JP3527458B2 - Cladding steel and chimney for the inner cylinder of a coal-fired power plant with excellent corrosion resistance at the weld zone - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can be used in a coal-fired power generation plant chimney inner cylinder clad steel and a chimney having excellent corrosion resistance of a welded portion, and particularly, can be used in a single-loop type coal-fired power generation plant. The present invention relates to a low-cost chimney inner cylinder clad steel having excellent corrosion resistance, and a high-performance chimney constructed by the clad steel.

[0002]

2. Description of the Related Art In recent years, as part of improving the performance of thermal power plants, the development of high corrosion-resistant, low-cost chimney inner cylinder steel that can be used in coal-fired power plants, that is, coal-fired power plants, is under consideration. .

Generally, in a chimney / flue of a thermal power plant, it is known that acid dew point corrosion due to SOx, NOx, CO _{2 and the} like contained in exhaust gas and local corrosion such as pitting corrosion and crevice corrosion due to Cl ⁻ occur. Has been. Among them, in the new plant of single loop type with simplified desulfurization equipment,
Cl ^- is condensed concentrated in the condensation water, a higher Cl than conventional environments ^- is assumed to be a concentration of the use environment.

Therefore, the development of an alloy having excellent general corrosion resistance in an acidic environment due to the acid dew point and excellent corrosion resistance in a high-concentration Cl ^- environment is under study.

Conventionally, with the aim of maintenance-free operation under these environments, at present, Ni such as Hastelloy is used.
Base alloys are used in some plants.

However, since Hastelloy-based Ni-based alloys are very expensive, it is the current situation that they cannot be applied in large quantities to an actual plant without significant cost reduction. Also, it is known that cheaper high alloy steel such as stainless steel can be used, but this alone does not significantly reduce the cost.

As a solution to this problem, there is a method in which the applied material is clad, and this has the potential for use in an actual plant for the first time. By this method, the laminated material has a function as corrosion resistance, and the base material has the required mechanical properties, so that it is possible to achieve high functionality and a significant cost reduction.

However, in the case of clad steel, deterioration of corrosion resistance caused by welding is a serious problem. That is, in the vicinity of the welded portion of the laminated material due to the influence of welding heat, Cr-Mo
Corrosion resistance deteriorates due to precipitation of intermetallic compounds and carbides of the system. This tendency becomes a particularly serious problem in the clad steel because the solution treatment is not performed from the viewpoint of the strength and toughness of the base metal, and C contained in the carbon steel of the base metal diffuses into the composite due to the thermal effect. . That is, in considering the possibility of applying the clad steel in the above plant, it is very important to take into consideration the deterioration of the corrosion resistance of the heat affected zone.

Regarding the corrosion resistance of the weld portion of the high alloy clad steel plate, No. 120 (1988), 1
Page 5, Japan Steel Pipe Technical Report, No. 127 (1989), 12
On page 7, it is reported for type 310 and high Ni alloy clad steel. It is disclosed in these documents that the deterioration of the corrosion resistance of the weld heat affected zone can be suppressed by lowering the C content of the composite material and adding Ti, Nb, or the like. Hereinafter, these techniques will be referred to as conventional technique 1.

Further, in order to evaluate the corrosion resistance in the above environment, various new alloys have been developed by an immersion test in an aqueous solution environment simulating condensed water in a chimney.

Japanese Unexamined Patent Publication No. 02-170946 discloses an alloy excellent in general corrosion resistance and crevice corrosion resistance in the environment of a flue and a desulfurization apparatus, and in Japanese Unexamined Patent Publication No. 10-237601, a neutral resistance. Chloride-corrosive austenitic stainless steels (hereinafter referred to as Prior Art 2) are disclosed.

[0012]

However, the above-mentioned prior art 1 is for investigating the presence or absence of deterioration in corrosion resistance in a corrosion test specified by JIS, and it is strongly acidic environment such as a plant to which the present invention is applied. In addition, the corrosion resistance including the welded part was not examined under the high-concentration Cl ^- concentration environment.

