JP7205277B2 - Heat-resistant alloy and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-resistant alloy and a method for producing the same.

In an automobile engine exhaust system, exhaust system parts such as an exhaust manifold, a turbocharger, a catalytic converter, and an exhaust pipe are connected to an exhaust gas outlet of the engine using flanges or the like. Gaskets are inserted into the joints of the flanges to ensure airtightness so that the exhaust gas does not leak to the outside.

A gasket (exhaust system gasket) used as a sealing component in the exhaust system as described above is a thin metal plate having a thickness of about 0.1 to 0.3 mm. A stepped portion called a bead is formed to surround the hole. In the exhaust system of automobiles, it is used by being sandwiched between the joints of flanges fixed with bolts and screws, and plays a role in preventing leakage of exhaust gas from the joints by the repulsive force of the bead. Since exhaust system gaskets are used under severe conditions such as being exposed to high-temperature exhaust gas for a long period of time, the beads are required to have high strength during and after holding at high temperatures. In particular, a turbo gasket used for a connecting portion with a turbocharger is used in a pressurized environment with a high temperature exceeding 700° C. and a high pressure. For this reason, a cold-rolled sheet of a precipitation-hardening Ni-based alloy such as Inconel 718 is currently used as a raw material for turbo gaskets.

However, since Ni-based alloys such as Inconel 718 contain a large amount of expensive Ni, the material cost is high. Therefore, cheaper materials are desired.

In response to such problems, for example, in Patent Document 1, C: 0.01 to 0.1%, 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%, Cu: 0.1 to 5.0%, Ti and Al The atomic % ratio Ti / Al with Ti / Al = 0.115 to 1.0
A heat-resistant alloy excellent in cold workability and overaging characteristics is disclosed, which is characterized by having an alloy composition in which the balance consists of unavoidable impurities and Fe.
In addition, in Patent Document 2, C: 0.10% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less (including 0%), S : 0.01% or less (including 0%), Ni: 25.0 to 60.0%, Cr: 10.0 to 20.0%, one or two of Mo and W are Mo + W / 2: 0 .05-5.0%, Al: more than 0.8% and 3.0% or less, Ti: 1.5-4.0%, Nb: 0.05-2.5%, V: 1.0% or less (including 0%), B: 0.001 to 0.015%, Mg: 0.0005 to 0.01%, S/Mg: 1.0 or less, N: 0.01% or less (0% (including 0%), O: 0.005% or less (including 0%), the balance being Fe and unavoidable impurities, and having a metal structure in which there is no precipitated γ' phase with an average equivalent circle diameter of 25 nm or more in the austenite matrix A metal gasket is disclosed that is characterized by:

On the other hand, recent engines are required to improve fuel efficiency and clean exhaust gas due to environmental problems, etc., and are required to burn at high temperatures. In particular, since the above-described turbocharger adjusts the gas pressure for the purpose of improving combustion efficiency, the exhaust system gasket is repeatedly exposed to high-temperature and high-pressure pressurized combustion gas for a long period of time. For this reason, the materials used for exhaust system gaskets, when held at high temperatures for long periods of time, are susceptible to overaging due to, for example, the recovery of the effects of processing (hardening), recrystallization, growth of precipitates, and coalescence. As a result, softening progresses. In addition, the bead is plastically deformed and the repulsive force is weakened. In other words, there is a problem that the sealing property is deteriorated.
In order to solve such problems, in recent years, there has been a demand for an excellent gasket that can withstand high-temperature and high-pressure operating environments. The material used for the gasket not only improves strength at high temperatures equivalent to combustion gas, but also can be processed into a shape that takes into account the deformation of the bead (as a specific example, it is possible to increase the bead height). Excellent processability is required. When the bead height is increased, the heat-resistant alloy plate applied to the gasket needs to have excellent workability at room temperature, specifically uniform elongation. However, Patent Documents 1 and 2 and others have hitherto failed to propose a heat-resistant alloy that achieves both excellent high-temperature strength and uniform elongation at room temperature.

Japanese Patent No. 3744084 WO2017/104755

The present invention has been made in view of the above problems. That is, it is an object of the present invention to provide a low-cost heat-resistant alloy excellent in high-temperature strength and uniform elongation at room temperature, which can be suitably applied to exhaust system gaskets and the like, and a method for producing the same.
In the present invention, excellent high-temperature strength and uniform elongation at room temperature means that the 0.2% yield strength at 750 ° C. is 500 MPa or more, the 0.2% yield strength at 750 ° C., and the uniform elongation at room temperature. means that the product of is 900 MPa·% or more.

