KR20170057412A - Austenitic stainless steel sheet and method for producing same - Google Patents

Abstract

0.1 to 1.5% of Mn, 0.1 to 1.5% of Cr, 15.0 to 22.0% of Cr, 4.5 to 10.0% of Ni, 0.10 to 2.0% of Cu and 0.1 to 2.0% of Mo, , An Nb: 0.02 to 0.50%, the balance Fe and impurities, an average crystal grain size of not more than 5.0 m, an unrecrystallized portion remaining ratio of not more than 3.0%, and an average aspect ratio of crystal grains of not more than 1.2 Austenitic stainless steel plate suitable for precision machining.

Description

TECHNICAL FIELD The present invention relates to austenitic stainless steel sheet and a method of manufacturing the same. BACKGROUND ART < RTI ID = 0.0 > AUSTENITIC STAINLESS STEEL SHEET AND METHOD FOR PRODUCING SAME &

The present invention relates to an austenitic stainless steel sheet and a method for producing the same.

The austenitic stainless steel sheet is widely used as a metal mask. For example, the metal mask is manufactured by precision machining such as etching, laser machining, and the like. It is known that these precision machining has a fine grain size of the material and improves the smoothness of the etched surface by increasing the degree of grain size.

For example, in Patent Documents 1, 2 and 3, the chemical composition is adjusted and the annealing after the final cold rolling is carried out at a temperature lower than usual at 500 to 850 캜 to suppress the crystal grain growth and secure the smoothness of the etching surface An austenitic stainless steel sheet has been proposed.

In particular, the invention disclosed in Patent Documents 2 and 3 suppresses crystal grain growth in the final annealing by adding Nb and precipitating carbonitride of Nb.

Japanese Unexamined Patent Application Publication No. 2-173214 Japanese Patent Application Laid-Open No. 2003-003244 Japanese Patent Application Laid-Open No. 2005-320587

In recent years, however, smoothness of a machined surface has been required in precision machining more than ever, and the method disclosed in Patent Documents 1 to 3 may not satisfy the requirements sufficiently. Particularly, in Patent Documents 2 and 3, in order to transform the lower structure into the lath-shaped martensite by the final cold rolling in the steel sheet containing Nb, it is necessary to melt Nb in the steel sheet to be provided for the final cold rolling. Therefore, in Patent Document 2, it is considered that the processing temperature of the intermediate annealing, which is the previous step of the final cold rolling, must be set at a high temperature of 1100 캜. In Patent Document 3, stress relieving annealing (final annealing) is performed at a temperature range of 550 ° C to 700 ° C to suppress warpage during etching by removing residual stress after temper rolling (final cold rolling). Here, in Patent Document 3, attention is paid to the point that the hardness is increased as shown in Table 2. For this purpose, it is necessary to retain the martensite by suppressing the reverse transformation to the austenite. Therefore, in Patent Document 3, it is considered that the final annealing temperature can not be reduced.

As described in Patent Documents 2 and 3, in the case of a material containing Nb, if Nb is contained in the austenite phase, the recrystallization is delayed, and the unrecrystallized portion remains in many cases. In actual production, crystal grains are not sufficiently fine and unrecrystallized portions are left uneven due to cold rolling or uneven operation of the annealing temperature. When these stainless steel sheets are precisely processed, the smoothness may be uneven .

An object of the present invention is to provide an austenitic stainless steel sheet suitable for precision processing such as etching and laser machining and a method for industrially stably producing such austenitic stainless steel sheet.

The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, the following findings were obtained.

(1) In order to smooth the surface after precision machining such as etching or laser machining, it is known that fine crystal grains without an unnecessary recrystallized portion are preferable. In addition to these, the smoothness of the precision machined surface is further improved by making the crystal grains into fine equiaxed grains.

(2) In order to make the crystal grains into fine equiaxed grains, it is insufficient to generate martensite by cold rolling and reverse-transform it.

(3) It is possible to change the morphology of the martensite from the lath shape to the cell shape by generating machined organic martensite at the beginning of the cold rolling and further reducing it, and as a result, You can get an organization.

(4) For this reason, it is considered effective to make the cold rolling rate 90% or more, and to make γ unstable by the chemical composition. However, the former is difficult from an industrial point of view, and the latter, if γ is excessively unstable, produces δ ferrite by melting or hot rolling, thereby promoting cracking in hot rolling or cold rolling.

(5) Therefore, it is effective to change the? Stability by performing a manufacturing process in which? Stability is high at the beginning of manufacture and? 'Is changed during final cold rolling. Therefore, in order to prevent the generation of delta ferrite as a material, annealing (intermediate annealing) is performed before the final cold-rolling so that C, N, which is a? Stabilizing element, is precipitated. As a result, in the subsequent cold rolling, it is easy to generate? '.

(6) When a part of Nb is precipitated as Nb (C, N) in the intermediate annealing, crystal grain growth can be suppressed by the pinning effect and the amount of dissolved Nb in the final annealing can be reduced, This is also effective in reducing the remaining ratio of the re-established government.

(7) When a part of Nb is precipitated as Nb (C, N) in the intermediate annealing, the? Stability can be lowered to the extent that? Ferrite is not produced. As a result, even if the rolling rate during operation is lower than expected or the final annealing temperature is uneven, a stable fine grain structure can be formed.

(8) In order to increase γ stability, the chemical composition of the material was also examined in detail. As a result, Cu is an element capable of adjusting the stability of the austenite phase together with the austenite generating element. When Mo is contained, the stacking defect energy is increased by the synergistic effect with Mo and the accumulation of strain in the austenite phase As shown in FIG. As a result, excessive work hardening is suppressed, and the load at the time of manufacturing thin plates is greatly reduced. Furthermore, in the case of being used after being subjected to press or bending before or after etching or laser machining, there is an effect that molding is facilitated by suppressing excessive work hardening.

(9) As described above, Nb carbonitride is precipitated by annealing at a temperature lower than usual in the annealing before the final cold rolling, and the stability of the austenite phase is controlled by adjusting the amount of solid solution C and the amount of solid solution N. Thereafter, the processed organic martensite to be formed is subjected to cold rolling to obtain a cell shape? 'Instead of the conventional lath shape?'. Thus, it is possible to obtain a pinning effect by the Nb carbonitride formed by the initial annealing in the final annealing step, as well as an equiaxed particle which is a fine particle and whose aspect ratio has decreased. As a result, it is possible to obtain an austenitic stainless steel sheet which is fine grains and is equiaxed grains, and the smoothness of the etched surface can be improved.

The present inventors have completed the present invention on the basis of the above findings. The present invention relates to the following austenitic stainless steel sheet and a method for producing the same.

(1) in mass%

C + N: 0.03 to 0.20%

Si: 0.1 to 1.5%

Mn: 0.10 to 1.5%

Cr: 15.0 to 22.0%

Ni: 4.5 to 10.0%

Cu: 0.10 to 2.0%

Mo: 0.1 to 2.0%

0.02 to 0.50% of Nb,

The remainder being Fe and impurities,

An average crystal grain size of 5.0 占 퐉 or less,

The remaining percentage of unreconciled government is 3.0% or less,

Wherein an average aspect ratio of crystal grains is 1.2 or less,

Austenitic stainless steel sheet.

(2) A method for producing an austenitic stainless steel sheet according to the above (1)

The base material is subjected to hot rolling, annealing and cold rolling,

A final annealing at a treatment temperature of less than 1000 占 폚, a final cold rolling at a total plate thickness reduction rate of 50% or more, and a final annealing at a treatment temperature of more than 700 占 폚 and not more than 950 占 폚.

According to the present invention, it is possible to obtain an austenitic stainless steel sheet which is fine grains and is equiaxed grains. Such an austenitic stainless steel sheet is suitable for precision machining such as etching and laser machining since the smoothness of the etched surface is excellent. The present invention can also industrially and stably produce the above-described austenitic steel.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view showing the difference between a conventional manufacturing method and a manufacturing method according to the present invention.
2 is a diagram showing the aspect ratio of the crystal grains.

The present invention is described in detail. In the following description, " mass% " is simply referred to as "% ".

1. Austenitic Stainless Steel Plate

(1) chemical composition

C + N: 0.03 to 0.20%

C and N are? -Stabilizing elements and, when dissolved, suppress the generation of delta ferrite at the time of hot rolling, and therefore it is necessary to contain them in an appropriate amount. C and N are precipitated at the time of intermediate annealing as a fine Nb compound in combination with Nb, or at the time of final annealing, and have the effect of suppressing crystal grain growth. Furthermore, the γ stability of the base material can be adjusted during the manufacturing process by dissolving the Nb carbonitride at the time of the hot-rolled sheet and precipitating it as Nb carbonitride at the time of intermediate annealing. Therefore, C and N should be contained in a total amount of 0.03% or more. It is preferably at least 0.05%. On the other hand, if the total content of C and N is too large, even when precipitated as an Nb compound at the time of intermediate annealing, a portion remains as solid solution C or solid solution N. As a result, No shape martensite is formed. Therefore, the upper limit is 0.20%. And preferably 0.16% or less. The content of C and N is preferably 0.01 to 0.10% and 0.01 to 0.15%, respectively.

Si: 0.1 to 1.5%

Si is used as a deagglomeration material for the application and contributes to strengthening of the steel. Therefore, the lower limit is set to 0.1%. However, if the Si content is excessively large, the etching rate is adversely affected. Therefore, the Si content is set to 1.5% or less. Preferably, it is 0.8% or less.

Mn: 0.10 to 1.5%

Mn contributes to prevention of brittle fracture and strengthening of steel during hot working. Therefore, the lower limit is set to 0.10%. However, since Mn is a strong? -Generating element, if the content is excessively large, the amount of the processed organic martensite produced at the time of cold rolling is small, and fine crystal grains can not be obtained by subsequent annealing. Therefore, the Mn content is set to 1.5% or less. More preferably, it is 1.2% or less.

Cr: 15.0 to 22.0%

Cr is an essential element of stainless steel and is an indispensable element that acts to increase the corrosion resistance by forming a metal oxide layer on the surface of the steel. It is contained in an amount of 15.0% or more. However, since Cr is a strong ferrite stabilizing element, when the content is too large, a large amount of delta ferrite remains after the solvent. This delta ferrite remarkably deteriorates the hot workability of the material. Therefore, the Cr content is set to 15.0 to 22.0%. The lower limit is preferably 15.0%, and the upper limit is preferably 19.0%.

Ni: 4.5 to 10.0%

Ni is a? -Generating element and is an indispensable element for stably obtaining a? -Phase at room temperature, and the lower limit is 4.5%. However, if the Ni content is too large, the? -Phase is too stabilized, and the processed organic martensite transformation during cold rolling is suppressed. Further, Ni is an expensive element, and an increase in the content leads to a significant increase in cost. Therefore, the upper limit value is 10.0%.

Cu: 0.10 to 2.0%

Cu is a? -Generating element and is an element capable of adjusting the stability of the? Phase similarly to Ni. In addition, since the material has an effect of softening it, when the cold rolling is performed at a high and high rolling rate as in the present invention, the load of rolling can be reduced. Cu is an austenite generating element and is an element capable of adjusting the stability of the austenite phase. In the case where Mo is contained, a synergistic effect with Mo increases the stacking defect energy, restrains the accumulation of deformation in the austenite parent phase, suppresses excessive work hardening, and greatly reduces the load during the manufacture of thin plates. Furthermore, in the case of being used after being subjected to press or bending before or after etching or laser machining, there is an effect that molding is facilitated by suppressing excessive work hardening. Therefore, the lower limit is set to 0.10%. On the other hand, if the Cu content is excessively large, it segregates at grain boundaries during the production process. This intergranular segregation significantly deteriorates the hot workability and makes the production difficult. Therefore, the upper limit value is 2.0%. The lower limit is preferably 0.2%, and the upper limit is preferably 1.0%.

Mo: 0.1 to 2.0%

Mo is a? -Generating element and is an element capable of adjusting the? Phase stability similarly to Ni. Since Mo is an element for forming a homogeneous oxide film, it has an effect of reducing etching unevenness. Mo is an element that increases the stacking defect energy by the synergistic effect with Cu and restrains the accumulation of deformation in the austenite parent phase, suppresses excessive work hardening, and greatly reduces the load during the manufacture of thin plates. In addition, when used before and after precision machining, such as pressing or bending, there is an effect that molding is facilitated by suppressing excessive work hardening. Therefore, the lower limit is set to 0.1%. However, if the Mo content is excessively large, the cost also increases. Therefore, the Mo content is set to 2.0% or less. And preferably 1.0% or less.

Nb: 0.02 to 0.50%

Nb generates fine carbides or nitrides, and inhibits crystal grain growth by the pinning effect. Further, by carbonitriding Nb in the intermediate annealing, the C content and N content in the base material are reduced, and the austenite stability is lowered to such an extent that no delta ferrite is produced. As a result, in the cold rolling after the intermediate annealing, the parent phase is transformed into martensite in an early stage, and then a large amount of cell-shaped martensite is produced. Nb has an effect of suppressing crystal grain growth, while if it exists in a solid solution state, recrystallization during annealing is delayed, and a non-recrystallized portion remains after annealing. Taking these effects into consideration, the lower limit value of the Nb content is set to 0.02%. However, if the content of Nb in the solid state is excessively large, the recrystallization during annealing is delayed, and a large amount of the non-recrystallized portion remains. If the non-recrystallized portion remains in a large amount, the smoothness of the precision-processed product is deteriorated. Therefore, the upper limit value is 0.50%. The lower limit is preferably 0.04%, and the upper limit is preferably 0.20%.

· Remainder: Fe and impurities

In the production of stainless steel, scrap raw materials are often used from the viewpoint of recycling promotion. As a result, various impurity elements are inevitably incorporated into the stainless steel. It is difficult to uniquely determine the content of the impurity element. Therefore, the impurity in the present invention means an element contained in an amount that does not inhibit the action and effect of the present invention. Examples of such impurities include P: not more than 0.05% and S: not more than 0.03%.

·etc

Md ₃₀ is a temperature at which 50% of the entire metal structure becomes martensite when a deformation of 30% is given, and is one of the indexes indicating the easiness of the processed organic martensite transformation. Therefore, Md ₃₀ is preferably in the range of 30 to 55 ° C. This range is because the processed organic martensitic transformation tends to occur.

SFE stands for stacked defect energy, and is one of indexes indicating the ease of forming a stacking fault. When the SFE is too low, a stacking defect tends to be formed, and it is difficult to sufficiently cause the machined organic martensite transformation. For this reason, the SFE is preferably 3 mJ / cm ² or more. This is because if it is within this range, the formation of lamination defects is easily suppressed and the processed organic martensite transformation is easily promoted sufficiently. The preferred upper limit of SFE is 100 mJ / cm < ^{2 &} gt ;.

(2) Metal structure of austenitic stainless steel sheet

Average crystal grain size: 5.0 μm or less

As the average crystal grain size becomes smaller, the roughness of the precision machined surface becomes smaller. This effect becomes conspicuous particularly when the average crystal grain size is 5.0 mu m or less. Therefore, the average crystal grain size is set to 5.0 μm or less. In order to further exhibit the effect, 3.0 μm or less is preferable. If the average crystal grain size is too small, the production cost is increased. Therefore, the lower limit is set to 0.3 μm. Considering the balance with the manufacturing cost, the lower limit is preferably 0.5 mu m. The average crystal grain size refers to the diameter of a circle having the same area as the average crystal grain area calculated by the quadratic method.

· Remaining rate of unconfirmed government: Not more than 3.0%

When a large amount of the unrecrystallized portion remains, when the stainless steel sheet is etched, only the portion thereof is preferentially etched with respect to the surrounding recrystallized grains, so that the smoothness may be impaired. Therefore, it is preferable to set the remaining non-recrystallization ratio to not less than 3.0% without harming the smoothness. Since production of a material having an extremely low residual recrystallized particle results in a decrease in production efficiency, the lower limit thereof is preferably 0.5%.

Average aspect ratio of crystal grains: not more than 1.2

The finer the particles of the crystal are, the smaller the roughness of the precision machined surface. As a result, the average aspect ratio (long axis length / short axis length) of the crystal grains is 1.2 or less. The long axis length in the present invention indicates the major axis length when the crystal grains are approximated to an ellipse. The short axis length in the present invention indicates the minor axis length when the crystal grains are approximated to an ellipse. For example, when the crystal grains have the shape shown in Fig. 2, the long side segment is the long axis and the short side segment is short axis. The smaller the average aspect ratio is, the better, and the lower limit is preferably 1.0%.

2. Manufacturing Method of Austenitic Stainless Steel Sheet

(1) Hot rolling, annealing, cold rolling

As the base material to be provided for the hot rolling in the present invention, it is preferable to use an ingot formed by dissolving molten steel having the chemical composition described above in a conduction furnace or an electric furnace, and injecting it into a mold, or a slab obtained by continuous casting. When the ingot is used, it is preferable to process the base material in a shape capable of hot rolling by cutting or the like. In the case of a slab, it is preferable to manufacture a slab (120 to 280 mm in thickness, 700 to 1200 mm in width, and 8 to 10 m in length) by continuous casting. It is preferable to heat the ingot or slab to a temperature in the range of about 1100 to 1300 ° C and then hot-roll to obtain a hot-rolled steel sheet having a thickness of about 2 to 10 mm. Thereafter, annealing treatment at 1000 to 1200 占 폚 and pickling treatment as in the prior art are carried out, and cold rolling with a rolling rate of 20 to 70% is carried out to obtain a cold-rolled steel sheet having a thickness of about 0.2 to 2.0 mm.

(2) intermediate annealing

In the present invention, the steel sheet obtained by cold rolling is subjected to intermediate annealing at a temperature lower than 1000 캜. This intermediate annealing is an annealing performed immediately before the final cold rolling described later. In the intermediate annealing, a part of Nb is precipitated as carbonitride without solidification, and an effect of lowering the austenite stability of the base material to such an extent that delta ferrite is not produced can be obtained. As shown in Fig. 1, when the intermediate annealing temperature exceeds 1050 DEG C, Nb is solidified in the steel, and in the final cold rolling, a lath-shaped martensitic transformation is caused and the recrystallization is delayed in the final annealing, There is a case where it remains. If the non-recrystallized portion remains, the smoothness may be uneven when precision processing is performed. Therefore, in the present invention, the treatment temperature of the intermediate annealing is carried out in a temperature range lower than 1000 占 폚.

The lower the treatment temperature, the lower the solubility C and the solute N, and hence the lower the austenite stability, and thus, the superiority in forming the cellular martensite. Therefore, the preferable treatment temperature is 980 占 폚 or lower, particularly preferably 950 占 폚 or lower. On the other hand, in order to sufficiently precipitate the carbonitride of Nb and reduce the load of cold rolling in the next step by softening the steel sheet, the lower limit is preferably 700 ° C, and more preferably 800 ° C. In order to decrease the austenite stability of the base material to some extent by precipitating sufficiently Nb carbonitride, that is, reducing the solid solution C and solid solution N, the annealing holding time is preferably 5 to 300 seconds. The rate of temperature rise to the treatment temperature and the cooling rate after annealing are not particularly limited but are preferably 10 to 30 ° C / sec and 10 to 20 ° C / sec (from the viewpoint of suppressing generation of carbonitride, Holding temperature to 300 占 폚). The atmosphere of the intermediate annealing is not particularly limited.

The generation of carbonitride of Nb can be determined by observation with a transmission electron microscope (TEM). The deposition amount of the carbonitride of Nb effective for transforming into the shape of a cell in the final cold rolling differs depending on the y stability of the base material, but a desired effect can be obtained by precipitating about 0.01% of Nb in the Nb in the steel sheet.

3. Final cold rolling

The steel sheet obtained by the intermediate annealing is subjected to final cold rolling with a total sheet thickness reduction ratio of 50% or more. The final cold rolling is the cold rolling performed at the end of the step of manufacturing the austenitic stainless steel sheet of the present invention. In order to achieve the object of the present invention, it is necessary to produce the processed organic martensite by cold rolling after the intermediate annealing, and to change the shape of the martensite from the lath shape to the cell shape. For this purpose, cold rolling at a total plate thickness reduction rate of 50% or more is carried out. The total plate thickness reduction rate is more preferably 60% or more. On the other hand, if the total plate thickness reduction rate is too large, it leads to quality deterioration. Therefore, the total plate thickness reduction rate is preferably 100% or less. Further, the cell-shaped martensite can be observed by a transmission electron microscope (TEM). By this observation, it can be seen that a martensite of a relatively granular cell structure is formed inside the lattice-shaped lath, so that it is easy to distinguish between the cell shape and the lath shape.

