JP2007275706A - Lubricant-coated steel sheet and treating liquid for filming lubricant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricant-coated high tensile steel sheet for hot rolled steel sheet and cold rolled steel sheet that is excellent in film removing property, chemical processability, adhesion, moldability, and can be broadly applied as vehicle steel materials. <P>SOLUTION: A lubricant coating where a lubricant including zinc stearate and wax is contained in a filming component including an alkali metal borate is formed on a surface of the steel sheet. It is preferable that solid content mass ratio of the lubricant and filming component is within a range of 0.1 to 2.0, and mass ratio of the zinc stearate and wax is within a range of 0.3 to 5.0. An amount of the lubricant coating adhered (the total mass of the alkali metal borate and lubricant) may be 10 to 1,000 mg/m<SP>2</SP>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lubricated steel sheet, in particular, a lubricated steel sheet excellent in film-removing property, and thus excellent in chemical conversion property, and a treatment liquid for forming a lubricating film used in the production thereof. The lubricated steel sheet according to the present invention can ensure stable film removal, chemical conversion, and adhesion, and can have good press formability and mold resistance, regardless of whether a hot-rolled steel sheet or a cold-rolled steel sheet is used as a base steel sheet. It can express galling.

Regardless of hot-rolled steel sheets and cold-rolled steel sheets, recently, high-strength steel has been widely adopted for various materials.
However, since the high-tensile steel sheet is not sufficiently formable from the beginning, seizure of the mold tends to occur when the high-tensile steel sheet is formed. Therefore, it is required to take measures to improve the formability of the steel sheet and to prevent seizure of the mold.

  As a means for improving the formability of the steel sheet, there is a method of applying an organic lubricating film typified by mill bond to the steel sheet surface. An organic lubricating film has a great effect of improving moldability, but since the thickness of the film is large, generation of press debris due to peeling of the film is inevitable during press working. The generated press dust has a problem that it contaminates the processed surface and causes surface defects. In particular, in precision equipment such as automotive torque converter parts, press residue, dirt, etc. remaining after processing cause internal machine operation failure. Therefore, there is a need for a steel plate lubrication treatment that can reduce press debris and ensure good potential.

In response to this demand, several proposals have been made regarding a lubrication treatment in which a lubricant film to which an inorganic material, particularly lithium silicate is applied, is formed on the steel sheet surface as follows.
For example, the lubricating film disclosed in Japanese Patent No. 2998790 (Patent Document 1) and Japanese Patent No. 2953654 (Patent Document 2) is a lithium silicate film to which an organic resin and a solid lubricant are added. In order to ensure the film-forming property and corrosion resistance of the film, the addition of an organic resin is a prerequisite.

  Japanese Patent No. 2857899 (Patent Document 3) discloses a lithium silicate film to which a solid lubricant is added. For the purpose of improving moldability, a concept of using both a high softening point wax and a low softening point wax is disclosed. However, since the surface of the film is substantially covered with wax having a low softening point (low melting point), the chemical conversion treatment property is poor.

  Japanese Patent Application Laid-Open No. 2002-307613 (Patent Document 4) discloses a lithium silicate film as a lubricated steel sheet having excellent chemical conversion properties, adhesiveness and formability. Specifically, the lithium content of the lithium silicate is Li / Si (atomic ratio) = 0.4 to 0.7, and the lubricant / lithium silicate mass ratio is 0.1 to 2.0. Good chemical conversion property, adhesiveness, and moldability can be obtained.

  JP 2000-309793 A (Patent Document 5) discloses a combination treatment of “inorganic salt + metal soap + wax” as an aqueous lubricant for plastic working of a metal material after chemical conversion treatment. The technology does not take into account film removal.

