JP6787246B2 - Alloy original plate for heat-resistant parts, alloy plate for heat-resistant parts, and gasket for exhaust system parts of engine - Google Patents

Description

The present invention relates to an alloy original plate for heat-resistant members, an alloy plate for heat-resistant members, and a gasket for an engine exhaust system member.

A gasket used as a heat-resistant member in an automobile engine or the like is a kind of sealing material (packing) in which a stepped portion called a bead is formed on a thin metal plate having a thickness of about 0.1 to 0.3 mm.

When the gasket is sandwiched between the connecting portions of the exhaust system members of the engine, the repulsive force of the elastically deformed bead seals the leakage of exhaust gas from the connecting portion. Since gaskets are used under harsh conditions where they are exposed to the environment where high-temperature exhaust gas is present for a long time and intermittently, the gasket material has high bead settling resistance at high temperatures and high strength. It is required to be sustainable.

Among the gaskets used in automobile engines, the materials for turbo gaskets used at high temperatures of about 700 ° C are currently Ni-based Cr and Fe, as well as a considerable amount of Nb and Mo, and a smaller amount of Al and An expensive Ni-based alloy cold-rolled plate such as precipitation hardening Inconel (registered trademark) 718 containing an alloying element such as Ti is used.

Therefore, there is a strong need for an alternative material having a lower Ni composition and lower cost than heat-resistant Ni-based alloys such as Inconel 718 and Inconel 625, excellent in high-temperature strength, and high settling resistance.

Patent Document 1 describes in terms of mass%, C: 0.15% or less, Si: 1.0% or less, Mn: 0.3% or less, Ni: 30 to 49%, Cr: 10 to 18%, Al: Chemistry containing 1.6 to 3.0%, containing 1.5 to 8.0% in total of one or more elements selected from Group IVa and Group Va, and the balance being Fe and impurities. Fe-Ni—Cr based heat resistant alloys having a composition are disclosed.

In Patent Document 2, in mass%, C: 0.02 to 0.30%, Si: 0.02 to 3.5%, Mn: 0.02 to 2.5%, Ni: 10 to 50%, It contains Cr: 12 to 25%, Ti: 1.0 to 5.0%, Al: 0.002 to 1.0%, and Nb: 0.1 to 3.0%, B: 0.001 to 0.01%, Mo: Contains one or more selected from 0.1 to 4.0%, and the total content of Ti, Al and Nb is 3.0 to 7.0%, at the grain boundaries. The weight ratio of the precipitated η phase (Ni ₃ Ti) and the gamma prime γ'phase (Ni ₃ (Al, Ti, Nb)) precipitated in the matrix γ phase crystal grains is 0.01 to 30.00%. , A heat-resistant stainless steel having a hot tensile strength of 800 N / mm ² or more at 600 ° C. is disclosed.

Japanese Unexamined Patent Publication No. 7-109539 Japanese Unexamined Patent Publication No. 2000-109955

However, although these conventional techniques have the advantage that they have a lower Ni content than Ni-based heat-resistant alloys such as Inconel 718 and can be manufactured at low cost, they are inferior to Inconel 718 and the like in terms of high-temperature strength and settling resistance. Was there. There is a demand for a gasket and its material whose high temperature characteristics are comparable to those of Inconel 718 and the like while saving the amount of Ni added.

As a result of diligent studies to solve the above problems, the present inventors have reduced the Ni content and reduced the Ni content, and Al, which is a product element of the gamma prime γ'phase (Ni ₃ (Al, Ti, Nb)), It was found that by optimizing the Ti and Nb contents, the heat resistance can be maintained and improved even if the Ni content is reduced.

That is, since the mechanical properties after aging for 1 to 400 hours at 700 ° C., which is the operating temperature of the gasket for the exhaust system member, are superior to those of the conventional material Inconel 718, the exhaust system member, particularly the gasket. It was found that it can be used as a heat-resistant alloy plate for use, and further studies were carried out to complete the present invention. The present invention is as listed below.

(1) In terms of mass%, C: 0.0020 to 0.10%, Si: 0.020 to 3.0%, Mn: 0.020 to 2.0%, P: less than 0.050%, S: Less than 0.010%, Cr: 12.0% or more and less than 25.0%, Ni: more than 35.0% and less than 50.0%, N: 0.0005 to 0.020%, Al: more than 3.0% Contains 5.0% or less, Ti: more than 1.5% and less than 3.0%, Mo: 1.0 to 2.5%, Nb: 2.25 to 4.00%, Cu: less than 0.3% When the contents (% by mass) of Ti, Nb and Al are [Ti], [Nb] and [Al], respectively, [Ti] / [Al] ≧ 0.50, [Nb] / [Al] An alloy base plate for heat-resistant members that satisfies the relationship of ≧ 0.75, has a chemical composition in which the balance is Fe and impurities, and exhibits a metal structure consisting only of an austenite phase.
When heat-treated at 700 ° C. for 1 hour, it exhibits a metallographic structure in which a Ni-based intermetallic compound is present in the austenite matrix, and the Ni-based intermetallics have an overall chemical composition constituting the Ni-based intermetallic compound. An alloy original plate for heat-resistant members, wherein the chemical compositions of Ni, Ti, and Nb contained in the compound account for more than 60%, 3.5% or more, and 0.8% or more, respectively, in atomic%.

(2) The alloy original plate for heat-resistant members according to (1), wherein the hardness reduction allowance before and after heat treatment at 700 ° C. for 1 hour and then holding at 700 ° C. for 400 hours is 40 HV or less.

(3) The alloy original plate for heat-resistant members according to (1) or (2), which contains at least one type of Co: 3.0% or less and W: less than 3.0% in mass%.

