JP2020059865A - Plated member - Google Patents

Abstract

To provide a plated member capable of suppressing delayed fracture.SOLUTION: A plated member 10 is provided with a member 11 to be plated 11 made of steel and an electrogalvanized layer 17 formed on a surface 16 of the member 11 to be plated, and in the electrogalvanized layer 17, crystal grains 20 having a diameter S of a circumscribed circle 22 of 20 to 60 μm are produced on an observation surface 21 that is spaced in a thickness direction of the electrogalvanized layer 17 apart a distance D of 5 to 20 μm from the surface 16.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a plated member, and particularly to a plated member having an electrogalvanized layer formed thereon.

  In a plated member obtained by subjecting a member to be plated made of steel to electrogalvanization, delayed fracture is often a problem because hydrogen atoms generated during electrogalvanization enter the member to be plated. Delayed fracture is a phenomenon in which a plated member under static stress breaks brittlely after a certain period of time. As a technique for suppressing delayed fracture, heat treatment (baking) in the range of 190 to 220 ° C. is generally performed for the purpose of releasing the absorbed hydrogen atoms from the plated member. Patent Document 1 discloses a technique of forming an electroless plating layer made of nickel or a nickel alloy for preventing the entry of hydrogen atoms on a member to be plated, and forming an electrogalvanized layer on the electroless plating layer.

JP, 2014-51686, A

  However, a technique for further suppressing delayed fracture of this type of plated member is required.

  The present invention has been made to meet this demand, and an object thereof is to provide a plated member capable of suppressing delayed fracture.

  In order to achieve this object, the plated member of the present invention comprises a member to be plated made of steel, and an electrogalvanized layer formed on the surface of the member to be plated, wherein the electrogalvanized layer is a member to be plated. Crystal grains having a diameter of the circumscribed circle of 20 to 60 μm appear on the observation surface that is separated from the surface by a distance of 5 to 20 μm in the thickness direction of the electrogalvanized layer.

  According to the plated member of claim 1, a crystal having a diameter of a circumscribed circle of 20 to 60 μm on an observation surface that is separated from the surface of the member to be plated by 5 to 20 μm in the thickness direction of the electrogalvanized layer. Grain appears. The crystal grains are grains grown by precipitation of zinc or an alloy containing zinc having a relatively low melting point, and the size of the crystal grains indicates high current efficiency during electrogalvanizing. By increasing the current efficiency during electrogalvanizing, the amount of electricity used for other than metal deposition can be reduced, so that the amount of hydrogen atoms generated during electrogalvanizing can be suppressed. As a result, hydrogen atoms that are occluded by the member to be plated during electrogalvanization can be reduced, and delayed fracture can be suppressed.

  According to the plated member of claim 2, of the crystal grains appearing in the visual field of 300 × 400 μm on the observation surface, the proportion of crystal grains having a circumscribed circle diameter of 20 to 60 μm is 60% or more and 100% or more. % Or less. Thereby, in addition to the effect of claim 1, delayed fracture can be further suppressed.

  According to the plated member of the third aspect, the member to be plated is a chain. Therefore, in addition to the effect of claim 1 or 2, delayed fracture when a tensile force is applied to the chain can be suppressed.

  According to the plated member of the fourth aspect, the electrogalvanized layer includes a glossy portion and a cloudy portion having a surface roughness relatively larger than that of the glossy portion. Since the area of the glossy portion is larger than the area of the cloudy portion, in addition to the effect according to any one of claims 1 to 3, the glossy feeling of the plated member can be secured.

  According to the plated member of the fifth aspect, the member to be plated is a chain in which a plurality of annular links are connected. The link includes a pair of curved portions facing each other, a linear portion adjacent to the curved portion, and a welding portion that joins the linear portions that are abutted to each other. Since the cloudy part exists at the boundary between the welded part and the straight part, in addition to the effect of the fourth aspect, it is possible to make it difficult to give a feeling of strangeness due to the cloudy part.

