JP4246085B2 - High Al content ferritic stainless steel sheet for weight detection sensor substrate, manufacturing method thereof, and weight detection sensor - Google Patents

Description

  The present invention relates to a high Al content ferritic stainless steel sheet for a weight detection sensor substrate of an automobile airbag, a manufacturing method thereof, and a weight detection sensor.

  Automobiles are equipped with seat belts and airbags as equipment for ensuring the safety of passengers. Recently, in order to further improve the performance of seat belts and airbags, there is a trend to control the operation of these safety equipment according to the weight (weight) of the occupant. For example, the deployment gas amount and deployment speed of the airbag are adjusted according to the weight of the occupant, and the pretension of the seat belt is adjusted. For that purpose, it is necessary to know the weight of the passenger sitting on the seat by some means. As an example of such means, there is a proposal that the load sensor (load cell) is arranged at the four corners of the seat rail and the seat weight including the weight of the occupant is measured by totaling the vertical loads applied to the load cell. (Patent Document 1).

  Various mechanical quantity sensors for detecting loads, pressures, and the like have been proposed depending on the type of substrate and the type of strain-sensitive material used for the resistance element. As a typical example, (1) a film made of a resin such as polyester, epoxy, polyimide or the like is used as a substrate, and a thin film resistance element made of a Cu—Ni alloy, Ni—Cr alloy or the like is formed on this surface by vapor deposition or sputtering. The formed substrate, (2) a substrate using a glass plate instead of the above resin film (Patent Document 2), and (3) a metal substrate whose surface is coated with a crystallized glass layer is used as a substrate, A material in which a resistive element is formed by applying and baking a paste (Patent Document 3) has been proposed.

  The magnitude of the mechanical quantity is measured as follows. When an external force or load is applied to the mechanical quantity sensor, the resistance element formed on the surface of the substrate is deformed together with the substrate. The applied mechanical quantity is detected by measuring a change in electrical resistance due to a change in the length and cross-sectional area of the resistance element between a pair of electrodes formed connected to the resistance element. Unlike other methods, the mechanical quantity sensor using a metal substrate with a crystallized glass layer formed on the surface as a substrate differs between the metal substrate and the crystallized glass layer and between the crystallized glass layer and the resistive element. Since the component elements are interdiffused, the adhesion between them is strong, making it ideal as a sensor for use in harsh environmental conditions. As a resistance element of this type of mechanical quantity sensor, one formed by applying, drying and firing a resistance paste containing ruthenium oxide as a resistance material is known.

  As the metal substrate used for the mechanical quantity sensor, various alloy materials such as horo steel, stainless steel, silicon steel, nickel-chromium-iron, nickel-iron, kovar, and invar, and clad materials thereof are selected. Patent Document 4 discloses a technique of using a stainless steel plate as a metal substrate. Patent Document 5 discloses a technique of using SUS430 as a metal substrate from the viewpoint of adhesion with an insulating glass layer. Since it is necessary to match the expansion coefficient of a metal base material with a glass layer in patent document 3, the technique made into SUS430 is specifically disclosed.

  However, the metal substrate of the above prior art has not been put into practical use because of insufficient glass adhesion and high-temperature oxidation resistance during firing. It is preferable that the sensor substrate is a stainless steel plate, and each layer of the insulating glass layer, the resistance element, and the electrode is solidified by firing (a conceptual diagram is shown in FIG. 1). Therefore, there has been a strong demand for stainless steel with high heat resistance and excellent glass adhesion that can be fired together with the sensor member when firing each layer at a high temperature.