As a result of intensive studies by the present inventors, it was found that both high-temperature strength and uniform elongation at room temperature can be achieved by appropriately controlling the alloy composition and controlling each process such as hot rolling, cold rolling, and annealing of the alloy. was found to be able to increase
The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) In mass%, C: 0.0003 to 0.0200%, Si: 0.02 to 2.00%, Mn: 0.02% to 2.00%, P: 0.050% or less, S : 0.0100% or less, Cr: 12.00% or more and less than 30.00%, Ni: 35.0 to 60.0%, N: 0.0200% or less, Nb: more than 1.00%. 50% or less, Al: more than 2.00%, 4.00% or less, Ti: 0-0.80%, V: 0-1.00%, Mo: 0-5.00%, W: 0-5 .00%, Cu: 0-1.00%, Co: 0-1.00%, B: 0-0.0100%, Zr: 0-0.0100%, Ca: 0-0.0050%, Mg : 0 to 0.0050%, with the balance being Fe and impurities, having a 0.2% yield strength at 750 ° C. of 500 MPa or more, and the above at 750 ° C. in units of MPa A heat-resistant alloy in which the product of 0.2% proof stress and uniform elongation at normal temperature in unit % is 900 MPa·% or more.
(2) The heat resistance according to (1), wherein the ratio of the maximum and minimum values of the total content of Al and Nb in elemental point analysis, in mass%, is 1.5 or more. alloy.
(3) In mass%, Ti: 0.10 to 0.80%, V: 0.10 to 1.00%, Mo: 0.50 to 5.00%, W: 0.02 to 5.00% , Cu: 0.01 to 1.00%, Co: 0.10 to 1.00%, or two or more thereof.
(4) In mass%, B: 0.0002 to 0.0100%, Zr: 0.0002 to 0.0100%, Ca: 0.0002 to 0.0050%, Mg: 0.0002 to 0.0050% The heat-resistant alloy according to any one of (1) to (3), containing one or more of
(5) A method for producing a heat-resistant alloy according to any one of (1) to (4), which comprises a solution heat treatment step of heating the alloy to 1050° C. or higher and holding it for 5 seconds or longer, and the solution heat treatment. A first cooling step of cooling the alloy after the step to a first temperature range of 750 to 850 ° C. at an average cooling rate of 15 ° C./sec or more, and cooling the alloy after the first cooling step to the first temperature. a second cooling step of cooling the alloy after the holding step to a second temperature range of 450° C. or less at an average cooling rate of 15° C./sec or more; A method for producing a heat-resistant alloy, comprising a temper rolling step of rolling the alloy after the second cooling step with a cumulative reduction rate of 3 to 45%.

According to the present invention, it is possible to provide an inexpensive heat-resistant alloy excellent in high-temperature strength and uniform elongation at room temperature, and a method for producing the same. Such a heat-resistant alloy can be suitably applied to exhaust system gaskets and the like.

The heat-resistant alloy according to one embodiment of the present invention (heat-resistant alloy according to the present embodiment) has, in mass %, C: 0.0003 to 0.0200%, Si: 0.02 to 2.00%, Mn: 0 .02% to 2.00%, P: 0.050% or less, S: 0.0100% or less, Cr: 12.00% or more and less than 30.00%, Ni: 35.0 to 60.0%, N: 0.020% or less, Nb: more than 1.00%, 3.50% or less, Al: more than 2.00%, 4.00% or less, and if necessary, Ti: 0.80 % or less, V: 1.00% or less, Mo: 5.00% or less, W: 5.00% or less, Cu: 1.00% or less, Co: 1.00% or less, B: 0.0100% or less , Zr: 0.0100% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, and the balance being Fe and impurities.
In addition, the heat-resistant alloy according to the present embodiment has a 0.2% yield strength at 750 ° C. of 500 MPa or more, a 0.2% yield strength (MPa) at 750 ° C., a uniform elongation (%) at room temperature, is 900 MPa·% or more. In general, the strength and elongation of a material show a trade-off relationship, but the heat-resistant alloy according to this embodiment provides high strength and high uniform elongation.

The reasons for each limitation will be described below.

