JP2020037123A - Diffusion-joined product and method for manufacturing the same - Google Patents

Abstract

To provide a diffusion-joined product obtained by using an austenitic stainless steel, in which a diffusion-joined boundary surface is hard to be peeled off, and a method for manufacture of the same.SOLUTION: The diffusion-joined product is provided in which a plurality of laminated steel plates having a prescribed chemical composition are joined to each other, and in which a diffusion-joined boundary surface is formed at a joint part of the steel plates, wherein when a plate thickness direction of the steel plate denotes a width direction of a cross section of the diffusion joined boundary surface in the steel plate thickness direction and when the diffusion-joined boundary surface denotes a width center, an Si enrichment degree (maximum Si amount/raw material Si amount) in an area having a full width of 10 μm, which is a ratio between a maximum Si amount and a raw material Si amount, is 5.0 or less, a joining rate of the diffusion- joined boundary surface is 60.0% or more. The method for manufacturing the diffusion-joined product is also provided.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a diffusion bonded product using an austenitic stainless steel plate that has been mainly subjected to precision processing, and a method for manufacturing the same. More specifically, the present invention relates to a precision component manufactured by diffusion bonding of an austenitic stainless steel plate that has been subjected to precision processing by photoetching or laser and a method of manufacturing the same.

  Photo etching is a method of forming a pattern on the surface of a metal plate, which is a material, by a photoresist method, dissolving the metal plate by etching by spraying or dipping, and processing the metal plate into almost the same shape as the photoresist pattern. It is. The laser processing is a processing method of forming holes and a predetermined pattern by melting the surface of a metal plate with a laser based on CAD data or the like.

  After photo-etching or laser processing, the processed stainless steel sheets are laminated, and the laminated stainless steel sheets are joined by holding them at a high temperature in a non-oxidizing atmosphere to produce an integrated part from many stainless steel sheets. Is done.

  Such a process is called a diffusion bonding process and is an important technique for molding a component processed into a complicated shape with high accuracy.

As a conventional technique relating to diffusion bonding, for example, in Patent Document 1, when stainless steel materials are brought into direct contact with each other and integrated by diffusion bonding, at least one of the two stainless steel materials to be brought into contact with each other starts austenite transformation in a temperature rising process. Applying a two-phase steel having _one point of temperature Ac at 650 to 950 ° C and an austenite + ferrite two-phase temperature range of 880 ° C or more, contact surface pressure of 1.0 MPa or less, and heating temperature of 880 to 1080 ° C A method of manufacturing a stainless steel diffusion bonded product, in which diffusion bonding is advanced while accompanied by grain boundary movement when the ferrite phase of the duplex stainless steel is transformed into an austenite phase within the range, is disclosed.

Patent Literature 2 discloses that a stainless steel material having a surface roughness Ra adjusted to be 0.30 μm or less is used as both stainless steel materials (hereinafter referred to as “steel materials before joining”) to be subjected to diffusion bonding. As the joining conditions, both the pre-joined steel materials reach the diffusion bonding temperature from a state where the average crystal grain size r ₀ is adjusted to 50 μm or less, and after maintaining at the diffusion joining temperature, the average crystal grain size r ₁ becomes 80 μm or less, A method for manufacturing a stainless steel diffusion bonded product applying a heat pattern in which (r ₁ −r ₀ ) / r ₀ is 2.0 or more is disclosed.

JP 2013-103271 A JP 2013-173181 A

  In the related art, there is a problem that a specific element such as Si is concentrated near the diffusion bonding interface, and the steel materials subjected to diffusion bonding are easily separated from the diffusion bonding interface.

  An object of the present invention is to provide a diffusion-bonded product using an austenitic stainless steel, in which a diffusion-bonding interface is unlikely to peel off, and a method for producing the same.

  The present inventors have conducted intensive studies on the diffusion bonding method and the element distribution near the diffusion bonding interface and the releasability of the diffusion bonding interface in order to solve the above problems, and as a result, by performing diffusion bonding under specific conditions. It has been found that the amount of Si concentrated near the diffusion bonding interface can be reduced, a diffusion bonding interface that is difficult to peel off can be provided, and the above problem can be solved.

  Furthermore, the present inventors have found that by subjecting the steel sheet before diffusion bonding to anodic electrolysis under predetermined conditions, the amount of Si on the surface of the steel sheet can be further reduced, and have found that the above problem can be solved.