JP-A-11-304579 Japanese Patent Publication No. 3-20682 JP-A-5-93659 JP 2000-180255 A Japanese Patent Laid-Open No. 10-38733

In order to improve the adhesion between the metal equipment and the glass layer when solidified by firing each layer of the crystallized glass layer, the strain sensitive resistance element, and the electrode, which is the insulating layer, to the stainless steel that is the base of the sensor, The expansion coefficient needs to be matched. Since firing is performed at 900 ° C. or lower, it is necessary that the linear expansion coefficient of 20 to 900 ° C. is approximated in addition to the vicinity of room temperature. When the difference in the average linear expansion coefficient is large, the adhesion between the metal substrate and the crystallized glass layer is remarkably lowered, so that it does not function as the base of the resistance element. The average linear expansion coefficient of the crystallized glass which is generally used while a 13~16 × 10 ^-6 / ℃, the average linear expansion coefficient of the conventionally used stainless steel 13 × 10 ^-6 / The difference in linear expansion coefficient between the stainless steel substrate and the glass layer was too large, and sufficient glass adhesion could not be realized.

  The present invention improves the high-temperature oxidation resistance during sintering with the crystallized glass layer and provides close contact with the glass layer by providing an optimum stainless steel as a metal base material for a vehicle airbag weight detection sensor substrate. The purpose is to improve performance.

  For this purpose, the present invention has been completed as a result of examining the components, the production method, the linear expansion coefficient, and the high-temperature oxidation resistance. A high Al content ferritic stainless steel sheet containing Ti and Zr in a metal substrate is obtained. It has been found that application meets such a purpose. The gist is as follows.

That is, the object of the present invention is achieved by the high Al-containing ferritic stainless steel sheet described in (1) to (6) below and a method for producing the same.
(1) In mass%,
C: 0.025% or less,
N: 0.025% or less,
C + N: 0.030% or less Cr: 12-30%,
Al: 2.5-8%,
A high Al-containing ferritic stainless steel sheet for a weight detection sensor substrate, comprising Zr: 0.02 to 0.2 % , the balance being Fe and inevitable impurities.
(2) The crystallized glass layer according to (1), further comprising at least one of La: 0.01 to 0.20% and REM: 0.01 to 0.20% , strain sensitive A high Al content ferritic stainless steel sheet for a weight detection sensor substrate provided with a resistance element .
(3) The crystallized glass layer according to (1) or (2), wherein the average linear expansion coefficient from 20 to 900 ° C. is 13.5 to 15.5 × 10 ⁻⁶ / ° C. A high Al content ferritic stainless steel sheet for a weight detection sensor substrate provided with a strain resistance element .
(4) The difference in average linear expansion coefficient from 20 to 900 ° C. between the stainless steel plate and the crystallized glass for weight detection sensor is less than 10%, according to any one of (1) to (3) A high Al-containing ferritic stainless steel sheet for a weight detection sensor substrate comprising the crystallized glass layer described above and a strain sensitive resistance element .
(5) The weight detection sensor comprising the crystallized glass layer and the strain sensitive resistance element according to any one of (1) to (4), wherein the stainless steel plate has an oxide film thickness of less than 0.38 μm. High Al content ferritic stainless steel sheet for substrates.
(6) The high Al content ferritic stainless steel sheet according to any one of (1) to (4) is punched into a desired shape, and then the close contact firing of the crystallized glass at 800 to 900 ° C. for 20 to 120 minutes. A method for producing a high Al content ferritic stainless steel sheet for a weight detection sensor substrate comprising a crystallized glass layer and a strain sensitive resistance element, characterized by performing a heat treatment.
(7) A weight detection sensor substrate comprising the high Al-containing ferritic stainless steel plate according to any one of (1) to (5), a crystallized glass layer coated on the substrate surface, and a surface of the crystallized glass layer And a pair of electrodes for detecting a change in electric resistance of the strain-sensitive resistor element.

  The high Al content ferritic stainless steel sheet of the present invention is a material for an automobile airbag weight detection sensor substrate excellent in glass adhesion and high-temperature oxidation resistance, and is an essential technology for a sensor substrate material that adheres an insulating layer, Its industrial value is remarkably great.

  The reason for limitation of the present invention will be described in detail below.