(4) Any of (1) to (3) containing one or more of B: 0.01% or less, Ca: 0.005% or less, and Mg: 0.002% or less in mass%. The described alloy original plate for heat-resistant members.

(5) In terms of mass%, C: 0.0020 to 0.10%, Si: 0.020 to 3.0%, Mn: 0.020 to 2.0%, P: less than 0.050%, S: Less than 0.010%, Cr: 12.0% or more and less than 25.0%, Ni: more than 35.0% and less than 50.0%, N: 0.0005 to 0.020%, Al: more than 3.0% Contains 5.0% or less, Ti: more than 1.5% and less than 3.0%, Mo: 1.0 to 2.5%, Nb: 2.25 to 4.00%, Cu: less than 0.3% When the contents (% by mass) of Ti, Nb and Al are [Ti], [Nb] and [Al], respectively, [Ti] / [Al] ≧ 0.50, [Nb] / [Al] An alloy plate for a heat-resistant member having a chemical composition in which the balance is Fe and impurities, which satisfies the relationship of ≧ 0.75, and exhibits a metal structure in which a Ni-based intermetallic compound is present in the austenite matrix, and the Ni The chemical compositions of Ni, Ti and Nb contained in the Ni-based intermetallic compound are more than 60%, 3.5% or more and 0.%, respectively, in atomic% with respect to the entire chemical composition constituting the intermetallic compound. An alloy plate for heat-resistant members, which occupies 8% or more.

(6) The alloy plate for a heat-resistant member according to (5), wherein the hardness reduction allowance before and after holding at 700 ° C. for 400 hours is 40 HV or less.

(7) The alloy plate for a heat-resistant member according to (5) or (6), which contains one or more of Co: 3.0% or less and W: less than 3.0% in mass%.

(8) In any of (5) to (7), which contains one or more of B: 0.01% or less, Ca: 0.005% or less, and Mg: 0.002% or less in mass%. The alloy plate for heat-resistant members described.

(9) In mass%, C: 0.0020 to 0.10%, Si: 0.020 to 3.0%, Mn: 0.020 to 2.0%, P: less than 0.050%, S: Less than 0.010%, Cr: 12.0% or more and less than 25.0%, Ni: more than 35.0% and less than 50.0%, N: 0.0005 to 0.020%, Al: more than 3.0% Contains 5.0% or less, Ti: more than 1.5% and less than 3.0%, Mo: 1.0 to 2.5%, Nb: 2.25 to 4.00%, Cu: less than 0.3% When the contents (% by mass) of Ti, Nb and Al are [Ti], [Nb] and [Al], respectively, [Ti] / [Al] ≧ 0.50, [Nb] / [Al] A gasket for an engine exhaust system member having a chemical composition in which the balance is Fe and impurities, satisfying the relationship of ≧ 0.75, and exhibiting a metallographic structure in which a Ni-based metal compound is present in the austenite matrix. The chemical compositions of Ni, Ti, and Nb contained in the Ni-metal-metal compound are more than 60% and 3.5% or more, respectively, in atomic% with respect to the entire chemical composition constituting the Ni-metal-metal compound. And a gasket for the exhaust system members of the engine, which is characterized by accounting for 0.8% or more.

(10) The gasket for an engine exhaust system member according to (9), wherein the hardness reduction allowance before and after holding at 700 ° C. for 400 hours is 40 HV or less.

(11) The gasket for an engine exhaust system member according to (9) or (10), which contains one or more of Co: 3.0% or less and W: less than 3.0% in mass%.

(12) In any of (9) to (11), which contains one or more of B: 0.01% or less, Ca: 0.005% or less, and Mg: 0.002% or less in mass%. Gaskets for the engine exhaust system components described.

According to the present invention, an alloy for heat-resistant members having a lower Ni content than a conventional Ni-based heat-resistant alloy and having the same or better heat resistance (0.2% proof stress and settling resistance in a high-temperature tensile test). We can provide original plates, alloy plates for heat-resistant members, and gaskets for exhaust system members of engines.

The alloy original plate for heat-resistant members, the alloy plate for heat-resistant members, and the gasket for the exhaust system member of the engine according to the present invention will be described. In the following description, "%" with respect to chemical composition or concentration means "% by mass" unless otherwise specified. The "%" for each chemical composition of Ni, Ti and Nb in the Ni-based intermetallic compound phase means "atomic%".

1. 1. Alloy original plate for heat-resistant member and alloy plate for heat-resistant member according to the present invention (1) Chemical composition First, essential elements will be described.

(1-1) C: 0.0020 to 0.10%
C combines with Ti, Nb, Cr, etc. to form carbides, and the carbides act as a reinforcing phase. However, when the C content exceeds 0.10%, the workability of the alloy plate for heat-resistant members deteriorates. The increase in Cr carbide causes a decrease in corrosion resistance. Therefore, the C content is 0.10% or less, preferably 0.030% or less, and more preferably 0.020% or less when molding an alloy plate for heat-resistant members with a high degree of processing. is there.

On the other hand, in order to reduce the C content to less than 0.0020%, the cost at the time of refining is increased and the normal temperature strength of the alloy plate for heat-resistant members is lowered. Therefore, the C content is 0.0020% or more, preferably 0.004% or more.

(1-2) Si: 0.020 to 3.0%
Si is an element added as a deoxidizing element during refining and an element that improves the oxidation resistance of the alloy plate for heat-resistant members. If the Si content is less than 0.020%, the cost during refining increases and the oxidation resistance of the alloy plate for heat-resistant members decreases. Therefore, the Si content is 0.020% or more, preferably 0.03% or more.

