JP2006161126A - Lubrication treated steel sheet having excellent chemical convertibility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubrication treated steel sheet having excellent adhesion and moldability, and having improved chemical convertibility, and to provide a treatment liquid for forming a lubrication film used for its production. <P>SOLUTION: A treatment liquid obtained by blending a lubricant composed of metal soap and wax in which the mass ratio of the metal soap/wax is 0.3 to 5.0, and a titania sol into a lithium silicate aqueous solution in which the atomic ratio of Li/Si is >0.5 is applied to the base material of a steel sheet, and drying is performed, so as to form a silicate based lubrication film comprising the lubricant and titania. The mass ratio of the lubricant/lithium silicate is 0.1 to 2.0, the mass ratio of the titania/lithium silicate is 0.001 to 0.1, and the total content of the lithium silicate, lubricant and titania in the lubrication film is 10 to 1,000 mg/m<SP>2</SP>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lubricated steel sheet, and more particularly to a lubricated steel sheet having excellent chemical conversion properties. Lubricated steel sheet according to the present invention is a hot-rolled steel sheet and a cold-rolled steel sheet, both of which can be used as a base steel sheet, can ensure good chemical conversion treatment, and the base steel grade is a high-strength steel. Since good press formability and mold galling resistance can be exhibited, it can be used for automobile body structural parts and other various parts.

Regardless of whether it is a hot-rolled steel sheet or a cold-rolled steel sheet, recently, high-strength steel has been widely adopted in various applications for the purpose of increasing strength and / or reducing weight.
However, high-strength steel is inherently inadequate in formability, so it is common to take measures to increase the formability of the material itself, or to mold seizure when molding such difficult-to-process materials. Therefore, it is necessary to prevent seizure of such a mold.

  As a conventional means for improving moldability, there is a method of applying an organic lubricating film typified by mill bond on the surface. However, since the thickness of the lubricating film is large, the film is peeled off during press processing, and generation of press debris is inevitable, and there is a problem that the generated press causes surface contamination and surface defects after processing. In particular, precision machinery such as torque converter parts for automobiles has a problem that the occurrence of press debris, dirt, etc. after processing may cause internal machine malfunctions, which can reduce press debris and is a good possibility. There is a need for a lubrication treatment that can secure the properties.

In response to such problems, several proposals have been made to apply a lubrication treatment using lithium silicate which is an inorganic compound as a film component as follows.
For example, the lubricating film disclosed in Patent Document 1 and Patent Document 2 is a lithium silicate film to which an organic resin and a solid lubricant are added, and an organic resin is added for the purpose of improving the film forming property and corrosion resistance of the film. On the premise.

  Patent Document 3 discloses a lithium silicate film in which a wax having a high softening point and a wax having a low softening point are used in combination as a lubricant for the purpose of improving moldability, but the chemical conversion treatment property is taken into consideration. Absent.

Patent Document 4 discloses a lithium silicate film as a lubricated steel sheet having excellent chemical conversion properties, adhesiveness, and formability. More specifically, the lithium silicate is Li / Si (atomic ratio) = 0.4 to 0.7, and the total amount of lubricant / lithium silicate mass ratio is 0.1 to 2.0. Processability, adhesiveness, and moldability can be obtained.
Japanese Patent No. 2998790 Japanese Patent No. 2953654 Japanese Patent No. 2857899 JP 2002-307613 A

  User demands regarding the performance of steel sheets for automobile body panels tend to become increasingly severe. For example, the technique described in Patent Document 4 may be required to further improve the chemical conversion processability.

  The present invention provides a lubricated steel sheet that is excellent in adhesion and formability, and has improved chemical conversion treatment performance compared to the lubricated steel sheet disclosed in Patent Document 4, and a treatment liquid for forming a lubricating film used in the production thereof. This is the issue.

  As a result of investigations based on the technique described in Patent Document 4, the inventors of the present invention achieved excellent results by forming a lubricating film by further containing titania sol in a treatment liquid containing lithium silicate and a lubricant. It has been found that the chemical conversion property can be further remarkably improved while maintaining the adhesiveness and moldability.

  The present invention is a lubricated steel sheet provided with a lubricating film composed of lithium silicate, a lubricant, and titania. Lithium silicate has a Li / Si (atomic ratio) greater than 0.5. The amount of lubricant in the lubricant film is such that lubricant / lithium silicate (mass ratio) = 0.1 to 2.0, and the amount of titania is titania / lithium silicate (mass ratio) = 0.001 to 0.00. It is an amount that becomes 1.

  From another aspect, the present invention is a treatment solution for forming a lubricating film, in which lithium silicate, a lubricant, and a titania sol are blended. Lithium silicate has a Li / Si (atomic ratio) greater than 0.5. The amount of lubricant in the treatment liquid is such that lubricant / lithium silicate (mass ratio) = 0.1 to 2.0, and the amount of titania sol is titania / lithium silicate (mass ratio) = 0.001 to 0. The amount is .1.

The lubricant is composed of wax and metal soap, and preferably metal soap / wax (mass ratio) = 0.3 to 5.0. The total amount of lithium silicate, lubricant and titania in the lubricating film of the lubricated steel sheet is preferably 10 to 1000 mg / m ² .

  According to the present invention, a high-performance lubricated steel sheet that can be applied to body structural parts such as a body panel required at a high level of chemical conversion property, adhesiveness, and formability, and precision equipment such as a torque converter is obtained. be able to. In particular, high-strength steel, which is expected to expand its application as a steel material for automobiles in the future, can be given improved formability that can withstand more severe formability, and at the same time chemical conversion treatment at a higher level than before Therefore, the industrial contribution of the present invention is extremely high.

  The kind of base material steel plate of the lubricated steel plate of the present invention is not particularly limited. In addition to high-strength steel, when metal galling becomes a problem, it can be widely applied to steel plates such as general low-coal and extremely low-carbon soft steel. Further, it may be a hot rolled steel plate or a cold rolled steel plate. There are no particular restrictions on the use of the lubricated steel sheet as long as chemical conversion, press formability, and adhesiveness are required and the results can be satisfied.

  The base steel plate may be a zinc-based or aluminum-based plated steel plate, for example, an electrogalvanized steel plate. Moreover, the base material steel plate may be subjected to a chemical conversion treatment for improving the corrosion resistance in advance.

  The lubricating film used in the present invention contains lithium silicate (lithium silicate) as a film component, and a lubricant and titania are blended therein. This lubricating film preferably contains essentially no organic resin (film forming property) that is a film component such as an acrylic resin or a urethane resin, which is usually added to the lubricating film. Even when such an organic resin is contained, the content is preferably limited to a very small amount of, for example, 1% by mass or less based on the mass ratio with respect to lithium silicate. For example, when an organic resin of about 5% by mass with respect to lithium silicate is contained, the effect of improving the chemical conversion treatment by titania blending is not seen, and the chemical conversion treatment can be performed regardless of whether titania is contained or not. descend. In addition, press dust tends to be generated.

  Lithium silicate forms a strong glassy film composed of fine silicate dry gel particles by applying and drying an aqueous solution. Therefore, it is presumed that the skeleton of the lubricating film is substantially composed of lithium silicate and has a film structure containing a lubricant and titania. However, titania may form part of the skeleton of the film.

  Lithium silicate which is a film component of the lubricating film has a lithium amount with a Li / Si ratio (atomic ratio) of more than 0.5. Since the film | membrane is easy to be removed by alkali degreasing, the one where Li / Si ratio is high improves chemical conversion treatment property. When particularly excellent chemical conversion properties are required, Li / Si is preferably 0.8 or more.

  If the Li / Si ratio exceeds 0.7, separation and precipitation may occur in the processing solution during storage, but the lubricant is applied by forcibly suspending the precipitated components by means such as vigorous stirring. May be formed. However, if the Li / Si ratio exceeds 4.0, the lubricity may be lowered. Therefore, the Li / Si ratio is preferably 4.0 or less.

  The Li / Si ratio of lithium silicate can be adjusted by using a combination of commercially available lithium silicates having different molar ratios, or by adding a silicate colloid or lithium hydroxide as necessary.

  Addition of a lubricant is effective for ensuring press formability. In the present invention, it is preferable to use a wax and a metal soap in combination as a lubricant. By using the metal soap in combination with waxes, it is possible to ensure good lubricity in a wide temperature range.

  Examples of the wax include polyethylene wax, carnauba wax, paraffin wax, and Teflon (registered trademark) wax. Since the silicate is water-soluble, a water-soluble wax having good dispersibility is preferable. Specifically, water-dispersible polyethylene wax, water-soluble Teflon (registered trademark) wax, or a mixed solution thereof can be used. The melting point of the wax is preferably higher than the drying temperature after coating when forming the lubricating film.

  Examples of the metal soap that can be used in the present invention include stearates, oleates, laurates, dodecylbenzenesulfonates, etc. Among them, zinc stearate is preferred.

  The addition amount of the lubricant (the total addition amount when the wax and the metal soap are used together as described above) is lubricant / lithium silicate (mass ratio) = 0.1 to 2.0, preferably 0.5 to 1. The amount is .5. When the amount is within this range, the workability and chemical conversion property of the lubricated steel sheet are improved, and adhesion can be ensured. If the mass ratio of the lubricant exceeds 2.0, the moldability improving effect is saturated, or conversely, the moldability tends to deteriorate with the weakening of the film, and the adhesiveness also deteriorates as described later. On the other hand, if the mass ratio of the lubricant is less than 0.1, the moldability becomes insufficient.

  According to a preferred embodiment of the present invention, when metal soap and wax are used together as a lubricant, the mass ratio of metal soap / wax is 0.3 to ensure lubricity at high temperature when emphasizing mold galling resistance. It is preferable to be in the range of 5.0, preferably 0.5 to 3.0.

  As described above, the adhesiveness can be ensured by adopting the silicate film as described above. The mechanism for improving the adhesiveness of the silicate film is thought to be because the adhesive surface and the silanol group react with each other to improve the adhesive force because the film surface has a large amount of silanol groups (Si-OH groups). . On the other hand, the wax applied as a lubricant is very inert and therefore basically does not react with the adhesive. Therefore, when a large amount of wax is added to the silicate film, silanol groups present on the surface of the lubricating film are reduced, and there is a problem that adhesiveness is deteriorated. Since the metal soap used in combination with the wax in the present invention is not as bad in compatibility with the adhesive as the wax, the addition of the metal soap is also effective from the viewpoint of suppressing adhesive deterioration.

  Accordingly, if the total amount of lubricant added is too large, the film becomes brittle and the interface peeling of the adhesive tends to occur in the lubricant film. From the viewpoint of adhesion, the amount of lubricant added is / Mass ratio of silicate to 2.0 or less. In order to ensure adhesion, the metal soap / wax ratio is preferably increased to 0.3 or more.

  Regarding chemical conversion treatment, lithium silicate is preferable among silicate films, and lithium silicate having a Li / Si ratio of more than 0.5 is particularly preferable. Further, as described above, the lubricant and titania have a great influence on the chemical conversion treatment.

  When the content of the lubricant is increased, the chemical conversion treatment property is improved. That is, the amount of silicate in the lubricating film is relatively reduced and the amount of silicate in contact with the steel sheet is reduced, so that the removability at the time of alkaline degreasing is improved. At that time, if the amount of the metal soap used as the lubricant is increased, the chemical conversion crystals become dense and the chemical conversion treatment property is further improved. Although the mechanism is not necessarily clear, it is presumed that uniform chemical crystals are likely to grow because chemical crystals are likely to grow starting from sites where metal soap is adsorbed on the steel plate. Therefore, also from the viewpoint of ensuring chemical conversion properties, the total amount of the lubricant in the present invention should be 0.1 or more in terms of mass ratio to silicate, and the metal soap / wax mass ratio should be increased to 0.3 or more. preferable.

  Furthermore, chemical conversion property improves greatly by containing titania. The mechanism is considered to be the same mechanism as the metal soap described above, but the effect of titania is greater than that of metal soap, and it is effective for improving chemical conversion treatment even with a small amount of addition compared to metal soap. work. The amount of titania is titania / lithium silicate (mass ratio) = 0.001 or more. Even if it is too much, the chemical conversion treatment improving effect is saturated, so the titania / lithium silicate mass ratio is set to 0.1 or less. A preferred range for the titania / lithium silicate mass ratio is 0.005 to 0.05.

  In order to contain titania in the film, it is preferable to contain titania sol in the treatment liquid as described later. That is, titania is preferably derived from titania sol (fine titania having an average primary particle size of colloidal level (several nm to several hundreds nm)).

  The lubricating film may further contain additional components other than those described above. Examples of such additional components include polyacrylic acid and nonionic surfactants that function as moldability improvers. In addition, a dispersing agent, an antifoaming agent, and a coloring agent for coloring the film may be contained in the lubricating film. The amount of such an additional component is preferably kept as small as possible (at most, 10% by mass or less based on lithium silicate).

