JP2000288605A - Cold rolling method for stainless steel thin sheet - Google Patents

Abstract

(57) [Abstract] [Problem] Stainless steel with excellent surface quality by adjusting the scale composition and amount of austenitic stainless steel during finish annealing, increasing the descaling speed during pickling, and reducing pickling unevenness. Manufacture thin steel sheets with high productivity. SOLUTION: In cold rolling of a stainless steel sheet whose rolling oil is an oil-in-water emulsion oil, this emulsion oil contains an alkali metal and / or an alkaline earth metal in a total amount of 30 ppm or more, and a rolled material. The total metal content, including wear powder, is less than 200 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold rolling method for a stainless steel sheet using an oil-in-water emulsion oil as a rolling oil, and more particularly, to finish annealing and pickling of a cold-rolled stainless steel sheet. The present invention relates to a cold rolling method for a stainless steel sheet, in which descaling property is improved and productivity can be improved.

[0002]

2. Description of the Related Art Cold rolling of stainless steel sheets requires a product with a high surface gloss, and the rolled material has a high deformation resistance and is susceptible to work hardening. A small-diameter work roll Sendzimir mill has been generally used, which has a small amount of iron introduced and can obtain a high rolling pressure.

[0003] However, in Sendzimir mill, the rolling roll
The structure of the rolling mill with 20 steps is complicated, and the roll diameter is 50-80 m
Since the diameter is as small as m, there is a problem that the rolling speed is restricted and productivity is low. So, to improve productivity,
High gloss cold rolling with a tandem mill having a large roll diameter has recently been attempted.

[0004] As rolling oil for cold rolling of stainless steel sheets, a neat oil, which is supplied as it is without emulsifying with water, a rolling oil based on a low-viscosity mineral oil has been used in many cases. In general, neat oil gives a product with a good surface gloss,
Since the cooling capacity is low, seizure easily occurs in high-speed rolling under high pressure.

A stock solution for an emulsion oil obtained by adding an emulsifier to a mineral oil is mixed with water so that the stock solution generally has a concentration of 3 to 10% by volume.
The oil-in-water emulsion is also used for cold rolling of stainless steel sheets.
Emulsion oil has a high cooling capacity because most of it is water.However, when it is used cyclically, abrasion powder generated by rolling accumulates. Is known to deteriorate extremely. Therefore, it has not been widely used for cold rolling of stainless steel sheets requiring surface gloss.

[0006] Japanese Patent Publication No. 4-60721 discloses that a Cr-based stainless steel plate is cold-rolled by controlling the amount of abrasion powder (iron impurities) in an emulsion oil used in a circulating manner within a certain range. It is disclosed that deterioration of the film (the occurrence of uneven gloss) can be prevented, and a stainless steel sheet having a good surface gloss can be manufactured using emulsion oil. JP-A-10-
No. 273688 discloses that when cold rolling is performed using a fine grain emulsion oil to which a small amount of sodium petroleum sulfonate has been added, a stainless steel sheet having a good surface gloss and also preventing the occurrence of uneven gloss can be obtained. It is shown.

[0007]

The rolling efficiency of a stainless steel sheet has been improved by cold rolling in a tandem mill. However, a stainless steel sheet cold-rolled in a tandem mill using emulsion oil has been developed. In the finish annealing / pickling performed subsequent to the cold rolling, the descalability was poor as compared with the case where neat oil was used in the cold rolling, and the finish annealing / pickling efficiency tended to decrease. This deterioration in descaling property was particularly remarkable in austenitic stainless steel sheets having a sheet thickness of less than 0.8 mm. Further, when cold rolling is performed in a reverse mill instead of in a tandem mill, the descalability tends to be further deteriorated.

[0008] As a method for improving the descaling property of a cold-rolled stainless steel sheet, as described in JP-B-55-2476 and JP-A-7-48700, a method of pickling and changing the composition of an acid solution are disclosed. Alternatively, a combination with a mechanical descaling method or the like is being studied, but in all cases, equipment improvement or introduction of new equipment is required, and equipment investment costs become enormous.

[0009] Finish annealing and pickling of a stainless steel sheet after cold rolling are often performed in a state where a stainless steel sheet using neat oil and a stainless steel sheet using emulsion oil are mixed in cold rolling. . Since the finish annealing / pickling is performed in the continuous processing line of the steel sheet coil, it is complicated to change the annealing / pickling conditions depending on whether the rolling oil used in the previous step is neat oil or emulsion oil, Unnecessarily low speed results, which hinders productivity.

[0010] The present invention is to improve the productivity of cold rolling of stainless steel sheet by tandem mill or reverse mill, and to provide a conventional continuous processing line with a cold rolled stainless steel sheet using emulsion oil. It is an object of the present invention to produce a stainless steel sheet with improved descalability when treated under the same standard finish annealing / pickling conditions as a cold-rolled material using neat oil, using the same as it is. .

In order to improve the descalability without changing the conditions of the finish annealing and pickling and without performing additional processing requiring equipment improvement, it is necessary to devise the cold rolling which is the preceding stage. is there. Accordingly, a more specific object of the present invention is to adjust the scale composition and the amount generated during finish annealing of a stainless steel sheet having a high finish annealing temperature represented by austenitic stainless steel, and to increase the descaling speed during pickling. Improve cold rolling method of stainless steel sheet with tandem mill using emulsion oil so that pickling unevenness can be reduced and stainless steel sheet with excellent surface quality can be manufactured with high productivity. It is to be.

[0012]

Means for Solving the Problems In order to solve the above problems, the present inventors have developed a scale generation state and a descaling state during finish annealing and pickling of a cold-rolled stainless steel sheet using emulsion oil. As a result of a detailed investigation and examination of the following, the following became clear.

I. Regarding the surface state after cold rolling and after finish annealing and pickling: (1) A stainless steel sheet cold-rolled using an emulsion oil is colder than a case using a neat oil. There are many thin oxide films (tempered color) presumed to have occurred during hot rolling. In particular, it is remarkable in the portion of the edge of the coil plate width of 20 to 100 mm in the rolling by the reverse tandem mill.

(2) The temper color at the time of cold rolling affects scale formation at the time of finish annealing, and the temper color portion is liable to generate scale residue in the subsequent pickling.

(3) When the emulsion oil is used, the amount of oil adhering to the surface of the steel sheet after rolling is extremely small as compared with the case where the neat oil is used, but the metal wear powder of the rolled material such as iron, chromium and nickel is reduced. Large amount of adhesion. In addition, the adhesion of metal wear powder on a steel plate is often uneven.

(4) The surface portion of the steel sheet to which a large amount of metal wear powder of the rolled material adheres is different from the surroundings in the scale generation state during annealing, and is liable to become scale residue and uneven gloss after pickling.

II. Improving descalability during finish annealing and pickling: (1) When a sodium compound is contained in the emulsion oil, metal abrasion powder adhering to the stainless steel sheet after cold rolling is reduced. The amount is reduced. Also, uneven adhesion of metal wear powder is unlikely to occur.

(2) When the emulsion oil contains a sodium compound, the scale state at the time of finish annealing changes, and the pickling property is improved.

(3) The effect of the sodium compound on the improvement of pickling properties is greater when the metal wear powder of a rolled material such as iron, chromium or nickel adheres to the surface of the cold-rolled stainless steel sheet.

(4) The above-mentioned effects of the sodium compound contained in the emulsion oil can be obtained also with other alkali metal compounds such as potassium compounds and / or alkaline earth metal compounds such as calcium compounds.

Based on the above findings, further study was made on the optimum amount of metal including alkali metal and alkaline earth metal (hereinafter sometimes collectively referred to as alkali metal, etc.) and metal wear powder of rolled material. Was obtained.

(1) Abrasion powder of a rolled material such as iron, chromium, nickel or the like generated by rolling is present in the used solution of the emulsion oil, and the metal present as the abrasion powder and the alkali metal coexist. The descaling property is improved in the state.

(2) If the amount of the alkali metal or the like at that time is 30 ppm or more in the emulsion oil, descalability is improved.

(3) Further, an alkali metal or the like and iron, chromium,
If the total metal concentration in the emulsion oil containing abrasion powders such as nickel exceeds 200 ppm, uneven gloss is generated on the surface of the thin steel sheet after pickling.

On the basis of the above results, when cold rolling a stainless steel plate using an oil-in-water emulsion oil,
The concentration of alkali metals and the like in the emulsion oil should be 30 ppm or more and the total metal concentration should be 200 ppm or less, and descaling during finish annealing and pickling of stainless steel sheet in tandem rolling and especially in reverse rolling. The present invention has been found to be effective in improving the performance, and the present invention has been completed.

According to the present invention, in cold rolling of stainless steel sheet using oil-in-water emulsion oil as a rolling oil, the emulsion oil used is an alkali metal and / or
Alternatively, the present invention is a cold rolling method for a stainless steel sheet, comprising an alkaline earth metal in a total concentration of 30 ppm or more and a total metal concentration of 200 ppm or less.

The cold rolling method of the present invention is advantageously applied particularly when the material of the stainless steel sheet is austenitic stainless steel having a high finish annealing temperature and remarkable scale generation during annealing.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is to improve the descalability of a stainless steel sheet using an oil-in-water emulsion oil at the time of finish annealing in cold rolling and to improve the productivity of a stainless steel sheet. A rolling method, wherein the emulsion oil used is an alkali metal and / or an alkaline earth metal
(I.e., alkali metal, etc.) in a total concentration of 30 ppm or more, and the total metal concentration of other metals such as iron, chromium, nickel, etc.
It is characterized by being below 0 ppm.

The oil-in-water emulsion oil used in the present invention is not particularly limited except that it has the above-mentioned metal concentration, and may be the same as conventional oils. Generally, an oil-in-water emulsion oil is prepared by preparing a large amount of a rolling oil stock solution containing a base oil, an emulsifier, and, if necessary, various additives (eg, an oil agent, an extreme pressure agent, a viscosity index improver, an antioxidant, etc.). It is an oil-in-water emulsion obtained by high-speed stirring with water. The base oil may be a conventional mineral oil, but other base oils such as synthetic esters and fats and oils may be used in combination with the mineral oil or may be used in place of the mineral oil.

As described above, the amount of the rolling oil stock solution in the emulsion oil is generally in the range of 3 to 10% by volume.
In the case of rolling in a tandem mill of a large-diameter roll mill having a diameter exceeding 300 mm, an emulsion oil having a lower stock solution concentration of 1 to 2% by volume may be used.

The alkali metal or the like contained in the emulsion oil used in the present invention is one or more metals selected from the group Ia alkali metals and the group IIa alkaline earth metals of the periodic table of the elements. Specific examples include metals such as lithium, potassium, sodium, magnesium, calcium, barium and the like.

The compound used for adding the alkali metal or the like to the emulsion oil may be an inorganic compound or an organic compound. The compound to which the alkali metal or the like is added may be either a rolling oil stock solution or water used for emulsification, or may be added after the rolling oil stock solution is emulsified (that is, added to the emulsion). is there. The compound to be used is preferably soluble in the stock solution of rolling oil or water to be added, but may be at least partially dispersed in the form of fine powder as long as uniform dispersion can be ensured.

Specific examples of compounds such as alkali metals include salts with inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, hydrofluoric acid, carbonic acid and silicic acid, salts with organic acids such as fatty acids and petroleum sulfonic acid, and Hydroxide, oxide, alkoxide and the like. The compound may be one produced industrially or one obtained by concentrating or extracting an alkali metal compound inevitably contained in industrial water.

In order to achieve the purpose of improving the descaling property, it is desirable that the alkali metal and the like be efficiently adhered to the steel sheet surface. In that sense, the compound such as an alkali metal used is preferably an organic acid salt such as a fatty acid salt or a petroleum sulfonic acid salt. In addition, such an organic acid salt such as an alkali metal, particularly a petroleum sulfonic acid salt may be added from the beginning as an additive (eg, an emulsifier) to a rolling oil stock solution. In some cases, the water used contains a trace amount of an alkali metal or the like. In that case, the concentration of the alkali metal or the like in the emulsion oil after the emulsion is formed, including the compound of the alkali metal or the like present in the rolling oil stock solution and / or water from the beginning, satisfies the range of the present invention. To

The compound such as an alkali metal is added at a concentration such that the content of the alkali metal or the like in the emulsion oil is 30 ppm or more. If the concentration is less than 30 ppm, the amount of alkali metal or the like adhering to the cold-rolled stainless steel sheet is small, and the scale (oxide film) formed on the surface during finish annealing is modified to remove the acid during pickling. The effect of improving the scale is hardly recognized. The concentration of alkali metal etc.
Preferably it is 50 ppm or more and 100 ppm or less.

As described above, the used emulsion oil is returned to the tank and used for circulation. During rolling, abrasion powder of the metal to be rolled (iron, chromium, nickel, etc. in the case of rolling a stainless steel plate) is inevitably mixed into rolling oil. Therefore, when the rolling oil is used cyclically, these metal wear powders accumulate in the rolling oil, and the content thereof gradually increases.

If the abrasion powder of the rolled material metal (eg, iron, chromium, nickel, etc.) generated by rolling is less than a certain range, the descalability is improved by coexisting with the alkali metal in the emulsion oil. And is beneficial for the purposes of the present invention. However, if the total metal concentration in the emulsion oil (concentration of all metals including alkali metal and rolled material metal abrasion powder) exceeds 200 ppm, unevenness of gloss on the thin steel sheet surface after pickling may occur. become. Therefore, the emulsion oil is controlled so that the total metal concentration in the emulsion oil becomes 200 ppm.

The management of the total metal concentration can be performed, for example, as described in Japanese Patent Publication No. 4-60721. That is, when the total metal concentration in the emulsion oil exceeds 200 ppm due to circulating use, remove the rolling oil near the liquid surface and near the bottom surface where the metal powder concentration of the emulsion oil in the tank is relatively high, The abrasion powder is removed by means of filtering with a suitable filter and removing the abrasion powder using a magnet because it adheres to the magnet, so that the total metal concentration becomes 200 ppm or less. This total metal concentration is preferably below 180 ppm, more preferably
Set to 150 ppm or less.

The concentration of the alkali metal and the like in the emulsion oil, the concentration of the metal abrasion powder, and the total metal concentration were determined by incinerating a sample of the emulsion oil, incinerating the resulting ash with a strong acid, and dissolving the solution. By analyzing by atomic absorption method,
It can be measured for each metal element. The sum of the obtained contents of the respective metals with respect to the alkali metal and the like (alkali metal + alkaline earth metal) is the content of the alkali metal and the like, and the total sum is the total metal content.

The cold rolling of the stainless steel sheet using the above-described emulsion oil may be carried out according to a conventional method. The rolling oil supply method is generally a circulation oil supply method, but is not limited thereto. There is no particular limitation on the rolled stainless steel sheet, but it can be applied to cold rolling to produce austenitic stainless steel sheet with a thickness of less than 0.8 mm, which has a large amount of scale due to high annealing temperature and poor descaling property. It is advantageous. The rolled material is generally obtained by annealing and pickling a hot-rolled stainless steel sheet.

The emulsion oil used in the present invention can be used for Sendzimir mill rolling. However, in order to make use of the effect of the present invention of improving the descaling property, the descaling property of the conventional rolling oil deteriorates. It is advantageous to apply to cold rolling in a continuous stand mill such as tandem mill rolling. Even more advantageously, when applied to a rolling mill such as reverse mill rolling, which is wound up for each pass, and the rolling time is relatively long and a temper color is likely to be generated during the rolling, removal by alkali metal or the like can be achieved. The effect of improving the scale is more remarkable.

The stainless steel sheet produced by cold rolling is subjected to continuous annealing (finish annealing) and pickling in the same manner as in the prior art. Although the scale generated by annealing is descaled by pickling, if the emulsion oil used at the time of cold rolling according to the present invention contains an alkali metal or the like, descaling at this time becomes easy, and there is no scale residue. It is possible to obtain a stainless steel sheet having high gloss and no uneven gloss. The effect of this alkali metal etc. depends on the annealing conditions.
(Temperature, time, atmosphere gas) and pickling conditions (acid bath composition, temperature). After the pickling, if necessary, finishing operations such as temper rolling and polishing finishing may be performed.

[0043]

[Example] SKD 11 steel, diameter 100 mm, surface roughness Ra = 0.13
Using a 4Hi reverse rolling mill having a work roll of μm and a backup roll having a diameter of 350 mm, 9 passes of rolling were performed on the rolled material shown in Table 1 under the rolling conditions shown in Table 2.

The rolling oil used had the composition and properties shown in Table 3. The rolling oil No. and the rolling oil stock solution for the oil-in-water emulsion oil according to the present invention, and the rolling oil No. is a neat oil for comparison. Rolling oil No. is Ca ion 3ppm
Rolled oil No. was prepared by using ion-exchanged water containing no alkali metal or the like, and 200 liters of an emulsion oil having a stock solution concentration of 10% by volume was prepared and used. Emulsion oil is prepared by stirring and mixing in a tank using a large stirrer (homomixer), and this emulsion oil is circulated to a rolling mill using a circulation pump for at least 30 minutes (while rolling Is not performed),
Emulsion oil concentration and emulsion particle size were stabilized and made uniform. Since neat oil is used as it is without mixing with water, such an operation is unnecessary.

As shown in Table 4, the compounds shown in Table 4 were added to either the stock solution of the rolling oil or the water used for the emulsion as a source of alkali metal or the like. The combination of the rolling oil and the additive compound and the amount added (in the case of an emulsion oil, the concentration after emulsification) were as shown in Table 5.

Using the cold rolling oil (emulsion oil or neat oil) thus obtained, the rolled material shown in Table 1 was continuously rolled up to a maximum of 10 coils. The emulsion oil circulated in an amount of 200 liters and the feed rate to the rolling mill was 65 L / min. The neat oil was circulated using a volume of 200 liters while feeding the mill at a rate of 65 L / min. The stainless steel sheet obtained by cold rolling was subjected to finish annealing, pickling and temper rolling under the conditions shown in Table 6.

The content of the alkali metal and the like in the rolling oil after the completion of the rolling of the final coil and the total metal content including the abrasion powder were determined from the results of analysis by ignition and atomic absorption analysis as described above. I asked.

The stainless steel sheet obtained by cold rolling of the final coil was visually evaluated for the presence of scale residue on the steel sheet after finish annealing and pickling. In addition, with respect to the steel sheet after temper-rolling this, while measuring the glossiness: Gs 60 at a measurement angle of 60 ° specified in JIS Z8741,
The degree of gloss unevenness in the plate width direction was evaluated by visual observation.
These evaluation criteria were as follows. SUS 430
Since the required gloss level differs between the material and the SUS 304 material, the gloss level was set to different standards. The results of these evaluations are also shown in Table 5.

Evaluation criteria for remaining scale ：: not confirmed, ：: slight, no problem in quality, ▲: many, degraded quality, ●: remarkable, need reprocessing (care).