It is a front view of the plating member in one embodiment. It is sectional drawing of the plated member in the II-II line of FIG. (A) is a schematic diagram of crystal grains in the early stage of the electrogalvanizing process, (b) is a schematic diagram of crystal grains in the middle stage of the plating process, and (c) is a schematic diagram of crystal grains after the plating process is completed. (A) is a schematic diagram of an observation surface of a plated member, and (b) is a schematic diagram of crystal grains. It is a front view of a part of plating member. FIG. 3 is a correlation diagram of the ratio of crystal grains having a circumscribed circle diameter of 20 to 60 μm and the limit stress / yield stress. It is a measurement result of the amount of diffusible hydrogen.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. First, with reference to FIG. 1, the structure of the plated member 10 in the embodiment of the present invention will be described. FIG. 1 is a front view of a plated member 10 according to one embodiment, and FIG. 2 is a sectional view of the plated member 10 taken along the line II-II in FIG.

  In the present embodiment, the plated member 10 will be described by taking a chain as an example. Examples of the chain include a chain block, a chain lever hoist, a load chain used for an electric chain block, and a chain sling used for a hoisting machine. It should be noted that a part of the intermediate portion of the plated member 10 in the longitudinal direction is omitted in FIG. 1, and a part of the cross section is enlarged in FIG.

  As shown in FIG. 1, in the plated member 10, a plurality of annular members 11 (links) formed in an O shape are connected. The member 11 to be plated is formed of a steel rod material such as carbon steel, alloy steel, special steel, and stainless steel. As the steel, steel subjected to surface hardening treatment such as carburizing, quenching and tempering, heat-treated steel, non-heat-treated steel, etc. are preferably used.

  The member to be plated 11 (link) is a pair of curved portions 12 facing each other, a first linear portion 13 that is adjacent to one end of the curved portion 12 and connects the curved portions 12, and is adjacent to the other end of the curved portion 12. A pair of second straight line portions 14 separated from the first straight line portion 13 and a welded portion 15 that joins the mutually joined second straight line portions 14 together are provided. The welded portion 15 is formed by electric resistance welding or the like on the second linear portions 14 that are butted against each other by bending the rod material to form the curved portion 12.

  As shown in FIG. 2, in the plated member 10, an electrogalvanized layer 17 is formed on the surface 16 of the member 11 to be plated. In the electrogalvanized layer 17, the distance (thickness) T between the surface 16 of the plated member 11 and the surface 18 of the electrogalvanized layer 17 is set to 5 μm or more in order to prevent rusting of the plated member 11. It The thickness T of the electrogalvanized layer 17 is measured by any of the microscope cross-section test method, magnetic force test method, electrolytic test method, and fluorescent X-ray test method defined in JIS H8501: 1999.

  The electrogalvanized layer 17 may contain components other than Zn, such as Zn-Ni plating, Zn-Fe plating, and Zn-Al plating, or may not contain components other than Zn. The composition of the electrogalvanized layer 17 generally contains 0 mass% or more and 20 mass% or less of Fe, 0 mass% or more and 1 mass% or less of Al, and further contains Pb, Sb, Si, Sn, Mg, Mn, Ni, One or two or more selected from Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and rare earth metals are contained in a total amount of 0% by mass to 20% by mass, and the balance is Zn and inevitable impurities.

  The crystal grains 20 of the electrogalvanized layer 17 will be described with reference to FIG. FIG. 3A is a schematic diagram of the member 11 to be plated in the early stage of the electrogalvanizing process, FIG. 3B is a schematic diagram of the member 11 to be plated in the middle stage of the plating process, and FIG. It is a schematic diagram of the to-be-plated member 11 after. In the electrogalvanizing step, the member 11 to be plated and a zinc electrode (not shown) are immersed in a plating solution containing a metal salt of zinc or a zinc alloy, and the member 11 to be plated is used as a cathode and the zinc electrode is used as an anode for electrolytic plating. Give. The zinc concentration of the plating solution is set to about 20 to 70 g / L, and the additive is not included in the plating solution or is contained in the plating solution in the minimum amount.

  As shown in FIG. 3A, metal atoms 19 containing zinc are deposited on the member to be plated 11 at the beginning of the plating process. Since zinc has a relatively low melting point, as shown in FIG. 3B, in the middle of the plating process, the metal atoms 19 grow and become crystal grains 20. The crystal grains 20 continue to grow and develop into a columnar shape extending in the thickness direction of the electrogalvanized layer 17 (vertical direction in FIG. 3B). The crystal grains 20 become larger as the electrogalvanized layer 17 becomes thicker.