On the other hand, the prior art 2 does not take into consideration the deterioration of the corrosion resistance of the heat-affected zone of the weld, and cannot be expected to have sufficient performance when used as a structure including the weld. In addition, the target environment is Cl ⁻ compared to the present invention.
Mild, such as low concentration and neutrality. Furthermore, since the alloys are designed so as not to be clad, it is impossible to use these alloys as a cladding material for clad steel plates.

Therefore, an object of the present invention is to use in a single-loop type coal-fired thermal power plant, and a low-cost chimney inner cylinder clad steel excellent in corrosion resistance of a welded part, and a high-performance constructed by this clad steel. To provide a chimney.

[0015]

In order to solve the above-mentioned problems, the present inventors prepared an alloy composed of Ni, Cr, Mo, Cu, N, etc., and used this alloy to obtain the cladding heat history. After the simulated rolling, the sample steel that had been cooled at 200 to 20 ° C./min was prepared, and after the V-shaped groove was processed on the sample steel thus prepared, the diameter was 1.2 mm in accordance with JIS Z3334. Welding was performed using a welding material equivalent to that of the 625 series alloy, and the created welds were subjected to an immersion test in a sulfuric acid solution in the presence of a high concentration of Cl ⁻ to examine the effects of each component on the corrosion resistance of the welds. It was

As a corrosion test solution simulating an actual environment, 50%
H₂S0_Four+ 20,000ppmCl ^-Adjust the solution to 8
A general corrosion test was conducted by immersion at 0 ° C for 24 hours,
The multiple regression analysis was performed on the relationship with the components.

As a result, the corrosion resistance index Isc (= Ni-0.6Cr + 1.5Mo + 7.5C) determined by the alloy composition
u + 122N) was established, and it became clear that the corrosion resistance of the welded portion was significantly improved until Isc = 45, and the effect of the corrosion resistance of the welded portion was saturated when Isc ≧ 45. FIG. 1 shows the relationship between the corrosion rate and Isc.

On the other hand, in order to evaluate the local corrosion resistance, a flat plate test piece of a welded portion to which an artificial clearance jig made of vinyl chloride is attached is used to perform a dipping test in the above corrosion test solution to perform the crevice corrosion resistance. Was evaluated. As a result, it was revealed that those having a corrosion resistance index Isc of 45 or more exhibit good crevice corrosion resistance, as in the result of the general corrosion resistance test.

When clad steel is used as a bonding material, sensitization during the cooling process after rolling and sensitization by the weld heat affected zone may occur, but the corrosion resistance index Isc is 45.
As described above, it has been found that the weld exhibits good intergranular corrosion resistance if the alloy component is within the range of the present invention.

As described above, the inventors of the present invention, including the heat-affected zone of welding, have general corrosion resistance and high Cl in a sulfuric acid environment.
^- After intensive investigations alloy showing good results on both the local corrosion resistance under concentration environment.

As a result, the components such as Ni, Cr, Mo, Cu and N are adjusted and lsc (= Ni-0.6Cr + 1.5).
It has been clarified that it is effective to set the corrosion resistance index represented by (Mo + 7.5Cu + 122N) to 45 or more.

The present invention was made on the basis of the above findings, and its features are as follows.

In the invention according to claim 1, the composite material is C:
0.02% or less, Cr: 23-27%, Ni: 21-2
7%, N: 0.1 to 0.3%, Cu: 1 to 2%, and at least one of Mo and W is Mo.
+ 1/2 × W: contained within the range of 3.5 to 5.0% (above, weight%), balance: substantially consisting of Fe, and the following formula (1), An alloy which satisfies, the base material is made of carbon steel, the solution
It is characterized by being used as it is rolled without chemical heat treatment .

In the invention according to claim 2, the composite material is C:
0.02% or less, Cr: 23-27%, Ni: 21-2
7%, N: 0.1 to 0.3%, Cu: 1 to 2%, and at least one of Mo and W is Mo.
+ 1/2 × W: contained in the range of 3.5 to 5.0%, further B: 0.01% or less, Zr: 0.5% or less (or more,
%), The balance: consisting essentially of Fe, and the following formula (1): An alloy which satisfies, the base material is made of carbon steel, the solution
It is characterized by being used as it is rolled without chemical heat treatment .

