JP2020041195A - Metallic gasket intermediate product, and manufacturing method of metallic gasket - Google Patents

Abstract

To provide a manufacturing technology of a metallic gasket capable of achieving excellent settling resistance, high temperature oxidation resistance, and gas leak resistance in a temperature range of 800°C or higher.SOLUTION: A prescribed precipitation treatment is conducted on a metal gasket intermediate product having a steel composition containing, by mass%, C: 0.100% or less, Si: 3.00% or less, Mn: 2.50% or less, Ni: 19.00 to 35.00%, Cr: 16.00 to 25.00%, Mo: 1.00% or less, Cu: 2.00% or less, Ti: 0 to 2.50%, Nb: 0 to 2.50%, Al: 2.00% or less, and having average crystal particle diameter of preferably 10 to 50 μm, and hardness of 400 HV or less.SELECTED DRAWING: Figure 1

Description

  INDUSTRIAL APPLICABILITY The present invention is particularly suitable for use in an environment where the material temperature can rise to a high temperature range exceeding 800 ° C., such as an engine of an internal combustion engine, an exhaust gas path member (an exhaust manifold, a catalytic converter), an injector, an EGR cooler, and a turbocharger. And an intermediate product for manufacturing a metal gasket of a type having a press-formed bead. Further, the present invention relates to a manufacturing method for obtaining a metal gasket from the intermediate product. The beads are already formed in the intermediate product of the present invention. By subjecting this intermediate product to heat treatment for strengthening precipitation, a metal gasket excellent in high-temperature strength can be obtained.

  2. Description of the Related Art In recent years, the exhaust gas temperature of an internal combustion engine has risen in accordance with high performance of automobile engines and environmental regulations, and the material temperature of a metal gasket may reach a high temperature range exceeding 800 ° C. Therefore, there is an increasing need for a highly reliable metal gasket capable of sufficiently maintaining gas sealing performance in an environment where it is exposed to a high temperature of about 800 ° C. for a long time, and in some cases, the temperature is expected to rise to a higher temperature. ing.

Until now, various stainless steel materials for heat-resistant gaskets have been developed, but there is a problem in applying to stainless steel materials used for a long time in a high temperature range around 800 ° C. For example, SUS301 and SUS431-based materials represented by the disclosures of Patent Documents 1, 2, and 3 are remarkably softened and inferior in sag resistance because the heating temperature corresponds to the decomposition temperature of the martensite phase. Patent Documents 4, 5, 6, and 7 disclose Fe-Cr-Mn-Ni austenitic stainless steel reinforced by N. These harden when containing a large amount of martensite or when the N content is high, and have a factor of causing a roughened surface of a processed portion at the time of molding into a gasket and deteriorating hermeticity. Poor reliability when used for hours. Patent Document 8 discloses an NCF718 (JIS G4902) -based nickel-based alloy (alloy D). Although this alloy is effective for precipitation strengthening at around 800 ° C., it is very expensive because it contains a large amount of Ni of 50 to 55%. Patent Documents 9 and 10 disclose SUH660 (JIS G4312) -based materials. However, when the temperature is increased to around 800 ° C. due to a low Cr content, oxidation resistance is significantly deteriorated. Further, the precipitation hardening ability at around 800 ° C. is inferior to that of NCF718, which is a nickel-based alloy, and the sag resistance when used in the 800 ° C. range is insufficient. Patent Document 11 discloses a material of a type in which the contents of Ni and Al are increased based on the SUH660 series. The number density of the γ 'phase (Ni ₃ (Al, Ti)) is increased by increasing the amount of Ni and Al, and the softening property by heating is improved, but the sag resistance is not improved. The reliability that can be achieved is not enough. Patent Document 12 discloses a relatively inexpensive austenitic stainless steel plate for a metal gasket assuming that the maximum temperature of the material is 600 to 800 ° C. However, there is room for further improvement in the excellent durability when used at around 800 ° C. for a long time or when the material temperature rises to a temperature higher than 800 ° C.

JP-A-7-3406 JP 2008-111192 A JP-A-7-278758 JP 2003-82441 A JP-A-7-3407 JP-A-9-279315 JP-A-11-241145 JP 2011-80598 A JP 2013-32851 A JP 2015-83718 A International Publication No. WO 2016/043199 Japanese Patent No. 6029611

  An object of the present invention is to provide a metal gasket which is exposed to a temperature of about 800 ° C. for a long time and may be heated to a higher temperature range in some cases. An object of the present invention is to provide a technology capable of realizing gas leakage.

  A heat-resistant metal gasket that seals a fastening point of a pipe member through which a high-temperature combustion gas flows is exposed to a high temperature while receiving a high fastening stress between both members to be fastened. Deformation during use of this type of gasket mainly involves high-temperature strength at the time of temperature rise and in the initial stage of high-temperature holding, and mainly creep deformation in the subsequent high-temperature holding stage. The “sag” of a metal gasket is a phenomenon that occurs mainly due to creep deformation.