The lubricating film may be provided on only one side of the base steel plate or on both sides. It is preferable that the adhesion amount of the lubricating film (the adhesion amount per one surface when the film is formed on both surfaces of the steel sheet) is such that the total amount of lithium silicate, lubricant, and titania is in the range of 10 to 1000 mg / m ^2. A more preferable range is 100 to 500 mg / m ² . If the adhesion amount is less than 10 mg / m ² , it is difficult to ensure moldability as high as a lubricating rust preventive oil, and if it exceeds 1000 mg / m ² , the lubricating film is too thick, and in the evaluation of adhesion, The problem of cohesive failure occurs and the film removal by alkali degreasing is insufficient with respect to the chemical conversion treatment property. If the adhesion amount is 100 mg / m ² or more, it is possible to ensure excellent formability over a mill bond that is excellent in formability, and if it is 500 mg / m ² or less, it is possible to ensure chemical conversion processability equivalent to that of a cold-rolled steel sheet. More preferred.

Next, the lubricating film forming treatment liquid according to the present invention will be described.
This lubricating film forming treatment liquid is composed of a solvent in which lithium silicate, a lubricant, and a titania sol are blended. When an additional component is used, it is also contained in the treatment liquid. The solvent is preferably water, but a water-miscible organic solvent such as alcohol may be used in combination with water. In principle, each blending component may be blended so as to obtain a desired film.

  This treatment liquid is prepared, for example, by preparing an aqueous solution of lithium silicate, adding lithium hydroxide or silicate colloid as necessary to adjust the Li / Si ratio of the lithium silicate, and then lubricating (preferably wax and metal soap). Can be dispersed and further mixed with titania sol. The order of addition of the components can be changed.

A lubricating film can be formed (that is, the lubricated steel sheet of the present invention can be produced) by applying the treatment liquid thus prepared to the steel sheet surface and drying it.
The treatment liquid may be applied by any method capable of forming a predetermined amount of the lubricating film. Specific application methods include a shower ringer method in which a treatment liquid is sprayed and squeezed to a predetermined amount with a roll, and a roll coating method in which coating is performed with a roll. In addition, a spin coat method, a dipping method, etc. are also possible. Drying after application can be carried out by any method as long as the film is dried. For example, it can be handled by hot air drying, and other drying means such as leaving it at room temperature or heating in a dryer can also be adopted.

  Next, the reason why the configuration of the lubricating film in the lubricated steel sheet of the present invention is determined as described above will be described more specifically with experimental data. In the following description, the amount of lithium silicate coating means the amount of adhesion of only lithium silicate, not the amount of adhesion of the entire coating. Further,% is% by mass unless otherwise specified. Further, the amount of titania sol in the figure is a mass ratio (titania / lithium silicate mass ratio) to lithium silicate as a titania solid content.

The lubricant used in the following tests is a water dispersible polyethylene wax and a metal soap zinc stearate.
(Chemical conversion processability)
Chemical conversion property was evaluated by the film removal rate (film removal rate) of the lubricating film in alkaline degreasing. The higher the film removal property, the better the chemical conversion film is formed. Based on this chemical conversion property, the Li / Si ratio of lithium silicate was determined.

Forming a silicate film (lithium silicate film amount = 200 mg / m ² ) in which the Li / Si ratio in lithium silicate is changed on the surface of JSC270D (sheet thickness = 0.8 mm) for automotive cold rolled steel sheet in accordance with the Japan Iron and Steel Federation standard A lubricated steel sheet was prepared.

  The treatment liquid used contained polyacrylic acid as a moldability improver in an aqueous solution of lithium silicate in an amount of 5% by mass with respect to the solid content in the liquid, and the pH was 11. No lubricant was included. Even when this treatment solution was allowed to stand, no separation or precipitation of silicate was observed. The treatment liquid was applied to the steel plate by a spin coater method and dried with warm air (maximum ultimate plate temperature of 50 ° C.) to form a lubricating film.

The lubricated steel sheet was subjected to alkaline degreasing under the following conditions:
Degreasing agent: FC-4420 (Nihon Parkerizing Co., Ltd.), concentration = 18 g / L,
Degreasing temperature: 40 ° C
Degreasing time: 3 minutes immersion.