<About the organization>
[0.2% yield strength at 750°C is 500 MPa or more]
[The product of the 0.2% proof stress (unit: MPa) at 750 ° C. and the uniform elongation (unit: %) at normal temperature is 900 MPa · % or more]
The heat-resistant alloy according to the present embodiment is manufactured by controlling the chemical composition and the manufacturing method within an appropriate range as described later. When used, a fine and dense γ' phase precipitated structure is obtained. More precisely, by controlling the chemical composition and manufacturing method within an appropriate range, it is believed that the precipitation of the γ' phase based on spinodal decomposition can be controlled. A structure (concentration modulation structure) is formed in which the concentrated regions are periodically and finely dispersed in the matrix austenite. Alternatively, a mixed structure is formed in which fine γ' phases are precipitated in some of them. Periodically means that multiple and equal numbers are observed at regular intervals. Fine means that the equivalent circle diameter is about 100 nm or less. Further, the enriched region indicates a region where the γ' phase forming element has a higher value than the average content of the base material.
A general γ' phase is a compound represented by Ni ₃ (Al, Nb, Ti) containing Ti, and is composed of three Ni atoms and one other element (Al, Nb, Ti). be done. This γ' phase is considered to exhibit an inverse temperature dependence in which the strength increases with increasing temperature. In the γ' phase and the enriched region, Ti may be enriched.

When the heat-resistant alloy is heated to a high temperature of about 750°C, the γ' phase is precipitated in the concentrated region of the γ' phase forming element. It is considered that the γ' phase precipitates periodically and finely because the concentrated regions are periodically and finely dispersed. Good high temperature strength is obtained when the distribution of the concentrated regions is short, dense and uniform. If the concentrated regions are not periodically and finely dispersed (for example, if they are aggregated and coarse), the precipitated γ' phase will also be coarse and have a low density, and the high-temperature strength will not be sufficiently improved. That is, it is presumed that the γ' phase that precipitates at high temperature can also be controlled by controlling the enriched region.
Since Al and Nb, which are γ'-phase-forming elements, are also solid-solution strengthening elements for the austenite phase that forms the matrix, the concentrated region becomes a harder region than the surroundings. Therefore, when the concentrated regions of the γ' phase-forming element are periodically and finely dispersed, the strength is improved by solid solution strengthening and dispersion strengthening. Even when used at high temperatures, a high-density and fine γ' phase precipitates, and even when held for a long time, the growth and coalescence of precipitates is thought to delay softening due to overaging. Precipitation strengthening is maintained. That is, overaging is suppressed and high strength is maintained. On the other hand, if the enriched regions and the γ' phase are finely dispersed, the uniform elongation hardly decreases. That is, it is considered that excellent workability is maintained. A high uniform elongation allows the formation of high beads.

When Ni, Al, and Nb are precipitated as a γ' phase at the stage of the heat-resistant alloy, the strength is increased, but the uniform elongation is decreased. Furthermore, when the exhaust system gasket is used at high temperatures thereafter, softening due to overaging, which is partly caused by the growth and coalescence of precipitates, is accelerated. Therefore, precipitation of the γ' phase is allowed as long as it is fine and in a small amount.

Although it is not easy to observe that the concentration modulated structure described above is obtained over the entire heat-resistant alloy, the 0.2% proof stress at 750 ° C. is 500 MPa or more, and the 0.2% proof stress at 750 ° C. If the product of (unit: MPa) and the uniform elongation at normal temperature (unit: %) is 900 MPa·% or more, it can be determined that the concentration modulation structure described above is obtained. Therefore, in the heat-resistant alloy according to the present embodiment, the 0.2% yield strength at 750 ° C. is 500 MPa or more, and the 0.2% yield strength at 750 ° C. (unit: MPa) and uniform elongation at room temperature (unit: %) and the product of 900 MPa·% or more is used as an index of the structure.

Since the heat-resistant alloy according to the present embodiment has the structure described above, the 0.2% proof stress at 750° C. is 500 MPa or more, so that sufficient high-temperature strength can be obtained when the heat-resistant alloy is used as a gasket. In addition, since it has excellent uniform elongation at room temperature, it has good workability when processed into a gasket, and can be processed into a gasket having a high bead height.

High-temperature strength and uniform elongation at room temperature can be obtained by the following methods.
A JIS No. 13 B tensile test piece described in JISG0567:2012 was taken from the direction (L direction) parallel to the rolling direction of the heat-resistant alloy, and a tensile test was performed at 750 ° C. in accordance with JISG0567:2012. Measure strength.
In addition, in order to evaluate the strength and elongation at room temperature, the uniform elongation is measured according to JISZ2241:2011 using a tensile test piece taken in the same manner. At that time, 0.2% yield strength at room temperature can also be measured.

