JPH10130790A - Heat resistant alloy excellent in cold workability and overaging characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precipitation hardening heat resistant alloy excellent in cold workability and capable of manufacturing heat resistant parts such as exhaust value for automobile engine by means of cold working, capable of direct aging treatment without application of solid solution heat treatment after cold working, capable of reducing manufacturing costs of heat resistant parts, and also capable of inhibiting overaging state even after long use in a high temp. state and, as a result, free from deterioration in properties. SOLUTION: This heat resistant alloy has a composition consisting of, by weight, 0.01-0.1% C, <=2% Si, <=2% Mn, 12-25% Cr, 0.2-2.0% (Nb+Ta), <1.5% Ti, 0.5-3.0% Al, 25-45% Ni, 0.1-5.0% Cu, and the balance Fe with inevitable impurities. Further, the ratio by atomic percentage between Ti and Al is regulated so that Ti/Al<=1.0 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precipitation hardening type heat resistant alloy suitable for use in exhaust valves, heat resistant bolts for automobile engines, exhaust gas catalyst knit meshes for automobile engines, etc., and particularly to cold workability and overageing properties. The present invention relates to an excellent heat-resistant alloy, and more particularly to a heat-resistant alloy which can be used by aging without being subjected to solution heat treatment after cold working.

[0002]

2. Description of the Related Art As a heat-resistant material used for an exhaust valve or the like for an automobile engine, a conventional high Mn austenitic heat-resistant steel JIS SUH35 has been used.
(Fe-9Mn-21Cr-4Ni-0.5C-0.4
N) or Ni-base superalloy JIS NCF751 (Ni-
15.5Cr-0.9Nb-1.2Al-2.3Ti-
7Fe-0.05C) and the like have been used.

The latter Ni-base superalloy is an alloy excellent in high-temperature strength, high-temperature oxidation, and high-temperature corrosion, but has a problem of high cost because it contains more than 70% of Ni. Therefore, attempts to reduce the amount of expensive Ni have been made,
Alloys with a Ni content of 40% or less have also been developed.

[0004] However, if the Ni content is further reduced, a performance problem arises.
It is difficult to reduce the content.

[0005] If the Ni content is further reduced, the stability of the structure at high temperatures is degraded due to the increase in Fe.
When used at high temperatures for a long time, the η phase (Ni ₃ T
i) is precipitated, resulting in a decrease in high-temperature strength and a decrease in toughness at room temperature. Thus, the reduction of the Ni content is naturally limited due to performance problems.

[0006] By the way, heat-resistant parts such as the exhaust valve for an automobile engine are conventionally subjected to hot upset processing,
It is manufactured by hot working such as hot extrusion, but heat-resistant parts such as exhaust valves for automobile engines have severe surface flaws and other required characteristics. The number of man-hours increases and the time required for processing is long, which is one factor that increases the cost. Therefore, it would be desirable to be able to manufacture this by cold working, since the cost could be further reduced.

However, conventionally provided or proposed heat-resistant materials are premised on hot working, and are materials from which a heat-resistant component cannot be directly produced by cold working. That is, in order to manufacture a heat-resistant component by cold working, it is required that the heat-resistant material has excellent cold workability.

By the way, even when excellent cold workability is imparted to a precipitation hardening type heat-resistant alloy, and it is possible to perform cold work using the same, usually, a solid solution is formed afterwards. It is necessary to perform aging treatment after applying heat treatment, to precipitate the precipitated components and express the required strength,
There is a problem that the number of steps for heat treatment is large.

[0009] This is because, when cold working is performed and aging treatment is performed as it is, aging is excessively accelerated due to strain remaining in the alloy during cold working, so that the Ni content is low and the Fe content is low.
This is because when the peak hardness increases, the steel rapidly softens after reaching the peak hardness and precipitates the η phase, which is an embrittlement phase. It is necessary to perform aging treatment.

However, in such a case, the number of steps for the heat treatment is increased, which increases the cost of heat-resistant parts. Therefore, in order to further reduce the manufacturing cost of heat-resistant parts, it is desirable to reduce the number of steps for the heat treatment.