However, if the Si content exceeds 3.0%, the alloy plate for heat-resistant members may be hardened and the workability may be deteriorated. Therefore, the Si content is 3.0% or less, and is preferably 1.0% or less when the alloy plate for heat-resistant members is molded with a high degree of processing.

(1-3) Mn: 0.020 to 2.0%
Like Si, Mn may be added as a deoxidizing element during refining. However, if the Mn content is less than 0.020%, the cost during refining will increase. Therefore, the Mn content is 0.020% or more, preferably 0.05% or more, and more preferably 0.07% or more from the viewpoint of refining cost.

However, if the Mn content exceeds 2.0%, the oxidation resistance of the alloy plate for heat-resistant members deteriorates at high temperatures and the material becomes hard. Therefore, the Mn content is 2.0% or less, and preferably 1.5% or less from the viewpoint of oxidation resistance and production stability of the alloy plate for heat-resistant members.

(1-4) P: Less than 0.050% P is an element harmful to hot workability and toughness. P is an impurity inevitably contained in ferrochrome as a raw material, but a content of less than 0.050% is permissible. Therefore, the P content is less than 0.050%, and is preferably 0.035% or less from the viewpoint of improving the workability of the alloy plate for heat-resistant members.

It is very difficult to remove P during refining, and it is preferable that the P concentration of the ferrochrome raw material is low in order to suppress the P content, but since low P ferrochrome is expensive, the P content is preferable. Is 0.005% or more, more preferably 0.010% or more.

(1-5) S: Less than 0.010% S is an element harmful to the hot workability and corrosion resistance of the alloy plate for heat-resistant members. S is an impurity inevitably contained in the raw material, and the lower the S content, the better the hot workability and corrosion resistance, but the content of less than 0.010% is permissible. Therefore, the S content is less than 0.010%, preferably less than 0.0030%, and even more preferably less than 0.0010%.

However, if the S content is reduced to less than 0.0002%, the desulfurization load increases and the refining cost increases. Therefore, the S content is preferably 0.0002% or more.

(1-6) Cr: 12.0 or more and less than 25.0% Cr is an essential element for ensuring the oxidation resistance and corrosion resistance of the alloy plate for heat-resistant members. If the Cr content is less than 12.0%, these effects are not exhibited. Therefore, the Cr content is 12.0% or more, and preferably 14.0% or more from the viewpoint of ensuring the oxidation resistance and corrosion resistance of the alloy plate for heat-resistant members.

On the other hand, when the Cr content is 25.0% or more, the workability and toughness of the alloy plate for heat-resistant members are deteriorated. Therefore, the Cr content is less than 25.0%, preferably 24.1% or less, and more preferably 23.5% or less from the viewpoint of manufacturing stability of the alloy plate for heat-resistant members.

(1-7) Ni: More than 35.0% and less than 50.0% Ni stabilizes the parent phase austenite, and at the same time, the intermetallic compound gamma prime γ'(Ni ₃ (Al, Ti, Nb)), gamma double prime γ "(Ni ₃ (Nb, Ti)), etc. are generated and are extremely important elements for ensuring the oxidation resistance and heat resistance of the alloy plate for heat-resistant members. Ni content. Is more than 35.0% in order to sufficiently secure the heat resistance of the alloy plate for heat-resistant members, and is preferably 37.5% or more from the viewpoint of further improving the heat resistance.

On the other hand, when the Ni content is 50.0% or more, the hot workability is lowered in addition to the increase in the alloy cost. Therefore, the Ni content is less than 50.0%, preferably 46.0% or less from the viewpoint of hot workability.

(1-8) N: 0.0005 to 0.020%
N may generate nitrides and reduce the workability of the alloy plate for heat-resistant members. Therefore, the N content is 0.020% or less, and is preferably less than 0.010% when the degree of processing required for the alloy plate for heat-resistant members is strict.

On the other hand, reducing the N content to less than 0.0005% leads to an increase in refining cost. Therefore, the N content is 0.0005% or less, and preferably 0.0010% or more from the viewpoint of manufacturing stability of the alloy plate for heat-resistant members.

(1-9) Al: More than 3.0% and 5.0% or less Al is an element constituting a Ni-based intermetallic compound such as gamma prime γ'and gamma double prime γ'that contribute to precipitation strengthening, and is Ti. The heat resistance of the alloy plate for heat-resistant members is improved without lowering the hot workability as compared with Nb and Nb. Therefore, the Al content is more than 3.0%, preferably 3.1% or more. ..

On the other hand, if the Al content exceeds 5.0%, the Ti and Nb compositions in the Ni-based intermetallic compound may be lowered, overaging may be promoted due to coarsening, and the high temperature resistance of the alloy plate for heat-resistant members may be promoted. Precipitation of the σ phase, which reduces fatigue characteristics, increases. Therefore, the Al content is 5.0% or less, and preferably less than 4.0% from the viewpoint of ensuring sufficient heat resistance.

(1-10) Ti: More than 1.5% and less than 3.0% Ti is an element that constitutes a Ni-based intermetallic compound such as gamma prime γ'and gamma double prime γ ″ that contribute to precipitation strengthening, and is Ni. , Al and Nb are important elements for ensuring the heat resistance of the alloy plate for heat-resistant members. In order to ensure the heat resistance of the alloy plate for heat-resistant members that can withstand use at 700 ° C., the Ti content is set. , 1.5% or more, preferably 1.8% or more.

On the other hand, when the Ti content exceeds 3.0%, the hot workability is deteriorated and the rolling load is increased, and the formation of an intermetallic compound phase that does not contribute to the high temperature strength of the alloy plate for heat-resistant members is promoted. Therefore, the Ti content is less than 3.0%, and is preferably less than 2.5% from the viewpoint of ensuring the production stability and high-temperature strength of the alloy plate for heat-resistant members.

(1-11) Mo: 1.0 to 2.5%
Mo is an element that greatly improves the heat resistance of the alloy plate for heat-resistant members without significantly impairing the hot workability as a solid solution strengthening element of the parent phase austenite. The Mo content is 1.0% or more, preferably 1.1% or more, in order to ensure the heat resistance of the alloy plate for heat-resistant members so that it can withstand use at a high temperature of about 700 ° C.

On the other hand, if the Mo content exceeds 2.5%, the rolling load may increase and casting cracks may occur. Therefore, the Mo content is 2.5% or less, preferably 2.0% or less.

(1-12) Nb: 2.25 to 4.00%
Nb, together with Ti, is an element that constitutes a Ni-based intermetallic compound such as gamma prime γ'and gamma double prime γ ″ that contribute to precipitation strengthening. Heat resistance that an alloy plate for heat resistant members can withstand use at 700 ° C. In order to ensure the properties, the Nb content is 2.25% or more, preferably 2.31% or more.

On the other hand, Nb tends to segregate in the vicinity of the grain boundaries of dendritic crystals during solidification, and the hot workability is lowered due to the local increase in strength and the increase in precipitates at the grain boundaries. Therefore, the Nb content is 4.00% or less, preferably 3.50% or less from the viewpoint of hot workability.

(1-13) Cu: Less than 0.3% Cu has a low melting point, and when it exists at a high concentration, it causes melt embrittlement during hot forging and hot rolling, and deteriorates hot workability. Therefore, the Cu content is less than 0.3%, and the lower the Cu content, the better the hot workability, so it is preferably less than 0.10%.

(1-14) [Ti] / [Al] ≧ 0.50, [Nb] / [Al] ≧ 0.75
When the contents (mass%) of Ti, Nb and Al are [Ti], [Nb] and [Al], respectively, the above relationship is satisfied. The reason for this will be explained.

In order to solve the above-mentioned problems, the present inventors have investigated a chemical composition utilizing a Ni-based intermetallic compound phase such as gamma prime γ'and gamma double prime γ', which are effective for high-temperature strengthening of alloy plates for heat-resistant members. , A cold rolled plate was prototyped.

As a result, depending on the chemical composition of Al, Ti, and Nb, which are constituent elements of the Ni-based intermetallic compound phase such as gamma prime γ'and gamma double prime γ', within the gamma prime γ'or gamma double prime γ' Despite the reduction of Ni content, Inconel 718's high-temperature use performance of alloy plates for heat-resistant members, which is indicated by 0.2% resistance at 700 ° C and hardness change (sag resistance) before and after aging at 700 ° C. It turned out to be equal to or better than the high temperature use performance.

Specifically, the chemical composition of the alloy plate for the heat-resistant member is within a certain predetermined range, the Ni composition in the precipitated Ni-based intermetallic compound phase exceeds 60% in atomic%, and the Ti composition is 3.5%. As described above, when the Nb composition is 0.8% or more, the hardness reduction allowance before and after aging at 700 ° C. for 400 hours is 40 HV or less.

In order to make the Ni composition, Ti composition and Nb composition in the Ni-metal-metal compound phase in this way, the chemical composition of the alloy plate for the heat-resistant member is set to A value: [Ti] / [Al] ≥ 0.50, B. Value: [Nb] / [Al] ≥ 0.75, and the material to be rolled using an induction heating (IH) device or the like between rough rolling and finish rolling in the hot rolling process of the alloy plate for heat-resistant members. The whole may be reheated, the cold rolling ratio of the final cold rolling may be 70% or less, and the aging treatment at 700 ° C. for 1 hour or more may be performed after the cold rolling.

Therefore, in the present invention, the A value: [Ti] / [Al] is 0.50 or more, preferably 0.51 or more, and more preferably 0.53 or more. The B value: [Nb] / [Al] is 0.75 or more, preferably 0.76 or more, and more preferably 0.77 or more.

Next, arbitrary elements contained as necessary will be described.
(1-15) One type of Co: Co: 3.0% or less and W: less than 3.0% acts as a solid solution strengthening element in the matrix austenite, and also in the operating temperature range of the alloy plate for heat-resistant members. It is an element that promotes the formation of gamma prime γ'that contributes to precipitation strengthening. However, if the Co content exceeds 3.0%, the alloy cost increases and casting cracks occur. Therefore, the Co content is 3.0% or less, preferably 2.5% or less. The Co content is preferably 0.10% or more in order to surely obtain the above-mentioned effect by containing Co.

Like Co, W is also an element that improves high-temperature strength as a solid solution strengthening element in the matrix austenite. However, if the W content is 3.0% or more, in addition to an increase in alloy cost, an increase in rolling load and casting cracking are caused. Therefore, the W content is less than 3.0%, preferably 2.0% or less. In order to surely obtain the above-mentioned effect by containing W, the W content is preferably 0.02% or more.
Co and W may be contained alone or in combination of the two.

(1-16) B: 0.01% or less, Ca: 0.005% or less, and Mg: 0.002% or less

B, Ca and Mg are all elements that contribute to the improvement of hot workability and moldability of the alloy plate for heat-resistant members. However, if the contents of B, Ca and Mg are excessive, not only the hot workability is deteriorated, but also casting cracking and nozzle clogging of the molten metal nozzle in the casting equipment may occur. Therefore, the B content is 0.01% or less, the Ca content is 0.005% or less, and the Mg content is 0.002% or less. In order to surely obtain the above-mentioned effect by containing B, Ca and Mg, the B content is preferably 0.0002% or more, the Ca content is preferably 0.0002% or more, and the Mg content is contained. The amount is preferably 0.0002% or more.

