JPH0770681A - High chrome austenitic heat resistant alloy - Google Patents

Abstract

(57) [Summary] [Objective] To provide a high chromium austenitic heat resistant alloy. [Constitution] C: more than 0.02% and 0.10% or less, Si: 1.0% or less,
Mn: 0.5% or less, Cr: 28-38%, Ni: 35-60%, Cu: 2-
6%, Ti: 0.1-1.0%, N: 0.05% or less and Al: 0.01
.About.0.3%, B: 0.001 to 0.01% and Zr:
A high chromium austenitic heat-resistant alloy excellent in high temperature strength and corrosion resistance, containing at least one of 0.01 to 0.1% and at least one of Mo: 0.5 to 3.0% and W: 1.0 to 6.0%. In addition to the above alloys, Nb: 0.1-1.0% or / and Mg: 0.0
One or more of 01 to 0.05% and Ca: 0.001 to 0.05% can be contained. [Effect] An inexpensive alloy that has excellent high-temperature strength even under severe high-temperature corrosive environments.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high chromium austenite heat resistant alloy which is excellent in high temperature strength and corrosion resistance in a severe high temperature corrosive environment such as a boiler or a chemical plant.

[0002]

2. Description of the Related Art In recent years, attention has been paid to ultra-high temperature and high pressure boilers for improving thermal efficiency in thermal power plants. In this boiler, the steam conditions are higher in temperature and pressure than in conventional boilers, and therefore the superheater tube material must meet even more stringent requirements for high temperature strength and corrosion resistance. Therefore, a high-strength and high-corrosion-resistant austenitic steel having higher high-temperature strength than the conventionally used 18-8 series stainless steel and also excellent in steam oxidation resistance and high-temperature corrosion resistance is required.

Generally, in order to improve corrosion resistance,
It is effective to increase the Cr content. But for example,
As seen in SUS310 STB steel containing about 25% Cr, the high temperature strength at 600 to 700 ° C is rather lower than that of 18-8 series stainless steel, and there is a problem of deterioration of toughness due to σ phase precipitation. Furthermore, when the Cr content is about 25%, the corrosion resistance is not sufficient in a severe corrosive environment.

As an alloy having relatively good corrosion resistance, there is an alloy having a Cr content increased to about 30%, for example, an alloy disclosed in Japanese Patent Laid-Open No. 59-153858. Below, the high temperature strength is insufficient to be applied as a single pipe. Further, when using a double pipe, there are many problems in terms of manufacturing cost and reliability.

While further increasing the Cr content to about 30%,
As those intended to improve the strength by adding Mo and W, there are disclosed in JP-A-60-100640, 61-174350,
There are heat-resistant alloys such as those disclosed in JP-A-61-276948 and JP-A-64-55352, but their strengths are not sufficient.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high chromium austenitic heat resistant alloy which has sufficient corrosion resistance even in a severe high temperature corrosive environment and excellent high temperature strength and is economically advantageous. Especially.

[0007]

Means for Solving the Problems The gist of the present invention is as follows (1)
It is in the heat-resistant alloy of (4).

(1) By weight%, C: more than 0.02% and 0.10% or less, Si: 1.0% or less, Mn: 0.5% or less, Cr: 28 to 38%, Ni:
35-60%, Cu: 2-6%, Ti: 0.1-1.0%, N: 0.05%
The following and Al: 0.01 to 0.3%, and B: 0.001
~ 0.01% and one or more of Zr: 0.01 to 0.1% and Mo:
A high chromium austenitic heat resistant alloy containing 0.5 to 3.0% and one or more of W: 1.0 to 6.0%, the balance being Fe and inevitable impurities and having excellent high temperature strength and corrosion resistance.

(2) In addition to the components of (1) above, further weight%
A high chromium austenite heat resistant alloy containing 0.1 to 1.0% of Nb, the balance being Fe and inevitable impurities and having excellent high temperature strength and corrosion resistance. (3) In addition to the above-mentioned component (1), further by weight%, Mg: 0.001
~ 0.05% and Ca: 0.001 ~ 0.05% containing one or more,
The balance is a high chromium austenitic heat resistant alloy consisting of Fe and unavoidable impurities with excellent high temperature strength and corrosion resistance.

(4) In addition to the components of (1) above, further wt%
And Nb: 0.1 to 1.0% and Mg: 0.001 to 0.0
A high chromium austenitic heat resistant alloy containing 5% and at least one of Ca: 0.001 to 0.05%, the balance being Fe and inevitable impurities, and having excellent high temperature strength and corrosion resistance.

In order to obtain sufficient corrosion resistance under the severe hot corrosion environment as described above, it is necessary to contain 28% or more of Cr. In such a Cr-Cr-Ni-Fe-based alloy having a high Cr content, the α phase precipitates within a predetermined Ni content range, which affects the strength.

The present inventors have conducted the research aiming at a dramatic improvement in the creep rupture strength of the conventional high Cr content austenitic steel, and as a result, obtained the following findings.

Addition of Ti greatly improves creep rupture strength. This is because Ti promotes the precipitation of α phase.

Addition of Cu significantly improves creep rupture strength. This is because the Cu-rich phase precipitates and contributes greatly to the high temperature strength improvement, the growth of the α phase is suppressed, and the α phase does not become coarse even after long-term use.

By adding Ti and Cu in combination, it is possible to obtain a highly corrosion-resistant alloy having a high temperature strength higher than that of the alloy disclosed in JP-A-60-100640. Moreover, since the high temperature strength can be greatly improved by the addition of inexpensive Cu, this alloy is economically excellent.

[0016]

The function and effect of the constituents of the alloy of the present invention and the reason why the proper content is determined as described above will be described below. % Means% by weight.

C: more than 0.02% and 0.10% or less C is an element effective for forming carbides and improving the tensile strength and creep rupture strength required for heat-resistant steel. If the C content is 0.02% or less, these desired effects cannot be obtained. On the other hand, if it exceeds 0.10%, the ductility and toughness of the alloy are greatly deteriorated. Therefore, the range of C content is 0.02
% And 0.10% or less.

Si: 1.0% or less Si is an element necessary for deoxidation and also contributes to improvement of oxidation resistance. However, if Si is present in excess of 1.0%, weldability and structural stability deteriorate. Considering these effects, the Si content is set to 1.0% or less.

Mn: 0.5% or less Mn is an element effective for deoxidation. However, if the Mn content exceeds 0.5%, the heat resistance property deteriorates. Therefore, the Mn content is set to 0.5% or less.

Cr: 28-38% Cr exerts an excellent action for improving corrosion resistance such as oxidation resistance, steam oxidation resistance or high temperature corrosion resistance, and in the present invention, forms an α phase which bears high temperature strength. It is an important element. However, if the content is less than 28%, these desired effects cannot be obtained. On the other hand, if it exceeds 38%, workability is deteriorated and the structure is destabilized. Therefore, the Cr content range is 28
~ 38%.

Ni: 35-60% Ni is an essential element for obtaining a stable austenite structure. Further, it is an element having an action of suppressing the precipitation of α phase. However, if the Ni content is less than 35%,
Securing of austenite structure becomes unstable. On the other hand, 60%
If it exceeds, the precipitation of the α phase is suppressed, the high temperature strength becomes insufficient, and a great economical disadvantage is brought about. Therefore, the range of Ni content is set to 35 to 60%.

Cu: 2 to 6% Cu is an element that improves high temperature strength, especially creep rupture strength. This is because the Cu-rich phase precipitates and contributes greatly to the high temperature strength improvement, the growth of the α phase is suppressed, and the α phase does not become coarse even after long-term use. However, if the content is less than 2%, the desired effect described above cannot be obtained. On the other hand, if it exceeds 6%, the ductility decreases and the workability also deteriorates.
Therefore, the range of the Cu content is set to 2 to 6%.

Ti: 0.1 to 1.0% Ti is an element which has a great influence on the precipitation of α phase. The inclusion of Ti promotes the precipitation of α phase. But 0.1%
If it is less than, this effect cannot be obtained. On the other hand, if it exceeds 1.0%, the precipitation of α-phase becomes excessive, which impairs the toughness after aging, that is, after long-term use. Therefore, the Ti content range is 0.1-
It was set to 1.0%.

N: 0.05% or less N is an element having an effect of improving high temperature strength and stabilizing an austenite structure. Therefore, it is effective as a substitute for Ni, which is an expensive element. However, if the N content exceeds 0.05%, nitrides will precipitate after long-term use at high temperature, resulting in deterioration of toughness after long-term use. Therefore, the N content is set to 0.05% or less.

Al: 0.01 to 0.3% Al is an effective element as a deoxidizing agent, and it is necessary to contain Al by 0.01% or more in order to obtain the effect. On the other hand, if it exceeds 0.3%, the workability is impaired. Therefore, the range of Al content is
It was set to 0.01 to 0.3%.

B and Zr: B is 0.001 to 0.01% and Zr is 0.
01 to 0.1% These elements are mainly effective for strengthening the grain boundaries of the alloy. However, if the content of B is less than 0.001% and the content of Zr is less than 0.01%, this effect cannot be obtained. On the other hand, when the B content exceeds 0.01% and the Zr content exceeds 0.1%, the creep rupture strength decreases and the weldability also deteriorates. Therefore, the content range of B is 0.001 to 0.
In the case of 01% and Zr, the content range was set to 0.01 to 0.1%.
These elements may be contained alone or in combination of two.

Mo and W: Mo is 0.5 to 3.0%, W is 1.0
~ 6.0% Mo and W are mainly effective as solid solution strengthening elements,
Improves creep rupture strength. However, these effects cannot be obtained if the Mo content is less than 0.5% and the W content is less than 1.0%. On the other hand, Mo content is 3.0
%, W content exceeding 6.0% deteriorates corrosion resistance and workability. Therefore, for Mo, the content range should be
0.5-3.0%, W content range 1.0-6.0%
And

These elements may be contained alone or in combination of two. However, when using two kinds in combination, it is desirable to keep the total content of Mo + (1/2) W to 3.0% or less.

The alloy of the present invention may further contain the following components in addition to the above components.

Nb: 0.1 to 1.0% Nb refines crystal grains and improves ductility. Further, it forms a solid solution in the austenite phase and Cr carbide and contributes to the improvement of creep rupture strength. However, if the Nb content is less than 0.1%, these effects cannot be obtained. On the other hand, if it exceeds 1.0%, toughness is deteriorated. Therefore, the range of Nb content is 0.1 to 1.
It was set to 0%.

Mg and Ca: 0.001 to 0.05% Mg and Ca are effective elements for improving workability. But,
If the content of each is less than 0.001%, this effect cannot be obtained. On the other hand, if it exceeds 0.05%, the workability is deteriorated. Therefore, the content range of Mg and Ca are both 0.0
It was set to 01 to 0.05%. These elements may be contained alone or in combination of two. However, 2
When combined with other species, the total content of Mg and Ca is 0.0
It is desirable to set it to 01 to 0.05%.

Although P and S are elements inevitably mixed in the alloy, it is desirable that P is 0.03% or less and S is 0.01% or less from the viewpoint of ensuring weldability and high temperature strength.

[0033]

EXAMPLE A 20 kg ingot obtained by melting alloys having the chemical compositions shown in Table 1 (1), Table 1 (2) and Table 1 (3) in a high frequency vacuum melting furnace was forged, cold rolled, and Each test piece was prepared from the test material that had been subjected to solution heat treatment at 1200 ° C, and a creep rupture test and a Charpy impact test after aging were performed.

The creep rupture test was conducted at 750 ° C. using a test piece having an outer diameter of 6 mm and a gauge length of 30 mm for 10 ³ hours and 10 ⁴
The breaking strength over time was determined. The Charpy impact test after aging was performed at 0 ° C. using a 2 mm V notch forming test piece having a thickness of 5 mm × a width of 10 mm × a length of 55 mm, which was prepared from a test material aged at 750 ° C. for 300 hours.

In Table 2 (1), Table 2 (2) and Table 2 (3), 10
³ hours and showing the Charpy impact value after breaking strength and aging of 10 ⁴ hours. Nos. 1 to 44 are examples of the present invention, and A to W are comparative examples. Comparative Examples A to F are conventional alloys disclosed in JP-A-61-276948, and Comparative Examples G and H are conventional alloys disclosed in JP-A-59-153858. Comparative Examples I to W are alloys whose components marked with * in the table are out of the range defined by the present invention.

[0036]

[Table 1 (1)]

[0037]

[Table 1 (2)]

[0038]

[Table 1 (3)]

[0039]

[Table 2 (1)]

[0040]

[Table 2 (2)]

[0041]

[Table 2 (3)]

FIG. 1 is a diagram showing the influence of the contents of Ti and Cu on the creep rupture strength. FIG. 2 is a diagram showing the influence of Cu content on creep rupture strength. FIG. 3 shows Table 2.
It is a figure which shows the example which compared the creep rupture strength about the alloy of this invention example and the comparative example from the result of this.

From FIG. 1, it is clear that the alloys having the Ti and Cu contents within the range defined by the present invention exhibit excellent creep rupture strength. From Figure 1, Figure 2 and Table 2, Cu
%, The effect of improving the creep rupture strength becomes conspicuous. On the other hand, even if it exceeds 6%, the creep rupture strength is not different from that of the inventive alloys and the toughness is significantly reduced.

Further, as is clear from Table 2 and FIG. 3, the inventive alloys of the present invention exhibit a very high creep rupture strength as compared with the comparative alloys A and B containing no Ti or Cu. Also,
Higher creep rupture strength is exhibited even when compared with Comparative Example alloys C to F containing Ti but not containing Cu. This is because Ti promotes the precipitation of the α phase, and the Cu-rich phase precipitated by Cu contributes greatly to the improvement of the high temperature strength.Also, the growth of the α phase is suppressed and the α phase becomes coarse even after long-term use. This is because it does not.

[0045]

The high chromium austenite heat resistant alloy of the present invention is an inexpensive alloy having excellent high temperature strength even in a severe high temperature corrosive environment. This alloy single pipe is more cost effective and more reliable than the conventional alloy double pipe.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of Ti and Cu contents on creep rupture strength.

FIG. 2 is a diagram showing the effect of Cu content on creep rupture strength.

FIG. 3 is a diagram showing an example in which creep rupture strengths of alloys of the present invention example and the comparative example are compared.

Claims (4)

[Claims] 1. By weight%, C: more than 0.02% and 0.10% or less,
Si: 1.0% or less, Mn: 0.5% or less, Cr: 28-38%, Ni: 35-
60%, Cu: 2 to 6%, Ti: 0.1 to 1.0%, N: 0.05% or less and Al: 0.01 to 0.3%, and B: 0.001 to 0.
01% and Zr: 0.01 to 0.1% or more and Mo: 0.5
-3.0% and W: 1.0-6.0%, and the balance is Fe and inevitable impurities. High chromium austenitic heat resistant alloy with excellent high temperature strength and corrosion resistance. 2. By weight%, C: more than 0.02% and 0.10% or less,
Si: 1.0% or less, Mn: 0.5% or less, Cr: 28-38%, Ni: 35-
60%, Cu: 2 to 6%, Ti: 0.1 to 1.0%, N: 0.05% or less, Al: 0.01 to 0.3% and Nb: 0.1 to 1.0%,
Furthermore, one or more of B: 0.001 to 0.01% and Zr: 0.01 to 0.1% and 1 of Mo: 0.5 to 3.0% and W: 1.0 to 6.0%.
A high-chromium austenitic heat-resistant alloy that contains at least one of the above and the balance is Fe and unavoidable impurities and has excellent high-temperature strength and corrosion resistance. 3. By weight%, C: more than 0.02% and 0.10% or less,
Si: 1.0% or less, Mn: 0.5% or less, Cr: 28-38%, Ni: 35-
60%, Cu: 2 to 6%, Ti: 0.1 to 1.0%, N: 0.05% or less and Al: 0.01 to 0.3%, and B: 0.001 to 0.
01% and Zr: 0.01 to 0.1% or more and Mo: 0.5
~ 3.0% and W: 1.0-6.0% or more and Mg:
A high chromium austenitic heat resistant alloy containing 0.001 to 0.05% and one or more of Ca: 0.001 to 0.05%, the balance being Fe and unavoidable impurities and having excellent high temperature strength and corrosion resistance. 4. By weight%, C: more than 0.02% and 0.10% or less,
Si: 1.0% or less, Mn: 0.5% or less, Cr: 28-38%, Ni: 35-
60%, Cu: 2 to 6%, Ti: 0.1 to 1.0%, N: 0.05% or less, Al: 0.01 to 0.3% and Nb: 0.1 to 1.0%,
Furthermore, one or more of B: 0.001 to 0.01% and Zr: 0.01 to 0.1% and 1 of Mo: 0.5 to 3.0% and W: 1.0 to 6.0%.
Species and above and Mg: 0.001-0.05% and Ca: 0.001-0.05
%, A high chromium austenite heat-resistant alloy that is excellent in high temperature strength and corrosion resistance and contains the balance of Fe and inevitable impurities.