JP3184657B2 - Covered arc welding rod 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 high Cr ferritic high strength heat resistant steel, and more particularly, to a coated arc for obtaining a weld metal having excellent creep characteristics, toughness and crack resistance at high temperatures. It concerns the welding rod.

[0002]

2. Description of the Related Art Ferritic heat-resistant steels, which have extremely excellent 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 steels for energy plants. As a welding material for heat-resistant steel, for example, JP-A-55-303
No. 54 discloses a coated arc welding rod for Cr-Mo steel. These methods define the amount of Ni or Mn to be added, contain an austenite phase stabilizing element, and reduce the coarse ferrite phase in the weld metal.
When a large amount of is contained, the creep rupture strength for a long time decreases, and Ni or Mn more than necessary lowers the crack resistance of the weld metal, so that a target high-performance welded joint cannot be obtained. .

In Japanese Patent Application Laid-Open No. 62-220300, in welding 9% Cr steel, an appropriate amount of W is added to a welding rod and W is limitedly coexisted in relation to the amount of Mo. V ₄
Suppresses over time at C _3, NbC precipitation, thereby improving the creep strength of the high-temperature long-time side by keeping further Mo ₂ C, the precipitation balance of W ₂ C in a proper range. 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, and N are specified and Creq is 13 or less. However, these techniques do not significantly improve the creep strength, and have a drawback that δ ferrite is precipitated in the martensite phase and significantly reduced from the toughness point of view. The δ ferrite phase is a significantly softer phase than the martensite in the matrix, and if such a soft second phase is dispersed in the hard matrix, the overall impact properties are significantly reduced.

[0004]

SUMMARY OF THE INVENTION The present invention focuses on the above circumstances, and reduces the coarse ferrite phase without impairing high-temperature strength, high-temperature creep rupture strength, and cracking resistance. It is an object of the present invention to provide a coated arc welding rod for high Cr ferritic heat resistant steel which can secure a weld metal having comparable strength, toughness and crack resistance.

[0005]

SUMMARY OF THE INVENTION The gist of the present invention is that C: 0.01 to 0.12%, Si:
0.3-2.4%, Mn: 0.3-1.9%, V: 0.
03 to 0.40%, Nb: 0.01 to 0.15%, N:
0.01 to 0.08%, Cr: 5.8 to 13%, Ni:
0.05 to 1.2%, Mo: 0.3 to 1.6%, W:
0.5 to 3.5%, Co: 1.0 to 5.0%, Cu:
0.5 to 4.0%, B: 0.001 to 0.05%, the balance being a steel core wire composed of Fe and inevitable impurities,
A coating agent including a metal carbon salt, a metal fluoride, an arc stabilizer, a slag forming agent, a deoxidizing agent, and a binder is contained, and the coating ratio (the ratio of the coating agent weight to the total weight of the welding rod) is 25 to 3
High Cr, characterized by being coated so as to be 5% by weight.
In the covered arc welding rod for ferritic heat resistant steel. Here, C, Si, Mn, V, Nb, N, Cr, N
It is also characterized in that some or all of the elements i, Mo, W, Co, Cu, and B are contained in the coating instead of the steel core wire.

[0006]

The most significant 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 is suppressed, the toughness is suppressed, and the creep rupture strength is significantly increased. It is in.

In the present invention, the aforementioned C, S
i, Mn, V, Nb, N, Cr, Ni, Mo, W, C
Although o, Cu, and B are often contained in a steel core wire, an approximate effect can be obtained by containing them in a coating agent. In the steel core wire, in addition to the above components, P: 0.02% by weight or less,
S: 0.02% by weight or less, Ti: 0.02% by weight or less,
O: May contain 0.05% by weight or less, with the balance being Fe and unavoidable impurities.

Hereinafter, the reasons for the limitation of the components in the present invention will be described in detail. C: 0.01 to 0.12% by weight C is required to be 0.01% by weight or more for securing hardenability and strength, but the upper limit is 0.12% by weight from the viewpoint of crack resistance.
And

Si: 0.3 to 2.4% by weight Si is added as a deoxidizing agent, but it is also necessary for securing welding workability. If the content is less than 0.3% by weight, pores are likely to be generated in the weld metal due to insufficient deoxidation. On the other hand, if the content exceeds 2.4% by weight, the toughness is reduced.

Mn: 0.3 to 1.9% by weight Mn is a component necessary not only for deoxidation but also for maintaining strength. The upper limit was set to 1.9% by weight because if it exceeds this, it is not preferable from the viewpoint of toughness, and the lower limit is set to 0.3% by weight as an amount required for deoxidation.

V: 0.03 to 0.40% by weight V is required to be at least 0.03% by weight from the viewpoint of preserving the strength by precipitating it as a carbonitride, while V is 0.40% by weight.
If the ratio exceeds the upper limit, the strength is rather reduced.
It was 40% by weight.