B, Ca and Mg may be contained alone or in combination of two or more.

(1-17) Remaining Remaining other than the above is Fe and impurities. Impurities include those contained in raw materials such as ore and scrap, and those contained in the manufacturing process.

(2) Chemical Compositions of Ni, Ti, and Nb in Ni-Intermetallic Compound Phase As described above, the alloy plate for heat-resistant members according to the present invention is austenite matrix after aging treatment at 700 ° C. for 1 hour or more. Ni-based intermetallic compounds are precipitated from. The chemical compositions of Ni, Ti and Nb account for more than 60%, 3.5% or more and 0.8% or more, respectively, in atomic% with respect to the total chemical composition constituting the Ni-based intermetallic compound. As a result, the hardness reduction allowance in the cross section of the alloy plate for heat-resistant members before and after aging at 700 ° C. for 400 hours becomes 40 HV or less.

Elements constituting the Ni-based intermetallic compound other than Ni, Ti, and Nb include Fe, Cr, Al, Mo, and Cu, and contain the above-mentioned optional elements (Co, W, B, Ca, Mg). In some cases, these elements are also included. For the austenite phase and the Ni-based intermetallic compound, the phases are identified by the electron diffraction image of a transmission electron microscope (TEM). Regarding the chemical composition of Ni, Ti and Nb contained in the Ni-based intermetallic compound, the Ni-based metal observed for each sample using an X-ray detector mounted on a scanning electron microscope (SEM). Arbitrarily select 5 intermetallic compounds, perform point analysis, and use the arithmetic average value of the atomic% as the content of each element.

(3) Hardness reduction allowance before and after holding at 700 ° C. for 400 hours The hardness reduction allowance before and after holding at 700 ° C. for 400 hours indicates the high temperature sagging resistance of the alloy plate and gasket for heat-resistant members according to the present invention. It is an index. Since a turbo gasket, which is a type of gasket, is exposed to high-temperature exhaust gas at around 700 ° C. for a long period of time, it is required to have sufficient high-temperature settling resistance with little bead settling even in such an environment.

The alloy plate used for the gasket has a decrease in hardness due to the coarsening of the Ni-based intermetallic compound during use, and the decrease in hardness causes the gasket to settle, thus exhibiting settling resistance during high-temperature use. As an index, the reduction allowance of hardness before and after holding at 700 ° C. for 400 hours is used.

The reason for limiting the holding time to 400 hours is that the decrease in hardness when held at 700 ° C. may change the hardness particularly after the lapse of 200 to 300 hours, and the amount of change after the lapse of 400 hours. This is because the hardness tends to decrease gradually with the passage of time.

In the gasket and the alloy plate for heat-resistant members according to the present invention, the hardness reduction allowance after aging heat treatment at 700 ° C. for 400 hours is set to 40 HV or less in Vickers hardness. When the hardness reduction allowance is more than 40 HV, the settling when used as a gasket is large, which causes a decrease in fuel consumption and generation of abnormal noise.

The decrease in hardness during use is caused by the coarsening of the Ni-based intermetallic compound responsible for strengthening and the change to another intermetallic compound that does not contribute to strengthening. The settling speed at this time is almost unchanged even in a material that has been subjected to aging heat treatment at a high temperature in advance or a material that has been used as a gasket for a certain period of time.

Therefore, the hardness reduction allowance before and after holding the material simulating the exhaust gas environment by aging heat treatment in the range of 600 to 800 ° C. and the gasket used in various exhaust gas environments at 700 ° C. for 400 hours, respectively. Even when investigated, the hardness reduction allowance does not exceed 40 HV.

In order to suppress the increase in the rate of settling in this way, microstructure control for suppressing the coarsening of Ni-based intermetallic compounds responsible for strengthening γ'etc. is an important factor, and Ni-based intermetallic compounds The chemical composition of Ni, Ti and Nb contained has a great influence.

2. Method for Manufacturing Alloy Original Plate for Heat-Resistant Members and Alloy Plate for Heat-Resistant Members According to the Present Invention A slab having the above-mentioned chemical composition is roughly rolled and finish-rolled hot to obtain a hot-rolled alloy plate. The alloy original plate for heat-resistant members according to the present invention is produced by repeatedly performing annealing (including solution heat treatment) and cold rolling. The final thickness of the alloy original plate for heat-resistant members is about 0.1 to 0.3 mm.

At this time, the material to be rolled is heated (reheated) between the rough rolling and the finish rolling, and the cold rolling ratio of the final cold rolling is set to 70% or less. The alloy plate for heat-resistant members according to the present invention is produced by subjecting the alloy original plate for heat-resistant members to an aging treatment. The aging treatment may be carried out, for example, by heating at 700 ° C. for 1 hour or longer.

As described above, the Ni composition in the Ni-based metal compound phase is 60% or more in atomic%, the Ti composition is 3.5% or more in atomic%, and the Nb composition is 0.8% or more in atomic%. In order to achieve the above-mentioned A value: [Ti] / [Al] ≧ 0.50, B value: [Nb] / [Al] ≧ 0.75, rough rolling and finish rolling in the hot rolling process. During this period, the entire material is reheated using an induction heating (IH) device, etc., the cold rolling ratio of the final cold rolling is reduced to 70% or less, and after the cold rolling, aging treatment at 700 ° C. for 1 hour or more is performed. Do.

