WO1994010353A1

WO1994010353A1 - Boiler alloy excellent in molten-salt corrosion resistance

Info

Publication number: WO1994010353A1
Application number: PCT/JP1993/001604
Authority: WO
Inventors: Kozo Denpo; Tetsuo Ishitsuka; Koichi Nose; Hiroyuki Ogawa
Original assignee: Nippon Steel Corporation
Priority date: 1992-11-05
Filing date: 1993-11-05
Publication date: 1994-05-11
Also published as: EP0667399A1; CA2148695A1; EP0667399A4

Abstract

A boiler alloy excellent in molten-salt corrosion resistance and workability, which contains Al, Co, Ni, Cr, and at least one of Mo and W, and further, if necessary, either at least one of Hf and Zr or at least one of Y, La and Ce, or alternatively both of at least one of Hf and Zr and at least one of Y, La and Ce, the balance consisting of Fe and inevitable impurities, and which satisfies the following conditions: 0.5 Co + Ni + 1.5 Cr « 65, 0.4 « (Ni + Cr)/(Co + Mo + 0.5 W) « 1.2.

Description

Description Boiler-use alloys with excellent resistance to molten salt corrosion

The present invention relates to a steel pipe used in a coal-fired boiler, a boiler for a refuse incinerator and the like, and particularly to an alloy for a boiler that exhibits excellent resistance in a molten salt corrosion environment.

Background art

High-temperature energy devices, such as fuel-fired boilers, fluidized-bed reactors, and coal gasification and liquefaction devices, are attracting attention in terms of coal utilization technology and garbage resource utilization technology, reflecting the recent energy situation. For example, in the case of fuel-fired boilers, petroleum use was mainly used in the past, but today the need for alternative energy use and effective use of garbage resources has been recognized. Effective utilization has been increasing.

However, even with such high-temperature energy equipment, the equipment design is based on the design concept when using oil, and the problems when coal is used and garbage are incinerated have not been sufficiently solved. For example, coal-fired boilers are manufactured with the same material composition as conventional oil-fired boilers. However, unlike coal-fired boilers, coal-fired boilers are different from oil-fired boilers in that solid ash falls inside the boiler due to clin force or floats in the combustion gas stream as fly ash in a molten state. However, significant damage due to high-temperature molten salt is caused. Such problems are well recognized by those skilled in the art. The solution is not clear yet, and there are almost no material countermeasures. Empirical design measures, such as reducing the flow velocity, Taking Only measures such as mounting are being taken. Even if the flow rate is restricted, even if the flow rate is restricted, a drift part with a higher flow velocity than expected can be created, and the protector itself will be damaged quickly even if a protector is used. However, there are many cases where it has no practical effect.

From the viewpoint of materials, as the boiler tube, 18-8 type austenitic stainless steel such as SUS304 steel and 321, 347, 316 steel, etc., and further, Incoloy 80% Alloys such as 0 and SUS310 are used. In addition, various high-temperature austenitic stainless steels are used as general high-temperature components, but none of them consider molten salt corrosion resistance and have experience in oil-fired boilers. It is only used for

As already mentioned, there are currently few material measures to prevent molten salt corrosion.However, if there are material measures, conversely, there will be more room in equipment design, miniaturization of equipment and improvement of thermal efficiency. We can expect profit such as.

An object of the present invention is to provide a material having high resistance to molten salt corrosion and excellent workability as seen in coal-fired boilers and boilers for refuse incinerators. Disclosure of the invention

The gist of the present invention is as follows.

1. By weight%, C: 0.1? Ό 'or less, Si: 2.5% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.005% or less, A1: 0.0 1~ 0.0 3.%, C o: 2 5~ 5 5 0 ', C r: 7~ 1 8, N i: 1 containing 0~ 4 0%, Mo: 2~4 %', W: 8 % Or less, and the remainder has a composition consisting of Fe and unavoidable impurities, and

0.5 Co + N i + l.5 C r≤ 6 5 An alloy for boilers excellent in molten salt corrosion resistance, which satisfies the condition of 0.4≤ (Ni + Cr) / (Co + Mo + 0.5W) ≤1.2.

2. In% by weight, C: 0.1% or less, Si: 2.5% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.005% or less, A1: 0.01 to

0.03 ¾ \ Co: 25-55%, Cr: 7-18%, Ni: 10-40%, Mo: 2-4%, W: 8% or less 1 or 2 types And further contains one or two of Hf: 0.2% or less and Zr: 0.2% or less, and the balance is composed of Fe and unavoidable impurities.

0.5 Co + N i + l.5 C r≤65

An alloy for boilers with excellent resistance to molten salt corrosion, characterized by satisfying the following condition: 0.4≤ (Ni + Cr) / (Co + Mo + 0.5W) ≤1.2.