Nb: 0.01 to 0.15% by weight Nb is precipitated as a carbonitride like V to secure the strength and is also important as an element that refines the crystal grains and increases the toughness, so that Nb is at least 0%. 0.01% by weight is required, but 0.1% by weight is required.
If the content exceeds 15% by weight, the effect is not only saturated but also lowers the weldability. Therefore, the upper limit is set to 0.15% by weight.

N: 0.01 to 0.08% by weight N, even if dissolved in a matrix or precipitated as a nitride, significantly contributes to creep resistance.
Need. On the other hand, when the content exceeds 0.08% by weight, a large amount of nitrides precipitates, and on the other hand, there arises a problem that the toughness is deteriorated. Therefore, the upper limit is set to 0.08% by weight.

Cr: 5.8 to 13% by weight Since Cr is a very important element for securing oxidation resistance and hardenability, at least 5.8% by weight is necessary. The upper limit is 13% by weight, since δ ferrite is precipitated at the same time as the crack resistance is impaired and the toughness is significantly deteriorated.
And

Ni: 0.05 to 1.2% by weight Ni is an element that suppresses the formation of ferrite and is effective in reducing embrittlement during use, and is essential for applications that are used at high temperatures for a long time. Although it is an element, its effect cannot be obtained if it is less than 0.05% by weight. On the other hand, if the content exceeds 1.2% by weight, the high-temperature creep characteristics deteriorate, so the upper limit is set to 1.2% by weight.

Mo: 0.3 to 1.6% by weight Mo is an element which remarkably enhances high-temperature strength by solid solution strengthening, and is added for the purpose of improving high-temperature strength characteristics against use temperature and pressure rise. In this case, the weldability is impaired and the toughness is reduced due to precipitation of δ ferrite. Therefore, the upper limit was set to 1.6% by weight as the addition range. On the other hand, in the coexistence with W, the effect of improving the high temperature strength, particularly the creep rupture strength on the high temperature long time side is 0.3% by weight or more, so the lower limit was set to 0.3% by weight.

W: 0.5 to 3.5% by weight W is the most excellent element as a solid solution strengthening element for imparting creep rupture strength of a 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 the content is less than 0.5% by weight, the effect cannot be exhibited in the coexistence with Mo, so the lower limit is set to 0.5% by weight. However, if it is added excessively, δ ferrite precipitates and the toughness of the weld metal decreases, and the welding workability also deteriorates. Therefore, the upper limit was set to 3.5% by weight.

Co: 1.0 to 5.0% by weight Co is an important element to offset the problem of precipitation of δ ferrite caused by the addition of Mo and W, and requires 1.0% by weight or more. However, if added in excess, the Ac ₁ point is lowered, so that high-temperature tempering becomes impossible and the structure cannot be stabilized. Therefore, the upper limit is set to 5.0% by weight.

Cu: 0.5 to 4.0% by weight Cu is an element that, like Co, cancels the problem of precipitation of δ ferrite caused by Mo and W, and requires 0.5% by weight or more. However, if added excessively, high temperature tempering becomes impossible and the structure cannot be stabilized, so the upper limit was set to 4.0% by weight.

B: 0.001 to 0.05% by weight B has the effect of increasing the effect of adding Mo and W excessively, but if less than 0.001% by weight, the effect is not effectively exhibited. On the other hand, if the content exceeds 0.05% by weight, the toughness of the weld metal decreases and the welding workability also decreases.

In the present invention, it is necessary to adjust each of the above components as a whole welding rod. In this case, the amount of each component of the entire welding rod is expressed by the following coverage A (%) in the case of carbon.
, And is a quantity represented by the following equation. [C of welding rod] = [C in core wire] × (100−A) / 1
00+ [C in coating agent] × A / 100

The coated arc welding rod according to the present invention is characterized in that, in addition to the above-mentioned components, lime, fluorite, alumina, iron powder, metal carbonate, metal fluoride, arc stabilizer and slag forming agent are contained in the coating agent.
Add an alkali component, rutile, etc. The range of the weight% (covering rate) of the coating agent with respect to the total weight of the coated arc welding rod is as follows.
It needs to be 25 to 35% by weight. If the content is less than 25% by weight, the function as a protective cylinder becomes insufficient, so that spatter increases, or the beat appearance deteriorates due to an insufficient amount of generated slag. On the other hand, if it exceeds 35% by weight, the amount of slag becomes too large, so that defects such as entrainment of slag tend to occur, and rod application becomes difficult when applied to a welded joint having a narrow groove width. Further, as a binder, mainly sodium silicate,
A water glass containing potassium silicate is used.

The coated arc welding rod of the present invention is manufactured by coating and coating with an ordinary welding rod coating machine and then firing at 300 to 550 ° C. to remove moisture.

[0024]

Embodiments of the present invention will be described below. In this example, as shown in Table 1, a coating agent having a composition shown in Table 2 was applied so that the coating rate was 30% on the outer periphery of a steel core wire (4.0 mm diameter) containing the element specified according to the present invention. Was applied to produce a coated arc welding rod.

