KR101146830B1 - Surface treated steel sheet having excellent anti oil-wettability and anti oil-diffusion - Google Patents

Abstract

In the surface-treated steel sheet, an antirust coating is formed on the surface of the zinc-based plated steel sheet, and the kinematic viscosity at 40 ° C is 51 to 69 mm2 / s at 100 ° C to at least the surface A of the antirust coating on the one side of the steel sheet. The contact angle of the lubricating oil having a kinematic viscosity of 11.1 to 14.9 mm 2 / s (however, the contact angle 30 seconds after forming droplets of lubricating oil on the surface of the rust-preventive coating at a steel plate surface temperature of 30 ° C.) is 10 ° or more. Preferably, the surface-treated steel sheet has a contact angle of the lubricating oil with respect to the rust-prevented thin surface A after plastic working at an elongation of 20%, more preferably 10 ° or more, and more preferably, the rust-prevented surface A and the The crack formation density in the said rustproof film surface A after plastic-processing the said surface-treated steel sheet at 20% of elongation is 200 or less per 100 micrometers. These surface-treated steel sheets are excellent in oil-wetting diffusion resistance, and can effectively suppress the bleeding of lubricating oil which causes a lack of lubricating oil in the bearing part in a component having a bearing holder portion.

Description

SURFACE TREATED STEEL SHEET HAVING EXCELLENT ANTI OIL-WETTABILITY AND ANTI OIL-DIFFUSION}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet excellent in oil-wetting diffusion, and more particularly, to motor cases (motor cases having bearing holders for supporting bearings) of various motors used in automobiles and AV-OA equipment. It relates to a suitable surface treated steel sheet.

The bearings are largely divided into rolling bearings and sliding bearings. However, many of the bearings of various motors used in electric motors used in automobiles, electronic recording devices such as HDDs, and electronic devices such as copying machines are sliding bearings. . In the sliding bearing, the lubricant is lubricated to the bearing part to prevent contact and adhesion between the rotating shaft and the bearing by the hydraulic oil generated mainly in the lubricating oil during rotation. Therefore, the lubricated oil supplied to the bearing part (usually the bearing part is lubricating oil). It is necessary to properly maintain the bearing member capable of impregnation. However, in the conventional motor, there is a problem of lubricating oil oozing out of the bearing part, and contact and adhesion between the rotating shaft and the bearing due to lack of lubricating oil easily occur, which causes vibration and noise of the motor.

Conventionally, for example, Japanese Patent Application Laid-Open No. 7-238934, 9-210065, etc. improve the bearing material, the structure of the bearing portion, and the structure around the bearing portion, in order to prevent lubrication of lubricating oil from the bearing portion. Although this was proposed, the effect of preventing lubricating oil bleeding from the bearing portion was not necessarily sufficient.

By the way, the bearings (bearing members) of various motors used in automobiles, OA and AV devices are generally supported and fixed to the bearing holders formed in the motor case, and the motor case is formed on the surface of the galvanized steel sheet. Plastic processing of surface treated steel sheets on which antirust coatings have been formed is widely used.

When lubricating oil is extruded from the bearing portion, the lubricating oil is extruded from the bearing (bearing member) to the inner surface of the motor case around the bearing holder portion. Conventional studies for preventing such lubricating oil leakage have been directed only to improvement of the bearing material, the bearing portion and the structure around the bearing portion, but the result was not sufficient.

On the other hand, the present inventors paid attention to the surface property of the motor case (surface treatment steel plate) in which the bearing holder part was formed, and examined the mechanism and the countermeasure which the lubricant bleeds from a bearing. As a result, lubricating oil bleeds out of the bearing because lubricating oil is wetted on the inner surface of the motor case (surface-treated steel sheet surface) including the bearing holder portion. I knew it was spreading. Therefore, by suppressing the lubricating oil wettability of the inner surface of the motor case (surface treated steel plate surface) including the bearing holder portion to a sufficiently low level, the penetration of the lubricating oil from the bearing into the inner surface of the motor case can be suppressed (that is, the lubricating oil is enclosed in the bearing). As a result, it has been found that the exudation of the lubricating oil which causes the lack of lubricating oil in the bearing portion can be effectively suppressed.

