JPWO2020071534A1 - Austenitic stainless steel sheet and its manufacturing method - Google Patents

Abstract

In this austenitic stainless steel sheet, the chemical composition of the steel sheet is C: 0.005 to 0.150%, Si: 1.0% or less, Mn: 1.5% or less, P: 0.10% in mass%. Below, S: 0.010% or less, Al: 0.10% or less, Cr: 15.0 to 20.0%, Ni: 6.0 to 15.0%, N: 0.005 to 0.150% , Mo: 0 to 2.0%, Cu: 0 to 1.5%, Nb: 0 to 0.500%, V: 0 to 0.150%, Ti: 0 to 0.300%, B: 0 to 0 0.010%, balance: Fe and impurities, Md30 value = 497-462 × (C + N) -9.2 × Si-8.1 × Mn-13.7 × Cr-20 × (Ni + Cu) -18. The Md30 value obtained by 7 × Mo is 60 ° C. or less, the area ratio of martensite is 5.0% or less in the surface layer portion, and the area ratio of austenitic grains having a {110} plane orientation is 50. % Or more.

Description

The present invention relates to an austenitic stainless steel sheet and a method for producing the same.
The present application claims priority based on Japanese Patent Application No. 2018-189321 filed in Japan on October 04, 2018, the contents of which are incorporated herein by reference.

A member having a high surface gloss is used for a housing of an electronic device which is a precision machined part, and for example, a member made of a stainless steel plate is often used. In recent years, in order to stably obtain a member having a high surface gloss, the member is required to have better polishability than before.

In view of such a situation, for example, in Patent Documents 1 to 4, improvement of polishability of a stainless steel sheet is studied.
Patent Document 1 discloses a method for manufacturing a mirror-finished stainless steel sheet for a curved mirror, which has a wrapping-finished surface gloss and excellent image quality.
Further, Patent Document 2 discloses an austenitic stainless steel for press forming having improved polishability for mirror finishing.

Patent Document 3 discloses a method for producing a stainless steel strip and a steel plate having excellent polishability.
Patent Document 4 discloses a method for producing a steel strip having few surface minute defects in the production of austenitic stainless steel, a martensitic stainless steel, or a ferrite + austenitic two-phase stainless steel.

However, as a result of studies by the present inventors, it has been found that sufficient polishability may not be obtained by the above-mentioned conventional technique, and there is still room for further improvement.

Further, the precision machined parts as described above are often manufactured by a method of laminating stainless steel plates and diffusing joining them at a high temperature. For example, a method is adopted in which fine holes or patterns are formed on the surface by photoetching or precision processing by a laser, and then the steel sheets are laminated and diffusion-bonded to produce the steel sheets. Demand for such precision machined parts and products is on the rise, and further expansion of applications for diffusion bonding is expected in the future.

Good bondability is required for steel sheets used for these applications.
For example, in Patent Documents 5 to 9, improvement of diffusion bondability is studied.
Patent Document 5 proposes a method for producing a diffusion-bonded product, which can carry out the work without applying special high-temperature heating or high surface pressure by utilizing the growth of crystal grains accompanying the phase transformation during diffusion bonding. ..
Patent Document 6 provides a stainless steel with excellent reliability of the joint portion, which has a diffusion bonding structure in which there are many locations where crystal grains on the steel material side extend beyond the pre-bonding interface and invade the mating side. Diffusion bonding products are disclosed.
Patent Document 7 discloses a steel sheet in which the diffusion bondability is improved by controlling the austenite phase fraction during diffusion bonding.
Patent Document 8 describes a stainless steel having excellent diffusion bonding properties, which has fine crystal grains with an average grain size of 0.001 to 5 μm in the foil thickness direction and an Al content of 0.5 to 8%. Steel foil is disclosed.
Patent Document 9 states that the etching surface becomes smooth and the diffusion bondability is improved by making the particles finer.

However, as a result of studies by the present inventors, it has been found that sufficient diffusion bondability may not be obtained by the above-mentioned prior art, and there is still room for further improvement.

Japanese Patent Application Laid-Open No. 3-169405 Japanese Patent Application Laid-Open No. 9-3605 Japanese Patent Application Laid-Open No. 62-253732 Japanese Patent Application Laid-Open No. 2000-273546 Japanese Patent Application Laid-Open No. 2013-103271 Japanese Patent Application Laid-Open No. 2013-173181 Japanese Patent Application Laid-Open No. 2016-89223 Japanese Patent Application Laid-Open No. 9-279310 International Publication No. 2016/043125

The present invention has been made to solve the above problems, and an object of the present invention is to provide an austenitic stainless steel sheet having good polishability. In the present invention, "having good polishability" means that smoothing can be easily performed by mechanical polishing. The austenitic stainless steel sheet preferably has good abrasiveness and further has good diffusion bondability.

(1) The austenite-based stainless steel plate according to one aspect of the present invention has a chemical composition of C: 0.005 to 0.150%, Si: 1.0% or less, Mn: 1.5% or less in mass%. , P: 0.10% or less, S: 0.010% or less, Al: 0.10% or less, Cr: 15.0 to 20.0%, Ni: 6.0 to 15.0%, N: 0 .005 to 0.150%, Mo: 0 to 2.0%, Cu: 0 to 1.5%, Nb: 0 to 0.500%, V: 0 to 0.150%, Ti: 0 to 0. 300%, B: 0 to 0.010%, total of Ca, Mg, Zr, Sn, Pb, W: 0 to 0.10%, balance: Fe and impurities, and Md30 calculated by the following formula (i). The value is 60 ° C. or less, the area ratio of martensite is 5.0% or less in the surface layer portion, and the area ratio of austenite grains having a {110} plane orientation is 50% or more.
Md30 value = 497-462 × (C + N) -9.2 × Si-8.1 × Mn-13.7 × Cr-20 × (Ni + Cu) -18.7 × Mo ... (i)
However, the element symbol in the above formula represents the content (mass%) of each element in steel, and if it is not contained, 0 is substituted.
(2) The austenitic stainless steel sheet according to (1) above has a chemical composition of Nb: 0.010 to 0.500%, a Md30 value of 20 to 60 ° C., and a surface layer portion. The average particle size of the austenitic grains in the above may be 5.0 μm or less, and the X-ray random intensity ratio of the austenitic grains in the {110} <112> orientation may be 8.5 or more.
(3) The austenite-based stainless steel plate according to (1) or (2) above has a chemical composition of% by mass, Mo: 0.1 to 2.0%, Cu: 0.1 to 1.5%. , Nb: 0.010 to 0.500%, V: 0.010 to 0.150%, Ti: 0.010 to 0.300%, and B: 0.001 to 0.010%. May contain one or more of them.
(4) The method for producing an austenitic stainless steel sheet according to another aspect of the present invention is the austenitic stainless steel sheet according to any one of (1) to (3) above, under the condition that the rolling ratio is 50% or less. A process for performing temper rolling is provided.

According to the above aspect of the present invention, an austenitic stainless steel sheet having good polishability can be obtained industrially stably.
Further, according to a preferred embodiment of the present invention, it is possible to obtain an austenitic stainless steel sheet having good diffusible bondability in addition to good abrasiveness.

It is a figure which shows the ODF of the cross section of φ2 = 45 °.

Hereinafter, each requirement of the austenitic stainless steel sheet (austenitic stainless steel sheet according to the present embodiment) according to the embodiment of the present invention will be described in detail.

1. 1. The reasons for limiting the chemical composition of each element are as follows. In the following description, "%" for the content means "mass%". In addition, the numerical range indicated by sandwiching "~" includes the numerical values at both ends of the range. On the other hand, the values indicated by "less than" and "greater than" are not included in the range.

C: 0.005 to 0.150%
C is a strong solid solution strengthening element that inexpensively increases the strength of the steel sheet. However, if the C content is excessive, coarse carbides are generated, and random crystal rotation occurs around the carbides during rolling deformation during hot rolling or cold rolling, thereby randomizing the crystal orientation. Therefore, the C content is set to 0.150% or less. The C content is preferably 0.130% or less, more preferably 0.120% or less.
On the other hand, if the C content is less than 0.005%, only an increase in manufacturing cost is caused, and a particularly effective effect cannot be obtained. Therefore, the C content is set to 0.005% or more. Further, C has an effect of suppressing recrystallization and grain growth by binding to Nb and precipitating as a fine Nb compound. When this effect is obtained, the C content is preferably 0.010% or more.

Si: 1.0% or less If the Si content is excessive, there is a high possibility that coarse oxides will be formed, and there is a concern that processability will deteriorate. Therefore, the Si content is 1.0% or less. The Si content is preferably 0.6% or less.
On the other hand, Si is an element that is used as a deoxidizing material during melting and also contributes to the strengthening of steel. When these effects are desired, the Si content is preferably 0.1% or more.

Mn: 1.5% or less Mn is a strong austenite-forming element. Therefore, if the Mn content is excessive, the amount of work-induced martensite generated during cold rolling is reduced, so that the accumulation in the {110} plane orientation after final annealing is reduced. In addition, fine crystal grains cannot be obtained. Therefore, the Mn content is set to 1.5% or less. The Mn content is preferably 1.2% or less.
On the other hand, Mn is an element that contributes to the prevention of brittle fracture during hot working and the strengthening of steel. When the above effect is desired, the Mn content is preferably 0.1% or more.

P: 0.10% or less P is an impurity element. If the P content exceeds 0.10%, the workability is significantly deteriorated. Therefore, the P content is limited to 0.10% or less. Since it is preferable that the P content is low, it may be 0%. However, setting the P content to less than 0.005% is not preferable in terms of cost. Therefore, the lower limit of the P content may be 0.005%.

S: 0.010% or less S is an impurity element. If the S content exceeds 0.010%, it causes melt embrittlement during hot working. Therefore, the S content is limited to 0.010% or less. Since the S content is preferably small, it may be 0%. However, setting the S content to less than 0.001% is not preferable in terms of cost. Therefore, the lower limit of the S content may be 0.001%.

Al: 0.10% or less Al is an impurity element. If the Al content exceeds 0.10%, the processability is lowered, oxides are generated at the time of bonding, and the diffusion bonding property is lowered. Therefore, the Al content is limited to 0.10% or less. Since it is preferable that the Al content is low, it may be 0%. However, setting the Al content to less than 0.01% is not preferable in terms of cost. Therefore, the lower limit of the Al content may be 0.01%.

Cr: 15.0 to 20.0%
Cr is a basic element of stainless steel, and is an element that forms an oxide layer on the surface of a steel material and exerts an action of enhancing corrosion resistance. In order to obtain this effect, the Cr content is set to 15.0% or more. The Cr content is preferably 16.0% or more.
On the other hand, Cr is a strong ferrite stabilizing element. Therefore, if the Cr content is excessive, δ ferrite is formed. This δ ferrite deteriorates the hot workability of the material. Therefore, the Cr content is set to 20.0% or less. The Cr content is preferably 19.0% or less.

Ni: 6.0 to 15.0%
Ni is an austenite-forming element and is an element having an action of stabilizing the austenite phase at room temperature. In order to obtain this effect, the Ni content is set to 6.0% or more. The Ni content is preferably 6.5% or more.
On the other hand, if the Ni content is excessive, the austenite phase becomes too stable and the process-induced martensitic transformation during cold rolling does not occur, so that the accumulation in the {110} plane direction decreases. In addition, Ni is an expensive element, and excessive increases in its content can lead to significant cost increases. Therefore, the Ni content is set to 15.0% or less. The Ni content is preferably 11.0% or less, more preferably 9.0% or less.

N: 0.005 to 0.150%
Like C, N is a solid solution strengthening element and is an element that contributes to improving the strength of steel. Further, it is not preferable from the viewpoint of cost that the N content is less than 0.005%. Therefore, the N content is set to 0.005% or more.
Further, N is bonded to Nb and precipitated as a fine Nb compound during hot rolling or annealing, and has an effect of suppressing recrystallization and grain growth. When this effect is obtained, the N content is preferably 0.010% or more.
On the other hand, if the N content is excessive, a large number of coarse nitrides are produced in the manufacturing process of the steel sheet. Since these coarse nitrides serve as a starting point of fracture and significantly deteriorate the hot workability, production becomes difficult when a large number of coarse nitrides are produced. Further, N is also a strong austenite stabilizing element like C, and if the N content is excessive, the processing-induced transformation required for grain refinement does not occur. Therefore, the N content is set to 0.150% or less. The N content is preferably 0.130% or less, more preferably 0.120% or less.

The austenitic stainless steel sheet according to the present embodiment is basically composed of the above-mentioned elements and the balance is Fe and impurities. However, in order to improve various properties, one or more selected from Mo, Cu, Nb, V, Ti, and B may be contained in the range described later. However, since these elements do not necessarily have to be contained, the lower limit thereof is 0%.
Here, the "impurity" is a component mixed with raw materials such as ore and scrap, and various factors in the manufacturing process when steel is industrially manufactured, and has an adverse effect on the austenitic stainless steel sheet according to the present embodiment. Means what is allowed within the range that does not give.

Mo: 0-2.0%
Mo is an element that improves the corrosion resistance of the material. Therefore, it may be contained as needed. When the above effect is desired, the Mo content is preferably 0.1% or more.
On the other hand, Mo is an extremely expensive element, and an excessive increase in its content causes a significant increase in cost. Therefore, even when it is contained, the Mo content is set to 2.0% or less. The Mo content is preferably 1.0% or less.

Cu: 0-1.5%
Cu is an austenite-forming element and is an effective element for adjusting the stability of the austenite phase. Therefore, it may be contained as needed. When the above effect is desired, the Cu content is preferably 0.1% or more.
On the other hand, if the Cu content is excessive, Cu segregates at the grain boundaries during the manufacturing process. Since such grain boundary segregation causes the hot workability to be significantly deteriorated, if Cu segregates at the grain boundaries, production becomes difficult. Therefore, even when it is contained, the Cu content is set to 1.5% or less. The Cu content is preferably 1.0% or less.

Nb: 0 to 0.500%
Nb is an element that produces fine carbides or nitrides during annealing. Since these fine carbides or nitrides suppress the grain growth of crystals by the pinning effect, Nb is an element effective for refining the crystal grains of the material. In addition, Nb is an element that develops the processed texture of austenite by dissolving it in solid solution or as a carbonitride by suppressing recrystallization during hot processing. Therefore, it may be contained.
When the average particle size of the austenite grains is 5.0 μm or less and the random intensity ratio of X-rays in the {110} <112> orientation of the austenite grains is 8.5 or more, the Nb content may be 0.010% or more. preferable. The Nb content is more preferably 0.030% or more, and even more preferably 0.040% or more.
On the other hand, if the Nb content is excessive, recrystallization is suppressed, a large amount of unrecrystallized portion remains after annealing, and hot workability deteriorates. In addition, Nb is an extremely expensive element, and an excessive increase in the content causes a significant increase in cost.
Therefore, even when it is contained, the Nb content is set to 0.500% or less. The Nb content is preferably 0.300% or less, more preferably 0.200% or less.

V: 0 to 0.150%
Ti: 0 to 0.300%
Both V and Ti are elements having the effects of suppressing recrystallization, strengthening the desired texture, and refining the crystal grains. Therefore, one or more selected from these may be contained as needed. In order to obtain the above effect, it is preferable to contain at least one selected from V: 0.010% or more and Ti: 0.010% or more.
On the other hand, if the above elements are excessively contained, the workability deteriorates. Therefore, even when it is contained, the V content is 0.150% or less and the Ti content is 0.300% or less.

B: 0 to 0.010%
B is an element that strengthens the grain boundaries and contributes to the improvement of hot workability. Therefore, it may be contained as needed. In order to obtain the above effect, the B content is preferably 0.001% or more.
On the other hand, if B is excessively contained, the workability is rather deteriorated. Therefore, even when it is contained, the B content is 0.010% or less.

As described above, the chemical composition of the austenitic stainless steel sheet according to the present embodiment contains essential elements and the balance is Fe and impurities, or contains essential elements and contains one or more arbitrary elements and the balance is Fe. And impurities. Examples of the "impurity" include Ca, Mg, Zr, Sn, Pb, W and the like in addition to the above-mentioned P, S and Al. The total amount of impurity elements such as Ca, Mg, Zr, Sn, Pb, and W excluding P, S, and Al is preferably 0.10% or less.

Md30 value: 60 ° C. or lower The Md30 value is an index showing the stability of austenite in the austenitic stainless steel sheet or the like according to the present embodiment, and is calculated from the chemical composition when rolled at a reduction ratio of 30%. It is a value considered to correspond to the temperature at which 50% by volume of processing-induced martensite is produced. When the Md30 value exceeds 60 ° C., the austenite that has been reverse-transformed during the heat treatment may become martensite again during the cooling process or temper rolling. In this case, the amount of austenite is reduced, and as a result, the area ratio of the grains having the {110} plane orientation is also reduced.
Therefore, the Md30 value obtained by the following formula (i) is set to 60 ° C. or lower. The Md30 value is preferably 55 ° C. or lower, and more preferably 50 ° C. or lower.
Md30 value (° C.) = 497-462 x (C + N) -9.2 x Si-8.1 x Mn-13.7 x Cr-20 x (Ni + Cu) -18.7 x Mo ... (i)
However, the element symbol in the above formula represents the content (mass%) of each element in steel, and if it is not contained, 0 is substituted.

When the Md30 value is 20 ° C. or higher, the transformation from austenite to process-induced martensite (martensite) during cold rolling and the reverse transformation from process-induced martensite to austenite during subsequent heat treatment are utilized. Fine crystal grains are obtained. It is also advantageous for the development of {100} plane orientation, especially {110} <112> orientation.
Therefore, when the average particle size of the austenite grains is 5.0 μm or less and the X-ray random intensity ratio of the {110} <112> orientation of the austenite grains is 8.5 or more, the Md30 value is 20 to 60 ° C. Is preferable. The Md30 value is more preferably 25 ° C. or higher, and even more preferably 30 ° C. or higher.