  In the present invention, in order to improve high-temperature strength and sag resistance, a chemical composition that can utilize precipitation strengthening by a precipitation phase generated at 600 to 800 ° C. is employed. However, in order to stabilize and significantly improve the set resistance, in addition to strengthening the grain boundary by the precipitation phase, it was found that it was extremely effective to construct a gasket with low residual stress in the bead portion. .

  In order to realize a gasket exhibiting a sufficient precipitation ability at 600 to 800 ° C. and having a low residual stress at the bead portion, in the present invention, C: 0.005 to 0.100%, Si: 0% by mass. 0.02 to 3.00%, Mn: 0.02 to 2.50%, Ni: 19.0 to 35.00%, Cr: 16.0 to 25.00%, Mo: 0.02 to 1.00 %, Cu: 0.01 to 2.00%, Ti: 0 to 2.50%, Nb: 0 to 2.50%, Al: 0.002 to 2.00%, N: 0.002 to 0.005% 200%, B: 0 to 0.010%, V: 0 to 0.50%, Zr: 0 to 0.50%, W: 0 to 0.50%, Ta: 0 to 0.50%, Co: 0 to 0.50%, REM (rare earth element except Y): 0 to 0.200%, Y: 0 to 0.200%, Ca: 0 to 0.100, Mg: 0 to 0.100, and Ti And the total content of Nb is 0.30 The present invention provides a metal gasket intermediate product having a press-formed bead on a surface of a steel sheet material having a chemical composition comprising at least% and a balance of Fe and unavoidable impurities and having a Vickers hardness HV30 of 400 HV or less on a rolled surface.

  In the above, B, V, Zr, W, Ta, Co, REM (a rare earth element other than Y), Y, Ca, and Mg are optional elements. Further, at least one of Ti and Nb must be contained.

  The steel plate material has an average crystal grain size of, for example, 10 to 50 μm in a cross section (L cross section) parallel to the rolling direction and the thickness direction.

The steel sheet material has a precipitation strengthening ability such that a ΔHV value represented by the following formula (1) becomes 50 or more by performing a heat treatment at, for example, 600 to 800 ° C. for 1 to 10 hours. When the annealed material is a steel plate material, for example, by applying a heat treatment in which the Vickers hardness HV30 of the rolled surface is 200 HV or less and maintained at 600 to 800 ° C. for 1 to 10 hours, the following formula (1) is obtained. Those having a precipitation strengthening ability with a ΔHV value of 150 or more are suitable targets.
ΔHV = H ₁ −H ₀ (1)
Here, H ₀ is the value of Vickers hardness HV30 of the rolling surface of the steel sheet material (HV), H ₁ is the value of Vickers hardness HV30 of the rolled surface after the heat treatment (HV).

  Further, the steel sheet material which is a material constituting the intermediate product specifically has, for example, the following properties. That is, a sample collected from the steel sheet was subjected to a 90 ° bending process at a bending radius R of 0.5 mm where the bending axis is a direction perpendicular to the rolling direction, and then subjected to a heat treatment of holding at 600 to 800 ° C. for 1 to 10 hours. When the test piece is manufactured, the absolute value of the residual stress in the direction of the ridge line at the bending ridge line of the test piece determined by the X-ray diffraction method is 200 MPa or less. The thickness of the steel sheet material is, for example, 0.10 to 0.50 mm.

  A metal gasket can be manufactured by subjecting the above intermediate product to a heat treatment at a temperature of 600 to 800 ° C. for 1 to 10 hours. This metal gasket is used by pressing the top of the bead against a contact partner.

  According to the present invention, a stainless steel material can be used to provide a metal gasket that exhibits excellent durability in an environment in which the material is exposed to a high temperature of about 800 ° C. for a long time and the material temperature may rise to a higher temperature range. .

The figure which showed typically the shape of the gasket test piece. The figure which showed typically the cross section in the state which set the gasket test piece to the restraining jig.

(Chemical composition)
Hereinafter, component elements of the metal gasket intermediate product of the present invention will be described. "%" Relating to the chemical composition of steel means "% by mass" unless otherwise specified.

  C is an element effective for improving high-temperature strength, and strengthens stainless steel by solid solution strengthening and precipitation strengthening. The C content needs to be 0.005% or more, and more preferably 0.010% or more. If the C content is too large, carbides of Ti and Nb are formed at the time of smelting, and the amount of Ti or Nb in the matrix (metal base) required for precipitation strengthening may be insufficient. The C content is limited to 0.100% or less, and may be controlled to less than 0.050%.

Si is a constituent element of the G phase, which is a precipitated phase of the Ni ₃ M ₂ Si type (M is Ti or the like). The G phase has the effect of strengthening the crystal grain boundaries and is effective in improving the sag resistance. The Si content needs to be 0.02% or more, and more preferably 0.40% or more. If the Si content is too large, the stability of the austenite phase is impaired, and the workability is reduced. The Si content is limited to a range of 3.00% or less. It may be controlled to less than 2.00% or 1.50% or less.