In the invention according to claim 3, the composite material is C
a: 0.02% or less, Al: 0.1% or less, La: 0.
It is characterized by containing at least one of 04% or less, Ce: 0.04% or less, and Y: 0.1% or less (or more, by weight).

In the invention according to claim 4, the composite material is T
i: 0.5% or less, Nb: 0.8% or less, Ta: 1.6
% Or less and V: 1.0% or less (or more, weight%) at least one kind is contained.

According to a fifth aspect of the present invention, the composite material is C
a: 0.02% or less, Al: 0.1% or less, La: 0.
04% or less, Ce: 0.04% or less, Y: 0.1% or less, at least one kind is contained, and Ti: 0.5%
Below, Nb: 0.8% or less, Ta: 1.6% or less, V:
It is characterized by containing at least one of 1.0% or less (or more, by weight).

The invention according to claim 6 is characterized in that it comprises any one of the clad steels according to claims 1 to 5 for the inner cylinder.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the components of the alloy in the present invention will be described below.

C (carbon): C forms a carbide by combining with Cr or the like due to the effect of cooling after clad rolling and the effect of heat of welding, and deteriorates corrosion resistance, particularly intergranular corrosion resistance, so the content thereof is C. Is as small as possible, and if it is 0.02% or less, deterioration of corrosion resistance is small. Therefore, the amount of C added is limited to 0.02% or less.

Cr (Chromium): Cr is a basic component of stainless steel, and is generally an element that improves the pitting corrosion resistance and crevice corrosion resistance of steel, but if it is added in an amount of less than 23%, its effect is not obtained. It is sufficient, and addition of at least 23% or more is necessary.
On the other hand, if added in excess of 27%, excessive segregation that occurs in the weld heat affected zone cannot be suppressed, and the intergranular corrosion resistance decreases. Therefore, the Cr addition amount is limited to the range of 23 to 27%.

Ni (nickel): Ni is an element effective in improving general corrosion resistance in a coexisting environment of sulfuric acid and high concentration Cl ⁻ and is a strong austenite phase stabilizing element. In order to ensure good corrosion resistance in the environment of the present invention, addition of 21% or more is essential. On the other hand, if added in excess of 27%, austenite becomes excessively stable due to the relationship with the above-mentioned amounts of Cr, Mo, N, etc. added, which adversely affects the hot crack resistance. Therefore, the amount of Ni added is 2
It is limited to within the range of 1 to 27%.

N (nitrogen): N is an element effective in improving the pitting corrosion resistance and crevice corrosion resistance of steel, and it is necessary to add 0.1% or more. However, if added in excess of 0.3%, blowholes are likely to occur during welding and the weldability is impaired. Therefore, the N addition amount is limited to the range of 0.1 to 0.3%.

Cu (copper): Cu is sulfuric acid, high concentration Cl ⁻
An element effective in improving general corrosion resistance in coexisting environments.
%, It is necessary to add more than 2%, but if it exceeds 2%, the effect is saturated and the hot cracking susceptibility is increased. Therefore, the Cu addition amount is limited to within the range of 1 to 2%.

Mo (molybdenum), W (tungsten): Mo and W are both effective elements for improving the pitting corrosion resistance and crevice corrosion resistance of steel. Mo + 1/2 × W is 3.5%
Sueman is not effective enough. On the other hand, Mo + 1/2 × W
When it exceeds 5.0%, sensitization in cooling after clad rolling is promoted, and excessive segregation in the weld heat affected zone and formation of an intermetallic compound phase with Fe, Cr, etc. can be suppressed. It disappears and the intergranular corrosion resistance decreases. Therefore, the addition amount of Mo + 1/2 × W is 3.5 to 5.0.
Limited to within the range of%. The effects of Mo and W on the corrosion resistance are the same whether they are added individually or in combination.