2. Metal structure In order to obtain good polishability, it is important to control the metal structure on the surface layer of the steel sheet. Specifically, it is necessary to adjust the area ratio of martensite and austenite grains having a {110} plane orientation in the surface layer portion of the steel sheet to the range shown below. Each regulation will be explained in detail. In the present embodiment, the surface layer portion of the steel plate means a region from the surface to a position of 1/10 of the plate thickness in the plate thickness direction.

Area ratio of martensite in the surface layer: 5.0% or less Martensite is a hard structure. Therefore, if martensite is excessively present on the surface layer of the steel sheet in the manufacturing stage before polishing, the polishability deteriorates. Further, as the area ratio of martensite increases, the area ratio of grains having the {110} plane orientation of austenite decreases relatively. Therefore, the area ratio of martensite on the surface layer of the steel sheet shall be 5.0% or less. The area ratio is preferably 4.0% or less, and more preferably 3.0% or less.
In addition, if the surface layer of the steel sheet contains a large amount of martensite, the martensite is transformed into the austenite phase when heat is applied by diffusion bonding or laser processing, and the flatness of the steel sheet is reduced, resulting in reduced diffusion bonding property. do. In addition, if the surface layer of the steel sheet contains a large amount of martensite, the area ratio of the austenite phase is reduced, so that the fraction of the grains having the {110} <112> orientation to the entire structure is also reduced. Therefore, from the viewpoint of diffusion bondability, the area ratio of martensite in the surface layer portion is preferably 5.0% or less.
In the austenitic stainless steel sheet according to the present embodiment, the structure other than martensite is substantially austenite.

The area ratio of martensite on the surface layer is determined by the following procedure.
First, for a surface parallel to the surface of a steel plate having an area of 100 μm × 100 μm or more obtained by electropolishing or chemically polishing the material, the fcc structure and the bcc structure are selected as crystal structures, and measurement is performed by EBSD. Then, a region that is not discriminated from the fcc structure, that is, a region having a bcc crystal structure, or a region that cannot be measured with high strain (however, none of them includes a linear region such as a grain boundary) is regarded as martensite, and its area is regarded as martensite. Find the rate.

If finish polishing with an abrasive such as colloidal silica is performed when preparing the sample, the austenite phase of the surface layer may undergo process-induced martensitic transformation. Therefore, be sure to prepare a sample by electrolytic polishing or chemical polishing. Further, in order to observe the surface layer portion which is a region from the surface to the position of 1/10 of the plate thickness in the plate thickness direction, the amount of polishing is limited to 1/10 of the plate thickness.

Area ratio of austenite grains having {110} plane orientation on the surface layer: 50% or more The {110} plane orientation is a typical main orientation of the rolled texture of austenite. Good polishability is ensured by setting the area ratio of the austenitic grains having the above-mentioned plane orientation in the surface layer portion of the austenitic stainless steel sheet according to the present embodiment to 50% or more. The area ratio of the austenite grains having the above-mentioned plane orientation is preferably 52% or more, and more preferably 55% or more. The upper limit is not particularly set, but if the area ratio of the austenite grains having the above-mentioned plane orientation exceeds 85%, the toughness decreases, so it is desirable to set the upper limit to 85%.

The area ratio of the austenite grains having the {110} plane orientation in the surface layer portion can be obtained by the following method.
First, in the surface layer portion of the material produced by the above method, a region having an area of 500 μm × 500 μm or more is measured by EBSD. Then, a region having a crystal structure of fcc and surrounded by a grain boundary of 15 ° or more is regarded as an austenite grain. Strictly speaking, the {110} plane orientation has a crystal orientation in which the <110> axis is parallel to the vector perpendicular to the surface of the steel plate (= the angle difference from the vector perpendicular to the surface is 0). In the form, an angle difference of 0 to 15 ° is allowed. The total area of the grains having the {110} plane orientation among the austenite grains is divided by the measured area, and the value multiplied by 100 is taken as the area ratio (%) of the austenite grains having the {110} plane orientation.

Average grain size of austenite grains in the surface layer: 5.0 μm or less By setting the average grain size of austenite grains in the surface layer to 5.0 μm or less, the number of crystal grains per unit area increases, and {110} <112> Since the frequency of existence of azimuth grains is averaged, it is considered that the diffusion bondability is improved. Further, when the average particle size of the austenite grains is 5.0 μm or less, the processed surface becomes smooth when etching processing or the like is performed.
Therefore, in order to improve the diffusion bondability, it is preferable that the average particle size of the austenite grains in the surface layer portion is 5.0 μm or less.

The average particle size of austenite grains is calculated by the following procedure.
First, in the surface layer portion of the material produced by the above method, an area of 100 μm × 100 μm or more was measured by EBSD, and among the regions determined to have an fcc structure, a region surrounded by a boundary with an orientation difference of 15 ° or more was 1 It is regarded as one crystal grain, and the average area S per crystal grain is calculated from the number of crystal grains contained in a predetermined area.
Then, from the average area, the average particle size D of the austenite grains is calculated by the following formula (iii).
D = (2S / π) ^0.5 ... (iii)

X-ray random intensity ratio of {110} <112> orientation: 8.5 or more The {110} <112> orientation is a typical main orientation of the rolled texture of austenite. High diffusion bondability is ensured by setting the accumulation in the same direction on the surface layer portion (joint surface) of the steel sheet to 8.5 or more. Therefore, when improving the diffusion bondability, it is preferable that the X-ray random intensity ratio in the {110} <112> orientation is 8.5 or more. The X-ray random intensity ratio in the {110} <112> orientation is more preferably 9.0 or more, and even more preferably 10.0 or more. The upper limit of the X-ray random intensity ratio of the {110} <112> orientation is not particularly set, but if the X-ray random intensity ratio exceeds 20.0, the orientation difference of 15 ° or more with the adjacent crystal grains cannot be satisfied. Since it does not act as an effective grain boundary, it is desirable to set this value as the upper limit.

The X-ray random intensity ratio of the {110} <112> orientation is calculated by the series expansion method based on a plurality of pole diagrams among the {200}, {311}, and {220} pole diagrams measured by X-ray diffraction. It may be obtained from the crystal orientation distribution function (referred to as Origination Distribution Function, ODF) representing the three-dimensional texture. The X-ray random intensity ratio in the present embodiment is a test obtained by measuring the X-ray intensity of a standard sample having no accumulation in a specific direction and a test material by an X-ray diffraction method or the like under the same conditions. It is a numerical value obtained by dividing the X-ray intensity of the material by the X-ray intensity of the standard sample. The standard sample used is one that does not have a specific accumulation in any of the surface measurements of {200}, {311}, and {220}. The method for preparing a standard sample is not specified, but it is prepared by compressing and sintering a metal powder having an fcc crystal structure stably at room temperature with Fe groups such as Fe-C, Fe-Ni, and Fe-Cr. It is common.
FIG. 1 shows an ODF having a cross section of φ2 = 45 ° in which the above-mentioned crystal orientation is displayed. Strictly speaking, the {110} <112> direction refers to the direction expressed by φ1 = 55 ° and Φ = 90 °. However, since measurement errors may occur due to test piece processing and sample setting, the maximum value in the range of φ1 = 50 to 60 ° and Φ = 85 to 90 ° is represented as the intensity ratio in this direction.

Here, as the crystal orientation, the orientation perpendicular to the plate surface is usually indicated by (hkl) or {hkl}, and the orientation parallel to the rolling direction is indicated by [uvw] or <uvw>. {Hkl} and <uvw> are generic names for equivalent planes, and (hkl) and [uvw] refer to individual crystal planes. That is, since the fcc structure is targeted in this embodiment, for example, (111), (-111), (1-11), (11-1), (-1-11), (-11-1), (-11-1) ), (1-1-1), (1-1-1) planes are equivalent and indistinguishable.
In such a case, these directions are collectively referred to as {111}.

Since ODF is also used to display the orientation of a crystal structure with low symmetry, it is generally expressed as φ1 = 0 to 360 °, Φ = 0 to 180 °, and φ2 = 0 to 360 °, and each orientation is expressed. It is displayed as (hkl) and [uvw]. However, in the present invention, since the fcc crystal structure having high symmetry is targeted, Φ and φ2 are expressed in the range of 0 to 90 °. Further, the range of φ1 changes depending on whether or not symmetry due to deformation is taken into consideration when performing the calculation, but in the present invention, φ1 is expressed as φ1 = 0 to 90 ° in consideration of symmetry. That is, a method is selected in which the average value of the same direction at φ1 = 0 to 360 ° is expressed on the ODF of 0 to 90 °. In this case, (hkl), [uvw] and {hkl} <uvw> are synonymous.
Therefore, for example, the X-ray random intensity ratio of (110) [1-12] of the ODF in the φ2 = 45 ° cross section shown in FIG. 1 is synonymous with the X-ray random intensity ratio of the {110} <112> orientation. be.

Further, the sample for X-ray diffraction is prepared as follows.
When improving the diffusion bondability, the X-ray random intensity ratio of the surface layer portion to be the bonding surface is important. For X-ray measurement, some mechanical polishing, chemical polishing, and electrolytic polishing are required to obtain the flatness of the measurement surface or to remove strain. Therefore, the surface layer portion from the surface of the steel sheet to the position of 1/10 of the plate thickness is adjusted so as to be the measurement surface.
When the measurement by X-ray diffraction is difficult, a statistically sufficient number of measurements may be performed by the EBSD (Electron Backscattering Pattern) method or the ECP (Electron Channeling Pattern) method.

The thickness of the austenitic stainless steel sheet according to the present embodiment is not limited, but is, for example, 0.5 mm or less.

3. 3. Manufacturing Method The method for manufacturing the austenitic stainless steel sheet according to the present embodiment is not particularly limited, but it can be manufactured by the method shown below. In the method for producing an austenitic stainless steel sheet according to the present embodiment, the steel is melted and cast by a conventional method to obtain a steel piece to be subjected to hot rolling. This steel piece may be made by forging or rolling a steel ingot, but from the viewpoint of productivity, it is preferable to manufacture the steel piece by continuous casting. Further, it may be manufactured by using a thin slab caster or the like.
The austenitic stainless steel sheet according to the present embodiment can be manufactured by applying a manufacturing method including the following steps to the obtained steel pieces.

(A) Heating step Normally, the steel pieces are cooled after casting and heated again for hot rolling. In the method for producing an austenitic stainless steel sheet according to the present embodiment, the heating temperature of the steel piece during hot rolling is 1150 ° C. or higher. This is because when the heating temperature is less than 1150 ° C., the coarse carbonitride remains undissolved, which may be the starting point of cracking during hot working, and promotes randomization of the texture during hot rolling (desirably). This is because the formation of the texture is suppressed). The heating temperature is preferably 1170 ° C. or higher. The upper limit of the heating temperature is not particularly specified, but heating above 1400 ° C. leads to a decrease in productivity and may lead to growth in an orientation that does not develop in normal rolling. Therefore, it is desirable to set the upper limit at 1400 ° C.
After casting the molten steel, a process such as continuous casting-direct rolling (CC-DR), in which hot rolling (without reheating) is performed before the temperature drops below 1150 ° C., may be adopted. ..

(B) Hot Rolling Step In the method for manufacturing an austenitic stainless steel sheet according to the present embodiment, hot rolling is performed on a heated steel piece. At that time, hot rolling is completed in a temperature range of 880 to 1000 ° C. If the end temperature of hot rolling is less than 880 ° C., the deformation resistance becomes too high, the productivity is significantly impaired, and the development of shear faults on the surface layer of the hot-rolled sheet is promoted. The end temperature is preferably 900 ° C. or higher.
On the other hand, when the end temperature of hot rolling exceeds 1000 ° C, recrystallization occurs in all rolling passes, and the degree of aggregation of the texture of the hot-rolled steel sheet decreases (the structure is randomized). The area ratio of austenite grains having 110} plane orientation is reduced. In addition, the X-ray random intensity ratio of the {110} <112> orientation at the surface layer portion also decreases. Therefore, the hot rolling end temperature is set to 1000 ° C. or lower. The end temperature is preferably 980 ° C. or lower, and more preferably 950 ° C. or lower.

Further, in the hot rolling step, the shape ratio L obtained by the following formula (ii) is set to 4.5 or less in the final two passes. When at least one of the shape ratios of the final two passes exceeds 4.5, friction between the steel plate and the rolling roll forms a layer called a shear fault on the surface layer of the hot-rolled plate, which has a different crystal orientation from the central layer of thickness. Will be done. Since the shear fault does not include the {110} plane orientation, the area ratio of austenite grains having the {110} plane orientation also decreases when the shear fault develops at the stage of hot rolling. Further, since the shear fault does not include the {110} <112> orientation, the {110} <112> of the surface layer portion is also reduced. The shape ratio L is preferably 4.2 or less, and more preferably less than 4.0. The lower limit of the shape ratio L is not particularly set, but if it is less than 2.5, the thickness of the hot-rolled plate becomes thick and the load of cold rolling becomes high. Therefore, it is desirable that the shape ratio is 2.5 or more in each of the final two passes. The shape ratio L is more preferably 2.8 or more, and further preferably 3.0 or more.

_{L = (√ (R × (} t in -t out))) / ((2t out + t in) / 3) ··· (ii)
However, the meanings of the symbols in the formula are as follows.
L: Shape ratio in the pass R: Roll radius (mm) in the pass
tin: Entry side plate thickness (mm) _{in the relevant path}
to _out : Outer plate thickness (mm) in the path

(C) Winding step A steel sheet (hot-rolled sheet) that has been hot-rolled under the above conditions is wound in a temperature range of 900 ° C. or lower. When the winding temperature exceeds 900 ° C., recrystallization proceeds during winding and the desired texture is weakened. The winding temperature is preferably 880 ° C. or lower, more preferably 850 ° C. or lower.
The lower limit of the take-up temperature is not particularly specified, but even if the take-up temperature is lower than 550 ° C., not only a special effect cannot be obtained, but also the strength of the coil becomes high and rewinding becomes difficult. Therefore, it is desirable that the winding temperature is 550 ° C. or higher.

After completing the above hot rolling, cold rolling and annealing are repeated once or a plurality of times in the same manner as in a general process to manufacture a steel sheet. At that time, only each final process is limited as described later. The temperature other than the final step is not particularly limited, but the general temperature of annealing other than the final step (intermediate annealing) is 900 to 1100 ° C.

(D) Final cold rolling process When the rolling ratio (rolling ratio) of the final cold rolling is less than 40%, the work texture is not formed and the {110} plane orientation does not develop. Therefore, the rolling ratio of the final cold rolling is set to 40% or more. Further, when the rolling ratio is less than 40%, the martensitic transformation during cold rolling does not occur sufficiently, and the granulation does not occur due to the subsequent reverse transformation during annealing. Therefore, the rolling ratio is set to 40% or more from the viewpoint of reducing the austenite particle size. The rolling ratio is preferably 45% or more, and more preferably 50% or more.
On the other hand, when the rolling ratio exceeds 90%, an orientation different from that of normal rolling develops, the area ratio of austenite grains having a {110} plane orientation decreases, and the load on the apparatus becomes extremely high. Therefore, the rolling ratio is set to 90% or less. The rolling ratio is preferably 85% or less, and more preferably 80% or less.

Furthermore, if the roll diameter of the rolling roll in the final cold rolling process is small, a shear fault is formed on the surface layer of the steel sheet due to friction between the steel sheet and the rolling roll, and an orientation different from the {110} plane orientation develops. do. Therefore, the roll diameter of the rolling roll in the final cold rolling step is set to 80 mm or more. The roll diameter is preferably 90 mm or more, and more preferably 100 mm or more.

(E) Final annealing step When the ultimate temperature of final annealing is less than 600 ° C., the processed α structure remains and the proportion of austenite grains having a {110} plane orientation decreases. Therefore, the polishability cannot be ensured. Further, when the final annealing temperature is less than 600 ° C., reverse transformation does not occur and the average particle size of austenite grains exceeds 5.0 μm. Therefore, the ultimate temperature in the final annealing is 600 ° C. or higher. The final annealing temperature is preferably 650 ° C. or higher, and more preferably 700 ° C. or higher.
On the other hand, when the ultimate temperature of final annealing exceeds 1000 ° C., grain growth is promoted, the particle size is coarsened, the toughness is lowered, and orientations other than the {110} plane orientation are developed. In addition, the X-ray random intensity ratio in the {110} <112> orientation also decreases. Therefore, the ultimate temperature in the final annealing is 1000 ° C. or lower. The ultimate temperature of final annealing is preferably 980 ° C or lower, and more preferably 970 ° C or lower.
The holding time at the annealing temperature (reached temperature) shall be 60 seconds or less. Holding for more than 60 seconds causes randomization of the texture and coarsening of the particle size. From this viewpoint, the holding time is preferably 30 seconds or less, more preferably 10 seconds or less.

In addition to the above production conditions, the hot-rolled sheet may be annealed (intermediate annealing) before cold rolling. The annealing temperature before cold rolling is preferably 600 to 1000 ° C. This is because if the temperature is lower than 600 ° C, the hot-rolled sheet is not sufficiently softened and the processing load during cold rolling becomes high. If the temperature exceeds 1000 ° C, the particle size becomes coarse and static recrystallization occurs. This is because the tissue is randomized as it progresses.

After final annealing, cold rolling (heat treatment rolling) for the purpose of adjusting the mechanical properties of the steel sheet, followed by reduction of residual stress (strain removal) that causes a change in the shape of the sheet and to the γ matrix. Heat treatment for the purpose of reverse transformation may be carried out. By these steps, the mechanical properties of the austenitic stainless steel sheet can be adjusted to a preferable range.
When performing temper rolling, it is desirable that the rolling ratio is 50% or less. This is because if the rolling ratio is 50% or less, it can be adjusted to the necessary mechanical properties specified in JIS standards (G4305) and the like. When heat treatment is performed, the heat treatment temperature is preferably 600 ° C. to 900 ° C., more preferably 650 to 850 ° C. This is because the effect of strain removal cannot be obtained below 600 ° C. and reverse transformation does not occur. Further, at a temperature exceeding 900 ° C., the effect of performance adjustment in cold rolling disappears.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Example 1>
Steel pieces having the chemical compositions shown in Table 1 are melted to produce steel pieces, and the steel pieces are heated and roughly rolled hot, and then Table 2-1 and Table 2-2. Finish rolling was performed under the conditions shown in. In Tables 2-1 and 2-2, SRT (° C) is the heating temperature of the steel piece, L1 is the shape ratio in the pass immediately before the final pass, L2 is the shape ratio in the final pass, and FT (° C). Indicates the temperature after the final pass of finish rolling, that is, on the finish side. CT (° C) indicates the take-up temperature.
After hot rolling, pickling is performed, intermediate cold rolling with a rolling reduction of 60% (intermediate cold rolling), intermediate annealing at 1050 ° C. for 20 minutes, and then final cold rolling to a thickness of 0.2 mm. Obtained a steel plate. CR (%) indicates the rolling ratio of the final cold rolling. Then, annealing was carried out to raise the temperature to the ultimate temperature indicated by AT (° C.).

