JPH06145909A - Alloy for boiler excellent in field workability - Google Patents

Abstract

PURPOSE:To contribute to the practicability and diffusion of a high temp. energy device by regulating the component compsn. of an alloy into a one of specified amounts of C, Si, Mn, Ca, Co, Cr, Ni, Mo and W, and the balance Fe and regulating the relationship of the elements to be added into a specified one. CONSTITUTION:The component compsn. of the alloy for a boiler is constituted of a one contg., by weight, <=0.1% C, <=2.5% Si, <=1% Mn, <=0.03% P, <=0.005% S, 0.01 to 0.08% Ca, 10 to 25% Co, 18 to 28% Cr and 10 to 50% Ni and contg. one or two kinds of 2 to 4% Mo and <=8% W, and the balance Fe with inevitable impurities. Then, 0.5Co+Ni+1.5Cr<=75 and 1.2<=(Ni+Cr)/(Co+Mo+0.5 W)<=2.8 are regulated. Furthermore, one or two kinds of <=0.2% Hf and <=0.2% Zr are incorporated therein. Thus, the alloy for a boiler showing excellent resistance to a molten salt corrosive environment and excellent in field workability can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention shows excellent resistance to a corrosive environment, especially when it is used in a molten salt corrosive environment such as a steel pipe of a coal-fired boiler, and has local workability. It relates to an excellent boiler alloy.

[0002]

2. Description of the Related Art A high temperature energy device represented by a fuel combustion boiler, a fluidized bed reactor, coal gasification, a liquefaction device, etc. has been attracting attention as a coal utilization technique reflecting recent energy circumstances. For example, in the case of a fuel-fired boiler, petroleum has been mainly used in the past, but today, as a result of recognizing the necessity of using alternative energy, the use of coal has tended to increase.

However, even in such a high-temperature energy device, the device design is carried out according to the design concept when using petroleum, and the problems when using coal are not solved sufficiently. For example, a coal fired boiler is manufactured with the same material composition as that of a conventional oil fired boiler. However, in coal-fired boilers, unlike oil-fired boilers, the solid ash content inside the boiler becomes a clinker and falls, or as molten fly ash floats in the combustion gas stream as fly ash, so high-temperature molten salt Severely damaged by. Such problems are well recognized by those skilled in the art, but the solution is not clear yet, there are few material measures, and empirical design measures such as reduction of flow velocity and mounting of protector are required. These are just the measures taken. However, even with a design measure, even if the flow velocity is limited, a drift part with a faster flow velocity than expected will be created, and even if a protector is used, the protector itself will be damaged quickly and there is no practical effect There are many cases.

In terms of materials, the boiler tube is made of SUS304 steel, the same as 321, 347, 31.
18-8 austenitic stainless steel such as 6 steel,
Further, alloys such as Incoloy 800 and SUS310 are used. Further, as a general high temperature member, various high temperature austenitic stainless steels are used, but none of these consider molten salt corrosion resistance, and based on experience in oil fired boilers etc. It is only used.

As described above, at present, there are few material measures for preventing molten salt corrosion. However, if there are material measures, there is a margin in the device design, and the device is downsized.
Benefits such as improved thermal efficiency can also be expected. However, even if the material has excellent corrosion resistance, local bending workability becomes a major problem for materials such as boiler steel pipes that are often subjected to local bending work.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a material having high resistance to a molten salt corrosive environment as found in a coal-fired boiler and having excellent on-site processability. It is in.

[0007]

The subject matter of the present invention is as follows. (1) C: 0.1% or less, Si: 2.5% by weight
Hereinafter, Mn: 1.0% or less, P: 0.03% or less, S:
0.005% or less, Ca: 0.01 to 0.08%, C
o: 10 to 25%, Cr: 18 to 28%, Ni: 10 to 10%
50%, Mo: 2 to 4%, W: 8% or less, one or two kinds are contained, and the balance is composed of Fe and unavoidable impurities, and 0.5Co + Ni + 1.5Cr ≦ 75 1 .2 ≦ (Ni + Cr) / (Co + Mo + 0.5W) ≦
A boiler alloy with excellent local workability, which satisfies the conditions of 2.8.

(2) C: 0.1% or less by weight, S
i: 2.5% or less, Mn: 1.0% or less, P: 0.03
% Or less, S: 0.005% or less, Ca: 0.01-0.
08%, Co: 10 to 25%, Cr: 18 to 28%, N
i: 10 to 50%, Mo: 2 to 4%, W: 8%
Contains one or two of the following, and further Hf: 0.2%
In the following, Zr: contains one or two of 0.2% or less, and the balance is composed of Fe and inevitable impurities,
And 0.5Co + Ni + 1.5Cr ≦ 75 1.2 ≦ (Ni + Cr) / (Co + Mo + 0.5W) ≦
A boiler alloy with excellent local workability, which satisfies the conditions of 2.8.