Reheating after rough rolling suppresses the temperature drop during hot rolling to prevent ear cracking, and affects the chemical composition of the Ni-based intermetallic compound phase precipitated after cold rolling. That is, the finish rolling temperature of hot rolling can be raised by utilizing reheating. As a result, the crystal grains are coarsened in the metal structure after hot rolling and after final cold rolling or final annealing, and the dislocation density after hot rolling is reduced.

Since such a metal structure has a low dislocation density, the formation rate of the Ni-based intermetallic compound phase at the grain boundaries increases. Further, it is considered that Ti and Nb are segregated at the grain boundaries, and the amount of Ti and Nb segregated per unit area of the grain boundaries increases due to coarse graining. Therefore, a Ni-based intermetallic compound phase having a higher Ti and Nb composition is generated from the grain boundaries.

At this time, the Ni-based intermetallic compound phase having a low Ti and Nb composition precipitated from the crystal grains does not affect the heat resistance of the alloy plate for heat-resistant members even if it is precipitated up to a certain amount, but if it is excessively precipitated. The alloy plate for heat-resistant members softens due to overaging during long-term aging. Therefore, the final cold rolling ratio is set to 70% or less, and dislocations that become nucleation sites in the crystal grains are suppressed to a certain amount or less.

The reason why the chemical composition of the alloy plate for heat-resistant members and the Ti and Nb compositions in the Ni-based intermetallic compound phase affect the hardness change before and after aging at 700 ° C. is not clear, but the Al content is set to a certain amount or more. As a result, the amount of precipitation of the Ni-based intermetallic compound phase increases significantly, and elements such as Ti and Nb, which have a slow diffusion rate in the matrix at 700 ° C., are contained in the precipitated Ni-based intermetallic compound phase. It is presumed that the synergistic effect of a large amount of solid dissolution slows down the growth rate of the Ni-based intermetallic compound phase, thereby reducing the change in hardness before and after aging at 700 ° C.

3. 3. Gasket according to the present invention The gasket according to the present invention is made of the above-mentioned alloy original plate for heat-resistant members according to the present invention, processed into a predetermined gasket shape, and attached as a part of an engine exhaust system member. Since the exhaust system member is heated to around 700 ° C. by using the engine, the processed alloy original plate for the heat-resistant member is aged to become the gasket according to the present invention. That is, the gasket according to the present invention has the above-mentioned chemical composition, and the compositions of Ni, Ti and Nb in the Ni-based intermetallic compound phase are more than 60%, 3.5% or more and 0 in atomic%, respectively. It has a characteristic of 8.8% or more.

Further, the gasket according to the present invention has a hardness reduction allowance of 40 HV or less in terms of cross-sectional hardness before and after holding at 700 ° C. for 400 hours.

Like other gaskets, the gasket according to the present invention has a bead such as a so-called half bead or full bead. The gasket according to the present invention seals the leakage of exhaust gas from the connecting portion by the repulsive force of the elastically deformed bead when it is sandwiched between the connecting portions of the exhaust system members of the engine.

The alloy original plate for heat-resistant members, which is the material of the gasket, exhibits a state before the Ni-based intermetallic compound is precipitated, that is, an austenite single-phase metal structure, and therefore has good workability. The alloy original plate for heat-resistant members according to the present invention is less likely to crack when the shape of the gasket is machined or the bead is formed, which contributes to the manufacturing quality of the gasket.

The gasket according to the present invention has a lower Ni content and heat resistance (0.2% proof stress at 700 ° C. and hardness before and after 700 ° C. aging) as compared with conventional gaskets made of Ni-based heat-resistant alloys such as Inconel 718. High temperature use performance indicated by hardness change (sag resistance)) is equal to or better than that.

The present invention will be described in more detail with reference to Examples.
A 25 kg alloy ingot having the chemical composition (mass%, balance Fe and impurities) shown in Tables 1 and 2 was melted. Tables 1 and 2 show the above-mentioned A and B values.

This alloy ingot was hot forged to obtain an alloy ingot having a thickness of 45 mm, and further hot rolled to obtain a hot-rolled plate having a plate thickness of 5.0 mm. At this time, in order to simulate reheating (IH heating) after rough rolling in an actual machine for some samples, the samples are placed in an atmospheric furnace at 1100 ° C. immediately after rough rolling, heated for 30 minutes, and then extracted. Then, finish rolling was performed immediately.

With respect to the hot-rolled plate thus obtained, a cold-rolled plate having a plate thickness of 0.2 mm was produced by repeating solution treatment and cold rolling at 1100 ° C.

The cold-rolled plate thus obtained was subjected to a tensile test at 700 ° C., a hardness measurement of the cross section as it was cold-rolled and after 400 hours of aging at 700 ° C. The tensile test at 700 ° C. was performed by a test method conforming to JIS G 0567. Regarding the measurement of the hardness of the cross section, the Vickers hardness test conforming to JIS Z 2244 was performed under the condition of a load of 500 grams (for the central part of the plate thickness in the L cross section (plate thickness cross section parallel to the rolling direction) of the cold-rolled plate). HV _0.5 ) was used. At this time, heat resistance is satisfied when the cross-sectional hardness is 425 HV or more, the 0.2% proof stress at a hardness of 350 HV or more after holding at 700 ° C. for 400 hours or more, and the reduction allowance before and after aging: 40 HV or less. It was judged that the sex was good. In the heat treatment after cold rolling and the heat treatment aging at 700 ° C., the heating rate was 3 ° C./s and the cooling was air cooling.

The final cold rolling ratio of the cold rolled plate produced in this manner, the reheating conditions after rough rolling at hot temperature, the Ni composition in the Ni-based intermetallic compound phase after aging at 700 ° C. for 1 hour, the Ti composition and Nb. The composition and evaluation results are shown in Tables 3-5. Underlines in Tables 1-5 indicate that they are outside the scope of the present invention or that the test results are not good.