  The gist of the present invention is as follows.

[1] A diffusion-bonded product according to one embodiment of the present invention is configured such that a plurality of laminated steel plates are bonded to each other, and the steel plates are expressed in terms of mass%.
C: 0.030% or less,
Si: 0.20 to 1.00%,
Mn: 0.6-1.5%,
Cr: 15.0 to 20.0%,
Ni: 6.0 to 9.0%,
Mo: 0.1-0.5%,
Cu: 0.1-0.5% and N: 0.030-0.150%
And Nb: 0.500% or less;
V: 0.500% or less and Ti: 0.500% or less.
A steel sheet having a chemical composition consisting of a balance of Fe and impurities,
A diffusion bonding interface is formed at the joint between the steel plates,
In the cross section of the diffusion bonding interface in the thickness direction of the steel sheet, the thickness direction of the steel sheet is defined as the width direction, and the maximum Si amount and the material Si amount in the entire width of 10 μm when the diffusion bonding interface is defined as the width center. The Si concentration (maximum Si content / material Si content), which is a ratio, is 5.0 or less;
The bonding rate at the diffusion bonding interface is 60.0% or more.

[2] In the method for producing a diffusion bonded article according to the above [1], the steel sheet having the chemical composition according to the above [1] and having a metal structure having an austenite average crystal grain size of 5.0 µm or less. When n times of anodic electrolysis is continuously performed using n sets of electrodes in an electrolytic solution having a pH of 5.0 or more and less than 12.0, the per unit area in the k-th anodic electrolysis is When the amount of electricity is σ _k (where k = 1 to n) and the sum of the amount of electricity per unit area in each anodic electrolysis treatment is Σσ _k , the sum of the amount of electricity が σ _k is given by the following equation (1). A first step of performing anodic electrolysis under conditions that satisfy the conditions,
A second step of directly laminating a plurality of the anodic-electrolyzed steel sheets and performing diffusion bonding at a diffusion bonding temperature of 850 to 1050 ° C. and a surface pressure of 0.03 to 30.00 MPa;
Are sequentially performed.
Σσ _k ≦ 25.0 (C / dm ² ) (1)

  Advantageous Effects of Invention According to the present invention, it is possible to provide a diffusion-bonded product using austenitic stainless steel and having a diffusion-bonding interface that is difficult to peel off, and a method for manufacturing the same.

FIG. 4 is a diagram for explaining a method of measuring a Si concentration near a diffusion bonding interface. FIG. 4 is a diagram illustrating a relationship between a Si concentration and a bonding rate according to the embodiment.

  An embodiment of the present invention will be described below. The diffusion-bonded product according to the present embodiment is configured such that a plurality of laminated steel plates are bonded to each other, the steel plate is a steel plate having a predetermined chemical composition, and a diffusion bonding interface is formed at a bonding portion between the steel plates. In the cross section of the diffusion bonding interface in the thickness direction of the steel sheet, the maximum Si amount and the material Si in a region having a total width of 10 μm when the thickness direction of the steel sheet is the width direction and the diffusion bonding interface is the center of the width. The Si concentration (maximum Si amount / material Si amount), which is a ratio with respect to the amount, is 5.0 or less, and the bonding rate at the diffusion bonding interface is 60.0% or more. In the present embodiment, an austenitic stainless steel sheet is used as a steel sheet used for diffusion bonding. However, it is preferable that the steel sheet has a small average crystal grain size from the viewpoint of the smoothness of the precision-machined surface, and that the steel sheet does not have a smut at the time of etching, but if the requirements specified in the present invention can be satisfied. The chemical composition of the steel sheet is not limited. The thickness of the steel sheet is not particularly limited, but may be 50 to 1000 μm.

  The present inventors have found that, by mass%, C: 0.030% or less, Si: 0.20 to 1.00%, Mn: 0.6 to 1.5%, Cr: 15.0 to 20.0% , Ni: 6.0-9.0%, Mo: 0.1-0.5%, Cu: 0.1-0.5%, and N: 0.030-0.150%, and further Nb. : An austenitic stainless steel sheet containing one or more of 0.500% or less, V: 0.500% or less and Ti: 0.500% or less, and having a chemical composition consisting of a balance of Fe and impurities; It has been confirmed that it can be used as the steel sheet of the diffusion bonded product according to the present embodiment. In the present embodiment, steel sheets having different chemical compositions may be diffusion-bonded to form a diffusion bonded article, or steel sheets having the same chemical composition may be diffusion-bonded to form a diffusion bonded article. The diffusion-bonded article according to the present embodiment requires that the average of the chemical compositions of a plurality of steel sheets stacked and diffusion-bonded be included in the chemical composition. In the case where a steel sheet having the same chemical composition is diffusion-bonded into a diffusion-bonded product, the chemical composition of the steel sheet and the chemical composition of the diffusion-bonded product (the average of the chemical compositions of a plurality of laminated and diffusion-bonded steel sheets) Are equal.

