JP5920555B1 - Austenitic stainless steel sheet and manufacturing method thereof - Google Patents

Abstract

% 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%, Nb: 0.02 to 0.50%, the balance being Fe and impurities, An austenite system suitable for precision processing such as etching and laser processing, having an average crystal grain size of 5.0 μm or less, an unrecrystallized portion residual ratio of 3.0% or less, and an average spectroscopic ratio of crystal grains of 1.2 or less. Stainless steel sheet.

Description

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

  Austenitic stainless steel plates are widely used such as metal masks. For example, the metal mask is manufactured by precision processing such as etching and laser processing. In these precision processing, it is known that the crystal grain size of the material is fine and the smoothness of the etched surface is improved by increasing the grain size.

  For example, in Patent Documents 1, 2, and 3, the chemical composition is adjusted, and annealing after the final cold rolling is performed at a temperature lower than usual at 500 to 850 ° C. An austenitic stainless steel sheet that ensures the smoothness is 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 Nb carbonitride.

JP-A-2-173214 JP 2003-003244 A Japanese Patent Application Laid-Open No. 2005-320587

  However, in recent years, smoothness of the processed surface is required more than ever for precision processing, and the methods disclosed in Patent Documents 1 to 3 may not fully satisfy the request. In particular, in Patent Documents 2 and 3, in a steel sheet containing Nb, in order to transform the lower structure into lath-shaped martensite by final cold rolling, Nb is dissolved in the steel sheet to be subjected to final cold rolling. There is a need. Therefore, in patent document 2, it is thought that the processing temperature of the intermediate annealing which is a pre-process of final cold rolling had to be set as high as 1100 degreeC. Moreover, in patent document 3, in order to suppress the curvature at the time of etching by the residual stress removal after temper rolling (final cold rolling), stress removal annealing (final annealing) is performed in the temperature range of 550 degreeC or more and 700 degrees C or less. ing. Here, Patent Document 3 focuses on increasing the hardness as shown in Table 2. For this purpose, it is necessary to suppress the reverse transformation to austenite and leave martensite. Therefore, in Patent Document 3, it is considered that the final annealing temperature had to be lowered.

  In the case of a material containing Nb as described in Patent Documents 2 and 3, when Nb is dissolved in the austenite phase, recrystallization is delayed, so that an unrecrystallized portion often remains. In actual production, due to operational variations in cold rolling and annealing temperatures, the crystal grains are not sufficiently refined, and unrecrystallized parts remain, and when these stainless steel sheets are precision processed The smoothness may vary.

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

  As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.

  (1) To date, it has been known that fine crystal grains having no unrecrystallized portion are desirable in order to smooth the surface after precision processing such as etching processing and laser processing. In addition to these, the smoothness of the precision machined surface is further improved by making the crystal grains into fine equiaxed grains.

  (2) Moreover, in order to make a crystal grain into a fine equiaxed grain, it is not enough to generate martensite by cold rolling and reversely transform it.

  (3) Forming work-induced martensite at the initial stage of cold rolling, and further reducing it can change the form of martensite from lath to cell, resulting in the targeted fine equiaxes A grain structure can be obtained.

  (4) To this end, it seems effective to set the cold rolling rate to 90% or more and to make γ unstable by the chemical composition. However, the former is difficult from an industrial aspect, and the latter is too unstable, and δ ferrite is generated by melting or hot rolling, which promotes cracking in hot rolling and cold rolling.

  (5) Accordingly, it is effective to change the γ stability by adopting a manufacturing process in which the γ stability is high in the initial stage of manufacture and the α ′ transformation is performed in the final cold rolling. Therefore, in order to prevent the formation of δ ferrite as a raw material, the material has a minimum γ stability, and annealing (intermediate annealing) is performed before the final cold rolling to precipitate C and N which are γ stabilizing elements. Thus, α ′ is easily generated in the subsequent cold rolling.

  (6) If a part of Nb is precipitated as Nb (C, N) by intermediate annealing, crystal grain growth can be suppressed by the pinning effect, and the amount of solid solution Nb in the final annealing is reduced. Therefore, it is effective for reducing the remaining ratio of the non-recrystallized portion.