  Mn is an austenite-forming element and can substitute a part of expensive Ni. Further, it has an effect of fixing S to improve hot workability. The Mn content needs to be 0.02% or more, and more preferably 0.40% or more. Since a large amount of Mn content causes a decrease in high-temperature strength and mechanical properties, the present invention limits the Mn content to 2.50% or less. It may be controlled to less than 2.00% or 1.50% or less.

  Ni is an essential element for obtaining a stable austenite structure, and also functions as a constituent element of a precipitation phase such as a G phase in the present invention. The Ni content requires a Ni content of 19.00 or more, and more preferably 22.00% or more. The higher the Ni content, the better the improvement in sag resistance. However, from the viewpoint of cost, the Ni content is desirably adjusted within the Ni content range of 35.00% or less. It may be controlled to 28.00% or less.

  Cr is an element necessary for improving corrosion resistance and high-temperature oxidation resistance. According to studies by the inventors, when the ultimate temperature of the material is about 750 ° C., it is possible to obtain characteristics that can be used as a gasket even with a Cr content of about 13%. However, when the material temperature becomes 800 ° C. or higher, the durability of the metal gasket largely depends on not only the high-temperature strength and sag resistance of the material but also the high-temperature oxidation resistance when the temperature is repeatedly increased and decreased. It turned out to be. As a result of various studies, in order to exhibit excellent durability in a gasket environment where the material temperature is expected to rise to 800 ° C. or more, from the viewpoint of improving the high-temperature oxidation resistance, the content of Cr containing 16.00% or more is considered. It is necessary to secure the quantity. 18.00% or more is more preferable. However, when a large amount of Cr is contained, a σ phase, which is a Fe, Cr type precipitation phase, is formed, which causes a reduction in strengthening ability and a decrease in toughness due to a precipitation phase such as a G phase. The Cr content is limited to 25.00% or less, and may be controlled to 23.00% or less.

Mo is effective in improving corrosion resistance, and becomes a carbonitride during high-temperature holding, and finely disperses, thereby contributing to improvement in high-temperature strength. The Mo content needs to be 0.02% or more. However, it has been found that when the Mo content increases, the gas leak resistance of a metal gasket whose temperature rises to 800 ° C. or more is insufficiently improved. According to the study by the inventors, when the Mo content increases, a Laves phase, which is a (Fe, Cr) ₂ Mo type precipitation phase, is formed, and the strengthening ability by the G phase is reduced. it was thought. It is necessary to limit the Mo content to 1.00% or less.

  Cu forms Cu-based precipitates with increasing temperature when used as a metal gasket, and contributes to improvement in high-temperature strength and softening resistance. The Cu content is 0.01% or more. However, a large amount of Cu causes a reduction in hot workability. The Cu content is allowed up to 2.00%.

Ti functions as a constituent element of a precipitation phase such as a G phase. However, excessive Ti content causes a decrease in surface quality due to inclusions. The Ti content is limited to 2.50% or less.
Nb functions as a constituent element of a precipitation phase effective for precipitation strengthening. Further, it forms a solid solution in the austenite matrix and contributes to an increase in hardness and an improvement in softening resistance. However, an excessive Nb content causes a reduction in hot workability due to a decrease in high-temperature ductility. In addition, since Nb is a constituent element for generating a (Fe, Cr) ₂ Nb type Laves phase, an excessive Nb content causes a reduction in the strengthening ability due to other effective precipitated phases such as a G phase. Nb content is limited to 2.50% or less.
In the present invention, one or more of the above Ti and Nb are contained, and the total content of Ti and Nb is set to 0.30% or more. More preferably, the total content of Ti and Nb is 0.80% or more.

  Al is effective as a deoxidizing agent, and it is necessary to secure a content of 0.002% or more. Further, it is also a constituent element of a precipitated phase effective for improving high-temperature strength. In order to sufficiently exert the precipitation strengthening ability by Al, it is effective to secure an Al content of 0.20% or more. However, when Al is excessively contained, the effect of strengthening the precipitated phase that contributes to strengthening of the crystal grain boundary is hindered, and the effect of improving the sag resistance may be reduced. The Al content is limited to 2.00%, and may be controlled to a range of 0.80% or less.

  N is an element effective for increasing the high-temperature strength of austenitic stainless steel. In the present invention, it is desirable to secure an N content of 0.002% or more, and more preferably 0.004% or more. If the N content is too large, carbides of Ti and Nb are formed at the time of smelting, which may lead to a shortage of the amount of Ti or Nb in a matrix (metal base) required for precipitation strengthening. The N content is limited to 0.200% or less, and may be controlled to less than 0.050%.