Accordingly, an object of the present invention is to effectively suppress the effusion of lubricating oil, which is excellent in oil-wetting diffusion, and applied to a part having a bearing holder portion for supporting a bearing such as a motor case or the like, which causes a lack of lubricating oil in the bearing portion. The present invention provides a surface-treated steel sheet that can be made.

DISCLOSURE OF INVENTION

This invention makes the following a summary.

[1] galvanized steel surface-treated steel sheet

The contact angle of the lubricating oil whose kinematic viscosity in 40 degreeC is 51-69mm <2> / s and the kinematic viscosity in 11.1-14.9mm <2> / s at least 100 degreeC with respect to the rust-proof film surface A on the one side of a steel plate (However, A surface-treated steel sheet having excellent oil-wet diffusion resistance, wherein the contact angle after 30 seconds after forming droplets of lubricating oil on the surface of the rust-preventive coating at a steel plate surface temperature of 30 ° C.

[2] The kinematic viscosity at 40 ° C of the surface-treated steel sheet of the above item [1] at 40 ° C on the rust-preventive coating surface A after plasticizing the surface-treated steel sheet at 20% elongation is 51 to 69 mm 2 / s, 100 ° C. The contact angle of the lubricating oil having a kinematic viscosity of 11.1 to 14.9 mm2 / s (however, the contact angle 30 seconds after forming a droplet of lubricating oil on the surface of the rust preventive film at a steel plate surface temperature of 30 ° C.) is 10 ° or more. Surface-treated steel sheet with excellent oil-wet diffusion.

[3] In the surface-treated steel sheet according to the above [1] or [2], a crack in the rust-preventive coating surface A after the rust-preventive coating surface A and the surface-treated steel sheet are plastically processed at an elongation of 20%. Surface-treated steel sheet having excellent oil-wet diffusion resistance, characterized in that the production density is 200 or less per 100㎛.

[4] A surface-treated steel sheet for parts having a bearing holder portion for supporting a bearing, which satisfies the condition of the rustproof coating surface A according to any one of [1] to [3].

[5] A surface-treated steel sheet for a motor case provided with a bearing holder portion for supporting a bearing, wherein the condition of the rust-preventive coating surface A according to any one of [1] to [3] is satisfied.

[6] A motor case comprising a bearing holder portion for supporting a bearing obtained by plastic working the surface-treated steel sheet according to any one of [1] to [3], wherein the rust-preventive coating surface A constitutes the case inner surface. Motor case characterized in that.

The surface-treated steel sheet of the present invention is excellent in oil-wetting diffusion property and, therefore, when applied to a part having a bearing holder part for supporting a bearing such as a motor case, the surface-treated steel sheet of lubricant Effusion can be effectively suppressed. For this reason, when applied to a motor case, the smooth sliding of the rotating shaft with respect to a bearing can be ensured for a long time, and the vibration and noise of a motor can be reduced, and long life can be aimed at.

1 is a view showing a typical pattern of the change over time of the contact angle immediately after droplet formation when the droplets of lubricating oil are formed on the solid surface and the contact angle thereof is measured.
2 is a cross-sectional view of a bearing holder portion side of a general motor case.

Carrying out the invention  for Best  shape

MEANS TO SOLVE THE PROBLEM The present inventors discovered that the outflow of the lubricating oil in a bearing part can be suppressed effectively by setting the contact angle of the lubricating oil with respect to the surface-treated steel plate surface used as an inner surface of a motor case more than predetermined level, and came to this invention. More preferably, the contact angle of the lubricating oil with respect to the surface-treated steel sheet surface after plastic working under predetermined processing conditions is set to a predetermined level or more, and furthermore, by regulating the generation density of microcracks present on the surface of the film, It was found that excellent lubricity inhibitory effect can be obtained.

Examples of the zinc-based plated steel sheet as a base of the surface-treated steel sheet of the present invention include a galvanized steel sheet, a Zn-Ni alloy plated steel sheet, and a Zn-Al-Mg alloy plated steel sheet (eg, Zn-6 mass% Al-3 mass%). Mg alloy plated steel sheet, Zn-11mass% Al-3mass% Mg alloy plated steel sheet), Zn-Al alloy plated steel sheet (for example, Zn-5mass% Al alloy plated steel sheet) and the like can be used. Further, in the plating layers of these various plated steel sheets, one kind of nickel, cobalt, manganese, iron, molybdenum, tungsten, titanium, chromium, aluminum, magnesium, lead, antimony, tin, copper, or the like as a small amount of dissimilar metal elements or impurities, or It is also possible to use a plated steel sheet containing two or more kinds. Moreover, it is also possible to use the multilayer plating steel plate which plated two or more layers of the same kind or a different kind among the above platings.