  (7) If a part of Nb is precipitated as Nb (C, N) by intermediate annealing, the γ stability can be lowered to the extent that δ ferrite is not generated. For this reason, even if the rolling rate at the time of operation becomes lower than expected or the final annealing temperature varies, it is possible to stably form a fine equiaxed grain structure.

  (8) In order to increase the γ stability, the chemical composition of the material was also examined in detail. As a result, Cu is an austenite-forming element and an element capable of adjusting the stability of the austenite phase. Further, when Mo is contained, the stacking fault energy is increased by a synergistic effect with Mo, thereby austenite. It also has a function of suppressing the accumulation of strain in the matrix. Thereby, excessive work hardening is suppressed and the load at the time of thin plate manufacture is reduced greatly. In addition, when it is used after being subjected to pressing or bending before or after etching or laser processing, there is an effect that these can be easily formed by suppressing excessive work hardening.

  (9) As described above, Nb carbonitride is precipitated by annealing at a lower temperature than usual in the annealing before the final cold rolling, and the amount of solid solution C and solid solution N is adjusted, and the austenite phase Control stability. After that, by performing cold rolling, the work-induced martensite to be formed is not a conventional lath shape α ′ but a cellular shape α ′. Thereby, in addition to the pinning effect by the Nb carbonitride formed by the initial annealing in the final annealing step, equiaxed grains having a fine grain and a reduced aspect ratio can be obtained. As a result, fine and equiaxed austenitic stainless steel sheets can be obtained, and the smoothness of the etched surface can be improved.

  Based on the above findings, the present inventors have completed the present invention. The gist of the present invention is the following austenitic stainless steel sheet and 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: 15.0-22.0%,
Ni: 4.5 to 10.0%,
Cu: 0.10 to 2.0%,
Mo: 0.1 to 2.0%,
Nb: 0.02 to 0.50%,
The balance is Fe and impurities,
The average crystal grain size is 5.0 μm or less,
Unrecrystallized portion remaining rate is 3.0% or less,
The average spectral ratio of the crystal grains is 1.2 or less,
Austenitic stainless steel sheet.

(2) A method for producing the austenitic stainless steel sheet of (1) above,
After hot rolling, annealing, cold rolling on the base material,
An intermediate annealing at a processing temperature of less than 1000 ° C., a final cold rolling with a total sheet thickness reduction rate of 50% or more, and a final annealing to be performed in a temperature range of 700 ° C. or more and 950 ° C. or less in order.
Manufacturing method of austenitic stainless steel sheet.

  According to the present invention, it is possible to obtain an austenitic stainless steel plate that is fine and equiaxed. Such an austenitic stainless steel plate is excellent in the smoothness of the etched surface, and is therefore suitable for precision processing such as etching and laser processing. The present invention can also produce the austenitic steel described above industrially stably.

FIG. 1 is a diagram showing the difference between the conventional manufacturing method and the manufacturing method of the present invention. FIG. 2 is a diagram showing an aspect ratio of crystal grains.

  The present invention will be described in detail. Hereinafter, “mass%” is simply referred to as “%”.

1. Austenitic stainless steel sheet (1) Chemical composition C + N: 0.03 to 0.20%
C and N are γ-stabilizing elements and need to be contained in appropriate amounts in order to suppress the formation of δ ferrite during melting and hot rolling. Furthermore, C and N combine with Nb and precipitate as a fine Nb compound during intermediate annealing or final annealing, and have the effect of suppressing crystal grain growth. In addition, the γ stability of the base material can be adjusted during the manufacturing process by forming a solid solution at the time of the hot-rolled sheet and precipitating as Nb carbonitride during intermediate annealing. Therefore, C and N need to be contained in total of 0.03% or more. Preferably it is 0.05% or more. On the other hand, if the total content of C and N is too large, even if it is precipitated as an Nb compound during intermediate annealing, a part remains as solute C or solute N, and the γ stability of the base material at the time of final cold rolling is increased. As a result, sufficient cellular martensite is not generated in the final cold rolling. Therefore, the upper limit is 0.20%. Preferably it is 0.16% or less. Moreover, it is preferable that content of C and N is 0.01 to 0.10% and 0.01 to 0.15%, respectively.