4. Final annealing

The steel sheet obtained by the final cold rolling is further subjected to final annealing at a temperature higher than 700 DEG C and 950 DEG C or lower. The final annealing is the last annealing in the step of producing the austenitic stainless steel sheet of the present invention. In the case of temper rolling, annealing is performed at the end of the temper rolling process. In the final annealing, the cellular martensite produced in the previous step is reversely transformed into fine, equiaxed austenite grains. At this time, if the final annealing temperature is too low, sufficient recrystallization can not be performed, and unrecrystallized particles having a large aspect ratio remain. On the other hand, if the final annealing temperature is too high, crystal grains coarsen. Therefore, the final annealing is performed at a temperature higher than 700 DEG C and 950 DEG C or lower. In order to more reliably manifest the effect, the lower limit of the final annealing temperature is preferably 800 캜, and the upper limit is preferably 930 캜. The atmosphere of the final annealing is not particularly limited.

From the viewpoints of erasing the non-recrystallized particles and inhibiting crystal grain coarsening, the annealing holding time is preferably 5 to 300 seconds. The rate of temperature rise up to the annealing temperature and the cooling rate after annealing are not particularly limited, but from the viewpoint of suppressing the coarsening of crystal grains in addition to reverse-transformation to equiaxed austenite grains by sufficient recrystallization, From the viewpoint of suppressing the Cr carbonitride, the heating rate is preferably 15 to 50 DEG C / sec, and the cooling rate is preferably 15 to 45 DEG C / sec (from the holding temperature to 300 DEG C).

[Example]

The chemical composition of the steel is shown in Table 1. Strength A to G have a chemical composition satisfying the requirements of the present invention, and H to N are comparative examples outside the scope of the present invention. A small ingot having the chemical composition shown in Table 1 was melted and cut to obtain a hot-rolling material having a thickness of 40 mm. Thereafter, the steel sheet was hot-rolled to a thickness of 4 mm, hot-rolled and then annealed at 1200 ° C, and cold-rolled to a thickness of 2 mm. Thereafter, it was annealed at 1150 占 폚 and cold-rolled to a predetermined thickness. The cold rolling rate after the annealing at 1150 占 폚, that is, the cold rolling rate of the cold rolling before the intermediate annealing, was the inverse calculation so that the thickness after the final cold rolling was 0.4 mm when the final cold rolling was carried out at the rolling rate shown in Table 2.

Thereafter, intermediate annealing, final cold rolling and final annealing were carried out under the conditions shown in Table 2 to obtain a steel sheet having a thickness of 0.4 mm. In the intermediate annealing, the temperature was raised to the intermediate annealing temperature at a temperature raising rate of 10 to 30 占 폚 / sec, maintained at the intermediate annealing temperature described in Table 2 for 5 to 300 seconds, then at a temperature decreasing rate of 10 to 20 占 폚 / 300 < 0 > C). In the final annealing, after the final cold rolling, the temperature is raised to a final annealing temperature at a temperature raising rate of 15 to 30 캜 / sec., Maintained at a final annealing temperature shown in Table 2 for 5 to 300 seconds, Temperature (from the holding temperature to 300 占 폚).

Microstructural photographs of the obtained steel sheet in the vertical direction in the rolling direction were photographed with a scanning electron microscope to calculate the average crystal grain size, the average aspect ratio of the crystal grains and the residual ratio of the non-crystal grain boundaries. The average crystal grain size and the average aspect ratio of the crystal grains were all calculated from the measurement results of 50 or more grains of each steel sheet. The remaining ratio of the non-recrystallized portion is obtained by recording 100 points or more of lattice points on the photographed photograph and confirming whether the lattice point is a crystal grain or an unrecorded portion. Then, the ratio of the total number of lattice points to the number of lattice points .

In addition, in order to evaluate the precision workability, the average roughness of the machined surface was examined in this embodiment. The average roughness was measured using a contact type roughness meter after etching until the plate thickness became half with a ferric chloride solution. The linear roughness (arithmetic mean roughness) of 4 mm in each of the direction perpendicular to the rolling direction and the direction parallel to the rolling direction was measured three times in each direction, and the measurement results of the six arithmetic mean roughness were also averaged to be representative values. It was judged that the average roughness of 0.10μm or less was a problem level as a metal mask. The results are shown in Table 2.