(1) Metal structure [Average austenite grain size before diffusion bonding: 5.0 μm or less]
By making the average value of the austenite grain size (hereinafter sometimes referred to as the average grain size of austenite) of the steel sheet before diffusion joining as small as 5.0 μm or less, the etched surface before diffusion joining becomes smooth. become. Further, the diffusion is actively generated through the crystal grain boundary having an increased area due to the refinement of the crystal grain, and the diffusion bonding property of the steel sheet is improved. Therefore, in the present embodiment, the upper limit of the average austenite grain size in the steel sheet before diffusion bonding is set to 5.0 μm.

  In the present embodiment, the average grain size of austenite in the steel sheet before diffusion bonding is measured by a cutting method described in Japanese Industrial Standards JIS G 0551: 2013 “Steel—Microscopic Test Method of Grain Size”.

[Average value of austenite grain size after diffusion bonding: 15.0 μm or less]
It is preferable that the average value of the austenite grain size after diffusion bonding is 15.0 μm or less, because the decrease in hardness after diffusion bonding is suppressed. By setting the average crystal grain size of austenite of the steel sheet before diffusion bonding to 5.0 μm or less, the average crystal grain size of austenite after diffusion bonding can be set to 15.0 μm or less. Therefore, in the present embodiment, the upper limit of the average crystal grain size of austenite after diffusion bonding may be set to 15.0 μm or 6.0 μm. However, it is not essential that the average crystal grain size of austenite after diffusion bonding is 15.0 μm or less, and even if it exceeds 15.0 μm, a diffusion bonded product according to the present embodiment can be obtained.

  In the present embodiment, the average crystal grain size of austenite after diffusion bonding is set in the range of ± 100 to 200 μm in the sheet thickness direction from the diffusion bonding interface described later in accordance with Japanese Industrial Standard JIS G 0551: 2013 “Steel-Grain Size. Microscopic Test Method ”.

(2) Junction (2-1) Element distribution near diffusion junction interface [Si concentration near diffusion junction interface: 5.0 or less]
A diffusion bonding interface is formed at the joint between the steel plates. If Si is concentrated near the diffusion bonding interface, the separation at the diffusion bonding interface becomes remarkable starting from the Si-enriched portion. Therefore, by reducing the amount of Si near the diffusion bonding interface, a diffusion bonding interface that is difficult to peel off is formed. The amount of Si distributed near the diffusion bonding interface is not always uniform, and there is usually a high possibility that peeling will occur from a region where the amount of Si is the largest. Therefore, it is important to analyze a plurality of regions near the diffusion bonding interface to confirm the maximum Si amount.
In the present embodiment, in the cross section of the diffusion bonding interface in the thickness direction of the steel sheet, the maximum Si amount and the material in the entire width of 10 μm in the case where the thickness direction of the steel sheet is the width direction and the diffusion bonding interface is the center of the width. By appropriately controlling the Si concentration (maximum Si amount / material Si amount) expressed as a ratio to the Si amount (Si amount of the steel sheet), separation at the diffusion bonding interface is suppressed. In the present embodiment, the upper limit of the Si concentration is set to 5.0, preferably 4.5, and more preferably 3.0. Although it is desirable that the Si concentration is as small as possible, the austenitic stainless steel sheet as the steel sheet contains 0.20 mass% or more of Si, and the Si existing on the surface of the austenitic stainless steel sheet by anodic electrolytic treatment before diffusion bonding. Is preferentially removed, it is technically difficult to reduce the maximum Si amount near the diffusion bonding interface to less than 0.14 mass%. Therefore, the lower limit of the Si concentration near the diffusion bonding interface after the diffusion bonding may be 0.7.

The method of measuring the Si concentration near the diffusion bonding interface in the present embodiment will be described in detail with reference to FIG. FIGS. 1A and 1B are diagrams illustrating a method of measuring the Si concentration near the diffusion bonding interface. FIG. 1A shows a cross section 1 of the diffusion-bonded product 10 which is parallel to the thickness direction of the steel plate 3. In FIG. 1A, reference numeral 2 is assigned to a bonding surface (diffusion bonding interface) between the laminated steel plates 3. In FIG. 1A and FIG. 1B, the observation field of view by EPMA is denoted by reference numeral 4.
FIG. 1B is an enlarged view of a cross section 1 parallel to the thickness direction of the steel plate 3 of the diffusion bonded product 10.
In the present embodiment, in the cross section 1, an area of 100 μm × 100 μm is analyzed for each visual field using EPMA so that each diffusion bonding interface 2 is located at the center of the width of the steel sheet 3 in the thickness direction. Is set to 0.25 μm, and a total of 9 or more visual fields are analyzed. In these observation fields, the maximum Si amount in each analysis region 5 (a region having a total width of 10 μm when the diffusion bonding interface is the center of the width) is defined as the maximum Si amount (see FIG. 1B). The amount of the raw material Si can be obtained by cutting out a test piece of a predetermined size from the diffusion bonded product and analyzing it by an ICP-OES (inductively coupled plasma emission spectroscopy) analysis method. By dividing the obtained maximum Si amount by the material Si amount, the Si concentration in the above region is obtained.

(2-2) Bonding rate [Bonding rate of diffusion bonding interface: 60.0% or more]
The bonding rate of the diffusion bonding interface in the diffusion bonding product according to the present embodiment is 60.0% or more. Of the areas where the steel plates are in contact with each other, the area that is actually joined does not reach 100%, and unjoined portions (mainly voids) may be formed in some cases. If there are many unbonded portions and the bonding ratio of the diffusion bonding interface is less than 60.0%, the diffusion bonding interface is easily peeled regardless of the presence or absence of Si concentration.
The bonding rate at the diffusion bonding interface is obtained by examining the void at the diffusion bonding interface by ultrasonic testing. Specifically, the diffusion bonding interface is evaluated by the transmission method, a position where the transmission pulse height is 25% or more is determined as the diffusion bonding interface, and a position where the transmission pulse height is 25% or less is determined as the void, and the area ratio of the diffusion bonding interface is determined. Is calculated, the bonding rate of the diffusion bonding interface is obtained. In the transmission method, in the process in which ultrasonic waves transmitted from the transmitting probe pass through the measuring object and are received by the receiving probe, scattering due to defects (mainly air gaps) in the measuring object, etc. This is a method of grasping the size and degree of a defect inside the measurement object from the degree of attenuation of the ultrasonic wave due to the cause. In the transmission method, the height of the transmitted pulse received after passing through the measurement object is measured as compared with the transmitted ultrasonic pulse. The closer the received transmitted pulse height is to 100%, the smaller the defects (mainly voids) in the object to be measured, and a better diffusion bonding interface is formed. The smaller the received transmitted pulse height is, the more the diffusion bonding is performed. Evaluate as defective. In this embodiment, the transmission pulse is measured at a pitch of 0.2 mm in each of the vertical and horizontal directions of the measurement target (diffusion bonding product), and the transmission pulse height becomes 25% or more with respect to the diffusion bonding interface area of the measurement target. The area ratio of the position is defined as the bonding ratio of the diffusion bonding interface. In the present embodiment, the area ratio of the position where the transmitted pulse height obtained by the above method is 25% or more is defined as the bonding ratio of the diffusion bonding interface regardless of the number of steel sheets laminated in the diffusion bonding product. .

Hereinafter, a method for manufacturing a diffusion bonded product according to the present embodiment will be described. In the method for producing a diffusion bonded article according to the present embodiment, a steel sheet having a predetermined chemical composition and a metal structure in which the average crystal grain size of austenite is 5.0 μm or less has a pH of 5.0 or more and 12.1. When n times of anodic electrolysis are continuously performed using n sets of electrodes in an electrolyte solution of less than 0, the amount of electricity per unit area in the k-th anodic electrolysis is σ _k (where k = 1 To n), and when the total amount of electricity per unit area in each anodic electrolysis treatment is Σσ _k , the total amount of electricity Σσ _k is calculated by the equation (1) (Σσ _k ≦ 25.0 (C / dm ²⁾ )), A first step of anodic electrolysis treatment under the conditions satisfying the above conditions, and a plurality of sheets of the anodic electrolysis-treated steel sheet are directly laminated, and a diffusion bonding temperature: 850 to 1050 ° C., a surface pressure: 0.03 to 30. A second step of performing diffusion bonding at 00 MPa. Hereinafter, each step will be described in detail.

(3) First step (anodic electrolytic treatment before diffusion bonding)
The concentration of Si near the diffusion bonding interface can be suppressed by performing the anodic electrolytic treatment described below. As a result, peeling of the diffusion bonding interface can be suppressed.

(3-1) Electrolyte used for anodic electrolysis before diffusion bonding [Electrolyte: pH of 5.0 or more and less than 12.0]
In order to reduce the amount of Si near the diffusion bonding interface, it is necessary to reduce the amount of Si on the steel sheet surface before diffusion bonding as much as possible. In order to efficiently reduce the amount of Si by subjecting the steel sheet before diffusion bonding to anodic electrolytic treatment, it is desirable to use an electrolytic solution having a pH of 5.0 or more and less than 12.0. This is because the solubility of Si to be removed increases in a weakly acidic to basic region. There is no problem even if a surfactant or the like is added to the electrolytic solution having the above pH. The temperature of the electrolytic solution is not particularly limited, and there is no problem as long as the temperature is equal to or higher than room temperature.
Examples of the electrolyte include an aqueous NaOH solution, an aqueous Na ₂ SO ₄ solution, a mixed aqueous solution of NaOH and Na ₂ SO _4, and a mixed aqueous solution of H ₂ SO ₄ and Na ₂ SO ₄ .

(3-2) Anodic Electrolysis Treatment Conditions Before Diffusion Bonding In the method of manufacturing a diffusion bonded product according to the present embodiment, n sets (where n is a natural number of 2 or more) of electrodes are used in the above-described electrolytic solution. When n times of anodic electrolysis are continuously performed, the amount of electricity per unit area in the k-th anodic electrolysis is σ _k (where k = 1 to n), and the amount of electricity per unit area in each anodic electrolysis is when the total amount of electricity was Shigumashiguma _k, the sum Shigumashiguma _k electric quantity, anodic electrolysis treatment under conditions satisfying the following equation (1). Here, n is the number of times of the anodic electrolytic treatment. The upper limit of n is not particularly limited, but may be, for example, any of 20 or less, 15 or less, 10 or less, and 5 or less.

Σσ _k ≦ 25.0 (C / dm ² ) (1)

If the total amount of electricity Σσ _k exceeds 25.0 (C / dm ² ), the electricity is consumed in a reaction different from the reaction for removing Si, so that Si cannot be sufficiently removed, and in some cases, such as Fe Elution of other elements relatively increases the amount of Si on the steel sheet surface. Therefore, the sum Σσ _{k of} electric quantities is set to 25.0 (C / dm ² ) or less. The more preferable total amount of electricity Σσ _k is 0.50 (C / dm ² ) or more and 21.0 (C / dm ² ) or less.

(4) Second step (diffusion bonding)
In the method for manufacturing a diffusion bonded article according to the present embodiment, by applying a specific temperature and surface pressure to perform diffusion bonding, the Si concentration near the diffusion bonding interface can be reduced to 5.0 or less. . Note that the number of steel sheets to be laminated and the atmosphere in diffusion bonding are not limited as long as the requirements specified in the present invention can be satisfied. However, the present inventors satisfy the conditions described below, It has been confirmed that the diffusion bonding product according to the present embodiment can be manufactured by setting the number of laminations to 10 and performing diffusion bonding in a non-oxidizing atmosphere.

(4-1) Diffusion bonding temperature [Diffusion bonding temperature: 850 to 1050 ° C]
If the diffusion bonding temperature is too low, diffusion of atoms is not sufficient, and the steel sheets are not diffusion bonded. Therefore, in this embodiment, the diffusion bonding temperature is set to 850 ° C. or higher. On the other hand, if the diffusion bonding temperature is too high, the high-temperature strength is reduced, so that it is deformed during diffusion bonding, and good dimensional accuracy of the diffusion bonded product cannot be obtained. Therefore, in this embodiment, the diffusion bonding temperature is set to 1050 ° C. or less. In the present embodiment, the diffusion bonding temperature refers to the surface temperature of the outermost steel sheet when the laminated steel sheets are kept at a constant temperature and a surface pressure is applied (diffusion bonding).

(4-2) Surface pressure during diffusion bonding [surface pressure: 0.03 to 30.00 MPa]
If the surface pressure during the diffusion bonding is too low, the area of the solid phase interface becomes small, and atoms in the solid phase do not diffuse sufficiently. As a result, Si is not sufficiently diffused, the maximum Si amount near the diffusion bonding interface becomes large, and the diffusion bonding interface is easily peeled. Therefore, in the present embodiment, the surface pressure during diffusion bonding is set to 0.03 MPa or more. On the other hand, if the surface pressure at the time of diffusion bonding is too large, it will be deformed at the time of diffusion bonding, and good dimensional accuracy of the diffusion bonded product cannot be obtained. Therefore, in the present embodiment, the surface pressure during diffusion bonding is set to 30.00 MPa or less. The surface pressure during diffusion bonding is preferably 10.00 MPa or less, and more preferably 5.00 MPa or less.

  According to the above-described manufacturing method, it is possible to manufacture the diffusion-bonded product according to the above-described embodiment, that is, the diffusion-bonded product in which the diffusion bonding interface is unlikely to be separated.

  A slab having the chemical composition shown in Table 1 was melted, and after hot rolling, annealing, and descaling were sequentially performed, cold rolling and annealing were performed to obtain an austenitic stainless steel sheet having a thickness of 0.1 mm. Obtained. The average crystal grain size of austenite of each austenitic stainless steel sheet after annealing and before diffusion bonding described later was measured by a cutting method described in Japanese Industrial Standards JIS G 0551: 2013 “Steel—Microscopic test method of crystal grain size”. . Table 1 shows the average crystal grain size of the obtained austenite.

Using these steel sheets (austenitic stainless steel sheets), anodic electrolytic treatment and diffusion bonding were performed to obtain diffusion bonded articles. In this example, a steel sheet having the same chemical composition was diffusion bonded to obtain a diffusion bonded product.
With respect to the obtained diffusion bonded product, the bonding ratio after diffusion bonding, the Si concentration, and the average crystal grain size of austenite after diffusion bonding were measured. In addition, a bending test was performed to confirm the presence or absence of peeling at the diffusion bonding interface. The anodic electrolysis treatment was performed using a treatment solution (aqueous sodium hydroxide solution) having a pH of 5.0 or more and less than 12.0 under the conditions shown in Tables 2 and 3. The average crystal grain size of austenite of each austenitic stainless steel sheet after diffusion bonding is within a range of ± 100 to 200 μm in the thickness direction from the diffusion bonding interface in accordance with Japanese Industrial Standard JIS G 0551: 2013 “Steel-Crystal”. Microscopic Test Method for Particle Size ".

  In diffusion bonding, ten austenitic stainless steel sheets subjected to etching processing are laminated, a surface pressure of 0.01 to 30.00 MPa is applied in a non-oxidizing atmosphere, and isothermal holding is performed in a temperature range of 800 to 1050 ° C. gave.

  The bonding rate at the diffusion bonding interface was obtained by examining the void at the diffusion bonding interface by ultrasonic testing. Specifically, an evaluation is performed at the diffusion bonding interface by the transmission method, and transmission pulses are measured at a pitch of 0.2 mm for each of the vertical and horizontal directions of the measurement object. The position of 25% or less was determined as a void, and the area ratio of the diffusion bonding interface was calculated to obtain the bonding ratio.

  The Si concentration was obtained by the following method. First, in a cross section of the diffusion-bonded product parallel to the thickness direction of the steel sheet, a range of 100 μm × 100 μm is measured using EPMA, and the measurement step is set to 0.25 μm. The analysis was performed for each visual field so that a total of 9 visual fields were analyzed. Of these observation visual fields, the maximum Si amount in each analysis region (a region having a total width of 10 μm when the diffusion bonding interface is the center of the width) was defined as the maximum Si amount. The amount of the material Si was obtained by cutting out a test piece having a predetermined size from the diffusion-bonded product and analyzing it by an ICP-OES (inductively coupled plasma emission spectroscopy) analysis method. By dividing the obtained maximum Si amount by the material Si amount, the Si concentration was obtained.

  A bending test for confirming peeling from the diffusion bonding interface is performed at a bending angle of 90 ° in accordance with JIS Z 2248: 2014, and after the bending test, the presence or absence of peeling is observed by observing the diffusion bonding interface with an optical microscope. confirmed. In Tables 2 and 3, x indicates that peeling was observed, and x indicates that no peeling was observed.

