JP6933294B2 - Steel sheet with lubricating film and its manufacturing method - Google Patents

Description

The present invention relates to a steel sheet having a lubricating film and a method for producing the same. The present invention particularly relates to a steel sheet having a lubricating film having excellent press moldability and a method for producing 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, they are press-formed and used. _{In addition, from the viewpoint of tightening CO 2} emission regulations in recent years, the ratio of high-strength steel sheets used tends to increase for the purpose of reducing the weight of the vehicle body.

However, especially for high-strength steel sheets having a tensile strength (TS) of more than 440 MPa, the surface pressure during press forming increases as the strength increases, and the hardness of the steel sheet approaches the hardness of the die. It has a problem that galling is likely to occur. That is, the mold is severely worn during continuous press molding, and the appearance of the molded product is spoiled, which has a serious adverse effect on the productivity of automobiles. Further, in such a high-strength steel sheet, the elongation of the material tends to be inferior as the strength increases, so that the steel sheet is liable to break during press forming.

Further, even for a steel sheet having a relatively low strength, it is necessary to enable more complicated molding in order to integrate parts and improve the design. As described above, it is necessary to further improve the press moldability.

As a method for improving the press formability of cold-rolled steel sheets and hot-rolled steel sheets, surface treatment on dies can be mentioned. Although surface treatment on the mold is a widely used method, this method has a problem that the mold cannot be adjusted after the surface treatment is applied to the mold. Further, there is a problem that the cost becomes high. Therefore, it is strongly required to improve the press formability of the steel sheet itself.

As a method for improving the press formability of the steel sheet itself, there is 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 containing a mixture of alkali metal borate, which is a film-forming component, and zinc stearate and wax as a lubricant, on a steel sheet.

Patent Document 2 discloses a technique for forming a lubricating film formed on a steel sheet by using lithium silicate as a film component and blending it with a lubricant composed of wax and metal soap.

In Patent Document 3, a lubricating film containing a polyurethane resin containing a silanol group or a polyurethane resin containing a hydroxyl group as a main component in a chain extender of the resin is formed on the surface of a steel plate with a thickness of 1 to 15 μm. Further, a lubricated steel plate having excellent continuous formability by high surface pressure processing is disclosed.

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

Further, in the field of cold forging, which is processed under particularly harsh conditions, a zinc phosphate film is formed as a lubricating film on the surface of a steel sheet, and then a bonde bondarube treatment of sodium stearate is applied before processing. Is commonly done.

Japanese Unexamined Patent Publication No. 2007-275706 JP-A-2002-307613 Japanese Unexamined Patent Publication No. 2001-234119 Japanese Unexamined Patent Publication No. 2000-167981

However, in Patent Documents 1 and 2, since wax and a sparingly soluble metal soap are contained as a lubricant, it is effective for galling resistance, but the film removing property (removability by alkaline degreasing) may not be sufficient. there were. As a result, the components of the lubricant that were not removed by alkaline degreasing are brought into the painting process where zinc phosphate treatment or the like is applied, and when they are removed there, the zinc phosphate treatment liquid is contaminated, which is normal. In some cases, a good coating film could not be obtained. Further, even if it is removed by alkaline degreasing, the alkaline degreasing liquid may be contaminated by mixing solid components in the alkaline degreasing liquid. Further, the techniques of Patent Documents 1 and 2 do not sufficiently satisfy the required characteristics for deep drawing molding and overhang molding.

Further, Patent Documents 3 and 4 use polyurethane resin or epoxy resin, and there are cases where weldability and film removal property are not sufficient. Further, the bonde-bondarube treatment has problems such as cost increase due to an increase in the treatment process and waste liquid treatment, and is not suitable for press molding for automobile bodies. Since steel sheets for automobiles are used after being press-formed and then subjected to welding / adhesion, degreasing (degreasing), chemical conversion treatment, and electrodeposition coating, it is at the same time important not to interfere with such post-processes. Further, in the steel sheet for automobiles, the body is assembled by welding and adhesion after press forming. At this time, if the adhesiveness is inferior, the strength of the vehicle body after the body is assembled is adversely affected as in the case where the weldability is inferior. Therefore, it is required to have excellent adhesiveness.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a steel sheet having a lubricating film having excellent press moldability, film removal property, and adhesiveness.

The present inventors have conducted various studies on the surface treatment of steel sheets in order to solve the above problems. As a result, they have found that the above problems can be solved by forming a lubricating film containing a specific fatty acid salt on the surface of the steel sheet, and have completed the present invention. Furthermore, it has been found that when the fatty acid salt molecules in the lubricating film are oriented in a specific direction, they exhibit particularly excellent lubrication performance.

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

[1] A lubricating film containing one or more fatty acid salts selected from sodium salts and potassium salts of fatty acids having 4 or more and 18 or less carbon atoms in one molecule is provided on at least one surface of the steel plate surface.
A steel sheet having a lubricating film in which the amount of the fatty acid salt adhered to one side of the steel sheet is 0.20 g / m ² or more and 3.00 g / m ^{2 or less.}
[2] Among the X-ray diffraction peaks derived from fatty acid salts obtained when thin film X-ray diffraction measurement is performed on the lubricating film, the X-ray diffraction peak intensity of the (001) plane is defined as _If .
The lubricating layer of the steel sheet after film removal of Fe obtained when performing the thin film X-ray diffraction measurement of the α-phase of the X-ray diffraction peak (110) of the X-ray diffraction peak intensity of the plane I _s,
When the amount of adhesion per unit area of the lubricating film is w (g / m ² ),
_{I f / (I s · w} ) is 5 or more, a steel sheet having a lubricating coating according to [1].
[3] The steel sheet having the lubricating film according to [2], wherein the fatty acid salt is sodium butyrate.
[4] Further, a rust preventive oil is applied to the surface of the lubricating film.
The steel sheet having the lubricating film according to any one of [1] to [3], wherein the amount of the rust preventive oil applied per one side of the steel sheet is 0.2 g / m ² or more and 3.0 g / m ^{2 or less.}
[5] The method for producing a steel sheet having the lubricating film according to any one of [1] to [4] above.
A solution containing at least one fatty acid salt selected from sodium salts and potassium salts of fatty acids having 4 or more and 18 or less carbon atoms in one molecule is applied to at least one side of the steel plate, dried, and dried. A method for manufacturing a steel plate having a lubricating film, which forms a lubricating film on the surface of the steel plate.
[6] The method for producing a steel sheet having 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 lower than the boiling point of the alcohol solution.
[7] In [5] or [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 lower than the boiling point of the alcohol solution. A method for producing a steel sheet having the described lubricating film.
[8] The method for producing a steel sheet having a lubricating film according to any one of [5] to [7], wherein the solution is applied to the steel sheet and then the surface of the steel sheet is heated to 250 ° C. or higher.

The steel sheet in the present invention includes a hot-rolled steel sheet and a cold-rolled steel sheet. Further, the steel sheet having the lubricating film of the present invention is also referred to as "lubricated steel sheet".

According to the present invention, a lubricated steel sheet having excellent press moldability, film removal property, and adhesiveness can be obtained.

According to the present invention, the coefficient of friction between the lubricated steel sheet and the mold or the like is significantly reduced. For this reason, in a high-strength steel sheet in which the surface pressure during press forming increases, the sliding resistance at the crack-risk part during press forming is small, the surface pressure is high, and excellent press forming is expected at the part where mold galling is expected to occur. A lubricated steel sheet having properties can be obtained. Further, it is possible to obtain a lubricated steel plate having stable and excellent press formability with respect to a steel plate having a relatively low strength that is subjected to complicated molding. Further, since the lubricated steel sheet obtained by the present invention is excellent in film removal property, it does not interfere with post-processes such as chemical conversion treatment and coating process after film removal. In addition, since it has excellent adhesiveness, it can be applied to parts used by joining with an adhesive.

It is a schematic front view which shows the friction coefficient measuring apparatus. It is the schematic perspective view which shows the shape and the dimension of the bead used in the condition 1 of an Example. It is the schematic perspective view which shows the shape and the dimension of the bead used in the condition 2 of an Example. It is a schematic diagram which showed the evaluation standard for evaluating the appearance after film formation.

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

The lubricated steel plate of the present invention contains one or more fatty acid salts selected from sodium salts and potassium salts of fatty acids having 4 or more and 18 or less carbon atoms in one molecule on the surface of the steel plate as a base material. It is characterized by having a lubricating film. Hereinafter, in the present specification, one or more fatty acid salts selected from sodium salts and potassium salts of fatty acids having 4 or more and 18 or less carbon atoms in one molecule are also 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 eliminated, and a portion that directly contacts the mold and the steel plate is generated. Furthermore, shear stress is generated on the surface of the steel sheet due to the adhesive force due to the direct contact between the mold and the steel sheet. In such a case, the fatty acid salt has an adhesion suppressing force that suppresses direct contact between the mold and the steel sheet. Further, in the fatty acid salt, when the film is formed on the steel sheet, the molecules are oriented to form a lubricating film having a layered structure. It is considered that such a film structure further improves the adhesion suppressing force and improves the lubricity.

It is considered that such an effect makes it possible to have excellent press formability even under high surface pressure conditions during press forming of a high-strength steel sheet or during complex forming of a steel sheet having a relatively low strength.

The number of carbon atoms in one fatty acid molecule of a fatty acid salt is 4 or more and 18 or less. 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 characteristics, that is, an effect of improving press moldability. On the other hand, if the number of carbon atoms of the fatty acid exceeds 18, the demembrane property may be deteriorated, and the chemical conversion treatment property which is important in the manufacture of automobiles may be lowered. In addition, the solubility in a solvent is also lowered, which makes it difficult to form a film. The number of carbon atoms of the fatty acid is preferably 7 or more. The number of carbon atoms of the fatty acid is preferably 16 or less, more preferably 12 or less.

The amount of the fatty acid salt attached is 0.20 g / m ² or more and 3.00 g / m ² or less as the amount of adhesion on one side of the steel sheet. If it is less than 0.20 g / m ² , sufficient press moldability cannot be obtained. On the other hand, ^{if it exceeds 3.00 g / m 2} , the adhesiveness may deteriorate. The amount of the fatty acid salt attached is preferably ^{0.50 g / m 2} or more as the amount of adhesion on one side of the steel sheet. The amount of the fatty acid salt attached is preferably ^{2.00 g / m 2} or less as the amount of adhesion on one side of the steel sheet.

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

The amount of fatty acid salt adhered is qualitatively and quantitatively analyzed by a liquid chromatograph / tandem mass spectrometer (LC / MS / MS) after dissolving the lubricating film on the steel plate surface with an acetonitrile / water = 1/1 (volume ratio) solution. be able to. A calibration curve was prepared in advance using an acetonitrile / water = 1/1 (volume ratio) solution containing a known amount of lubricating film component (fatty acid salt), and the fatty acids in the solution dissolved as described above. The salt can be measured by LC / MS / MS and the amount of the lubricating film component (fatty acid salt) adhering to the surface of the steel plate can be quantitatively analyzed by the calibration curve method.

In the present invention, the fatty acid salt is a sodium salt, a potassium salt, or both of the fatty acids. In the case of metal salts other than sodium and potassium, they are insoluble in water and inferior in film removal property, and the chemical conversion treatment property after film removal is deteriorated.

The lubricating film may contain components other than the fatty acid salt. However, it is preferable not to contain any component other than the fatty acid salt from the viewpoint of further enhancing the demembrane property. That is, the lubricating film is preferably formed only of fatty acid salts. In this case, the solvent (water, alcohol, etc.) used for producing the lubricating film may remain in the lubricating film after drying.

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

By using an X-ray diffractometer and obtaining an X-ray diffraction pattern of the lubricating film on the surface of the steel plate by a thin film X-ray diffraction method, information on the crystal structure of the fatty acid salt in the lubricating film (molecular orientation of the fatty acid salt) can be obtained. be able to. As the value of the X-ray diffraction peak intensity, a value obtained by subtracting the background value from the measured X-ray peak intensity was used. Since the X-ray diffraction peak on the (001) plane can be obtained particularly strongly from the fatty acid salt formed on the surface of the steel plate, the X-ray diffraction peak intensity _If on the (001) plane is used as an evaluation index of the molecular orientation of the fatty acid salt. However, the absolute value of the X-ray diffraction peak intensity varies depending on the measurement conditions and the amount of the lubricating film adhered. Therefore, the thin film X-ray diffraction measurement of the steel plate from which the lubricating film has been removed is performed under the same conditions as the thin film X-ray diffraction measurement of the lubricating film, and the X-ray diffraction peak of Fe derived from the steel plate on the (110) plane of the α phase. measuring the X-ray diffraction peak intensity I _s, by using the ratio I _{f /} I _s of I _f and I _s, was it possible to assess the effect of molecular orientation of the fatty acid salt to remove the influence of the measuring conditions. Further, by using the adhesion amount of the lubricant film per unit area w a (g / ^{m 2)} at a _I f / _{I s} by dividing the _{I f / (I s · w} ) as an index, the effect of the adhesion of the lubricating film It can be removed to evaluate the molecular orientation of the fatty acid salt in the lubricating film. For these reasons, in the present invention, using the _{I f / (I s · w} ) as a molecular orientation of an indicator of the fatty acid salt in the lubricating film in.
As the conditions for thin film X-ray diffraction measurement, a thin film X-ray diffractometer (RIGaku RINT1500, Cu radiation source) is used to generate X-rays under the conditions of 50 kV and 250 mA, and 2θ = 2 ° for each measurement sample. Conditions for measuring with ~ 50 ° and an incident angle of 0.5 ° can be mentioned.
If the removal of the lubricating film is confirmed by measuring the amount of the lubricating film attached, the method of removing the film is not particularly limited. ), And then washed with pure water for 30 seconds to remove the film. Further, 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 the film removal and the adhesion area (covering area) of the lubricating film on the surface of the steel sheet.

The lubricating film containing a fatty acid salt having 4 or more and 18 or less carbon atoms has an adhesion suppressing force that suppresses direct contact between the mold and the steel sheet. Therefore, the lubricating film by providing the _surface, regardless of the value of _{/ I f (I s · w} ), although a steel sheet having excellent press formability is _{obtained, I f / (I s ·} w) is 5 In the above case, the adhesion suppressing power is further strengthened by strengthening the interaction between the molecules of the fatty acid salt in the lubricating film, and further excellent press moldability can be obtained. _{I f / (I s · w} ) If 10 or more, it is possible to obtain a particularly excellent press formability. In particular, among the fatty acid salts, sodium butyrate has a significantly improved lubricity by controlling the molecular orientation. Sodium butyrate has 4 carbon atoms, which is smaller than the preferable range of carbon atoms of the fatty acid described above, but the press formability is improved by controlling the molecular orientation in the lubricating film. Can be.

Further, it is preferable to apply rust preventive oil to the surface (upper layer) of the lubricating film at 0.2 g / m ² or more and 3.0 g / m ^{2 or less.} The fatty acid sodium salt and the fatty acid potassium salt are highly water-soluble and have excellent film-removing properties, but on the other hand, they may fall off when water droplets are formed due to dew condensation or the like during storage or transportation. Therefore, by applying rust preventive oil to the surface of the lubricating film, the lubricating film is protected, the water resistance is improved, and it is possible to prevent the lubricating film from falling off during storage or transportation.

Next, a method of forming the lubricating film will be described.

The lubricating film of the present invention can be formed by applying a solution of the fatty acid salt 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. Further, when drying, it is preferable to heat-dry. Since unevenness (spots formed by agglomeration of lubricating film components, etc.) is likely to occur in the drying process, it is preferable to dry within 5 seconds from the viewpoint of suppressing unevenness.

Further, as a method for improving the unevenness of the lubricating film, it is preferable to use an alcohol solution of a 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 considered to be that alcohol has a lower surface tension than water and can dissolve fatty acid salts, so that it spreads uniformly on the surface of the steel sheet to obtain a uniform film after drying. Examples of the alcohol include, but are not limited to, methanol, ethanol, propanol and the like.

In order to increase the solubility of the fatty acid salt in alcohol, it is preferable to heat the alcohol solution to 50 ° C. or higher. In the case of an alcohol solution, unevenness in the drying process is less likely to occur than in an aqueous solution, but in order to obtain a more uniform film, it is preferable to dry within 5 seconds even when an alcohol solution is used. The heating temperature of the alcohol solution is preferably equal to or lower than the boiling point of the alcohol solution.

Further, the temperature of the steel sheet when the alcohol solution is applied to the steel sheet may be set to 50 ° C. or higher. By setting the temperature of the steel sheet when the alcohol solution is applied to the steel sheet to 50 ° C. or higher, unevenness in the drying process can be more easily suppressed. The temperature of the steel sheet when the alcohol solution is applied to the steel sheet is preferably equal to or lower than the boiling point of the alcohol solution.

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

Further, it is preferable to heat the surface of the steel sheet to 250 ° C. or higher after applying the solution of the fatty acid salt to the steel sheet. After applying the solution to the steel sheet, the surface of the steel sheet is heated to 250 ° C. or higher during drying or after drying to melt the fatty acid salt on the surface of the steel sheet and form a lubricating film with high orientation of the fatty acid salt molecules when solidifying. Obtainable. This drying method is particularly preferable to be used when forming a film using sodium butyrate, which has a large 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 the heating temperature is preferably 300 ° C. or lower because the surface of the steel sheet may be oxidized and darkened to cause deterioration in appearance when heated above 300 ° C. If the steel sheet is heated to 250 ° C. or higher when the fatty acid salt solution is applied, the solvent evaporates at the same time as the application, making it difficult to form a uniform lubricating film. Therefore, the temperature should be 250 ° C. or higher. The surface of the steel sheet must be heated during or after drying.

Hereinafter, the present invention will be described with reference to Examples. The present invention is not limited to the following examples.

Using a cold-rolled steel sheet A (TS: 270 MPa) having a plate thickness of 0.8 mm and a high-strength cold-rolled steel sheet B (TS: 590 MPa) having a plate thickness of 1.2 mm, a bar of the treatment liquid (solution of fatty acid salt) shown in Table 1 was used. After coating with a coater, it was dried with a hot air dryer to form a lubricating film on the surface of the steel sheet. The drying temperature (steel plate surface temperature) at the time of drying was as shown in Tables 2 and 3.

The amount of the lubricating film component (fatty acid salt) adhered to the surface of the lubricated steel sheet obtained as described above was measured. In addition, the friction coefficient was measured as a method for evaluating the press formability, and the sliding characteristics were evaluated. Furthermore, as a method for evaluating the demembrane property, the demembrane property due to alkali was evaluated. In addition, water resistance, adhesiveness, molecular orientation of fatty acid salts in the lubricating film, and appearance of the film were also evaluated. The methods for evaluating the amount of fatty acid salt adhered, press moldability (sliding characteristics), film removal property, film appearance, water resistance, adhesiveness, and molecular orientation are as follows.