[In mass %, the maximum/minimum value, which is the ratio of the maximum and minimum contents of Al and Nb in elemental point analysis, is 1.5 or more]
In the heat-resistant alloy according to the present embodiment, in the concentration modulation structure, the maximum/minimum value, which is the ratio of the maximum and minimum total contents of Al and Nb in elemental point analysis, is 1.5 or more. is preferably
When the maximum value of the total content of Al and Nb is 1.5 times or more the minimum value of the total content of Al and Nb, it becomes a clear enrichment that exceeds the measurement error, and the high temperature strength of the material is clear and rise significantly. Although it is not necessary to limit the upper limit, if Ni ₃ Al and Ni ₃ Nb are the upper limits of each compound, the content is 25 atomic %. That is _, about 13.3% by mass of Al in Ni ₃ Al and about 34.5% by mass of Nb in Ni ₃ Nb. A value of 34.5% by mass is obtained. In the heat-resistant alloy according to the present embodiment, the total of the Al content and the Nb content is more than ^3.0 % by mass. The maximum/minimum value is about 11.5 or less. However, in the process of forming the compound, if the compound is in a fine state of less than 1 nm ³ during the formation process, the value may change due to the inclusion of (other elements of) the base material. There is

The ratio between the maximum and minimum total contents of Al and Nb can be determined by three-dimensional elemental mapping using a three-dimensional atom probe (3D-AP). A sample is processed from the vicinity of the half position (t/2) of the thickness t of the alloy plate, and the measurement area is 0.005 μm ³ or more. The mass % of an element at each measurement point is expressed as a ratio of the number of atoms measured in a constant volume of surroundings (1 nm ³ ).

<About chemical composition>
C: 0.0003% to 0.0200%
C is an element that combines with Ti and Nb to form carbide. When Ti and Nb form carbides, the amount of γ' phase, which is a strengthening phase that contributes to the improvement of high-temperature strength, decreases. Therefore, a lower C content is desirable. Therefore, the C content should be 0.0200% or less.
On the other hand, if the C content is less than 0.0003%, the manufacturing cost increases significantly. Therefore, the C content is made 0.0003% or more.

Si: 0.02% to 2.00% Si is an element effective as a deoxidizing element during refining. Si is also an element that improves the oxidation resistance and high-temperature strength of the alloy. In order to obtain these effects, the Si content is set to 0.02% or more. Preferably, it is 0.030% or more.
On the other hand, if the Si content is too high, the alloy becomes hard and workability deteriorates. Therefore, the Si content is set to 2.00% or less. It is preferably 1.50% or less, more preferably 1.00% or less.

Mn: 0.02% or more and 2.00% or less If the Mn content is too high, the hot workability deteriorates, and the oxidation resistance at high temperatures remarkably deteriorates. Therefore, the Mn content should be 2.00% or less.
On the other hand, Mn is mixed from raw material scrap and the like, and it is necessary to reduce the use of scrap in order to greatly reduce the Mn content. Reducing scrap usage leads to increased costs. Therefore, the Mn content should be 0.02% or more. Preferably, it is 0.05% or more.

P: 0.050% or less P is an impurity element contained in ferrochromium, which is one of the raw materials of the alloy. Since P is detrimental to hot workability and toughness, the P content is limited to 0.050% or less. Preferably, it is 0.035% or less.
Since it is preferable that the P content is as small as possible, the lower limit is 0%. However, removal of P during refining is difficult, and in order to reduce the P content, it is necessary to use ferrochromium with a low P concentration as a raw material. Since ferrochrome with a low P concentration is expensive, an attempt to reduce the P content more than necessary increases the cost. Therefore, the P content may be 0.005% or more.

S: 0.0100% or less S is an impurity element contained in raw material scraps. Since S is harmful to hot workability and corrosion resistance, the S content is limited to 0.0100% or less. Preferably, it is 0.0050% or less.
Since it is preferable that the S content is as small as possible, the lower limit is 0%. However, an attempt to reduce the S content more than necessary increases the desulfurization load during refining, resulting in an increase in cost. Therefore, the S content may be 0.0002% or more.

Cr: 12.00% or more and less than 30.00% Cr is an essential element from the viewpoint of ensuring corrosion resistance as a heat-resistant alloy. From the viewpoint of ensuring sufficient corrosion resistance, the Cr content is set to 12.00% or more. Preferably it is 14.00% or more.
On the other hand, if the Cr content is too high, coarse compounds such as the σ phase are formed during annealing, the material becomes embrittled, and the workability also deteriorates. Therefore, the Cr content should be less than 30.00%. Preferably, it is 20.00% or less.

Ni: 35.0% or more and 60.0% or less Ni is a strong austenite stabilizing element and is an essential element for obtaining an austenite matrix in the microstructure. Ni is also an extremely important element for obtaining a γ' phase (Ni ₃ (Al, Nb, Ti)), which is a strengthening phase that contributes to the improvement of high-temperature strength. From the viewpoint of securing strength at high temperatures as a heat-resistant material, the Ni content is set to 35.0% or more. It is preferably 37.5% or more, more preferably 40.0% or more.
On the other hand, if the Ni content is too high, in addition to increasing the cost, the deformation resistance during hot working becomes high, making the manufacture difficult. Therefore, the Ni content is set to 60.0% or less. It is preferably 53.0% or less, more preferably 50.0% or less.