Ni-0.6Cr + 1.5Mo + 7.5C
u + 122N ≧ 45: As described above, this parameter is the corrosion resistance index Isc indicating the corrosion resistance. If Isc ≧ 45 is satisfied, the corrosion resistance of the welded portion, the crevice corrosion resistance and the intergranular corrosion resistance of the welded portion are satisfied. improves. Therefore, the corrosion resistance index Isc is limited to 45 or more.

B (boron), Zr (zirconium):
B and Zr have the effect of delaying the grain boundary precipitation of precipitates during cooling after hot rolling in the process of manufacturing the alloy, and in order to exert an effect of improving the intergranular corrosion resistance, if a small amount is added, good. However, when B is added in an amount of more than 0.01% and Zr is added in an amount of more than 0.5%, a compound having a low melting point is likely to be generated in the grain boundary,
Weld hot cracking is likely to occur. Therefore, the amount of B added is
The amount of added Zr is limited to 0.01% or less and 0.5% or less.

Ca (calcium), Al (aluminum), La (lanthanum), Ce (cerium), Y (yttrium): Ca, Al, La, Ce, and Y are all sulfides and oxides in steel. Since it is produced and has the effect of improving hot workability by the action of desulfurization and deoxidation, it can be optionally added. However, Ca is 0.02%, Al
Is 0. 1%, La is 0.04%, Ce is 0.04
%, Y is 0. Additions exceeding 1% each adversely affect the hot susceptibility to welding. Therefore, the Ca content is 0.02% or less, and the Al content is 0. l% or less, L
a content is 0.04% or less, Ce content is 0.04%
%, And the Y content is 0. Limit to 1% or less.

Ti (titanium), Nb (niobium), Ta
(Tantalum), V (vanadium): Ti, Nb, Ta,
V is a strong carbide-forming element, has a function of fixing carbon in steel as a stable carbide, and has a function of preventing deterioration of corrosion resistance due to precipitation of chromium carbide, and thus can be arbitrarily added. However, Ti is 0.5%, N
If b is added in an amount of 0.8%, Ta is added in an amount of 1.6%, and V is added in an amount of more than 1.0%, adversely affect the weld hot cracking susceptibility. Therefore, the Ti content is 0.5%
Hereinafter, the Nb content is 0.8% or less, and the Ta content is
The V content is limited to 1.6% or less and 1.0% or less.

[0040]

EXAMPLES Next, the present invention will be further described with reference to examples.

Steel N of the present invention having the chemical composition shown in Table 1.
o. Comparative steel N having 1 to 13 and the chemical composition shown in Table 2
o. 14-31 were prepared.

[0042]

[Table 1]

[0043]

[Table 2]

Next, each steel was vacuum-melted in an experimental furnace, the thus obtained steel ingot was heated to 1150 ° C., and slab rolling and finish rolling were performed to prepare a steel sheet having a thickness of 6 mm.
Then, the steel plate thus prepared was combined with a base material of a low carbon steel plate having a thickness of 60 mm to obtain 60 + 6 mm.
Assembled into a slab. Then 1250 on this slab
After heating at ℃, hot finish rolling at 900 ℃, after rolling,
It was cooled at a cooling rate of 60 ° C./min to prepare a 20 + 2 mm clad steel sheet test material.

Next, the test material thus prepared was
Groove width 40 mm, open one side 45 degrees (total 90 degrees) V
The groove of the mold is processed and conforms to JIS Z3334.
Using welding material equivalent to 625 series alloy with a diameter of 1.2 mm 1
By 00% C0 ₂ were carbon dioxide gas welding. The welding conditions at this time were a current of 160 A, a voltage of 25 V, and a welding speed of 30.
cm / min, 1 pass.

Then, a test piece having a dimension of thickness 1.5 mm × width 80 mm × length 20 mm including the welded metal and the heat-affected zone by half was sampled from the surface layer with the extra layer removed, and the following test was conducted. Was done.

The corrosion test of the simulated real environment is 50% H ₂ SO ₄
+20,000 ppm Cl ^- solution, 24 at 80 ° C
A general corrosion test was carried out by immersion for a time, and the corrosion rate at that time was measured.