3. By weight%, C: 0.1% or less, Si: 2.5% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.005% or less, A1: 0.01 to

0.03%, C0: 25 to 55%, Cr: 7-1.8%, Ni: 10 to 40%, Mo: 2 to 4%, W: 8% or less 1 or 2 Contains one or more of Y: 0.1% or less, La: 0.1% or less, Ce: 0.1% or less, and consists of remaining force <Fe and unavoidable impurities Having a composition, and

0.5 Co + N i + l.5 C r≤65

An alloy for boilers with excellent resistance to molten salt corrosion, which satisfies the condition of 0.4≤ (Ni + Cr) / (Co + Mo + 0.5W) ≤1.2.

4. By weight%, C: 0.1% or less, Si: 2.5% or less, Mn: 1.0

% Or less, P: 0.03% or less, S: 0.005% or less, A1: 0.01 ~ ^{0.03 0 ό, C o: 25~} 55%, C r: 7~ 1 8, 0 0, N i: 1 containing 0~ 40%, Mo: 2 - 4%, W: 8% or less of one Or 2 types, Hf: 0.2% or less, Zr: 0.2 or less, 1 or 2 types and Y: 0.1% or less, La: 0.1% or less, Ce: 0.1% Contains one or more of the following, has a composition consisting of residual force <Fe and unavoidable impurities, and

0.5 Co + N i + l.5 C r≤65

An alloy for boilers that is excellent in molten salt corrosion resistance and satisfies the condition of 0.4≤ (Ni + Cr) / (Co + Mo + 0.5W) ≤1.2. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

First, the reasons for limiting the range of each component in the present invention as described above will be described.

If the content of C exceeds 0.1%, workability deteriorates and intergranular corrosion cracking is likely to occur, so the upper limit was set to 0.1%.

Si is a necessary component as a deoxidizing component, but if its content exceeds 2.5%, hot workability deteriorates, so the upper limit was set to 2.5%.

Like Mn, Mn becomes brittle when added with an excess of deoxidizing force, so its upper limit was set to 1.0% '.

P is an unavoidable impurity, but if its content exceeds 0.03%, grain boundary segregation becomes significant, so the upper limit was set to 0.03%.

S is an unavoidable impurity, but if its content exceeds 0.005%, the hot workability deteriorates remarkably and the production becomes impossible, so the upper limit was set to 0.005%. A 1 is the utility of course as a deoxidizer, it can be on the alloy surface to produce a A1 ₂ 0 _3, to reduce the damage caused by molten salt. But because the added pressure amount is not generated by A1 ₂ 0 ₃ coating on the alloy surface is less than 0.0 1%, it is necessary to set the lower limit and 0.0 1%. On the other hand, if added in excess of 0.03%, the additive properties deteriorate, so the upper limit was set to 0.03%.

Co, Ni, Cr, Mo and W improve the molten salt corrosion resistance and corrosion resistance, but their effects do not appear when only each element is added alone, but only when combined elements are used. . Thus, the present inventors assumed that the operating conditions of a real boiler would be, and conducted a study to obtain a material with excellent resistance to molten salt corrosion in an environment of 500 hot boilers.

(1) Co, Ni and Cr amounts

0.5 C o + N i + 1.5 C r≤ 65

and

(2) Ni, Cr, Co, Mo, W

When the condition of 0.7 ≤ (N i + C r) / (C o + Mo + 0.5 W) ≤ 1.2 is satisfied, the following addition amount demonstrates the most effective properties of alloying elements It became clear.

In addition, the results of a study in a high-temperature boiler environment of 600 ° C

(3) Co, Ni and Cr amounts are

0.5 Co + N i + l. 5 C r≤55

and

(4) Ni, Cr, Co, Mo, W

If the condition of 0.4 ≤ (N i + Cr) / (Co + Mo + 0.5W) ≤ 0.7 is satisfied, the following addition amount should exhibit the characteristics of the alloy element most effectively. Became clear.

C 0 coexists with Ni, Cr, Mo and W to improve molten salt corrosion resistance At 500 ° C, if the content is less than 25%, there is no significant effect, and to obtain the desired molten salt corrosion resistance, increase the amount of other alloying elements. Therefore, the lower limit is set at 25% because it is economically disadvantageous. On the other hand, if the content exceeds 55%, the effect of improving the molten salt corrosion resistance when used at 600 ° C decreases, so the upper limit was set to 55%.

Ni has the effect of improving the corrosion resistance, but if it is less than 10%, it has no effect.Because it is not economical to increase the amount of other alloying elements in order to obtain the desired corrosion resistance, its lower limit is set. Was determined to be 10%. On the other hand, even if it exceeds 40%, further improvement of the effect is not recognized, and the upper limit is set to 40% in consideration of economy.

An element that significantly improves corrosion resistance in the presence of C i ^ i N i, Mo, and W. No significant effect is obtained with less than 7% addition, while the effect is increased with addition of more than 18%. Since no further improvement was observed, the upper limit was set at 18%.

Mo improves the molten salt corrosion resistance together with C o, and particularly has an effect of improving the molten salt corrosion resistance due to an increase in hardness. However, if the content is less than 2%, the hardness is not sufficient. On the other hand, if the content exceeds 4%, the hardness is excessively increased and the workability deteriorates. Therefore, the addition range is set to 2 to 4%.

