JP2019171403A - Stainless hot rolled steel sheet and stainless cold rolled steel sheet - Google Patents

Abstract

To provide a stainless cold rolled steel sheet excellent in surface appearance.SOLUTION: In a stainless hot rolled steel sheet having a scale on the surface, and a stainless cold rolled steel sheet manufactured by subjecting it to cold rolling, a mean thickness of a scale on the stainless rolled steel sheet is 5.0-8.0 μm, and a standard deviation of the scale thickness is 2.0 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ferritic stainless steel cold-rolled steel sheet having excellent surface appearance and a hot-rolled steel sheet as a material thereof.

  Stainless steel is used in various applications. In particular, ferritic stainless steel used for household electrical appliances and kitchen appliances is required to have an excellent surface appearance without unevenness. A method for producing a ferritic stainless steel having a good surface property is disclosed in Patent Document 1, for example.

  Patent Document 1 discloses a manufacturing method for obtaining a ferritic stainless steel sheet having good surface properties by prescribing the concentration of the pickling solution and the dipping time in the pickling solution when pickling the hot-rolled steel sheet. It is disclosed.

JP 2004-169089 A (published on June 17, 2004)

  However, with the technique disclosed in Patent Document 1, it is difficult to eliminate the unevenness in the scale thickness of the hot-rolled steel sheet, and as a result, uneven gloss occurs due to the unevenness in the cold-rolled steel sheet. There is.

  An object of one embodiment of the present invention is to realize a stainless cold-rolled steel sheet having excellent surface appearance.

  In order to solve the above problems, a stainless hot-rolled steel sheet according to an aspect of the present invention is a stainless hot-rolled steel sheet having a scale on its surface, and the average thickness of the scale is 5.0 μm to 8.0 μm. And the standard deviation of the thickness of the scale is 2.0 or less.

  According to one embodiment of the present invention, a stainless cold-rolled steel sheet having excellent surface appearance can be realized.

It is a flowchart which shows an example of the manufacturing method of the ferritic stainless steel cold-rolled steel plate in one Embodiment of this invention. It is a flowchart which shows an example of the hot rolling process in the said manufacturing method. It is a figure for demonstrating the said hot rolling process. (A) is the schematic diagram of the cross section of the ferritic stainless steel hot-rolled steel plate obtained after the hot rolling process in one Example of this invention, (b) is the hot rolling process in one comparative example of this invention. It is a schematic diagram of the cross section of the ferritic stainless steel hot-rolled steel plate obtained later. (A) is a photograph showing the surface appearance of a ferritic stainless steel hot-rolled steel sheet obtained after the hot rolling step in one embodiment of the present invention, and (b) is a hot rolling in one comparative example of the present invention. It is a photograph which shows the surface external appearance of the ferritic stainless steel hot-rolled steel plate obtained after the process. It is a graph which shows the thickness of the scale in the surface of the ferritic stainless steel hot rolled sheet steel of one Example and comparative example of this invention. (A) is a photograph showing the surface appearance of a ferritic stainless steel cold-rolled steel sheet in one example of the present invention, and (b) is after the finishing step of the ferritic stainless steel cold-rolled steel sheet in one comparative example of the present invention. It is a photograph showing the surface appearance.

  Embodiments of the present invention are described in detail below. In the present specification, “A to B” means “A or more and B or less”. Further, various physical properties listed in the present specification mean values measured by the methods described in Examples described later unless otherwise specified. Further, in this specification, unless otherwise specified, “%” used to indicate the composition means “% by mass”. Further, in the present specification, “slab” means a slab obtained by casting and a state during rough rolling in the hot rolling process, and “hot rolled steel sheet” means during finish rolling in the hot rolling process and The state after finish rolling is meant, and the “cold rolled steel sheet” means a state where the hot rolled steel sheet is subjected to annealing, pickling and cold rolling.

<Hot rolled steel sheet>
The hot-rolled steel sheet in one embodiment of the present invention is a ferritic stainless steel hot-rolled steel sheet, and has a scale on its surface.

〔scale〕
The scale is a layer existing on the surface of the hot-rolled steel sheet, and mainly contains an oxide of iron or chromium. The scale in one embodiment of the present invention is generated on the surface of the slab in the heating step during the hot rolling step. Thereafter, it remains with a certain thickness on the surface of the hot-rolled steel sheet obtained by the hot-rolling step.

(Requirements for thickness)
In the hot-rolled steel sheet, the average thickness of the scale is 5.0 μm to 8.0 μm. If the average thickness of the scale is too thick, the load in removing the oxidized scale in the subsequent pickling process increases. Alternatively, if the average thickness of the scale is too thick, it becomes difficult to remove the oxidized scale in the subsequent pickling step. If the average thickness of the scale is too thin, for example, in the rolling process during the hot rolling process, the lubricity between the roll and the slab may be reduced and wrinkles may be generated on the surface of the slab. From the viewpoint of suppressing an increase in the load of removing oxide scale in the pickling step and suppressing the remaining oxide scale, the average thickness of the scale is preferably 8.0 μm or less, and more preferably 7.5 μm or less. Further, from the viewpoint of suppressing generation of wrinkles on the surface of the slab, the average thickness of the scale is preferably 5.0 μm or more, and more preferably 5.5 μm or more.

  In the hot-rolled steel sheet, the standard deviation of the scale thickness is 2.0 or less. If the standard deviation is too large, unevenness of the thickness of the scale is a factor, and uneven glossiness occurs in the cold-rolled steel sheet. The standard deviation is preferably 2.0 or less, and more preferably 1.8 or less, from the viewpoint of suppressing the occurrence of uneven gloss and enhancing the uniformity of the appearance of the surface of the cold-rolled steel sheet.

(Influence of scale)
When the hot-rolled steel sheet with excessively and unevenly attached scale is subjected to a cold rolling process, unevenness of the scale causes surface irregularities in the cold-rolled steel sheet. This unevenness is considered to be a factor of appearance unevenness (finishing unevenness) on the surface of the cold-rolled steel sheet.

(Adjustment method)
The average thickness and standard deviation of the scale can be adjusted by adjusting the number of rollings in the hot slab rolling process (the number of rough rolling processes), the number of scale removing processes, and the timing thereof.

(Measuring method)
The average thickness and standard deviation of the scale can be obtained from the measurement result of the thickness of the scale. The thickness of the scale can be measured from a hot-rolled steel sheet that has been subjected to a hot rolling process in which the scale state is substantially determined.

〔Stainless steel〕
The cold-rolled steel sheet produced from the hot-rolled steel sheet has a good appearance in which unevenness in appearance such as unevenness in gloss is suppressed. For applications that require a good appearance, such as household electrical appliances and kitchen appliances, inexpensive ferritic ferritic stainless steels are preferred and can be suitably used.

[Component composition of ferritic stainless steel]
What is necessary is just to have a well-known metal composition as a ferritic stainless steel. For example, the ferritic stainless steel contains iron as a main component, and contains carbon (C) of 0.120% by mass or less, silicon (Si) of 1.00% by mass or less, manganese (1.20% by mass or less). Mn), 0.040 mass% or less phosphorus (P), 0.030 mass% or less sulfur (S), 0.60 mass% or less nickel (Ni), 16.00 mass% to 18.00 mass% The chromium (Cr) may be included, and the A value may be in the range of 20 to 60.

(carbon)
If the content of carbon in the ferritic stainless steel is too large, the workability and toughness of the ferritic stainless steel may be lowered, and if too small, the toughness of the slab of the ferritic stainless steel may be lowered. The content is preferably 0.010% by mass or more, and more preferably 0.030% by mass or more from the viewpoint of manufacturability of slabs of ferritic stainless steel. The content is preferably 0.120% by mass or less, and more preferably 0.100% by mass or less, from the viewpoint of suppressing the deterioration of workability and toughness of the ferritic stainless steel.

(Silicon)
If the silicon content in the ferritic stainless steel is too large, the ferritic stainless steel may be cured, and if it is too small, the oxidation resistance may be inferior. The content is preferably 0.20% by mass or more, and more preferably 0.35% by mass or more from the viewpoint of obtaining oxidation resistance. In addition, the content is preferably 1.00% by mass or less, and more preferably 0.75% by mass or less, from the viewpoint of suppressing the hardening of the ferritic stainless steel.

(manganese)
If the manganese content in the ferritic stainless steel is too large, the toughness of the ferritic stainless steel cold-rolled steel sheet may be lowered, and if it is too small, the toughness of the slab of the ferritic stainless steel may be lowered. The content is preferably 0.10% by mass or more, and more preferably 0.20% by mass or more, from the viewpoint of suppressing a decrease in toughness in the slab. Further, the content is preferably 1.20% by mass or less, and more preferably 1.00% by mass or less, from the viewpoint of suppressing a decrease in toughness of the ferritic stainless steel.

(Rin)
If the content of phosphorus in the ferritic stainless steel is too large, the hot workability and toughness of the ferritic stainless steel may be reduced. The content is preferably 0.040% by mass or less and more preferably 0.035% by mass or less from the viewpoint of suppressing the hot workability and toughness of the ferritic stainless steel.

(sulfur)
If the content of sulfur in the ferritic stainless steel is too large, it may react with manganese or the like to generate inclusions that are the starting point of corrosion. The content is preferably 0.030% by mass or less and more preferably 0.015% by mass or less from the viewpoint of suppressing the formation of inclusions.

(nickel)
If the content of nickel in the ferritic stainless steel is too large, the ferritic stainless steel may become hard and cause ductility to decrease, and if it is too small, the corrosion resistance is poor. The content is preferably 0.10% by mass or more, and more preferably 0.20% by mass or more from the viewpoint of obtaining corrosion resistance. Further, the content is preferably 0.60% by mass or less, and more preferably 0.50% by mass or less, from the viewpoint of suppressing a decrease in ductility of the ferritic stainless steel.

(chromium)
If the chromium content in the ferritic stainless steel is too large, the ferritic stainless steel may become hard and cause the ductility to deteriorate, and if it is too small, the corrosion resistance is poor. From the viewpoint of obtaining corrosion resistance, the content is preferably 16.00% by mass or more. The content is preferably 18.00% by mass or less, and more preferably 17.50% by mass or less from the viewpoint of suppressing a decrease in ductility of the ferritic stainless steel.

(A value)
The A value of ferritic stainless steel is determined by the following equation (1). In addition, the value of the mass% which is content of each component in ferritic stainless steel is substituted for C, Si, Mn, Ni, Cr, Mo, Cu, and N on the right side.
A = 420C-11.5Si + 7Mn + 23Ni-11.5Cr-12Mo + 9Cu + 470N + 189 (1)

  If the A value obtained by the formula (1) is too large, it becomes hard after hot rolling and the handling load of the hot-rolled steel sheet increases, and if it is too small, the toughness of the slab decreases and the handling load increases. The A value obtained from the above formula (1) is preferably 20 to 60 from the viewpoint of considering the manufacturability of ferritic stainless steel.

(Inevitable impurities)
The ferritic stainless steel may further contain inevitable impurities. Inevitable impurities are components other than the inorganic components described above, and are unintended inorganic components to be mixed. Examples of inevitable impurities include molybdenum (Mo), copper (Cu), and nitrogen (N). The content of inevitable impurities may be in a range in which the effect of the present embodiment can be obtained. For example, the total amount may be 0.30% by mass or less.

[Method for producing hot-rolled steel sheet]
The said hot-rolled steel plate can be manufactured using the well-known method of manufacturing a hot-rolled steel plate except including the process of implement | achieving the specific matter of the thickness of the scale mentioned above.

  The average thickness and standard deviation of the scale described above can be measured by measuring the hot-rolled steel sheet before the cold rolling process described above. Further, the average thickness and standard deviation of the scale can be appropriately adjusted depending on, for example, the number of rollings in the hot rolling process, the number of scale removing processes, and the timing thereof. Therefore, design the hot rolling process while considering other desired conditions such as the thickness of the hot rolled steel sheet, and checking the measurement results of the hot rolled steel sheet before the cold rolling process as necessary. By doing so, it is possible to manufacture a hot-rolled steel sheet having the aforementioned average thickness and standard deviation of the scale.

  FIG. 1 is a flowchart showing an example of a method for manufacturing a cold-rolled steel sheet in the present embodiment. As shown in FIG. 1, the manufacturing method includes a casting process (step S1), a hot rolling process (step S2), an annealing process (step S3), a pickling process (step S4), and a cold rolling process (step S5). ), An annealing / pickling process (step S6) and a finishing process (step S7). FIG. 2 is a flowchart showing an example of a hot rolling process in the present embodiment. As shown in FIG. 2, a heating process (step S11), a scale removal process (step S12), a rough rolling process (step S13), a finishing process (step S14), and a winding process (step S15) may be included. FIG. 3 is a schematic view showing an example of a hot rolling process in the present embodiment.

[Casting process]
The casting process is a process for manufacturing a slab. The casting process can be performed by a known method. For example, there is a method of obtaining a slab by cutting an ingot produced by continuously conveying and cooling molten steel by a continuous casting method to a desired length.

[Hot rolling process]
As shown in FIGS. 2 and 3, the hot rolling process includes a heating process (S11), a scale removing process (S12), a rough rolling process (S13), a finish rolling process (S14), and a winding process (S15). It is the process of giving the process which contains to the said slab.

(Heating process)
The heating step is a step of heating the slab for rolling. In the heating step, a heating furnace 1 having a heating zone for heating the slab after casting to a predetermined temperature and a soaking zone for soaking the slab heated in the heating zone to a predetermined temperature is used. A known apparatus can be used for the heating furnace 1.

(Scale removal process)
A scale removal process is a process of removing the scale adhering to the surface of a slab during hot rolling. The scale removal step can be applied to the slab any number of times at any timing from the end of the heating step to the end of the rough rolling step. In the manufacturing method, the scale removal step is performed from the viewpoint of appropriately controlling the scale distribution and thickness on the surface of the slab. The scale removal step can be performed by a normal method as the scale removal step, and is, for example, a step of injecting high-pressure water onto the surface of the slab. In the scale removing step, the scale can be removed using a plurality of scale removing devices 2a to 2d and 3a to 3d shown in FIG. In FIG. 3, the example using the multi-stage rolling mill provided with the roller which can rotate bidirectionally as the rough rolling mills 4 and 5 is shown.

(Rough rolling process)
The rough rolling step is a step of performing rough rolling a plurality of times on the slab heated by the heating step, and a known method can be used. The rough rolling process means a single process in which a high-temperature slab is pressed in the thickness direction while moving from one side to the other. The number of rough rolling treatments can be determined according to the desired thickness of the hot-rolled steel sheet, and is usually appropriately selected from 3, 5 and 7 times. In the rough rolling treatment, rolling is performed by the rough rolling mills 4 and 5, and a known apparatus can be used.

  When the rough rolling treatment is performed a plurality of times, the slab subjected to the heat treatment can be rolled using a plurality of rough rolling mills and rolled to a desired thickness. Such multiple times of rough rolling may be performed by reciprocating the heat-treated slab to the multi-stage rough rolling mill a plurality of times. Furthermore, a plurality of the above multi-stage rough rolling mills can be used. By such rough rolling and scale removal, the scale thickness on the slab surface is uniformly reduced. From the viewpoint of limiting the length of the slab in the stretching direction and the length of the width in the slab stretching direction and preventing the deflection of the slab during rolling, the above multi-stage rolling mill in the hot rolling process Is preferably used.

(Other processes)
The hot rolling process of the slab may further include processes other than the heating process, the scale removing process, and the rough rolling process described above as long as the effect of the present embodiment is obtained. It is possible to employ | adopt the well-known process in the well-known manufacturing method including the continuous casting of a slab for these other processes. Examples of other processes include a finish rolling process in which finish rolling is performed on the slab that has undergone the rough rolling process, and a winding process in which the hot-rolled steel sheet that has undergone the finish rolling process is wound.

<Cold rolled steel sheet>
The cold-rolled steel sheet in one embodiment of the present invention is manufactured by cold rolling, annealing / pickling and temper rolling on a hot-rolled steel sheet. The temper rolling is performed on the cold-rolled steel sheet in the finishing process. The cold-rolled steel sheet according to the present embodiment uses a hot-rolled steel sheet having a scale thickness substantially sufficiently thin and substantially uniform according to the present embodiment, and thus exhibits a uniform appearance without unevenness. Such an excellent surface appearance of the cold-rolled steel sheet can be sufficiently confirmed by visual observation, but can be expressed by measurement of the following physical properties.

[Surface appearance of cold-rolled steel sheet]
The whiteness of the cold-rolled steel sheet is 20.0 or less. When the whiteness is within this range, it can be said that the steel sheet is a cold-rolled steel sheet that does not substantially include a dark portion in finishing unevenness. The whiteness can be measured by a known method for measuring the whiteness of a cold-rolled steel sheet. For example, the whiteness can be measured by REFECTOMETER (TC-6D) manufactured by Tokyo Denshoku.

  The glossiness at 60 ° of the cold-rolled steel sheet is 430 or more. When the glossiness is within this range, it can be said that the steel sheet is a cold-rolled steel sheet that does not substantially include a dark part in finishing unevenness. The glossiness can be measured by a known method for measuring the 60 ° glossiness of a cold-rolled steel sheet. For example, the glossiness can be measured by HANDY GLOSSMETER (PG-1M) manufactured by Nippon Denshoku Industries Co., Ltd.

  The surface average roughness (Ra) of the cold-rolled steel sheet is 0.100 or less. If the surface average roughness is within this range, it can be said that the scale thickness in the hot-rolled steel sheet was sufficiently uniformly controlled. The surface average roughness (Ra) of the cold-rolled steel sheet can be measured by a known method for measuring the surface roughness of the cold-rolled steel sheet. For example, the surface average roughness (Ra) of the cold-rolled steel sheet can be measured by SURFCOM 2900DX manufactured by Tokyo Seimitsu Co., Ltd.

  From the viewpoint of enhancing the uniformity of the appearance of the cold-rolled steel sheet, it is preferable that the physical properties have small variations in the cold-rolled steel sheet. For example, the difference between the maximum value and the minimum value of the whiteness is preferably 1.0 or less from the above viewpoint. Moreover, it is preferable from said viewpoint that the difference of the maximum value of the said glossiness and the minimum value is 20 or less. Furthermore, the difference between the maximum value and the minimum value of the surface average roughness (Ra) of the cold-rolled steel sheet is preferably 0.020 or less from the above viewpoint.

[Method for producing cold-rolled steel sheet]
The said cold-rolled steel plate can be manufactured by the normal method which manufactures a cold-rolled steel plate from a hot-rolled steel plate except using the hot-rolled steel plate mentioned above. More specifically, the cold-rolled steel sheet is produced by subjecting the hot-rolled steel sheet to cold rolling. The manufacturing method of the cold-rolled steel sheet may further include various known processes other than the cold rolling process. For example, the said manufacturing method may include one or both of an annealing process and a pickling process, before giving a cold rolling process to a hot-rolled steel plate. Moreover, the manufacturing method may include one or both of an annealing / pickling process and a finishing process after the cold rolling process.

<Summary>
The hot-rolled steel sheet according to the first aspect of the present invention is a stainless-steel hot-rolled steel sheet having a scale on its surface, the average thickness of the scale being 5.0 μm to 8.0 μm, and The standard deviation of thickness is 2.0 or less. Therefore, according to the said structure, the cold-rolled steel plate of stainless steel excellent in the surface external appearance can be implement | achieved.

  The hot-rolled steel sheet in the second aspect of the present invention may be a hot-rolled steel sheet of ferritic stainless steel in the first aspect. According to the said structure, it is suitable for the application to the use which requires the outstanding surface appearance.

  The hot rolled steel sheet according to the third aspect of the present invention is the same as the second aspect, except that C: 0.120% by mass or less, Si: 1.00% by mass or less, Mn: 1.20% by mass or less, P: 0. 0.040% by mass or less, S: 0.030% by mass or less, Ni: 0.60% by mass or less, Cr: 16.00% by mass to 18.00% by mass, the balance including Fe and inevitable impurities, The A value calculated | required by above-mentioned Formula (1) may be the range of 20-60. According to the said structure, it is much more effective from a viewpoint of application to the use which requires the outstanding surface appearance.

  The cold-rolled steel sheet according to the fourth aspect of the present invention is a cold-rolled steel sheet produced by cold rolling at least one of the hot-rolled steel sheets according to the first to third aspects. According to the said structure, the cold-rolled steel plate of stainless steel excellent in the surface external appearance is realizable.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

〔Example〕
The materials shown in Table 1 below were dissolved. In Table 1, the numerical value represents mass%, and the balance is iron. The obtained molten steel was cast, cooled, and cut to a predetermined length to produce a ferritic stainless steel slab (cast slab 1) of Example 1.