  The test results are summarized in Tables 2 and 3.

In Examples 1 to 11 in Table 2, the diffusion bonding temperature and the surface pressure satisfy the ranges specified in the present invention, and the appropriate conditions (Σσ _k ≦ 25.0 (C / dm ² ) satisfying the expression (1). )), The anodic electrolytic treatment is performed. Therefore, the concentration of Si became 5.0 or less, and a diffusion bonding interface which did not peel in the peel test and was hard to peel was obtained.

  In Comparative Examples 1 and 2 in Table 2, the diffusion bonding temperature satisfies the range specified by the present invention, but the surface pressure is lower than the range specified by the present invention. Therefore, the Si concentration was larger than 5.0, and the bonding ratio was smaller than 60.0%, which did not show a sufficient result in the peeling test.

  In Comparative Examples 3 and 4 in Table 2, the surface pressure satisfies the range specified by the present invention, but the diffusion bonding temperature is lower than the range specified by the present invention. Therefore, in Comparative Example 3, the Si concentration was larger than 5.0, and the bonding ratio was smaller than 60.0%, so that a sufficient result was not shown in the peeling test. In Comparative Example 4, the diffusion bonding interface was not formed, and the bonding rate was 0%, which did not show a sufficient result in the peeling test.

  FIG. 2 is a diagram illustrating the relationship between the Si concentration and the bonding rate in Examples 1 to 11 and Comparative Examples 1 to 3 in Table 2. As is clear from FIG. 2, it can be seen that in the example where the Si concentration is 5.0 or less, the joining rate is 60.0% or more. On the other hand, it can be seen that in the case where the Si concentration is outside the range of the present invention (more than 5), the joining ratio is less than 60.0%.

Examples 11-1 to 11-5 in Table 3 show that the diffusion bonding temperature and the surface pressure satisfy the ranges defined by the present invention, and that the conditions (Σσ _k ≦ 25. 0 (C / dm ² )). On the other hand, in Comparative Example 11-6, the electrolysis conditions deviate from the range of Expression (1). Therefore, the Si concentration was larger than 5.0, and the bonding ratio was smaller than 60.0%, which did not show a sufficient result in the peeling test.

1 Cross section parallel to the thickness direction 2 Diffusion bonding interface 3 Steel plate 4 Observation field of view 5 Analysis area 10 Diffusion bonded product

Claims (2)

A plurality of laminated steel plates are joined to each other,
The steel sheet is expressed in mass%
C: 0.030% or less,
Si: 0.20 to 1.00%,
Mn: 0.6-1.5%,
Cr: 15.0 to 20.0%,
Ni: 6.0 to 9.0%,
Mo: 0.1-0.5%,
Cu: 0.1-0.5% and N: 0.030-0.150%
And Nb: 0.500% or less;
V: 0.500% or less and Ti: 0.500% or less.
A steel sheet having a chemical composition consisting of a balance of Fe and impurities,
A diffusion bonding interface is formed at the joint between the steel plates,
In the cross section of the diffusion bonding interface in the thickness direction of the steel sheet, the thickness direction of the steel sheet is defined as the width direction, and the maximum Si amount and the material Si amount in the entire width of 10 μm when the diffusion bonding interface is defined as the width center. The Si concentration (maximum Si content / material Si content), which is a ratio, is 5.0 or less;
A diffusion-bonded article having a bonding rate of 60.0% or more at the diffusion bonding interface. The steel sheet having the chemical composition according to claim 1 and having a metal structure in which the average grain size of austenite is 5.0 μm or less, in an electrolytic solution having a pH of 5.0 or more and less than 12.0, When n times of anodic electrolysis are continuously performed using n sets of electrodes, the amount of electricity per unit area in the k-th anodic electrolysis is σ _k (where k = 1 to n), when the total amount of electricity per unit area in the electrolytic process and Shigumashiguma _k, the sum Shigumashiguma _k of the quantity of electricity includes a first step of anodic electrolysis treatment under conditions satisfying the following formula (1),
A second step of directly laminating a plurality of the anodic-electrolyzed steel sheets and performing diffusion bonding at a diffusion bonding temperature of 850 to 1050 ° C. and a surface pressure of 0.03 to 30.00 MPa;
The method according to claim 1, wherein the steps are sequentially performed.
Σσ _k ≦ 25.0 (C / dm ² ) (1)

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