Regarding the obtained austenitic stainless steel sheet, the area ratio of martensite (α'), the average particle size of austenite grains (γ), the area ratio of austenite grains having {110} plane orientation, and {110} <112 in the surface layer portion. > The X-ray random intensity ratio of the orientation was measured.

The average particle size of austenite grains and the area ratio of martensite in the surface layer were measured by the following methods. First, an EBSD was used to measure a surface having an area of 500 μm × 500 μm and parallel to the steel plate surface at a position 1/10 of the plate thickness in the plate thickness direction from the steel plate surface. Then, among the regions determined to have the fcc structure, the region surrounded by the boundary having an orientation difference of 15 ° or more is regarded as one crystal grain, and the number of crystal grains contained in the predetermined area is used to determine the number of crystal grains per crystal grain. The average area S was calculated. From the average area, the average particle size D of the austenite grains was calculated by the above formula (iii).
Further, a region that is not discriminated from the fcc structure, that is, a region having a bcc crystal structure or a region that cannot be measured due to high strain is regarded as martensite (however, linear regions such as grain boundaries are excluded). The area ratio was calculated.
The area ratio of martensite (α'area ratio) and the average particle size of austenite grains (γ particle size) show the average values after final annealing.

The area ratio ({110} plane γ area ratio) of the austenite grains having the {110} plane orientation of the surface layer portion was measured as follows.
First, with respect to a surface parallel to the surface of the steel sheet similar to the above, a region having an area of 500 μm × 500 μm was measured by EBSD. Then, a region having a crystal structure of fcc and surrounded by grain boundaries of 15 ° or more is regarded as an austenite grain, and the <110> axis faces 0 to 15 ° with respect to a vector perpendicular to the surface of the steel plate. The grains having a crystal orientation were defined as austenite grains having a {110} plane orientation. Then, the total area of the grains having the {110} plane orientation was divided by the measured area and multiplied by 100 to obtain the area ratio of the austenite grains having the {110} plane orientation.

The X-ray random intensity ratio ({110} <112> X-ray random intensity ratio) in the {110} <112> orientation of the surface layer portion of the steel sheet was measured as follows.
First, the steel sheet is mechanically polished and buffed, and then electropolished to remove strain, and the sample is adjusted so that the surface parallel to the surface of the steel sheet, which is 1/10 of the thickness of the steel sheet, becomes the measurement surface. X-ray diffraction was performed using. X-ray diffraction of a standard sample without accumulation in a specific orientation was also performed under the same conditions.
Based on the {200}, {311}, and {220} pole figures obtained by X-ray diffraction, ODF was obtained by a series expansion method. Then, the X-ray random intensity ratio was determined from this ODF. For the X-ray diffraction of the surface layer portion, the front side of the steel sheet was measured.

The polishability of the above austenitic stainless steel sheet was evaluated.
The polishability was evaluated as follows.
After collecting a test piece having a length of 100 mm, a width of 150 mm, and a thickness of 0.2 mm from the above austenitic stainless steel plate, the surface pressure of the collected test piece is 8.0 N / cm ² , and the abrasive grain # 400 is alumina. Polishing was performed under the conditions of a rotation speed of 300 rpm and a polishing time of 10 seconds. Then, the roughness Ra after polishing was measured according to JIS B 0601: 2013. In this example, when the roughness Ra after polishing is 0.050 μm or less, it is judged that the austenitic stainless steel sheet has good polishability.

Further, the diffusion bondability of the above austenitic stainless steel sheet was evaluated as follows.
After stacking two 50 mm × 50 mm (× thickness) steel sheets collected from the above austenitic stainless steel sheet, a stress of 30 MPa was applied and the steel sheet was held at 900 ° C. for 30 seconds for diffusion bonding. Then, the voids at the diffusion joint were evaluated by ultrasonic flaw detection.
The diffusion junction was evaluated by the transmission method, and the position where the transmission pulse height was 25% or more was determined as the diffusion junction and the position where the transmission pulse height was less than 25% was determined as the void portion, and the area ratio of the diffusion junction was calculated.
In this example, when the area ratio of the diffusion joint portion is 70% or more, it is judged that the diffusion bondability of the austenitic stainless steel sheet is good.

In the transmission method, in the process in which ultrasonic waves transmitted from the transmitting probe pass through the measurement object and are received by the receiving probe, the ultrasonic waves are generated due to causes such as scattering due to defects in the measurement object. This is a method of grasping the size and degree of defects inside the object to be measured from the degree of attenuation. The height of the transmitted pulse received after passing through the object to be measured is measured as compared with the transmitted ultrasonic pulse. It is evaluated that the closer the received transmission pulse height is to 100%, the less defects are in the object to be measured and good diffusion bonding is performed, and the smaller the received transmission pulse height is, the poorer the bonding is.
In this embodiment, tap water is used as the contact medium, and a 0.4 mm thick austenitic stainless steel plate, preferably an austenitic stainless steel plate in the chemical composition range of the present application, is used as a calibration test piece to vibrate the ultrasonic probe. After adjusting the child diameter to 0.5 mm, the transmitted pulse was measured at a pitch of 0.2 mm for each of the vertical and horizontal directions of the measurement target.