N: 0.0200% or less N is an element that combines with Al, Nb, and Ti to form nitrides. When Al, Nb, and Ti form nitrides, the amount of γ' phase, which is a strengthening phase, is reduced. Therefore, the lower the N content is, the better. Therefore, the N content is limited to 0.0200% or less. Preferably, it is 0.0150% or less.
Since the smaller the N content, the lower limit is 0%. However, if the N content is reduced more than necessary, the N removal load during refining will increase and the cost will rise. Therefore, the N content may be 0.0003% or more.

Nb: More than 1.00%, 3.50% or less Nb is an element that constitutes the γ' phase, which is a strengthening phase, and the γ' phase in which Nb is dissolved has high high-temperature strengthening ability. The Nb content is more than 1.00% in order to ensure high-temperature strength. It is preferably 1.50% or more, more preferably 1.70% or more.
On the other hand, Nb is an element that lowers the melting point of the alloy and makes hot working at high temperatures difficult. Therefore, the Nb content should be 3.50% or less. It is preferably 3.00% or less, more preferably 2.80% or less.

Al: more than 2.00%, 4.00% or less Al is an element that constitutes the γ' phase, which is a strengthening phase that contributes to an increase in high-temperature strength. Its strengthening ability is not as good as that of Ti and Nb, but compared to Ti and Nb, it has the effect of stably maintaining the γ' phase for a long time. From the viewpoint of stably maintaining high-temperature strength after long-term aging, the Al content is set to more than 2.00%. It is preferably 2.20% or more, more preferably 2.30% or more.
On the other hand, if the Al content is excessive, the melting point of the alloy is lowered, making hot working at high temperatures difficult. Therefore, the Al content is set to 4.00% or less. It is preferably 3.70% or less, more preferably 3.50% or less.

The heat-resistant alloy according to the present embodiment may contain the above elements (essential elements), and the balance may be Fe and impurities. However, in order to improve various properties, the following elements may be included instead of part of Fe. In order to reduce the alloy cost, it is not necessary to intentionally add these optional elements to the steel, so the lower limit of the content of these optional elements is 0%.
The term "impurities" refers to components that are unintentionally included from raw materials or from other manufacturing processes during the steel sheet manufacturing process.

Ti: 0-0.80%
Ti is an element that constitutes the γ' phase, which is a strengthening phase, and is an element that contributes to the improvement of high-temperature strength. Therefore, it may be contained as necessary. To obtain the above effects, the Ti content is preferably 0.10% or more.
On the other hand, when a large amount of Ti is contained and the Ti content in the γ' phase increases, the γ' phase tends to change to the η phase which does not contribute to the improvement of high-temperature strength. In addition, C, N and Ti in the alloy form coarse carbides and nitrides, significantly deteriorating hot workability and cold workability. Also, since the melting point of the alloy is lowered by the content of Ti, if the content of Ti is excessive, hot working at high temperature becomes difficult. Therefore, even if Ti is contained, the content of Ti should be 0.80% or less. Preferably, it is 0.60% or less.

V: 0-1.00%
V is an element that contributes to the improvement of high-temperature strength through solid-solution strengthening. In order to obtain this effect, it may be contained. To obtain the above effects, the V content is preferably 0.10% or more.
On the other hand, V combines with C and N to form carbides and nitrides. If the V content is too high, coarse carbides and nitrides are formed, degrading the workability of the material. Therefore, even when it is contained, the V content is set to 1.00% or less. Preferably, it is 0.80% or less.

Mo: 0-5.00%
Mo is an element that dissolves in the austenite phase, which is the matrix, and contributes to the improvement of the high-temperature strength. Therefore, it may be contained as necessary. When obtaining the above effect, it is preferable to set the Mo content to 0.50% or more.
On the other hand, if a large amount of Mo is contained, the deformation resistance during hot working increases, making it difficult to hot roll to a predetermined thickness. In addition, the precipitation of coarse Laves phases is promoted during high-temperature long-term aging, and the high-temperature strength is lowered. Therefore, even if Mo is contained, the Mo content should be 5.00% or less. Preferably, it is 4.00% or less.

W: 0-5.00%
W is an element that dissolves in the austenite matrix and contributes to the improvement of high-temperature strength. Therefore, it may be contained as necessary. In order to obtain the above effects, the W content is preferably 0.02% or more.
On the other hand, if a large amount of W is contained, the deformation resistance during hot working increases, making it difficult to hot roll to a predetermined thickness. In addition, the precipitation of coarse Laves phases is promoted during high-temperature long-term aging, and the high-temperature strength is lowered. Therefore, even when W is contained, the W content is set to 5.00% or less. Preferably, it is 4.00% or less.