The surface-treated steel sheet of the present invention is a surface-treated steel sheet having a rust-preventive coating formed on the surface of the zinc-based plated steel sheet, and has a kinematic viscosity at 40 ° C of 51 to 69 mm 2 / s, at least with respect to the rust-preventive coating surface A on the one side of the steel sheet. The contact angle of the lubricating oil having a kinematic viscosity of 11.1 to 14.9 mm 2 / s at 100 ° C. (but the contact angle 30 seconds after forming the droplets of the lubricating oil on the surface of the rust-preventive coating at a surface temperature of 30 ° C.) is preferably 10 ° or more, preferably 15 degrees or more, More preferably, it is 25 degrees or more. An antirust film has a main component as an organic component and / or an inorganic component for obtaining desired antirust performance.

Fig. 1 shows a typical pattern of the change over time of the contact angle immediately after droplet formation when a droplet of lubricating oil is formed on the solid surface and the contact angle is measured. On the solid surface where lubricating oil is hard to get wet, the contact angle hardly changes with time. On the solid surface where lubricating oil is easy to get wet, the contact angle rapidly decreases immediately after droplet formation, and stabilizes after a certain time. Since the contact angle stabilizes at least 30 seconds after forming a droplet with respect to the rust-preventive coating which has an organic component and / or an inorganic component as a main component of this invention, since the contact angle used by this invention is The contact angle after 30 second was formed after the droplet of lubricating oil was formed on the surface of antirust film.

The measurement of the contact angle of the lubricating oil with respect to the rust-proof film surface A is performed as follows, for example. Lubricant liquid whose kinematic viscosity at 40 ° C is 51 to 69 mm2 / s and the kinematic viscosity at 100 ° C is 11.1 to 14.9 mm2 / s at the surface temperature of the steel sheet at 30 ° C. A drop is formed, the contact angle is continuously measured with a contact angle meter, and the value of the contact angle 30 seconds after the formation of the droplet on the rust-proof film surface A is the contact angle of the rust-proof film surface A. Moreover, as lubricating oil whose kinematic viscosity in 40 degreeC is 51-69mm <2> / s, and the kinematic viscosity in 100 degreeC is 11.1-14.9mm <2> / s, For example, "ALL TIME J652" made by NOK Cruber Co., Ltd. (40 degreeC) Kinematic Viscosity at: 60 mm2 / s, Kinematic Viscosity at 100 ° C: 13 mm2 / s and Polite-7 (PSL-7) (Kinematic Viscosity at 40 ° C: 60 mm2 / s, Kinematic Viscosity at 100 ° C) : 13 mm 2 / s) can be used. As the contact angle meter, "Drop Master 500" manufactured by Cooperative Interface Science Co., Ltd. can be used, for example.

The contact angle of the lubricating oil to this rust preventive coating surface A is the most important requirement in the present invention, and excellent oil-wet diffusion resistance can be obtained by satisfying the above condition. Increasing the contact angle increases the interfacial tension of the lubricating oil on the rust-preventive coating surface A. However, the interfacial tension is a force that moves in the direction in which the lubricating oil is to be spherical. It is thought that the oil-wet diffusion resistance is improved. By setting the contact angle of the lubricating oil to 10 ° or more, preferably 15 ° or more, more preferably 25 ° or more, the lubricating oil bleeding out of the bearing which causes a lack of lubricating oil which causes contact and adhesion between the rotating shaft and the bearing can be effectively prevented. It can be suppressed.

In the surface-treated steel sheet of the present invention, the contact angle of the lubricating oil may be set to the above condition with respect to the rust-preventive coating surface A on the one side of the steel sheet that is at least the inner surface side of the motor case.

The motor case provided with the bearing holder part is normally manufactured by performing plastic processing, such as press molding, on a surface-treated steel sheet. Fig. 2 shows a cross section of the bearing holder portion side of a general motor case, 1 is a motor case obtained by press molding a surface treated steel sheet, 2 is a bearing holder portion machined and formed at the end of the motor case 1, The bearing (bearing member) supported and fixed in the bearing holder portion 2, 4 is a motor rotation shaft freely supported by the bearing 3, and 5 is a washer. When the surface-treated steel sheet is molded to the shape of the motor case (motor case having a bearing holder portion) shown in Fig. 2, in many cases, plastic processing is performed before and after the elongation 20%, and the plastic working prevents the surface of the rust-preventive coating surface (A). The contact angle of the lubricating oil with respect to is often small. Therefore, it is preferable that the contact angle of the lubricating oil with respect to the rust-preventive coating surface A after the plastic working of the surface-treated steel sheet at 20% elongation is 10 ° or more, preferably 15 ° or more, more preferably 25 ° or more. .

The larger the contact angle of the lubricating oil to the rust-preventive coating surface A is, the better the oil-wet diffusion property is, but on the other hand, if the processing oil is splashed during plastic processing such as press molding, the processing becomes difficult. It is preferable that the contact angle of the said lubricating oil with respect to) is less than 90 degrees.

In addition, the micro cracks present on the rust-preventive coating surface A also influence the lubricating oil wettability, and excellent oil-wetting diffusion property can be obtained only by controlling the contact angle of the lubricating oil described above. It was found that better oil-wet diffusion resistance can be obtained. It is thought that this is because the microcracks promote the wetting and diffusibility of the lubricating oil by the capillary action.

Specifically, the production density of cracks present on the rust-preventive coating surface A is 200 or less, more preferably 150 or less, and more preferably 100 or less, per 100 µm, thereby providing particularly excellent oil-wet diffusion. You can get the last name. Herein, the generation density of cracks is observed by using an electron microscope, for example, by observing the surface of the surface-treated steel sheet at an acceleration voltage of 5 kV and 2000 times, and counting the number of cracks per 100 µm. As the electron microscope, "JCM-5600" made by Nippon Electronics Co., Ltd. can be used, for example.

In addition, cracks on the coating surface are easily introduced when the surface-treated steel sheet is plastically processed (mainly press-molded) in a motor case or the like, and therefore, the antirust film surface (A) after the surface-treated steel sheet is plastically processed at an elongation of 20%. Also about the crack generation density in, it is preferable to set it as 200 or less per 100 micrometers, More preferably, it is 150 or less, More preferably, it is 100 or less.

The surface-treated steel sheet of the present invention may have one or more underlayers (for example, chemical conversion coatings) on the lower layer of the rust preventive coating.

Although the surface-treated steel sheet of this invention can be used for a suitable use, it is especially suitable for the components provided with the bearing holder part for supporting a bearing (slide bearing), especially for the motor case shown in FIG.

When manufacturing the motor case provided with the bearing holder part for supporting a bearing (sliding bearing) using the surface-treated steel sheet of this invention, a surface-treated steel sheet is pressed so that the rustproof film surface A may become a case inner surface side. It processes by shaping | molding etc. and shape | molds to the motor case shown in FIG.

Next, the manufacturing method of the surface-treated steel sheet of this invention is demonstrated.

The surface-treated steel sheet of the present invention is formed by attaching a surface treatment liquid (surface treatment composition) for an rust-preventive coating on the surface of a zinc-based plated steel sheet (including a case where an undercoat is formed), and drying it to form an rust-preventive coating. Are manufactured. The surface treatment liquid is mainly composed of an organic component and / or an inorganic component for imparting antirust performance to the coating, and the type and additive components are particularly limited as long as the surface treatment liquid can form an antirust coating that satisfies the conditions of the present invention. However, as an example of the means for securing the contact angle of the lubricating oil that satisfies the conditions of the present invention, at least one component selected from (i) a surfactant, (ii) fine particles having a particle diameter of 0.05 to 5 μm, and (i) a fluorine resin Addition is an example.

Examples of the surfactant include ionic surfactants, nonionic surfactants, and amphoteric surfactants, and one or more kinds thereof can be used.

Examples of the fine particles having a particle diameter of 0.05 to 5 μm include solid lubricating agents such as polyolefin waxes such as polyethylene wax and polypropylene wax, lanolin wax, montan wax, micro-crystallin wax, paraffin wax, carnauba wax and the like. These can be mentioned and 1 or more types of these can be used.

The fluorine-based resin is a resin obtained by polymerization of ethylene and derivatives thereof in which at least one hydrogen atom is substituted with fluorine, and polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylethyl copolymer resin (PFA), copolymer of fluoroethylene and vinyl ethyl, tetrafluoroethylene and ethylene copolymer (ethylene tetrafluoroethylene-ethylene copolymer resin: ETFE), copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), etc. Although it is mentioned as an example, if it has a CF bond, the kind is not specifically limited. One or more types of those which are made to be ionic or nonionic and are dispersed in water can be used.

In addition, the compounding quantity of 1 or more types of addition components chosen from (i) surfactant, (ii) microparticles | fine-particles of (0.0) -5 micrometers of particle diameters, (i) fluorine-type resin, is 0.1-20 mass% in the ratio of solid content in a surface treatment liquid, More preferably, it is suitable to set it as 0.5-15 mass%, More preferably, it is about 1-10 mass%. If the blending amount is less than 0.1 mass%, the oil-wet diffusion resistance may become insufficient, whereas if the blending amount exceeds 20 mass%, the corrosion resistance may deteriorate.

The mechanism by which the rust-preventive film formed by using the surface treatment liquid containing the above-mentioned additives is not necessarily clear, but the surface-free energy of the rust-preventive coatings containing the additives decreases. It is estimated.

In order to reduce the crack generation density at the rust-preventive coating surface A, in particular, the crack generation density after plastic processing of the surface-treated steel sheet at an elongation of 20%, the film thickness of the rust-preventive coating is preferably 3 µm or less. This is because if it exceeds 3 mu m, cracks are easily introduced due to residual stress in the film. The film thickness is more preferably 1.5 µm or less, and particularly preferably 0.8 µm or less.

In the rust-preventive coating of the present invention, the surface treatment liquid as described above is attached to a zinc-based plated steel sheet surface (or base film surface) by, for example, a coating method, an immersion method, a spray method, or the like, followed by heating and drying. It is formed by. As the heat drying means, a dryer, a hot stove, a high frequency induction furnace, an infrared furnace, or the like can be used. In addition, when adding a solid lubricant, it is preferable that a drying temperature is more than the softening point of a solid lubricant, since it can lower the surface free energy of an antirust film more.

Example

The surface treatment liquid was prepared by mix | blending suitably the surfactant shown in Table 2, the microparticles shown in Table 3, and the fluorine-type resin shown in Table 4 to the antirust process liquid containing a silica, a silane coupling agent, and an acrylic resin as a main component.

Alkaline degreasing treatment of the zinc-based galvanized steel sheet shown in Table 1, which is a treated original, followed by water washing and drying, followed by coating the surface treatment liquid with a bar coater, and immediately afterwards, the surface temperature of the steel sheet is several seconds to several tens of seconds. It heat-dried so that it might become, and the surface treatment film (antirust film) was formed. The film thickness of this surface treatment film was adjusted by the concentration of the surface treatment liquid, and the film thickness of the film was quantified by observing the film cross section with an electron microscope.

About the obtained surface-treated steel sheet, the contact angle of the lubricating oil with respect to the film surface, and the crack formation density of the film surface were measured. The results are shown in Table 5 together with the film structure of the surface treated steel sheet. In addition, the results of evaluating the oil-wet diffusion resistance of the surface-treated steel sheet are shown in Table 6.

The measurement of the contact angle of the lubricating oil with respect to the film surface, the crack formation density of the film surface, and the evaluation of oil-wet diffusion resistance were performed as follows. In addition, these measurement and evaluation were performed about the test material (raw material) which did not perform plastic processing, and the test material (plastic processing material) which performed plastic processing, respectively. In the plastic working process, the surface-treated steel sheet was stretched at an elongation rate of 10 mm / min and an elongation rate of 20% using an electronic universal testing machine ("CATY" manufactured by YONEKURA Co., Ltd.).

(1) Contact angle of lubricant to coating surface

As lubricating oil for contact angle measurement, a lubricating oil having a kinematic viscosity at 40 ° C of 51 to 69 mm2 / s and a kinematic viscosity at 100 ° C of 11.1 to 14.9 mm2 / s (`` ALL TIME J 652 '' manufactured by NOK Crew Bar Co., Ltd.) Used. With this lubricant, droplets are formed on the surface of the test material (surface treated steel sheet) at 30 ° C, and the contact angle is continuously measured using a contact angle meter (Drop Master 500, manufactured by Cooperative Interface Science). The value after 30 second was made into the contact angle after forming.

(2) Crack formation density on the film surface

Using an electron microscope (JCM-5600, manufactured by Nippon Electronics Co., Ltd.), the surface of the test specimen (surface treated steel sheet) was observed at an acceleration voltage of 5 kV and 2000 times, and five places where crack formation was likely to be high were selected. The number of cracks of the 20 micrometer-long portion (100 micrometers in length in total of 5 places) was counted in each place, and the crack number of the total of five places was made into the crack generation density per 100 micrometers.

(3) oil-wet diffusion resistance

Lubricating oil having a kinematic viscosity of 51 to 69 mm2 / s at 40 ° C and a kinematic viscosity of 11.1 to 14.9 mm2 / s at 100 ° C was placed in a container and erected vertically. In the state which immersed the lower end part of the test material in the lubricating oil in a container, it was left to stand at room temperature 30 degreeC for 3 days, and the permeable spread of the lubricant was measured. The evaluation criteria are as follows.

◎: less than 0.5 cm

○: height 0.5 cm or more, less than 1.0 cm

○-: permeate spread more than 1.0cm, less than 1.5cm

(Triangle | delta): The height which permeate spreads more than 1.5 cm and less than 3.0 cm

×: height of 3.0 cm or more

Claims (7)

A surface-treated steel sheet having a rust-proof film formed on the surface of a galvanized steel sheet,
The rust preventive coating includes a surface treatment liquid in which at least one component selected from a surfactant, fine particles having a particle diameter of 0.05 to 5 μm, and a fluorine-based resin is added to an rust preventing treatment solution mainly containing silica, a silane coupling agent and an acrylic resin. Is formed by adhering, heating and drying,
Contact angle of lubricating oil whose dynamic viscosity in 40 degreeC is 51-69mm <2> / s and the kinematic viscosity in 11.1-14.9mm <2> / s with respect to the rust-proof film surface A on the one side of steel plate at least. (However, the contact angle after 30 seconds after forming a droplet of lubricating oil on the surface of the rust-prevented coating film at a steel plate surface temperature of 30 ° C.) is a surface excellent in oil-wetting diffusion, characterized in that it is 10 ° or more and less than 90 °. Processed steel sheet. A surface-treated steel sheet having a rust-proof film formed on the surface of a galvanized steel sheet,
The rust preventive coating includes a surface treatment liquid in which at least one component selected from a surfactant, fine particles having a particle diameter of 0.05 to 5 μm, and a fluorine-based resin is added to an rust preventing treatment solution mainly containing silica, a silane coupling agent and an acrylic resin. Is formed by adhering, heating and drying,
Contact angle of lubricating oil having a kinematic viscosity of 51 to 69 mm2 / s at 40 ° C and a kinematic viscosity of 11.1 to 14.9 mm2 / s at 100 ° C to the rust-preventive film surface A after plastic working of the surface-treated steel sheet at 20% elongation. The surface-treated steel sheet having excellent oil-wetting diffusion resistance, wherein the contact angle after 30 seconds after forming droplets of lubricating oil on the surface of the rust-prevented coating film at a steel plate surface temperature of 30 ° C. The method of claim 1,
The surface having excellent oil-wet diffusion resistance, characterized in that the crack formation density at the rust-preventive surface (A) after plastic processing of the rust-proof coating surface (A) and the surface-treated steel sheet at an elongation of 20% is 200 or less per 100 µm. Processed steel sheet. The method of claim 2,
The crack-producing density at the rust-preventive surface (A) after plastic processing of the rust-resistant coating surface (A) and the surface-treated steel sheet at an elongation of 20% is excellent in oil-wetting diffusion, characterized in that 200 or less per 100 µm. Surface-treated steel sheet. The surface treatment steel sheet for components provided with the bearing holder part for supporting a bearing characterized by satisfy | filling the conditions of the rustproof film surface (A) in any one of Claims 1-4. The surface treatment steel sheet for motor cases provided with the bearing holder part for supporting a bearing characterized by satisfy | filling the conditions of the rustproof film surface (A) in any one of Claims 1-4. A motor case comprising a bearing holder portion for supporting a bearing obtained by plastic working the surface-treated steel sheet according to any one of claims 1 to 4, wherein the rust-preventive coating surface A constitutes the case inner surface. Motor case.

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