(3) Weight%, C: 0.1% or less, S
i: 2.5% or less, Mn: 1.0% or less, P: 0.03
% Or less, S: 0.005% or less, Ca: 0.01-0.
08%, Co: 10 to 25%, Cr: 18 to 28%, N
i: 10 to 50%, Mo: 2 to 4%, W: 8%
It contains one or more of the following, and further contains one or more of Y: 0.1% or less, La: 0.1% or less, and Ce: 0.1% or less, with the balance being It has a composition of Fe and inevitable impurities, and has 0.5Co + Ni + 1.5Cr ≦ 75 1.2 ≦ (Ni + Cr) / (Co + Mo + 0.5W) ≦
A boiler alloy with excellent local workability, which satisfies the conditions of 2.8.

(4) Weight%, C: 0.1% or less, S
i: 2.5% or less, Mn: 1.0% or less, P: 0.03
% Or less, S: 0.005% or less, Ca: 0.01-0.
08%, Co: 10 to 25%, Cr: 18 to 28%, N
i: 10 to 50%, Mo: 2 to 4%, W: 8%
Contains one or two of the following, and further Hf: 0.2%
Hereinafter, one or two of Zr: 0.2% or less and Y: 0.1% or less, La: 0.1% or less, Ce: 0.1
% Or less, and one or more of them are contained, and the rest is F
e and unavoidable impurities, and 0.5Co + Ni + 1.5Cr ≦ 75 1.2 ≦ (Ni + Cr) / (Co + Mo + 0.5W) ≦
A boiler alloy with excellent local workability, which satisfies the conditions of 2.8.

The present invention will be described in detail below.

[0012]

First, the reason why the range of each component is limited as described above in the present invention will be described. If C exceeds 0.1%, the workability deteriorates and intergranular corrosion cracking easily occurs, 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%, the hot workability deteriorates, so the upper limit was set to 2.5%.

Mn has a deoxidizing action like Si, but if added excessively, it becomes brittle, so the upper limit was set to 1.0%. P is an unavoidable impurity, but its content is 0.03
%, The 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 it becomes impossible to manufacture, so the upper limit was set to 0.005%.

Needless to say, Ca has an effect as a deoxidizing agent, but it forms S and CaS which are impurity elements, promotes ferrite transformation with CaS as a nucleus, and as a result, a material having a relatively low hardness can be obtained. Becomes However, if the addition amount is less than 0.01%, CaS is not generated, and the lower limit value needs to be 0.01%. On the other hand, even if added over 0.08%, the effect is saturated, so the upper limit is 0.0
8%.

Co is an element which improves the molten salt corrosion resistance in the coexistence with Ni, Cr, Mo and W, but if the content thereof is less than 10%, no remarkable effect is exerted and the desired molten salt corrosion resistance is obtained. In order to obtain it, it is necessary to increase the amount of other alloy elements, which is economically disadvantageous. Therefore, the lower limit value is set to 10%. On the other hand, if the content exceeds 25%, the workability decreases, so the upper limit was set to 25%.

Ni has the effect of improving the corrosion resistance,
If it is less than 10%, the effect is not obtained, and it is necessary to increase the amount of other alloying elements to obtain the desired corrosion resistance, which is uneconomical. Therefore, the lower limit is set to 10%. On the other hand, even if it exceeds 50%, no further improvement in the effect is recognized, so the upper limit value was set to 50% in consideration of economic efficiency. Cr is Ni, Mo,
It is an element that significantly improves the corrosion resistance when coexisting with W.
Addition of less than 8% does not produce a significant effect, while 28%
Even if added in excess, no further improvement in effect is observed, so the upper limit was made 28%.

Mo, together with Co, improves the molten salt corrosion resistance, and in particular has the effect of improving the molten salt corrosion resistance from the increase in hardness. However, if it is less than 2%, the hardness is not sufficient, while if it is added in excess of 4%, the hardness is excessively increased and the workability is deteriorated. Therefore, the addition range is set to 2 to 4%. W is also M
As with o, hardness increase improves molten salt corrosion resistance, but even if added over 8%, there is no further improvement and workability deteriorates, so the upper limit was made 8%.

Of the above alloy elements, Co, Ni, C
Although r, Mo and W improve the molten salt corrosion resistance and the corrosion resistance, their effects do not appear when only each element is added alone, and the effects are exhibited only by the combined addition. Therefore, the present inventors have conducted research to obtain a material excellent in molten salt corrosion resistance and in-situ workability in a high temperature boiler environment of 400 ° C. As a result, (1) Co, Ni and Cr contents are 0.5Co + Ni + 1. 5Cr ≦ 75 and (2) Ni, Cr, Co, Mo, W amount 1.2 ≦ (Ni + Cr) / (Co + Mo + 0.5W) ≦
It was revealed that when the condition of 2.8 is satisfied, the characteristics of the alloy element are most effectively exhibited with the above-mentioned addition amount.