W also improves the molten salt corrosion resistance by increasing the hardness, similar to Mo, but adding more than 8% does not further improve the effect and also impairs the workability. 8%.

Since Hf improves the strength at high temperatures even with a small amount of addition, the upper limit was set to 0.2%.

Although Zr acts as a deoxidizing element, no further improvement in the effect is observed even if the added amount exceeds 0.2%, so the upper limit was set to 0.2%.

Y, La and Ce have the effect of further improving hot workability, If hot working is carried out under severe conditions, the effect of adding any element exceeding 0.1% will not be recognized even if added in excess of 0.1%. The contents were each 0.1% or less. The present inventors melted, manufactured, and hot-rolled an alloy having varied amounts of Co, Ni, and Cr to obtain a sheet having a thickness of 7 mm. After holding at 50 ° C for 30 minutes, heat-treating with water cooling, cut out a test piece of thickness 2mm, width 15mm and length 80mm from the plate at right angles to the rolling direction, and bend it. After the application, the test piece was held in a device heated to 500 ° C. and 600 ° C., and a mixed molten salt of NaC 1 —KC 1 was applied for 500 hours. Then, the test was performed, and the degree of apparent change before and after the test was observed. Scientific analysis of these results revealed that the aforementioned conditions existed among Co, Ni, and Cr. Example

1 ton of each of the alloys having the component compositions shown in Tables 1 to 6 was melted using a vacuum induction heating furnace, cleaned by ESR treatment, and fabricated into an ingot with a cross section of 50 Omm x 250 mm. Then, hot-rolled into a sheet having a thickness of 7 mm, and then kept at a temperature of 150 ° C. for 30 minutes, and then subjected to a water-cooling heat treatment. A test piece with a thickness of 2 mm, a width of 15 mm, and a length of 80 mm was cut out, and this test piece was folded back at the center in the length direction. The results are shown in Table 4 (continuation of Table 3) and Table 6 (continuation of Table 5). Then apply NaC 1 -KC 1 mixed salt, hold in a device heated at 500 ° C. and 600 ° C., test for 500 hours, and change appearance The results of the measurement of the degree were investigated.

From the results shown in Table 2, Table 4, and Table 6, the comparative alloy material is resistant to molten salt corrosion It is clear that the alloys 1 to 37 and 38-74 of the present invention have excellent molten salt corrosion resistance and workability and excellent properties, while their workability is not so good. It is.

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A = l / 2Co + Ni + 3 / 2Cr B = (Ni + Cr) / (Co + Mo + l / 2W)

Workability 〇: No cracks or wrinkles due to processing, △: Wrinkles generated, X: Cracks generated

〇: No dents on surface, dents on X surface Corrosive

Industrial applicability

According to the present invention, an alloy having excellent resistance to a molten salt corrosive environment and excellent additivity can be obtained, thereby contributing to the practical use and widespread use of high-temperature energy devices that have been attracting attention in recent years. Very large.

Claims

The scope of the claims

1. By weight%, C: 0.1% or less, Si: 2.5% or less, Mn: 1.0% or less, F: 0.03% or less, S: 0.005% or less, A1: 0.01 to 0.03%, Co : 25 to 55%, Cr: 7 to 18%, Ni: 10 to 40%, Mo: 2 to 4%, W: 8% or less. The remainder has a composition consisting of Fe and unavoidable impurities, and

0.5 Co + N i +1.5 C r≤65

2. By weight%, C: 0.1% or less, Si: 2.5% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.005% or less, A1: 0.01 to 0.03%, C o: 25 to 55%, Cr: 7 to 18%, Ni: 10 to 40%, Mo: 2 to 4%, W: 8% or less Hf: 0.2% or less, and Zr: 0.2% or less of the following, and the balance is composed of Fe and unavoidable impurities.

0.5 Co + N i + l.5 C r≤65

3. By weight%, C: 0.1% or less, Si: 2.5% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.005% or less, A1: 0.01 to 0.03%, Co : 25 to 55%, Cr: 7 to 18%, Ni: 10 to 40%, Mo: 2 to 4%, W: 8% or less. Further, Y: 0.1% or less, La: 0.1% or less, Ce: 0.1% or less Contains one or more of them, and the rest has a composition consisting of Fe and unavoidable impurities; and

0.5 Co + N i + l.5 C r≤65

4. In% by weight, C: 0.1% or less, Si: 2.5% or less, Mn: 1.0% or less, P: 0.03% or less, S: 0.005% or less, A1: 0.01 to 0.03% ', Co: 25 to 55%, Cr: 7 to 18%, Ni: 10 to 40%, Mo: 2 to 4%, W: 8% or less 1 or 2 types Hf: 0.2% or less, Zr: 1 or 2 of 0.2% or less, Y: 0.1% or less, La: 0.1% or less, Ce: 1 or 2 of 0.1% or less At least one species, the balance being Fe and unavoidable impurities, and

0.5 Co + N i + l.5 C r≤65

0.4≤ (N i + C r) / (Co + Mo + 0.5W) ≤ 1.

An alloy for boilers with excellent resistance to molten salt corrosion, characterized by satisfying the following conditions: