JPH05285691A - Submerged arc welding method for high-cr ferritic heat resisting steel - Google Patents

Abstract

PURPOSE:To improve the creep rupture strength and toughness of a weld metal by specifying the relation between the Co or Cu in a welding wire or flux and the contents of Mo, W, and Ni. CONSTITUTION:The compsn. of the wire is formed, by weight, of 0.03 to O.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, 0.01 to 0.08% N, and the balance Fe and unavoidable impurities. The compsn. of the flux is formed of 10 to 30% CaF2, 10 to 40% either or both of CaO and MgO, 10 to 40% Al2O3 and 5 to 25% SiO2. The wire and the flux are so combined as to contain 0.3 to 1.6% Mo, 0.5 to 3.5% W, 0.05 to 1.2% Ni and 1.0 to 5.0% Co or Cu. Further, the wire and the flux are so combined as to contain Mo, W, Ni, Co or Cu in the relation of (Mo+W)/(Ni+Co or Cu) <=2.0. High-Cr ferritic heat resisting steels are submerged arc welded by the combination.

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, for latent arc welding which provides a weld metal having excellent creep characteristics, toughness, and crack resistance at high temperatures. It is related to the method.

[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 fear 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, JP-A-60-257 is used.
C, Si, Mn, Cr, M in a welding wire such as the 9Cr-Mo steel welding wire disclosed in Japanese Patent No. 991.
A welding wire has been proposed in which the amount of o and Ni is limited and one or two of Nb and V are added to make the content (Nb + V) 0.3% or less. Further, in Japanese Unexamined Patent Publication No. 2-280993, C, Si, M as in 8-12Cr-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, N is limited and the Cr equivalent is 13% or less. However, these conventional techniques do not attempt to significantly improve the creep strength, and may structurally cause δ-ferrite to crystallize in the martensite phase. If it is a remarkably soft phase and 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 formed, which has the drawback of lowering the toughness of the weld metal.

[0003]

DISCLOSURE OF THE INVENTION The present invention suppresses 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, and improves the cleave rupture strength of the weld metal. It improves toughness.

[0004]

The gist of the present invention is that C: 0.03 to 0.12% by weight and Si:
0.3% or less, Mn: 0.3 to 1.5%, Cr: 8 to 1
3%, Nb: 0.01 to 0.15%, V: 0.03 to
0.40%, N: 0.01 to 0.08%, with the balance being Fe and unavoidable impurities, and a weight ratio of C,
aF ₂ ; 10 to 30%, one or both of CaO and MgO; 10 to 40%, Al ₂ O ₃ ; 10 to 40%, Si
O ₂ ; a flux containing 5 to 25% by weight of the formula (M = M in wire + M × 0.7 in flux) Mo: 0.3 to 1.6%, W: 0.5 ~ 3.5%,
Ni: 0.05 to 1.2%, Co or: Cu; 1.0 to
Combined so as to contain 5.0%, Mo, W,
(Mo + W) / (Ni + C) between Ni, Co or Cu
u or Co) ≦ 2.0, which is a latent arc welding method for high Cr ferritic heat-resistant steel.

[0005]

The greatest feature of the present invention is that Co or Cu is added to the welding wire or flux, and Mo, W, Ni, C is added.
o or Cu content and (Mo + W) / (Ni + Co or Cu) ≦ 2.0 coexist for a limited time, which suppresses the formation of δ ferrite in the weld metal obtained by welding and suppresses creep rupture. This is where the strength and toughness have been remarkably enhanced. The reasons for limiting each component of the present invention will be described first from the wire.

C: 0.03 to 0.12% C is required to be 0.03% or more in order 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 deoxidizer, it is also an element that improves oxidation resistance. However, if it exceeds 0.3%, the toughness deteriorates. Therefore, Si is limited to 0.3% or less. Mn: 0.3 to 1.5% Mn is a component required not only for deoxidation but also for strength retention. If it is less than 0.3%, there is no effect, and if it exceeds 1.5%, the toughness deteriorates. Therefore, Mn is limited to 0.3 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 precipitates as a carbonitride to secure the strength, and is also important as an element that gives toughness by refining crystal grains. If it is 0.01% or less, the effect is not obtained and
If it exceeds 15%, not only the effect is saturated but also the toughness and weldability are deteriorated. Therefore, Nb is 0.01%
Limit to ~ 0.15%.

V: 0.03 to 0.40% V is deposited as carbonitride and is effective in securing strength. If it is less than 0.03%, there is no effect, and if it exceeds 0.40%, the strength is rather lowered. Therefore, V is 0.03%
Limit to ~ 0.40%. N: 0.01 to 0.08% N contributes as a remarkable creep resistance even if it forms a solid solution in the matrix or precipitates as a nitride. If it is less than 0.01%, there is no effect, and if it exceeds 0.08%, a large amount of nitride is deposited, conversely the toughness deteriorates, and blowholes occur. Therefore, N is limited to 0.01 to 0.08%.