As is clear from the results shown in Tables 2-1 and 2-2, Examples of the present invention (Test Nos. 1-3, 5, 7, 9, 11, 13, 15, 17, 22, 24, 26, 28) , 31, 33, 35, 37, 39, 44), the area ratio of martensite was reduced and the {110} plane orientation was developed, so that the polishability was excellent.

In addition, among them, the test No. For 3, 9, 13, 22, 24, 26, 28, 31, 33, 35, 37, 39, 44, the average particle size of the austenite grains is even smaller, and X in the {110} <112> orientation of the austenite grains. Since the line random intensity ratio was high, the diffusion bondability was also excellent.

On the other hand, Test No. 18 to 21, 41, and 43 are comparative examples using steel whose chemical composition is outside the specified range of the present invention. Test No. At 18, the C content was too high, so that the texture was randomized and the {110} plane orientation was not sufficiently developed. Test No. In No. 19, since the Cr content was too high, cracks occurred during hot rolling and the test was stopped. Test No. At 20, 21 and 43, the Md30 value was too high and the amount of martensite was excessive, so that the polishability was lowered.
Test No. In No. 41, the Nb content was too high, so that the hot workability was deteriorated and cracks were generated at the end of the hot-rolled plate, so that the test was stopped.

Test No. 4, 6, 8, 10, 12, 14, 16, 23, 25, 27, 29, 30, 32, 34, 36, 38 are all manufactured although their chemical compositions satisfy the provisions of the present invention. This is a comparative example in which the desired texture could not be obtained as a result of the conditions deviating from the preferable range of the present invention.

Test No. In 4, 6, 25 and 27, the shape ratio of rolling in both or any one of the final two stages of hot rolling was more than 4.5. Therefore, a shear structure developed on the surface layer of the hot-rolled sheet. As a result, the development of the {110} plane orientation after cold rolling annealing was finally suppressed, and the polishability was lowered. Test No. In 8 and 29, the end temperature of hot rolling was too high. In addition, the test No. No. 8 also had a high take-up temperature. Therefore, recrystallization proceeded and the desired texture did not develop.

Test No. At 10 and 32, the rolling ratio in cold rolling was too low, so that the texture did not develop. Test No. In No. 12, the roll diameter of the rolling roll in the final cold rolling was too small, so that a shear texture developed on the surface layer of the steel sheet. Test No. At 14 and 36, the temperature reached by the final annealing was too low, so that reverse transformation did not occur and the martensite fraction increased. Test No. At 16 and 38, the reaching temperature for annealing was too high, so that recrystallization proceeded and the desired texture was not sufficiently developed. Therefore, in these examples, the polishability was inferior.
Test No. In No. 23, the heating temperature before hot rolling was low. Therefore, the randomization of the texture during hot rolling was promoted. As a result, the desired organization was not fully developed.
Test No. In No. 30, the finish rolling completion temperature was low. Therefore, the development of shear faults in the surface layer was promoted. As a result, the desired organization was not fully developed.
Test No. In No. 34, the winding temperature was high. Recrystallization proceeded during winding. As a result, the desired organization was not fully developed.

<Example 2>
Steels having the chemical compositions (A, I, F2, I2) shown in Table 1 are melted to produce steel pieces, and the steel pieces are heated and roughly rolled hot, and then subsequently. Finish rolling was performed under the conditions shown in Table 3. After hot rolling, pickling was performed, intermediate cold rolling with a rolling reduction of 55%, intermediate annealing at 1120 ° C. for 20 minutes, and then final cold rolling. Then, annealing was carried out to raise the temperature to the ultimate temperature indicated by AT (° C.). Further, after annealing, temper rolling was performed at the rolling ratios shown in Table 3, and strain removal annealing was performed.

As can be seen from Table 3, good polishability was obtained even when temper rolling and strain relief annealing were performed. In addition, all of these examples had the necessary mechanical properties specified in JIS standards (G4305) and the like.

According to the present invention, an austenitic stainless steel sheet having good polishability can be obtained industrially stably. Therefore, the austenitic stainless steel sheet according to the present invention is suitable as a material for members such as housings of electronic devices that require high surface gloss.

Claims (4)

The chemical composition is mass%,
C: 0.005 to 0.150%,
Si: 1.0% or less,
Mn: 1.5% or less,
P: 0.10% or less,
S: 0.010% or less,
Al: 0.10% or less,
Cr: 15.0 to 20.0%,
Ni: 6.0-15.0%,
N: 0.005 to 0.150%,
Mo: 0-2.0%,
Cu: 0-1.5%,
Nb: 0 to 0.500%,
V: 0 to 0.150%,
Ti: 0 to 0.300%,
B: 0 to 0.010%,
Total of Ca, Mg, Zr, Sn, Pb, W: 0 to 0.10%,
Remaining: Fe and impurities,
The Md30 value obtained by the following formula (i) is 60 ° C. or lower, and the temperature is 60 ° C. or lower.
In the surface layer portion, the area ratio of martensite is 5.0% or less, and the area ratio of austenite grains having a {110} plane orientation is 50% or more.
Austenitic stainless steel plate.
Md30 value = 497-462 x (C + N) -9.2 x Si-8.1 x Mn-13.7 x Cr-20 x (Ni + Cu) -18.7 x Mo ... (i)
However, the element symbol in the above formula represents the content of each element in steel in mass%, and if it is not contained, 0 is substituted. The chemical composition contains Nb: 0.010 to 0.500%.
The Md30 value is 20 to 60 ° C.
The average particle size of the austenite grains in the surface layer portion is 5.0 μm or less, and the X-ray random intensity ratio of the {110} <112> orientation of the austenite grains is 8.5 or more.
The austenitic stainless steel sheet according to claim 1. When the chemical composition is mass%,
Mo: 0.1 to 2.0%,
Cu: 0.1 to 1.5%,
Nb: 0.010 to 0.500%,
V: 0.010 to 0.150%,
Ti: 0.010 to 0.300%, and
B: 0.001 to 0.010%,
Contains one or more selected from,
The austenitic stainless steel sheet according to claim 1 or 2. The austenitic stainless steel sheet according to any one of claims 1 to 3 is provided with a step of performing temper rolling under a condition that the rolling ratio is 50% or less.
Manufacturing method of austenitic stainless steel sheet.

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