JP2600043B2 - Submerged arc welding method 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 welding material for a high-strength heat-resistant steel having a high toughness, and more particularly to a latent-arc welding for providing a weld metal having excellent creep characteristics, toughness and crack resistance at high temperatures. It concerns the method.

[0002]

2. Description of the Related Art As a steel material for an energy plant of a high temperature and high efficiency type, there is a strong demand for a ferritic heat-resistant steel which has extremely excellent creep strength and has little fear of stress corrosion cracking as seen in austenitic stainless steel. Materials are starting to be used. As a welding material developed for ferritic heat-resistant steel, for example, Japanese Patent Application Laid-Open No. 60-257
No. 991, the C, Si, Mn, Cr, M in a welding wire such as the welding wire for 9Cr-Mo steel.
There has been proposed a welding wire in which the amounts of o and Ni are limited, and one or two of Nb and V are added to make (Nb + V) 0.3% or less. Further, Japanese Patent Application Laid-Open No. Hei 2-280993 discloses that C, Si, M
Welding materials have been proposed in which the amounts of n, Cr, Ni, Mo, W, V, Nb, Al, N, and the amount of Cr added are limited to 13% or less. However, these prior arts do not attempt to significantly improve the creep strength, and may systematically crystallize δ ferrite in the martensite phase. It is a very soft phase and if such a soft second phase disperses 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.

[0003]

SUMMARY OF THE INVENTION The present invention suppresses the formation of δ-ferrite crystallized in martensite of the obtained weld metal in latent arc welding in which welding is performed with a large heat input, and reduces 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, 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%, the balance being the weight ratio to the wire composed of Fe and unavoidable impurities,
CaF _2: One or both of 10 to 30%, CaO and _{MgO: 10~40%, Al 2 O} 3: 10~40%, S
iO ₂ : combined with a flux containing 5 to 25%
Arc welding method for high Cr ferritic heat resistant steel
In the wire and the flux, respectively.
Is Mo, W, Ni, Co or
These four components containing Cu and determined by the following formula
Is in weight ratio, Mo: 0.
3 to 1.6%, W: 0.5 to 3.5%, Ni: 0.05
To 1.2%, Co or Cu: 1.0 to 5.0% in the range
And (Mo + W) / (Ni + Co or C
u) Adjust the content of each component so as to satisfy ≦ 2.0.
And a sub- arc welding method for high Cr ferritic heat-resistant steel. M = M in the wire + 0.7 × M in the flux formula (where M is each element (Mo, W, Ni, Co or
Is the content of Cu)

[0005]

The most important feature of the present invention is that Co or Cu is added to a welding wire or a flux and Mo, W, Ni, C
(Mo + W) / (Ni + Co or Cu) ≦ 2.0, which is limited coexistence with the amount of o or Cu, suppresses the formation of δ ferrite in the weld metal obtained by welding, and causes creep rupture. The strength and toughness have been significantly improved. Hereinafter, the reasons for limiting each component of the present invention will be described first with reference to wires.

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 Si is added as a deoxidizing agent, but is also an element for improving oxidation resistance. However, if it exceeds 0.3%, toughness deteriorates. Therefore, Si is limited to 0.3% or less. Mn: 0.3-1.5% Mn is a component necessary not only for deoxidation but also for maintaining strength. If it is less than 0.3%, there is no effect, and if it exceeds 1.5%, toughness deteriorates. Therefore, Mn is limited to 0.3 to 1.5%.

Cr: 8 to 13% Cr is a very important element for securing oxidation resistance and hardenability, and at least 8% is necessary. 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% Nb precipitates as a carbonitride similarly to V to secure strength, and is also important as an element that refines crystal grains and gives toughness. When the content is 0.01% or less, the effect is not obtained.
If it exceeds 15%, the effect is not only saturated, but also the toughness and the weldability are reduced. Therefore, Nb is 0.01%
Limit to ~ 0.15%.