In JP-A-2004-99949 (Patent Document 6), the surface of the metal material for plastic working was selected from phosphate, sulfate, borate, silicate, molybdate and tungstate. After contacting at least one inorganic compound with an aqueous treatment liquid mainly composed of at least one lubricant selected from metal soap, wax, polytetrafluoroethylene, molybdenum disulfide and graphite, and drying, It is disclosed to form a two-layer lubricating film separated into a base layer mainly composed of the inorganic compound located on the interface side with the metal and a lubricant layer principally composed of the lubricant located on the surface side. .
Japanese Patent No. 2998790 Japanese Patent No. 2953654 Japanese Patent No. 2857899 JP 2002-307613 A JP 2000-309793 A Japanese Patent Laid-Open No. 2004-99949

  The object of the present invention is to ensure film removal properties, chemical conversion properties, adhesive properties, and moldability required for automotive steel materials to be coated after press molding, and is therefore applicable to vehicle body panels. It is to provide a lubricated steel sheet based on a hot-rolled steel sheet or a cold-rolled steel sheet.

  Unlike the plated steel sheet, the press formability is also important in the lubrication treatment of the hot-rolled steel sheet and the cold-rolled steel sheet, but rather, suppression of mold galling during pressing is a problem. In the future, as the application of high-strength steel sheets as automotive structural members expands, the suppression of mold galling is expected to become a greater problem.

  Accordingly, a further problem of the present invention is to ensure the film-removing property, chemical conversion property, and adhesiveness required as a steel sheet for a vehicle body panel, and particularly severe formability is required. Lubricating based on hot-rolled steel sheets and cold-rolled steel sheets, ensuring press formability and galling resistance that can withstand car body structural parts It is to provide a treated steel sheet.

  The conventional technology described in the above-mentioned patent document includes a lubrication film excellent in all of film removal property, chemical conversion treatment property, and adhesiveness in addition to lubricity that provides good press formability and mold galling resistance. There was no one with.

  For example, the lubricated steel sheet having a lithium silicate film described in Patent Document 4 can ensure good press forming with a small amount of lubricant film, so that generation of mold galling and press debris is suppressed and adhesion is excellent. However, it was still insufficient for chemical conversion treatment and film removal.

  Lubricated steel sheets for automobiles are often painted after press forming, and therefore, it is required to completely remove the lubricating film before chemical conversion treatment by alkali degreasing performed as pre-coating treatment. This is because the chemical film is difficult to adhere to the portion where the lubricating film remains, and therefore the coating is not applied, which causes uneven coating.

  The present inventors pay attention to the fact that the film-forming component is an inorganic compound, and especially the anti-molding resistance is better than the case where it is an organic compound. Of course, the lubricity is excellent, and the adhesiveness is excellent. A good lubricating film was investigated.

  As a result, when the film forming component is an alkali metal borate, by using a specific metal soap (zinc stearate) in combination with wax as a lubricant, it is significantly better than the conventional lithium silicate film. The present inventors have found that excellent film-removing properties can be obtained, and have reached the present invention.

  The present invention is a lubricated steel plate provided with a lubricating film containing a lubricant in a film forming component on the steel sheet surface, the film forming component is an alkali metal borate, and the lubricant is zinc stearate and A lubricated steel sheet, characterized in that it is a mixture with wax.

The solid mass ratio of the lubricant / film-forming component is preferably in the range of 0.1 to 2.0, and the mass ratio of zinc stearate / wax is preferably in the range of 0.3 to 5.0. Moreover, it is also preferable that the total amount of the film forming component and the lubricant is 10 to 1000 mg / m ² .

  From another aspect, the present invention contains a film-forming component comprising an alkali metal borate and a lubricant comprising zinc stearate and a wax, and the solid content mass ratio of the lubricant / film-forming component is 0. It is a treatment liquid for forming a lubricating film, which is in the range of 1 to 2.0, and the mass ratio of zinc stearate / wax is in the range of 0.3 to 5.0.

  This treatment liquid may further contain at least one component selected from polyacrylic acid and a nonionic surfactant. This component exhibits the effect of increasing the stability of the treatment liquid by acting as a dispersant in the treatment liquid. The pH of the treatment liquid is preferably in the range of 10-13.

  According to the present invention, by using an alkali metal borate instead of lithium silicate as an inorganic film forming component, excellent adhesiveness similar to that described in Patent Document 4 using lithium silicate, The film-removing property can be greatly improved while ensuring the lubricity and the mold resistance. As a result, even if the amount of adhesion is relatively large for improving lubricity, good film-removing properties and chemical conversion treatment properties necessary for wide application as steel for automobiles can be obtained, and die seizure can be prevented. At the same time, the chemical conversion property and the adhesiveness are further improved, so that the lubricated steel plate can be more suitably applied to automobiles.