・ Si: 0.1-1.5%
Si is used as a deoxidizing material during melting and contributes to strengthening of steel. Therefore, the lower limit is 0.1%. However, when the Si content is excessively large, there is an adverse effect of decreasing the etching rate. Therefore, the Si content is 1.5% or less. Preferably, it is 0.8% or less.

Mn: 0.10 to 1.5%
Mn contributes to the prevention of brittle fracture during hot working and the strengthening of steel. Therefore, the lower limit is made 0.10%. However, since Mn is a strong γ-forming element, if the content is excessively large, there is little work-induced martensite generated during cold rolling, and fine crystal grains cannot be obtained by subsequent annealing. Therefore, the Mn content is 1.5% or less. More preferably, it is set to 1.2% or less.

・ Cr: 15.0-22.0%
Cr is a basic element of stainless steel, is an indispensable element that forms a metal oxide layer on the surface of the steel material and enhances the corrosion resistance, and is contained at 15.0% or more. However, since Cr is a strong ferrite stabilizing element, if the content is too large, a large amount of δ ferrite remains after melting. This δ ferrite significantly deteriorates the hot workability of the material. Therefore, the Cr content is 15.0 to 22.0%. A preferred lower limit is 15.0% and a preferred upper limit is 19.0%.

・ Ni: 4.5-10.0%
Ni is a γ-forming element, an indispensable element for stably obtaining a γ phase at room temperature, and the lower limit is set to 4.5%. However, if the Ni content is too high, the γ phase is too stabilized, and the work-induced martensitic transformation during cold rolling is suppressed. Furthermore, Ni is an expensive element, and an increase in the content causes a significant increase in cost. Therefore, the upper limit is set to 10.0%.

Cu: 0.10 to 2.0%
Cu is a γ-forming element, and is an element capable of adjusting the stability of the γ phase in the same manner as Ni. Moreover, since there exists an effect which softens a raw material, when performing cold rolling with a high big rolling rate like this invention, the load of rolling can be reduced. Further, Cu is an austenite generating element and is an element capable of adjusting the stability of the austenite phase. When Mo is contained, the stacking fault energy is increased by a synergistic effect with Mo, the accumulation of strain in the austenite matrix is suppressed, excessive work hardening is suppressed, and the load at the time of manufacturing the thin plate Is greatly reduced. In addition, when it is used after being subjected to pressing or bending before or after etching or laser processing, there is an effect that these can be easily formed by suppressing excessive work hardening. Therefore, the lower limit is 0.10%. On the other hand, when Cu content increases excessively, it segregates at a grain boundary in a manufacturing process. This grain boundary segregation significantly deteriorates hot workability and makes manufacture difficult. Therefore, the upper limit is set to 2.0%. A preferred lower limit is 0.2% and a preferred upper limit is 1.0%.

Mo: 0.1-2.0%
Mo is a γ-forming element, and is an element capable of adjusting the stability of the γ phase in the same manner as Ni. Further, Mo is an element that forms a homogeneous oxide film, and therefore has an effect of reducing etching unevenness. In addition, Mo is an element that increases the stacking fault energy and suppresses the accumulation of strain in the austenite matrix due to a synergistic effect with Cu, suppresses excessive work hardening and increases the load during thin plate manufacturing. Reduce. Furthermore, when used by performing processing such as pressing and bending before and after precision processing, there is an effect that these moldings can be easily performed by suppressing excessive work hardening. Therefore, the lower limit is 0.1%. However, when the Mo content is excessively high, the cost increases. Therefore, the Mo content is set to 2.0% or less. Preferably it is 1.0% or less.

・ Nb: 0.02-0.50%
Nb generates fine carbides or nitrides, and suppresses crystal grain growth by a pinning effect. Further, by precipitating Nb carbonitride by 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 δ ferrite is not generated. As a result, in the cold rolling after the intermediate annealing, the matrix phase undergoes martensite transformation at an early stage, and then a large amount of cellular martensite is generated. In addition, Nb has an effect of suppressing crystal grain growth, but if present in a solid solution state, Nb delays recrystallization during annealing, and causes unrecrystallized portions to remain after annealing. Considering these effects, the lower limit of the Nb content is 0.02%. However, if the content of Nb in a solid solution state is excessive, recrystallization during annealing is delayed and a large amount of unrecrystallized portions remain. If a large amount of non-recrystallized portion remains, it becomes a factor of reducing the smoothness of a precision processed product. Therefore, the upper limit is 0.50%. A preferred lower limit is 0.04%, and a preferred upper limit is 0.20%.

-Remainder: Fe and impurities In the production of stainless steel, scrap raw materials are often used from the viewpoint of promoting recycling. For this reason, various impurity elements are inevitably mixed in 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 impair the effects of the present invention. Examples of such impurities include P: 0.05% or less and S: 0.03% or less.

-Others Md ₃₀ is a temperature at which 50% of the entire metal structure becomes martensite when a strain of 30% is applied, and is one of the indexes representing the likelihood of processing-induced martensite transformation. Thus, _{Md 30} is preferably in the range of 30 to 55 ° C.. This is because within this range, processing-induced martensite transformation is likely to occur.

SFE means stacking fault energy, and is one of the indexes indicating the ease of forming stacking faults. If SFE is too low, stacking faults are likely to be formed, and it will be difficult to cause sufficient processing-induced martensitic transformation. For this reason, it is preferable that SFE shall be 3 mJ / cm < ² > or more. This is because if it is within this range, the formation of stacking faults can be easily suppressed, and the processing-induced martensitic transformation can be sufficiently promoted. A preferable upper limit of SFE is 100 mJ / cm ² .

(2) Metal structure of austenitic stainless steel plate ・ Average crystal grain size: 5.0 μm or less When the average crystal grain size becomes small, the roughness of the precision machined surface becomes small. This effect is particularly prominent when the average crystal grain size is 5.0 μm or less. For this reason, an average crystal grain diameter shall be 5.0 micrometers or less. In order to further exert the effect, 3.0 μm or less is desirable. If the average crystal grain size is too small, the production cost increases, so the lower limit is set to 0.3 μm. Considering the balance with the manufacturing cost, the lower limit is preferably 0.5 μm. The average crystal grain size represents the diameter of a circle having the same area as the average crystal grain area calculated by the quadrature method.

-Residual ratio of non-recrystallized portion: 3.0% or less When a large amount of non-recrystallized portion remains, when etching a stainless steel plate, only that portion is preferentially etched with respect to the surrounding recrystallized grains. The smoothness may be impaired. Therefore, it is preferable to set the non-recrystallized residual ratio to 3.0% or less so as not to impair the smoothness. Since the production of a material having an unrecrystallized grain residual rate that is too low brings about a decrease in production efficiency, the lower limit is preferably 0.5%.

-Average aspect ratio of crystal grains: 1.2 or less The finer the equiaxed grains, the smaller the roughness of the precision machined surface. Therefore, the average aspect ratio of crystal grains (long axis length / short axis length) is set to 1.2 or less. The long axis length in the present invention represents the long axis length when the crystal grains are approximated to an ellipse. Moreover, the minor axis length in the present invention represents the minor axis length when a crystal grain is approximated to a great circle. For example, when the crystal grains have a shape as shown in FIG. 2, the longer line segment is the major axis and the shorter line segment is the minor axis. The smaller the average aspect ratio, the better. The lower limit is preferably 1.0%.

