JPS6149705A - Manufacture of cold rolled stainless-steel sheet excellent in surface property - Google Patents

Abstract

PURPOSE:To manufacture a stainless steel sheet having excellent surface properties, free from white stripes and gold dust flaws, etc. regardless of belt grinding, and poor gloss due to surface roughening, by positively generating heat streaks in cold rolling a stainless steel sheet. CONSTITUTION:In cold rolling a stainless steel sheet by a multipass cold rolling mill such as a Sendzimir mill having a small work roll of <=100mm. diam.; heat streaks are uniformly generated on the surface of stainless steel sheet by previously cold rolling it 1-2 passes by using a work roll having a 0.5-3.0mum surface roughness Ra, before cold rolling it >=2 times at a >=20% draft for every pass by using a work roll having a <=0.18mum surface roughness Ra. Successively, the sheet is cold rolled >=2 times at a 8-20% draft for every pass by using a work roll having a <=0.18mum surface roughness Ra. Thus, a stainless steel sheet excellent in surface properties can be manufactured.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention uses stainless steel sheets and copper strips with excellent surface properties (in the present invention, these are It relates to a method for manufacturing all stainless steel sheets (collectively referred to as stainless steel sheets).

[Conventional technology]

In addition to being used to take advantage of its corrosion resistance, stainless steel can also be used to take advantage of its natural luster. In particular, bright annealed (hereinafter referred to as BA) products of stainless steel sheets are used for various decorative items and items that can be lightly processed without impairing their surface beauty.

Therefore, for purposes of use, it is particularly required that the surface be glossy and dust-free and free from scratches.

Stainless steel sheet BA products are manufactured by annealing a hot rolled material, descaling it without annealing, cold rolling, annealing in a non-numerical atmosphere, and temper rolling. In order to produce products with excellent surface gloss, it is necessary to obtain a cold rolling method that has excellent surface properties without microscopic surface defects.

If there are flaws on the surface of the material before cold rolling that remain even after cold rolling, it is necessary to remove the flaws, and belt grinding (hereinafter referred to as CG) is usually performed. Also,
In ferritic stainless steel sheets, irregularities due to shot blasting performed during the descaling process of hot-rolled materials or grooves due to intergranular corrosion caused by annealing and washing become covered during rolling, and the product sheet is processed. When a protective coating is applied to a product board and exposed to heat, the cover rises and sparkles (called gold dust).
As a countermeasure against this, CG was performed before cold rolling. However, in the case of ferritic stainless steel sheets, the CG grinding marks cause a surface defect called "white streaks" and deteriorate the surface gloss. This is a striped collection of microscopic dents (called oil bits) that are created when rolling oil is retained in geometric spaces such as the grinding grooves of the CG, and is forced into the rolling plate without a place to escape during rolling. Chiru. For this reason, the conventional manufacturing method for BA products is to neutralize the effects of these grinding marks by cold rolling for two hours, followed by intermediate annealing, or by pickling after CG. However, in this manufacturing method, the intermediate annealing pickling and intermediate rolling steps are
A pickling process is required, which is disadvantageous compared to the one-time cold rolling method in terms of cost and manufacturing time.

In addition, in austenitic stainless steel sheets, when cold-rolling a hot-rolled material with uneven edges or intergranular corrosion that occurs during pickling of cast iron, "skin roughness" occurs.
A whitish pattern called ``white'' appears and the surface gloss deteriorates significantly. CG was unavoidably used as a preventive measure, but it was disadvantageous in terms of cost and manufacturing time.

In addition, as a cold rolling method for manufacturing stainless steel sheets with good surface gloss, all work rolls with a surface roughness Ra of 0.2 to 1.0 μm are used in passes before the finishing pass of Sendzimir rolling, and finishing IJ? It is known from Japanese Patent Publication No. 57-13362 to use a work roll having a surface roughness Ra of 0.1 .mu.m or less and to set the rolling reduction to 18 to 25 inches. This method is based on the above conditions in order to prevent the occurrence of heat scratches caused by the lack of rolling oil film between the work roll and the stainless steel plate during cold rolling (l), and is not a definitive measure to improve gloss. I can't get it.

[Problem that the invention seeks to solve]

The present invention prevents "gold dust flaws" or "rough skin" from occurring even if the surface of the steel sheet before cold rolling has irregularities due to shot blasting or intergranular corrosion due to annealing or pickling. The purpose of the present invention is to manufacture a stainless steel plate with excellent surface properties that does not cause "white streaks" even if there are CG grinding marks.

That is, the first object of the present invention is to process CGt before cold rolling.
- It is possible to produce a ferritic stainless steel sheet that does not produce white streaks even when cold rolling is carried out, and therefore has excellent surface gloss even with a single cold rolling process.

A second object of the present invention is to produce a ferritic stainless steel sheet with excellent surface gloss and which does not suffer from "gold dust flaws" even if it is not subjected to CGt treatment before cold rolling.

A third object of the present invention is to produce an austenitic stainless steel sheet with excellent surface gloss, which does not suffer from poor gloss due to "rough skin" even without performing CG before cold rolling.

[Means to solve the problem]

In the case of normal cold rolling,
As described in Publication No. 2, heat scratch (
In the present invention, the occurrence of heat streaks is prohibited.

This is due to the occurrence of heat streaks, which cause defects called "samidare pattern" on the surface of the product, which deteriorates the quality of narrow surfaces, and significant wear of the rolls.

However, the inventor of the present invention improved the surface quality before rolling by actively generating this "heat streak" and removing the outermost surface layer of the steel plate by grinding it with rolls. On the other hand, if the steel sheet is subsequently rolled under conditions that repair this "heat streak", a cold-rolled sheet with very good surface quality can be obtained, and such a steel sheet can be used as B.
BA with excellent surface gloss after A treatment and temper rolling
It was discovered that the product could be manufactured. It has also been found that a 2B product produced by cold rolling, annealing and pickling, and then temper rolling can also provide a product with excellent gloss.

That is, the present invention performs rolling that uniformly generates heat streaks over the entire surface of the stainless steel plate (hereinafter referred to as heat streaks) in multi-pass cold rolling of a stainless steel plate using small-diameter work rolls, and then repairs the heat streaks. Rolling (hereinafter referred to as repair rolling) is performed, and the first invention is heat streak rolling, in which all work rolls with a surface roughness Ra of 0.18 μm or less are used and rolling is continuously performed at a reduction rate of 20%/pass or more. Two or more passes are carried out, and as repair rolling, a work roll with a surface roughness R, a of 0.18 μm or less is used, and rolling with a reduction ratio of 8%/pass or more and 20%/pass or more is performed in succession for two or more passes. According to the second invention, as a pretreatment for heat streak rolling,
Rolling using work rolls with a surface roughness Ra of 0.5 μm or more and 3.0 μm or less (hereinafter referred to as rough roll rolling) is
After passing or two passes, rolling with the same roughness and reduction ratio as in the first invention is performed as heat streak rolling for one pass or 2 passes or more, and as repair rolling, rolling is performed in the same manner as in the first invention. It is characterized by doing.

The stainless steel sheets targeted by the present invention are ferritic,
Any of the austenitic, martensitic, or two-phase types may be used. The stainless steel sheet before cold rolling in the present invention may be a hot rolled material that has been annealed or descaled without annealing, or one that has been cold rolled, annealed, and descaled. The surface of the stainless steel plate may have CG polishing marks,
It may have irregularities due to shovel blasting, or may have intergranular corrosion due to annealing or pickling, and may be in any form.

In the present invention, multi-pass cold rolling using small-diameter work rolls refers to reverse rolling (moving the plate back and forth) using a multi-pass rolling mill such as a Sendzimir rolling mill that uses rolls with a diameter of 100 cm or less as work rolls; Alternatively, it refers to tandem rolling using multiple such rolling mills. Further, the surface roughness Ra is the center line average roughness specified in JIS BO601.

[Effect]

During cold rolling, there are two types of lubrication conditions at the interface between the rolls and the rolled material: a fluid lubrication state where the rolling oil film is thick and the surface of the rolled material can freely deform, and a fluid lubrication state where the oil film is very thin and the deformation of the surface of the rolled material is restrained by the rolls. It is said that there is a boundary lubrication state in which the surface of the material after rolling becomes a replica of the roll, and a metal contact state in which the oil film is broken and the roll and the material to be rolled come into contact.

In the method of the present invention, by rolling 20% or more in one pass using a work roll with a surface roughness Ra of 0.18 μm or less, the interface between the work roll and the stainless steel sheet is brought into metal contact state, and the steel sheet Generates heat streaks on the surface. When heat streaks are generated on the surface of the steel sheet by such heat streak rolling, various surface defects that existed before rolling are cured. However, if heat streaks occur locally, even if repair rolling is performed subsequently, a product with uniform gloss cannot be obtained because the surface properties of the areas where heat streaks have occurred and those where no heat streaks have occurred are different. Therefore, in order to generate heat streaks uniformly, in the first invention, the heat streak rolling is performed continuously two times or with a shaving, and in the second invention, as a pretreatment for heat streak rolling, After performing rough roll rolling using a work roll having a surface roughness Ra of Q and 5 μm or more and 3.0 μm or less, heat streak rolling is performed for one or two passes or more.

However, as mentioned above, heat streaks are also a defect called "samidare pattern," so if cold rolling is finished with heat streaks still occurring, it will cause problems in subsequent processes.
Even if rough rolling is performed, a product with excellent surface gloss cannot be obtained. Therefore, following heat streak rolling, a work roll with a surface roughness Ra of 0.18 μm or less was used.
By rolling 10 inches or more and less than 20% in a pass,
The interface between the work roll and the stainless steel plate is brought into a state of boundary lubrication to repair heat streaks. When such repair rolling is carried out continuously for 2 or more times, heat streaks are repaired over the entire surface of the steel sheet, and a cold rolled stainless steel sheet with excellent surface properties is obtained.

In this state, cold rolling is completed, BA treatment is performed, and temper rolling is performed to obtain a BA product with extremely excellent surface gloss. In addition, when cold rolling is followed by temper-pickling and temper rolling, a 2B product with excellent surface gloss can be obtained.

In heat streak rolling, when the surface roughness Ra of the work roll is 0.18 μm or more, during cold rolling, due to the thick rolling oil film interposed between the recesses on the roll surface and the steel plate surface, the In general, the fluid bath 1 is in a smooth B or boundary lubrication state, and p1 heat streaks occur uniformly and become a problem. Heat streaks occur when the lubrication between the roll and the rolled material is in metal-to-metal contact, so rolling under high pressure to thin the oil film, reducing the viscosity of the rolling oil, rolling at low speed, and reducing the relative roughness difference between the roll and the plate is necessary. This can easily occur due to conditions such as reduction in oil temperature, oil temperature, or the entire plate temperature. In experiments conducted by the inventor, heat streaks can be easily generated by rolling at a rolling reduction rate of 20%/pass or higher using a work roll with a surface roughness Ra of 0.18 μm or less. Ta.

In the first invention, in order to uniformly generate heat streaks, heat streak rolling must be carried out continuously for 2 to 4 times.
It is necessary to do this more than once, and it is desirable to do it multiple times. However, in this case, it may not be possible to ensure the number of times of repair rolling due to the product size. For this reason, in the second invention, as a pretreatment for heat streak rolling, the surface roughness Ra is 0.5 μm or more and 3.0 μm or more.
Rough roll rolling is performed using work rolls of .mu.m or less to uniformly generate heat streak generation nuclei on the surface of the stainless steel sheet. In this rough roll rolling, if the surface roughness Ra of the work roll is as fine as 0.5 μm, it is difficult to uniformly form flaws that become the core of heat streaks. In addition, if the roughness of the work roll is rougher than 3.0 μm, gold dust flaws may occur in ferritic stainless steel sheets during subsequent cold rolling, and surface roughness may occur in austenitic stainless steel sheets. There is a risk. By performing such rough roll rolling, it is possible to uniformly generate heat streaks even in one pass of heat streak rolling. Methods for making rough rolls include increasing the abrasive grains of the roll grinding wheel, etching, and shot peening, but the aim is to uniformly form the core of heat streaks as mentioned above. Therefore, the method of increasing the roughness is not limited.

In repair rolling, the surface roughness Ra- of the work roll is 0.
．． If it is coarser than 18 μm, the roughness of the steel plate surface after cold rolling will not be as rough as the roll surface, and it will be difficult to obtain a product with good surface gloss even if temper rolling is performed. Restoration rolling improves the surface gloss of the rolled plate. As shown in Figure 1, there are differences in gloss recovery due to rolling oil, but according to actual rolling accuracy, 2 passes or more is desirable, 3 to 4 passes for ferrite, and 5 to 6 passes for austenitic. It turns out.

〔Example〕

Table 11 Table 2 shows an example of an example.

The meanings of the ranks in the table are as follows: Glossy rank and white streak rank: A, B, C pass; D, E: fail; rough texture rank, G, D (Gold-Dust) rank: A, 13 is a pass, and C is a fail. Serial numbers 1 to 5 (Table 1) are manufacturing examples of BA products made of ferritic stainless steel sheets.3.
0+m++ thick hot-rolled plate was annealed for '6, CG was performed,
Chilled by cold rolling once to a thickness of 0.60 m.

Serial number 1 is a comparative example using the conventional rolling method. All work rolls with a surface roughness of 0.20 μm from the 1st to 6th center groove were used to prevent heat streaks from occurring. %/pass rolling, and the seventh pass (final pass) uses a work roll with a surface roughness of 0.04 μm.
Rolling was performed at a reduction rate of 17%/f. Although no gold dust was generated, both gloss and white streaks were rejected.

Serial number 2 is an example of the first invention, in which white streaks are significantly improved and gloss is also improved. Serial numbers 3 to 5 are examples of the second invention, and by performing rough roll rolling, the number of times of heat streak rolling can be completely reduced by 1/s, and in serial number 5, even one pass of heat streak rolling can uniformly heat the I was able to create a streak. Serial numbers 4 and 5 were all palanque in terms of gloss, white streaks, and gold dust. Note that for the first pass of serial number 2 and the first to second passes of serial number 4, conventional rolling was performed using all work rolls with a surface roughness of 0.1 to 0.2 μm.

For serial numbers 6 to 10 (Table 2), the CG step was omitted.

The rest are the same as serial numbers 1 to 5, and this is an example of manufacturing a BA product of ferritic stainless steel plate. Series @6 is a comparative example using a conventional rolling method, and was rolled under the same conditions as serial number 1. Because CG is used, gloss and white streaks are serial number 1.
Although the quality was good, gold dust was generated and the product was rejected. Serial numbers 7 to 9 are examples in which the stain, gloss, white streak, and gold dust were all improved by applying the second invention.

The serial number 10 is for the work roll of rough roll rolling.
This is an example of using a material that has been blasted to a dull finish.
This is a comparative example in which the gold dust was rejected because the surface roughness was 3.5 μm, which exceeded the range of the present invention. Even if a dull finishing roll is used for rough rolling, there is no problem as long as the surface roughness is in the range of 0.5 μm or more and 3.0 μm below the embankment, as shown in serial numbers 8 and 9.

Serial numbers 11 to 14 (Table 2) are manufacturing examples of BA products of austenitic stainless steel sheets. at 0.6
Chilled by cold rolling to a thickness of 0s+m. Serial number 11 is a comparative example using the conventional rolling method, using a work roll with a surface roughness of 0.20 μm from the 1/th pass to the 9th pass.
12 to 20 minutes, taking care not to cause heat streaks.
%/pass, and the 10th pass (final pass) uses a work roll with a surface roughness of 0.03 μm, and the rolling reduction rate is 11.
%/Nox rolling was performed. I failed the test because of my rough skin. Serial number 12 is an example of the first invention, serial number 13.14 is an example of the second invention, and both gloss and roughness have been improved. In the first pass of serial number 12, conventional rolling was performed using a work roll with a surface roughness of 0.20 μm.

In addition to the above examples, it has been recognized that both 7-elite type and austenite type are effective when applied to zBf)a products.

It should be noted that even if the method of the present invention is applied after the intermediate annealing and pickling of two cold rollings, the method of the present invention will not be effective, and it is also possible to apply the method to other steel types (common steel, silicon steel, etc.).

〔effect〕

According to the present invention, even without performing CG, a cold-rolled stainless steel sheet with excellent surface properties can be obtained without gold dust flaws in ferritic stainless steel sheets or surface roughening in austenitic stainless steel sheets, and thereby the surface BhH products and 2B products with excellent gloss are obtained. Furthermore, in the case of ferritic steel, even if CG is performed to remove surface flaws generated during hot rolling, white stripes do not occur.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the influence of rolling oil and the number of passes for repairing heat streaks. Axis I 2 3 4 Ha0 S Surface number

Claims (2)

[Claims] (1) In multi-pass cold rolling of stainless steel sheets using small-diameter work rolls, use work rolls with a surface roughness Ra of 0.18 μm or less, and perform two or more consecutive rolling passes at a rolling reduction rate of 20%/pass or more. Then, using a work roll with a surface roughness Ra of 0.18 μm or less, continuous rolling was performed at a reduction rate of 8%/pass or more and 20%/less than pass. te2
A method for producing a cold-rolled stainless steel sheet with excellent surface properties, characterized by repairing heat streaks on the surface of the stainless steel sheet by performing more than one pass, and then completing the cold rolling. (2) In multi-pass cold rolling of stainless steel sheets using small diameter work rolls, the surface roughness Ra is 0.5 μm or more3
．． 1 pass or 2 passes using a work roll of 0 μm or less
After rolling for more than one pass, use a work roll with a surface roughness Ra of 0.18 μm or less and perform one or more rolling passes at a reduction rate of 20%/pass or more to generate heat streaks uniformly over the entire surface of the stainless steel sheet. Then, using a work roll with a surface roughness Ra of 0.18 μm or less, rolling is performed at a reduction rate of 8%/pass or more and 20%/pass or more in succession for two or more passes to remove heat streaks on the surface of the stainless steel sheet. A method for manufacturing a cold rolled stainless steel sheet with excellent surface quality, which comprises repairing and finishing cold rolling.