No. in Table 3 Nos. 1 to 23 are examples of the present invention that satisfy all the conditions specified in the present invention. 24 to 60 are comparative examples that do not satisfy the conditions specified in the present invention.

No. 1 to 23 are 700 ° C. high temperature tensile test 0.2% proof stress: 1168 to 1373 MPa, cross-sectional hardness at room temperature: 406 to 531 HV _0.5 , cross-sectional hardness measured at room temperature after holding at 700 ° C. for 400 hours: 372. ~ 612HV _0.5 , reduction allowance for cross-sectional hardness (sag resistance): -120 to 38HV, and Ni content is reduced to 35.2-49.7% compared to conventional Ni-based heat-resistant alloys. Despite this, it can be seen that the heat resistance (0.2% proof stress and settling resistance of the high temperature tensile test) is equal to or better than that.

On the other hand, N0.24 to 60 do not satisfy the chemical composition and A and B values specified in the present invention, do not satisfy the final cold rolling ratio, or do not reheat, and therefore are between Ni-based metals. Ti composition in the compound phase: less than 3.5% in atomic%, Nb composition: less than 0.8% in atomic%, hardness after 400 hours aging heat treatment at 700 ° C. and hardness reduction allowance before and after aging. Either was not good. This will be described in detail.

No. In 24 and 26, since the A value was below the lower limit of the range of the present invention, the Ti content in the Ni-based intermetallic compound phase was lower than the lower limit of the range of the present invention, and the settling resistance was low.
No. In No. 25, since the B value was below the lower limit of the range of the present invention, the Nb content in the Ni-based intermetallic compound phase was lower than the lower limit of the range of the present invention, and the settling resistance was low.

No. No. 27 had a low proof stress of 0.2% in the 700 ° C. high temperature tensile test because the C content exceeded the upper limit of the present invention.
No. No. 28 had a low proof stress of 0.2% in the 700 ° C. high temperature tensile test because the C content was below the lower limit of the present invention.

No. 29 had low settling resistance because the Si content exceeded the upper limit of the range of the present invention.
No. No. 30 had a low proof stress of 0.2% in the 700 ° C. high temperature tensile test because the Si content was below the lower limit of the range of the present invention.

No. In No. 31, the settling resistance was low because the Mn content exceeded the upper limit of the range of the present invention.
No. No. 32 had a low proof stress of 0.2% in the 700 ° C. high temperature tensile test because the Mn content was below the lower limit of the range of the present invention.

No. No. 33 had a low proof stress of 0.2% in the 700 ° C. high temperature tensile test because the P content exceeded the upper limit of the range of the present invention.
No. No. 34 had a low yield strength of 0.2% in the 700 ° C. high temperature tensile test because the S content exceeded the upper limit of the range of the present invention.

No. No. 35 had low settling resistance because the Cr content exceeded the upper limit of the range of the present invention.
No. No. 36 had a low proof stress of 0.2% in the 700 ° C. high temperature tensile test because the Cr content was below the lower limit of the range of the present invention.

No. No. 37 had a low yield strength of 0.2% in the 700 ° C. high temperature tensile test because the Ni content exceeded the upper limit of the range of the present invention.
No. No. 38 had a low yield strength of 0.2% in the 700 ° C. high temperature tensile test because the Ni content was below the lower limit of the range of the present invention.

No. 39 had low settling resistance because the N content exceeded the upper limit of the range of the present invention.
No. No. 40 had a low proof stress of 0.2% in the 700 ° C. high temperature tensile test because the N content was below the lower limit of the range of the present invention.

No. No. 41 had low settling resistance because the Al content exceeded the upper limit of the range of the present invention.
No. No. 42 had a low proof stress of 0.2% in the 700 ° C. high temperature tensile test because the Al content was below the lower limit of the range of the present invention.

No. 43 had low settling resistance because the Ti content exceeded the upper limit of the range of the present invention.
No. In No. 44, since the Ti content is below the lower limit of the range of the present invention, the Ti content in the Ni-based intermetallic compound phase is lower than the lower limit of the range of the present invention, and the 700 ° C. high temperature tensile test 0.2% proof stress and resistance The settling property was low.

No. No. 45 had low sag resistance because the Mo content exceeded the upper limit of the range of the present invention.
No. In No. 46, the Mo content was below the lower limit of the range of the present invention, so that the 700 ° C. high temperature tensile test 0.2% proof stress and settling resistance were low.

No. 47 had low sag resistance because the Nb content exceeded the upper limit of the range of the present invention.
No. No. 48 had a low proof stress and settling resistance of 0.2% in a high temperature tensile test at 700 ° C. because the Nb content was below the lower limit of the range of the present invention.

No. 49 had a low proof stress and settling resistance of 0.2% in a high temperature tensile test at 700 ° C. because the Cu content exceeded the upper limit of the range of the present invention.
No. In No. 50, the Ti content in the Ni-based intermetallic compound phase is within the range of the present invention because the Ni, Nb content exceeds the upper limit of the range of the present invention and the Al, Ti content is below the lower limit of the range of the present invention. The yield strength was low by 0.2% in the high temperature tensile test at 700 ° C.

No. In order to prevent reheating after rough rolling, No. 51 to 56 are more particularly No. At 55, the B value was below the lower limit of the range according to the present invention, and No. In 56, the Ni, Nb content exceeds the upper limit of the range of the present invention and the Al, Ti content falls below the lower limit of the range of the present invention. Therefore, the Ti, Nb content in the Ni-based intermetallic compound phase is the present invention. It was below the lower limit of the range of, and the settling resistance was low.