2. Manufacturing method of austenitic stainless steel sheet (1) Hot rolling, annealing, cold rolling After the molten steel having the above-described chemical composition is melted in a converter or an electric furnace, the base material to be used for hot rolling in the present invention, It is preferable to use an ingot formed by casting into a mold or a slab obtained by continuous casting. When using an ingot, the base material is preferably processed into a shape that can be hot-rolled by cutting or the like. In the case of a slab, a slab (thickness 120 to 280 mm, width 700 to 1200 mm, length 8 to 10 m) is preferably manufactured by continuous casting. After heating this ingot or slab to the temperature range of about 1100-1300 degreeC, it is good to hot-roll and make a hot-rolled steel plate about 2-10 mm thick. Thereafter, an annealing treatment performed at 1000 to 1200 ° C. and a pickling treatment similar to the conventional one are performed, and further a cold rolling with a rolling rate of 20 to 70% is performed to obtain a cold rolled steel sheet of about 0.2 to 2.0 mm. Is good.

(2) Intermediate annealing In the present invention, the steel sheet obtained by cold rolling is subjected to intermediate annealing in a temperature range of less than 1000 ° C. This intermediate annealing is annealing performed immediately before the final cold rolling described later. In the intermediate annealing, an effect of lowering the austenite stability of the base material to such an extent that δ ferrite is not generated can be obtained because a part of Nb is not dissolved but precipitated as carbonitride. As shown in FIG. 1, when the intermediate annealing temperature exceeds 1050 ° C., Nb dissolves in the steel, and in the final cold rolling, a lath-like martensitic transformation occurs, and recrystallization is delayed in the final annealing. A recrystallized part may remain. In addition, if the non-recrystallized portion remains, the smoothness may vary when precision processing is performed. Therefore, in the present invention, the intermediate annealing is performed in a temperature range of less than 1000 ° C.

  The lower the treatment temperature, the lower the solid solution C and the solid solution N, and the lower the austenite stability, which is advantageous for forming cellular martensite. Therefore, a preferable processing temperature is 980 ° C. or lower, and particularly preferable is 950 ° C. or lower. On the other hand, the lower limit is preferably 700 ° C. and more preferably 800 ° C. in order to sufficiently precipitate Nb carbonitride and reduce the load of cold rolling in the next step by softening the steel sheet. Also, in order to sufficiently precipitate Nb carbonitride, that is, to reduce solid solution C and solid solution N, thereby reducing the austenite stability of the base material to some extent, the annealing holding time is 5 to 300 seconds. It is desirable. Moreover, although the temperature increase rate to process temperature and the cooling rate after annealing are not specifically limited, from a viewpoint of suppressing the production | generation of the Cr carbonitride which is easy to coarsen, 10-30 degree-C / sec, 10-20 degree-C / sec, respectively. It is preferable that it is a second (from holding temperature to 300 degreeC). The atmosphere of the intermediate annealing is not particularly limited.

  The formation of Nb carbonitrides can be determined by observation with a transmission electron microscope (TEM). The amount of precipitation of Nb carbonitride that is effective for transforming into a cell shape in the final cold rolling varies depending on the γ stability of the base metal, but about 0.01% of Nb in the steel sheet is about 0.01%. The target effect can be obtained by precipitating.

3. Final cold rolling The steel plate obtained by the intermediate annealing is subjected to final cold rolling with a total thickness reduction rate of 50% or more. Final cold rolling is cold rolling performed at the end in the process 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 generate work-induced martensite by cold rolling after intermediate annealing and further change the form of martensite from lath to cell. For this purpose, cold rolling with a total sheet thickness reduction rate of 50% or more is performed. The total thickness reduction rate is more preferably 60% or more. On the other hand, if the total plate thickness reduction rate is too large, the quality deteriorates. Therefore, the total plate thickness reduction rate is preferably 100% or less. The cellular martensite can be observed with a transmission electron microscope (TEM). Since this observation shows that martensite having a relatively granular cell structure is generated inside the streak-like lath, it is easy to distinguish between the cell-like and lath-like shapes.

4). Final annealing The steel plate obtained by the final cold rolling is further subjected to final annealing at a temperature exceeding 700 ° C and not more than 950 ° C. The final annealing is the last annealing performed in the process of manufacturing the austenitic stainless steel sheet of the present invention. When temper rolling is performed, the annealing is performed last in the process before temper rolling. In the final annealing, the cellular martensite generated in the previous step is reversely transformed into fine and equiaxed austenite grains. At this time, if the final annealing temperature is too low, sufficient recrystallization is not performed and unrecrystallized grains having a large aspect ratio remain. On the other hand, if the final annealing temperature is too high, the crystal grains become coarse. Accordingly, the final annealing is over 700 ° C. and 950 ° C. or less. In order to exhibit the effect more reliably, the lower limit of the final annealing temperature is preferably 800 ° C., and the upper limit is preferably 930 ° C. The atmosphere of the final annealing is not particularly limited.

