Cold rolling method for stainless steel sheet and method for manufacturing stainless steel sheet

Abstract

To obtain a stainless steel sheet having excellent surface appearance after cold rolling. [Solution] A soluble water-soluble lubricant containing a base oil (A), a fatty acid (B), an extreme pressure agent (C), a water-soluble polymer (D), and an amine (E) is supplied to a rolling mill, and a stainless steel sheet is cold-rolled using the supplied soluble water-soluble lubricant. After cold rolling, the soluble water-soluble lubricant is recovered, a surfactant is added to the soluble water-soluble lubricant, and the soluble water-soluble lubricant with the surfactant added is supplied to the rolling mill.

Description

Technical Field

[0001] The present invention relates to a cold rolling method for stainless steel sheets and a method for manufacturing stainless steel sheets.

Background Art

[0002] In metal products that affect purchasing desire and the like depending on the product appearance, the surface quality of the metal sheet (for example, stainless steel sheet) used for the metal product is important.

[0003] Conventionally, in the cold rolling of stainless steel sheets, in order to obtain a uniform and beautiful surface, an oil agent (mineral oil, ester oil, etc.) that does not contain moisture is used as a lubricant (rolling lubricant). However, since the oil agent is flammable, there is a concern of fire due to sparks generated at the time of breakage of the stainless steel sheet or seizure of the bearing.

[0004] Therefore, a water-soluble lubricant may be used for the cold rolling of stainless steel sheets. Water-soluble lubricants include types such as emulsion type, soluble type, and solution type, and are used in a state of being mixed with water and dissolved or emulsified. That is, a water-soluble lubricant is a lubricant that contributes to rolling lubrication in a state containing moisture. Patent Documents 1 to 2 disclose techniques for cold rolling stainless steel sheets and the like using an emulsion type water-soluble lubricant.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Soluble-type water-soluble lubricants are sometimes used as lubricants (rolling lubricants) when cold-rolling stainless steel sheets. In this case, from an economic standpoint, soluble water-soluble lubricants (hereinafter, for convenience, also simply referred to as "lubricants") are recovered after use in cold rolling and reused repeatedly. However, during repeated use, different types of oils may become mixed into the lubricant. In such cases, the lubrication state may change locally or become uneven, which can easily cause defects such as spots on the surface of cold-rolled stainless steel sheets.

[0007] Furthermore, Patent Document 2 discloses a technique for removing foreign oils mixed into a lubricant. However, complete removal is extremely difficult, and even if it could be completely removed temporarily, it would be impossible to avoid contamination by other oils before the product reaches the rolling mill.

[0008] This invention has been made in view of the above points, and aims to provide a stainless steel sheet with excellent surface appearance after cold rolling. [Means for solving the problem]

[0009] As a result of diligent research, the inventors of this invention discovered that the above objective can be achieved by adopting the following configuration, and thus completed the present invention. In other words, the present invention provides the following [1] to [4]. [1] A method for cold rolling a stainless steel sheet using a soluble water-soluble lubricant containing a base oil (A), a fatty acid (B), an extreme pressure agent (C), a water-soluble polymer (D), and an amine (E), wherein the base oil (A) is at least one selected from the group consisting of refined mineral oil, natural oils and fats and synthetic esters, the fatty acid (B) is at least one selected from the group consisting of monocarboxylic acids and dicarboxylic acids, the extreme pressure agent (C) is at least one selected from the group consisting of tricresyl phosphite, zinc dialkyldithiophosphate, sulfur esters, olefin polysulfides and dialkyl polysulfides, and the water-soluble polymer (D) has a weight-average molecular weight of 500 or more and 40,000 A method for cold rolling stainless steel sheets, wherein the polyalkylene glycol-based high molecular weight polymer is less than 0. The amine (E) is at least one alkanolamine selected from the group consisting of monoethanolamine, diglycolamine, monoisopropanolamine, 2-amino-2-methylpropanol, 2-(sec-butylamino)ethanol, diethanolamine, diisopropanolamine, N-methylethanolamine, N-ethylethanolamine, triethanolamine, triisopropanolamine, and cyclohexylamine EO adduct, and after cold rolling, the soluble water-soluble lubricant is recovered, a surfactant is added to the soluble water-soluble lubricant, and the soluble water-soluble lubricant with the surfactant added is supplied to the rolling mill. [2] The cold rolling method for stainless steel sheets according to [1] above, wherein the amount of the surfactant added is 20% by mass or more relative to the concentration of the dissimilar oil in the soluble water-soluble lubricant. [3] The cold rolling method for stainless steel sheets according to [1] or [2] above, wherein the soluble water-soluble lubricant to which the surfactant above has been added is stirred before being supplied to the rolling mill. [4] A method for producing a stainless steel sheet after cold rolling, using the method described in any of [1] to [3] above. [Effects of the Invention]

[0010] According to the present invention, a stainless steel sheet with excellent surface appearance after cold rolling can be obtained. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing an example of equipment used for cold rolling stainless steel sheets. [Figure 2] This is a schematic diagram showing an example of the surface of a stainless steel sheet after cold rolling. [Modes for carrying out the invention]

[0012] [Cold rolling method for stainless steel sheets] The following describes the cold rolling method for stainless steel sheets according to this embodiment. This description also serves as a description of the manufacturing method for stainless steel sheets.

[0013] The cold rolling method for stainless steel sheets in this embodiment is, in general terms, a method of supplying a soluble water-soluble lubricant to a rolling mill and cold rolling the stainless steel sheet using the supplied soluble water-soluble lubricant. In this embodiment, after cold rolling, the soluble water-soluble lubricant is recovered, a surfactant is added to the recovered soluble water-soluble lubricant, and the soluble water-soluble lubricant with the added surfactant is supplied to the rolling mill.

[0014] Furthermore, "soluble water-soluble lubricant" refers to "Type A2" of "water-soluble cutting fluid" as defined in JIS K 2241:2017 "Cutting Fluids". When a soluble water-soluble lubricant is dispersed in water using an appropriate method, small-particle oil droplets (specifically, for example, with an average particle size of about 0.1 μm as measured using a Coulter counter) may be formed. In the following, "soluble water-soluble lubricants" may sometimes be simply referred to as "lubricants."

[0015] The "stainless steel sheet" is a steel sheet having a component composition containing 10.0 to 35.0% by mass of Cr. For example, it includes austenitic stainless steel sheets, austenite-ferrite two-phase stainless steel sheets, ferritic stainless steel sheets, martensitic stainless steel sheets, and the like. Hereinafter, the "stainless steel sheet" may sometimes be simply referred to as the "steel sheet".

[0016] FIG. 1 is a schematic diagram showing an example of a group of equipment 11 used for cold rolling of a stainless steel sheet. The equipment group 11 includes a rolling mill 1. The rolling mill 1 shown in FIG. 1 is a 12-stage cluster rolling mill, but it is not limited to this as long as it is a machine capable of performing cold rolling, and it may be a tandem rolling mill, a reversing rolling mill, or the like. Immediately below the rolling mill 1, a filtration facility 2 and a tank 3 are arranged in this order. The tank 3 houses a lubricant (not shown). The tank 3 and the rolling mill 1 are connected via a pump 4. The tank 3 is equipped with a drain 5, a surfactant supply port 6, and a stirrer 7, which will be described later. Furthermore, the equipment group 11 includes a liquid chromatography device 8. The liquid chromatography device 8 may be connected to the tank 3 via, for example, the drain 5.

[0017] In such a configuration, by driving the pump 4, a lubricant is supplied from the tank 3 to the rolling mill 1. In the rolling mill 1, cold rolling is performed on the steel sheet S using the supplied lubricant. At this time, more specifically, the supplied lubricant is sprayed in the vicinity of the work roll of the rolling mill 1. The shape of the steel sheet S is not particularly limited and may be a long strip shape or a cut sheet. Regarding the cold rolling using a lubricant, the conditions thereof are not particularly limited, and conventionally known conditions can be adopted.

[0018] The lubricant supplied to the rolling mill 1 and used for cold rolling of the steel sheet S falls through the filtration equipment 2, where foreign matter (solids) is removed, and then returns to tank 3. In this way, the lubricant is recovered. The recovered lubricant is then supplied again from tank 3 to the rolling mill 1 by pump 4. In this manner, the lubricant is repeatedly recycled and reused.

[0019] In this embodiment, the soluble water-soluble lubricant (lubricant) used in circulation is diluted with water and contains the base oil (A), fatty acid (B), extreme pressure agent (C), water-soluble polymer (D), and amine (E) described later.

[0020] The base oil (A) is at least one selected from the group consisting of refined mineral oil, natural oils and fats, and synthetic esters.

[0021] Examples of refined mineral oils include naphthenic mineral oils, paraffinic mineral oils, and aromatic mineral oils. Examples of natural oils and fats include animal and vegetable oils such as soybean oil, rapeseed oil, castor oil, palm oil, coconut oil, lard, beef tallow, lard, whale oil, and rice bran oil. Examples of synthetic esters include monoesters of fatty acids and / or synthetic fatty acids obtained from beef tallow, palm oil, coconut oil, castor oil, etc., and aliphatic monohydric alcohols having 8 to 18 carbon atoms; and di, tri, or tetraesters of the above fatty acids and / or synthetic fatty acids and polyhydric alcohols such as ethylene glycol, neopentyl glycol, trimethylolpropane, and pentaerythritol.

[0022] Fatty acid (B) is at least one selected from the group consisting of monocarboxylic acids and dicarboxylic acids.

[0023] Monocarboxylic acids and dicarboxylic acids may each be aliphatic or aromatic. Examples of aliphatic monocarboxylic acids include aliphatic saturated monocarboxylic acids having 3 to 18 carbon atoms (preferably 6 to 12 carbon atoms), and specific examples include hexanoic acid, heptanoic acid, octanoic acid, isooctanoic acid, nonanoic acid, isononanoic acid, and 2-butyloctanoic acid. Examples of aliphatic dicarboxylic acids include aliphatic saturated dicarboxylic acids having 4 to 12 carbon atoms, such as succinic acid, adipic acid, azelaic acid, and sebacic acid. Examples of aromatic monocarboxylic acids include toluic acid, phenoxyacetic acid, thiophenoxyacetic acid, methoxybenzoic acid, p-tert-butylbenzoic acid, ethoxybenzoic acid, and hydroxybenzoic acid. Examples of aromatic dicarboxylic acids include phthalic acid, isophthalic acid, and terephthalic acid.

[0024] The content of fatty acid (B) is not particularly limited, and may be, for example, 1 to 60 parts by mass, or 10 to 50 parts by mass, per 100 parts by mass of base oil (A).

[0025] The extreme pressure agent (C) is at least one selected from the group consisting of tricresyl phosphite, zinc dialkyldithiophosphate, sulfur esters, olefin polysulfides, and dialkyl polysulfides.

[0026] Examples of alkyl groups that zinc dialkyldithiophosphate may possess include primary or secondary alkyl groups having 4 to 12 carbon atoms. Examples of sulfurized esters include sulfurized fats and oils obtained by sulfurizing animal and vegetable oils and fats such as beef tallow, pork tallow, fish oil, rapeseed oil, and soybean oil by any method; esters obtained by sulfurizing unsaturated fatty acid esters (such as methyl unsaturated fatty acids) obtained by reacting unsaturated fatty acids with alcohols by any method; and esters obtained by sulfurizing mixtures of animal and vegetable oils and unsaturated fatty acid esters by any method. Examples of olefin polysulfides include reaction products of olefins having 3 to 20 carbon atoms (such as propylene, isobutylene, and diisobutylene) or their di- to tetramers with sulfurizing agents (such as sulfur and sulfur halides). Examples of dialkyl polysulfides include dibenzyl sulfide and di-t-nonyl polysulfide, and the sulfur content is preferably 10 to 50% by mass.

[0027] The content of the extreme pressure agent (C) is not particularly limited, and may be, for example, 1 to 60 parts by mass, or 6 to 30 parts by mass, per 100 parts by mass of base oil (A).

[0028] Water-soluble polymer (D) is a polyalkylene glycol-based high molecular weight polymer with a weight-average molecular weight of 500 or more and less than 40,000.

[0029] Specific examples of water-soluble polymers (D) include polyoxyethylene oxypropylene glycol, polyoxyethylene oxypropylene glycol allyl ether, and butoxypolyoxyethylene oxypropylene glycol allyl ether.

[0030] The weight-average molecular weight (Mw) is a polystyrene-converted value obtained by gel permeation chromatography (GPC) measurement using tetrahydrofuran as the solvent.

[0031] The content of the water-soluble polymer (D) is not particularly limited, and may be, for example, 1 to 40 parts by mass, or 2 to 20 parts by mass, per 100 parts by mass of base oil (A).

[0032] Amine (E) is at least one alkanolamine selected from the group consisting of monoethanolamine, diglycolamine, monoisopropanolamine, 2-amino-2-methylpropanol, 2-(sec-butylamino)ethanol, diethanolamine, diisopropanolamine, N-methylethanolamine, N-ethylethanolamine, triethanolamine, triisopropanolamine, and cyclohexylamine EO (ethylene oxide) adducts.

[0033] The content of amine (E) is not particularly limited, and may be, for example, 1 to 40 parts by mass, or 2 to 20 parts by mass, per 100 parts by mass of base oil (A).

[0034] A soluble water-soluble lubricant containing a base oil (A), a fatty acid (B), an extreme pressure agent (C), a water-soluble polymer (D), and an amine (E), which may be a commercially available product before dilution with water, for example, Daido Chemical's Diroll RS-012.

[0035] When lubricants are reused in a circular fashion, contamination with dissimilar oils (described later) is unavoidable, although the degree and type of contamination varies. If a lubricant contaminated with dissimilar oils is used in cold rolling, the dissimilar oils may be accidentally drawn into the roll bite (the part that is rolled and undergoes plastic deformation by the roll), causing surface defects such as spotted patterns. Please refer to Figure 2 (details will be described later). As shown in Figure 2, the surface of the steel sheet S after cold rolling has a spotted pattern 21 (areas where cloudiness has occurred) and normal areas 22, and when comparing the two, there may be a difference of 10% or more in glossiness. The greater the difference in kinematic viscosity between the lubricant and the dissimilar oil, the greater the difference in gloss. In this case, if the kinematic viscosity is "different oil > lubricant", the gloss level tends to be "spotted pattern < normal area", and if the kinematic viscosity is "different oil < lubricant", the gloss level tends to be "spotted pattern > normal area". Note that the kinematic viscosity of a lubricant is the kinematic viscosity of the lubricant after it has been diluted with water.

[0036] Based on the above, we define different types of oils as follows: In other words, a different type of lubricant is a lubricant that has a kinematic viscosity different from that of the lubricant. Here, "different kinematic viscosities" means a difference of 10% or more in kinematic viscosity. If the difference in kinematic viscosity is smaller than this, the risk of spotting is low even if a different type of oil is mixed into the lubricant, so it is not defined as a different type of oil. The kinematic viscosity is measured at 40°C in accordance with JIS K 2283:2000 "Crude oil and petroleum products - Kinematic viscosity test method and viscosity index calculation method" (unit: mm²). 2 ( / s)

[0037] Dissimilar lubricants are, in principle, lubricants that were not used as lubricants for cold rolling (rolling lubricants). They may be liquid, such as mineral oil or ester oil, and may be semi-solid, such as grease, and may contain virtually no water. More specifically, examples of dissimilar lubricants include bearing lubricants for rolling mill rolls; hydraulic fluids for reduction cylinders; lubricants and rust-preventive oils that adhere to steel sheets in processes prior to cold rolling; and machine oils used in processes such as rolling, recovery, storage, and coating. The kinematic viscosity of these dissimilar lubricants is high, sometimes several hundred times that of lubricants.

[0038] Such dissimilar oils inevitably become mixed into lubricants that are recycled. Therefore, the inventors focused on and investigated how to neutralize foreign oils even if they are mixed into a lubricant. As a result, they found that foreign oils can be neutralized by adding a surfactant.

[0039] Surfactants typically have a hydrophilic portion and a lipophilic (hydrophobic) portion. Examples of surfactants include anionic surfactants such as sodium petroleum sulfonate salts; cationic surfactants such as benzalkonium-type quaternary ammonium salts; and nonionic surfactants such as polyoxyethylene, polyoxyethylene alkyl ethers, polyoxyethylene hydrogenated castor oil, and polyoxyethylene polyoxypropylene glycol.

[0040] Furthermore, in this embodiment, an antifoaming agent having both a hydrophilic and a lipophilic portion may be used as the surfactant, and an antifoaming agent with strong lipophilicity is preferred. Examples of such antifoaming agents include silicone-based antifoaming agents, polyether-based antifoaming agents, emulsion-based antifoaming agents, metal soap-based antifoaming agents, and amide wax-based antifoaming agents, and commercially available products may be used.

[0041] Examples of commercially available silicone-based defoamers include KS-530, KS-531, KF-6701, KS-66, FA-600, and KM-85 from Shin-Etsu Chemical Co., Ltd.; AquaLene SB-520, AquaLene SB-630, and Floren AO-5 from Kyoeisha Chemical Co., Ltd.; and SN Deformer 121N and SN Deformer 1315 from Sunopco Corporation.

[0042] Examples of commercially available polyether-based defoamers include Adekanol LG-109 and Adekanol LG-294 from ADEKA Corporation; and SN Deformer 157, SN Deformer 247, SN Deformer 375, SN Deformer 470, and SN Deformer 777 from Sunopco Corporation.

[0043] Examples of commercially available emulsion-type defoamers include Nopco KF-99, SN Deformer 381, SN Deformer 388N, and SN Deformer 419 from Sunopco; FC2901, FC2913, SILFOAM SRE, and SILFOAM SE47 from Asahi Kasei Wacker Silicone; KM-73, KM-71, and KM-7750 from Shin-Etsu Chemical Co., Ltd.; and 95 ANTIFOAM EMULSION, FS Antifoam 025, and AFE-1530 ANTIFOAM EMULSION from Dow Toray.

[0044] Examples of commercially available metal soap-based defoamers include Nopco DF-122, Nopco DF-122-NS, Nopco NDW, Nopco NXZ, SN Deformer 269, and SN Deformer 1010, all manufactured by Sunnopco.

[0045] Examples of commercially available amide wax-based defoamers include Nopco 267-A, Nopco DF-124-L, SN Deformer TP-39, SN Deformer 477T, SN Deformer 477-NS, SN Deformer 479, SN Deformer 1044, SN Deformer 1320, SN Deformer 1340, SN Deformer 1360, and SN Deformer 5100, all manufactured by Sunnopco.

[0046] Surfactants may be used individually or in combination of two or more types. In this embodiment, the surfactant is a different substance from the lubricant described above.

[0047] Next, we will explain the amount of surfactant to be added. The amount of surfactant added is, for example, 20% by mass or more relative to the concentration of the dissimilar oil in the lubricant. 50% by mass or more is preferred, 80% by mass or more is more preferred, and 100% by mass or more is even more preferred, because it provides a superior effect in neutralizing the dissimilar oil.

[0048] On the other hand, adding an excessive amount of surfactant will saturate the effect of neutralizing the foreign oils. Also, as mentioned above, when a soluble water-soluble lubricant (lubricant) is diluted with water, small oil droplets may be formed. However, if the amount of surfactant added is excessive, an emulsion may be formed between the foreign oils and the surfactant, making it impossible to maintain these oil droplets. For this reason, the amount of surfactant added should be, for example, 500% by mass or less, or even 300% by mass or less, relative to the concentration of the foreign oils in the lubricant.

