KR20170044756A

KR20170044756A - Austenitic stainless steel sheet which is not susceptible to diffusion bonding

Info

Publication number: KR20170044756A
Application number: KR1020177009165A
Authority: KR
Inventors: 히로시 가미오; 마사요시 사와다; 유이치 후쿠무라
Original assignee: 신닛테츠스미킨 카부시키카이샤
Priority date: 2014-09-10
Filing date: 2015-09-10
Publication date: 2017-04-25
Also published as: JP6376218B2; CN106687622B; CN106687622A; WO2016039429A1; JPWO2016039429A1; KR101939510B1

Abstract

Austenitic stainless steel sheet having a coating on at least a part of its surface, wherein the austenitic stainless steel sheet has a chemical composition of C: 0.01 to 0.10%, Si: 0.2 to 2.0%, Mn: 1.5 Not more than 1.0%, Mo: not more than 1.0%, Cr: not less than 15.0% nor more than 22.0%, Ni: not less than 4.5% nor more than 10.0%, Cu: not more than 1.0%, Nb: not more than 0.30% Fe and inevitable impurities, wherein the coating has a maximum Si content of 10.0% or more and a maximum Fe content of 8.5% or less in a range of 10 nm to 10 nm from the surface layer, and the Si-enriched layer has a thickness of 5 nm or more. This steel sheet is difficult to undergo diffusion bonding even at a high temperature.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an austenitic stainless steel sheet,

The present invention relates to an austenitic stainless steel sheet which is difficult to diffusion-bond.

Austenitic stainless steels are used for heat-resistant parts such as exhaust system gaskets for automobiles and motorcycles that require high heat resistance. From the viewpoint of improving the fuel economy, the exhaust temperature rises year by year, and these heat-resistant parts are sometimes exposed to high temperatures of 700 ° C or higher. At such a high temperature, there is a problem that the material is bonded to peripheral parts in addition to softening of the material. This is a phenomenon called diffusion bonding where the atoms of the contacted parts are mutually diffused.

For example, Patent Document 1 proposes a ferritic stainless steel which is difficult to diffusion-bond by adding 3 to 10% of Al to produce an Al ₂ O ₃ film.

Japanese Patent Application Laid-Open No. 2011-032524

In the ferritic stainless steel as in the technique of Patent Document 1, a sufficient high-temperature strength as an exhaust system gasket can not be obtained. In addition, as disclosed in Patent Document 1, when a large amount of Al is added, inclusions made of AlN are likely to be produced, and a thin component such as a gasket gives a significant adverse effect on fatigue characteristics.

An object of the present invention is to industrially and stably provide an austenitic stainless steel which is difficult to diffuse and bond even at a high temperature in order to solve the problems of the prior art.

The present inventors considered that the diffusion bonding property is greatly affected by the surface coating of the steel sheet and examined the relationship between the composition and thickness of the coating film and the structure of the film forming material and the diffusion bonding property. As a result, it has been found that reducing Fe in the film, then concentrating the amount of Si present as SiO ₂ in the film, and thickening the Si-enriched layer are effective in suppressing diffusion bonding.

SiO ₂ in the austenitic stainless steel surface coating film is less likely to disappear even at high temperatures as compared with Cr ₂ O ₃ , which is a coating film of stainless steel, and has an effect of suppressing the bonding. Since Fe exists in a large amount in the base material of the austenitic stainless steel, it can exist as Fe oxide in the vicinity of the bonding interface. However, the Fe oxide is easily lost in the diffusion bonding process as compared with the above-mentioned SiO ₂ and Cr ₂ O ₃ . Therefore, when a large amount of Fe exists in the vicinity of the bonding interface, it is difficult to suppress the diffusion of Fe even when SiO ₂ in the surface coating is concentrated, and the effect of suppressing the bonding becomes insufficient. Therefore, it is important to reduce Fe in the surface coating film to concentrate Si present as SiO ₂ .

As a result of a detailed examination of the production method, the heat treatment conditions effective for forming a film having a high Si content as described above were found. For example, Fig. 1 shows the relationship between the heat treatment temperature (占 폚), the maximum Si amount (mass%) in the stainless steel surface coating film after the heat treatment, and the Si thickened layer thickness (nm). In addition this experiment, N _2: 90vol% and H _2: using a heat treatment furnace in a mixed gas atmosphere containing 10vol% (dew point -50 ℃), went to change the number of temperature. As shown in Fig. 1, it was found that the maximum amount of Si in the surface coating film becomes extremely large at the specific heat treatment temperature, and the Si thickened layer becomes thick. Specifically, the heat treatment conditions are the treatment temperature, the atmosphere, and the dew point. The treatment temperature is a temperature after cracking for a predetermined time in a heat treatment furnace set at a predetermined temperature, specifically, the same as the set temperature of the heat treatment furnace. With this knowledge, it is possible to form the Si-enriched layer on the surface, but it is not necessarily possible to reduce Fe on the surface, and the suppression of the bonding is insufficient.

Therefore, the inventors of the present invention have conducted studies on a method capable of industrially stably forming a Si-enriched layer after reducing Fe in the film, and as a result, it has been found that electrolytic treatment is preferably carried out at a high current density. 2 shows the relationship between the current density (mA / cm ² ) at the electrolytic treatment and the maximum amount of Si (mass%) in the stainless steel surface coating film. As shown in Fig. 2, it has been found that an austenitic stainless steel sheet capable of achieving the object of the present invention industrially and stably can be obtained because the amount of Si in the film becomes very large at a specific current density.

The present invention has been made based on the above-described findings, and its gist of the invention is as follows.

(1) An austenitic stainless steel sheet having a coating formed on at least a part of its surface,

Wherein the chemical composition of the austenitic stainless steel sheet is, by mass%

C: not less than 0.01% and not more than 0.10%

Si: not less than 0.2% and not more than 2.0%

Mn: 1.5% or less,

Mo: 1.0% or less,

Cr: not less than 15.0% nor more than 22.0%

Ni: not less than 4.5% and not more than 10.0%

Cu: 1.0% or less,

Nb: 0.30% or less,

N: not less than 0.01% and not more than 0.15%

The remainder being Fe and unavoidable impurities,

Wherein the coating has a Si-enriched layer having a maximum Si content of 10.0% or more and a maximum Fe content of 8.5% or less in a range of 10 nm to 10 nm from the surface layer,

Wherein the Si-enriched layer has a thickness of 5 nm or more and is difficult to diffuse and adhere to the surface of the austenitic stainless steel sheet.

According to the present invention, an austenitic stainless steel which is difficult to diffuse and bond even at a high temperature can be industrially and stably provided.

Fig. 1 is a diagram showing the relationship between the heat treatment temperature (占 폚), the maximum amount of Si (mass%) in the stainless steel surface coating film after heat treatment, and the thickness of Si thickened layer (nm).
2 is a graph showing the relationship between the current density (mA / cm ² ) at the electrolytic treatment and the maximum Si amount (mass%) in the stainless steel surface coating film after the heat treatment.
3 is a diagram showing the definitions of the maximum Si amount (mass%) and the Si-enriched layer thickness (nm) based on the relationship between the distance (nm) from the surface and the amount of Si (mass%).
4 is a diagram showing the relationship between the ratio (%) of the grain boundary over the bonding interface and the maximum Si content (mass%) in the Si-enriched layer.
Fig. 5 is a diagram showing the relationship between the ratio (%) of the grain boundary over the bonding interface and the maximum Fe amount (mass%) in the Si-enriched layer.
6 is a diagram showing the relationship between the ratio (%) of the grain boundary over the bonding interface and the thickness of the Si-enriched layer (nm).

1. Chemical composition of austenitic stainless steel sheet

The chemical composition of the steel sheet of the present invention is specified by adding the chemical composition necessary for obtaining the austenitic stainless steel sheet to the heat resistance such as high temperature strength and the chemical composition necessary for obtaining the high Si coating. Specifically, it is as follows. Here,% means mass%.

C: 0.01% or more and 0.10% or less

C is an element contributing to strengthening at high temperature by strengthening of solid solution or precipitation strengthening. Therefore, C is contained in an amount of 0.01% or more. It is preferably 0.03% or more. If it is contained in a large amount, coarse Cr carbide precipitates at the grain boundaries at the time of heat treatment, and oxidation resistance at high temperature is lowered, so that the content thereof is set to 0.10% or less. And preferably 0.08% or less.

Si: not less than 0.2% and not more than 2.0%

Si is one of the most important elements in the steel sheet of the present invention. Si is an element which acts to form a coating film of high Si content composed of SiO ₂ on the surface of a steel sheet, making diffusion bonding difficult. Therefore, Si is contained at 0.2% or more. , Preferably not less than 0.31%, and more preferably not less than 0.5%. If it is contained in a large amount, the toughness is lowered and the composition of the plate is deteriorated, so that the content thereof is set to 2.0% or less. , Preferably 1.8% or less, and more preferably 1.20%.

Mn: 1.5% or less

Mn is an element contributing to prevention of brittle fracture and strengthening of steel during hot working. However, if it is contained in a large amount, the corrosion resistance is deteriorated, and the content thereof should be 1.5% or less. Or less, preferably 1.35% or less, and more preferably 1.2% or less. The lower limit contains 0%, but it is mixed inevitably about 0.001% from the iron raw material and usually remains in the steel sheet. Therefore, 0.001% is a practical lower limit. In order to reliably obtain the above effect, it is preferably 0.21% or more, more preferably 0.5% or more.

Mo: 1.0% or less

Mo is an element contributing to improvement of corrosion resistance. However, even if it is contained in a large amount, since the cost is greatly increased, the content thereof should be 1.0% or less. , Preferably not more than 0.80%, more preferably not more than 0.7%. The lower limit contains 0%, but it is mixed inevitably about 0.001% from the iron raw material and remains in the steel sheet. Therefore, 0.001% is a practical lower limit. In order to reliably obtain the above effect, the content is preferably 0.02% or more, more preferably 0.5% or more.

Cr: 15.0% or more and 22.0% or less

Cr is a basic element of stainless steel and is an element that acts to increase the corrosion resistance by forming a metal oxide layer Cr ₂ O ₃ on the surface of a steel sheet. Therefore, Cr is contained in an amount of 15.0% or more. It is preferably at least 16.1%, more preferably at least 17.0%. However, Cr is a strong ferrite stabilizing element, and if it is contained in a large amount, δ ferrite which inhibits the hot workability of the material is produced, so that its content is 22.0% or less. It is preferably 21.0%, more preferably 20.0% or less.

Ni: not less than 4.5% and not more than 10.0%

Ni is an austenite generating element and is an element necessary for stabilizing the austenite phase at room temperature. Ni is also an effective element for improving the high temperature strength. Therefore, Ni is contained in an amount of 4.5% or more. It is preferably at least 4.9%, more preferably at least 5.0%. However, if it is contained in a large amount, the processed organic martensite transformation during cold rolling is suppressed. Also, Ni is an expensive element, and the addition of a large amount causes a considerable increase in cost. Therefore, the Ni content should be 10.0% or less. Preferably 9.5% or less, and more preferably 8.0% or less.

Cu: not more than 1.0%

Cu is an austenite generating element and is an element capable of adjusting the stability of the austenite phase. However, if it is contained in a large amount, it segregates at the grain boundaries during the production process and remarkably hinders hot workability, and it may become difficult to manufacture. Therefore, it should be 1.0% or less. Preferably 0.8% or less, and more preferably 0.70% or less. The lower limit contains 0%, but it is mixed inevitably about 0.001% from the iron raw material and remains in the steel sheet. Therefore, 0.001% is a practical lower limit. In order to reliably obtain the above effect, the content is preferably 0.02% or more, more preferably 0.5% or more.

Nb: not more than 0.30%

Nb forms a fine carbide or nitride, contributes to enhancement of strength, and is an element that acts to suppress softening by recrystallization at a high temperature. However, if it is contained in a large amount, it causes an increase in cost, so it should be 0.30% or less. Preferably 0.20% or less, and more preferably 0.079% or less. The lower limit contains 0%, but it is mixed inevitably about 0.001% from the iron raw material and remains in the steel sheet. Therefore, 0.001% is a practical lower limit. In order to reliably obtain the above effect, it is preferably 0.01% or more.

N: not less than 0.01% and not more than 0.15%

N is a solid solution strengthening element like C and contributes to improvement of high temperature strength. Therefore, N is contained by 0.01% or more. Preferably 0.03% or more, and more preferably 0.04% or more. On the other hand, if it is contained in a large amount, a large number of coarse nitrides which are a starting point of fracture are produced in the course of producing the steel sheet, and the hot workability deteriorates, which makes production difficult. Preferably 0.13% or less, and more preferably 0.12% or less.

In the chemical composition of the austenitic stainless steel sheet according to the present invention, the balance is Fe and inevitable impurities.

2. Si thickened layer

The austenitic stainless steel sheet of the present invention has a coating film formed on at least a part of its surface and has a maximum Si content of 10% or more and a maximum Fe content of 8.5% or less Si concentrated layer. The film is an oxide film mainly composed of an oxide.

Maximum amount of Si in the range from the surface layer to 10 nm: not less than 10.0%

In order to suppress diffusion bonding at a high temperature, it is effective to keep the coating on the surface of the steel sheet suppressing diffusion at a high temperature. The Si in the film in the present invention exists mainly as Si oxide (SiO ₂ ). The Si oxide is stably present at a high temperature as compared with Cr oxide which is a general coating composition of stainless steel.

Therefore, diffusion bonding of stainless steel parts can be suppressed even at a high temperature by increasing the amount of Si in the range of 10 nm from the surface layer (coating film surface). In order to obtain this effect, the Si content on the outermost surface of the film is set to 10.0% or more. , Preferably at least 12.5%, and more preferably at least 14.0%.

Since the amount of Si on the outermost surface of the coating varies under the Si amount of the steel sheet and the film reforming heat treatment condition, the upper limit is not specifically defined, but the upper limit is 30.0% on the practical steel sheet.

Maximum Fe amount in the range from the surface layer to 10 nm: not more than 8.5%

Since Fe exists in a large amount in the base material of the austenitic stainless steel, it can exist as Fe oxide in the vicinity of the bonding interface. However, the Fe oxide easily dissipates in the diffusion bonding process compared to SiO ₂ and Cr ₂ O ₃ . Therefore, when a large amount of Fe exists in the vicinity of the bonding interface, it is difficult to suppress diffusion of Fe even when SiO ₂ in the surface coating is concentrated, and the effect of suppressing bonding is insufficient. Therefore, the maximum amount of Fe in the range from the surface layer to 10 nm is set to 8.5% or less.

Thickness of Si thickened layer: 5 nm or more

As described above, when the amount of Si in the film is large, diffusion bonding is suppressed. However, when the Si-enriched layer is thin, when the film is exposed to a high temperature for a long time, the film is gradually decomposed into metal and oxygen gas and the stainless steel parts are bonded. Therefore, the thickness of the Si thickened layer should be 5 nm or more. Preferably 8 nm or more.

Here, the definition of the thickness of the Si thickened layer will be described. Fig. 3 shows the definitions of the maximum amount of Si (mass%) and the thickness of Si-enriched layer (nm) based on the relation between the distance (nm) from the surface and the amount of Si (mass%). As shown in Fig. 3, the thickness of the Si-enriched layer is a thickness until the amount of Si becomes 1/2 of the maximum amount of Si (1/2 Si amount in the figure).

3. Manufacturing Method

Next, a method suitable for manufacturing the austenitic stainless steel sheet of the present invention will be described. The solvent, hot rolling, and the like may be performed in the same manner as in the conventional method. Hereinafter, the conditions of the film-modifying heat treatment and the film-reforming electrolytic treatment as the final finishing treatment are shown, but there is no particular condition for the treatment other than these treatments.

3-1. Film reforming heat treatment

As described above, it is important that the amount of Si in the outermost surface of the coating film (10 nm from the surface layer) is 10% or more as a surface state difficult to diffuse and adhere. In general, the finish annealing of the austenitic stainless steel is performed in a mixed atmosphere of H ₂ and N ₂ in order to maintain the gloss of the surface, and the temperature is about 1100 to 1150 ° C.

However, at such a temperature, it is difficult to obtain a coating film having a large amount of Si as specified in the steel sheet of the present invention (see Fig. 1). Further, when cold rolling is performed after finishing annealing, the film is partially broken and divided, and a new Cr oxide film is formed on the new face, and the amount of Si in the film is sometimes reduced.

Annealing (film modified heat treatment) is preferably carried out by keeping in a mixed atmosphere of H ₂ and N ₂ to 750 ~ 1000 ℃. To form a predetermined Si-enriched layer on the surface layer of the coating (see Fig. 1). A preferable lower limit of the treatment temperature is 800 占 폚, and a preferable upper limit is 950 占 폚. Further, the as furnace time is not particularly defined as long as the steel sheet can be cracked at the above-mentioned treatment temperature. However, if the time is too short, the Si concentration in the coating film may become insufficient, so that the ash time is preferably 10 seconds or more.

If the dew point of the mixed atmosphere of H ₂ and N ₂ is high, the film formed at the time of the heat treatment becomes the coating of the Cr oxide main body, so that the dew point is preferably set to -45 ° C or lower. Preferably -60 DEG C or less. On the other hand, in order to obtain an excessively low dew point, a large cost is required, so that the dew point is practically -70 ° C or higher. Preferably -65 DEG C or more.

For the mixing ratio (H ₂ / N ₂₎ of H ₂ and N ₂ is not specifically limited, the mixing ratio is preferably not less than 1/19 to the atmosphere exhibits a sufficient reducing. On the other hand, it is preferable to increase the proportion of expensive hydrogen gas to 1/2 or less because there is a problem in economical efficiency.

3-2. Membrane reforming electrolytic treatment

Usually, an electrolytic washing treatment is performed in which a steel sheet after heat treatment is subjected to an electrolytic treatment in a predetermined liquid to remove a film formed by the heat treatment. The film reforming electrolytic treatment is common to the conventional electrolytic cleaning treatment in that an electrolytic treatment is performed in a predetermined liquid, but the film reforming electrolytic treatment is performed to reduce Si in the film and to concentrate Si in the film It is very different in that it is. Concretely, it is preferable to pass the steel sheet through a nitric acid aqueous solution having a liquid temperature of 30 to 50 ° C and a concentration of 5 to 10% while applying a voltage so that the steel sheet is positive. If the temperature or the concentration of the liquid is too low, a sufficient reforming effect can not be obtained. If the temperature or the concentration of the liquid is too high, the surface roughness of the steel sheet may be increased or the electrolytic bath may be damaged.

This electrolytic treatment is preferably carried out so that the current density is 100 mA / cm ² or more with respect to the plate area. Thereby, after the Fe in the film is reduced on the surface of the steel sheet, Si is concentrated (see Fig. 2). It is preferably at least 150 mA / cm ² . In the surface enrichment of Si by electrolysis, Fe or Cr is eluted by the oxidation reaction and is removed from the surface in the electrolysis process, but Si existing as SiO ₂ remains on the surface without further oxidation.

When the current density is less than 100 mA / cm ² , Si is not concentrated on the surface of the steel sheet, and particularly when the current density is about 20 mA / cm ² of the current density in the ordinary electrolytic cleaning treatment, the amount of Si may decrease Reference).

On the other hand, if the current density is excessively large, the steel sheet is excessively shaved off, the yield decreases, and the surface of the steel sheet becomes rough, so that the current density is preferably 300 mA / cm ² or less (see FIG. And preferably 250 mA / cm ² or less.

If the energization time is short, the degree of enrichment of Si is small. Therefore, the energization time is preferably 10 seconds or more. Preferably at least 15 seconds. Although the upper limit of the energizing time is not specifically defined, the upper limit is about 60 seconds in practice.

In the electrolytic treatment tank, a voltage may be applied to the steel plate as a positive electrode or a negative electrode, or a voltage may be applied repeatedly alternately in positive and negative directions. In this case, too, the time required for energizing the steel sheet is 10 seconds or more.

Example

Although the embodiments of the present invention are described below, the conditions in the embodiments are examples of conditions adopted to confirm the feasibility and effect of the present invention, and the present invention is limited to this one conditional example no. The present invention does not depart from the gist of the present invention, and various conditions can be adopted as long as the object of the present invention is achieved.

(Example 1)

Table 1 shows the chemical composition of the steel of the test specimen.

[Table 1]

A small ingot having the chemical compositions A to G shown in Table 1 was melted and subjected to cutting, hot rolling, annealing, descaling, cold rolling and annealing three times. Thereafter, the plate thickness was adjusted to 0.2 mm by finishing rolling, and then the film-reforming heat treatment and the film reforming electrolytic treatment were carried out under the conditions shown in Table 2 below. A test piece was taken from the obtained steel sheet, and the characteristics were investigated in the following manner. The results are also shown in Table 2.

Maximum Si amount, maximum Fe amount, and Si thickened layer thickness

While the coating film formed on the surface of the steel sheet was sputtered with Ar ions, the amount of Si and the amount of Fe from the outermost surface of the film to a depth of about 100 nm or less were measured using GD-OES (see Fig. 3). The maximum Si amount is the amount of Si (mass%) at which the Si amount becomes the maximum, the maximum amount of Fe is the amount of Fe (mass%) at which the amount of Fe is the maximum and the Si thickened layer thickness is the maximum Si amount To the position where the amount of Si becomes one-half of the Si amount.

Identification of major constituents of surface oxides

The steel sheet was cut to include the surface oxide by FIB processing, and the crystal structure and composition of the surface oxide were analyzed using TEM-EDS to identify the main constituent material of the surface oxide.

Bonding

The steel sheet was processed into two ø8 mm disc test pieces. Two test specimens were superimposed, and a load of 20 MPa was applied in a vacuum chamber at 750 DEG C, and the resultant was pressed for 30 seconds.

After pressurization, the superimposed test pieces were taken out of the chamber, and a case where two test pieces were not bonded was evaluated as & cir &, and the test pieces filled with the resin seemed to be bonded but were polished and then the cross section of the bonding surface was observed with an optical microscope , The case where the ratio of the crystal grains over the bonding interface was less than 10% was evaluated as?, And the case where the ratio of the crystal grains over the bonding interface was not less than 10% was evaluated as?. These results are shown in Table 2 and plotted in Figs.

[Table 2]

Steel sheets 1 to 7 (inventive examples) shown in Table 2 are steel sheets that satisfy the requirements of the present invention and are difficult to be diffusion-bonded. The steel sheets 8 to 13 of the comparative examples are steel sheets that are easy to diffuse and bond. The steel sheet 8 has an extremely low maximum amount of Si in the coating film. This is because the temperature of the film-reforming heat treatment is low. The steel sheet 9 is a steel sheet which is susceptible to diffusion bonding since the dew point at the time of the film reforming heat treatment is high and the Cr oxide is the coating of the main body.

The steel sheet 10 is SUS304 which was manufactured under relatively common manufacturing conditions. The heat treatment temperature or the current density at the electrolytic treatment is a general condition, but the maximum amount of Si in the film is low and the depth of the Si-enriched layer is small. The steel sheet 11 is a steel sheet which is susceptible to diffusion bonding without causing Si to be concentrated on the surface of the steel sheet even by a film-modifying heat treatment under appropriate conditions because the maximum amount of Si is extremely low.

The steel sheet 12 is a steel sheet which is susceptible to diffusion bonding because the maximum amount of Si in the coating film is low and the depth of the Si-enriched layer is small. This is because no film reforming heat treatment or film reforming electrolytic treatment is performed. In the steel sheet 13, the maximum amount of Si in the coating is in the range specified in the present invention, but the maximum amount of Fe is excessive, so it is a steel sheet which is susceptible to diffusion bonding. This is because the energization time as the negative electrode is long.

As shown in Figs. 4 to 5, by setting the maximum amount of Si in the Si-enriched layer to 10% by mass or more, the Si-enriched layer thickness to 5 nm or more, and the maximum amount of Fe in the Si-enriched layer to 8.5% or less, And the effect of suppressing diffusion bonding is exhibited. In the figure, " & cir & In this example, the maximum amount of Si in the film is in the range specified in the present invention, but the maximum Fe amount is excessive, so that the ratio of the grain boundaries over the bonding interface has been increased.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to stably provide an austenitic stainless steel which is difficult to diffuse and bond even at a high temperature. Therefore, the present invention is highly likely to be used in the stainless steel manufacturing and utilization industry.

Claims

An austenitic stainless steel sheet having a coating on at least a part of its surface,
Wherein the chemical composition of the austenitic stainless steel sheet is, by mass%
C: not less than 0.01% and not more than 0.10%
Si: not less than 0.2% and not more than 2.0%
Mn: 1.5% or less,
Mo: 1.0% or less,
Cr: not less than 15.0% nor more than 22.0%
Ni: not less than 4.5% and not more than 10.0%
Cu: 1.0% or less,
Nb: 0.30% or less,
N: not less than 0.01% and not more than 0.15%
The remainder being Fe and unavoidable impurities,
Wherein the coating has a Si-enriched layer having a maximum Si content of 10.0% or more and a maximum Fe content of 8.5% or less in a range of 10 nm to 10 nm from the surface layer,
Wherein the Si-enriched layer has a thickness of 5 nm or more and is difficult to diffuse and adhere to the surface of the austenitic stainless steel sheet.