  As shown in FIG. 3 (c), the electrogalvanized layer 17 is separated from the surface 16 of the member 11 to be plated by a distance D of 5 to 20 μm in the thickness direction of the electrogalvanized layer 17 (FIG. 3 (c) vertical direction). ), The crystal grains 20 appear on the observation surface 21 separated from each other. In this embodiment, the observation surface 21 is a polished surface of the surface 18 of the electrogalvanized layer 17. However, the present invention is not limited to this, and when the thickness T (see FIG. 2) of the electrogalvanized layer 17 is 20 μm or less, the surface 18 of the electrogalvanized layer 17 can naturally be used as the observation surface. is there.

  The distance D between the surface 16 of the member to be plated 11 and the observation surface 21 is set to 5 to 20 μm because the crystal grains 20 become larger as the electrogalvanized layer 17 becomes thicker, so that the measurement conditions are kept constant. This is because The reason why the distance D is not set to a constant value and a range of 5 to 20 μm is provided is that the thickness T of the electrogalvanized layer 17 varies depending on the use and size of the member 11 to be plated. This is because the distance D between the surface 16 of the member 11 and the observation surface 21 can be selected within the range of 5 to 20 μm.

  FIG. 4A is a schematic view of the observation surface 21 of the plated member 10, and FIG. 4B is a schematic view of the crystal grains 20. As specified in JIS G0553: 2008, after observing the observation surface 21 by immersing the plated member 10 in a corrosive liquid such as ethanol nitrate (nital), the observation surface 21 is observed with a microscope such as a metal microscope or SEM. . The diameter S of the circumscribed circle 22 of the crystal grain 20 can be measured by arithmetically processing the microscope image of the observation surface 21. In the plated member 10, crystal grains 20 having a circumscribed circle 22 having a diameter S of 20 to 60 μm appear on the observation surface 21.

  On the other hand, when the zinc concentration of the plating solution is about 15 g / L and the additive is sufficiently contained in the plating solution, the additive is adsorbed to the member 11 to be plated and the metal atom 19, and thereafter Partially suppress metal precipitation and refine crystal grains. Further, the additive reduces the roughness of the surface 18 of the electrogalvanized layer 17 and develops the gloss of the electrogalvanized layer 17. In this case, the grain size of the crystal grains appearing on the observation surface 21 is generally 1 μm or less.

  When an additive or the like of the plating solution suppresses the deposition of metal atoms 19, the current efficiency becomes low, and the amount of electricity added to the plating solution that is not used for metal deposition is used for the generation of hydrogen atoms. . Then, the amount of hydrogen atoms generated increases, and the possibility that a large number of hydrogen atoms penetrate into the plated member 11 increases. On the other hand, in this embodiment, the current efficiency during electrogalvanizing is increased by adjusting the concentrations of zinc and additives in the plating solution.

  The appearance of the crystal grains 20 having the diameter S of the circumscribing circle 22 of 20 to 60 μm on the observation surface 21 indicates the high current efficiency during electrogalvanizing. By increasing the current efficiency during electrogalvanizing, it is possible to reduce the amount of electricity during electrogalvanizing that is used in addition to metal deposition. As a result, the amount of hydrogen atoms generated during electrogalvanizing can be suppressed, and the number of hydrogen atoms stored in the plated member 11 during electrogalvanizing can be reduced. Therefore, delayed fracture of the plated member 10 can be suppressed.

  It should be noted that the proportion of the crystal grains 20 having a diameter S of the circumscribing circle 22 of 20 to 60 μm is 60% or more among the crystal grains 20 appearing in a rectangular visual field of 300 × 400 μm on the observation surface 21. preferable. Since it can be said that the current efficiency at the time of electrogalvanizing can be further increased by this, the delayed fracture of the plated member 10 can be further suppressed.

