to 1 according to M + 0.7 × M in flux and M in flux. 0.2%, at least one of Cu and Co: 1.0 to 5.0%, Ta: 0.001 to For high Cr ferritic heat-resisting steel characterized by containing 0.5% and satisfying the relationship of (Mo + W) / (Ni + Cu + Co) ≦ 1.8 among the amounts of Mo, W, Ni, Cu and Co. Submerged arc welding method. 2. The latent arc welding method for high Cr ferritic heat-resistant steel according to claim 1, wherein the wire further contains B: 0.0001 to 0.005%.