  In particular, in high-tensile steels that are expected to expand in application as automotive steel materials in the future, it can withstand severer forming, and chemical conversion processability is an essential performance as automotive steel materials that were difficult to apply by conventional processing. In terms of securing adhesiveness, the industrial contribution of the present invention is extremely high.

  The base steel plate of the lubricated steel plate of the present invention is a steel plate of a wide range of steel types including not only high-strength steel but also general low-carbon, ultra-low-carbon soft steel, various alloy steels, etc. Can be selected according to required performance. The base steel plate may be either a hot rolled steel plate or a cold rolled steel plate. However, since the lubricated steel sheet of the present invention can impart excellent press formability, a particularly excellent formability improving effect can be obtained when a high-strength steel sheet that is difficult to press form is used as a base steel sheet.

  The use of the lubricated steel sheet of the present invention is intended for automobile structural materials such as an automobile body, but is not limited thereto, and the present invention can be applied to any steel sheet for press forming. In order to make use of the advantageous properties of the lubricated steel sheet of the present invention, applications requiring chemical conversion treatment, press formability, and adhesion are preferred. That is, it is an application in which an adhesive is used for bonding after press molding and further painting is performed. However, it can of course be used for applications where a joining method other than adhesion (eg, welding) is employed.

  The lubricated steel sheet of the present invention includes a lubricating film in which a lubricant is contained in a film forming component made of an alkali metal borate on the surface of a base steel sheet. The film forming component of the lubricating film does not substantially contain an organic resin such as an acrylic resin or a urethane resin that is contained as a film forming component in a conventional general lubricating film. That is, the film-forming component is substantially completely inorganic and consists essentially of alkali metal borate. However, if the amount is 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less of the film forming component based on the solid content, one or two of the other film forming components (organic or inorganic) are used. More than one species can coexist. Examples of alkali metal borates (hereinafter also simply referred to as borates) include potassium tetraborate and sodium tetraborate, but are not limited thereto.

  In order to ensure press formability, a lubricant is contained in the lubricating film. As a lubricant, a mixture of wax and metal soap is used. Many waxes have a relatively low melting point (melting point ≦ 130 ° C.), and the effect of improving moldability is particularly large in the temperature range from room temperature to the melting point of the wax. However, the lubricity at high temperatures (≧ 130 ° C.) at which die seizure during strong processing is likely to occur is insufficient. Such lubricity at high temperatures can be ensured by a metal soap. By using a metal soap and a wax together as a lubricant, it is possible to ensure a good lubricity and thus a moldability improving effect in a wide temperature range.

  A film composed of a combination of an alkali metal borate and a lubricant (metal soap + wax) exhibits high lubricating performance, especially high mold resistance, and forms a lubricating film with excellent adhesion, resulting in press debris generation Can be suppressed. In this case, it was found that when the metal soap used as the lubricant is zinc stearate, the film removal property of the lubricant film is remarkably improved as compared with the case where other metal soaps are used. As a result, for example, when a degreasing liquid having a reduced degreasing power such as a repeatedly used degreasing liquid is used, a good film-removing property is obtained. Turn into.

  Examples of the wax that can be used in the present invention include polyethylene wax, carnauba wax, paraffin wax, and wax. Since the silicate is water-soluble, a wax having good dispersibility or solubility in water is preferable. Specifically, water-dispersible polyethylene wax, Teflon (registered trademark) wax, or a mixture thereof can be preferably used.

  As the metal soap, zinc stearate is used as described above. However, other metal soaps may be used in combination as long as the amount is smaller than that of zinc stearate. When another metal soap is used in combination, the amount of the other metal soap is preferably 30% by mass or less, more preferably 10% by mass or less, based on the total metal soap.