  B is an optional additive element, which promotes the fine precipitation of carbonitride, which is effective in increasing the high-temperature strength, and suppresses grain boundary segregation of S and the like in the hot rolling temperature range, thereby preventing the occurrence of edge cracks. Present. When B is added, it is more effective to make the content 0.0005% or more. If an excessive amount of B is added, a low-melting-point boride is likely to be formed, which may rather degrade hot workability. The B content is limited to 0.010% or less.

  V is an optional additive element and forms a precipitate effective for increasing hardness and improving sag resistance. When V is added, it is more effective to set the content to 0.05% or more, and it is more effective to set the content to 0.10% or more. Excessive V content causes a reduction in workability and toughness. V content is limited to 0.50% or less.

  Zr is an optional additive element and is effective in improving high-temperature strength, and has an effect of improving high-temperature oxidation resistance when added in a small amount. When Zr is added, it is more effective to make the content 0.01% or more, and it is even more effective to make the content 0.05% or more. Excessive Zr content causes σ embrittlement and impairs the toughness of the steel. Zr content is limited to 0.50% or less.

  W is an optional additive element and is effective for improving high-temperature strength. When W is added, it is more effective to set the content to 0.05% or more, and it is more effective to set the content to 0.10% or more. If W is contained excessively, the steel becomes excessively hard, and the raw material cost increases. W content is limited to 0.50% or less.

  Ta is an optional additive element and is effective in improving high-temperature strength. When Ta is added, it is more effective to set the content to 0.05% or more, and it is more effective to set the content to 0.10% or more. Excessive Ta content causes a reduction in productivity and toughness. Ta content is limited to 0.50% or less.

  Co is an optional additive element and is effective in improving high-temperature strength. When Co is added, it is more effective to set the content to 0.05% or more, and it is more effective to set the content to 0.10% or more. If Co is contained excessively, the steel becomes excessively hard, and the raw material cost increases. The Co content is limited to 0.50% or less.

  REM (a rare earth element other than Y), Y, Ca, and Mg are optional additives, and all are effective in improving hot workability and oxidation resistance. When one or more of these elements are added, it is more effective that the content of each element to be added is 0.001% or more. Even if it is added in excess, the above effects are saturated. REM (rare earth element except Y) may be added in a content range of 0.200% or less, Y is 0.200% or less, Ca is 0.100% or less, and Mg is 0.100% or less.

(Average crystal grain size)
The metal gasket intermediate product of the present invention is more preferably formed of a steel sheet material having an average crystal grain size of 10 to 50 μm in a cross section (L cross section) parallel to the rolling direction and the thickness direction. By increasing the average crystal grain size to some extent, a decrease in creep resistance can be suppressed, which is advantageous in securing sag resistance of the metal gasket. On the other hand, if the average crystal grain size is too large, depending on the shape of the bead, the surface of the bead projection formed by press molding may be rough, and the gas leak resistance of the metal gasket may be deteriorated. The average crystal grain size is measured as follows.

(Method for measuring average crystal grain size)
After polishing the L section of the steel sheet, the austenitic crystal grain boundaries are revealed by etching with aqua regia (hydrochloric acid: nitric acid = 3: 1) to prepare an observation surface, and a microscope image of the observation surface is obtained. . On the microscope image, draw a straight test line that passes through the center of the plate thickness and has a length of 1/2 or more of the plate thickness and that is parallel to the plate thickness direction, and counts the number n of intersections between the test line and the grain boundaries. Then, an average line segment length L (μm) per crystal grain of a test line crossing the inside of the crystal grain is obtained. The average line length L, a test line distance L ₀ of intersection closest to the nearest intersection and the other end to one end of the ([mu] m), and divided by the value of n-1. One or more test lines are set at randomly selected L-direction positions so that the total number of crystal grains crossing the test line is 250 or more. When setting a plurality of test lines, one crystal grain should not be crossed by a plurality of test lines. The arithmetic mean value of the average line segment length L (μm) obtained in each test line is defined as the average crystal grain size (μm) of the steel sheet.

〔Hardness〕
The metal gasket intermediate product of the present invention is in a state in which a press-formed bead is formed on a steel sheet material that has not been subjected to precipitation strengthening treatment. The Vickers hardness HV30 of the rolled surface (surface perpendicular to the plate thickness direction) of the material steel plate is preferably 400 HV or less, and more preferably 350 HV or less. If it is too hard, workability may be insufficient depending on the shape of the metal gasket bead. Here, the Vickers hardness HV30 is a Vickers hardness at a test force of 294.2 N according to JIS Z2244: 2009. When an annealed material is used as the steel sheet material, the Vickers hardness HV30 of the above-mentioned rolling surface (the surface perpendicular to the thickness direction) is, for example, 200 HV or less. Although the lower limit of the hardness is not particularly defined, it is usually 145 HV or more in the case of steel having the above chemical composition.