  Further, from the viewpoint of eradication of non-recrystallized grains and suppression of grain coarsening, the annealing holding time is desirably 5 to 300 seconds. The rate of temperature rise to the annealing temperature and the cooling rate after annealing are not particularly limited, but it impairs the crystallographic coarsening while inhibiting reverse transformation to equiaxed austenite grains by sufficient recrystallization, and inhibits etching properties From the viewpoint of suppressing coarse Cr carbonitrides, the rate of temperature rise is preferably 15 to 50 ° C./sec, and the cooling rate is preferably 15 to 45 ° C./sec (from the holding temperature to 300 ° C.). .

  Table 1 shows the chemical composition of the steel of the test material. Steels A to G have chemical compositions that satisfy the provisions of the present invention, and steels 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 into a hot rolling material having a thickness of 40 mm. Then, after hot-rolling to thickness 4mm and annealing after hot-rolling at 1200 degreeC, it cold-rolled to thickness 2mm. Then, it annealed at 1150 degreeC and cold-rolled to predetermined plate | board thickness. The cold rolling rate of the cold rolling performed after annealing at 1150 ° C., that is, the cold rolling before intermediate annealing, is the thickness after the final cold rolling when the final cold rolling is performed at the rolling rates shown in Table 2. Was calculated so as to be 0.4 mm.

  Thereafter, intermediate annealing, final cold rolling, and final annealing were performed 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 is increased at a temperature increase rate of 10 to 30 ° C./second up to the intermediate annealing temperature, held at the intermediate annealing temperature shown in Table 2 for 5 to 300 seconds, and then the temperature decrease of 10 to 20 ° C./second. The temperature was lowered at a rate (from the holding temperature to 300 ° C.). Further, in the final annealing, after the final cold rolling, the temperature is increased to a final annealing temperature at a temperature rising rate of 15 to 30 ° C./second, and held at the final annealing temperature shown in Table 2 for 5 to 300 seconds. The temperature was decreased at a temperature decrease rate of -30 ° C / second (from the holding temperature to 300 ° C).

  A microstructure photograph of the obtained steel sheet in the rolling direction was taken with a scanning electron microscope, and the average crystal grain size, the average aspect ratio of the crystal grains, and the residual ratio of the non-recrystallized portion were calculated. Both the average crystal grain size and the average aspect ratio of the crystal grains were calculated from the measurement results of 50 or more grains of each steel plate. The remaining ratio of the non-recrystallized portion is calculated by writing 100 or more lattice points on the photographed image and confirming whether the lattice point is a crystal grain or an unrecrystallized portion. It was calculated from the ratio of the number of grid points.

  Further, in order to evaluate the precision workability, in this example, the average roughness of the processed surface was investigated. The average roughness was measured using a contact-type roughness meter after etching until the plate thickness was reduced to half with a ferric chloride solution. Measure the line roughness (arithmetic average roughness) of 4 mm each in the direction perpendicular to the rolling direction and the direction parallel to the rolling direction three times in each direction, and further average the measurement results of the six arithmetic average roughnesses as representative values. evaluated. An average roughness of 0.10 μm or less was judged as a satisfactory level for a metal mask. The results are shown in Table 2.

  Steel plates 1 to 12 in Table 2 are examples of the present invention and are excellent in smoothness of precision processed surfaces. In addition, when the sample was extract | collected from the steel plate before final annealing after completion | finish of final cold rolling, and the structure | tissue observation was performed by TEM, it has confirmed that it transformed to the cellular martensite. In addition, the smoothness of the precision processed surface was determined by using the average roughness of the etched surface measured using a contact-type roughness meter after etching the steel plate with a ferric chloride solution until the plate thickness was reduced to half.