When a heat-resistant component such as an exhaust valve for an automobile engine is manufactured using a precipitation hardening type heat-resistant alloy, the following other problems are inherent. That is, when a heat-resistant component made of this kind of precipitation hardening type heat-resistant alloy is used for a long time at a high temperature, aging proceeds over time, and the alloy is softened and deteriorated in a so-called overaged state.

Therefore, a heat-resistant alloy used for heat-resistant parts is required to have excellent overaging characteristics, which does not cause softening and deterioration even when used at a high temperature for a long time.

[0013]

The invention of the present application has been made to solve such a problem. Thus, the heat-resistant alloy according to claim 1 of the present application has a C content of 0.01 to 0.1% by weight.
1%, Si: ≤ 2%, Mn: ≤ 2%, Cr: 12 to 25
%, Nb + Ta: 0.2 to 2.0%, Ti: less than 1.5%, Al: 0.5 to 3.0%, Ni: 25 to 45%, C
u: 0.1 to 5.0%, characterized by having an alloy composition consisting of unavoidable impurities and Fe.

According to a second aspect of the present invention, in the first aspect, one or more of W, Mo, and V are further expressed by weight%, and W: ≦ 3%, Mo: ≦ 3%, V : ≦ 1%, and ＷW + Mo + V: ≦ 3%.

According to a third aspect of the present invention, there is provided the method according to any one of the first and second aspects, wherein Ni + Co: 25 to 45% by weight,
Co: characterized by being contained in the range of ≦ 5%.

Claim 4 of the present application is directed to Claims 1, 2,
3, Ti, Al, Nb and Ta are in atomic%
And Ti + Al + Nb + Ta: 4.5 to 7.0%.

Claim 5 of the present application is directed to Claims 1, 2,
In any one of 3 and 4, the ratio Ti / Al in atomic% of Ti and Al is Ti / Al: ≦ 1.0.

Claim 6 of the present application is directed to Claims 1, 2,
In any one of 3, 4, and 5, M represented by the following formula is M: ≦ 0.95. M = (0.717Ni + 0.858Fe + 1.142C)
r + 1.90Al + 2.271Ti + 2.117Nb +
2.224Ta + 1.001Mn + 1.90Si + 0.
615 Cu) / 100 (however, each element is atomic%)

The seventh aspect of the present invention relates to the first, second, and third aspects.
In any one of 3, 4, 5, and 6, one or two kinds of B and Zr may be further added by weight% of B: 0.001 to 0.01%,
Zr: characterized in that it is contained in the range of 0.001 to 0.1%.

Claim 8 of the present application is directed to Claims 1, 2,
3, 4, 5, 6, or 7, characterized in that Ca + Mg is contained in a range of 0.001 to 0.01% by weight of Ca + Mg.

Claim 9 of the present application is directed to Claims 1, 2,
In any one of 3, 4, 5, 6, 7, and 8, P, S,
O and N are weight%, respectively: P: ≦ 0.02%, S: ≦
0.01%, O: ≦ 0.01%, N: ≦ 0.01%.

[0022]

The heat-resistant alloy of the present invention has a low Ni content and is inexpensive, and has excellent cold workability. In addition, heat-resistant parts such as exhaust valves for automobile engines can be cold-worked. It is possible to manufacture, and the manufacturing cost of the heat-resistant component can be reduced. That is, it is possible to reduce both the cost of the heat-resistant alloy material itself and the manufacturing cost of a heat-resistant component using the same.

The heat-resistant alloy of the present invention has one feature in that Cu is contained in a predetermined range. This Cu has a function of increasing stacking fault energy to suppress work hardening, thereby providing a heat-resistant alloy. The cold workability in is effectively improved.

The heat-resistant alloy of the present invention also has the following features. That is, when this heat-resistant alloy is directly subjected to aging treatment without solution heat treatment after cold working, aging proceeds properly due to strain remaining inside the alloy without overaging.

In addition, even when the battery is used at a high temperature for a long period of time, the overaging state is suppressed, and the life of the heat-resistant component is prolonged. This is mainly due to T:
i: less than 1.5%, especially when Ti / Al: ≦ 1.0 (atomic% ratio) (claim 5), better aging characteristics and excess Aging suppression properties can be provided.

The ratio between Ti and Al (atomic% ratio)
Ti / Al is an important factor that affects the aging speed of the alloy together with the strain remaining inside the alloy. As the value of Ti / Al increases, aging is promoted, and conversely, as the value of Ti / Al decreases, The aging is delayed.

According to the present invention, Ti is used so that the aging proceeds properly during the aging treatment by using the strain generated during the cold working as a driving force.
The value of / Al is kept small. In the present invention, the solution heat treatment after cold working can be omitted during the production of heat-resistant parts, so that the production cost of heat-resistant parts can be further reduced.

In the present invention, C, Si, Mn, C
r, Nb + Ta, Ti, Al, Ni, Cu, and one or more of W, Mo, V,
%, Mo: ≤ 3%, V: ≤ 1% and 1 / 2W + Mo +
V: Can be contained in a range of ≦ 3% (claim 2). These are solid-solution strengthening elements, and by including these elements, the strength of the heat-resistant alloy can be effectively increased.

In the present invention, Ni + Co: 25-45
%, Co: ≦ 5% (claim 3). Co has almost the same effect as Ni, and thus Co can be contained up to a range of 5% by partially substituting Ni.

In the present invention, Ti, Al, Nb, and Ta can be set to Ti + Al + Nb + Ta: 4.5 to 7.0% by atom% (claim 4), and is an index indicating the stability of the γ phase. M: ≦ 0.95 (claim 6). Further, if necessary, one or two of B and Zr may be used in an amount of 0.001 to 0.01% of B and 0.001 to 0% of Zr.
It can be contained in the range of 1% (claim 7). By containing these B and Zr, the grain boundaries can be strengthened.

In the present invention, Ca + Mg is further converted to Ca + M
g: 0.001 to 0.01% can be contained (claim 8), thereby improving hot workability.

Further, if P, S, O, N are P: ≦ 0.02%,
S: ≦ 0.01%, O: ≦ 0.01%, N: ≦ 0.01
% (Claim 9). These are impurity components, and by controlling these impurity components within the above range, the properties of the heat-resistant alloy can be further improved.

As is clear from the above description, the heat-resistant alloy of the present invention exhibits its original features when subjected to direct aging treatment without performing solution heat treatment after cold working.

Next, the reasons for limiting each chemical component in the present invention will be described in detail. C: 0.01% to 0.1% C, by adding 0.01% or more of Ti, Nb, Cr
Improves the high temperature strength of the alloy by forming carbides in combination with the alloy. On the other hand, when the content is more than 0.1%, a large amount of MC carbide is precipitated to lower the hot workability of the alloy, and at the time of working, the carbide serves as a starting point to generate a flaw. Therefore, in the present invention, the content is 0.01 to 0.1.
Specify within the range of 1%.

Si: ≦ 2% Si is useful as a deoxidizing element and improves oxidation resistance. However, if the content exceeds 2%, the cold workability of the alloy decreases, so the upper limit is set to 2%.

Mn: ≦ 2% Mn is useful as a deoxidizing element like Si, but when contained in a large amount, not only impairs the high-temperature oxidation properties of the alloy but also impairs the toughness of the η phase (Ni ₃ Ti). The upper limit is set to 2% to promote precipitation.

Cr: 12 to 25% Cr is a useful element for improving the high-temperature oxidation and corrosion of the alloy. Therefore, it is necessary to contain 12% or more of Cr. However, when the content exceeds 25%, the austenite phase becomes unstable, the σ phase which is an embrittlement phase precipitates, and the toughness of the alloy decreases. Therefore, in the present invention, the upper limit of Cr is set to 2
5%. A desirable range of Cr is 12 to 20%.

Nb + Ta: 0.2 to 2.0% Nb and Ta are both γ 'phase (γ prime phase) and Ni ₉ (Al,
Ti, Nb, Ta) is an element that forms the γ ′ phase, which can effectively increase the high-temperature strength of the alloy. However, in order to obtain the effect, it is necessary to contain Nb + Ta in an amount of 0.2% or more. However, if the content exceeds 2.0%, δ-phase Ni ₃ (Nb, Ta) precipitates, and the toughness of the alloy decreases. Therefore, in the present invention, the upper limit is set to 2.0%.

Ti: less than 1.5% Ti combines with Ni, Al, Nb and Ta to form a γ 'phase. However, when the content is 1.5% or more, the content of Ti becomes relatively larger than the content of Al, and aging is excessively promoted. Therefore, in the present invention, Ti
Is regulated to a smaller amount up to 1.5%.

Al: 0.5-3.0% Al is the most important element that combines with Ni to form a γ ′ phase. If the content is less than 0.5%, the precipitation amount of the γ ′ phase becomes insufficient.
%. On the other hand, when the content exceeds 3.0%, the hot workability of the alloy decreases. Therefore, in the present invention, the upper limit is set to 3.0%.

Ni: 25 to 45% Ni is an element forming austenite which is a matrix of the alloy, and improves the heat resistance and corrosion resistance of the alloy. Further, it is an essential component for precipitating the γ ′ phase as a strengthening phase. In addition, Ni has a function of stabilizing the structure at a high temperature, and in order to sufficiently exhibit these effects, Ni is required.
% Or more. On the other hand, if it is contained in a large amount exceeding 45%, the cost of the alloy is increased because such Ni is an expensive element, so that the object of the present invention cannot be achieved. In addition, this N
In the present alloy, i increases the hardness in the solid solution state and lowers the cold workability. Therefore, in the present invention, the upper limit of the content is set to 45%.

Cu: 0.1-5.0% Cu is an essential component for enhancing the cold workability of the alloy. As described above, Cu has the function of increasing stacking fault energy to suppress work hardening, and effectively improves cold workability by its action. However, if the content is less than 0.1%, a sufficient effect cannot be expected, and if the content exceeds 5.0%, the effect is little improved and the hot workability is deteriorated. Therefore, in the present invention, the content of Cu is set to 0.1 to 5.0%. A desirable content range is 0.5 to 3.0%.

W: ≤ 3% Mo: ≤ 3% V: ≤ 1% 1 / 2W + Mo + V: ≤ 3% W, Mo, and V are elements that improve high-temperature strength by solid solution strengthening. When W and Mo are added in excess of 3% and V is added in excess of 1%, the effect tends to be saturated, and the cost increases and the cold workability decreases, so the content is reduced to 1 / 2W + Mo.
+ V: ≦ 3%

Ni + Co: 25-45% Co: ≦ 5% Co has almost the same effect as Ni, and therefore Ni can be contained in the alloy in a form that partially replaces Ni. That is, Ni + Co: Co within a range satisfying the condition of 25 to 45%.
Can be contained in the alloy. However, Co
Is an expensive element compared to Ni, so the upper limit is 5.0%
And

Ti + Al + Nb + Ta: 4.5 to 7.0 atomic% Ti, Al, Nb, and Ta are all constituent elements of the γ ′ phase. If there is a sufficient amount of Ni, the amount of precipitation of the γ 'phase is proportional to the sum of the contents of these elements. The high temperature strength of the alloy is proportional to the amount of the γ 'phase precipitated. In the present invention, in order to sufficiently develop the high-temperature strength of the alloy, it is necessary to contain 4.5 atomic% or more. On the other hand, if the total exceeds 7.0 atomic%, the strength increases but the hot workability decreases. Therefore, in the present invention, the upper limit of the total sum of these elements is set to 7.0 atomic%.

Ti / Al: ≦ 1.0 (atomic% of each element) The η phase (Ni ₃ Ti) of the intermetallic compound which precipitates during long-time use at a high temperature deteriorates the mechanical properties of the alloy. The precipitation of the η phase depends on the ratio of the Ti content to the Al content (Ti / Al)
Depends on. That is, as the ratio of Ti / Al increases, η
Precipitation of the phase is likely to occur. Therefore, in the present invention, the value of Ti / Al is set to 1.0 or less so that the η phase does not precipitate after long-time use, and that aging does not excessively proceed when directly aging after cold working. Note that Ti / A
A desirable lower limit of 1 is 0.2.

M: ≦ 0.95 where M = (0.717Ni + 0.858Fe + 1.1
42Cr + 1.90Al + 2.271Ti + 2.117
Nb + 2.224Ta + 1.001Mn + 1.90Si
+0.615 Cu) / 100 (where each element is atomic%) This M is an index indicating the stability of the γ phase, and this M is 0.1%.
If it exceeds 95, the intermetallic compound σ phase will precipitate. This σ phase degrades the mechanical properties of the alloy. When M is larger than 0.95, hot workability also deteriorates. Therefore, in the present invention, M is restricted to 0.95 or less.

B: 0.001 to 0.01% Zr: 0.001 to 0.1% B and Zr segregate at crystal grain boundaries to strengthen the grain boundaries. The effect is sufficiently exhibited when the content is 0.001% or more. However, if the content of B exceeds 0.01% and the content of Zr exceeds 0.1%, hot workability is impaired, so the content is set to the respective upper limit values or less.

Ca + Mg: 0.001 to 0.01% These elements are all added as deoxidizing and desulfurizing elements when the alloy is melted, and have the effect of improving the hot workability of the alloy. The effect appears from 0.001% as Ca + Mg. However, when the content exceeds 0.01%, the hot workability is deteriorated. Therefore, the upper limit is set to 0.
01%.

P: ≦ 0.02% S: ≦ 0.01% O: ≦ 0.01% N: ≦ 0.01% These are all impurities, and P and S are alloys. Reduces hot workability. O and N form oxides or nitrides (non-metallic inclusions) and deteriorate the mechanical properties of the alloy. Therefore, in the present invention, the respective upper limits are set to 0.02%, 0.01%, 0.01%, 0.01%.
%.

[0051]

Next, embodiments of the present invention will be described in detail. 50 kg of various alloys having the chemical compositions shown in Table 1 were melted in a vacuum induction furnace according to the process of FIG. 1 to obtain an ingot.
Then, the ingot was soaked at 1100 ° C. for 16 hours, and subsequently forged and rolled in a temperature range of 1100 ° C. to 900 ° C. to obtain a round bar having a diameter of 16 mm. Then, the round bar is heated at 1050 ° C. for 30 minutes and then heat-treated under oil-cooling conditions.
A cold compression test (temperature: room temperature) was performed at 75%, and the cold workability was examined by examining the crack generation rate at that time.
Here, the cold compression test was performed in accordance with the following standards of the Japan Society for Technology of Plasticity Cold Forging Subcommittee.

[0052]

[Table 1]

[Table 2]

On the other hand, the heat-treated round bar was 750
Measurement of Vickers hardness at room temperature (load (P)) for each of the specimens that had been aged under the conditions of heating and air cooling after heating for 4 hours at 100 ° C. × 100 hours and those that had been subjected to aging treatment under the conditions of air cooling after heating at 800 ° C. × 100 hours. 1 kgf).

In addition, a compression test (cold working) was performed on the heat-treated round bar at an upsetting rate of 70%, and thereafter, it was heated at 750 ° C. for 4 hours or 100 hours and then aged under air-cooling conditions. A Vickers hardness measurement (at a load of 1 kgf) at room temperature was performed on each of the treated sample and the sample that had been heated at 800 ° C. for 100 hours and then aged under the condition of air cooling, and together with the microstructure of the sample after compression and aging treatment Observations were made.

The heat-treated round bar was drawn with a 50
% Forward extrusion, followed by heating at 750 ° C. × 4 hours, and then aging treatment under air-cooling conditions was performed on a rotating bending fatigue test at 800 ° C.

The results are shown in Tables 2 and 3.
Each test was performed under the following conditions.

[0057]

[Table 3]

[0058]

[Table 4]

<Test conditions> Cold compression forging test Crack generation rate when a test piece having a diameter of 15 mm and a height of 22.5 mm was axially upset forged and worked at an upset rate of 70% and 75%. Was evaluated to evaluate cold workability.
Here, the upsetting ratio ε is expressed by the following equation. ε = (h ₀ −h _c ) / h ₀ × 100, where h _{0 is} the original height of the test piece, h _{c is} the height of the test piece after deformation. Each test was performed for n = 5 test pieces. went.

Measurement of Hardness The Vickers hardness was measured using a Vickers hardness meter at a measurement load of 1 kg.

Fatigue Test A smooth test piece having a diameter of 8 mm was cut out from each test material after forward extrusion, and a rotary bending fatigue test was performed using an Ono-type rotary bending fatigue tester. The number of repetitions when the stress amplitude was 294 MPa was determined by averaging two samples.

From the results in Table 2, it can be seen that the heat-resistant alloy of the present invention has excellent cold workability, and that sufficient hardness can be obtained by aging after cold working. In the case of direct aging treatment after cold working, the η phase does not precipitate and the overaged state does not occur, and the hardness does not decrease so much even under a high temperature state for a long time, that is, the overaged state is reached. It turns out that it is suppressed. Table 3
From the results of the fatigue test, the heat-resistant alloy of the present invention shows that the fatigue resistance is equal or superior.

Although the embodiment of the present invention has been described in detail, this is merely an example, and the present invention can be implemented in variously modified forms without departing from the gist thereof.

[0064]

As described above, the heat-resistant alloy of the present invention has a low Ni content and is inexpensive, and has excellent cold workability, and is suitable for cold work of heat-resistant parts such as exhaust valves for automobile engines. , And the manufacturing cost of the heat-resistant component can be reduced. That is, it is possible to reduce both the cost of the heat-resistant alloy material itself and the manufacturing cost of a heat-resistant component using the same.

The heat-resistant alloy according to the present invention has one feature in that Cu is contained in a predetermined range. This Cu has a function of increasing stacking fault energy and suppressing work hardening, thereby providing a heat-resistant alloy. The cold workability in is effectively improved.

In the heat-resistant alloy of the present invention, the aging speed is suppressed by lowering the content of Ti with respect to the content of Al. Specifically, when the aging treatment is performed directly after cold working, the aging is properly performed. , Especially Ti / Al
Value: When ≦ 1.0, the aging speed is optimized, and when aging treatment is performed directly after cold working, optimal hardness and strength are exhibited without overaging, and the aging speed is high at high temperatures. When used for a long time, aging progresses over time and the overaging state is suppressed, and the life of the heat-resistant component can be extended.

[Brief description of the drawings]

FIG. 1 is a process explanatory diagram for explaining a heat-resistant alloy manufacturing process, a heat treatment, and a process of preparing various test pieces in an embodiment of the present invention.

Claims (9)

[Claims] C: 0.01 to 0.1% Si: ≦ 2% Mn: ≦ 2% Cr: 12 to 25% Nb + Ta: 0.2 to 2.0% Ti: 1.5% by weight% Less than Al: 0.5-3.0% Ni: 25-45% Cu: 0.1-5.0% Cold workability and excess characteristic characterized by having an alloy composition consisting of the balance of unavoidable impurities and Fe. Heat resistant alloy with excellent aging characteristics. 2. The method according to claim 1, wherein at least one of W, Mo, and V is W: ≦ 3% Mo: ≦ 3% V: ≦ 1% and ＷW + Mo + V: ≦ A heat-resistant alloy having excellent cold workability and overageing properties, characterized in that it is contained in the range of 3%. 3. The method according to claim 1, wherein the weight percentage is
A heat-resistant alloy having excellent cold workability and overageing properties, characterized in that it contains Ni + Co: 25-45% Co: ≦ 5%. 4. The method according to claim 1, wherein
A heat-resistant alloy having excellent cold workability and overageing characteristics, wherein i, Al, Nb, and Ta are atomic% and Ti + Al + Nb + Ta is 4.5 to 7.0%. 5. The cold working according to claim 1, wherein a ratio Ti / Al of atomic percent of Ti and Al is Ti / Al: ≦ 1.0. Alloy with excellent heat resistance and overaging characteristics. 6. The cold workability and overaging property according to claim 1, wherein M represented by the following formula is M: ≦ 0.95. Excellent heat resistant alloy. M = (0.717Ni + 0.858Fe + 1.142C)
r + 1.90Al + 2.271Ti + 2.117Nb +
2.224Ta + 1.001Mn + 1.90Si + 0.
615 Cu) / 100 (however, each element is atomic%) 7. The method according to claim 1, wherein one or two of B and Zr are further contained by weight% of B: 0.001 to 0.01% and Zr: 0. A heat-resistant alloy excellent in cold workability and overaging characteristics, characterized in that it is contained in the range of 0.001 to 0.1%. 8. The method according to claim 1, wherein Ca + Mg is contained in a range of 0.001 to 0.01% by weight of Ca + Mg. Heat-resistant alloy with excellent cold workability and overageing properties. 9. The method of claim 1, 2, 3, 4, 5, 6, 7, 8, or 9.
Wherein P, S, O, and N are each in weight% and P: ≦ 0.02% S: ≦ 0.01% O: ≦ 0.01% N: ≦ 0.01% Heat-resistant alloy with excellent cold workability and overageing characteristics.