After immersion degreasing under the above conditions, the film removal rate of the lubricating film by alkali degreasing was determined from the amount of Si before and after degreasing (Si intensity in fluorescent X-rays) according to the following formula.
Film removal rate = (Si strength before degreasing−Si strength after degreasing) / (Si strength before degreasing)
The result is shown in FIG. When the Li amount of the lithium silicate film is 0.4 or more in the Li / Si ratio, about 3/4 or more of the film, and when the Li / Si ratio exceeds 0.5, almost all of the film can be removed. It was possible to secure a good film removal property. This tendency was not different even when titania sol was added to the treatment liquid, and the same results as in FIG. 1 were obtained.

(Formability)
The blending amount of metal soap and wax was examined based on moldability.
Using the same JSC270D cold rolled steel sheet (thickness = 0.8 mm) as above, changing the total amount of lubricant and titania sol (titania / lithium silicate mass ratio) added to the lithium silicate aqueous solution with Li / Si ratio = 1.0. A lubricating film was formed using the treated liquid. The application and drying methods are the same as above.

Lithium silicate coating amount: 150 mg / m ²
Lubricant: zinc stearate / polyethylene wax mass ratio = 1
Titania / lithium silicate mass ratio = 0, 0.001 or 0.1.

This lubricated steel sheet was subjected to a cylindrical deep drawing test after applying ² g / m ² of general rust preventive oil (Nox-Rust 550HN: manufactured by Parka Kosan Co., Ltd.). The cylindrical deep drawing test conditions were as shown in FIG.

As comparative examples, on the same cold-rolled steel sheet, Preton R860 (oil coating amount = 2 g / m ² , manufactured by Sugimura Chemical Co., Ltd.) was applied as a highly lubricious rust preventive oil, and MC560J (coating amount = 1. Those subjected to ² g / m ² (manufactured by NOF Corporation) were also evaluated by the same cylindrical deep drawing test.

Admission decision:
The lubricity was judged by the molding limit wrinkle suppression pressure. It was considered to be acceptable if it was equivalent to or better than high-lubricating rust preventive oil (Preton R860), and equivalent to or better than Millbond (MC560J).

  The results are shown in FIG. If the total lubricant content is 0.1 or more in terms of the total lubricant / silicate mass ratio, it is equivalent to or better than high-lubricating rust preventive oil. It can be seen that the sex can be secured. On the other hand, when the mass ratio exceeds 1.5, the moldability starts to deteriorate, and when it exceeds 2.0, a tendency that the moldability is inferior to the mill bond can be confirmed. Further, even when titania sol was added so that the titania / lithium silicate mass ratio was 0.001 or 0.1, the molding limit wrinkle holding pressure was not changed.

Next, the influence of the blending ratio of metal soap and wax was examined by measuring the dynamic friction coefficient.
Using the same JSC270D cold-rolled steel sheet (thickness = 0.8 mm) as in the above-described degreasing evaluation, using a treatment liquid based on lithium silicate with a Li / Si ratio = 1.0, zinc stearate as a lubricant And the blending ratio of water dispersible wax was changed. Other processing conditions were as follows, and the formation of the lubricating film was performed in the same manner as described above. Titania was added as a titania sol.

Lithium silicate coating amount: 200 mg / m ²
Lubricant: total amount 200 mg / m ² (total amount of lubricant / lithium silicate mass ratio = 1),
Titania / lithium silicate mass ratio: 0 or 0.1
On the formed lubricating film, general rust preventive oil (Nox-Rust 550HN: manufactured by Parka Kosan Co., Ltd.) 2 g / m ² was applied.

  The evaluation was carried out by a Bowden test (adhesion slip tester) in which galling is likely to occur in an extremely high surface pressure state. Under severer pressing conditions, the heat generated by processing increases the mold and material temperature, and mold galling is more likely to occur.To simulate this situation, the Bowden test is performed at room temperature. In addition to the above, the case where the plate temperature was set to 150 ° C. was also carried out. Detailed test conditions of the Bowden test are shown in FIG.

As a comparative material, as described above, high-lubricating rust preventive oil (Preton R860) and mill bond (MC560J) were simultaneously evaluated.
Admission decision:
The acceptance / rejection determination was made with the coefficient of friction when reciprocating 30 times. As a judgment criterion at that time, a coefficient of friction (= 0.19) or less of a highly lubricious rust preventive oil at room temperature is acceptable, and a coefficient of friction (≧ 0.07) equal to or greater than that of mill bond is suitable. .