(1) Analysis of Lubricating Film Composition and Fatty Acid Salt Adhesion A liquid chromatograph / tandem mass spectrometer (LC / MS / MS) was used to measure the lubricating film composition and fatty acid salt adhesion formed on the steel plate. A sample of a lubricated steel sheet collected in a 30 mm square 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 a solution to a constant volume of 100 mL was used for the measurement. Then, the amount of adhesion of the lubricating film component (fatty acid salt) (the amount of film adhesion in Tables 2 and 3) was determined from the calibration curve prepared in advance.

(2) Evaluation method of press formability (sliding characteristics) In order to evaluate the press formability, the friction coefficient μ of each test material of the lubricated steel sheet was measured as follows.

FIG. 1 is a schematic front view showing a friction coefficient measuring device. As shown in the figure, the sample 1 for measuring the coefficient of friction (hereinafter referred to as sample 1) collected from the test material is fixed to the sample table 2, and the sample table 2 is fixed to the upper surface of the horizontally movable slide table 3. Has been done. A vertically movable slide table support 5 having a roller 4 in contact with the slide table 3 is provided on the lower surface of the slide table 3, and by pushing up the slide table support 5, the bead 6 presses the load N on the sample 1 for measuring the friction coefficient. The first load cell 7 for measuring the above is attached to the slide table support base 5. The 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 located above the rail 9 at one end of the slide table 3. It is installed. As a lubricating oil, Preton R352L, a cleaning oil for pressing manufactured by Sugimura Chemical Industrial Co., Ltd., was applied to the surface of Sample 1 for a test.

2 and 3 are schematic perspective views showing the shape and dimensions of the beads used. The lower surface of the bead 6 slides while being pressed against the surface of the sample 1. The shape of the bead 6 shown in FIG. 2 is 10 mm in width, 5 mm in length in the sliding direction of sample 1, and curved surfaces having a curvature of 1.0 mmR at both ends in the sliding direction, and the lower surface of the bead on which sample 1 is pressed has a width of 10 mm. It has a flat surface with a length of 3 mm in the sliding direction. 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, a curved surface having a curvature of 4.5 mmR at both ends in the sliding direction, and a width of 10 mm on the lower surface of the bead on which the sample 1 is pressed. It has a flat surface with a length of 50 mm in the sliding direction.

The friction coefficient measurement test was performed under the following two conditions.
[Condition 1]
Using the bead shown in FIG. 2, the pressing load N: 400 kgf and the sampling speed of the sample (horizontal moving speed of the slide table 3) were set to 100 cm / min.
[Condition 2]
Using the bead shown in FIG. 3, the pressing load N: 400 kgf and the sampling speed of the sample (horizontal moving speed of the slide table 3) were set to 20 cm / min.

The coefficient of friction μ between the test material and the bead was calculated by the formula: μ = F / N. It can be evaluated that the smaller the friction coefficient μ is, the better the press formability is. Specifically, a friction coefficient μ of 0.120 or less under condition 1 and a friction coefficient μ of 0.140 or less under condition 2 were evaluated as having excellent press formability and passed the evaluation. If the evaluation is passed in this test, it can be evaluated that the press formability is excellent even under high surface pressure conditions and complicated molding. The friction coefficient μ under condition 1 is preferably 0.100 or less, more preferably 0.090 or less. The friction coefficient μ under the condition 2 is preferably 0.120 or less, more preferably 0.110 or less.

(3) Evaluation method of film removal property For film removal property, the test material is immersed in an alkaline degreasing solution (FC-E6403, manufactured by Nippon Parkering Co., Ltd.) for 30 seconds, and then washed with pure water for 30 seconds. The evaluation was made based on the amount of the lubricating film component (fatty acid salt) remaining on the surface (residual amount of the film). It can be evaluated that the smaller the residual amount of the film, the better the film removal property.

(4) Appearance evaluation method The appearance of the lubricating film was visually evaluated. Based on the appearance sample shown in FIG. 4, a uniform lubricating film without spots having a diameter of 1 mm or more (a portion where the lubricating film components are aggregated) is evaluated as A, and a lubricating film having spots having a diameter of 1 mm or more is evaluated as B. evaluated.

