JP2003041352A - Hot-rolled stainless steel sheet and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot-rolled steel sheet of a raw material to be cold rolled, for obtaining a stainless steel sheet superior in luster, and a manufacturing method there for. SOLUTION: The hot-rolled stainless steel sheet for cold rolling is characterized by having an average tilt angle θa of 6 degree or greater, which is defined by the expression (1), in a surface roughness curve: θa =Σ tan<-1> (ΔYi /ΔX)}/n...(1), where Σis the sum from i equals one to n, ΔYi indicates, when the roughness curve is equally divided into n pieces of lines along a standard length L, a difference between a vertical distance from a point of intersection of the dividing line with the roughness curve to the surface of the steel sheet and the distance from the adjacent point, and ΔX indicates L/n (normally, ΔX is 2-5 μm). The method for manufacturing the above hot-rolled stainless steel sheet is characterized by jointly using a shot blast if needed, in a pickling treatment process, without using a polishing brush between pickling tanks. A ferritic stainless steel sheet which requires higher luster, is characterized by making the maximum surface roughness Ry to be 8 μm or more, in addition to the above property. The manufacturing method is characterized by making a weight loss in pickling to be 7.5 g/m<2> or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolled steel sheet used for producing a cold rolled stainless steel sheet and a method for producing the hot rolled steel sheet.

[0002]

2. Description of the Related Art Stainless steel sheets have excellent corrosion resistance, and the glossy surface produced in a factory is often used as it is as the surface of the final product. Therefore, in manufacturing a steel sheet, various manufacturing methods have been improved in order to obtain a product having excellent gloss and no uneven gloss.

The production of ordinary cold rolled stainless steel sheet is
The hot-rolled material is annealed / pickled, cold-rolled, annealed and temper-rolled. Annealing after cold rolling is carried out to control the mechanical properties of the steel sheet.In the case of bright annealing, most of them are temper-rolled as they are, but when they are performed in the air, the oxide film becomes thicker, so pickling is necessary. After removing it, temper rolling is performed. The shiny surface of a stainless steel sheet is obtained mainly by the transfer of the surface of a rolling roll in the final stage of cold rolling or in temper rolling. Therefore, regarding the surface of the rolls or the rolling conditions in these rollings, sufficient control is performed to obtain the surface gloss of the steel sheet.

However, even if the rolling conditions and the surface of the rolling rolls are sufficiently controlled in the cold rolling stage, the product surface after the cold rolling may have uneven luster stretched in the rolling direction or a better luster. In some cases, good gloss may not be obtained in the ferritic stainless steel sheet that is required.

It is thought that the cause is that the surface condition before rolling, for example, the effect of surface oxidation in hot rolling and subsequent annealing treatment remains, and the surface is removed by performing a coil grinder. Most can be improved by scraping. However, the grinding of the surface by the coil grinder has a slow processing speed to be carried out to a sufficiently effective state, and further, the yield of the steel is lowered and the cost is greatly increased.

Various proposals have been made as countermeasures against adverse effects on surface gloss due to factors other than rolling factors such as roll surface roughness and rolling lubrication.
For example, in Japanese Unexamined Patent Publication No. 5-317908, it is assumed that the presence of a SiO ₂ layer existing on the surface of a steel sheet before temper rolling causes uneven gloss, and by removing this SiO ₂ layer, a stainless steel sheet having a uniform gloss The invention of the manufacturing method is disclosed.
JP-A-2000-328142 discloses, austenitic, martensitic or duplex stainless steel stainless steel, the winding temperature of hot rolling, the highest temperature reached in the annealing step,
An invention of a manufacturing method is disclosed in which the soaking time and the heating / cooling rate are regulated, respectively, and the nitric acid concentration and the hydrofluoric acid concentration in the pickling step are limited to reduce uneven gloss. Further, the method of the invention disclosed in Japanese Patent Laid-Open No. 7-32004 as a method for producing a ferritic stainless steel sheet having an excellent gloss has a total content of C and N of 0.10% by mass,
Then, cold rolling is performed with a rolling roll having a reduced surface roughness.

However, the above-mentioned improvements lead to an increase in manufacturing costs such as an increase in the number of processes and strengthening of control, and even when these improvements are carried out, a stainless steel sheet having excellent luster cannot be obtained sufficiently stably. Sometimes.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a hot-rolled steel sheet which is a raw material for obtaining a cold-rolled stainless steel sheet having no uneven gloss and excellent surface gloss, and a method for producing the same.

[0009]

Means for Solving the Problems The present inventors initially conducted various studies for the purpose of obtaining stable and excellent surface gloss on a ferritic stainless steel sheet by cold rolling. The ferritic stainless steel sheet is required to have more uses requiring more luster than the austenitic and martensitic stainless steel sheets, and is required to be manufactured at a lower cost.

In order to improve the surface gloss as much as possible, the surface roughness of the rolling rolls, the pass schedule, the use of lubrication and the like were controlled and various investigations were conducted. Even under similar rolling conditions, hot rolling before cold rolling was performed. The difference in gloss may appear depending on the steel plate. Therefore, products having good surface gloss after cold rolling and products having poor surface gloss were selected, and the surface of the hot rolled steel sheet was investigated for them.

As a result, when the surface of the product has a particularly high gloss, the surface of the hot-rolled steel sheet before cold rolling has uniform irregularities with a size of about 10 μm, whereas the product with a slightly inferior gloss. The surface of the hot-rolled steel sheet when it becomes the surface consists of concave portions and flat portions, and the size or average diameter of the concave portions is 20 to 30 μm.
It was about m, and the recess occupied about 40% of the surface.

[0012] Regarding the product after cold rolling having inferior surface gloss, when the surface was further enlarged and examined in detail, it was found that an oil pit was formed because the rolling oil used for lubrication in cold rolling was confined. The so-called concave defect and the defect called collapse due to material inflow from the convex portion to the concave portion occurred. On the other hand, on the surface of the steel sheet with excellent gloss,
Almost no such defects are recognized.

From the above results, if there is a large concave portion surrounded by the smooth portion on the surface before cold rolling, the rolling oil is easily confined during the cold rolling, and the concave portion is surrounded by the smooth portion around the rolling oil. It was presumed that the material flow-in increased and oil pits and collapses occurred, resulting in poor gloss. When the number of smooth parts is small and the pitch of the irregularities is not large, it is considered that the lubricating oil easily flows out and the collapse is small.

As a result of studying a more quantitative display method for the surface state of the hot rolled steel sheet before cold rolling which affects the surface gloss of this product, the surface roughness was measured parallel to the rolling direction and the maximum surface roughness was measured. It has been found that the regulation may be performed by R _y and the average inclination angle θ _a of the profile of the roughness measurement curve.

As shown in FIG. 1, the inclination angle θ of the roughness curve is obtained by drawing a line B perpendicular to the steel plate surface at an interval ΔX with respect to the reference length direction of the roughness curve A, and a line perpendicular to the curve A separated by ΔX. The difference ΔY in the vertical distance between the two intersections with B is obtained by the following formula.

[0016]

[Equation 1]

The average inclination angle θ _a is obtained by repeatedly measuring θ along the direction of the reference length L as shown in the following equation and averaging the measured values.

[0018]

[Equation 2]

Here, ΔY _i : When the roughness curve is divided into n equal parts along the reference length L, the difference ΔX in the vertical distance between the intersection of the dividing line and the roughness curve at the two adjacent points to the steel plate surface. : L / n (where ΔX is 2 to 5 μm).

When the average inclination angle θ _a of the roughness curve of the surface roughness of the hot-rolled steel sheet shows a small value, the area of the smooth portion increases, the oil pits increase after cold rolling, and the collapse further increases. There is a tendency. If the maximum surface roughness R _y is also small, it is considered that there is a similar tendency. Then, as a result of examining the manufacturing conditions for obtaining the hot rolled steel sheet having _a large θ _a and _a large R _y as a cold-rolled material, the following has been revealed.

That is, the conventional use of a grinding brush between pickling tanks for the purpose of sufficient removal of an oxide film, or the execution of coil grinding after pickling increases the flat part of the surface and recesses. Is not preferable because it increases the size. On the other hand, by not performing grinding brush or coil grinding, and then controlling the pickling by the pickling reduction amount and increasing it more than usual, θ _a of the hot-rolled steel sheet is increased and R _y is also increased. growing.

As described above, regarding the ferritic stainless steel sheet, a hot rolled steel sheet as a rolling material for obtaining a cold rolled steel sheet with excellent gloss and a manufacturing method thereof have been clarified. It was found that the steel sheet not only has improved surface gloss after cold rolling, but also has uneven gloss.

Austenitic or martensitic stainless steel sheets are not required to have glossiness as much as ferritic stainless steel sheets, but generally uneven glossiness is likely to occur. Therefore, these steel sheets are pickled by the above-mentioned method in which a grinding brush between pickling tanks is not used in the pickling process, and the average inclination angle of the profile of the roughness measurement curve shown by the formula. Cold rolling was performed so that θ _a was increased. As a result, it was revealed that even these steel sheets were extremely effective in eliminating uneven gloss. It is considered that this is because the area of the smooth portion is decreased by the increase of the average inclination angle θ _{a and the} partial difference is eliminated by the decrease of the oil pits and the uneven gloss is eliminated.

That is, not only ferritic but also austenitic or martensitic stainless steels are prepared by setting the surface roughness of the hot-rolled steel sheet as a raw material in such _a state that θ _a shown by the formula is large. It is possible to obtain a cold-rolled stainless steel plate having no unevenness.

Further, when the grinding brush between the pickling tanks is not used, the target θ _a can be obtained even if shot blasting is also used to assist the scale removal on the surface.

Based on the results of the above examination, the present invention was completed by further clarifying the limiting conditions and the like. The gist of the present invention is as follows.

(1) A hot-rolled stainless steel sheet for cold rolling, which has a surface roughness such that the average inclination angle θ _a of the roughness curve represented by the above equation is 6 ° or more.

(2) The method for producing a cold rolled stainless steel hot rolled steel sheet according to the above (1), wherein a grinding brush between pickling tanks is not used in the pickling process.

(3) In the pickling treatment step, shot blasting is applied as an aid to descaling, and the grinding brush between the pickling tanks is not used, and the stainless steel hot rolling for cold rolling according to (1) above is used. Steel plate manufacturing method.

(4) Cold rolling characterized in that the maximum surface roughness R _y is 8 μm or more, and the average inclination angle θ _a of the roughness curve represented by the formula is 6 ° or more. Ferritic stainless steel hot rolled steel sheet for use.

(5) In the pickling process, the grinding brush between the pickling tanks is not used, and the pickling loss is 7.5 g / m ² or more, (1) or (4) For manufacturing a ferritic stainless steel hot rolled steel sheet for cold rolling.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION The surface roughness of the hot rolled stainless steel sheet of the present invention is such that the average inclination angle θ _a of the roughness curve expressed by the above equation is 6 ° or more. The type of stainless steel may be any of ferritic, austenitic, and martensitic, and when rolled into a cold-rolled steel sheet, it is possible to obtain an article with excellent gloss without uneven gloss.

Here, it is desirable that the reference length L for obtaining the average inclination angle θ _a is about 1 to 3 mm and ΔX is in the range of 2 to 5 μm. This is because if it deviates from this range, the surface condition of the steel sheet cannot be displayed accurately.

The reason why θ _{a is set} to 6 ° or more is that if it is less than 6 °, uneven gloss after cold rolling is likely to occur and the surface gloss is also deteriorated. However, it is preferable that the average inclination angle θ _a is 20 ° or less at the maximum, and if the average inclination angle θ _a is larger than this, seizure or surface defects are likely to occur.