  The results are shown in FIG. 5 (test results at room temperature) and FIG. 6 (test results at 150 ° C.). From FIG. 5, as for the lubricity at room temperature, the higher the wax ratio, the better the lubricity. As the zinc stearate ratio increased, the lubricity decreased and mold galling was likely to occur. When the mass ratio of zinc stearate / wax is ≦ 5.0, the lubricity equal to or higher than that of the highly lubricating rust preventive oil can be secured, and when the mass ratio is 3.0 or less, the lubricity is further improved and superior to the mill bond. High lubricity was obtained.

  From FIG. 6, as for the lubricity at high temperature (= 150 ° C.), contrary to the above, the lubricity improved remarkably as zinc stearate was added to the wax. A zinc stearate / wax mass ratio ≧ 0.3 was required to ensure a friction coefficient ≦ 0.19 equivalent to that of a highly lubricious rust preventive oil at room temperature. When the mass ratio was in the range of 0.5 to 3.0, very excellent lubricity was obtained even at high temperatures.

Although the lubricity at high temperature was considerably lowered even when the mill bond was applied, the preferred blend ratio of the metal soap / wax in the present invention can ensure extremely excellent lubricity at high temperature, and therefore, mold galling resistance, It was found that excellent lubricity superior to that of the mill bond was obtained. In any case, addition of titania sol did not affect the lubricity.

(Adhesiveness)
By using the same JSC270D cold-rolled steel sheet (plate thickness = 0.8 mm) as described above, and using a treatment liquid based on lithium silicate with a Li / Si ratio = 1.0, the total amount of lubricant was changed. The effect of the amount of lubricant on the adhesion was examined by an adhesion test. Other processing conditions were as follows, and the formation of the lubricating film was performed in the same manner as described above.

Lithium silicate coating amount: 150 mg / m ²
Lubricant: zinc stearate / polyethylene wax mass ratio = 1
Titania sol / lithium silicate: 0.1
On the formed lubricating film, general rust preventive oil (Nox-Rust 550HN: manufactured by Parka Kosan Co., Ltd.) 2 g / m ² was applied.

  The adhesion test was carried out using PV5306 (Henkel Hakusui Co., Ltd.), which is an epoxy-based structural adhesive, under the conditions shown in FIG. 7, and the adhesion was evaluated based on the shear tensile strength after this adhesion. At that time, there may be a problem of compatibility with rust preventive oil, so apply rust preventive oil, stack it at room temperature, take a curing period of 7 days, and then adhere to make it adherent. Tested.

As comparative examples, Preton R860 (oil amount = 2 g / m ² manufactured by Sugimura Chemical Co., Ltd.), a highly lubricious rust preventive oil, and MC560J manufactured by Millbond (application amount = 1.2 g / m ² , manufactured by Nippon Oil & Fats Co., Ltd.) were applied. The thing was also used for the adhesion test.

Admission decision:
The acceptance / rejection judgment was made based on the adhesive strength, which is the tensile strength by the shear tensile test. As a criterion, a region where an adhesive strength equal to or higher than a mill bond, which may cause a problem of lowering adhesive strength with a structural adhesive, can be secured is determined to be acceptable. Moreover, the area | region which can ensure the adhesiveness equivalent to or more than what apply | coated the high-lubricity rust preventive oil was judged to be suitable.

  The test results are shown in FIG. In FIG. 3 which is the moldability evaluation result, even if the total amount of the lubricant is large, good cylindrical deep drawing formability higher than that of the high-lubricating rust preventive oil can be secured, but from FIG. 8, the total amount of the lubricant is large. Then, it turns out that adhesive strength falls and it becomes difficult to ensure favorable adhesiveness. That is, when the mass ratio of the lubricant / lithium silicate exceeds 2.0, the adhesive strength is lower than that of a mill bond that causes a problem in adhesiveness, and the adhesiveness is deteriorated. Further, in the evaluation of formability (FIG. 3), the formability equal to or better than that of the mill bond was ensured. When this mass ratio was in the range of 0.5 to 1.5, from FIG. It can be seen that an adhesive strength equal to or higher than that of rust oil can be ensured and is in a suitable range.

  In this adhesion test, the non-treated material coated only with general rust preventive oil on cold-rolled steel sheet has the best adhesion, and the high lubricity rust preventive oil is slightly inferior, but Milbond is coated with rust preventive oil. Compared to the above, the adhesive strength is greatly reduced, and it can be seen that the adhesion evaluation by this test can simulate the current adhesion problem well.

  Assuming an automobile body panel, in addition to the epoxy-based structural adhesive used in this example, there are mastic type adhesives with low adhesive strength such as a high rust preventive spot sealer. For lubricated steel sheets, it was also confirmed that these mastic adhesives can ensure good adhesion.

  As shown in Table 1, various lithium silicate aqueous solutions having different amounts of Li (Li / Si ratio) were prepared, and a water-dispersible polyethylene wax having a melting point of 60 ° C. (abbreviated as PE in Table 1) as a wax. Zinc stearate (abbreviated as St-Zn in Table 1) was added and dissolved or dispersed as a metal soap, and titania sol was added and mixed to prepare a lubricating film forming treatment liquid.

  This treatment liquid is roll-coated on one surface of a predetermined steel sheet selected for each test so that a predetermined amount of lubricating film adhesion amount (total amount of lithium silicate, lubricant, and titania solid content of titania sol) is obtained. Drying (maximum reached plate temperature = 50 ° C.) was performed to form a lubricating film.

As a comparative material, MC560J (coated amount = 1.2 g / m ² ) of Millbond and a silicate-based lubricating film for comparison were also used for evaluation. The comparative silicate-based lubricating film had the same film structure as above (No. 1, 5) except that no titania sol was added.

These various types of lubricated steel plates were tested for chemical conversion treatment, press formability, mold galling resistance, press haze resistance, and adhesion evaluation in the following manner.
(Chemical conversion processability)
JSC590R (sheet thickness = 1.0 mm), which is a 590 MPa class high yield ratio cold rolled steel sheet of the Japan Iron and Steel Federation standard, was used as a processing original plate, and after various lubrication treatments, it was subjected to chemical conversion treatment. The reason why high-strength steel is used in this test is that high-strength steel sheets are originally inferior in chemical conversion properties compared to general mild steel.

  After the immersion degreasing using the alkaline degreasing liquid FC-E2001 (manufactured by Nihon Parkerizing Co., Ltd.) on the test piece of the lubricated steel plate, the zinc phosphate chemical conversion treatment liquid PB-WL35 (manufactured by Nihon Parkerizing Co., Ltd.) is used. Chemical conversion treatment was performed under specified conditions. In addition to appearance observation, the formed chemical conversion film was observed for the microscopic scale state of the phosphate crystal by SEM observation (magnification × 500 times) to determine the scale generation area ratio.

Judgment criteria: Ske generation area ratio by SEM observation ◎: 0%
○: 1 to 5%
Δ: 5 to 10%,
X:> 10%.

(Press formability)
Used as the Japan Iron and Steel Federation processing original sheet to JSC270D (thickness = 0.8 mm) is a mild steel plate of standards, (after treatment, the general anti-rust oil 2 g / ^{m 2} oiling) Various lubricating treatment After performing the aforementioned The same cylindrical deep drawing test (see FIG. 2) was performed. The evaluation criteria are as follows, as described above.

Criteria: Molding limit wrinkle suppression pressure ◎ +: ≧ 425 kN
A: ≧ 375 kN (mill bond or more),
○: 150 to 375 kN (high lubricity rust preventive oil or more),
X: <150 kN.

(Type galling resistance)
Used as a process master plate JSH440W the (thickness = 3.2 mm) is 490MPa grade general purpose hot-rolled steel sheet of the Japan Iron and Steel Federation Standards, various lubricating processing (2 g / ^{m 2} oiling generally rust-preventive oil after processing) performed Later, a die squeeze test was performed by bending the crank press. The processing conditions and the evaluation method at that time are as shown in FIG. 9 and the following, and the normal film remaining rate in the tenth sample after the continuous ten-sheet molding with the ironing rate = 15% (the normal part remaining in FIG. 9) The galling resistance was evaluated based on the rate and display.

As a judgment standard, a mill bond (MC560J, coating amount = 1.2 g / m ² ) having good mold galling resistance has a normal film residual ratio = 75% indicated under the same conditions. The one that did not cause galling was taken as the best.

Processing conditions:
Sample size: 25x150mm,
Clearance: 2.72 mm (ironing rate = 15%),
Number of moldings: 10 continuous
Judgment criteria: normal film remaining rate ◎: 100%,
○: 75 to 100%
X: 75% or less.