[0049] Furthermore, if too much surfactant is added, the lubricating properties (rolling lubricity) of the lubricant may change. For this reason, from the viewpoint of maintaining good lubricity, it is preferable that the amount of surfactant added is less than or equal to the concentration of the soluble water-soluble lubricant (lubricant). The concentration of a soluble water-soluble lubricant (lubricant) refers to the concentration of the lubricant component (active ingredient) when diluted with water, and is, for example, 0.1 to 30.0% by mass, but may also be 1.5 to 20.0% by mass, or 3.5 to 10.0% by mass.

[0050] In the equipment group 11 shown in Figure 1, when adding a surfactant, first, the lubricant inside the tank 3 is collected using the drain 5 attached to the tank 3. Next, the concentration of different oil components in the collected lubricant is measured using a liquid chromatography apparatus 8. This measurement is carried out in accordance with, for example, JIS K 0124:2011 "General Rules for High-Performance Liquid Chromatography" and JIS K0136:2015 "General Rules for High-Performance Liquid Chromatography Mass Spectrometry". Subsequently, based on the measured concentrations of the different oils, an appropriate amount of surfactant is added to the lubricant inside tank 3 from the surfactant supply port 6 attached to tank 3.

[0051] The timing for sampling the lubricant and measuring the concentration of different oils (and then adding the surfactant) is not particularly limited, but from the viewpoint of continuously maintaining the effect of obtaining stainless steel sheets with excellent surface appearance, it is preferable to do so at least daily.

[0052] After the addition of the surfactant, it is preferable to stir the lubricant inside the tank 3 (the lubricant with the surfactant added) using the agitator 7 attached to the tank 3 before supplying it to the rolling mill 1 using the pump 4, because this provides a better effect in neutralizing the foreign oils.

[0053] The lubricant is diluted with water in tank 3 to an appropriate concentration before the start of cold rolling in rolling mill 1, for example, and is ready for circulation. A surfactant may also be added during this dilution process. [Examples]

[0054] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples described below.

[0055] <Cold rolling using lubricants> Using the equipment group 11 described in Figure 1, stainless steel sheets (steel plates S) were cold-rolled while circulating a soluble water-soluble lubricant (lubricant). For the steel plate S, we used SUS430 steel strip (plate thickness: 5 mm, plate width: 1000 mm, mass per coil: 20 tons) that had been hot-rolled and then pickled. Using rolling mill 1 (work roll diameter: 100 mm, work roll surface roughness Ra: 0.3 μm), cold rolling was performed on 10 coils under the following conditions, depending on the target plate thickness of 3 mm to 1 mm: number of rolling passes: 4 to 10 passes, reduction ratio per pass: 10 to 20%, rolling speed: 100 to 500 mpm. As a lubricant, a soluble water-soluble lubricant (Daido Chemical Co., Ltd.'s Diroll RS-012) was diluted with water to a concentration of 5.0% by mass (kinematic viscosity at 40°C: 0.8 mm²). 2 I used / s.

[0056] After each coil of cold rolling was completed, a sample of lubricant was taken from inside the tank 3 using the drain 5, and the concentrations of different lubricants were measured using a liquid chromatography apparatus 8. In Examples 1 to 6, surfactants were added in the amounts shown in Table 1 below, relative to the concentration of the different oils. A commercially available metal soap-based defoamer (SN Deformer 269, manufactured by Sunopco) was used as the surfactant. Subsequently, the remaining coils were cold-rolled in the same manner.

[0057] After adding the surfactant, in Examples 3 and 5 only, the lubricant inside Tank 3 (lubricant with added surfactant) was stirred using a stirrer 7. "Yes" is indicated in the "Stirring" column of Table 1 below if stirring was performed, and "No" is indicated if stirring was not performed.

[0058] On the other hand, in Comparative Example 1, no surfactant was added, and cold rolling was continuously performed for 10 coils.