  In addition to moldability, the lubricant affects chemical conversion properties and adhesiveness. Therefore, the amount of lubricant (total amount of wax and metal soap) is preferably such that the mass ratio of lubricant / film-forming component is 0.1 to 2.0, and this mass ratio is more preferably 0.5 to 1.5. When the amount of the lubricant is within this range, the formability and chemical conversion property of the lubricated steel plate are improved, and adhesion can be ensured. If the mass ratio exceeds 3.0, the moldability improving effect is saturated, or rather, the formability tends to deteriorate and the adhesiveness deteriorates with the weakening of the film. On the other hand, if the weight ratio is less than 0.1, the moldability becomes insufficient.

  The mass ratio of the metal soap / wax is preferably 0.3 to 5.0, more preferably 0.5 to 3.0. Within this range, the lubricity at high temperatures can be improved when emphasis is placed on mold resistance.

  Regarding the adhesiveness, even if the film forming component is an alkali metal borate, it is possible to ensure good adhesiveness as in the case of the silicate film. On the other hand, the wax used as a lubricant is very inert and basically does not react with the adhesive. Accordingly, when the lubricating film contains a large amount of wax, the adhesiveness deteriorates. On the other hand, metal soaps are not as bad as adhesives as waxes. Therefore, using metal soap as a lubricant in combination with wax is also effective in suppressing deterioration of adhesiveness.

  Regarding the influence of the lubricant on the chemical conversion property, if the amount of the lubricant added is increased, the film removal property is improved, and thus the chemical conversion property is improved. From the viewpoint of ensuring chemical conversion properties, it is preferable that the mass ratio of the lubricant / film forming component is 0.1 or more and the mass ratio of the metal soap / wax is 0.3 or more.

  In addition to the above-mentioned components, the lubricating film has at least one component selected from polyacrylic acid and a nonionic surfactant as a dispersant for the purpose of improving the stability of the treatment liquid and the moldability of the lubricating film. Furthermore, it is preferable to contain. The preferred dispersant is polyacrylic acid (PA), but conventional nonionic surfactants such as polyoxyethylene ethers such as polyoxyethylene lauryl ether (POLE) can also be used.

  When using a dispersant selected from polyacrylic acid and a nonionic surfactant, the amount of the dispersant in the lubricating film (and thus in the total solid content of the treatment liquid) is 0.1 to 5% by mass, preferably 0.5 to 2% by mass. If the content is less than 0.1% by mass, the intended effect cannot be obtained sufficiently. May have an effect.

  The lubricated steel sheet of the present invention is produced by applying a lubricating film forming treatment liquid containing the above-described components to the steel sheet surface and drying. That is, the lubricating film forming treatment liquid contains an alkali metal borate, a lubricant wax and zinc stearate, and optionally other components such as the dispersant. The total amount of lubricant is such that the mass ratio of lubricant / film-forming component is 0.1 to 2.0. The mass ratio of the zinc stearate / wax of the lubricant is preferably 0.3 to 5.0.

  The pH of the treatment liquid affects the liquid stability. In the present invention, the treatment solution pH is preferably 10-13. If the pH is less than 10, the solubility of the alkali metal borate is lowered and a precipitate is easily generated. If the pH is 13 or higher, the dispersion of the lubricant is lowered and the separation becomes easy.

  The treatment liquid for forming a lubricating film of the present invention includes, for example, adding polyacrylic acid and / or a nonionic surfactant (when used) to an aqueous solution of an alkali metal borate, and further adding a lubricant wax and a metal soap. It can be prepared by adding, stirring well, and dispersing the lubricant in the liquid.

The film amount of the lubricating treatment film (the total amount of the film forming component and the lubricant, that is, the total amount of alkali metal borate + wax + zinc stearate in the present invention) is in the range of 10 to 1000 mg / m ² . The more preferable range is 100 to 500 mg / m ² . When the adhesion amount is less than 10 mg / m ² , it becomes difficult to ensure moldability similar to that of a highly lubricating antirust oil. On the other hand, when the adhesion amount exceeds 1000 mg / m ² , the lubricating film becomes too thick and cohesive failure occurs in the film in the adhesion evaluation, and the film removal by alkali degreasing tends to be incomplete, and the chemical conversion The processability may deteriorate.

With regard to formability, if the adhesion amount of the lubricating film is 100 mg / m ² or more, the formability more than the mill bond excellent in formability can be secured, and if it is less than 500 mg / m ² , the chemical conversion treatment property equivalent to that of the cold-rolled steel sheet is obtained. It can be secured.

  The method of applying the treatment liquid is not particularly limited as long as a predetermined amount of lubricating film can be formed. Specific application methods include a shower ringer method in which a treatment liquid is sprayed and squeezed to a predetermined amount with a roll, a roll coating method in which coating is performed with a roll, and the like. In addition, as for drying after the treatment liquid, it is sufficient that the film is dried, and it can be handled by hot air drying, but it may be heated in a heating furnace.

  A wax, a metal soap, and a dispersant were added to an aqueous solution of potassium tetraborate serving as a film forming component, and the mixture was thoroughly stirred and dispersed uniformly to prepare a lubricating film forming treatment solution. For comparison, a lubricating film forming treatment solution was similarly prepared using an aqueous solution of lithium silicate having a Li / Si atomic ratio of 0.5 or 1.0 as a film forming component.

The composition of each treatment solution is summarized in Table 1. In the table, silicate means lithium silicate, and borate means potassium tetraborate (that is, alkali metal borate).
The waxes, metal soaps and dispersants used were as follows (in parentheses are symbols used in Table 1):
Wax: Water-soluble polyethylene wax (PE)
Metal soap: zinc stearate (St-Zn) or calcium stearate (St-Ca, for comparison)
Dispersant: polyacrylic acid (PA).

  This treatment liquid is roll-coated on one surface of a predetermined steel sheet for each test so that a predetermined amount of lubricating film adheres to the surface (amount based on the solid content of lithium silicate or alkali metal borate), and is dried with hot air ( (Plate temperature = 50 ° C.) to form a lubricating film.

As a comparative material, MC560J (coating amount = 1.2 g / m ² ) of Millbond was prepared and used for evaluation.
The formed lubricating film was evaluated for chemical conversion treatment, moldability, galling resistance, press-fogging resistance, and adhesion. The evaluation method and criteria are as follows. These test results are summarized in Table 2.

(Chemical conversion processability)
A 590 MPa class high yield ratio cold rolled steel sheet JSC590R (sheet thickness = 1.0 mm) of the Japan Iron and Steel Federation standard was used as a processing original sheet, and a lubricating film to be tested was formed on one side of the steel sheet, and then subjected to a chemical conversion treatment test. The reason for adopting high-strength steel in this test is that high-strength steel sheets are originally inferior in chemical conversion properties compared to general mild steel.

  The lubricated steel plate to be tested was degreased by immersing in FC-E2001 (manufactured by Nippon Parkerizing) adjusted to pH = 10 for 60 seconds, and then subjected to chemical conversion treatment under specified conditions using PB-WL35 (manufactured by Nippon Parkerizing). . The appearance of the formed chemical conversion film and the SEM observation (magnification: × 500 times) of the growth state of the conversion crystal were used to observe the micro-scale state of the crystal.

Judgment criteria: Skelet generation area ratio obtained by SEM is
A = less than 1%, O = 1-5%, Δ = 5-10%, x> 10%. In addition, in order to obtain a uniform coating appearance, the scale generation area ratio is required to be 0% (that is, evaluation is ◎).

(Press formability)
After using a mild steel plate JSC270D (plate thickness = 0.8 mm) of the Japan Iron and Steel Federation standard as a processing base plate, a lubricating film to be tested was formed on one side of this steel plate, and after applying 2 g / m ^{2 of} general rust preventive oil, The cylindrical deep drawing test was performed as shown in 1. The evaluation criteria are as follows.

Criteria: Molding limit wrinkle suppression pressure is
◎ + ≧ 425 kN, ◎ ≧ 375 kN (more than mill bond), ○ = 150 to 375 kN (more than high-lubricating rust preventive oil), x <150 kN
(Type galling resistance)
A 490 MPa class general-purpose hot-rolled steel sheet JSH440W (thickness = 3.2 mm) of the Japan Iron and Steel Federation standard was used as a processing original plate, a lubricating film to be tested was formed on one side, and a general rust preventive oil was applied at 2 g / m ² . After that, the mold caulking property evaluation by crank press bending was performed. The processing conditions and the evaluation method at that time are as shown in FIG. 2, and the normal part remaining rate in the 10th sample after the continuous 10 sheet molding was evaluated at the ironing rate = 15%.