V: 0.03 to 0.40% V is precipitated as carbonitride and is effective in securing the strength. If the content is less than 0.03%, there is no effect, and if it exceeds 0.40%, the strength is rather reduced. Therefore, V is 0.03%
Limit to ~ 0.40%. N: 0.01 to 0.08% N contributes as remarkable creep resistance even if it is dissolved in the matrix or precipitates as nitride. If the content is less than 0.01%, the effect is not obtained. If the content is more than 0.08%, a large amount of nitride precipitates, conversely, the toughness is deteriorated, and blow holes are generated. 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 slag, significantly reducing O in the weld metal, and improving the toughness. In addition, the melting point of the slag is lowered, the penetration is made shallower, the removability of the slag 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. Therefore, CaF ₂ is limited to 10 to 30%. One or both of CaO and MgO; 10 to 40% Both CaO and MgO are strong basic components and are effective in reducing O in the weld metal together with CaF ₂ . Also, CaO, M
gO is a component having high fire resistance, and CaF _{2 having} a low melting point.
It is effective in adjusting the melting characteristics of the flux containing, and adjusting the bead shape. If it is less than 10%, the effect is not obtained. If it exceeds 40%, the flux is hardly melted, the bead surface loses smoothness, and welding defects such as undercut occur. Therefore, one or both of CaO and MgO are
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 used in multi-pass welding, and the bead can be used well, and slag entrainment and undercuts can be prevented. If it is less than 10%, there is no effect, and if it exceeds 40%, slag entrainment and undercut tend to occur. Thus limiting the Al ₂ O ₃ 10 to 40%. SiO ₂ ; 5% to 25% SiO ₂ is effective in adjusting the viscosity of slag and improving the bead appearance, but is less effective when less than 5%, and 25%
If it exceeds, the viscosity increases and slag entrainment occurs. Thus limiting the SiO ₂ 5 to 25%.

The raw materials can be added together with the single substance in the form of a compound containing the above-mentioned components, ore or a molten flux. For example, the raw materials used include CaF ₂ ; fluorite, molten flux, etc., CaO; carbonated lime, molten flux, etc., MgO; magnesia clinker, molten flux, etc., Al ₂ O ₃ ; 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 to adjust components that are oxidized and consumed.

Further, the reasons for limiting the components to be added in combination of the wire and the flux will be described. 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 increasing the use 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%, the effect is not obtained, and if it exceeds 1.6%, δ ferrite is crystallized, so that 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 a 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 coexistence with Mo, and if it exceeds 3.5%, δ ferrite is crystallized and the toughness of the weld metal is reduced. Therefore, W is limited to 0.5 to 3.5%.

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 a high temperature, such as the welding material of the present invention. Is an indispensable element. 0.0
If it is less than 5%, the effect is not obtained, and if it exceeds 1.2%, the high-temperature creep characteristics are deteriorated. Therefore, Ni is 0.05-1.
Limit to 2%. Co: 1.0 to 5.0% Co is an important element that, like Ni, cancels the problem of crystallization of δ ferrite caused by the addition of Mo and W, and requires at least 1.0% or more. However, if it exceeds 5.0%, the Acl point is lowered, high-temperature tempering becomes impossible, and the structure cannot be stabilized. Therefore, Co
Limit to 5.0%.

Cu: 1.0 to 5.0% Cu, like Co and Ni, is an important element for canceling the problem of crystallization of δ ferrite caused by the addition of Mo and W, and at least 1.0% or more. Need. But 5.0
%, The Acl point is lowered, high temperature tempering becomes impossible, and 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 the toughness in the present alloy system. Mo and W are effective elements for improving the high-temperature strength of the weld metal, but crystallize δ ferrite and deteriorate the toughness. Ni, Co, and Cu 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. (Mo + W) / (Ni + Co or Cu) is 2.
If it exceeds 0, δ ferrite is crystallized and toughness deteriorates. Therefore, it is limited to (Mo + W) / (Ni + Co or Cu) ≦ 2.0. Hereinafter, effects of the welding method of the present invention will be described with reference to examples.

[0015]

EXAMPLES The wires used in the experiments were melted in a vacuum melting furnace, forged, rolled, and drawn to produce 3.2 mmφ. The composition of the wire is shown in Table 1, where W1 to W6 are wires used in the present invention, and W7 to W12 are wires used in comparative examples. The bond flux used in the experiment was prepared by mixing ore ore powder, a composite compound, and the like used as ordinary flux raw materials, stirring, granulating using water glass, and firing at 400 ° C. for about 2 hours. The composition of the flux is shown in Table 2, where F1 to F5 are the flux used in the present invention and F6 to F6.
F10 is used in the comparative example. The wire shown in Table 1 and the flux shown in Table 2 were combined, and the test base material shown in Table 3 was used to obtain a groove (thickness T = 20 mm, groove angle θ = 30 °, root gap = 12 mm), and the arc welding was performed under the welding conditions shown in Table 4. After the obtained weld metal was post-heat treated at 740 ° C. for 4 hours,
A creep rupture test and a ² mm V notch impact test at a test temperature of 0 ° C. were performed at 0 ° C. and a stress of 20 kgf / mm ² .
Tables 5 and 6 show the combinations of the wire and the flux and the results of the accuracy test. Regarding the welding workability test, the judgment was made after each pass welding.

In the example of the present invention, 1 to No. In No. 13, excellent welding workability and weld metal were obtained. No. 14 is C, Cr, N deficiency in the wire, Mo, W, Co deficiency and Ni excess due to the combination of wire and flux. Fifteen
Indicates insufficient C, Cr, N in the wire, insufficient Co or Cu due to the combination of wire and flux, and excessive Ni, N
o. No. 16 has excess Si, N and Nb in the wire, insufficient Mo and excess W due to the combination of wire and flux, and (Mo + W) / (Ni + Co) exceeds 2.0. Reference numeral 17 denotes excess C, Si, and Cr in the wire, and Ni and Cu deficiencies due to the combination of wire and 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. 18 is excessive in Nb and N in the wire, insufficient W and excessive Ni due to the combination of the wire and the flux. No. 20 is excessive in Mn and V in the wire, excess Mo due to the combination of wire and flux, 21, no. 22 is A in the flux
l ₂ O ₃ deficiency and excess CaO, no. No. 23 has an excessive amount of CaO and MgO in the flux and an insufficient amount of SiO ₂ , excessive Mo due to the combination of the wire and the flux, 24
Are CaF ₂ deficiency in flux, SiO ₂ excess, Mo and W excess due to combination of wire and flux, (Mo +
W) / (Ni + Co) exceeds 2.0.

No. 25 is CaO and Mg in flux
Insufficient sum with O, excess Al ₂ O _3, excess Mo, Cu due to combination of wire and flux, no. 26 is excess 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
Excess, No. No. 28 is excessive Co due to the combination of wire and flux. Reference numeral 29 denotes C, Cr, N deficiency in the wire, Al ₂ O ₃ deficiency and CaF _{2 in the} flux, Mo, Cu or C due to the combination of the wire and the flux.
o lack and excessive Ni, 30 is Mn, V in the wire
Excess, CaF ₂ deficiency in flux and SiO ₂ excess, Mo excess due to combination of wire and flux, (Mo
+ W) / (Ni + Co) exceeded 2.0, and problems such as poor welding workability, deterioration of mechanical properties, 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]

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

[Brief description of the 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.

Claims (2)

(57) [Claims] 1. In weight ratio Containing the balance of Fe and inevitable impurities in weight ratio High Cr Cr used in combination with a flux containing
In the method for welding submerged arc for ferritic heat-resistant steel,
And / or in the flux
Only Mo, W, Ni, Co, and the following formula
Content M in each of these four components determined by
But, by weight ratio, , And satisfy (Mo + W) / (Ni + Co) ≦ 2.0.
And a sub-arc welding method for high Cr ferritic heat-resistant steel , wherein the content of each component is adjusted . M = M in the wire + 0.7 × M in the flux ... where M is each element (Mo, W, Ni, Co)
Content) 2. In weight ratio Containing the balance of Fe and inevitable impurities in weight ratio High Cr Cr used in combination with a flux containing
In the method for welding submerged arc for ferritic heat-resistant steel,
And / or in the flux
Only Mo, W, Ni, Cu, and the following formula
Content M in each of these four components determined by
But, by weight ratio, , And satisfy (Mo + W) / (Ni + Cu) ≦ 2.0.
And a sub-arc welding method for high Cr ferritic heat-resistant steel , wherein the content of each component is adjusted . M = M in the wire + 0.7 × M in the flux ... where M is each element (Mo, W, Ni, Cu)
Content)