Cu: 0-1.00%
Cu is an element that dissolves in the austenite matrix and has the effect of increasing the high-temperature strength. Therefore, it may be contained as necessary. In order to obtain the above effects, the Cu content is preferably 0.01% or more.
On the other hand, when the Cu content is excessive, edge cracks may occur during hot rolling. Therefore, even if Cu is contained, the content of Cu should be 1.00% or less. Preferably, it is 0.80% or less.

Co: 0-1.00%
Co is an element that forms a solid solution in the γ' phase as a substitute for Ni, and is an element that contributes to the improvement of high-temperature strength. Therefore, it may be contained. To obtain the above effects, the Co content is preferably 0.10% or more.
On the other hand, if a large amount of Co is contained, in addition to an increase in cost, the deformation resistance during hot working increases, making it difficult to hot roll to a predetermined thickness. Therefore, even if Co is contained, the Co content should be 1.00% or less. Preferably, it is 0.90% or less.

B: 0 to 0.0100%
B is an element that segregates at grain boundaries, strengthens the grain boundaries, suppresses slippage at the grain boundaries, and contributes to the improvement of high-temperature strength. Therefore, it may be contained. The B content is preferably 0.0002% or more in order to obtain the above effects due to the B content.
On the other hand, if a large amount of B is contained, the grain boundary segregation becomes remarkable, and the hot workability remarkably deteriorates. Therefore, even when it is contained, the B content is made 0.0100% or less. Preferably, it is 0.0090% or less.

Zr: 0 to 0.0100%
Zr is an element that segregates at grain boundaries, and by strengthening the grain boundaries, suppresses slippage at the grain boundaries and contributes to improvement of high-temperature strength. Therefore, it may be contained. The Zr content is preferably 0.0002% or more in order to obtain the above effects due to the Zr content.
On the other hand, if a large amount of Zr is added, the grain boundary segregation becomes remarkable, and the hot workability remarkably deteriorates. Therefore, even if Zr is contained, the Zr content should be 0.0100% or less. Preferably, it is 0.0080% or less.

Ca: 0-0.0050%
Ca is an element that has the effect of improving hot workability. Improved hot workability can reduce manufacturing costs. In order to obtain this effect, it may be contained. When obtaining the above effect, it is preferable to set the Ca content to 0.0002% or more.
On the other hand, if the Ca content is too high, troubles such as clogging of the molten metal nozzle will occur during casting, making production extremely difficult. Therefore, even when Ca is contained, the content of Ca should be 0.0050% or less. Preferably, it is 0.0040% or less.

Mg: 0-0.0050%
Mg is an element that has the effect of improving hot workability. Improved hot workability can reduce manufacturing costs. In order to obtain this effect, it may be contained. When obtaining the above effects, the Mg content is preferably 0.0002% or more.
On the other hand, if the Mg content is too high, troubles such as clogging of the molten metal nozzle will occur during casting, making production extremely difficult. Therefore, even if Mg is contained, the content of Mg should be 0.0050% or less. Preferably, it is 0.0040% or less.

As described above, the heat-resistant alloy according to the present embodiment contains the above essential elements with the balance being Fe and impurities, or contains one or more of the above essential elements and optional elements, with the balance being Fe and It has a chemical composition consisting of impurities.

<About manufacturing method>
Next, a preferred method for manufacturing the heat-resistant alloy according to this embodiment will be described. The heat-resistant alloy plate according to the present embodiment can obtain the effect as long as it has the above characteristics regardless of the manufacturing method. However, the following method is preferable because it can be produced stably.

Specifically, the heat-resistant alloy according to this embodiment can be manufactured by a manufacturing method including the following steps (a) to (e).
(a) a solution heat treatment step in which the alloy is heated to 1050 ° C. or higher and held for 5 seconds or longer; A first cooling step (c) of cooling at a cooling rate; a holding step (d) of holding the alloy after the first cooling step in the first temperature range for 10 to 30 seconds; A second cooling step (e) in which the alloy after the second cooling step is cooled at an average cooling rate of 15 ° C./s or more to a temperature range of 3 to 45%.

[Solution heat treatment step]
The heat-resistant alloy according to this embodiment contains many alloying elements, and various compounds are precipitated during the manufacturing process. Therefore, in order to obtain a structure such as that described above, a solution heat treatment is required to once dissolve the precipitates into the matrix. Therefore, solution heat treatment is performed at a temperature of 1050° C. or higher for 5 seconds or longer.
On the other hand, if the solution heat treatment temperature is too high or the treatment time is too long, the cost will increase. Therefore, it is preferable that the solution heat treatment temperature is 1200° C. or less and the holding time is 600 seconds or less.
The heat-resistant alloy to be subjected to the solution heat treatment process is not limited. For example, a steel ingot having a predetermined chemical composition (% by mass) is melted, the steel ingot is hot-rolled by hot forging and/or hot rolling, annealed and pickled, and then cold-rolled. A spread plate may be used.