For the local corrosion resistance test, a long-term immersion test under conditions close to the actual environment was carried out using a flat plate test piece of a welded part to which an artificial clearance jig made of vinyl chloride was attached. That is, C
_{^{l -: 20,000ppm, S0 4 2-}} : 800ppm, C
a ²⁺ : 8,400ppm, Mg ²⁺ : 1,800ppm, pH5, temperature adjusted to 80 ℃ in an aqueous solution of 3,000
It was immersed for 0 hour and evaluated for the presence of crevice corrosion.

Further, as an intergranular corrosion test for judging the influence of the clad rolling and welding heat on the stability of the phase, the presence or absence of precipitates and the corrosion resistance, a ferric sulfate test according to JIS G0572, that is, A striker test was conducted.

Further, the resistance to welding hot cracking was evaluated by the Balestrain test. The test is non-filler TI
While simulating welding with a heat input of 18 KJ / cm with G, a bending strain of 1.0% was applied to the test piece, and the total crack length was measured after cooling.

The results of these tests are shown in Tables 3 and 4.

[0052]

[Table 3]

[0053]

[Table 4]

In Table 3, No. Nos. 1 to 13 of the invention steel Nos. 1 to 13 of the present invention, in Table 4, No. 14 to 31 are comparative steel Nos. 14 shows comparative test pieces according to 14-31.

As is apparent from Table 3, the test piece N of the present invention is
o. In all of Examples 1 to 13, the corrosion rate in the general corrosion test was 7 g / m ² · h or less, and good corrosion resistance was exhibited. No crevice corrosion has occurred. In the intergranular corrosion test by the striker test, the corrosion rate was 1 g / m ² · h or less, and it was confirmed to have a sound structure. Furthermore,
There was no problem with the welding hot crack resistance in the vale train test.

On the other hand, as is clear from Table 4, the comparative test piece No. No. 31 does not satisfy the corrosion resistance index Isc ≧ 45, and the corrosion resistance of the welded portion in a high Cl ⁻ concentration environment is poor,
7 g / m ² . It shows a large corrosion rate exceeding h.

Comparative test piece No. In each of Nos. 15 and 21, Isc is 45 or more within the range of the present invention, but the comparative test piece No. No. 15 has a low Ni content outside the range of the present invention,
Comparative test piece No. In No. 21, the Cu content is low outside the range of the present invention. For this reason, the comparative test piece No. 15 and 21 are
In both cases, the corrosion rate in the general corrosion test was 7 g / m ² . h, and the corrosion resistance is insufficient.

Comparative test piece No. 17 and 19 both have Isc within the scope of the present invention, but the comparative test piece No.
No. 17 had a Cr content outside the range of the present invention and was small. No. 19 has a small N content outside the range of the present invention. Therefore, the crevice corrosion resistance is insufficient.

Comparative test piece No. Isc of 23 and 25 is within the scope of the present invention, but Mo + 1/2 × W
Since the amount is out of the range of the present invention, the crevice corrosion resistance is insufficient.

Comparative test piece No. In No. 14, Isc is within the range of the present invention, but the amount of C is out of the range of the present invention and is excessive, and carbide precipitation at grain boundaries causes poor intergranular corrosion resistance.

Comparative test piece No. For No. 18, Isc was within the range of the present invention, but the amount of Cr was outside the range of the present invention and was excessive. 24 and 26 are both I
Although sc is within the range of the present invention, the amount of Mo + 1/2 × W is out of the range of the present invention and is excessive, and the intergranular compound precipitation deteriorates the intergranular corrosion resistance.

Comparative test piece No. Isc of 16, 20, and 22 is within the scope of the present invention, but the comparative test piece N
o. In No. 16, the amount of Ni is outside the range of the present invention and is excessive,
The amount of N in the comparative test piece 20 is out of the range of the present invention and is excessive, and the amount of Cu in the comparative test piece 22 is outside the range of the present invention and is excessive. For this reason, both deteriorate the susceptibility to hot cracking.

Comparative test piece No. 27, 28, 29, 30
Is Isc within the scope of the present invention, but the comparative test piece No. No. 27 is the B amount and the comparative test piece No. 28 is Zr
Amount, comparative test piece No. 29 is Ca amount, comparative test piece N
o. In No. 30, the Ti content is out of the range of the present invention and is excessive, so that all of them have insufficient resistance to hot cracking.

Although not shown in the table, Al, L
It was also confirmed that the hot crack resistance was insufficient when a, Ce, Y, Nb, Ta, and V were excessive.

[0065]

As described above, according to the present invention, it is possible to provide a clad steel having excellent corrosion resistance of the welded portion under the environment of a coal-fired power plant chimney and a high-performance chimney to which the same is applied. In addition, industrially useful effects are brought about by reducing plant maintenance costs.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a corrosion resistance index Isc and a corrosion rate in an actual test environment simulated solution test.

Front page continuation (72) Inventor Tetsuo Sakiyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. (72) Inventor Ryuji Hirai 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. (72) Inventor Katsuyuki Hirao 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd.Hiroshima Works (72) Inventor Katsuri Hajima 4-22 Kannon Shinmachi, Nishi-ku, Hiroshima Prefecture Mitsubishi Heavy Industries Within Hiroshima Works (72) Inventor Yoshikazu Yamada 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Inside Hiroshima Laboratory (56) Reference JP-A-2-170946 (JP, A) HEI 10-237601 (JP, A) JP-A-9-104953 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (6)

(57) [Claims] 1. A composite material comprising C: 0.02% or less, Cr: 23 to 27%, Ni: 21 to 27%, N: 0.1 to 0.3%, Cu: 1 to 2%. In addition, at least one of Mo and W is contained within the range of Mo + 1/2 × W: 3.5 to 5.0% (above, weight%), and the balance: substantially from Fe. And the following formula (1), An alloy satisfying a base material, characterized in that it consists of carbon steel, is used as it rolled without solution heat treatment
Clad steel for coal-fired power plant chimney inner cylinders with excellent corrosion resistance at the welded part. 2. The composite material comprises C: 0.02% or less, Cr: 23 to 27%, Ni: 21 to 27%, N: 0.1 to 0.3%, Cu: 1 to 2%. In addition, at least one of Mo and W is contained within the range of Mo + 1/2 × W: 3.5 to 5.0%, and further B: 0.01% or less, Zr: 0. 0.5% or less (or more, by weight) at least one kind is contained, and the balance: substantially consisting of Fe, and the following formula (1): An alloy satisfying a base material, characterized in that it consists of carbon steel, is used as it rolled without solution heat treatment
Clad steel for coal-fired power plant chimney inner cylinders with excellent corrosion resistance at the welded part. 3. The composite material comprises: Ca: 0.02% or less, Al: 0.1% or less, La: 0.04% or less, Ce: 0.04% or less, Y: 0.1% or less ( At least one of the above (% by weight) is contained, and the clad steel for a coal-fired power plant chimney inner cylinder having excellent corrosion resistance of a welded portion according to claim 1 or 2. 4. The composite material, of Ti: 0.5% or less, Nb: 0.8% or less, Ta: 1.6% or less, V: 1.0% or less (above, weight%) The clad steel for a coal-fired power plant chimney inner cylinder having excellent corrosion resistance of a welded portion according to claim 1 or 2, containing at least one kind. 5. The composite material comprises: Ca: 0.02% or less, Al: 0.1% or less, La: 0.04% or less, Ce: 0.04% or less, Y: 0.1% or less. At least one of the above is included and Ti: 0.5% or less, Nb: 0.8% or less, Ta: 1.6% or less, V: 1.0% or less (or more, weight%) Clad steel for a coal-fired power plant chimney inner cylinder having excellent corrosion resistance of the welded portion according to claim 1 or 2, containing at least one of the above. 6. A coal-fired thermal power plant excellent in corrosion resistance of a welded portion, characterized in that any one of the clad steels according to claims 1 to 5 is used for an inner cylinder. chimney.