Next, the reasons for limiting the flux components will be described. CaF ₂ ; 10 to 30% CaF ₂ has the effect of increasing the basicity of the slag, remarkably reducing O in the weld metal, and improving toughness. In addition, the melting point of the slag is lowered to make the penetration shallow, and the slag releasability is improved, and the bead shape and appearance are improved. 10
If it is less than 30%, the effect is not obtained, 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%. One or both of CaO and MgO; 10-40% CaO and MgO are both strongly basic components and are effective for reducing O in the weld metal together with CaF ₂ . Also, CaO, M
gO is a component with high fire resistance and has a low melting point of CaF ₂
It is effective for adjusting the melting characteristics of the flux containing a and adjusting the bead shape. If it is less than 10%, there is no effect, and if it exceeds 40%, the flux is difficult to melt, the bead surface loses smoothness, and welding defects such as undercut occur. Therefore, one or both of CaO and MgO should be 10
Limit 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-known 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 entrapment and undercutting 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%, it has no effect, and 25%.
If it exceeds, 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 to be used, CaF ₂ ; fluorite, molten flux, etc., CaO; lime carbonate, molten flux, etc., MgO; magnesia clinker, molten flux, etc., Al ₂ O ₃ ; alumina, molten flux, etc. Further, in addition to the essential components, metal powder, alloy powder, etc., deoxidizing agent, etc. can be added in order to adjust the components that are consumed by oxidation.

Further, the reasons for limiting the components added in the combination of the wire and the flux will be described. Mo: 0.3 to 1.6% Mo is an element that remarkably enhances high temperature strength by solid solution strengthening, and is added for the purpose of raising the operating temperature and pressure. W
Coexistence with is effective in improving high-temperature strength, especially creep rupture strength at high temperature for a long time. If it is less than 0.3%, the effect is not obtained, and if it exceeds 1.6%, δ ferrite is crystallized and the toughness is deteriorated. Therefore, Mo is 0.3%
Limit 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. In particular, the effect of improving creep rupture strength at high temperature for a long time 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 lower the toughness of the weld metal. Therefore, W is limited to 0.5 to 3.5%.

Ni: 0.05 to 1.2% Ni is an element which suppresses the formation of ferrite and is effective in reducing embrittlement during use, and is used for a long time at high temperature such as the welding material of the present invention. Is an essential element for. 0.0
If it is 5% or less, the effect is not obtained, and if it exceeds 1.2%, the high temperature creep property is deteriorated. Therefore, Ni is 0.05 to 1.
Limit to 2%. Co: 1.0 to 5.0% Like Ni, Co is an important element that cancels out the problem of crystallization of δ ferrite caused by the addition of Mo and W, and requires at least 1.0%. However, if it exceeds 5.0%, the Acl point is lowered, and high temperature tempering becomes impossible, so that the structure cannot be stabilized. Therefore, Co is 1.0 to
Limit to 5.0%.

Cu: 1.0 to 5.0% Like Co and Ni, Cu is an important element that offsets the problem of crystallization of δ ferrite caused by the addition of Mo and W, and is at least 1.0% or more. Need. But 5.0
If it exceeds%, the Acl point is lowered and high temperature tempering becomes impossible, so that the structure cannot be stabilized. Therefore, Cu is 1.
Limit to 0-5.0%. (Mo + W) / (Ni + Co or Cu) ≦ 2.0 (Mo + W) / (Ni + Co or Cu) ≦ 2.0 is very important in balancing the high temperature strength and toughness in the present 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, Co and Cu are elements that suppress the formation of ferrite and improve toughness. Due to the coexistence effect of these elements, the high temperature strength and good toughness of the weld metal can be obtained. (Mo + W) / (Ni + Co or Cu) is 2.
If it exceeds 0, δ ferrite is crystallized and the toughness deteriorates. Therefore, it is limited to (Mo + W) / (Ni + Co or Cu) ≦ 2.0. The effects of the welding method of the present invention will be described below with reference to examples.

[0015]

Example The wire used in the experiment was melted in a vacuum melting furnace, forged, rolled and drawn to obtain 3.2 mmφ. The composition of the wire is shown in Table 1. W1 to W6 are the wires used in the present invention, and W7 to W12 are the wires used in the comparative example. The bond flux used in the experiment was prepared by mixing ore powder, a complex compound, and the like, which are commonly used as a flux raw material, stirred, granulated using water glass, and fired at 400 ° C. for about 2 hours. The composition of the flux is shown in Table 2. F1 to F5 are the fluxes used in the present invention, and F6 to
F10 is used in the comparative example. The wire shown in Table 1 and the flux shown in Table 2 are combined and the test base metal shown in Table 3 is used to form a groove (thickness T = 20 mm, groove angle θ = 30 °, root gap =) as shown in FIG. 12 mm) was formed and latent arc welding was performed under the welding conditions shown in Table 4. After the post-heat treatment of the obtained weld metal at 740 ° C. for 4 hours, 60
A creep rupture test and a ² mmV notch impact test at a test temperature of 0 ° C. were carried out at a stress of 0 ° C. and 20 kgf / mm ² .
Tables 5 and 6 show the combinations of the wire and the flux and the results of their accuracy tests. Regarding the welding workability test, the judgment was made after welding of each pass.