[First cooling step]
[Holding step]
After the solution heat treatment step, the alloy is cooled to a temperature range of 750 to 850° C. (first temperature range) at an average cooling rate of 15° C./sec or more. After cooling, the alloy is held within this temperature range for 10-30 seconds. By holding in this temperature range, spinodal decomposition occurs and a predetermined concentration modulation structure is obtained.
If the average cooling rate to the first temperature range is less than 15° C./sec, the γ′ phase precipitates during cooling, and the desired concentration modulation structure cannot be obtained. Although it is not necessary to limit the upper limit of the average cooling rate, it may be set to 100° C./sec or less due to equipment restrictions and the like.
Further, when the retention time is less than 10 seconds, the spinodal decomposition does not proceed sufficiently, and a predetermined concentration modulation structure cannot be obtained. When the holding time exceeds 30 seconds, a large amount of γ' phase precipitates and the uniform elongation decreases.
If the cooling stop temperature is lower than 750° C., harmful precipitate phases such as σ phases are formed, and the high temperature strength is lowered. On the other hand, when the temperature exceeds 850°C, a large amount of γ' phase precipitates, and the uniform elongation decreases.

[Second cooling step]
After the holding step, the heat-resistant alloy is cooled down to 450° C. or lower (second temperature range) at an average cooling rate of 15° C./second or higher.
If the average cooling rate is less than 15°C/sec, the γ' phase may precipitate in the heat resistant alloy.

[Temperature rolling process]
The alloy after the second cooling step is subjected to rolling (pass rolling) with a cumulative reduction rate of 45% or less. High-temperature strength can be increased by performing temper rolling. From the point of view of improving the high-temperature strength, the cumulative rolling reduction is set to 3% or more. Preferably, it is 5% or more.
On the other hand, if the cumulative rolling reduction in temper rolling exceeds 45%, the uniform elongation at room temperature decreases, making working difficult.

In the method for producing a heat-resistant alloy according to the present embodiment, as described above, after the solution heat treatment, holding may be performed between the first cooling step and the second cooling step. Cool to 450°C or less at a cooling rate of 15°C/sec or more, then reheat to a temperature range of 750 to 850°C and hold for 10 to 30 seconds, average cooling rate of 15°C/sec or more and 450°C or less. It may be cooled down to 45% or less and rolled at a cumulative reduction rate of 45% or less.
In the case of a process including such reheating, it is not preferable to perform rolling after solution treatment and before reheating. If rolling is performed after solution treatment and before reheating, a phase that does not contribute to the improvement of high-temperature strength precipitates from the dislocations introduced by rolling. .

According to the manufacturing method described above, the heat-resistant alloy according to the present embodiment can be obtained.

Next, examples of the present invention will be described. The conditions in the examples are one example of conditions adopted for confirming the feasibility and effect of the present invention, and the present invention is based on this one example of conditions. It is not limited. Various conditions can be adopted in the present invention as long as the object of the present invention is achieved without departing from the gist of the present invention.

25 kg steel ingots having the chemical compositions (steel Nos. 1 to 29) described in Table 1 were melted. This steel ingot was formed into a thickness of 45 mm by hot forging. After that, the steel sheet was hot rolled to a thickness of 5.0 mm, further annealed and pickled, and then cold rolled to obtain an intermediate cold rolled sheet.
This intermediate cold-rolled sheet was subjected to solution heat treatment (heat treatment time: 2 minutes) under the conditions shown in Table 2-1, and then cooled as shown in Table 2-1. Then, under the conditions shown in Table 2-1, aging heat treatment was performed at 750 to 850°C, and cooled to 300°C at various cooling rates.
After cooling, the intermediate cold-rolled sheet was subjected to temper rolling (finish cold rolling) at the cumulative rolling reduction shown in Table 2-2.