  FIG. 5 is a front view of a part of the plated member 10. As shown in FIG. 3 (c), the surface 18 of the electrogalvanized layer 17 has irregularities and little gloss, so that, for example, the plated members 10 or the plated members 10 and an abrasive (not shown) may be used as necessary. Are rubbed with each other or subjected to a blast treatment or the like to reduce the roughness of the surface 18 of the electrogalvanized layer 17.

  As shown in FIG. 5, the electrogalvanized layer 17 of the plated member 10 whose surface 18 has a reduced roughness has a glossy portion 23 and a cloudy portion 24 having a surface roughness relatively larger than that of the glossy portion 23. Consists of. The glossy portion 23 is a portion where the surface 18 of the electrogalvanized layer 17 is sufficiently rubbed, and the cloudy portion 24 is a portion which is less rubbed or is not rubbed as compared with the glossy portion 23. In the plated member 10, since the area of the glossy portion 23 is larger than the area of the cloudy portion 24, the glossy feeling of the plated member 10 can be secured.

  Further, the cloudy portion 24 exists at the boundary between the welded portion 15 of the plated member 10 and the second straight portion 14. Since the welded portion 15 and the second straight portion 14 have different textures, it is possible to prevent the cloudy portion 24 from giving an uncomfortable feeling. In the present embodiment, the welded portion 15 is thicker than the second linear portion 14, so that the clouded portion 24 is formed at the corner between the second linear portion 14 and the welded portion 15. By forming the cloudy portion 24 in the corner, it is possible to further reduce the feeling of strangeness caused by the cloudy portion 24.

  The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

(Create sample)
A chain (member to be plated) having five circular annular links made of steel was dipped in a plating solution to prepare various samples (plated members) which were subjected to electrogalvanization with a target thickness of 20 μm. In each sample, the zinc concentration of the plating solution, the concentration of the additive, and the current density during plating were varied to vary the grain size of the crystal grains appearing on the surface of the electrogalvanized layer. The material and dimensions of the link (steel) of each sample and the temperature of the plating solution were kept constant. Each sample was not so-called baked.

  After polishing the surface of the electrogalvanized layer of each sample and corroding it with ethanolic nitrate (nital) to reveal the structure of the observation surface (polishing surface), using a metallurgical microscope, a rectangle with a size of 300 × 400 μm Among the crystal grains appearing in the field of view, the ratio (%) of the crystal grains having a circumscribed circle diameter of 20 to 60 μm was measured by image processing. In addition, it was confirmed that the distance between the surface of the member to be plated and the observation surface was in the range of 5 to 20 μm by the microscope cross-section test method defined in JIS H8501: 1999.

(Delayed fracture resistance)
A tensile test was performed by grasping both ends of each sample (chain) in the length direction and applying a tensile force of 10 mm / min to each sample. The maximum loading time for applying tensile force was 168 hours. The maximum stress at which rupture did not occur during 168 hours when tensile force was applied was defined as the critical stress, and the delayed fracture resistance was evaluated by the ratio of the critical stress and the yield stress. When the critical stress / yield stress is 1.00 or more, the delayed fracture resistance is excellent, and when it is less than 1.00, the delayed fracture resistance is inferior.

  FIG. 6 is a correlation diagram of a ratio of crystal grains having a circumscribed circle diameter of 20 to 60 μm (hereinafter, simply referred to as “proportion”) and a limit stress / yield stress among crystal grains appearing in a visual field of 300 × 400 μm. Is. As shown in FIG. 6, the sample having a ratio of 0% had a critical stress / yield stress of 0.86 (less than 1.00). In the sample of 0%, the grain size of the crystal grains appearing on the observation surface was 1 μm or less.

  On the other hand, the critical stress / yield stress of the sample (ratio> 0%) in which the crystal grains having a circumscribed circle diameter of 20 to 60 μm existed in the visual field was 1.00 or more. Therefore, it was revealed that the delayed fracture can be suppressed by the appearance of the crystal grains having the circumscribed circle diameter of 20 to 60 μm in the visual field.

  In addition, there was a tendency that the limit stress / yield stress increased as the ratio increased. Particularly, when the ratio was 60% or more and 100% or less, the critical stress / yield stress was 1.20 or more. When the limit stress / yield stress is 1.20 or more, the sample is significantly deformed (stretched) when a tensile force is applied, so that it is not a brittle fracture (delayed fracture). Therefore, it was revealed that the effect of suppressing delayed fracture is remarkably high when the ratio is 60% or more.

