JP3332771B2 - Corrosion and heat resistant Ni-base casting alloy for waste incinerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to castability, weldability, and high temperature that exhibit excellent high-temperature corrosion resistance in an atmosphere in which dust such as waste gas from a refuse incineration boiler contains chlorides, sulfates, oxides, and the like. The present invention relates to a corrosion-resistant and heat-resistant Ni-based cast alloy for a refuse incinerator having good strength characteristics and good structural stability during long-term use at high temperatures.

[0002]

2. Description of the Related Art Municipal waste, industrial waste, and the like contain a wide variety of substances.
1, Na that generates and simultaneously contains SO ₂ ,
Alkaline or alkaline earth metals such as K and Ca or P
Reacts with heavy metals such as b and Zn to generate dust containing a mixed salt of chloride and sulfate having a low melting point. In the presence of such corrosive gas and attached dust, conventional low alloy steels, stainless steels, Ni-based alloys, and Co-based alloys exhibit large corrosion rates. Above all, boilers for recovering waste heat from the above-mentioned combustion furnaces and generating power are highly corroded and damaged by boiler pipes and accessories, and the boilers are highly efficient in terms of energy saving, resource saving and environmental protection. There is a demand for a high-temperature corrosion-resistant material for boilers, which exhibits excellent corrosion resistance against erosion.

For example, an existing alloy, Alloy 625 (2
1Cr-9Mo-4Fe-4Nb-0.2Ti-0.2
Al-Ni bal.), Alloy 825 (21Cr-3)
Mo-42Ni-2Cu-1Ti-Fe bal.) Is known to exhibit relatively good corrosion resistance in such an environment, but contains a large amount of Al, Ti, and Nb, and thus Ni ₃ Nb Because intermetallic compounds such as are precipitated,
Although high-temperature strength is high, when used in castings and the like, corrosion resistance is reduced and castability is inferior. In addition, when used at a high temperature of 500 ° C. or more for a long time, precipitation of an intermetallic compound occurs, which tends to cause embrittlement. Further, the inclusion of a high concentration of Mo also causes inhomogeneity such as segregation and an increase in cost. Alloy 825 is lower in cost than Alloy 625, but at high temperatures of 500 ° C. or higher, the corrosion resistance deteriorates, so that the working temperature is limited.

Further, as an alloy exhibiting good castability, plastic workability, and structural stability under the above-mentioned environment, A
Cr-N excluding Al, Ti and Nb from LLoy 625
i-Fe-Mo alloys have been proposed (for example, Sanicro 65 from Sandvik, International Patent Application No. PCT / SE95 / 00).
561). However, from Alloy 625, Al, Ti, N
With the exception of b and the like and the addition of Fe and Mo, the alloys need to be improved in their properties because their strength characteristics and corrosion resistance deteriorate.

[0005]

SUMMARY OF THE INVENTION In view of the circumstances of the prior art, the present invention provides excellent high-temperature corrosion resistance in an atmosphere where dust containing chlorides, sulfates, oxides and the like such as exhaust gas from a refuse incineration boiler exists. Refuse incineration with good castability, weldability, high-temperature strength characteristics, and structural stability during long-term use at high temperatures
An object of the present invention is to provide a corrosion-resistant and heat-resistant Ni-based casting alloy for a device .

[0006]

According to the present invention, (1) C: 0.01 to 0.3%, Si: 0.5% or less, P:
0.03% or less, S: 0.03% or less, Cr: 24 to 3
0%, Fe: 1 to 8%, Mn: 0.1 to 2%, Ti:
A garbage grill containing 0.05 to 0.6% and Mo: 3 to 10%, with the balance being Ni and unavoidable impurities.
And heat-resistant Ni-base cast alloy for rejecting equipment and (2) the above (1)
And one or more elements selected from the group consisting of N, W, rare earth metals, alkaline earth metals, B, Nb and Ta, in addition to the components of : 0.
5-4%, rare earth metal: 0.1% or less, alkaline earth metal: 0.01% or less, B: 0.001-0.01%, N
b and / or Ta: a corrosion-resistant and heat-resistant Ni-base casting alloy for a refuse incinerator characterized by containing 0.5% or less.

[0007] Cast corrosion resistant Ni base for incineration device of the present invention
In order to solve the above-mentioned problems of the prior art, the alloy forming alloy was found as a result of intensive research to develop a casting material having excellent high-temperature corrosion resistance that can be used under high-temperature corrosive conditions such as a waste combustion environment. Things. The alloy of the present invention has an increased Cr and a small amount of Ti added compared to the above-mentioned conventional alloy, has excellent corrosion resistance not found in conventional Ni-based alloys, and its components and compositions are the same as those of conventional materials. In comparison, it has the following features.

[0008] High-temperature corrosion occurring in an environment in which a combustion gas containing Cl or S and molten dust adhere is a complex corrosion in which a plurality of reactions occur simultaneously. The reactions include a chloride reaction by HCl, Cl ₂ or chloride, SOx, There are sulfurization reaction by H ₂ S or sulfate, oxidation reaction by O ₂ , H ₂ O, etc. and dissolution reaction to molten salt. Under the condition where these occur simultaneously, corrosion is optimized by optimizing the amounts of Cr, Mo, Fe and Ni. It is necessary to suppress the reaction.

Austenitic stainless steel or Cr-N
Cr is Cr in the i-Fe-Mo alloy. _TwoO_ThreeSuch as oxide
Or protective film forming elements that form these composite oxides
Is effective for oxidation and sulfidation.
And usually contains Cr: 15% by weight or more.
On the other hand, Ni and Mo are effective for chloride
Usually 14% by weight or more of Ni is added to form a tenite structure.
Mo is effective when added at about 4% by weight or more.
(For example, Japanese Patent Application No. 8-86585). Cr and Fe are additive amounts
Although it may be harmful in some cases,
The quantity has not yet been fully elucidated.

The present inventors have conducted intensive studies on the range of components that do not contain Al, which is harmful to the structure stability under the complex corrosion reaction, minimize Nb, and provide the best corrosion resistance.
A new component composition mainly composed of r, Ni, Fe, and Mo was found. Unprecedented high corrosion resistance is these 4
Exhibited by the combined effect of elements
Cr not present in i-base alloy: 24 to 30% by weight, Mo: 3-1
It is essential to add a small amount of Fe (1 to 8% by weight) in addition to the addition of 0% by weight.

When Si is added in a large amount, an intermetallic compound such as Ni ₃ Si precipitates to cause structural instability at high temperatures,
Problems such as embrittlement, difficult plastic working, and reduced weldability are likely to occur. In order to solve such problems, it is necessary to appropriately set the compounding ratio of Si. In the alloy of the present invention, the amount of Si is regulated to 0.5% by weight or less.

Nb and / or Ta are effective elements for corrosion resistance to Cl. However, Nb and / or Ta are regulated to 0.5% by weight or less in order to enhance high-temperature structural stability and prevent embrittlement, and to limit Cr to 24% or less.
By adding 30% by weight, the corrosion resistance could be improved. Further, Mo is harmful to the stability of the austenitic structure. In addition, under the condition of a large amount of S, Mo not only deteriorates the corrosion resistance but also increases the cost.
3 to 10% by weight less than or equal to loy625
Was added. Further, Ti was added in an amount of 0.05 to 0.6% by weight in order to refine the casting crystal grains and improve the strength.
Since P and S are harmful to weldability and corrosion resistance, 0.00
It was restricted to 3% by weight or less.

In order to improve the high temperature tensile properties and the creep properties of the alloy of the present invention, a small amount of C and Ti was added to enhance precipitation strengthening and solid solution strengthening by carbide. Similar effects are N, B, W
And the like can be achieved by adding a small amount thereof. Further, the addition of trace amounts of Mn, rare earth metals (La, Ce, Y, Hf, etc.) and alkaline earth metals (Ca, Mg, etc.) contributes to cleaning of the alloy, and has an effect of improving weldability and castability. In particular, rare earth metals are considered to be effective for corrosion resistance against oxidation reactions and the like.