  The present inventor was completed as a result of examining the components, manufacturing method, linear expansion coefficient and high-temperature oxidation resistance of stainless steel, and applied a high Al content ferritic stainless steel sheet containing Ti or Zr as a metal substrate. Thus, an automotive airbag weight detection sensor substrate material having excellent glass adhesion is provided.

  First, the reasons for limiting each component range of the stainless steel targeted by the present invention will be described.

  C, N: When C and N are present in excess of 0.025%, the toughness of the hot-rolled steel strip, which is a cold-rolled material, is reduced and the manufacturability of the material, that is, the cold-rollability is deteriorated. 0.025% or less, and the total amount of C + N is 0.03% or less. A preferable range is 0.010% or less for each of C and N, and a total amount of C + N is 0.010% or less.

  Cr: Cr is the most basic element that ensures the heat resistance or high temperature oxidation resistance of stainless steel. In the present invention, when the content is less than 12%, these characteristics are not sufficiently ensured. On the other hand, when the content exceeds 30%, the toughness and ductility of the hot-rolled steel strip are particularly lowered and the manufacturability of the material is deteriorated. Therefore, the Cr component range is 12-30%. A preferred range is 15-16%.

Al: Al is an element that significantly improves high-temperature oxidation resistance and electrical resistivity of ferritic stainless steel, and at the same time, the linear expansion coefficient increases as the Al content increases. Therefore, in the present invention, the linear expansion coefficient can be approximated and matched even for crystallized glass layers having various linear expansion coefficients by the alloy design in which Al mass% is mainly adjusted. FIG. 2 shows a Cr—Al map of an average linear expansion coefficient from room temperature (20 ° C.) to 900 ° C. It can be seen that the average linear expansion coefficient does not depend on the Cr content, but substantially depends only on the Al content. FIG. 3 shows the relationship between the Al content and the average linear expansion coefficient. The approximate expression of the average linear expansion coefficient from room temperature (20 ° C.) to 900 ° C./(10 ⁻⁶ / ° C.) is 12.8 + 0.28 * (Al mass%) at 8 mass% Al or more, and more than 8 mass% Al. Then, it can be expressed by 2.9 + 1.4 * (Al mass%). If this element is 2.5% or less, the high-temperature oxidation resistance is insufficient. On the other hand, if the content exceeds 8%, the average linear expansion coefficient increases rapidly, and the toughness of the hot-rolled steel strip is remarkably lowered, which deteriorates the manufacturability of the material. Therefore, the Al component range is set to 2.5 to 8%. A preferred range is 4-6%.

  Ti: Ti is an element effective in improving the high-temperature oxidation resistance of ferritic stainless steel and improving the adhesion of the oxide film. This effect can be exhibited with a Ti content of 0.02% or more. However, excessive Ti addition reduces the toughness of the hot rolled steel strip and degrades the manufacturability of the material. In particular, when it exceeds 0.2%, the toughness is significantly deteriorated. Therefore, the component range is set to 0.02 to 0.2% or less. A preferable range is 0.04 to 0.10%.

  Zr: Zr is an element that has the same effect as Ti, is effective in improving the high-temperature oxidation resistance of ferritic stainless steel, and improves the adhesion of the oxide film. This effect can be exhibited by addition of 0.02% or more of Zr. However, excessive addition of Zr deteriorates the oxidation resistance and at the same time reduces the toughness of the hot-rolled steel strip and deteriorates the manufacturability of the material. In particular, when it exceeds 0.2%, the toughness is significantly deteriorated. Therefore, the component range is set to 0.2% or less. A preferable range is 0.05 to 0.15%.

  La, REM: La, REM can be selectively added in the present invention. REM is a mixture of La, Ce, Pr, and Nd, and is unpurified for each single element. It is an element that is extremely effective in improving the adhesion of alumina oxide film and effective in improving high-temperature oxidation resistance. This effect can be exhibited by addition of 0.01% or more of La or REM. However, the addition of excess La and REM deteriorates oxidation resistance, and at the same time, forms a liquid phase at the grain boundary to reduce hot workability, thereby deteriorating material manufacturability. Therefore, the component range is set to 0.20% or less. A preferable range is 0.03 to 0.10%.

Next, the stainless steel targeted by the present invention will be described. The difference in average linear expansion coefficient from 20 to 900 ° C. between the high Al content ferritic stainless steel plate of the present invention and the crystallized glass for weight detection sensor substrate is less than 10%. In order to improve the adhesion between the metal substrate and the glass layer when the crystallized glass layer, the strain sensitive resistance element and the electrode layer, which are insulating layers, are solidified by firing on the stainless steel which is the sensor substrate, both It is necessary to match the linear expansion coefficient. Since the firing is performed at 900 ° C. or less, it is desirable that the linear expansion coefficient of 20 to 900 ° C. is approximated in addition to the vicinity of room temperature. When the difference in average linear expansion coefficient is more than 10%, the adhesion between the metal substrate and the crystallized glass layer is remarkably lowered, so that it does not function as the base of the resistance element. Generally used crystallized glass has an average linear expansion coefficient of 13 to 16 × 10 ⁻⁶ / ° C.

The average coefficient of linear expansion of 20 to 900 ° C. of the high Al content ferritic stainless steel sheet of the present invention is preferably 13.5 to 15.5 × 10 ⁻⁶ / ° C. The defining formula of the linear expansion coefficient α is L _T = L ₂₀ (1 + αT). Here, L _20: length at 20 ℃, L _T: is the length of the temperature T. In the high Al content ferritic stainless steel sheet of the present invention, when the 20 to 900 ° C. is less than 13.5 × 10 ⁻⁶ / ° C. and more than 15.5 × 10 ⁻⁶ / ° C., the adhesion to the crystallized glass layer is low. Not secured.

  The high Al content ferritic stainless steel sheet of the present invention is a cold-rolled annealed sheet obtained by cold rolling a hot-rolled steel strip followed by annealing and descaling.

  After the cold-rolled annealed sheet of the high Al content ferritic stainless steel sheet of the present invention is punched into a desired shape, it is fired with a glass layer. Firing conditions are 800 to 900 ° C. and 20 to 120 minutes. If it is less than 800 ° C., the adhesiveness is insufficient due to insufficient mutual diffusion between the stainless steel plate and the glass layer. On the other hand, if it exceeds 900 ° C., the heat resistance of the glass layer is insufficient. The firing time is the total time of a plurality of heat treatments. If it is less than 20 minutes, the adhesion is insufficient due to insufficient mutual diffusion. On the other hand, if it exceeds 120 minutes, an oxide film having a submicron thickness is formed by the progress of oxidation, so that the so-called temper color is colored and the temper color resistance is deteriorated. There is no direct effect on the sensor characteristics, but the metallic luster on the stainless steel surface disappears.

  In the present invention, the thickness of the oxide film formed by the baking treatment with the crystallized glass layer is less than 0.38 μm. If it exceeds 0.38 μm, it corresponds to the wavelength of visible light (0.38 μm to 0.78 μm), so an interference color such as blue-green is formed. In the case of 0.38 μm or less, no interference color is formed and the temper color resistance is excellent.

  The automobile airbag weight detection sensor of the present invention includes a substrate (1) made of a metal base material of a high Al content ferritic stainless steel plate, a crystallized glass layer (2) coated on the substrate surface, and the crystallized glass layer. A weight detection sensor comprising a strain sensitive resistor element (4) formed on the surface of the substrate and a pair of electrodes (3) for detecting a change in electrical resistance of the strain sensitive resistor element (FIG. 1) It is. Since the high Al content ferritic stainless steel substrate has good adhesion to the crystallized glass layer (2), the metal substrate (1), the crystallized glass layer (2), the electrode (3), and the strain sensitive resistance element ( The baking process of 4) can be performed simultaneously or the number of baking processes can be reduced.

  Hereinafter, the present invention will be specifically described with reference to Examples.

Example 1
High Al content ferritic stainless steels having the components shown in Table 1 were melted by the converter AOD method or the vacuum melting method. After cleaning the surface of these steels, the hot rolling end temperature is 880 ° C to 9 ° C.
Hot rolled at 00 ° C., wound at a hot rolling coiling temperature of 400 ° C. to 750 ° C., cooled by water cooling, and formed into a hot rolled steel strip having a thickness of 5 mm and 3.8 mm. Subsequently, after descaling by shot and pickling, cold rolling was performed to obtain plate thicknesses of 3 mm and 2 mm. Subsequently, it was annealed at 920 ° C., and further descaled by salt treatment and pickling to produce a cold-rolled steel sheet. Thereafter, it was punched into a desired shape and subjected to an adhesion firing heat treatment of the crystallized glass at 850 ° C. for 40 minutes. Crystallized glass having an average linear expansion coefficient of 14.5 × 10 ⁻⁶ / ° C. was used.

  The evaluation test was carried out by the following method.

  The components were analyzed by sampling a test piece from the steel plate. For C, S, N, gas analysis method (N is inert gas melting-heat conduction measurement method, C, S is oxygen gas combustion-infrared absorption method), and other elements are fluorescent X-ray analyzers ( SHIMADZU, MXF-2100).

Evaluation of manufacturability (cold workability) was conducted by taking an impact test by taking a V-notch Charpy test piece of subsize (thickness 5 mm or 3.8 mm) compliant with the JIS standard in parallel with the rolling direction, and an impact value of 2 kgf Evaluation was made at a temperature (vT2: ° C.) at which / cm ² is reached. When vT2 exceeds 90 ° C., even if preheating is performed in advance using a heating apparatus such as a box annealing furnace, the risk of sheet breakage due to impact or the like becomes extremely high when cold rolling is performed, which is substantially Since it cannot be cold-rolled, it was set as x.

Evaluation of high-temperature oxidation resistance was performed by using a sample whose surface was polished with a # 400 count and an oxidation increase after 900 ° C. for 120 minutes in the atmosphere. A case where the increase in oxidation was 0.2 mg / cm ² or less was indicated by ◯, and a case where the increase in oxidation was more than 0.2 mg / cm ² was indicated by x. Comparative Example No. No. 13 (sample symbol 13) shows that Cr is outside the lower limit of the claims, and No. of the comparative example. No. 15 (sample symbol 15) is inferior in oxidation resistance because Al is outside the lower limit of the claims.

The linear expansion coefficient was measured by an ISO standard test method, and an average linear expansion coefficient in a temperature range of room temperature (20 ° C.) to 900 ° C. was evaluated. The average coefficient of linear expansion ○ those range of ^{13.5~15.5 × 10 -6 / ℃, 13.5} × 10 -6 / ℃ or less than 15.5 × 10 ^-6 / ° C. greater × ones It showed in. In the present invention example, the difference in average linear expansion coefficient from 20 to 900 ° C. between the high Al content ferritic stainless steel sheet and the crystallized glass for weight detection sensor substrate is within 10%.

  The glass adhesion was evaluated by a tape peeling test JIS H 8504 (plating adhesion test method). The case where the crystallized glass layer was peeled off was indicated by ×, and the case where the crystallized glass layer was not peeled was indicated by ○. The metal substrate of the component of the present invention has greatly improved glass adhesion. Comparative Example No. No. 15 (sample symbol 15) had an Al content below the lower limit of the range of the present invention and poor glass adhesion.

(Example 2)
The sample of sample symbol 1 (No. 1) in Table 1 was subjected to a firing heat treatment under the conditions shown in Table 2. The average linear expansion coefficient of the crystallized glass was 14.5 × 10 ⁻⁶ / ° C. as in Example 1.

  The film thickness was measured using GDS (Glow Discharge Emission Spectroscopy). The apparatus is a JY5000RF-PSS type manufactured by JOBIN YVON (France), and the measurement area is 4 mmφ. The sputter speed was determined by the depth after discharging the Japanese steel standard sample JSS65-13 for 250 seconds. Four types of calibration samples such as Japanese steel standard samples JSS65-13, JSS171-1, and JSS1001-1 were used.

  Temper color resistance was determined by visual observation of the presence or absence of a visible light color.

Reference Example No. 1 and no. No. 25 employs the firing conditions of the present invention and is excellent in both glass adhesion and temper color resistance. Comparative Example No. In No. 26, the firing temperature deviated from the upper limit, and the glass adhesion, film thickness, and temper color resistance were all poor. Comparative Example No. In No. 27, the firing time exceeded the upper limit, and the film thickness and temper color resistance were poor. Comparative Example No. In No. 28, the firing time deviated from the lower limit, and the glass adhesion was poor. Comparative Example No. In No. 29, the firing temperature was outside the lower limit, and the glass adhesion was poor.

  The present invention is a technology applicable to a material for an automobile airbag weight detection sensor substrate.

It is a conceptual diagram of the mechanical quantity sensor of this invention. Cr-Al map of average linear expansion coefficient from room temperature (20 ° C) to 900 ° C Relationship between Al content and average linear expansion coefficient at room temperature (20 ° C) to 900 ° C

Explanation of symbols

1 Metal substrate made of high Al content ferritic stainless steel sheet
2 Crystallized glass layer
3 electrodes
4 strain sensitive resistance elements
5 Bolt hole

Claims (7)

% By mass
C: 0.025% or less,
N: 0.025% or less,
C + N: 0.030% or less Cr: 12-30%,
Al: 2.5-8%,
High Al content ferritic stainless steel for weight detection sensor substrate comprising crystallized glass layer, strain sensitive resistance element, characterized in that it contains Zr: 0.02 to 0.2 % , the balance being Fe and inevitable impurities steel sheet. The crystallized glass layer and the strain sensitive resistance element according to claim 1, further comprising at least one of La: 0.01 to 0.20% and REM: 0.01 to 0.20%. high Al-containing ferritic stainless steel sheet for weight detection sensor substrate provided. 3. The crystallized glass layer and the strain sensitive resistance element according to claim 1, wherein an average linear expansion coefficient from 20 to 900 ° C. is 13.5 to 15.5 × 10 ⁻⁶ / ° C. High Al content ferritic stainless steel sheet for weight detection sensor substrate. Crystallized glass of any of claims 1 to 3, wherein the difference in average linear expansion coefficient from crystallizing 20 of the glass up to 900 ° C. is less than 10% - the stainless steel plate and the weight detection sensor High Al content ferritic stainless steel sheet for weight detection sensor substrate comprising layers and strain sensitive resistance elements . The thickness of the oxide film of the stainless steel plate is less than 0.38 μm, and the high Al content for a weight detection sensor substrate comprising a crystallized glass layer and a strain sensitive resistance element according to any one of claims 1 to 4 Ferritic stainless steel sheet. The high Al content ferritic stainless steel sheet according to any one of claims 1 to 4 is punched into a desired shape, and subsequently subjected to an adhesion firing heat treatment of crystallized glass at 800 to 900 ° C for 20 to 120 minutes. A method for producing a high Al content ferritic stainless steel sheet for a weight detection sensor substrate comprising a crystallized glass layer and a strain sensitive resistance element .   A weight detection sensor substrate comprising the high Al-containing ferritic stainless steel plate according to any one of claims 1 to 5, a crystallized glass layer coated on the surface of the substrate, and a feeling formed on the surface of the crystallized glass layer. A weight detection sensor comprising a strain resistance element and a pair of electrodes for detecting a change in electrical resistance of the strain sensitive resistance element.

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