(5) Evaluation method of water resistance Water resistance is a lubricating film component (fatty acid) that remains on the surface of a steel sheet after a test material in which rust preventive oil is applied to the surface in the coating amount shown in Table 3 is immersed in tap water for 30 seconds. It was evaluated by determining the amount of salt) adhering (the amount of film adhering after immersion in water). The test was conducted using the rust preventive oil Antilast P2000 manufactured by JXTG Energy Co., Ltd. as the rust preventive oil. When the water resistance is good, the change in the amount of film adhered before and after immersion in tap water is small.

(6) Adhesiveness evaluation method A test piece obtained by processing a lubricated steel sheet to a size of 100 x 25 mm is dipped in rust preventive oil and then leaned vertically for 24 hours to remove excess oil. An epoxy adhesive was uniformly applied to a 13 mm portion to a thickness of 0.2 mm, then overlapped with a clip, sandwiched, baked at 180 ° C. for 20 minutes, dried and cured. After cooling, a shear tensile test was performed with an autograph tester to measure the shear adhesive force. Based on the case where the same shear tensile test was performed using two steel plates (original plates) that did not form a lubricating film, the same adhesive strength (90% or more) was evaluated as ○ (passed evaluation, excellent adhesive strength). Inferior ones (less than 90%) were evaluated as x (evaluation failed, inferior adhesive strength).

(7) Method for evaluating the molecular orientation of the fatty acid salt in the lubricating film For the evaluation of the molecular orientation of the fatty acid salt in the lubricating film, two samples of lubricated steel sheets collected in a 20 mm square were used, and one was used. Immerse in an alkaline degreasing solution (FC-E6403, manufactured by Nippon Parkering Co., Ltd.) for 30 seconds, then wash with pure water for 30 seconds to remove the film, and the mass of the steel sheet before and after the film removal and the adhesion of the lubricating film on the surface of the steel sheet. From the area (covering area), the amount of adhesion w (g / m ² ) of the lubricating film per unit area was determined. In addition, it was confirmed that the lubricating film had been removed and used for the following measurements.
First, using a sample from which the lubricating film has not been removed, an X-ray is generated under the conditions of 50 kV and 250 mA using a thin film X-ray diffractometer (RIGaku RINT1500, Cu radiation source), and the incident angle is 0.5. As °, an X-ray diffraction pattern is obtained by thin film X-ray diffraction measurement in the range of 2θ = 2 ° to 50 °, and the X-ray diffraction peak intensity _If of the (001) plane of the X-ray diffraction peaks derived from the fatty acid salt is determined. Obtained. Perform a thin film X-ray diffraction measurement of a sample film removal the lubricating film in the same conditions to obtain an X-ray diffraction peak intensity I _s of α phase (110) plane of X-ray diffraction peak of Fe from the steel sheet.
As the value of the X-ray diffraction peak intensity, the value obtained by subtracting the background value from the measured X-ray diffraction peak intensity was used. Adhesion amount w (g / ^{m 2)} divided by _I f / _(I s · w) larger the fatty acid salt in the lubricating coating in the I _f and _{I s} ratio _I f / _{I s} the lubricating film per unit area The molecular orientation was evaluated as having a high molecular orientation.

The results obtained from the above are shown in Tables 2 and 3. Further, as a comparative example, the result of performing the bonde bondarube treatment using PB-181X (manufactured by Nippon Parkering Co., Ltd.) for the bonde treatment and LUB-235 (manufactured by Nippon Parkering Co., Ltd.) for the bonder lube treatment (Table). Nos. 46 and 47) in 2 are also shown.

The following can be seen from the results shown in Table 2. No. 3 to 10, 12 to 24, 26 to 28, 31 to 3, 35 to 38, 41 to 45, 48 to 51 are examples of inventions, which are excellent in press moldability, film removal property, and adhesiveness. .. No. 1 to which a sodium butyrate solution was applied and dried at 250 ° C. or higher. Nos. 37 and 38 have a drying temperature of less than 250 ° C. and have the same amount of film adhesion. The value of _{I f / (I s · w} ) compared to 12,35,36 molecular orientation of the large fatty acid salt has significantly improved press formability is particularly excellent.