As a criterion for judgment, the normal part remaining rate under the same conditions of a mill bond (MC560J, coating amount = 1.2 g / m ² ) having good mold galling resistance is 75%. The thing which does not generate galling was taken as the best.

Processing conditions: Sample size: 25 × 150 mm; Clearance: 2.72 mm (squeezing rate = 15%); Number of moldings: 10 consecutive judgment criteria: Normal part remaining rate is
(Double-circle) = 100%, (circle) = 75-100% (mill bond or more), x <75%.

  In addition, by observing the appearance of the side wall of the sliding part in this test, the occurrence of press debris at the sliding part was evaluated. The mold coating test rubs and peels off the lubricant film, and the film builds up on the mold and reattaches to the steel plate, so that press debris reattaches to the galling part, but it is a problem if it can be removed by steam degreasing. Judged to be none.

Judgment criteria: Side wall appearance observation,
◎: No blackening occurs due to press debris, ○: Black discoloration occurs due to press debris but can be removed by steam degreasing, ×: Black discoloration occurs due to press debris, and cannot be removed due to vapor degreasing

(Adhesiveness)
After using a mild steel plate JSC270D (plate thickness = 0.8 mm) of the Japan Iron and Steel Federation standard as a processing base plate, a lubricating film to be tested was formed on one side, and 2 g / m ^{2 of} general rust preventive oil was applied. The adhesion test shown was carried out. The evaluation criteria are as follows.

Judgment criteria: Adhesive strength
◎ ≧ 4.0 kN (high lubricity rust preventive oil or more), ○ = 3.5-4.0 kN (mill bond or more), x <3.5 kN.

  As can be seen from the results in Table 2, according to the present invention, when the film forming component is an alkali metal borate and the lubricant is wax and zinc stearate, the film forming component is lithium silicate and the lubricant is the same. Or, compared with the case where the film forming components are the same and the metal soap of the lubricant is calcium stearate, the film removal property of the lubricant film is remarkably improved, and an alkaline degreasing solution having a low degreasing power at pH = 10 is sufficient for the lubricating film. The film could be removed, and stable chemical conversion treatment could be ensured.

  That is, even when the film forming component is an alkali metal borate, the same excellent moldability, mold galling resistance, suppression of press debris generation, and adhesion as in the case of the lithium silicate film can be obtained. Moreover, the film-removing property and the chemical conversion property, which were weak points of lithium silicate, were improved.

It is a schematic diagram of the moldability evaluation method by cylindrical deep drawing. It is a schematic diagram which shows the evaluation test method and its measuring method of mold-proof galling resistance. It is a schematic diagram of an adhesiveness (structural adhesive) evaluation test method.

Claims (6)

  Lubricated steel sheet having a lubricating film containing a lubricant in the film forming component on the surface of the steel sheet, wherein the film forming component is an alkali metal borate, and the lubricant is a mixture of zinc stearate and wax Lubricated steel sheet, characterized in that   The solid content mass ratio of the lubricant / film forming component is in the range of 0.1 to 2.0, and the mass ratio of zinc stearate / wax is in the range of 0.3 to 5.0. Lubricated steel sheet as described in 1. The total amount of the film-forming component and the lubricant is 10 to 1000 mg / m ^2, lubricated steel sheet according to claim 1 or 2.   It contains a film-forming component comprising an alkali metal borate and a lubricant comprising zinc stearate and wax, and the solid content mass ratio of the lubricant / film-forming component is within the range of 0.1 to 2.0. A treatment liquid for forming a lubricating film, wherein the mass ratio of zinc stearate / wax is in the range of 0.3 to 5.0.   The processing liquid for lubricating film formation of Claim 4 which further contains at least 1 sort (s) chosen from polyacrylic acid and nonionic surfactant as a dispersing agent.   The treatment liquid for forming a lubricating film according to claim 5 or 6, wherein the pH is in the range of 10 to 13.

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