  In addition, by observing the appearance of the side wall, which is the sliding part in this test, the state of occurrence of press debris at the sliding part was evaluated. According to the mold galling test, the lubricating film rubs and peels off, and the film builds up on the mold and reattaches to the steel plate, so that the press debris reattaches to the mold galling part, and the part turns black. When debris could be removed by steam degreasing, it was judged that there was no problem.

Judgment criteria: Side wall appearance observation ◎: No blackening occurred due to press residue,
○: Blackening occurs due to press residue, but blackening can be removed by degreasing.
×: Blackening occurs due to press residue and cannot be removed by degreasing.

(Adhesiveness)
Used as the Japan Iron and Steel Federation processing original sheet to JSC270D (thickness = 0.8 mm) is a mild steel plate of standard (generally rust-preventive oil after treatment 2 g / ^{m 2} oiling) various lubricated after the same as above An adhesion test (see FIG. 7) was performed. The evaluation criteria are as follows, as described above.

Judgment criteria: Adhesive strength A: ≧ 4.0 kN (high lubricity anti-rust oil),
○: 3.5 to 4.0 kN (mill bond or more),
X: <3.5 kN.

  In the above tests, both ◎ and ○ are acceptable. These test results are shown together in Table 1 together with the components and composition of the treatment liquid for forming the lubricating film and the amount of the lubricating film (total amount of lithium silicate, wax, metal soap, and titania solids).

  As can be seen from the results in Table 1, Example No. In comparison with silicate-based lubricating coatings containing no titania of 1 and 5, 2-4 and no. In the silicate-based lubricating film containing 6 to 12 titania, the chemical conversion treatment was remarkably improved. As can be seen from the comparison with the same Li / Si ratio, the addition of titania sol to the treatment liquid has no adverse effect on the moldability and adhesiveness, and the chemical conversion processability is maintained while maintaining excellent moldability and adhesiveness. It turns out that it can improve to the same level as a mill bond.

The influence of degreasing by alkali degreasing and the amount of lithium in lithium silicate is shown. It is a schematic diagram of the productivity evaluation method by cylindrical deep drawing. It is a graph which shows the influence of the total amount of lubricants on the limit wrinkle suppression pressure. It is a schematic diagram of the galling resistance evaluation method by a Bowden test. It is a graph which shows the influence of the metal soap and the wax compounding ratio on the friction coefficient in the galling resistance evaluation by the Bowden test at room temperature. It is a graph which shows the influence of the metal soap and the wax compounding ratio on a friction coefficient by the galling resistance evaluation by the Bowden test at 150 ° C. It is a schematic diagram of an adhesiveness (structural adhesive) evaluation test method. It is a graph which shows the influence of the lubricant total amount which has on adhesive strength. It is a schematic diagram which shows the evaluation test method and its measuring method of mold-proof galling resistance.

Claims (7)

  A lubricated steel sheet having a lubricating film composed of lithium silicate, a lubricant, and titania, wherein Li / Si (atomic ratio) of lithium silicate is more than 0.5, and the amount of lubricant in the lubricating film is Lubricant / lithium silicate (mass ratio) = 0.1 to 2.0, and titania amount is titania / lithium silicate (mass ratio) = 0.001 to 0.1. Lubricated steel sheet, characterized.   The lubricated steel sheet according to claim 1, wherein the lubricant comprises a wax and a metal soap, and the metal soap / wax (mass ratio) is 0.3 to 5.0. Lubricated steel sheet according to claim 1 or 2 lithium silicates in the lubricating layer, the total amount of lubricant and titania is 10 to 1000 mg / ^{m 2.}   The lubricated steel sheet according to any one of claims 1 to 3, wherein the lubricating film contains essentially no organic resin as a film component.   A treatment liquid for forming a lubricating film in which lithium silicate, a lubricant and titania sol are blended, wherein Li / Si (atomic ratio) of lithium silicate is more than 0.5, and the amount of lubricant in the treatment liquid is a lubricant. / Lithium silicate (mass ratio) = 0.1 to 2.0, and the amount of titania sol is titania / lithium silicate (mass ratio) = 0.001 to 0.1. A treatment liquid for forming a lubricating film.   The treatment liquid for forming a lubricating film according to claim 5, wherein the lubricant comprises a wax and a metal soap, and the metal soap / wax (mass ratio) is 0.3 to 5.0.   The treatment liquid for forming a lubricating film according to claim 5 or 6, which essentially does not contain an organic resin as a film component.

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