No. 1 of the present invention example. 1-No. No. 13 was excellent in weldability and weld metal, but was No. No. 14 is C, Cr, N deficiency in the wire, Mo, W, Co deficiency due to the combination of the wire and flux, and excessive Ni, No. 15
Is C, Cr, N deficiency in the wire, Co or Cu deficiency due to the combination of wire and flux, and Ni excess, N
o. No. 16 is Si, N excess and Nb deficiency in the wire, Mo deficiency and W excess due to the combination of the wire and the flux, and (Mo + W) / (Ni + Co) exceeds 2.0. 17 is an excessive amount of C, Si and Cr in the wire, and lack of Ni and Cu due to the combination of the wire and the flux.
(Mo + W) / (Ni + Co) exceeds 2.0,
No. 18 is Mn, V deficiency in the wire, (Mo + W) /
(Ni + Co) exceeds 2.0, No. No. 18 is Nb and N excessive in the wire, W is insufficient and Ni is excessive due to the combination of the wire and the flux, and No. No. 20 is excessive Mn and V in the wire, excessive Mo due to the combination of the wire and the flux, and No. 20. 21, No. 22 is A in the flux
L ₂ O ₃ shortage and CaO excess, No. No. 23 was excessive in the sum of CaO and MgO in the flux and was insufficient in SiO ₂ , and was excessive in Mo due to the combination of the wire and the flux. 24
Is insufficient CaF ₂ in the flux, excessive SiO ₂ , Mo and W excessive due to the combination of wire and flux, (Mo +
W) / (Ni + Co) exceeds 2.0.

No. 25 is CaO and Mg in the flux
Insufficient sum with O and Al ₂ O ₃ excess, Mo and Cu excess due to combination of wire and flux, No. 26 is excessive CaF ₂ in the flux and insufficient sum of CaO and MgO,
Excessive Co due to combination of wire and flux, N
o. 27 is Cu by the combination of wire and flux
Excessive, No. No. 28 is excessive Co due to the combination of wire and flux, No. 28 29 is C, Cr, N deficiency in the wire, Al ₂ O ₃ deficiency in the flux and CaF ₂ excess, Mo, Cu or C depending on the combination of the wire and the flux.
o Shortage and excessive Ni, No. 30 is Mn and V in the wire
Excessive, CaF ₂ shortage in flux and SiO ₂ excessive, Mo excess due to combination of wire and flux, (Mo
Due to the individual reasons that + W) / (Ni + Co) exceeds 2.0, problems such as poor workability in welding, deterioration of mechanical properties, and generation of cracks and blowholes were recognized.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

[Table 5]

[0023]

[Table 6]

[0024]

EFFECTS OF THE INVENTION The welding material according to the present invention has a conventional content of 9% to 12% C.
Compared with the welding material for r steel, the creep strength at high temperature is remarkably increased, and it is also excellent in characteristics such as toughness and weldability. As shown in Table 4, when the combination of welding materials satisfies the requirements of the present invention, not only the high temperature creep properties but also the toughness and weldability are superior to those that do not meet the requirements of the present invention (Comparative Example). It is clear that Used in various power generation boilers, chemical pressure vessels, etc. 9
By using the welding material according to the present invention when welding ~ 12% Cr steel, the reliability of the welded joint can be greatly improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a groove shape of a welded portion used in an example.

[Explanation of symbols]

 1 Welded material 2 Backing material.

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 to 0.15 % V: 0.03 to 0.40% N: 0.01 to 0.08%, with the balance being Fe and inevitable impurities in the weight ratio to CaF ₂ ; 10 to 30% CaO and MgO One or both; a flux containing 10 to 40% Al ₂ O ₃ ; 10 to 40% SiO ₂ ; 5 to 25% in a weight ratio of Mo: 0.3 to 1.6% W: 0. 5 to 3.5% Ni: 0.05 to 1.2% Co: 1.0 to 5.0% in combination so as to further contain Mo, W, Ni, C
A latent arc welding method for high Cr ferritic heat-resistant steel, characterized in that a relationship of (Mo + W) / (Ni + Co) ≦ 2.0 is established between the amounts of o. (M = M in wire + 0.7 x M in flux 2. 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 to 0.15 % V: 0.03 to 0.40% N: 0.01 to 0.08%, with the balance being Fe and inevitable impurities in the weight ratio to CaF ₂ ; 10 to 30% CaO and MgO One or both; a flux containing 10 to 40% Al ₂ O ₃ ; 10 to 40% SiO ₂ ; 5 to 25% in a weight ratio of Mo: 0.3 to 1.6% W: 0. 5 to 3.5% Ni: 0.05 to 1.2% Cu: 1.0 to 5.0% in combination so as to further contain Mo, W, Ni, C
A latent arc welding method for high Cr ferritic heat-resistant steel, characterized in that a relationship of (Mo + W) / (Ni + Cu) ≦ 2.0 is established between u amounts. (M = M in wire + 0.7 x M in flux)
formula