For the cold-rolled sheet (heat-resistant alloy) produced in this way, a JIS No. 13B tensile test piece was taken from the direction (L direction) parallel to the rolling direction of each cold-rolled sheet for high-temperature strength evaluation, and JIS G 0567:2012, a tensile test was performed at 750° C. to measure the 0.2% yield strength.
In order to evaluate the strength and ductility at room temperature, the 0.2% proof stress and uniform elongation were measured using a tensile test piece taken in the same manner in accordance with JISZ2241:2011.
In addition, for some examples, the ratio of the maximum value to the minimum value of the total content of Al and Nb was determined by three-dimensional elemental mapping using a three-dimensional atom probe (3D-AP). The sample was processed from the vicinity of the half position (t/2) of the thickness t of the alloy plate, and the measurement area was set to 0.005 μm ³ or more. The mass % of the element at each measurement point was expressed as a ratio of the number of atoms measured in a constant volume (1 nm ³ ) of the surroundings. Regarding the ratio of the maximum value to the minimum value of the total content of Al and Nb, the notation of "-" in the table indicates that it has not been measured.
Table 2-2 shows 0.2% proof stress at 750°C (0.2% PS _750°C , MPa), 0.2% proof stress at normal temperature (0.2% PS _RT , MPa)) and uniform elongation (u- El _RT ,%), the product of 0.2% yield strength at 750°C and uniform elongation at room temperature (0.2% PS _750°C x u-El _RT , MPa·%).

In these tests, if the 0.2% proof stress at 750 ° C. is 500 MPa or more, and the product of the 0.2% proof stress at 750 ° C. and the uniform elongation at room temperature is 900 MPa % or more, sufficient properties determined to have
In addition, in the above-described invention examples, the maximum/minimum values of the contents of Al and Nb in elemental point analysis were all 1.5 or more. On the other hand, the values in Comparative Examples described later were all less than 1.5.

As can be seen from Tables 1 to 2-2, production No. 1, which is an example of the invention. In 1 to 20, the 0.2% proof stress at 750°C was 500 MPa or more, and the product of the 0.2% proof stress at 750°C and the uniform elongation at room temperature was 900 MPa·% or more.
On the other hand, production No. 1, which is a comparative example in which the chemical composition is outside the scope of the present invention or the production conditions are outside the scope of the present invention. In Nos. 21 to 38, either the 0.2% yield strength at 750°C or the product of the 0.2% yield strength at 750°C and the uniform elongation at room temperature did not satisfy the predetermined characteristics. It is considered that this is because the density modulation structure was not formed.

Claims (5)

in % by mass,
C: 0.0003 to 0.0200%,
Si: 0.02 to 2.00%,
Mn: 0.02% to 2.00%,
P: 0.050% or less,
S: 0.0100% or less,
Cr: 12.00% or more and less than 30.00%,
Ni: 35.0 to 60.0%,
N: 0.0200% or less,
Nb: more than 1.00%, 3.50% or less,
Al: more than 2.00%, 4.00% or less,
Ti: 0 to 0.80%,
V: 0 to 1.00%,
Mo: 0-5.00%,
W: 0 to 5.00%,
Cu: 0 to 1.00%,
Co: 0 to 1.00%,
B: 0 to 0.0100%,
Zr: 0 to 0.0100%,
Ca: 0 to 0.0050%,
Mg: 0 to 0.0050%, containing
having a chemical composition with the balance being Fe and impurities,
0.2% proof stress at 750 ° C. is 500 MPa or more, and
A heat-resistant alloy, wherein the product of the 0.2% proof stress at 750° C. in units of MPa and the uniform elongation at room temperature in units of % is 900 MPa·% or more. The maximum/minimum value, which is the ratio of the maximum and minimum values of the total content of Al and Nb in elemental point analysis, in mass%, is 1.5 or more, according to claim 1 The heat-resistant alloy described. in % by mass,
Ti: 0.10 to 0.80%,
V: 0.10 to 1.00%,
Mo: 0.50-5.00%,
W: 0.02 to 5.00%,
Cu: 0.01 to 1.00%,
3. The heat-resistant alloy according to claim 1, containing one or more of Co: 0.10 to 1.00%. in % by mass,
B: 0.0002 to 0.0100%,
Zr: 0.0002 to 0.0100%,
Ca: 0.0002 to 0.0050%,
The heat-resistant alloy according to any one of claims 1 to 3, characterized by containing one or more of Mg: 0.0002 to 0.0050%. A method for producing a heat-resistant alloy according to any one of claims 1 to 4,
A solution heat treatment step of heating the alloy to 1050 ° C. or higher and holding it for 5 seconds or longer;
a first cooling step of cooling the alloy after the solution heat treatment step to a first temperature range of 750 to 850° C. at an average cooling rate of 15° C./sec or more;
a holding step of holding the alloy after the first cooling step in the first temperature range for 10 to 30 seconds;
a second cooling step of cooling the alloy after the holding step to a second temperature range of 450° C. or lower at an average cooling rate of 15° C./sec or higher;
A temper rolling step of rolling the alloy after the second cooling step with a cumulative reduction rate of 3 to 45%;
A method for producing a heat-resistant alloy, comprising: