KR102612323B1 - Steel sheet with lubricating film and method of manufacturing the same - Google Patents

Abstract

In order to provide a steel sheet with excellent press formability and a lubricating film with excellent film removal and adhesion properties, sodium salts and potassium salts of fatty acids having a carbon atom number of 4 to 18 per molecule are applied to at least one side of the surface of the steel sheet. A steel sheet having a lubricating film containing at least one type of fatty acid salt selected from the following, wherein the adhesion amount of the fatty acid salt per side of the steel sheet is 0.20 g/m 2 or more and 3.00 g/m 2 or less.

Description

Steel sheet with lubricating film and method of manufacturing the same

The present invention relates to a steel sheet having a lubricating film and a method of manufacturing the same. The present invention particularly relates to a steel sheet having a lubricating film excellent in press formability and a method for manufacturing the same.

Cold-rolled steel sheets and hot-rolled steel sheets are widely used in a wide range of fields, mainly for automobile body applications, and in such applications, press forming is performed and provided for use. Additionally, in light of recent strengthening of CO ₂ emission regulations, the use rate of high-strength steel sheets tends to increase for the purpose of reducing vehicle body weight.

However, especially for high-strength steel sheets with a tensile strength (TS) exceeding 440 MPa, the surface pressure during press forming increases with the increase in strength, and the hardness of the steel sheet approaches that of the mold, so mold wear occurs. I have a task that is easy. In other words, during continuous press molding, mold wear is severe and the appearance of the molded product is damaged, which has a serious negative impact on the productivity of automobiles. In addition, since the elongation of such high-strength steel sheets tends to decrease as the strength increases, fracture of the steel sheets is likely to occur during press forming.

In addition, even for steel plates with relatively low strength, there is a need to enable more complex forming in order to integrate parts and improve design. As described above, further improvement in press formability is necessary.

A method of improving the press formability of cold-rolled steel sheets and hot-rolled steel sheets includes surface treatment of molds. Although surface treatment of a mold is a widely used method, there is a problem in this method that the mold cannot be adjusted after surface treatment is applied to the mold. Additionally, there is a problem of increased costs. Therefore, there is a strong demand to improve the press formability of the steel plate itself.

A method of improving the press formability of the steel sheet itself includes a technique of forming a lubricating film on the surface of the steel sheet.

For example, Patent Document 1 discloses a technique for forming a lubricating film on a steel sheet containing an alkali metal borate as a film forming component and a mixture of zinc stearate and wax as a lubricant.

Patent Document 2 discloses a technique for forming a lubricating film on a steel sheet, which is composed of lithium silicate as a film component and a lubricant made of wax and metal soap mixed with it.

Patent Document 3 describes high surface pressure processing in which a lubricating film containing a polyurethane resin containing a silanol group or a polyurethane resin containing a hydroxyl group among the chain extenders of the resin as a main component is formed on the surface of a steel sheet to a thickness of 1 to 15 μm. A lubricated steel sheet with excellent continuous formability is disclosed.

Patent Document 4 discloses a technique for forming an alkali-soluble organic film containing a lubricant added to an epoxy resin on a steel sheet.

In addition, in the field of cold forging, which is processed under particularly harsh conditions, it is better to form a zinc phosphate film as a lubricating film on the surface of the steel sheet and then perform bonderizing-bonder lube treatment, which involves applying sodium stearate. It is running normally.

Patent Document 1: Japanese Patent Laid-Open No. 2007-275706 Patent Document 2: Japanese Patent Laid-Open No. 2002-307613 Patent Document 3: Japanese Patent Laid-Open No. 2001-234119 Patent Document 4: Japanese Patent Laid-Open No. 2000-167981

However, since Patent Documents 1 and 2 contain wax or poorly soluble metal soap as a lubricant, although they are effective against wear resistance, film removal properties (removability by alkaline degreasing) are sometimes insufficient. As a result, there were cases where the components of the lubricant that were not removed by alkaline degreasing were brought into the painting process where zinc phosphate treatment etc. were performed, and when removed there, they contaminate the zinc phosphate treatment liquid and a normal paint film could not be obtained. Moreover, even if it was removed by alkaline degreasing, there were cases where solid components were mixed into the alkaline degreasing liquid, contaminating the alkaline degreasing liquid. Additionally, the techniques of Patent Documents 1 and 2 did not sufficiently satisfy the required characteristics regarding deep drawing and bulging forming.

Additionally, Patent Documents 3 and 4 used polyurethane resin or epoxy resin, and there were cases where the weldability and film removal properties were not sufficient. In addition, the bonderizing-bonder rube treatment involves an increase in cost due to an increase in the treatment process and problems with wastewater treatment, and is not suitable for press molding for automobile bodies. Since automotive steel sheets are used by welding/bonding, defilming (degreasing), chemical treatment, and electrodeposition coating after press forming, it is important not to interfere with these post-processes. In addition, automotive steel sheets are press formed and then assembled into the body by welding and bonding. However, if the adhesiveness is poor at this time, as in the case of poor weldability, it has a negative effect on the strength of the car body after body assembly. , excellent adhesion is required.

The present invention has been made in view of these circumstances, and its purpose is to provide a steel sheet with excellent press formability and a lubricating film with excellent film removal and adhesion properties.

In order to solve the above problems, the present inventors conducted various studies regarding the surface treatment of steel sheets. As a result, it was discovered that the above problem could be solved by forming a lubricating film containing a specific fatty acid salt on the surface of the steel sheet, and the present invention was completed. Additionally, it was found that particularly excellent lubricating performance is exhibited when the fatty acid salt molecules in the lubricating film are oriented in a specific direction.

That is, the gist of the present invention is as follows.

[1] On at least one side of the surface of the steel sheet, there is a lubricating film containing at least one fatty acid salt selected from the sodium and potassium salts of fatty acids having a carbon atom number of 4 to 18 per molecule, and the amount of the fatty acid salt per one side of the steel sheet is A steel plate with a lubricating film with an adhesion amount of 0.20 g/m2 or more and 3.00 g/m2 or less.

[2] The X _- ray diffraction peak intensity of the (001) plane among the X-ray diffraction peaks derived from fatty acid salts obtained when thin film The X-ray diffraction peak _intensity of the (110) plane of the α phase among the X-ray diffraction peaks of Fe obtained when performing thin film When, I _f /(I _s ·w) is 5 or more, a steel sheet with a lubricating film described in [1].

[3] The steel sheet having a lubricating film according to [2], wherein the fatty acid salt is sodium butyrate.

[4] In addition, the lubrication according to any one of [1] to [3], which is achieved by applying a rust preventive oil to the surface of the lubricating film, and the amount of the rust preventive oil applied per side of the steel sheet is 0.2 g/m2 or more and 3.0 g/m2 or less. A steel plate with a coating.

[5] A method for producing a steel sheet with a lubricating film according to any one of [1] to [4] above, comprising: at least one type of fat selected from sodium salts and potassium salts of fatty acids having 4 to 18 carbon atoms per molecule; A method of manufacturing a steel sheet with a lubricating film in which a solution containing an acid acid is applied to at least one side of a steel sheet and then dried to form a lubricating film on the surface of the steel sheet.

[6] The method for manufacturing a steel sheet with a lubricating film according to [5], wherein the solution is an alcohol solution, and the temperature of the alcohol solution is 50° C. or higher and the boiling point or lower of the alcohol solution.

[7] The steel sheet having a lubricating film according to [5] or [6], wherein the solution is an alcohol solution, and the temperature of the steel sheet when the alcohol solution is applied to the steel sheet is 50° C. or higher and is lower than the boiling point of the alcohol solution. Manufacturing method.

[8] The method for manufacturing a steel sheet with a lubricating film according to any one of [5] to [7], in which the solution is applied to the steel sheet and then the surface of the steel sheet is heated to 250°C or higher.

In addition, the steel sheet in the present invention includes hot rolled steel sheet and cold rolled steel sheet. In addition, the steel sheet having the lubricating film of the present invention is also called a “lubricated steel sheet.”

According to the present invention, a lubricated steel sheet that is excellent in press formability and also has excellent film removal properties and adhesion properties is obtained.

According to the present invention, the coefficient of friction between the lubricated steel sheet and the mold is significantly reduced. For this reason, in high-strength steel sheets where the surface pressure increases during press forming, sliding resistance is small in areas at risk of cracking during press forming, and lubrication has excellent press formability in areas where surface pressure is high and mold wear is expected to occur. A treated steel sheet is obtained. In addition, for steel sheets with relatively low strength that undergo complex forming, lubricated steel sheets with stable and excellent press formability can be obtained. In addition, since the lubricated steel sheet obtained by the present invention has excellent film removal properties, post-processes such as chemical conversion treatment and painting processes after film removal are not hindered. Additionally, because it has excellent adhesiveness, it can be applied to parts that are used by joining together with an adhesive.

1 is a schematic front view showing a friction coefficient measuring device.
Figure 2 is a schematic perspective view showing the shape and dimensions of the bead used in Condition 1 of Example.
Figure 3 is a schematic perspective view showing the shape and dimensions of the bead used in Condition 2 of Example.
Figure 4 is a schematic diagram showing evaluation criteria for evaluating the appearance after film formation.

Hereinafter, embodiments of the present invention will be described. Additionally, the present invention is not limited to the following embodiments.

The lubricated steel sheet of the present invention is characterized by having a lubricating film on the surface of the steel sheet as a base material containing at least one fatty acid salt selected from sodium and potassium salts of fatty acids having a carbon atom number of 4 to 18 per molecule. do. Hereinafter, in this specification, one or more types of fatty acid salts selected from the sodium salts and potassium salts of fatty acids having the number of carbon atoms per molecule from 4 to 18 are simply referred to as fatty acid salts.

The lubrication mechanism by fatty acid salts is considered as follows. During sliding, a high surface pressure is generated between the mold and the steel plate, lubricating oil is excluded, and a part in direct contact is created between the mold and the steel plate. Additionally, shear stress occurs on the surface of the steel sheet from the adhesion force caused by direct contact between the mold and the steel sheet. In this case, the fatty acid salt has an adhesion inhibitory effect that prevents direct contact between the mold and the steel plate. Additionally, when the fatty acid salt is encapsulated on a steel plate, the molecules are oriented and a lubricating film with a layer-like structure is formed. It is thought that this film structure further improves adhesion inhibition and improves lubricity.

It is believed that this effect makes it possible to have excellent press formability even under high surface pressure conditions during press forming of high-strength steel sheets or during complex forming of steel sheets with relatively low strength.

The number of carbon atoms in one fatty acid molecule of fatty acid salt is 4 to 18. When the number of carbon atoms of the fatty acid is less than 4, it is difficult to obtain a sufficient effect of improving sliding properties, that is, improving press formability. On the other hand, if the number of carbon atoms of the fatty acid exceeds 18, the film removal property may deteriorate and the chemical treatment property, which is important in automobile manufacturing, may decrease. Additionally, the solubility in solvents decreases, making encapsulation difficult. The number of carbon atoms of the fatty acid is preferably 7 or more. Additionally, the number of carbon atoms of the fatty acid is preferably 16 or less, and more preferably 12 or less.

The adhesion amount of fatty acid salts on one side of the steel plate shall be 0.20 g/m2 or more and 3.00 g/m2 or less. If it is less than 0.20 g/m2, sufficient press formability cannot be obtained. On the other hand, when it exceeds 3.00 g/m2, adhesiveness may deteriorate. The adhesion amount of fatty acid salt on one side of the steel plate is preferably 0.50 g/m2 or more. Additionally, the adhesion amount of fatty acid salt on one side of the steel plate is preferably 2.00 g/m2 or less.

Additionally, the amount of fatty acid salt attached can be analyzed by the following method.

The amount of fatty acid attached can be analyzed qualitatively and quantitatively by dissolving the lubricating film on the surface of the steel sheet with a solution of acetonitrile/water = 1/1 (volume ratio) and using liquid chromatography/tandem mass spectrometry (LC/MS/MS). . In advance, a calibration curve was prepared using an acetonitrile/water = 1/1 (volume ratio) solution containing an existing amount of lubricating film component (fatty acid salt), and the fatty acid salt in the solution dissolved as above was analyzed by LC/MS/ It is possible to quantitatively analyze the adhesion amount of lubricating film component (fatty acid salt) attached to the surface of the steel sheet by measuring by MS and using the calibration curve method.

In the present invention, the fatty acid salt is the sodium salt or potassium salt of the above-mentioned fatty acid, or both. In the case of metal salts other than sodium and potassium, they are insoluble in water, have poor film removal properties, and chemical treatment properties after film removal deteriorate.

The lubricating film may contain components other than fatty acid salts. However, from the viewpoint of further improving film removal properties, it is preferable not to contain components other than fatty acid salts. That is, it is preferable that the lubricating film is formed only from fatty acid salts. In this case, the solvent (water, alcohol, etc.) used when producing the lubricating film may remain in the lubricating film after drying.

The molecular orientation of fatty acid salts in the lubricating film can be evaluated by the following method.

By using an X-ray diffraction device and obtaining an . In addition, the value of the X-ray diffraction peak intensity was calculated by subtracting the background value from the measured X-ray peak intensity. Since the X-ray diffraction peak of the (001 ₎ plane is particularly strong for the fatty acid salt formed on the surface of the steel sheet, it is appropriate to use the However, the absolute value of the X-ray diffraction peak intensity changes depending on the measurement conditions and the amount of lubricating film adhered. Therefore, thin-film By measuring the diffraction peak intensity I _s and using the ratio I _f /I _s of I _f and I _s , the influence of measurement conditions was eliminated, making it possible to evaluate the influence of the molecular orientation of fatty acid salts. In addition, by using I _f /(I s ·w), which is I _f /(I _s ·w) divided by I f /I _s by the adhesion amount of lubricating film per unit area w (g/㎡), the influence of the adhesion amount of lubricating film is removed and the fat in the lubricating film is removed. It is possible to evaluate the molecular orientation of the acid salt. For the above reasons, in the present invention, I _f /(I _s ·w) was used as an index of the molecular orientation of fatty acid salts in the lubricating film.

In addition, as conditions for thin film X-ray diffraction measurement, a thin film X-ray diffraction device (RINT1500 manufactured by Rigaku, Cu ray source) is used to generate °, conditions for measuring at an incident angle of 0.5°.

In addition, if the removal of the lubricating film is confirmed by measuring the adhesion amount of the lubricating film, the method of removing the film is not particularly limited. For example, the steel sheet with the lubricating film is treated with an alkaline degreasing solution (FC-E6403, Nippon Packaging Co., Ltd.) It can be defilmed by immersing it in water (manufactured by Nihon Parkerizing Co., Ltd.) for 30 seconds and then washing it with pure water for 30 seconds. Additionally, the adhesion amount w (g/m 2 ) of the lubricating film per unit area can be obtained from the mass of the steel sheet before and after defilming and the adhesion area (covered area) of the lubricating film on the surface of the steel sheet.

A lubricating film containing a fatty acid salt with a carbon atom number of 4 to 18 has an adhesion inhibition effect that prevents direct contact between the mold and the steel plate. Therefore, by providing the lubricating film on the surface, a steel sheet with excellent press formability can be obtained regardless of the value of I _f /(I _s ·w), but when I _f /(I _s ·w) is 5 or more, As the interaction between fatty acid salt molecules in the lubricating film becomes stronger, the adhesion inhibition power becomes stronger, and even better press formability can be obtained. When I _f /(I _s ·w) is 10 or more, particularly excellent press formability can be obtained. In particular, among the fatty acid salts, sodium butyrate significantly improves lubricity by controlling the molecular orientation. The number of carbon atoms of sodium butyrate is 4, which is less than the preferred range of carbon atoms for the fatty acids described above. However, by controlling the molecular orientation in the lubricating film, press formability can be further improved.

Additionally, it is preferable to apply 0.2 g/m2 or more and 3.0 g/m2 or less of rust preventive oil to the surface (upper layer) of the lubricating film. While fatty acid sodium salts and fatty acid potassium salts have high water solubility and excellent film removal properties, there is a possibility that they may fall off if water droplets adhere to them due to condensation, etc. during storage or transportation. Therefore, by applying rust preventive oil to the surface of the lubricating film, the lubricating film is protected, water resistance is improved, and the lubricating film can be prevented from falling off during storage or transportation.

Next, the method of forming the lubricating film will be explained.

The lubricating film of the present invention can be formed by applying the solution of the fatty acid salt above to at least one side of a steel sheet and drying it. Examples of the fatty acid salt solution include an aqueous solution and an alcohol solution. Moreover, when drying, it is preferable to heat dry. Since stains (spots caused by coagulation of lubricating film components, etc.) are likely to occur during the drying process, it is preferable to dry within 5 seconds to suppress stains.

Additionally, as a method of improving stains on the lubricating film, it is preferable to use an alcohol solution of fatty acid salt. By dissolving the fatty acid salt in alcohol, applying this alcohol solution to at least one side of the steel sheet, and drying it, a more uniform lubricating film can be formed. The reason for this is that alcohol has a lower surface tension than water and can dissolve fatty acid salts, so it is thought that alcohol spreads uniformly on the surface of the steel sheet, thereby forming a uniform film after drying. Examples of the alcohol include methanol, ethanol, and propanol, but are not particularly limited to these.

In order to increase the solubility of fatty acid salts in alcohol, it is desirable to heat the alcohol solution to 50°C or higher. In the case of an alcohol solution, stains are less likely to occur during the drying process than an aqueous solution, but in order to create a more uniform film, it is preferable to dry within 5 seconds even when using an alcohol solution. Additionally, the heating temperature of the alcohol solution is preferably below the boiling point of the alcohol solution.

Additionally, the temperature of the steel sheet when applying the alcohol solution to the steel sheet may be 50°C or higher. By setting the temperature of the steel sheet at 50°C or higher when applying the alcohol solution to the steel sheet, it becomes easier to further suppress stains during the drying process. It is preferable that the temperature of the steel sheet when applying the alcohol solution to the steel sheet is below the boiling point of the alcohol solution.

The drying method is not particularly limited, but drying can be done by heating the steel sheet with IH (induction heating) or hot air.

In addition, after applying the solution of the fatty acid salt to the steel sheet, it is preferable to heat the surface of the steel sheet to 250°C or higher. By applying the solution to a steel sheet and then heating the surface of the steel sheet to 250°C or higher during or after drying, the fatty acid salt melts on the surface of the steel sheet, and when solidified, a lubricating film with high orientation of the fatty acid molecule can be obtained. This drying method is particularly preferably used when forming a film using sodium butyrate, which has a significant effect of improving lubricity by improving the orientation of fatty acid salt molecules. The heating temperature is more preferably 270°C or higher. The upper limit of the heating temperature is not particularly limited, but if heated above 300°C, the surface of the steel sheet may be oxidized and black spots may appear, thereby deteriorating the appearance. Therefore, the heating temperature is preferably 300°C or lower. Additionally, if the steel sheet is heated above 250°C when applying the fatty acid salt solution, the solvent evaporates at the same time as application, making it difficult to form a uniform lubricating film. Therefore, heating the surface of the steel sheet above 250°C is necessary. must be during or after drying.

Example

Hereinafter, the present invention will be explained by examples. Additionally, the present invention is not limited to the following examples.

Cold-rolled steel sheet A (TS: 270 MPa) with a sheet thickness of 0.8 mm and high-strength cold-rolled steel sheet B (TS: 590 MPa) with a sheet thickness of 1.2 mm were used, and the treatment solution (fatty acid salt solution) shown in Table 1 was applied with a bar coater. Afterwards, it was dried with a hot air dryer to form a lubricating film on the surface of the steel sheet. In addition, the drying temperature (steel plate surface temperature) during drying was as shown in Tables 2 and 3.

[Table 1]

For the lubricated steel sheet obtained as above, the amount of adhesion of the lubricating film component (fatty acid salt) on the surface of the steel sheet was measured. Additionally, as a method of evaluating press formability, friction coefficient was measured and sliding characteristics were evaluated. In addition, as a method of evaluating film removal, film removal by alkali was evaluated. In addition, water resistance, adhesion, molecular orientation of fatty acid salts in the lubricating film, and appearance of the film were also evaluated. The evaluation methods for fatty acid adhesion amount, press formability (sliding characteristics), film removal properties, film appearance, water resistance, adhesion, and molecular orientation are as follows.

(1) Analysis of lubricating film composition and fatty acid adhesion amount

Liquid chromatography/tandem mass spectrometry (LC/MS/MS) was used to measure the composition of the lubricating film formed on the steel plate and the amount of adhesion of fatty acid salts. A sample of a lubricated steel sheet taken at 30 mm ² was placed in a beaker, 40 mL of acetonitrile/water = 1/1 (volume ratio) was added, and ultrasonic extraction was performed for 30 minutes. This was repeated twice, and the solution adjusted to 100 mL was used for measurement. Then, the adhesion amount of the lubricating film component (fatty acid salt) (film adhesion amount in Tables 2 and 3) was determined from the calibration curve prepared in advance.

(2) Evaluation method for press formability (sliding properties)

In order to evaluate press formability, the friction coefficient μ of each specimen of the lubricated steel sheet was measured as follows.

1 is a schematic front view showing a friction coefficient measuring device. As shown in the same drawing, a sample 1 (hereinafter referred to as sample 1) for measuring the friction coefficient collected from a specimen is fixed to a sample stage 2, and the sample stage 2 is a slide that can be moved horizontally. It is fixed to the upper surface of the table (3). A slide table support 5 capable of moving up and down with a roller 4 in contact with the slide table 3 is provided on the lower surface of the slide table 3, and by pushing this up, the friction coefficient measurement sample 1 is moved by the bead 6. A first load cell (7) for measuring the pressing force N is attached to the slide table support (5). A second load cell (8) for measuring the sliding resistance force F for moving the slide table (3) in the horizontal direction while applying the pressing force is installed on the rail (9) at one end of the slide table (3). It is attached at the top. Additionally, as a lubricant, Freeton R352L, a press cleaning oil manufactured by SUGIMURA Chemical Industrial Co., Ltd., was applied to the surface of the sample 1 and the test was performed.

Figures 2 and 3 are schematic perspective views showing the shape and dimensions of the beads used. The lower surface of the bead (6) is slid while pressed firmly against the surface of the sample (1). The shape of the bead 6 shown in FIG. 2 has a width of 10 mm, a length of 5 mm in the sliding direction of the sample 1, and the lower portions of both ends in the sliding direction are composed of curved surfaces with a curvature of 1.0 mm R, and the sample 1 is pressed tightly. The lower surface of the bead has a flat surface with a width of 10 mm and a length in the sliding direction of 3 mm. The shape of the bead 6 shown in FIG. 3 has a width of 10 mm, a length of 59 mm in the sliding direction of the sample 1, and the lower portions of both ends in the sliding direction are composed of curved surfaces with a curvature of 4.5 mm R, and the sample 1 is pressed tightly. The lower surface has a flat surface with a width of 10 mm and a length in the sliding direction of 50 mm.

The friction coefficient measurement test was performed under the two conditions shown below.

[Condition 1]

The bead shown in FIG. 2 was used, the pressing load N was 400 kgf, and the sample pulling speed (horizontal moving speed of the slide table 3) was 100 cm/min.

[Condition 2]

The bead shown in FIG. 3 was used, the pressing load N was 400 kgf, and the sample pulling speed (horizontal moving speed of the slide table 3) was 20 cm/min.

The friction coefficient μ between the test material and the bead was calculated using the formula: μ=F/N. The smaller the friction coefficient μ, the better the press formability can be evaluated. Specifically, if the friction coefficient μ in Condition 1 was 0.120 or less, and the friction coefficient μ in Condition 2 was 0.140 or less, the press formability was said to be excellent and the evaluation was passed. Additionally, if the test passes the evaluation, it can be evaluated as having excellent press formability even under high surface pressure conditions or during complex molding. The friction coefficient μ in condition 1 is preferably 0.100 or less, and more preferably 0.090 or less. The friction coefficient μ in condition 2 is preferably 0.120 or less, and more preferably 0.110 or less.

(3) Method for evaluating membrane detachment

The film removal property was tested by immersing the test material in an alkaline degreasing solution (FC-E6403, manufactured by Japan Packaging Co., Ltd.) for 30 seconds and then washing it with pure water for 30 seconds. The lubricating film component (fatty acid salt) remaining on the surface of the steel sheet was tested. It was evaluated by the amount of adhesion (amount of film remaining). The smaller the amount of film remaining, the better the film removal properties can be evaluated.

(4) Appearance evaluation method

The appearance of the lubricating film was evaluated visually. Based on the appearance sample shown in Figure 4, a uniform lubricating film without spots (coagulated portions of lubricating film components) of 1 mm or more in diameter was evaluated as A, and a lubricating film with spots of 1 mm or more in diameter present was evaluated as B. It was evaluated as.

(5) Water resistance evaluation method

Water resistance was evaluated by immersing a test material coated with rust preventive oil on the surface at the amount shown in Table 3 in tap water for 30 seconds and then determining the amount of adhesion of the lubricating film component (fatty acid salt) remaining on the surface of the steel sheet (amount of film adhesion after immersion in water). did. Additionally, as a rust preventive oil, a test was performed using antirust P2000, a rust preventive oil manufactured by JXTG Energy Co., Ltd. When water resistance is good, the change in the amount of film adhesion before and after immersion in tap water is small.

(6) Adhesion evaluation method

Two test pieces were processed from a lubricated steel plate to a size of 100 After uniformly applying it to a thickness of 0.2 mm, it was overlapped and clipped together, baked at 180°C for 20 minutes, and dried and cured. After cooling, a shear tensile test was performed using an autograph tester and the shear adhesion was measured. Based on the case where a similar shear tensile test was performed using two steel plates (original plates) without a lubricating film, the adhesion is equivalent (90% or more) to ○ (evaluation passed, adhesion is excellent), and the adhesion is inferior. Those (less than 90%) were evaluated as × (failed evaluation, poor adhesion).

(7) Method for evaluating the molecular orientation of fatty acid salts in the lubricating film

To evaluate the molecular orientation of fatty acid salts in the lubricating film, two samples of lubricated steel sheets taken at 20 mm ² were used, and one was soaked in an alkaline degreasing solution (FC-E6403, manufactured by Japan Packaging Co., Ltd.) for 30 seconds. Immersion is performed, followed by washing with pure water for 30 seconds to defilm, and from the mass of the steel sheet before and after defilming and the adhesion area (covered area) of the lubricating film on the surface of the steel sheet, the adhesion amount of the lubricating film per unit area is w (g/m2). was obtained. Additionally, it was confirmed that the lubricating film was defilmed and used for the following measurements.

First, using a sample whose lubricating film has not been removed, a thin film X-ray diffraction device (RINT1500 manufactured by Rigaku, Cu ray source) is used to generate = An X-ray diffraction pattern was obtained by thin film X-ray diffraction measurement in the range of 2° to 50°, and the X-ray diffraction peak intensity I _f of the (001) plane among the fatty acid-derived Thin _- film

In addition, the value of the X-ray diffraction peak intensity was calculated by subtracting the background value from the measured X-ray diffraction peak intensity. It is said that the larger I _f /(I _s · _w ), which is the ratio of _{I f and} I _s divided by the adhesion amount of lubricating film per unit area w (g/㎡), the higher the molecular orientation of fatty acid salts in the lubricating film. Orientation was evaluated.

The results obtained above are shown in Tables 2 and 3. In addition, as a comparative example, a bonderizing-bonder rub treatment was performed using PB-181X (manufactured by Nippon Packaging Co., Ltd.) for the bonderizing treatment and LUB-235 (manufactured by Nippon Packaging Co., Ltd.) for the bonder lube treatment. The results (Nos. 46 and 47 in Table 2) are also shown.

[Table 2]

[Table 3]

From the results shown in Table 2, the following can be seen. Nos. 3 to 10, 12 to 24, 26 to 28, 31 to 33, 35 to 38, 41 to 45, and 48 to 51 are invention examples, and are excellent in press formability, and also excellent in film removal and adhesion. do. Nos. 37 and 38, which were coated with a sodium butyrate solution and dried above 250℃, have a drying temperature of less than 250℃, and I _f /(I _s ·w) compared to Nos. 12, 35, and 36, which have the same amount of film adhesion. The value of is large, the molecular orientation of the fatty acid salt is greatly improved, and the press formability is particularly excellent.