The steel sheets 1 to 12 in Table 2 are the examples of the present invention and have excellent smoothness of the precision machined surface. After completion of the final cold rolling, a sample was taken from the steel sheet before final annealing, and the structure was observed by TEM. As a result, it was confirmed that the steel sheet was transformed into a cell-shaped martensite. The smoothness of the precision machined surface was determined by using the average roughness of the etched surface measured using a contact type roughness meter after the steel sheet was etched with a ferric chloride solution until the plate thickness became half.

The steel sheets 13 to 25 are comparative examples, and the smoothness of the precision machined surface is poor. This will be described in detail below.

Since the intermediate annealing temperature of the steel sheet 13 is high and there is no precipitation of Nb carbonitride in the intermediate annealing, the martensite produced by the final rolling is mainly in the form of a lase, the average grain size after the final annealing is relatively fine, And the average aspect ratio of the crystal grains is large.

Since the final cold rolling rate is insufficient, the steel sheet 14 has few martensite to be produced, and the produced martensite is mainly in a lath shape, and the average aspect ratio of the crystal grains after final annealing is large.

In the steel sheet 15, the final annealing temperature is high, the crystal grains grow large, and the smoothness of the processed surface is bad.

Since the final annealing temperature is low in the steel sheet 16, the recrystallized grains are small, but a large amount of the unrecrystallized portion remains, and the average roughness of the processed surface is large.

Since the intermediate annealing temperature is high and there is no precipitation of Nb carbonitride in the intermediate annealing, the steel sheet 17 has martensite mainly formed by the final rolling after that, and the average grain size after final annealing is relatively fine, A large amount of unrecrystallized portions remain, and the average aspect ratio of the crystal grains is large.

The steel sheet 18 satisfies the requirements of the present invention at the intermediate annealing temperature, but since the final annealing temperature is low, the reverse transformation of the martensite to the austenite produced by the final cold rolling is insufficient, Can not be calculated. In addition, since the structure of this steel sheet is composed of a large amount of martensite and a non-recrystallized austenite, the roughness of the precision machined surface is very large.

The steel sheets 19 to 25 are comparative examples in which the chemical composition is out of the range of the present invention and at least one of the average grain size, the unrecrystallized portion remaining ratio and the average aspect ratio of the crystal grains is out of the range specified in the present invention.

Steel plates 19 and 20 have a low amount of Nb and can not adjust the austenite stability even with intermediate annealing at a low temperature.

The steel sheet 21 has a high amount of Ni and a high amount of C + N, and has a very high austenite stability and does not generate cell-shaped martensite due to final cold rolling.

Since the steel sheet 22 has a small amount of Cu and a low austenite stability, a large amount of martensite remains after final annealing, and crystal grain size and the like can not be calculated. Also, the roughness after processing is large.

The steel sheet 23 contains a large amount of Cu, and no cell-shaped martensite is produced by final cold rolling.

The steel sheet 24 contains a large amount of Nb, and a large amount of the non-recrystallized portion remains after the final annealing.

The steel sheet 25 has a large amount of Mn and Ni, and has a very high austenite stability, and no cell-shaped martensite is produced even by the final cold rolling.

[Industrial Availability]

According to the present invention, it is possible to obtain an austenitic stainless steel sheet which is fine grains and is equiaxed grains. Such an austenitic stainless steel sheet is suitable for precision machining such as etching and laser machining since the smoothness of the etched surface is excellent. The present invention can also industrially and stably produce the above-described austenitic steel.

Claims (2)

In terms of% by mass,
C + N: 0.03 to 0.20%
Si: 0.1 to 1.5%
Mn: 0.10 to 1.5%
Cr: 15.0 to 22.0%
Ni: 4.5 to 10.0%
Cu: 0.10 to 2.0%
Mo: 0.1 to 2.0%
0.02 to 0.50% of Nb,
The remainder being Fe and impurities,
An average crystal grain size of 5.0 占 퐉 or less,
The remaining percentage of unconfirmed governments is 3.0% or less,
An average aspect ratio of crystal grains is 1.2 or less. A method for producing an austenitic stainless steel sheet according to claim 1,
The base material is subjected to hot rolling, annealing and cold rolling,
A final annealing at a treatment temperature of less than 1000 占 폚, a final cold rolling at a total plate thickness reduction rate of 50% or more, and a final annealing at a treatment temperature of more than 700 占 폚 and not more than 950 占 폚.

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