On the other hand, No. 1 which is an original plate without a lubricating film. Comparative examples 1 and 39 are inferior in press moldability. No. 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 are inferior in press moldability. No. 25 and 30 are comparative examples in that the amount of the lubricating film component adhered (the amount of the film adhered) is insufficient, and is inferior in press moldability. No. 29 and 34 have a film adhesion amount ^{of more than 3.00 g / m 2} and are inferior in adhesiveness. No. Examples 46 and 47 are comparative examples in which the bonde-bondarube treatment was performed, and it can be seen that although the lubricity is excellent, the metal soap film does not remove the film, so the film removal property is inferior and the adhesiveness is also inferior. ..

In addition, the following can be seen from the results shown in Table 3. No. not coated with rust preventive oil. No. 61 to 64 and the amount of rust preventive oil applied was 0.1 g / m ^2. In 65 to 68, the amount of the lubricating film component adhered after immersion in water (the amount of film adhered after immersion in water) is significantly reduced from the original amount of film adhered, and the water resistance is inferior. On the other hand, ^{No. 1 coated with 0.2 g / m 2} or more of rust preventive oil. 69 to 84 have excellent water resistance.

Since the lubricated steel sheet of the present invention is excellent in press moldability, it can be applied in a wide range of fields mainly for automobile body applications.

1 Sample for friction coefficient measurement 2 Sample table 3 Slide table 4 Roller 5 Slide table support 6 Bead 7 1st load cell 8 2nd load cell 9 Rail N Pressing load F Sliding resistance (pulling load)

Claims (6)

A lubricating film containing one or more fatty acid salts selected from sodium salts and potassium salts of fatty acids having 4 or more and 18 or less carbon atoms in one molecule is provided on at least one surface of the steel plate surface.
Ri 3.00 g / ^{m 2} or less der deposition amount 0.20 g / ^{m 2} or more per steel sheet side of said fatty acid salt,
Of the X-ray diffraction peaks derived from fatty acid salts obtained when thin film X-ray diffraction measurement is performed on the lubricating film, the X-ray diffraction peak intensity of the (001) plane is defined as _If .
The lubricating layer of the steel sheet after film removal of Fe obtained when performing the thin film X-ray diffraction measurement of the α-phase of the X-ray diffraction peak (110) of the X-ray diffraction peak intensity of the plane I _s,
When the amount of adhesion per unit area of the lubricating film is w (g / m ² ),
_{I f / (I s · w} ) is 5 or more, a steel sheet having a lubricating coating. The steel sheet having the lubricating film according to claim 1 , wherein the fatty acid salt is sodium butyrate. Further, a rust preventive oil is applied to the surface of the lubricating film.
The steel sheet having the lubricating film according to claim 1 or 2 , wherein the coating amount of the rust preventive oil per one side of the steel sheet is 0.2 g / m ² or more and 3.0 g / m ^{2 or less.} The method for producing a steel sheet having the lubricating film according to any one of claims 1 to 3.
After applying a solution containing one or more fatty acid salts selected from sodium salt and potassium salt of fatty acids having 4 or more and 18 or less carbon atoms in one molecule to at least one side of the steel plate,
A method for producing a steel sheet having a lubricating film, in which the surface of the steel sheet is heated to 250 ° C. or higher during or after drying to form a lubricating film on the surface of the steel sheet. The method for producing a steel sheet having a lubricating film according to claim 4 , wherein the solution is an alcohol solution, and the temperature of the alcohol solution is 50 ° C. or higher and lower than the boiling point of the alcohol solution. The lubricating film according to claim 4 or 5 , 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 lower than the boiling point of the alcohol solution. Method of manufacturing steel sheet to have.

Images