(Precipitation strengthening ability of steel sheet material)
The steel sheet material constituting the intermediate product of the metal gasket of the present invention is subjected to a heat treatment of, for example, being maintained at 600 to 800 ° C. for 1 to 10 hours, so that the precipitation strengthening that the ΔHV value represented by the following formula (1) becomes 50 or more. It has a function. In the present specification, the heat treatment that brings about the precipitation strengthening is referred to as “precipitation treatment”. When a material having a hardness of 200 HV or less, for example, is applied as a steel sheet material, a material exhibiting a precipitation strengthening ability with a ΔHV value of 150 or more represented by the following equation (1) is a suitable target.
ΔHV = H ₁ −H ₀ (1)
Here, H ₀ is the value of Vickers hardness HV30 of the rolling surface of the steel sheet material (HV), H ₁ is the value of Vickers hardness HV30 of the rolled surface after the heat treatment (HV).
In a steel sheet having the above-mentioned chemical composition and adjusted to the above-mentioned hardness, the precipitation strengthening ability in which the above-mentioned ΔHV value becomes 50 or more can be obtained.

(Residual stress reduction performance)
The metal gasket intermediate product of the present invention is in a state where a press-formed bead has already been formed. However, a bead was formed by pressing a steel sheet material that had not been subjected to a precipitation treatment. After the bead is formed, the bead is subjected to the precipitation treatment, so that the residual stress in the bead portion generated during the bead forming can be reduced by heating the precipitation treatment. The steel sheet material used for the intermediate product of the present invention has such a property that when subjected to a test simulating bead forming and subsequent precipitation treatment, the residual stress in the processed portion is significantly reduced. Specifically, after a sample taken from the steel plate is subjected to 90 ° bending at a bending radius R of 0.5 mm where the bending axis is perpendicular to the rolling direction, and then heat-treated at 600 to 800 ° C for 1 to 10 hours. The absolute value of the residual stress in the ridge line direction at the bending ridge line of the test piece determined by the X-ray diffraction method when the test piece subjected to the above is manufactured is 200 MPa or less. In a steel sheet having the above-mentioned chemical composition and adjusted to the above-mentioned hardness, the performance of reducing the residual stress in which the absolute value of the residual stress is 200 MPa or less can be obtained. There has been no metal gasket intermediate product formed by forming a press-formed bead on such a steel sheet.

(How to determine residual stress)
The above-mentioned residual stress is measured by changing the 並 angle stepwise in a plane including the bending ridge line, and examining the change in the plane spacing of the austenitic crystal {220} plane due to the irradiation of the Cr-Kα ray. Done by The ψ angle has nine steps of 0 °, 5 °, 10 °, 15 °, 20 °, 25 °, 30 °, 40 °, and 45 °. (Sin ² ψ, 2θ) at each ψ angle is plotted in an orthogonal coordinate system in which the horizontal axis is sin ² ψ and the vertical axis is 2θ, and the residual is calculated by the following equation (2) from the slope of the straight line obtained by the least square method. Stress σ (MPa) can be determined.
σ = K · ∂ (2θ) / ∂ (sin ² ψ) (2)
Here, 2θ is the diffraction angle (°) of the austenitic crystal {220} plane, and ψ is the angle (°) between the sample surface normal and the crystal surface normal. K is a constant determined from the Young's modulus and Poisson's ratio when the material is in an unstrained state, and can be calculated here as K = 196000 MPa.
Since the residual stress in the ridge direction generated by the above test becomes a compressive stress, σ determined by the equation (2) becomes a negative value. Therefore, in order to evaluate the magnitude of the compressive residual stress, the magnitude of the absolute value of σ (a positive numerical value excluding the minus sign) is adopted as an evaluation index.

(High temperature hardness)
The steel plate material constituting the metal gasket intermediate product of the present invention has a high-temperature hardness of 75 HV or more in a high-temperature hardness test in which the temperature is raised to 800 ° C., held at 800 ° C. for 5 minutes, and then held at a load of 300 g for 30 seconds. That is, the steel sheet material has the ability to generate a precipitation phase effective for improving the high-temperature strength by a relatively short-time heat treatment at 800 ° C. for 5 minutes.

[Method of manufacturing intermediate products]
The steel sheet material used for the metal gasket intermediate product of the present invention can be manufactured using a general stainless steel sheet mass production facility. Specifically, the following steps can be exemplified.
Melting → Continuous casting → Hot rolling → Hot rolled sheet annealing → Cold rolling → (Intermediate annealing → Intermediate cold rolling) → Finish annealing → (Finish cold rolling)
Here, the intermediate annealing and the intermediate cold rolling in parentheses can be performed once or plural times as necessary. Although not described above, pickling is appropriately performed after each annealing. The finish annealing can be set, for example, in the range of 1000 to 1100 ° C. and soaking in the range of 0 to 60 seconds. The cooling after the finish annealing is preferably performed so that the average cooling rate from the annealing temperature to 400 ° C. is, for example, 10 ° C./s or more. The finish annealing conditions are preferably set so that the average crystal grain size of the steel sheet material is 10 to 50 μm and the hardness of the rolled surface after finish annealing is 200 HV or less. The finish cold rolling reduction can be, for example, 30 to 75%. The finish cold rolling ratio may be set so that the hardness HV30 of the rolled surface after the finish cold rolling is 400 HV or less, more preferably 350 HV or less. In this way, it is possible to obtain a steel sheet material to be processed into a gasket shape. Further, the finish cold rolling may be omitted, and the finish annealing material may be a steel plate material. The thickness of the steel sheet material is, for example, 0.10 to 0.50 mm.