In the production of the hot rolled steel sheet having the above-mentioned surface roughness state, the grinding brush between the pickling tanks is not used in the process of annealing / pickling after hot rolling, and the coil grinding after pickling is performed. Will not be applied. Such a treatment for abrading the surface of the steel sheet increases the smooth surface of the hot rolled steel sheet and increases the diameter of the recesses, which easily causes defects such as oil pits and collapse during cold rolling. This is because the uneven gloss on the surface is deteriorated.

If no grinding brush is used between the pickling tanks,
When the descaling becomes insufficient or when it is desired to perform the descaling sufficiently, shot blasting may be performed as an auxiliary and then pickling may be performed.

When it is desired to obtain a cold rolled steel sheet of ferritic stainless steel which is particularly excellent in gloss, the maximum surface roughness R _y defined by JIS-B-0601 is 8 μm or more and the roughness expressed by the formula is used. The average inclination angle θ _a of the height curve is 6 ° or more. The reason why R _{y is set} to 8 μm or more is that with a roughness of less than 8 μm, minute defects that are considered to be oil pits are slightly increased in the steel sheet after cold rolling, resulting in poor gloss.
However, R _y of more than 30 μm is unlikely to occur in ordinary pickling, and even if it is obtained, the surface of the roll is likely to be roughened during rolling, resulting in poor gloss.

The pickling of the hot-rolled steel sheet for obtaining such a cold-rolled ferritic stainless steel sheet having a particularly high gloss is not limited to the above-mentioned use of the grinding brush between the pickling tanks and the pickling. The pickling weight loss should be 7.5 g / m ² or more. This is because the maximum surface roughness R _y cannot be 8 μm or more with a pickling weight loss of less than 7.5 g / m ² .
However, excessive pickling loss causes NOX generation and plate thickness reduction, so it is preferable not to exceed 200 g / m ² .

The acid used for pickling is not particularly limited as long as it can be descaled and can achieve the required pickling weight loss, and is not particularly limited, and one or more kinds of sulfuric acid, hydrochloric acid, nitric acid, fluorinated nitric acid and the like can be used. It suffices to carry out the combination with a pickling tank.

Further, even with a steel plate whose average inclination angle θ _a of the roughness curve is less than 6 ° by ordinary pickling, if repickling is performed by such a method without using a grinding brush, θ _a
Can be set to 6 ° or more, and uneven gloss can be suppressed and gloss can be improved.

In order to obtain a cold-rolled steel sheet product having excellent surface gloss using the above hot-rolled steel sheet, the reduction rate per pass is set to 10% or more, and the total reduction rate is set to 50% or more. Desirably, if the production is carried out according to the various conditions after cold rolling for producing a glossy steel sheet that has been conventionally used, a stainless steel cold-rolled steel sheet having even more excellent surface gloss can be obtained.

[0042]

[Examples] [Example 1] SUS304, SUS304L, SUS316 and SUS316L as austenitic stainless steels, SUS420J2 as martensitic stainless steels, and SUS430 as ferritic stainless steels were each hot-rolled into a steel plate with a width of 1 m, and then continuously annealed. After annealing in a pickling facility, pickling was performed. The annealing conditions were the usual conditions generally applied to these steels, and the pickling was the conditions shown in Table 1. Plate thickness at that time,
Table 2 shows the presence or absence of shot blasting and the use of a grinding brush between the pickling tanks.

The surface roughness of the obtained steel plate was investigated by using test pieces taken from the front and rear ends of the steel plate coil. In that case, the roughness curve was measured using a stylus type surface roughness meter, and the maximum surface roughness R _y and the average inclination angle θ _a were obtained from this. The measurement direction of the roughness curve was parallel to the rolling direction, the reference length L was 2 mm, ΔX was 2 μm, and n was 1000. Table 2 shows the average values of the front and rear ends of the steel plate coil.

These hot-rolled steel sheets were cold-rolled by cold-rolling rolls having the same surface finish, temper-rolled at 0.8% after annealing, and evaluated for uneven gloss. The surface roughness of the rolling roll at the final stage of cold rolling was _Ra 0.15 μm, the surface roughness of the rolling roll for temper rolling was 0.02 μm for _Ra , and the rolling reduction of annealing temper rolling was 0.8%. The uneven gloss was evaluated by visual comparison with a reference sample divided into 5 grades, and given a rating of 1 to 5. The higher the score, the better, but practically 2
The above evaluation points are passed. The evaluation points of this uneven gloss are also shown in Table 2.

As is clear from the results shown in Table 2, in the case of hot-rolled steel sheets having an average inclination angle θ _a of the roughness curve of the surface roughness of less than 6 °, the evaluation of uneven gloss is 1 in all cases, and as a product. It can be seen that the unfavorable gloss unevenness occurs. The hot-rolled steel sheets having a gloss unevenness evaluation of 1 were all subjected to a grinding brush between the pickling tanks.

[0046]

[Table 1]

[0047]

[Table 2]

[Example 2] Hot-rolled steel sheets of SUS304, SUS304L, SUS316, and SUS420J subjected to normal pickling using a grinding brush between pickling tanks were pickled under the pickling conditions shown in Table 1. Re-pickling was performed without using the grinding brush in between.

As a result of measuring the surface roughness of the steel sheet before re-pickling, the average inclination angles θ _a of the roughness curves were all below 6 °. These steel sheets were re-pickled, the surface roughness was measured, and cold rolling was performed to investigate uneven gloss. The method for measuring the surface roughness, the conditions for cold rolling, the method for evaluating uneven gloss, and the like are all the same as in Example 1.

The results are shown in Table 3. Even when the average inclination angle θ _a of the roughness curve is less than 6 ° by the ordinary pickling method, the pickling method of the present invention is applied. It can be seen that a hot-rolled steel sheet in which the occurrence of uneven gloss is suppressed after cold rolling is obtained.

[0051]

[Table 3]

Example 3 Hot-rolled thickness 3.0 mm, width 1
A 000 mm ferritic stainless steel strip (SUS430) coil was annealed under the conditions of heating at 950 ° C. for 3 minutes, and pickling was performed by passing through three tanks with the same immersion distance. The first and second tanks are both 200g / L sulfuric acid solution at 80 ° C and the third tank is 50g / L nitric acid + 25g / L hydrofluoric acid mixed acid solution or 100g / L nitric acid solution. The pickling was carried out both with and without a grinding brush between the pickling tanks.
Moreover, the thing which applies a coil grinder after pickling was also added. After pickling, the surface roughness was investigated at the front and rear ends of the coil. The method for measuring the surface roughness is the same as in Example 1.

Table 4 collectively shows the pickling conditions adopted, the presence / absence of the use of the grinding brush between the pickling tanks, and the measurement results of the surface roughness. In addition, the measurement result of the surface roughness is an average value of the front end portion and the rear end portion of the coil.

[0054]

[Table 4]

These hot-rolled steel sheets were cold-rolled to a thickness of 1.0 mm, subjected to recrystallization annealing in a continuous annealing pickling line to remove the surface oxide film, and temper-rolled to obtain product steel sheets. The rolling roll at the final stage of cold rolling, which greatly affects the surface gloss, had a surface roughness _{Ra of} 0.15 μm, and the temper rolling used a roll having _a surface roughness _Ra of 0.02 μm, and the rolling reduction was 0.8%.

The product steel sheet was evaluated for uneven gloss in the same manner as in Example 1, and samples were taken at the rolling front end and the rear end, and magnified by a microscope for the presence of concave marks and collapse. Further, to measure the surface gloss of G _{S (60} °) on the basis of the glossiness measurement of JIS-Z-8741. The results are shown together in Table 4.

As can be seen from the results in Table 4, the hot-rolled steel sheet having the maximum surface roughness R _y and the average inclination angle θa within the ranges defined by the present invention has excellent surface gloss and uneven gloss after cold rolling. It is clear that there is no. The hot-rolled steel sheet is obtained by eliminating the grinding brush between the pickling tanks and picking up the coil grinder during pickling.

[Embodiment 4] Ferrite as in Embodiment 3
Conditions shown in Table 5 after annealing a stainless steel plate (SUS430)
Was pickled. At the front and back of the steel strip
Before and after pickling.
The weight loss of pickling was measured by the cleaning agent, and
And measure the surface roughness curve to determine the maximum surface roughness R_yand
Average tilt angle θ _aI asked. The results are also shown in Table 5.

[0059]

[Table 5]

As is clear from these results, when the pickling weight was set to 7.5 g / m ² or more without using the grinding brush between the pickling tanks and the coil grinder, the maximum surface roughness R _y was A steel sheet having _a thickness of 8 μm or more and an average inclination angle θ _a of 6 ° or more is obtained.

These steel sheets were further cold-rolled in the same manner as in Example 3, and the uneven glossiness and the glossiness were measured. The results are also shown in Table 5.
As shown in Table 1, it can be seen that the product steel sheet after cold rolling obtained from a hot rolled steel sheet having R _y of 8 μm or more and θ _a of 6 ° or more has excellent glossiness with little unevenness in gloss.

[0062]

INDUSTRIAL APPLICABILITY When the hot rolled steel sheet of stainless steel of the present invention is used as a cold rolling material, the obtained steel sheet product has less unevenness in surface gloss and can have an excellent glossiness. The method of the present invention for obtaining such a hot-rolled steel sheet is easy to apply to actual production, and is also effective for rationalizing the production of steel sheet products having excellent surface gloss.

[Brief description of drawings]

FIG. 1 is a diagram illustrating how to determine an average inclination angle θ _a of _a roughness curve.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahiro Takahashi             Sumitomo Metal Industry Co., Ltd.             Ceremony Company Kashima Steel Works (72) Inventor Yuu Chihara             Sumitomo Metal Industry Co., Ltd.             Ceremony Company Kashima Steel Works (72) Inventor Akira Miyakoshi             Sumitomo Metal Industry Co., Ltd.             Ceremony Company Kashima Steel Works (72) Inventor Masataka Sakai             Sumitomo Metal Industry Co., Ltd.             Ceremony Company Kashima Steel Works F term (reference) 4K053 PA03 PA12 QA01 RA16 RA17                       SA06 TA03

Claims (5)

[Claims] 1. A hot-rolled stainless steel sheet for cold rolling, which has a surface roughness such that an average inclination angle θ _a of a roughness curve represented by the following formula is 6 ° or more. Here, ΔY _i : When the roughness curve is equally divided into n along the reference length L, the difference ΔX: L / n in the vertical distance between the intersection of the dividing line and the roughness curve at the two adjacent points to the steel plate surface. (However, ΔX is 2 to 5 μm) 2. The method for producing a hot-rolled stainless steel sheet for cold rolling according to claim 1, wherein a grinding brush between pickling tanks is not used in the pickling step. 3. The hot rolling stainless steel for cold rolling according to claim 1, wherein in the pickling treatment step, shot blasting is performed as an aid to descaling, and a grinding brush between pickling tanks is not used. Steel plate manufacturing method. 4. Cold rolling characterized by having a maximum surface roughness R _y of 8 μm or more and an average inclination angle θ _a of the roughness curve represented by the above formula of 6 ° or more. Ferritic stainless steel hot rolled steel sheet for use. 5. The pickling treatment step, wherein no grinding brush is used between the pickling tanks, and the pickling loss is 7.5 g / m ² or more. For manufacturing a ferritic stainless steel hot rolled steel sheet for cold rolling.