(Hydrogen analysis)
The sample was immersed in a 10% NaOH aqueous solution, and the plating on the surface was completely removed by utilizing the anodic dissolution reaction. Then, the center of the sample in the length direction was cut to obtain a rod-shaped test piece having a length of 20 mm. Immediately after collecting the test piece, hydrogen analysis was performed using a thermal desorption analyzer. The analysis start temperature was 25 ° C., the analysis end temperature was 400 ° C., and the temperature rising rate was 100 ° C./hour, and the amount of released hydrogen (wt.ppm / min), which is the amount of hydrogen released from the test piece at each temperature, was measured. . Hydrogen released from room temperature to less than 300 ° C. is generally called diffusible hydrogen. This diffusible hydrogen is said to be the cause of delayed fracture. FIG. 7 shows the measurement results of the amount of diffusible hydrogen in the sample having a ratio of 80% (Example) and the sample having a ratio of 0% (Comparative Example).

  As shown in FIG. 7, it was found that the example can significantly reduce the amount of hydrogen released from room temperature to 300 ° C. as compared with the comparative example. It is clear that the embodiment can suppress delayed fracture as compared with the comparative example because the hydrogen absorption amount of the example is extremely smaller than that of the comparative example.

  Although the present invention has been described based on the embodiments, the present invention is not limited to the above embodiments, and various improvements and modifications are possible without departing from the spirit of the present invention. It can be easily guessed.

  In the embodiment, the chain in which a plurality of annular links (members 11 to be plated) formed in an O shape (elliptical shape) are connected has been described, but the present invention is not limited to this. For example, in order to prevent the links from being entangled with each other, it is naturally possible to replace the link (member to be plated 11) with an annular stud link formed in a substantially θ shape in which the intermediate portion of the link is connected by a stud. is there.

  In the embodiment, the plated member 10 has been described by taking the chain as an example, but the present invention is not limited to this. For example, it is of course possible to electrogalvanize steel screws, springs, gears, PC steel bars and the like to form plated members.

  In the embodiment, the case where the electrogalvanized layer 17 is present on the surface of the plated member 10 has been described, but the present invention is not limited to this. For example, it is naturally possible to perform a chromate treatment on the plated member 10 to form a chromate film on the surface of the electrogalvanized layer 17.

  In the example, the sample was cut to obtain a test piece with a length of 20 mm for hydrogen analysis, but the present invention is not limited to this. The length of the test piece can be appropriately set in the range of, for example, 7 to 20 mm depending on the size of the sample.

10 plated member 11 plated member 12 curved portion 14 second straight portion (straight portion)
15 Welded portion 16 Surface of plated member 17 Electrogalvanized layer 20 Crystal grain 21 Observation surface 22 Circumscribing circle 23 Glossy portion 24 Cloudy portion D Distance S Diameter

Claims (5)

A member to be plated made of steel,
An electrogalvanized layer formed on the surface of the member to be plated,
The electrogalvanized layer has crystal grains with a circumscribed circle diameter of 20 to 60 μm on an observation surface that is separated from the surface of the member to be plated by 5 to 20 μm in the thickness direction of the electrogalvanized layer. The exposed plated parts.   The ratio of the crystal grains having a circumscribed circle diameter of 20 to 60 μm is 60% or more and 100% or less among the crystal grains appearing in the visual field of 300 × 400 μm on the observation surface. Plated member.   The plated member according to claim 1, wherein the member to be plated is a chain. The electrogalvanized layer includes a glossy portion and a cloudy portion having a relatively large surface roughness than the glossy portion,
The plated member according to claim 1, wherein an area of the glossy portion is larger than an area of the cloudy portion. The member to be plated is a chain in which a plurality of annular links are connected,
The link includes a pair of curved portions facing each other, a linear portion adjacent to the curved portion, and a welding portion that joins the linear portions that are abutted to each other,
The plated member according to claim 4, wherein the cloudy portion exists at a boundary between the welded portion and the linear portion.

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