On the other hand, the comparative examples No. 1 and 39, which are original plates without a lubricating film, are inferior in press formability. Nos. 2, 11, and 40 are comparative examples in that the number of carbon atoms per molecule of the fatty acid salt is less than 4, and their press formability is poor. Nos. 25 and 30 are comparative examples in that the adhesion amount of the lubricating film component (film adhesion amount) is insufficient, and the press formability is inferior. For No.29 and 34, the film adhesion amount exceeds 3.00 g/m2 and the adhesiveness is poor. Nos. 46 and 47 are comparative examples in which the bonderizing-bonder rub treatment was performed, and it can be seen that although the lubricity is excellent, the film removal property is poor because the metal soap film does not remove the film, and the adhesiveness is also poor.

Additionally, the following can be seen from the results shown in Table 3. For Nos. 61 to 64, which are not coated with anti-rust oil, and Nos. 65 to 68, which are coated with 0.1 g/m2 of rust preventive oil, the adhesion amount of the lubricating film component after water immersion (film adhesion amount after water immersion) is significantly reduced from the original film adhesion amount. and its water resistance is poor. On the other hand, Nos. 69 to 84, to which 0.2 g/m2 or more of anti-rust oil is applied, have excellent water resistance.

Since the lubricated steel sheet of the present invention has excellent press formability, it can be applied in a wide range of fields, especially automobile body applications.

One; Sample 2 for friction coefficient measurement; sample stand
3; slide table 4; Roller
5; slide table support 6; bead
7; first load cell 8; 2nd load cell
9; rail N; pressing force
F; Sliding resistance (pull load)

Claims (8)

On at least one side of the surface of the steel sheet, there is a lubricating film containing at least one fatty acid salt selected from sodium salts and potassium salts of fatty acids having a carbon atom number of 4 to 18 per molecule,
The adhesion amount of the fatty acid salt per side of the steel plate is 0.20 g/m2 or more and 3.00 g/m2 or less,
The X-ray diffraction peak intensity of the (001) plane among the fatty acid salt _- derived X-ray diffraction peaks obtained when thin-film
The X-ray diffraction peak _intensity of the (110) plane of the α phase among the X-ray diffraction peaks of Fe obtained when thin-film
When the adhesion amount per unit area of the lubricating film is w (g/㎡),
A steel sheet with a lubricating film, wherein I _f /(I _s ·w) is 5 or more. According to claim 1,
A steel sheet with a lubricating film, wherein the fatty acid salt is sodium butyrate. According to claim 1,
In addition, it is achieved by applying rust preventive oil to the surface of the lubricating film,
A steel sheet with a lubricating film, wherein the amount of rust preventive oil applied per side of the steel sheet is 0.2 g/m2 or more and 3.0 g/m2 or less. According to claim 2,
In addition, it is achieved by applying rust preventive oil to the surface of the lubricating film,
A steel sheet with a lubricating film, wherein the amount of rust preventive oil applied per side of the steel sheet is 0.2 g/m2 or more and 3.0 g/m2 or less. A method for manufacturing a steel sheet having a lubricating film according to any one of claims 1 to 4, comprising:
A solution containing one or more types of fatty acid salts selected from the sodium and potassium salts of fatty acids having a number of carbon atoms per molecule of 4 to 18 is applied to at least one side of a steel sheet, and then the surface of the steel sheet is incubated at 250°C during or after drying. A method of manufacturing a steel sheet with a lubricating film, characterized by heating to the above temperature to form a lubricating film on the surface of the steel sheet. According to claim 5,
The solution is an alcohol solution, and the temperature of the alcohol solution is 50° C. or higher and the boiling point or lower of the alcohol solution. According to claim 5,
The solution is an alcohol solution, and the temperature of the steel sheet when the alcohol solution is applied to the steel sheet is 50° C. or higher and the boiling point or lower of the alcohol solution. According to claim 6,
The solution is an alcohol solution, and the temperature of the steel sheet when the alcohol solution is applied to the steel sheet is 50° C. or higher and the boiling point or lower of the alcohol solution.

Images