Since Hf improves the strength at high temperature even when added in a small amount, its upper limit is set to 0.2%. Zr acts as a deoxidizing element, but even if the addition amount exceeds 0.2%, no further improvement of the effect is recognized, so the upper limit was set to 0.2%. Y, La and Ce have the effect of further improving the hot workability, so they are added as necessary when hot working is performed under severe conditions, but any element exceeds 0.1%. Even if added, no further improvement in the effect was observed, and even a deterioration phenomenon appeared, so the content was made 0.1% or less.

The inventors of the present invention melt-cast alloys having different amounts of Co, Ni, and Cr, cast, and hot-roll to obtain a plate material having a plate thickness of 7 mm, which is then heated to 1050 ° C. for 30 minutes. After holding, after water-cooling heat treatment, a test piece having a thickness of 2 mm, a width of 15 mm and a length of 80 mm was cut out from the plate material at right angles to the rolling direction, and after bending, the test piece was subjected to 400
The mixture was kept in an apparatus heated to 0 ° C., a mixed molten salt of NaCl-KCl was applied, a test was conducted for 500 hours, and the degree of change in appearance before and after the test was observed. As a result of scientific analysis of these results, it became clear that the above-mentioned conditions exist between Co, Ni, and Cr.

[0021]

EXAMPLES 1 ton of each of the alloys having the composition shown in Tables 1 to 4 was melted by using a vacuum induction heating furnace and ES
After being cleaned by R treatment and cast into an ingot having a cross section of 500 mm × 250 mm, it is hot-rolled into a plate material having a plate thickness of 7 mm, which is then kept at a temperature of 1050 ° C. for 30 minutes and then subjected to a water-cooling heat treatment. A test piece having a thickness of 2 mm, a width of 15 mm, and a length of 80 mm was cut out from the plate material at right angles to the rolling direction, the test piece was folded back at the center in the length direction, and the workability at that time was evaluated. 1),
The results are shown in Table 4 (continued from Table 3). Then NaCl-KC
The mixed molten salt (1) was applied, and the mixed molten salt was kept in an apparatus heated to 400 ° C. and tested for 500 hours, and the result of measuring the degree of change in appearance was investigated.

From the results shown in Tables 2 and 4, the comparative alloy materials are not so good in molten salt corrosion resistance and workability, while the alloys of the present invention 1 to 37 are all molten salt resistant. It is clear that the corrosivity and workability are good and have excellent properties.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

EFFECTS OF THE INVENTION According to the present invention, since it is possible to provide an alloy for a boiler that exhibits excellent resistance to a molten salt corrosive environment and is excellent in on-site processing, a high temperature energy device that has been attracting attention in recent years. It greatly contributes to the practical application and spread of the.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Ogawa 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division

Claims (4)

[Claims] 1. 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, Ca: 0.01 to 0.08.
%, Co: 10 to 25%, Cr: 18 to 28%, Ni:
10 to 50%, Mo: 2 to 4%, W: 8% or less, one or two kinds are contained, and the balance is composed of Fe and inevitable impurities, and 0.5Co + Ni + 1.5Cr ≦ 75 1.2 ≦ (Ni + Cr) / (Co + Mo + 0.5W) ≦
A boiler alloy with excellent local workability, which satisfies the conditions of 2.8. 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, Ca: 0.01 to 0.08.
%, Co: 10 to 25%, Cr: 18 to 28%, Ni:
10% to 50%, Mo: 2 to 4%, W: 8% or less, 1 or 2 types, and Hf: 0.2% or less, Zr: 0.2% or less 1 One or two, and the balance is Fe and unavoidable impurities, and 0.5Co + Ni + 1.5Cr ≦ 75 1.2 ≦ (Ni + Cr) / (Co + Mo + 0.5W) ≦
A boiler alloy with excellent local workability, which satisfies the conditions of 2.8. 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, Ca: 0.01 to 0.08.
%, Co: 10 to 25%, Cr: 18 to 28%, Ni:
10 to 50%, Mo: 2 to 4%, W: 8% or less of 1 type or 2 types, further Y: 0.1% or less,
La: 0.1% or less, Ce: 0.1% or less, one or more of them are contained, and the balance is composed of Fe and inevitable impurities, and 0.5Co + Ni + 1.5Cr ≦ 75 1 .2 ≦ (Ni + Cr) / (Co + Mo + 0.5W) ≦
A boiler alloy with excellent local workability, which satisfies the conditions of 2.8. 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, Ca: 0.01 to 0.08.
%, Co: 10 to 25%, Cr: 18 to 28%, Ni:
10% to 50%, Mo: 2 to 4%, W: 8% or less, 1 or 2 types, and Hf: 0.2% or less, Zr: 0.2% or less 1 Seed or two and Y:
0.1% or less, La: 0.1% or less, Ce: 0.1% or less, one or more of them are contained, and the remainder has a composition of Fe and inevitable impurities, and 5Co + Ni + 1.5Cr ≦ 75 1.2 ≦ (Ni + Cr) / (Co + Mo + 0.5W) ≦
A boiler alloy with excellent local workability, which satisfies the conditions of 2.8.