[0014] The cast alloy of the present invention exhibits sufficient performance in the as-cast or welded state.
By performing at 000 to 1200 ° C., the performance can be further improved. Forging and hot working are 100
Optimally, it is performed in the range of 0 to 1200 ° C.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The alloy of the present invention is excellent in the presence of Cl and S due to the combined effect of adding Ni, Cr, Mo, and Fe as its main constituent elements and a small amount of Mn, C, and Ti. Demonstrates high-temperature corrosion resistance, prevents precipitation of a large amount of intermetallic compounds during long-term use at high temperatures, stabilizes the metallographic structure, improves castability and weldability, and improves manufacturability of casting, weld overlay, etc. Demonstrates excellent performance as a high-temperature corrosion-resistant material. The effect of each element and the reason for limiting the alloy element composition will be described below in addition to the above.

(1) C: If the content of C is increased, it promotes grain boundary precipitation of chromium carbide and so on, deteriorating corrosion resistance and promoting embrittlement. Therefore, the upper limit is 0.3% by weight.
And On the other hand, the addition of a small amount is effective for improving the high temperature strength and the creep resistance, and the lower limit is set to 0.01% by weight. A preferable range is 0.015 to 0.08% by weight.

(2) Si: Si is high Cr, high Mo Ni
Since the base alloy causes segregation and is harmful to weldability and structural stability, and addition of a small amount does not lead to improvement in corrosion resistance, the alloy of the present invention is restricted to 0.5% by weight or less, preferably 0.1% by weight or less. did.

(3) P and S: P and S contained as impurities not only deteriorate corrosion resistance, but also reduce hot workability.
A smaller amount is preferable in order to deteriorate workability such as weldability, and the upper limit is set to 0.03% by weight.

(4) Cr, Fe: These elements are each
Re Cr_TwoO_Three, Fe_ThreeO_Four(Fe_TwoO _Three) As burning gas
Is an element that forms a dense oxide film in
r is SOx or H_TwoHigh temperature corrosion ring by S or sulfate
It is known as an effective corrosion resistance imparting element in the environment. Departure
In the bright alloy, Cr and Fe are each 24 to 30% by weight (preferably
Preferably 24-28% by weight), 1-8% by weight (preferably
3-6% by weight). Corrosion resistance improves with more Cr
But the upper limit is 30 times because the tissue stability deteriorates.
%. On the other hand, when Fe is too much, corrosion resistance is deteriorated.
Therefore, the upper limit was set to 8% by weight.

(5) Mn: Mn has an effect of improving corrosion resistance, workability, and weldability by adding a small amount of Mn, in addition to eliminating harm caused by impurities due to a de-S effect, etc. 0.1 to 2% by weight, preferably 0.5 to
A small amount of 1.5% by weight was added.

(6) Ti: Ti is generally used as an oxygen scavenger, but if it is added in a large amount, an intermetallic compound is formed and the stability of the structure and the plastic workability are deteriorated.
6% by weight. The preferred range is 0.1 to 0.3.
% By weight.

(7) Mo: Mo is an element that contributes to the improvement of corrosion resistance and strength together with the addition of Cr. However, when added in a large amount, the high-temperature structure stability is deteriorated, so the upper limit was set to 10% by weight. On the other hand, to improve properties such as weldability and corrosion resistance, it is necessary to add 3% by weight or more. A preferred range is 4 to 8% by weight.

(8) Ni: Ni is an element necessary for obtaining an austenite single phase structure, is a base metal of the present alloy, and is an element indispensable for improving corrosion resistance to Cl.

Further , the corrosion-resistant heat-resistant N for the incinerator of the present invention is used.
The i-base cast alloy contains the above-mentioned elements as basic constituent components. The properties of the above-mentioned basic composition alloys can be improved by adding a small amount or a small amount of the following elements according to the purpose.

(9) N: N is effective for improving high-temperature strength by precipitation of nitride or solid solution strengthening. In addition, it is effective in preventing intergranular corrosion.
It is added in the range of 0.05 to 0.5% by weight to promote aging.

(10) W: W is an element having the same effect as Mo. However, since addition of a large amount is harmful to machinability, it is preferable to add a small amount of 0.5 to 4% by weight.

(11) Rare earth metals: La, Ce, Y, H
rare earth elements such as f improve the adhesion of the oxide film,
It is effective for improving sulfuration resistance and oxidation resistance, and is also effective for cleaning materials. Therefore, it can be added in a range of 0.1% by weight or less that does not significantly change mechanical properties.

(12) Alkaline earth metals: Alkaline earth metals such as Ca and Mg are used to strengthen the crystal grain boundaries of the Ni-based alloy and to improve the creep resistance.
A trace amount of not more than 01% by weight can be added.

(13) B: The addition of a small amount of B is effective for strengthening the crystal grain boundaries, but the addition of a large amount leads to embrittlement due to precipitation of intermetallic compounds and deterioration of workability. %. The preferred range is 0.001
0.005% by weight.

(14) Nb, Ta: Nb and Ta are effective elements for improving corrosion resistance and strength, but are liable to form carbides and nitrides, cause structural instability and embrittlement, and promote aging precipitation. In order to worsen the weldability, it is desirable that the amount is as small as possible, and the total is suppressed to 0.5% by weight or less, preferably 0.1% by weight or less.

The corrosion-resistant and heat-resistant Ni-based casting alloy for a refuse incinerator according to the present invention is an incinerator for burning non-uniform waste such as municipal waste, industrial waste and sludge, and a boiler, metal parts, grate and the like attached thereto. Can be suitably applied to members that require high-temperature corrosion resistance. In addition, it exhibits excellent weldability, corrosion resistance, heat resistance, and microstructure stability as a high-temperature corrosion-resistant material for fossil fuel combustion equipment, chemical plants, and general equipment placed in a similar high-temperature atmosphere containing Cl and S. Various forms of casting, welding materials or forgings, seamless pipes, and the like can be used as the corrosion-resistant and heat-resistant Ni-based cast alloy for refuse incinerators .
In addition, by producing powder, it can be used as thermal spray, overlay, powder molded product, and the like.

[0032]

[Example 1]

In order to evaluate the corrosion resistance of a corrosion-resistant heat-resistant Ni-based cast alloy for a refuse incinerator of the present invention in a refuse incinerator combustion gas environment,
A corrosion test was performed in a simulated laboratory environment. In the test, as shown in FIG. 1, ash (composition of Table 1) 2 filled in a magnetic crucible 1 was used.
After embedding the test piece 3 in a container and keeping the mixed gas having the composition shown in Table 1 at 550 ° C. or 650 ° C. in an airtight container at 600 ml / min for 100 hours, the corrosion loss is measured. Was. As a test piece, a raw material having a composition shown in Table 2 was used, and 20 kg of the raw material was subjected to vacuum melting to adjust the components and cast into a mold to produce an ingot. The alloy of the present invention had good castability, and no casting defects such as blowholes and shrinkage cavities were observed. From this ingot, a small test piece having a length of 14 mm, a width of 14 mm, and a thickness of 3 mm was processed and used. Table 3 shows the test results.

From the results shown in Table 3, the test materials E, F, G, H, I, J and K, which are the alloys of the present invention, have a Cl shown in Table 1 of 2.2.
It can be seen that, under the adhesion condition of the actual ash of 4% by weight, for example, the corrosion weight loss is smaller than that of the comparative alloy A (625 alloy), and that it has excellent corrosion resistance as compared with other comparative alloys.
In addition, the occurrence of local corrosion such as intergranular corrosion which is often observed in this kind of environment is hardly recognized. As shown in Table 3, the alloys H, I, and J of the present invention have improved corrosion resistance as compared with E, F, and G. As shown in Table 2, W, N, rare earth metals (REM: misch metal =
Ce + La), Mg and B are added in small amounts,
It can be seen that the effects of these small addition elements are demonstrated.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

Example 2 In order to investigate the structural stability of the alloy of the present invention during long-term use at high temperature and the tendency of precipitation of intermetallic compounds, a test piece having the composition shown in Table 2 was used at 600 ° C. and 700 ° C. A heating test was performed at 1000C for 1000 hours, and a change in hardness was examined. Note that the test was performed using a vertical 14
mm, 14 mm in width, and 3 mm in thickness. The test results are shown in Table 4. The alloys E, F, G, and
For H, I, J, and K, the change in hardness is small at 600 ° C. and 700 ° C. (about HV 177 or less), indicating that the tissue stability is excellent. On the other hand, in Comparative Alloy A, HV274
The above shows a large change in hardness due to precipitation of the intermetallic compound.

In particular, Nb, Al and Ti are important for the stability of the structure.
In the amount, the increase in hardness due to precipitation of the intermetallic compound is large. Comparative alloys B, C, and D have a small change in hardness, but as shown in Table 3, are inferior in corrosion resistance as compared with the alloys of the present invention, and have practical problems. The alloy of the present invention containing substantially no Al, keeping Nb to a minimum or less, and adding a small amount of Ti up to 0.6% by weight has little precipitation of such intermetallic compounds.

[0039]

[Table 4]

Example 3 A welding test was performed on representative test materials used in Example 2. As shown in Fig. 2, welding was performed on a 20-mm-thick plate-shaped test piece using the 625 filler or without the filler by the TIG method, and the welding defects and weld cracks on the surface and cross section were confirmed. went. The results are as shown in Table 5, and it was confirmed that the alloy of the present invention did not show any harmful defects in the weld bead and the HAZ, and had good weldability.

[0041]

[Table 5]

[0042]

The corrosion-resistant and heat-resistant Ni-base for the waste incinerator according to the present invention.
Cast alloys have excellent high-temperature corrosion resistance in high-temperature corrosive environments containing a large amount of Cl and S, such as in combustion gas from refuse incinerators, and have good castability, structural stability during long-term use at high temperatures, and weldability. It is an excellent corrosion and heat resistant Ni-base cast alloy. This corrosion-resistant and heat-resistant Ni-based casting alloy can be supplied inexpensively in any form such as a casting, weld overlay or powder.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a state of a corrosion test in Example 1.

FIG. 2 is an explanatory diagram showing a state of a welding test in Example 3.

Continuation of front page (72) Inventor Hirokazu Morii 12 Nishiki-cho, Naka-ku, Yokohama-shi, Kanagawa Prefecture Examiner, Mitsubishi Heavy Industries, Ltd. Yokohama Works Kengo Koyanagi (56) References JP-A-7-3369 (JP, A) JP-A-7-3368 (JP, A) JP-A-5-59475 (JP, A) JP-A-7-242971 (JP, A) JP-A-7-34166 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) C22C 19/05

Claims (2)

(57) [Claims] 1. C: 0.01 to 0.3% by weight, S
i: 0.5% or less, P: 0.03% or less, S: 0.03
%, Cr: 24 to 30%, Fe: 1 to 8%, Mn:
0.1 to 2%, Ti: 0.05 to 0.6%, Mo: 3 to
A corrosion-resistant and heat-resistant Ni-base casting alloy for a refuse incinerator , comprising 10% and the balance consisting of Ni and unavoidable impurities. 2. In addition to the components of claim 1, one or more elements selected from the group consisting of N, W, rare earth metals, alkaline earth metals, B, Nb, and Ta are added in an amount of N: 0. 05
0.5%, W: 0.5-4%, rare earth metal: 0.1%
Or less, alkaline earth metal: 0.01% or less, B: 0.0
A corrosion-resistant and heat-resistant Ni-base cast alloy for a refuse incinerator , characterized in that the alloy contains 0.1 to 0.01% and Nb and / or Ta: 0.5% or less.