Furthermore, No. In Nos. 57 to 60, the Ti and Nb contents in the Ni-based intermetallic compound phase were below the lower limit of the range of the present invention because the final cold rolling ratio was too high, and the settling resistance was low.

Claims (12)

By mass%, C: 0.0020 to 0.10%, Si: 0.020 to 3.0%, Mn: 0.020 to 2.0%, P: less than 0.050%, S: 0.010 %, Cr: 12.0% or more and less than 25.0%, Ni: more than 35.0% and less than 50.0%, N: 0.0005 to 0.020%, Al: more than 3.0% 5.0 % Or less, Ti: more than 1.5% and less than 3.0%, Mo: 1.0 to 2.5%, Nb: 2.25 to 4.00%, Cu: less than 0.3%, Ti When the contents (% by mass) of Nb and Al are [Ti], [Nb] and [Al], respectively, [Ti] / [Al] ≧ 0.50, [Nb] / [Al] ≧ 0. An alloy base plate for heat-resistant members that satisfies the relationship of 75, has a chemical composition in which the balance is Fe and impurities, and exhibits a metal structure consisting only of an austenite phase.
When heat-treated at 700 ° C. for 1 hour, it exhibits a metallographic structure in which a Ni-based intermetallic compound is present in the austenite matrix, and the Ni-based intermetallics have an overall chemical composition constituting the Ni-based intermetallic compound. An alloy original plate for heat-resistant members, wherein the chemical compositions of Ni, Ti, and Nb contained in the compound account for more than 60%, 3.5% or more, and 0.8% or more, respectively, in atomic%. The alloy original plate for heat-resistant members according to claim 1, wherein the hardness reduction allowance before and after heat treatment at 700 ° C. for 1 hour and then holding at 700 ° C. for 400 hours is 40 HV or less. The alloy original plate for a heat-resistant member according to claim 1 or 2, which contains one or more of Co: 3.0% or less and W: less than 3.0% in mass%. The heat-resistant member according to any one of claims 1 to 3, which contains at least one of B: 0.01% or less, Ca: 0.005% or less, and Mg: 0.002% or less in mass%. Alloy original plate. By mass%, C: 0.0020 to 0.10%, Si: 0.020 to 3.0%, Mn: 0.020 to 2.0%, P: less than 0.050%, S: 0.010 %, Cr: 12.0% or more and less than 25.0%, Ni: more than 35.0% and less than 50.0%, N: 0.0005 to 0.020%, Al: more than 3.0% 5.0 % Or less, Ti: more than 1.5% and less than 3.0%, Mo: 1.0 to 2.5%, Nb: 2.25 to 4.00%, Cu: less than 0.3%, Ti When the contents (% by mass) of Nb and Al are [Ti], [Nb] and [Al], respectively, [Ti] / [Al] ≧ 0.50, [Nb] / [Al] ≧ 0. An alloy plate for heat-resistant members that satisfies the relationship of 75 and has a chemical composition in which the balance is Fe and impurities.
It exhibits a metallographic structure in which Ni-based intermetallic compounds are present in the austenite matrix.
The chemical compositions of Ni, Ti and Nb contained in the Ni-based intermetallic compound are more than 60% and 3.5% or more, respectively, in atomic% with respect to the entire chemical composition constituting the Ni-based intermetallic compound. An alloy plate for heat-resistant members, which occupies 0.8% or more. The alloy plate for a heat-resistant member according to claim 5, wherein the hardness reduction allowance before and after holding at 700 ° C. for 400 hours is 40 HV or less. The alloy plate for a heat-resistant member according to claim 5 or 6, which contains one or more of Co: 3.0% or less and W: less than 3.0% in mass%. The heat-resistant member according to any one of claims 5 to 7, which contains one or more of B: 0.01% or less, Ca: 0.005% or less, and Mg: 0.002% or less in mass%. Alloy plate. By mass%, C: 0.0020 to 0.10%, Si: 0.020 to 3.0%, Mn: 0.020 to 2.0%, P: less than 0.050%, S: 0.010 %, Cr: 12.0% or more and less than 25.0%, Ni: more than 35.0% and less than 50.0%, N: 0.0005 to 0.020%, Al: more than 3.0% 5.0 % Or less, Ti: more than 1.5% and less than 3.0%, Mo: 1.0 to 2.5%, Nb: 2.25 to 4.00%, Cu: less than 0.3%, Ti When the contents (mass%) of Nb and Al are [Ti], [Nb] and [Al], respectively, [Ti] / [Al] ≧ 0.50, [Nb] / [Al] ≧ 0. A gasket for an engine exhaust system member that satisfies the relationship of 75 and has a chemical composition in which the balance is Fe and impurities.
It exhibits a metallographic structure in which Ni-based intermetallic compounds are present in the austenite matrix.
The chemical compositions of Ni, Ti and Nb contained in the Ni-based intermetallic compound are more than 60% and 3.5% or more in atomic%, respectively, with respect to the entire chemical composition constituting the Ni-based intermetallic compound. A gasket for engine exhaust system members, which is characterized by accounting for 0.8% or more. The gasket for an engine exhaust system member according to claim 9, wherein the hardness reduction allowance before and after holding at 700 ° C. for 400 hours is 40 HV or less. The gasket for an engine exhaust system member according to claim 9 or 10, which contains one or more of Co: 3.0% or less and W: less than 3.0% in mass%. The exhaust gas of the engine according to any one of claims 9 to 11, which contains one or more of B: 0.01% or less, Ca: 0.005% or less, and Mg: 0.002% or less in mass%. Gasket for system members.