  Next, the cast slab 1 was subjected to a hot rolling process under the conditions shown in the examples of Table 2. More specifically, after performing heat treatment under the conditions shown in Table 2, five rough rolling treatments were performed. Further, an appropriate number of scale removal treatments were performed at an appropriate timing after the heating step and during the rough rolling step. Thus, a hot-rolled steel sheet for cold rolling was obtained. The thickness of the scale of the hot-rolled steel sheet was measured by the following method, and the average thickness of the scale and the standard deviation of the thickness of the scale were determined from the obtained measurement results. As a result, the average thickness of the scale of the hot-rolled steel sheet is 6.9 μm at the scale portion that appears black in FIG. 5A, and 6.7 μm at the scale portion that appears white, and the standard deviation of the scale thickness appears black. It was 1.8 at the spot and 1.6 at the scale spot that appeared white.

[Measurement of scale thickness in hot-rolled steel sheet]
A hot-rolled steel plate having a length of 300 mm was collected from the hot-rolled steel plate after hot rolling, and a cut piece having a width of 25 mm and a length of 10 mm was produced from the black-scaled scale portion and the white-scaled scale portion of the hot-rolled steel plate. . The produced cut piece was embedded in a resin lump, and the cut surface of the test piece was subjected to buff polishing from rough polishing with emery paper to make the cut surface a mirror surface. The cross section of the hot-rolled steel sheet in the mirror surface of the test piece was observed with an optical microscope (manufactured by OLYMPUS / GX71), and the scale thickness of 10 mm length per piece was measured with ten pieces. Then, the measured values were averaged to determine the average thickness (Tm) of the scale thickness, and the standard deviation (Sd) of the scale thickness was determined from the measured values.

  The hot-rolled steel sheet was subjected to annealing treatment, pickling treatment, cold rolling treatment, annealing / pickling treatment, and finishing treatment to produce a ferritic stainless steel cold-rolled steel plate of the example.

[Comparative example]
Cold-rolled steel sheets of ferritic stainless steel were produced in the same manner as in the Examples except that the hot rolling treatment was performed under the conditions shown in Comparative Examples in Table 2. The average thickness of the scale in the hot-rolled steel sheet obtained in the hot rolling process of this comparative example is 8.9 μm at the scale portion that appears black in FIG. 5B, and 5.0 μm at the scale portion that appears white. The standard deviation of the thickness was 2.3 at the black scale and 1.9 at the white scale.

  FIG. 4A schematically shows the cross-sectional state of the hot-rolled steel sheet of the example, and FIG. 5A shows a photograph showing the surface state. FIG. 4B schematically shows the cross-sectional state of the hot-rolled steel sheet of the comparative example, and FIG. 5B shows a photograph showing the surface state. Furthermore, the result of having measured the thickness of the scale in the hot-rolled steel plate of an Example and a comparative example is shown in FIG.

[Evaluation]
The cold rolled steel sheets of Examples and Comparative Examples were evaluated by the following methods.

  The white square represents the thickness of the scale that appears relatively bright in the photograph of FIG. 5, and the black square in FIG. 6 represents the thickness of the scale that appears relatively black in the photograph of FIG. .

[Surface appearance of cold-rolled steel sheet]
(1) Whiteness of cold-rolled steel sheet The whiteness of the surface of the cold-rolled steel sheet was measured for the cold-rolled steel sheets of Examples and Comparative Examples. Specifically, at any 11 points at 100 mm intervals on the surface of the cold-rolled steel sheet, REFECTOMETER (TC-6D) manufactured by Tokyo Denshoku Co., Ltd. is used as a measuring device and cold-rolled based on the conditions of JIS Z 8715. The whiteness of the surface of the steel sheet was measured. And the average value of the obtained measured value was made into the whiteness (W) of the cold-rolled steel plate. Further, the difference (ΔW) between the maximum value and the minimum value of the measured whiteness was determined.

(2) Glossiness of cold-rolled steel sheet The 60-degree glossiness of the surface of the cold-rolled steel sheet was measured for the cold-rolled steel sheets of Examples and Comparative Examples. Specifically, at any 11 points at 100 mm intervals on the surface of the cold-rolled steel sheet, Nippon Denshoku Industries Co., Ltd., HANDY GLOSSSMETER (PG-1M) is used as a measuring device, based on the conditions of JIS Z 8741. The surface gloss of the cold rolled steel sheet was measured. And the average value of the obtained measured value was made into the glossiness (G) of the cold-rolled steel plate. Further, the difference (ΔG) between the maximum value and the minimum value of the measured glossiness value was obtained.

[Surface condition of cold-rolled steel sheet]
About the cold-rolled steel plate of the Example and the comparative example, the surface shape of the cold-rolled steel plate was measured. Specifically, at any 11 points at 100 mm intervals on the surface of the cold-rolled steel sheet, SURFCOM 2900DX manufactured by Tokyo Seimitsu Co., Ltd. is used as a measuring device, and the surface average roughness of the cold-rolled steel sheet is based on the conditions of JIS B 0601. The thickness (Ra) was measured. And the average value of the obtained measured value was made into the average roughness of the cold-rolled steel plate.

  Table 3 shows the average thickness (μm), standard deviation, and surface properties of the cold-rolled steel sheet in the examples and comparative examples. Moreover, the photograph which shows the surface state in the cold rolled steel sheet of an Example is shown to (a) of FIG. 7, and the photograph which shows the surface state in the cold rolled steel sheet of a comparative example is shown in (b) of FIG. 7, respectively.

[Discussion]
As shown to (a) of FIG. 5, compared with the hot rolled steel sheet of the ferritic stainless steel of a comparative example, it was confirmed that the nonuniformity is clearly small in the hot rolled steel sheet of the ferritic stainless steel of an Example. . In addition, as shown in FIG. 6, in the ferritic stainless steel hot-rolled steel sheet of the example, the thickness of the scale at the portion that appears black (shown by a black square in FIG. 6) and the scale at the portion that appears white There was almost no difference from the thickness (indicated by a white square in FIG. 6).

  On the other hand, as shown in FIG. 5 (b), in the hot rolled steel sheet of the ferritic stainless steel of the comparative example, unevenness (a part that looks black and a part that looks white) was confirmed on the surface. Moreover, as shown in FIG. 6, in the hot rolled steel sheet of the ferritic stainless steel of the comparative example, the thickness of the scale at the portion that looks black (shown by a black circle in FIG. 6) and the scale at the portion that looks white The difference from the thickness (indicated by white circles in FIG. 6) was large.

  In addition, as is apparent from FIG. 7A, the cold-rolled steel sheet of the example was confirmed to have a sufficiently good surface appearance without confirming irregular bright and dark striped patterns that would cause uneven finishing. It was. Moreover, it was confirmed that the whiteness and glossiness of the cold-rolled steel sheets of the examples are generally within preferable ranges, and the surface average roughness (Ra) is sufficiently small.

  On the other hand, as is apparent from FIG. 7B, the comparative cold-rolled steel sheet was sufficiently visually confirmed to have irregular stripe patterns of light and dark due to finishing unevenness. Moreover, as shown in FIG. 7B, the cold rolled steel sheet of the comparative example had a low average value of whiteness and a wider range of variation. Further, the cold rolled steel sheet of the comparative example had a low average gloss value and a wider range of variation. Furthermore, the cold rolled steel sheet of the comparative example also had a larger surface average roughness (Ra).

DESCRIPTION OF SYMBOLS 1 Heating furnace 2a, 2b, 2c, 2d, 3a, 3b, 3c, 3d Scale removal apparatus 4, 5 Coarse rolling mill 6, 7, 8 Slab 9, 10 Hot rolled steel plate

Claims (4)

A stainless hot-rolled steel sheet having a scale on its surface,
An average thickness of the scale is 5.0 to 8.0 μm, and a standard deviation of the thickness of the scale is 2.0 or less.   The stainless hot-rolled steel plate according to claim 1, wherein the hot-rolled steel plate is a ferritic stainless steel hot-rolled steel plate. The ferritic stainless steel is C: 0.120 mass% or less, Si: 1.00 mass% or less, Mn: 1.20 mass% or less, P: 0.040 mass% or less, S: 0.030 mass% Hereinafter, Ni: 0.60% by mass or less, Cr: 16.00% by mass to 18.00% by mass, the balance including Fe and unavoidable impurities, A value obtained by the following formula (1) The range is from 20 to 60. The stainless hot-rolled steel sheet according to claim 2, wherein:
A = 420C-11.5Si + 7Mn + 23Ni-11.5Cr-12Mo + 9Cu + 470N + 189 Formula (1)
(C, Si, Mn, Ni, Cr, Mo, Cu, and N represent mass% values that are the contents of the respective components in the ferritic stainless steel).   A stainless cold-rolled steel sheet produced by cold rolling the stainless hot-rolled steel sheet according to any one of claims 1 to 3.