  The steel plates 13 to 25 are comparative examples, and are inferior in smoothness of precision processed surfaces. This will be described in detail below.

  Since the steel plate 13 has a high intermediate annealing temperature and no precipitation of Nb carbonitride during the intermediate annealing, the martensite produced by the final rolling is mainly lath-shaped, and the average grain size after the final annealing is relatively fine. However, many unrecrystallized parts remain and the average aspect ratio of the crystal grains is large.

  Since the steel sheet 14 is insufficient in the final cold rolling rate, the generated martensite is small, the generated martensite is mainly lath-shaped, and the average aspect ratio of the crystal grains after the final annealing is large.

  The steel plate 15 has a high final annealing temperature, large crystal grains have grown, and the smoothness of the processed surface is poor.

  Since the steel plate 16 has a low final annealing temperature, recrystallized grains are small, but a large amount of unrecrystallized portions remain, and the average roughness of the processed surface is large.

  Since the steel plate 17 has a high intermediate annealing temperature and there is no precipitation of Nb carbonitride during the intermediate annealing, the martensite produced in the subsequent final rolling is mainly lath-shaped, and the average grain size after the final annealing is compared. However, many unrecrystallized portions remain and the average aspect ratio of the crystal grains is large.

  The steel plate 18 has an intermediate annealing temperature that satisfies the provisions of the present invention, but because the final annealing temperature is low, the reverse transformation of martensite generated in the final cold rolling into austenite is insufficient, and in the usual method, crystal grains The diameter cannot be calculated. Moreover, since the structure of this steel plate is composed of a large amount of martensite and non-recrystallized austenite, the roughness of the precision machined surface is extremely large.

  Steel plates 19 to 25 are comparative examples in which the chemical composition is outside the range of the present invention, and at least one of the average crystal grain size, the remaining ratio of non-recrystallized portion, and the average aspect ratio of the crystal grains is outside the range defined by the present invention. It is.

  The steel plates 19 and 20 have a low Nb amount, and the austenite stability cannot be adjusted even by intermediate annealing at a low temperature.

  The steel sheet 21 has a high Ni content and a high C + N content and an extremely high austenite stability, and no cellular martensite is generated in the final cold rolling.

  Since the steel plate 22 has little Cu and low austenite stability, a large amount of martensite remains after the final annealing, and the crystal grain size and the like cannot be calculated. Moreover, the roughness after processing is also large.

  The steel plate 23 contains a large amount of Cu, and cellular martensite is not generated in the final cold rolling.

  The steel plate 24 contains a large amount of Nb, and a large amount of unrecrystallized portions remain after the final annealing.

  The steel plate 25 has a large amount of Mn and Ni, has a very high austenite stability, and no cellular martensite is generated even in the final cold rolling.

  According to the present invention, it is possible to obtain an austenitic stainless steel plate that is fine and equiaxed. Such an austenitic stainless steel plate is excellent in the smoothness of the etched surface, and is therefore suitable for precision processing such as etching and laser processing. The present invention can also produce the austenitic steel described above industrially stably.

Claims (2)

% By mass
C + N: 0.03 to 0.20%,
Si: 0.1 to 1.5%,
Mn: 0.10 to 1.5%,
Cr: 15.0-22.0%,
Ni: 4.5 to 10.0%,
Cu: 0.10 to 2.0%,
Mo: 0.1 to 2.0%,
Nb: 0.02 to 0.50%,
The balance is Fe and impurities,
The average crystal grain size is 5.0 μm or less,
Unrecrystallized portion remaining rate is 3.0% or less,
The average spectral ratio of the crystal grains is 1.2 or less,
Austenitic stainless steel sheet. It is a manufacturing method of the austenitic stainless steel sheet according to claim 1,
After hot rolling, annealing, cold rolling on the base material,
An intermediate annealing at a processing temperature of less than 1000 ° C., a final cold rolling with a total sheet thickness reduction rate of 50% or more, and a final annealing to be performed in a temperature range of 700 ° C. or more and 950 ° C. or less in order.
Manufacturing method of austenitic stainless steel sheet.

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