SUS 430 material glossiness evaluation criteria ○: 550 or more, □: 550 to 550, ▲: less than 500 (unsuitable for quality).

Evaluation standard of glossiness of SUS 304 material ○: 450 or more, □: 400 to 450, ▲: less than 400 (unsuitable for quality).

Evaluation criteria for degree of uneven glossiness : ：: not confirmed, □: slight, no problem in quality, ：: remarkable, inappropriate quality.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

[Table 6]

As can be seen from Table 5, when stainless steel is cold-rolled using the emulsion oil according to the present invention, finish annealing and pickling are performed despite the reverse mill rolling using the emulsion oil. No subsequent scale residue is observed, the surface gloss after temper rolling is high and uniform, and an excellent surface quality equal to or higher than that when using neat oil can be obtained. On the other hand, conditions deviating from the present invention,
And in the conventional method, annealing under the same conditions as neat oil
In pickling, the quality becomes unsuitable due to uneven gloss.

FIG. 1 is a graph showing the results of scale remaining and uneven gloss shown in Table 5 for the SUS 304 material with respect to the content of alkali metals and the like in rolling oil (emulsion oil) and the total metal content. It is. From this figure, a stainless steel sheet cold-rolled in a state in which the wear powder of the rolled material (metal powder such as iron, chromium, and nickel) and the alkali metal coexist in the emulsion in an amount within the range specified in the present invention, It turns out that it is excellent in descaling property. In particular, when the SUS 304 material is cold-rolled, if the content of alkali metals and the like is 30 ppm or more and the content of all metals is 200 ppm or less, improvement in descalability is ensured.

[0061]

According to the present invention, the descalability of cold rolled stainless steel sheet using finish emulsion annealing and pickling in a tandem mill or reverse mill is improved, and neat oil is improved. The same annealing as when using
Under pickling conditions, it becomes possible to produce cold-rolled stainless steel sheets having excellent surface quality comparable to the case where neat oil is used, and the productivity of cold-rolled stainless steel sheets is greatly improved.

More specifically, the scale composition and the amount of the steel sheet having a high finish annealing temperature typified by austenitic stainless steel are cold-rolled by the above-mentioned mill, and the scale composition and the amount of the steel sheet produced during the pickling are adjusted. By increasing the descaling speed and reducing the pickling unevenness, it becomes possible to produce a stainless steel sheet having excellent surface quality with high productivity.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the content of an alkali metal and the like in an emulsion oil and the total metal content (metal content including abrasion powder of a rolled material such as iron, chromium, and nickel) on descalability. .

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C10M 173/00 C10M 173/00 (72) Inventor Satoshi Matsushita 4-33, Kitahama, Chuo-ku, Osaka-Sumitomo Inside Metal Industry Co., Ltd. (72) Inventor Masayoshi Sakakibara 1-4-1, Tsujido Shindai, Fujisawa City, Kanagawa Prefecture Inside Kyodo Yushi Co., Ltd. (72) Inventor Norihiro Ueya 1-4-1, Tsujido Shindai, Fujisawa City, Kanagawa Prefecture Cooperative Y-Fat Co., Ltd. F term (reference) 4E002 AA07 AD05 BA01 BA03 BC08 BD09 BD10 CB03 4H104 AA01C AA13C AA16C AA17C AA18C AA20C AA21C BB02C BB15C BG06C DA02A EA21Z EB02 EB14 FA01 FA02 LA20 PA28

Claims (2)

[Claims] Claims: 1. In cold rolling a stainless steel sheet using an oil-in-water emulsion oil as a rolling oil, the emulsion oil used contains an alkali metal and / or an alkaline earth metal in a concentration of 30 ppm or more in total, A cold rolling method for a stainless steel sheet, wherein the total metal concentration is 200 ppm or less. 2. The method according to claim 1, wherein the material of the stainless steel sheet is austenitic stainless steel.