Austenitic stainless steel sheet for photoetching with excellent surface smoothness between the material surface and the etched surface, and method for manufacturing the same.

Abstract

This invention provides stainless steel that has excellent smoothness on both the plate surface and the etched surface, enabling the manufacture of high-quality paper feeding spurs that do not generate paper dust or scratches even when subjected to high-speed printing. [Solution] An austenitic stainless steel sheet for etching, wherein, by mass%, C: 0.010% or more, 0.10% or less; Si: 0.02% or more, 1.0% or less; Mn: 0.6% or more, 1.6% or less; Ni: 5.0% or more, 15.0% or less; Cr: 15.0% or more, 20.0% or less; Mo: 0.05% or more, 2.5% or less; W: 0.005% or more, 0.2% or less; Cu: 0.05% or more, 0.8% or less; N: 0.01% or more, 0.3% or less; B: 0.0001% or more, 0.0005% or less; Sn: 0.002% or more, 0.02% or less; the remainder consists of Fe and unavoidable impurities; the ratio of the Cr concentration at the outermost surface to the Cr concentration in the base material is 0.90 or more; and the surface roughness (Ra) is 0.1 μm or less.

Description

Technical Field

[0001] The present invention relates to an austenitic stainless steel sheet excellent in the smoothness of the surface and the etching surface of a material and used for photolithographic etching, and a method for manufacturing the same.

Background Art

[0002] Photolithographic etching forms an oxidation-resistant resist film on the metal surface in the shape of a product by the photoresist method, dissolves unnecessary parts with an etching solution, and then removes the resist film to obtain a product. Since it is suitable for multi-variety and small-batch production of parts with complex shapes, it is widely adopted for processing stainless steel thin plates and foils.

[0003] Examples of parts produced using such a processing method include the gimbal spring of a hard disk, the slit of a rotary encoder, the metal mask for vacuum evaporation used as a jig when producing ICs and LSIs, the platen for paper feeding of an inkjet printer, and many others.

[0004] For example, in the platen for paper feeding, with the improvement of the quality of printed images, dedicated glossy paper and the like have come to be used, so that scratches on the printed paper caused by the platen have become a problem. In addition, when paper powder is generated when the platen rubs the printed paper surface, in that case, the paper powder adheres to the peripheral surface and the vicinity thereof, which is the part where the paper powder contacts the printed paper surface of the platen, and further problems such as the paper powder absorbing ink and soiling the printed paper surface occur. Recently, with the strong demand for high-speed printing, the problem caused by paper powder has become prominent again, and countermeasures are required.

[0005] It is known that the quality of the spur teeth is strongly related to the generation of paper dust. The teeth are the left and right ends of the spur shown in Figures 1(c) and 2(c). Microscopically, the ends dig into the printed paper, so the parts that come into contact with the printed paper are both the plate surface (the lower end surface in both figures) and the surface formed by etching (the inclined surface in both figures). Paper dust occurs because the degree of smoothness of the plate surface and the etched surface that come into contact with the printed paper is low, and it has been found that if the surface roughness (Ra) is ≤ 0.10 μm or less, paper dust will be generated but will not adhere.

[0006] For example, Patent Document 1 describes how dislocations and martensite are introduced into the crystal grains to increase the etching rate within the crystal grains, and how this etching rate within the crystal grains is made equivalent to that of the crystal grain boundaries to obtain a smooth etched surface. Furthermore, the smoothness of the material surface is achieved during the final rolling process, which involves cold rolling at a rolling rate of 20% to 80% using rolling rolls with a surface roughness (Ra) of 0.2 μm or less. However, even with the application of this technology, it is currently difficult to suppress the adhesion of paper dust.

[0007] Furthermore, Patent Document 2 proposes a method for increasing the etching speed by having a segregated segregation layer on the plate surface with a Ni concentration difference of 1.5 mass% or more, where the areas with higher Ni concentrations are preferentially etched. However, this technology is a technology that improves the processing speed and does not relate to the smoothness of the etched surface, which is related to the generation of paper dust.

[0008] In addition, Patent Document 3 describes reducing the carbon content to 0.03 mass% or less to suppress the masking effect caused by corrosion products called smut, which consist of carbides, and refining the average grain size to 15 μm or less to increase the etching rate at grain boundaries. Furthermore, it describes including 0.01 to 0.3 mass% of Nb to suppress coarse carbides and grain growth. However, the surface roughness achievable with this technique is only about 0.3 μm in Ra, making it difficult to achieve a smooth surface with an Ra of 0.10 μm or less, which is considered to be the point at which paper dust accumulation is not observed. Therefore, it does not solve the above-mentioned problems arising from the recent increase in processing speed.

[0009] As such, there is currently no suitable stainless steel material available for paper feed spurs that can keep up with the increasing printing speeds of today. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Patent No. 4332670 [Patent Document 2] Japanese Patent Publication No. 2020-164905 [Patent Document 3] Japanese Patent Publication No. 2003-3244 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] The present invention aims to provide an etchable stainless steel sheet that has excellent smoothness on both the plate surface and the etched surface, meaning that even after etching, the shape changes of the plate surface and the etched surface are minimal. This stainless steel sheet can be used to manufacture spurs of superior quality that do not generate paper dust or scratches, even when subjected to today's high-speed printing. [Means for solving the problem]

[0012] The inventors first conducted a detailed investigation into the cause of paper dust generation. The characteristics of the paper dust generated due to high-speed printing were observed to be: (1) the individual particles were smaller than before, and (2) the paper dust appeared to be agglomerating during high-speed printing. Furthermore, (3) it was found that the paper surface was slightly rough at the point where the boundary between the stainless steel surface and the etched surface came into contact. Therefore, the inventors decided to create a spur etched from one side of the plate and investigate the effect of (3) on paper dust generation by bringing it into contact over a larger area.

[0013] Figure 1 shows a schematic cross-sectional view of the manufacturing process of a spur by etching. In Figure 1(a), resist 20 is applied to the entire back surface of the alloy plate 10 of the present invention, and resist 21 is applied to the front surface in the desired spur shape. In Figures 1(a) and 1(b), etching is performed by a conventional method, and dissolution proceeds as indicated by the arrows. After removing resists 20 and 21, the spur shown in Figure 1(c) is obtained.

[0014] Figures 1(c) and 2(c) show schematic cross-sectional views of two types of spurs fabricated by single-sided etching. Observation of these spurs revealed, as shown in both figures, that the alloy plate melted during etching, and differences in the sharpness of the tip were observed just before penetration. Broadly speaking, these could be classified into two types: those with small shape changes (melting proceeding monotonically until the end), as shown in Figure 1(c), and those with large shape changes (melting changing midway), as shown in Figure 2(c). It was also found that some lots showed large shape changes, while others showed very small changes. This suggests the influence of the chemical composition of the alloy plate, and further investigation is planned.

[0015] Furthermore, when paper feeding tests were conducted with the manufactured spurs, it was confirmed that those with large shape changes during etching generated a lot of paper dust, while those with small shape changes generated less paper dust.

[0016] Therefore, in order to clarify the relationship between shape changes and chemical composition, the surface of the plate was precisely analyzed. As a result, it was found that the elemental concentrations on the surface differed slightly from lot to lot. Since this was an analysis of elements present in trace amounts, it is likely that errors were included, but Cr, Ni, Mo, W, Cu, Sn, and B were extracted as candidates.

[0017] When the concentration of each element in the alloy was varied and its effects were investigated, it was found that when the Cr concentration on the plate surface was high and the concentration inside the plate was similar to that of the base material, the shape change was small, while conversely, when the Cr concentration on the plate surface was low, the shape change was large. From this, it was estimated that the cause of the defect was that when etching was performed from one side of the plate, the properties of the spur tooth tip changed because the part with a different Cr concentration was etched just before penetration. In other words, as shown in the schematic cross-sectional view of Figure 2, when etching is performed in the same way as in Figure 1 using an alloy plate 11 with a low surface Cr concentration, Cr-deficient layers 12 and 13 are formed, and as shown in Figure 2(b), it is thought that the dissolution of the Cr-deficient layer 13 progresses just before the etching penetrates.

[0018] The candidate elements appear to affect the Cr concentration on the surface, with Sn, Mo, W, and B having a particularly significant impact on defect occurrence. Sn, Mo, and W tended to be more beneficial when concentrated on the plate surface, while B was sometimes undetectable, and it was presumed that a lower concentration of B resulted in a better shape.

[0019] Based on the above, by appropriately adding and controlling these elements, we have invented a stainless steel that maintains excellent smoothness even after etching, yields a good etched surface with less shape change than conventional materials, and is suitable for high-quality etched products such as spurs.

[0020] The present invention has been completed based on the findings obtained as described above. The austenitic stainless steel sheet for etching processing of the present invention contains, in mass %, C: 0.010% or more and 0.10% or less, Si: 0.02% or more and 1.0% or less, Mn: 0.6% or more and 1.6% or less, Ni: 5.0% or more and 15.0% or less, Cr: 15.0% or more and 20.0% or less, Mo: 0.05% or more and 2.5% or less, W: 0.005% or more and 0.2% or less, Cu: 0.05% or more and 0.8% or less, N: 0.01% or more and 0.3% or less, B: 0.0001% or more and 0.0005% or less, Sn: 0.002% or more and 0.02% or less, with each element being restricted, the balance being Fe and inevitable impurities, and is characterized in that the ratio of the Cr concentration on the outermost surface to the Cr concentration in the base material part is 0.90 or more, and the surface roughness (Ra) is 0.1 μm or less.

[0021] In the austenitic stainless steel sheet for etching processing of the present invention, it is a preferred embodiment that Ti: 0.001% or more and 0.008% or less, Nb: 0.003% or more and 0.08% or less, Co: 0.05% or more and 0.40% or less.

[0022] The present invention also provides a method for manufacturing the above-described austenitic stainless steel sheet for etching processing. In manufacturing the austenitic stainless steel sheet for etching processing, after hot rolling the obtained slab, cold rolling is performed with a rolling reduction rate of 30% or more, and then heat treatment is performed at 800°C or more and 950°C or less. After passing through a rolling process in which cold rolling is performed at a rolling reduction rate of 20% or more and 80% or less during the final rolling, stress relief heat treatment is performed at 520°C or more and 750°C or less in a bright annealing furnace.

Brief Description of the Drawings

[0023] [Figure 1] It is a schematic cross-sectional view showing an etching process for obtaining a pattern from the austenitic stainless steel sheet of the present invention. [Figure 2] It is a schematic cross-sectional view showing an etching process for obtaining a pattern from a steel sheet that does not satisfy the component range of the present invention. [Figure 3] It is a schematic diagram of a paper feeding tester in an example.

Embodiments for Carrying Out the Invention

[0024] The reasons for limiting each chemical component of the austenitic stainless steel sheet for etching processing of the present invention will be described. In the following description, “%” indicates “mass %”. C: 0.010 or more and 0.10% or less C is an austenite phase stabilizing element and an important element for ensuring strength. Therefore, an addition of at least 0.010% is necessary. However, if it is present in a large amount, precipitation on Cr carbides becomes easy depending on the heat treatment conditions, leading to sensitization and deteriorating corrosion resistance. Therefore, the upper limit is set to 0.10%. The preferable lower limit of the content is 0.015%, the more preferable lower limit is 0.020%, the preferable upper limit is 0.06%, and the more preferable upper limit is 0.04%.

[0025] Si: 0.02% or more and 1.0% or less Si is an important element having a deoxidizing effect. Therefore, an addition of at least 0.02% is necessary. However, it is also an element that promotes the precipitation of σ phase, which deteriorates corrosion resistance. Therefore, the upper limit of the Si content is set to 1.0%. The preferable lower limit of the content is 0.30%, the more preferable lower limit is 0.40%, the preferable upper limit is 0.8%, and the more preferable upper limit is 0.7%.

[0026] Mn: 0.6% or more and 1.6% or less Mn is an element added as a deoxidizer. It has the effect of stabilizing the austenite phase and increasing the solubility of N, thus suppressing the formation of carbonitrides and contributing to ensuring corrosion resistance. Therefore, it is necessary to contain 0.6% or more. However, excessive addition forms MnS, which becomes the starting point of pitting corrosion and deteriorates corrosion resistance. Also, coarse MnS makes the etching surface non-uniform and reduces smoothness. Therefore, the upper limit of the Mn content is set to 1.6%. The preferable lower limit of the content is 0.8%, the more preferable lower limit is 1.0%, the preferable upper limit is 1.5%, and the more preferable upper limit is 1.4%.

[0027] Ni: 5.0% or more and 15.0% or less Ni is an element that stabilizes the austenite phase, suppressing the precipitation of intermetallic compounds such as the σ phase, and is an important element that improves pitting corrosion resistance and overall corrosion resistance. For this reason, it is necessary to include Ni at a concentration of 5.0% or more. However, since a Ni content exceeding 15.0% leads to high costs, the Ni content was set to be between 5.0% and 15.0%. The preferred lower limit of Ni content is 5.5%, the more preferred lower limit is 6.0%, the preferred upper limit is 14.0%, and the more preferred upper limit is 13.0%.

[0028] Cr:15.0% or more and 20.0% or less Cr is an element that improves pitting corrosion resistance, crevice corrosion resistance, and intergranular corrosion resistance. If the content falls below 15.0%, corrosion resistance deteriorates, and if it exceeds 20.0%, costs increase, so the content was limited to between 15.0% and 20.0%. The preferred lower limit of the content is 16.0%, the more preferred lower limit is 17.0%, the preferred upper limit is 19.0%, and the more preferred upper limit is 18.0%.

[0029] Mo: 0.05% or more and 2.5% or less Mo is a corrosion-resistant element that improves pitting corrosion resistance and crevice corrosion resistance. In this invention, it is also an important element that reduces the roughness of the plate surface formed by annealing and pickling, and suppresses the formation of areas with low Cr concentration on the surface. This minimizes changes in the shape of the etched surface. However, excessive Mo content greatly promotes the precipitation of the σ phase and deteriorates corrosion resistance. For this reason, the Mo content was set to 0.05% to 2.5%. The preferred lower limit of content is 0.06%, the more preferred lower limit is 0.07%, the preferred upper limit is 2.4%, and the more preferred upper limit is 2.3%.

[0030] W: 0.005% or more and 0.2% or less W, like Mo, is an element that improves pitting corrosion resistance and crevice corrosion resistance. In this invention, it is also an important element that reduces the roughness of the plate surface formed by annealing and pickling, and suppresses the formation of areas with low Cr concentration on the surface. This minimizes changes in the shape of the etched surface. However, excessive W content greatly promotes the precipitation of the σ phase and deteriorates corrosion resistance. For this reason, the W content should be between 0.005% and 0.2%. The preferred lower limit is 0.008%, the more preferred lower limit is 0.01%, the preferred upper limit is 0.19%, and the more preferred upper limit is 0.18%.

[0031] Cu: 0.05% or more and 0.8% or less Cu is an austenitically stable element, and while its content of 0.05% or more improves corrosion resistance, it degrades hot workability above 0.8%. Therefore, the Cu content should be between 0.05% and 0.8%. The preferred lower limit is 0.10%, the more preferred lower limit is 0.14%, the preferred upper limit is 0.5%, and the more preferred upper limit is 0.3%.

[0032] N: 0.01% or more and 0.3% or less N is an element that stabilizes the austenite phase, suppressing the precipitation of the σ phase and effectively improving strength. It also significantly improves pitting corrosion resistance and crevice corrosion resistance, similar to Cr, Mo, and W. Therefore, at least 0.01% addition is necessary. However, excessive N content leads to the precipitation of large amounts of carbonitrides, reducing corrosion resistance. Accordingly, the upper limit for N content should be 0.3%. A preferred lower limit is 0.03% or higher, a more preferred lower limit is 0.05%, a preferred upper limit is 0.20%, and a more preferred upper limit is 0.15%.

[0033] B: 0.0001% or more and 0.0005% or less B is an impurity element that can inevitably be mixed into steel from scrap and other sources, and in this invention, it is an element added to improve hot workability. It is essential in the steel of this invention, which contains Sn, which reduces hot workability. For this purpose, an addition of at least 0.0001% is necessary. It also affects the surface roughness after annealing and pickling, and the surface roughness deteriorates rapidly when the B content exceeds 0.0005%. This is presumed to be because the scale generated during annealing becomes porous, and the surface becomes rough after pickling. For this reason, the B content should be between 0.0001% and 0.0005%. The preferred lower limit of the content is 0.00012%, the more preferred lower limit is 0.00014%, the preferred upper limit is 0.00040%, and the more preferred upper limit is 0.00030%.

[0034] Sn: 0.002% or more and 0.02% or less In this invention, Sn is an important element that reduces the surface roughness of the plate formed by annealing and pickling, and suppresses the formation of areas with low Cr concentration on the surface. This minimizes changes in the shape of the etched surface. In addition, the addition improves the corrosion resistance of grain boundaries due to Sn segregation at grain boundaries. These effects are small when the amount added is less than 0.002%. Furthermore, if the amount added exceeds 0.02%, the hot workability deteriorates, so the upper limit was set to 0.02% or less. The preferred lower limit is 0.0025%, the more preferred lower limit is 0.003%, the preferred upper limit is 0.014%, and the more preferred upper limit is 0.010%.

[0035] The ratio of the Cr concentration at the outermost surface to the Cr concentration in the base material is 0.90 or higher. Furthermore, we will explain why the ratio of the Cr concentration at the outermost surface to the Cr concentration in the base material was set to 0.90 or higher. In the process of manufacturing stainless steel sheets, after atmospheric annealing, a Cr-enriched oxide scale is formed, resulting in the formation of a Cr-deficient layer with deteriorated corrosion resistance directly beneath the oxide scale. The oxide scale is removed using nitrate and hydrofluoric acid in the pickling process, but the Cr-deficient layer directly beneath it remains. When the ratio of the Cr concentration at the outermost surface to the Cr concentration in the base material is 1.0, the ease of etching of each crystal grain becomes equal, and a smooth etched surface can be obtained, so a value close to 1.0 is desirable. The ratio of the Cr concentration at the outermost surface to the Cr concentration in the base material was limited to 0.90 or higher as a value that does not affect smoothness. A preferred range is 0.94 or higher, and a more preferred range is 0.96 or higher.

[0036] Ti: 0.001% or more and 0.008% or less Ti forms precipitates with C or N, improving resistance to intergranular corrosion. It is also an effective element in preventing grain coarsening. However, excessive content leads to the formation of excess Ti nitrides, which form clusters and cause surface defects. For this reason, the Ti content should be between 0.001% and 0.008%. The preferred lower limit of the content is 0.002%, the more preferred lower limit is 0.003%, the preferred upper limit is 0.007%, and the more preferred upper limit is 0.006%.

[0037] Nb: 0.003% or more and 0.08% or less Nb, like Ti, forms precipitates with C or N, improving intergranular corrosion resistance and refining the crystal grains. However, increasing its content degrades hot workability. Therefore, the Nb content should be between 0.003% and 0.08%. The preferred lower limit is 0.004%, the more preferred lower limit is 0.006%, the preferred upper limit is 0.07%, and the more preferred upper limit is 0.06%.

[0038] Co: 0.05% or more and 0.40% or less Co, like C and N, is an element that stabilizes the austenite phase. C and N cannot be added in large quantities because they form carbonitrides with Ti and other elements, causing surface defects. However, Co does not form carbonitrides, which is advantageous. The effect of Co can be obtained with an addition of 0.05% or more. However, since adding large amounts leads to an increase in raw material costs, it is limited to 0.4% or less. The preferred lower limit is 0.075%, the more preferred lower limit is 0.10%, the preferred upper limit is 0.35%, and the more preferred upper limit is 0.30%.

[0039] Surface roughness (Ra) of the material surface and etched surface: 0.10 μm or less. Paper dust is generated because the degree of smoothness between the unetched material surface in contact with the printed paper surface and the etched surface is low. It has also been found that if the surface roughness (Ra) is ≤ 0.10 μm or less, paper dust will be generated but will not adhere. The surface roughness of the material surface can be improved by heat treatment in a bright annealing furnace during stress relief heat treatment, which suppresses the formation of oxide scale and results in a smooth surface. The etching surface can be improved by adding Sn to enhance the corrosion resistance of the grain boundaries and by making the etching rate at the grain boundaries and within the grains equal, thereby reducing the irregularities of the etched surface and resulting in a smooth surface. The preferred upper limit for surface roughness (Ra) is 0.08 μm or less, and the more preferred upper limit is 0.06 μm or less.

[0040] Next, we will explain the reasons for the limitations on the manufacturing method of the present invention. First, the reason why the initial cold rolling ratio is 30% or more is that if the rolling ratio is less than 30%, sufficient strain to drive recrystallization will not be introduced, resulting in a mixed grain structure during subsequent heat treatment and roughening of the etched surface. Therefore, the rolling ratio was set to 30% or more. The preferred lower limit for the rolling ratio is 35%, and the more preferred lower limit is 40%.

[0041] The annealing method according to the present invention is acceptable if performed using conventional methods. Furthermore, methods for removing scale formed on the surface by pickling are employed as needed. Alternatively, methods for controlling the oxidation potential of the atmosphere to suppress the formation of oxide scale are also preferred. For example, a method called bright annealing is performed in a nitrogen + hydrogen atmosphere with a hydrogen content of 70% or more, and a 100% hydrogen atmosphere is more preferable. In the first annealing after cold rolling, the annealing temperature must be 950°C or lower to prevent roughening of the etched surface due to grain coarsening. A preferred upper limit for the annealing temperature is 940°C, and a more preferred upper limit is 930°C. Furthermore, to restore the ductility necessary for subsequent cold rolling, the temperature must be 800°C or higher. A preferred lower limit is 810°C, and a more preferred lower limit is 820°C.

[0042] Next, in the final cold rolling, a rolling ratio of 20% or more is required to obtain a uniform and finer grain with a consistent dislocation distribution within the grains. Here, cold rolling at a rolling ratio exceeding 80% increases the risk of cracking and fracture during rolling, so the upper limit of the rolling ratio was set at 80%. The preferred lower limit of the rolling ratio is 32%, the more preferred lower limit is 35%, the preferred upper limit is 75%, and the more preferred upper limit is 70%.

[0043] The heat treatment after final rolling is a stress relief heat treatment performed in a BA atmosphere. Below 520°C, the residual stress inside the stainless steel sheet does not become homogenized, causing warping during etching; therefore, the lower limit temperature was set at 520°C. Furthermore, above annealing temperatures of 750°C, the etched surface tends to become rough due to the growth of recrystallized crystal grains; therefore, 750°C was set as the upper limit. The preferred lower limit for the stress relief heat treatment is 525°C, the more preferred lower limit is 530°C, the preferred upper limit is 745°C, and the more preferred upper limit is 740°C. [Examples]

[0044] Next, an example demonstrating the effects of the present invention will be described. Material plates made from alloys A to R and alloys S to X, with the respective component compositions shown in Table 1, were prepared. Specifically, raw materials such as scrap were placed in an electric furnace and melted, and decarburized by oxygen blowing using AOD (Argon Oxygen Decarburization) and / or VOD (Vacuum Oxygen Decarburization). After the refining process in AOD or VOD, the temperature was adjusted while stirring with Ar by ladle refining. Finally, a slab with a thickness of 200 mm was manufactured by continuous casting.

[0045] The manufactured slabs were heated to 1200-1270°C and hot-rolled to produce coils. The slabs were hot-rolled to a thickness of 3 mm, and then, after an annealing and pickling process, the 3 mm thickness was cold-rolled to a thickness of 0.8 mm (rolling ratio 73.3%) to produce coils. Subsequently, for evaluation such as etching, the slabs were annealed at 925°C, followed by pickling to remove surface scale, and then cold-rolled again to 0.2 mm (rolling ratio 75%). Finally, SR treatment (stress relief heat treatment) was performed in a BA atmosphere at 550°C and these coils were subjected to testing.

[0046] The obtained steel plates were evaluated using the method described below. [Preparation of spur test specimens] From the obtained 0.2 mm thick steel plate, a resist was applied, and a spur with an outer diameter of 25 mm, a tooth height of 1.25 mm, and 24 teeth arranged circumferentially was fabricated from the original plate on which the spur was drawn by single-sided etching. The etching conditions were to spray ferric chloride solution (temperature: 60°C, specific gravity: 1.45, oxidation-reduction potential: 680 mV) onto the surface of the material at a pressure of 0.26 MPa for 34 minutes to fabricate the spur.

[0047] [Paper dust generation test] Fifteen spur test pieces were stacked, their tooth tips aligned, and secured. A paper feeding test was then conducted to compare the presence and amount of paper dust generated. A schematic diagram of the paper feeding test machine is shown in Figure 3. The printing paper 40 used in the test was fed towards the spur test piece 14 by two rollers, the main roller 32 and the pressure roller 30, and discharged by a spur consisting of the discharge roller 31 and the secured spur test piece 14. The test was conducted with a humidity of 80%, which affects the generation of paper dust. The paper feeding speed was adjusted to 50 sheets / min by the rotation speed of the two rollers. After feeding 1000 sheets of plain paper, the weight of the generated paper dust was measured and evaluated. Paper dust was collected by drawing air around the test piece and capturing it with a filter. The filter with the paper dust attached was then measured, and the weight was determined from the difference between the filter weight before the test and the filter weight before the test.

[0048] For evaluation, a score of ◎ was given if the amount of paper dust generated was less than 500 mg, ○ if it was 500 mg or more but less than 700 mg, △ if it was 700 mg or more but less than 1000 mg, and × if it was 1000 mg or more.

[0049] [Cr concentration analysis of the surface and base material] The Cr concentration on the surface of the obtained 0.2 mm thick steel plate was analyzed using a Marcus-type high-frequency glow discharge surface analyzer (GDS, HORIBA, GD-Profiler2). The GDS is a device that performs elemental concentration profiling analysis in the depth direction by sputtering the sample with Ar plasma and causing the sputtered atoms to emit atomic light. Sputtering was performed from the surface in the thickness direction of the plate, and the value showing the lowest Cr concentration was defined as the surface Cr concentration, and the area where the ladle Cr% was reached from the surface was measured as the base material. The evaluation was as follows: a ratio of Cr concentration between the surface and the base material of 0.96 or higher was ◎, 0.94 or higher and less than 0.96 was ○, 0.90 or higher and less than 0.94 was △, and less than 0.90 was ×. The measurement conditions were pulse mode for excitation mode, Ar sputtering method for sputtering, sputtering pressure of 600 MPa, sputtering output of 8.75 W, pulse frequency of 100 Hz, and the analysis area was 4 mm in diameter.

[0050] [Surface roughness measurement of material surfaces and etched surfaces] Surface roughness (Ra) was measured by cutting a 50mm square test piece from the obtained 0.2mm thick steel plate. A resist was applied to the entire back surface and to a 25mm x 50mm rectangular area in the center of the 50mm x 50mm front surface. Surface roughness measurement test pieces were prepared by single-sided etching. The etching conditions involved spraying ferric chloride solution (temperature: 60°C, specific gravity: 1.45, oxidation-reduction potential: 680mV) onto the material surface at a pressure of 0.26MPa for 34 minutes to prepare the surface roughness measurement test piece. The prepared test piece was measured three times at a magnification of 1200x using a 3D laser microscope (KEYENCE, VK-X3000) at a length of 200μm, and the average value of the average arithmetic roughness was measured. The surface roughness of the material surface was measured along the direction parallel to the rolling direction. The surface roughness of the etched surface was measured around the halfway point of the thickness with the surface roughness test piece fixed vertically. The evaluation criteria were as follows: surface roughness (Ra) of 0.06 μm or less was marked with ◎, between 0.06 μm and 0.08 μm was marked with ○, between 0.08 μm and 0.10 μm was marked with △, and above 0.10 μm was marked with ×.

[0051] [Measurement of average crystal grain size] The average grain size was the grain size in the width direction of the plate in a cross-section perpendicular to the rolling direction. The grain size was measured at the center of the plate thickness, 100 μm in the thickness direction. The embedded sample was prepared by vertically embedding a 25 mm wide × 10 mm long piece of steel plate cut from the obtained 0.2 mm thick steel plate. The etching conditions were a 10% oxalic acid aqueous solution at 60°C with a current of 4 mA for up to 90 seconds. Using a digital microscope (KEYENCE, VHX-8000), the grain size along five vertical lines was measured from 2000x cross-sectional microstructural images, and the average of 10 fields of view was calculated to determine the average grain size. The evaluation was as follows: average grain size of 3.0 μm or less was marked with ◎, between 3.0 μm and 3.5 μm was marked with ○, between 3.5 μm and 4.0 μm was marked with △, and above 4.0 μm was marked with ×.

[0052] [Evaluation of hot workability] After hot-rolling a coil to a thickness of 3 mm and subjecting it to annealing and pickling, the number of sleeve-shaped defects found in the coil was counted and evaluated. The evaluation was converted to the number of defects per 10 m, with ◎ indicating fewer than 2 defects, ○ indicating 2 to less than 4 defects, △ indicating 4 to less than 6 defects, and × indicating 6 or more defects.

[0053] 〔comprehensive evaluation〕 For the overall evaluation, examples containing only ◎, ○, or △ in each of the above evaluations were marked as passing, while examples containing even one × were marked as failing. Note that entries that did not meet the scope of an independent claim were enclosed in parentheses.

[0054] Table 1 shows the evaluation results for each alloy. Alloys A to R are examples of inventions that satisfy the conditions of the present invention, while alloys S to X are comparative examples.

[0055] The alloys A to R shown in Table 1 contain sufficient amounts of Sn, Mo, and W, which suppresses the formation of areas with low Cr concentration on the surface, thereby reducing the change in spur shape and suppressing the generation of paper dust.

[0056] Because S, T, and W alloys have low Mo, W, or Sn content, low Cr regions form on the surface, resulting in significant changes in the shape of the spur teeth and generating a large amount of paper dust.

[0057] Because the U alloy had a high B content, the scale formed during annealing became porous, resulting in a decrease in the surface roughness (Ra) of the material surface.

[0058] Alloys V and X had either a low B content or a high Sn content, resulting in numerous sleeve-shaped defects due to reduced hot workability.

[0059] Using alloy A shown in Table 1, spur test specimens were obtained from 0.2 mm thick steel plates under the manufacturing conditions shown in Table 2. Steel plates No. 1 to 4 are examples of the invention that satisfy the conditions of the present invention, while steel plates No. 5 to 9 are comparative examples.

[0060] The steel plates No. 1 to 4 shown in Table 2 were rolled sufficiently to prevent the formation of a mixed grain structure, and heat-treated at an appropriate temperature to achieve a uniform structure. Furthermore, stress relief heat treatment in a bright annealing furnace resulted in a smooth material surface, which suppressed the generation of paper dust.

[0061] After air annealing and pickling with nitrate-hydrofluoric acid, the surface roughness of steel plate No. 5 was roughened by oxide scale, resulting in the generation of a large amount of paper dust.

[0062] Because the annealing temperature of steel sheet No. 6 was high at 1000°C after cold rolling, the etched surface became rough due to grain coarsening, and a large amount of paper dust was generated.

[0063] Because the final rolling ratio of steel plate No. 7 was low at 18%, it developed a mixed grain structure, and a large amount of paper dust was generated due to the roughening of the etched surface.

[0064] Because the stress relief heat treatment temperature for steel plate No. 8 was high at 800°C, a large amount of paper dust was generated due to roughening of the etched surface caused by a mixed grain structure resulting from partial recrystallization.

[0065] Because the initial cold rolling rate of steel sheet No. 9 was low at 25%, sufficient strain was not introduced to drive recrystallization. As a result, a mixed grain structure developed during the subsequent annealing process, the etched surface became rough, and a large amount of paper dust was generated.

[0066] [Table 1]

[0067] [Table 2] [Explanation of Symbols]

[0068] 10, 11: Alloy plate, 12, 13: Cr-deficient layer, 14: Spur, 20, 21: Resist, 30: Pressure roller, 31: Paper output roller, 32: Main roller, 40: Printing paper

Claims

1. In mass percent, C: 0.010% or more, 0.10% or less, Si: 0.02% or more, 1.0% or less, Mn: 0.6% or more, 1.6% or less, Ni: 5.0% or more, 15.0% or less, Cr: 15.0% or more, 20.0% or less, Mo: 0.05% or more, 2.5% or less, W: 0.005% or more, 0.2% or less, Cu: 0.05% or more, 0.8% or less, N: 0.01% or more, 0.3% or less, B: 0.0001% or more, 0.0005% or less, Sn: 0.002% or more, 0.02% or less, An austenitic stainless steel sheet for etching, characterized in that each element is limited to a certain extent, the remainder consists of Fe and unavoidable impurities, the ratio of the Cr concentration at the outermost surface to the Cr concentration in the base material is 0.90 or higher, and the surface roughness (Ra) is 0.1 μm or less.

2. Ti: 0.001% or more, 0.008% or less, Nb: 0.003% or more, 0.08% or less, Co: 0.05% or more, 0.40% or less, The austenitic stainless steel sheet for etching according to claim 1, characterized in that it is the same as the one described in claim 1.

3. A method for manufacturing an austenitic stainless steel sheet for etching according to claim 1 or 2, characterized in that the obtained slab is hot-rolled, then cold-rolled with a rolling ratio of 30% or more, then heat-treated at 800°C to 950°C, then cold-rolled at a rolling ratio of 20% to 80% during the final rolling process, and finally subjected to a stress-relieving heat treatment in a bright annealing furnace at 520°C to 750°C.

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