  The above steel sheet material is subjected to press working to form a metal gasket shape, and a metal gasket intermediate product of the present invention having a press-formed bead on the surface of the steel sheet material is obtained. Since the steel sheet material has not been subjected to a precipitation treatment before being processed into a gasket shape, it has good press formability. Further, the residual stress applied to the bead portion by the press forming can be reduced as compared with the case where the steel sheet which has already been subjected to the precipitation treatment is used as the material.

[Metal gasket manufacturing method]
By subjecting the metal gasket intermediate product of the present invention obtained as described above to a precipitation treatment, a metal gasket can be manufactured. The precipitation treatment can be performed under heat treatment conditions of holding at 600 to 800 ° C. for 1 to 10 hours. Cooling after heating and holding is preferably air-cooled to suppress deformation during cooling. By holding in this temperature range, a precipitate phase effective in improving high-temperature strength and sag resistance is formed in crystal grains and in crystal grain boundaries. In addition, the residual stress applied to the bead portion by press molding is reduced, and excellent sag resistance can be realized. The obtained metal gasket is used by pressing the top of the bead against a contact partner.

  The steel shown in Table 1 was melted, hot-rolled to a thickness of 4.0 mm, subjected to annealing and pickling, and then subjected to the steps of “cold rolling, annealing, and pickling” twice, and then to finish cooling. Rolling was performed to obtain a steel sheet material having a sheet thickness of 0.25 mm. In the final annealing (final annealing), the atmosphere of the final annealing was air in all cases, and the cooling after the final annealing heating was air cooling. The finish cold rolling rate was 40%. However, in some examples (No. 18 to be described later), the finish cold rolling was omitted, and a cold-rolled annealed steel sheet having a sheet thickness of 0.25 mm was produced and used as a steel sheet material. The following survey was conducted for each steel sheet material.

(Average crystal grain size)
With respect to the L section of the steel sheet, the average crystal grain size was determined in accordance with the above-mentioned "measurement method of average crystal grain size".

(Hardness)
The Vickers hardness HV30 at a test force of 294.2 N according to JIS Z2244: 2009 was measured on the rolled surface (surface perpendicular to the thickness direction) of the steel plate.

(ΔHV)
The precipitation treatment was performed under the conditions shown in Table 2, the Vickers hardness HV30 of the rolled surface after the precipitation treatment was measured by the same method as described above, and the index ΔHV value indicating the change in hardness due to the precipitation treatment was determined by the above (1). ) Expression.

(Residual stress after precipitation processing for bent part)
A sample collected from a steel sheet material was subjected to a 90 ° bending process at a bending radius R of 0.5 mm where the bending axis was perpendicular to the rolling direction, and then subjected to the precipitation treatment conditions shown in Table 2 (measured for the above ΔHV measurement). A test piece for measuring residual stress was prepared by performing a precipitation treatment under the same conditions as the above precipitation treatment). X-rays are irradiated on the ridgeline of the bent portion of the test piece using a microscopic X-ray stress measuring device (PSPC microscopic X-ray stress measuring device, manufactured by Rigaku Denki Co., Ltd.). The residual stress .sigma. In the direction of the ridgeline of the bent portion was determined by the above equation (2) by the method according to (1). The measurement conditions were as follows: tube current: 30 mA, tube voltage: 40 kV, X-ray: Cr-Kα, collimator: 0.5 mm, peak search: half-width width midpoint method.

(High temperature hardness of 800 ° C)
A test piece of 5 mm square was cut out from the steel sheet material, and the surface thereof was dry-polished with emery abrasive paper having a count of 1000 (particle size P1000 specified in JIS R6010: 2000). The test piece was measured for high-temperature hardness at 800 ° C. using a high-temperature hardness tester. The measurement conditions were as follows: after the temperature was raised to 800 ° C., the test preheating time at 800 ° C .: 5 minutes (based on JIS Z2252), the hardness measurement load holding time: 30 seconds (based on JIS Z2252), and the measurement load: 300 g.
Table 2 shows the above results.

(High temperature oxidation resistance)
A specimen of 25 mm × 35 mm was sampled from the steel sheet material, and subjected to the precipitation treatment under the precipitation treatment conditions shown in Table 2 (the same conditions as those for the above-mentioned ΔHV measurement). A dry polishing finish with emery abrasive paper of JIS R6010: 2000 particle size P400), and a heat treatment of one cycle of “heating at 800 ° C. in the atmosphere for 5 minutes → cooling at room temperature in the atmosphere for 5 minutes” is continuously performed for 2000 times. The cycle was performed, and the oxidation increase / decrease (mg / cm ² ) was determined by the following equation (3).
Oxidation increase / decrease (mg / cm ² ) = (W ₂₀₀₀ −W ₀ ) / S ₀ (3)
Here, W ₂₀₀₀ is the mass (mg) of the test piece after 2,000 cycles, W ₀ is the mass (mg) of the test piece before the test, and S ₀ is the surface area (cm ² ) of the test piece before the test.
A steel sheet whose oxidation increase / decrease amount is 0 to 1.00 mg / cm ² can be evaluated as having high-temperature oxidation resistance suitable for a metal gasket material used at a temperature of 800 ° C. or higher. Therefore, those having an oxidation increase / decrease of 0 to 1.00 mg / cm ² were evaluated as ○ (high-temperature oxidation resistance; good), and the others were evaluated as × (high-temperature oxidation resistance; poor), and the 評 価 evaluation was judged to be acceptable. It should be noted that the steel sheet whose oxidation increase / decrease amount is a negative value has a reduced mass due to peeling of the oxide scale.
The oxidation test results show the high-temperature oxidation resistance of the metal gasket described later, and are shown in Table 3 described later as the characteristics of the metal gasket.

(Production of metal gasket intermediate products)
Next, the above steel sheet material is subjected to press forming to form a ring shape having an outer diameter of 50 mm and an inner diameter of 32 mm, and a bead having a width of 3 mm and a height of 0.5 mm around the inner edge of the ring. Metal gasket intermediate products were manufactured. FIG. 1 schematically shows the shape of the metal gasket intermediate product. The drawing on the right side in FIG. 1 shows a cross-sectional shape (only one side with respect to the ring center) cut through a plane parallel to the thickness direction and passing through the center of the ring of the metal gasket intermediate product. The bead height is indicated by the symbol h.

(Production of metal gasket)
Except for some examples (Nos. 39 and 40), the above-mentioned metal gasket intermediate product was subjected to the precipitation treatment under the precipitation treatment conditions shown in Table 2 (the same conditions as those for the above-mentioned ΔHV measurement). By applying, a metal gasket was produced. Nos. 39 and 40 are examples in which a metal gasket intermediate product was used as it is as a metal gasket. The following survey was conducted for each metal gasket.

(Sag resistance)
For each metal gasket, the following restraint tests A and B were performed, and the difference in bead height after the tests was determined to determine the amount of set.

Restraint test A;
A metal gasket that has not yet been subjected to a tightening history (hereinafter referred to as a “new metal gasket test piece”) was set on a steel restraining jig. FIG. 2 schematically shows a cross section in a state where the gasket test piece is set on a restraining jig. The gasket test piece 1 was sandwiched between the contact mating members 2, and was uniformly tightened by the fastening bolt 3 with a predetermined torque. There are four fastening bolts 3 equally around the gasket test piece 1, and in FIG. 2, only the fastening bolts 3 and nuts are shown for convenience in appearance. After the fastening, the fastening with the fastening bolt 3 was loosened and the load was unloaded, and the gasket test piece 1 was taken out.

Restraint test B;
Another new metal gasket test piece was set on the restraining jig in the same manner as described above. The tightening torque was the same as in the restraint test A. This restraining jig was held in the air at 800 ° C. for 300 hours while the gasket test piece 1 was restrained, and then allowed to cool in a room at room temperature. After cooling, nitrogen gas is applied to the gasket test piece 1 and the upper and lower contact mating materials 2 at a normal temperature at a pressure of 0.5 MPa from a gas introduction pipe 4 attached to only one contact mating material 2 of the restraining jig. The gas was introduced into the enclosed space, and the flow rate (cm ³ / min) of the gas leaking from the space to the outside was measured. Thereafter, the fastening with the fastening bolts 3 was loosened and the load was unloaded, and the gasket test piece 1 was taken out.

The bead height indicated by the symbol h in FIG. 1 was measured for each of the gasket test pieces after the restraint tests A and B. Then, the “set amount” (μm) was determined by the following equation (4).
Set amount (μm) = h _A −h _B (4)
Here, h _A is the bead height (μm) of the test piece after the restraint test A, and h _B is the bead height (μm) of the test piece after the restraint test B.
A metal gasket having a “sag amount” of 50 μm or less can be evaluated as exhibiting extremely excellent sag resistance at a temperature of 800 ° C. or more. Therefore, the sag amount of 50 μm or less was evaluated as （(sag resistance; good), the others were evaluated as × (sag resistance; poor), and the 評 価 evaluation was judged as pass. Table 3 shows the results.