[0025]

[Table 1]

[0026]

[Table 2]

Using each of the obtained coated arc welding rods, a 20 mm thick ASTM standard A387 Gr
22,9Cr-1Mo steel, 9Cr-1Mo-Nb-V
-W steel, 9Cr-0.5Mo-Nb-V-W steel, 12C
An r-Nb-VW steel was prepared by using a groove (thickness T =
20 mm, groove angle θ = 20 °, root gap L = 1
2 mm) and arc welding was performed. The welding conditions were a welding current of 160 amps and a welding heat input of 20 kJ / c.
m, a preheat / interpass temperature of 150 to 200 ° C., and a welded joint was produced in a downward position.

After the obtained weld metal was post-heat treated at 760 ° C. for 5 seconds, a creep rupture test and a ² mm V notch impact test at a test temperature of 0 ° C. were conducted at 600 ° C. and a stress of 250 N / mm ² . Table 3 shows the results of the above creep rupture tests in terms of rupture time (hr).
(J).

[0029]

[Table 3]

Each of W-1 to W-10 satisfies all of the requirements of the present invention, and the weld metal structure is a martensite single phase structure without precipitation of δ ferrite, and the toughness and creep after post heat treatment. A weld metal having good fracture characteristics and excellent weldability was obtained.

The welding rods W-11 to W-20 are comparative examples. The welding rod W-11 is an example of a 2.25% Cr-1% Mo-based welding rod used for ordinary heat-resistant steel, and the welding rod W-12 is a heat rod with further improved high-temperature corrosion resistance. It is a welding rod for exchangers, but compared to the welding rod of the present invention,
Remarkably low creep rupture strength. 9C welding rod W-13
Although it is an example of an r-1Mo-Nb-VW-based welding rod, since the C content is significantly higher than that of the welding rod of the present invention, cracking occurred during welding, and crack resistance and impact value were reduced. Welding rod W
In the case of -14, the N content exceeded the upper limit, and brohole was generated in the weld metal and the toughness was poor. The creep rupture characteristic of welding rod W-15 was reduced due to the absence of B. Welding rod W-16 is 9Cr-0.5Mo-Nb
The creep rupture strength is low because the V content exceeds the upper limit in the -V-W system. Welding rod W-17 is 12Cr-0.5Mo-N
In the bVW system, the Nb content was lower than the lower limit, and the creep rupture strength was low, δ ferrite was generated, and the toughness was lowered. The welding rod W-18 was a 9Cr-0.5Mo-Nb-VW system, in which W and B were separated, δ ferrite was generated, and toughness was reduced. Mo and W are removed from the welding rod W-19, and the creep rupture strength is low. In the welding rod W-20, Co and Cu are removed, the creep rupture strength is low, δ ferrite is generated, and the toughness is low.

[0032]

The welding material of the present invention has a conventional 9% to 12% C
Compared with a coated arc welding rod for r-steel, it has significantly increased creep strength at high temperatures, and has excellent properties such as toughness and weldability. For example, as shown in the table, those satisfying the requirements of the present invention have not only high-temperature creep properties but also those not satisfying the requirements of the present invention (Comparative Example),
It is clear that the toughness and weldability are excellent.
9-1 used for various power generation boilers, chemical pressure vessels, etc.
By using the welding material according to the present invention when welding 2% Cr steel or the like, the reliability of the welded joint can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a groove shape of a welded portion used in an embodiment.

[Explanation of symbols]

 1 Material to be welded 2 Backing material

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-305396 (JP, A) JP-A-1-214991 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 35/30 B23K 35/36-35/365

Claims (2)

(57) [Claims] C .: 0.01 to 0.12% Si: 0.3 to 2.4% Mn: 0.3 to 1% by weight as an element other than Fe with respect to the total weight of the coated arc welding rod. 9.9% V: 0.03 to 0.40% Nb: 0.01 to 0.15% N: 0.01 to 0.08% Cr: 5.8 to 13% Ni: 0.05 to 1.2 % Mo: 0.3 to 1.6% W: 0.5 to 3.5% Co: 1.0 to 5.0% Cu: 0.5 to 4.0% B: 0.001 to 0.05 %, The balance being a steel core wire composed of Fe and unavoidable impurities, containing a coating agent including a metal carbonate, a metal fluoride, an arc stabilizer, a slag forming agent, a deoxidizing agent, and a binder. Ratio (the ratio of the coating agent weight to the total weight of the welding rod) is 25.
A coated arc welding rod for high Cr ferritic heat-resistant steel, coated so as to have a concentration of about 35% by weight. 2. C, Si, Mn, V, Nb, N, Cr,
2. The coating for high Cr ferritic heat resistant steel according to claim 1, wherein a part or all of the elements of Ni, Mo, W, Co, Cu, and B are contained in the coating instead of the steel core wire. Arc welding rod.