[0059] <evaluation> Figure 2 is a schematic diagram showing an example of the surface of a steel sheet S after cold rolling. For each coil (steel sheet S) after cold rolling, a 1m square area in the center of the longitudinal direction (rolling direction RD) was visually observed. For some coils (steel sheets S), as shown in Figure 2, spotted patterns 21 and normal areas 22 without spotted patterns 21 were observed on the surface. The spotted patterns 21 were cloudy oval in shape, and their length (distance in the rolling direction RD) was several millimeters. The number of spotted patterns 21 with a length of 2 mm or more was measured, and this number was expressed as the number of spotted patterns (unit: pieces / m). 2 ) was calculated as follows. For each example and comparative example, 10 coils were measured in the same manner, and the average value was adopted as the number of spotted patterns. The results are shown in Table 1 below. The fewer the number of spot patterns, the better the surface appearance after cold rolling can be considered to be.

[0060] [Table 1]

[0061] <Summary of Evaluation Results> As shown in Table 1 above, it was found that Examples 1 to 6, in which surfactants were added, had fewer spot patterns and superior surface appearance after cold rolling compared to Comparative Example 1, in which no surfactants were added.

[0062] Comparing Examples 1, 2, 4, and 6, in which stirring was not performed after the addition of the surfactant, it was observed that as the amount of surfactant added increased, the number of spotted patterns decreased, and the surface appearance after cold rolling tended to be superior.

[0063] Furthermore, comparing Examples 2 and 3, which differ only in whether or not the mixture was stirred after the addition of the surfactant, it was found that Example 3, which was stirred, had fewer spot patterns and a superior surface appearance after cold rolling compared to Example 2, which was not stirred. This was also true in Examples 4 and 5, which differed only in whether or not the mixture was stirred after the addition of the surfactant.

[0064] Furthermore, when a commercially available antifoaming agent was used as the surfactant and the steel plate S was cold-rolled in the same manner as above while circulating the lubricant, the same results as above were obtained. [Explanation of Symbols]

[0065] 1: Rolling mill 2: Filtration equipment 3: Tank 4: Pump 5: Drain 6: Surfactant supply port 7: Agitator 8: Liquid chromatography apparatus 11: Equipment group 21: Spotted pattern 22: Normal part RD: Rolling direction S: Steel plate (stainless steel plate)

Claims

1. A method for cold rolling a stainless steel sheet using a soluble water-soluble lubricant containing a base oil (A), a fatty acid (B), an extreme pressure agent (C), a water-soluble polymer (D), and an amine (E), which is supplied to a rolling mill. The base oil (A) is at least one selected from the group consisting of refined mineral oil, natural oils and fats, and synthetic esters. The fatty acid (B) is at least one selected from the group consisting of monocarboxylic acids and dicarboxylic acids. The extreme pressure agent (C) is at least one selected from the group consisting of tricresyl phosphite, zinc dialkyldithiophosphate, sulfur esters, olefin polysulfides, and dialkyl polysulfides. The water-soluble polymer (D) is a polyalkylene glycol-based high molecular weight polymer having a weight-average molecular weight of 500 or more and less than 40,000. The amine (E) is at least one alkanolamine selected from the group consisting of monoethanolamine, diglycolamine, monoisopropanolamine, 2-amino-2-methylpropanol, 2-(sec-butylamino)ethanol, diethanolamine, diisopropanolamine, N-methylethanolamine, N-ethylethanolamine, triethanolamine, triisopropanolamine, and cyclohexylamine EO adducts. After the cold rolling, the soluble water-soluble lubricant is recovered. A surfactant is added to the aforementioned soluble water-soluble lubricant. A method for cold rolling a stainless steel sheet, comprising supplying the soluble water-soluble lubricant containing the surfactant to the rolling mill.

2. The cold rolling method for stainless steel sheets according to claim 1, wherein the amount of surfactant added is 20% by mass or more relative to the concentration of the dissimilar oil in the soluble water-soluble lubricant.

3. The method for cold rolling a stainless steel sheet according to claim 1, wherein the soluble water-soluble lubricant to which the surfactant has been added is stirred before being supplied to the rolling mill.

4. A method for producing a stainless steel sheet after cold rolling, using the method described in any one of claims 1 to 3.

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