(Gas leak resistance)
The gas leak resistance was evaluated based on the gas leak flow rate measured when the above-described restraint test B was performed. If the gas leak flow rate in this test is 10.0 cm ³ / min or less, it can be determined that the metal gasket, which is heated to a temperature around 800 ° C. or higher, has excellent sealing performance. Therefore, those having a gas leak flow rate of 10.0 cm ³ / min or less were evaluated as ○ (gas leak resistance; good), and the others were evaluated as × (gas leak resistance; poor), and the 評 価 evaluation was judged to be acceptable. Table 3 shows the results.

  The metal gasket obtained by subjecting the metal gasket intermediate product of the present invention to a precipitation treatment was excellent in high-temperature oxidation resistance, sag resistance and gas leak resistance.

  On the other hand, in Comparative Example No. 31, the temperature of the precipitation treatment was low, so that the residual stress at the bead portion was high, and the residual stress was large during the restraint test B simulating the use of the gasket due to the decrease in the residual stress. A "fall" has occurred. Nos. 32 to 36 are examples in which steel having a chemical composition that does not satisfy the requirements of the present invention is used. In these examples, gaskets excellent in all of high-temperature oxidation resistance, sag resistance and gas leak resistance could not be obtained. Nos. 37 and 38 were subjected to the above-described tests as metal gaskets without using a metal gasket intermediate product that had not been subjected to a precipitation treatment. In this case, sag resistance and gas leak resistance were poor due to the high residual stress in the bead portion.

DESCRIPTION OF SYMBOLS 1 Gasket test piece 2 Contact partner material 3 Fastening bolt 4 Gas introduction pipe

Claims (8)

  In mass%, C: 0.005 to 0.100%, Si: 0.02 to 3.00%, Mn: 0.02 to 2.50%, Ni: 19.0 to 35.00%, Cr: 16.00 to 25.00%, Mo: 0.02 to 1.00%, Cu: 0.01 to 2.00%, Ti: 0 to 2.50%, Nb: 0 to 2.50%, Al : 0.002 to 2.00%, N: 0.002 to 0.200%, B: 0 to 0.010%, V: 0 to 0.50%, Zr: 0 to 0.50%, W: 0 to 0.50%, Ta: 0 to 0.50%, Co: 0 to 0.50%, REM (rare earth element except Y): 0 to 0.200%, Y: 0 to 0.200%, Ca: 0 to 0.10, Mg: 0 to 0.10, and the total content of Ti and Nb is 0.30% or more, and has a chemical composition consisting of the balance of Fe and unavoidable impurities. HV30 is less than 400HV Metal gasket intermediate product with a press-formed bead on the surface of a steel sheet material.   2. The metal gasket intermediate product according to claim 1, wherein the steel sheet material has an average crystal grain size of 10 to 50 μm in a cross section (L cross section) parallel to the rolling direction and the thickness direction. 3. The said steel plate material has a precipitation strengthening ability which becomes (DELTA) HV value represented by following formula (1) 50 or more by performing heat processing which maintains for 1 to 10 hours at 600-800 degreeC. Or the metal gasket intermediate product according to 2.
ΔHV = H ₁ −H ₀ (1)
Here, H ₀ is the value of Vickers hardness HV30 of the rolling surface of the steel sheet material (HV), H ₁ is the value of Vickers hardness HV30 of the rolled surface after the heat treatment (HV). The above-mentioned steel sheet material has a Vickers hardness HV30 of 200 HV or less on the rolled surface, and is subjected to a heat treatment of holding at 600 to 800 ° C for 1 to 10 hours, so that a ΔHV value represented by the following formula (1) is 150 or more. The metal gasket intermediate product according to claim 1 or 2, which has a precipitation strengthening ability to become:
ΔHV = H ₁ −H ₀ (1)
Here, H ₀ is the value of Vickers hardness HV30 of the rolling surface of the steel sheet material (HV), H ₁ is the value of Vickers hardness HV30 of the rolled surface after the heat treatment (HV).   The steel sheet material is subjected to a 90 ° bending process at a bending radius R = 0.5 mm in which a bending axis is a direction perpendicular to the rolling direction to a sample collected from the steel sheet, and then a heat treatment is performed at 600 to 800 ° C. for 1 to 10 hours. The absolute value of the residual stress in the ridgeline direction at the bending ridgeline of the test piece determined by the X-ray diffraction method when producing a test piece subjected to the above-mentioned method is 200 MPa or less. Metal gasket intermediate products described in.   The metal gasket intermediate product according to any one of claims 1 to 5, wherein the steel sheet material has a thickness of 0.10 to 0.50 mm.   A method for producing a metal gasket, comprising subjecting the intermediate product of the metal gasket according to any one of claims 1 to 6 to a heat treatment at a temperature of 600 to 800 ° C for 1 to 10 hours.   The method for manufacturing a metal gasket according to claim 7, wherein the metal gasket is used by pressing the top of the bead against a contact partner.

Images