CN111005042A

CN111005042A - Plated component

Info

Publication number: CN111005042A
Application number: CN201910951099.6A
Authority: CN
Inventors: 八木健太郎; 滨本利一
Original assignee: Fec Chain Corp
Current assignee: Fec Chain Corp
Priority date: 2018-10-05
Filing date: 2019-10-08
Publication date: 2020-04-14
Also published as: TW202014558A; JP2020059865A; TWI719658B; JP7140624B2

Abstract

The invention provides a plated member capable of suppressing delayed fracture. The plated member (10) has a steel member (11) to be plated and a zinc plating layer (17) formed on the surface (16) of the member (11) to be plated, and crystal grains (20) having a diameter (S) of 20 to 60 [ mu ] m of a circumscribed circle (22) appear on an observation surface (21) separated from the surface (16) of the member (11) to be plated by a distance (D) of 5 to 20 [ mu ] m in the thickness direction of the zinc plating layer (17) in the zinc plating layer (17).

Description

Plated component

Technical Field

The present invention relates to a plated member, and more particularly, to a plated member having a zinc plating layer formed thereon.

Background

In the case of a plated member in which a plated member made of steel is zinc-plated, there is a problem that hydrogen atoms generated during zinc plating often intrude into the plated member to cause delayed destruction. The delayed fracture is a phenomenon in which a plated member subjected to static stress is subjected to brittle fracture after a lapse of time. As a technique for suppressing the delayed fracture, for the purpose of releasing the absorbed hydrogen atoms from the plated member, for example, heat treatment (baking) is generally performed at 190 to 220 ℃. Patent document 1 discloses a technique of forming an electroless plating layer made of nickel or a nickel alloy for preventing hydrogen atoms from entering a member to be plated, and forming a zinc plating layer on the plating layer.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2014-51686

Disclosure of Invention

Problems to be solved by the invention

However, a technique for further suppressing the delayed fracture of such a plated member is required.

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

Means for solving the problems

In order to achieve the object, a plated member of the present invention has a plated member made of steel and a zinc plating layer formed on a surface of the plated member, wherein the zinc plating layer has crystal grains with a diameter of 20 to 60 μm of a circumscribed circle on an observation surface separated from the surface of the plated member by a distance of 5 to 20 μm in a thickness direction of the zinc plating layer.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the plated member described in the first aspect, the crystal grains having a diameter of 20 to 60 μm which circumcircle the surface of the member to be plated are present on the observation surface separated from the surface of the member to be plated by a distance of 5 to 20 μm in the thickness direction of the zinc plating layer. The crystal grains are formed by precipitating and growing zinc or an alloy containing zinc having a low melting point, and the size of the crystal grains indicates the level of current efficiency in electrogalvanizing. By improving the current efficiency in electrogalvanizing, the amount of electricity used other than the deposited metal can be reduced, and the amount of hydrogen atoms generated in electrogalvanizing can be suppressed. As a result, hydrogen atoms absorbed into the member to be plated can be reduced during the zinc electroplating, and therefore, the delayed fracture can be suppressed.

According to the plated member described in the second aspect, the proportion of crystal grains having a diameter of 20 to 60 μm that circumcircle is 60% to 100% of crystal grains appearing in a visual field of a size of 300X 400 μm on an observation surface is 60% to 100%. Thus, in addition to the effect of the first aspect, hysteresis breakdown can be further suppressed.

According to the plated member of the third aspect, the plated member is a chain. Therefore, in addition to the effects of the first or second aspect, hysteresis breakage when a tensile force is applied to the chain can be suppressed.

According to the plated member described in the fourth aspect, the zinc plating layer has a glossy portion and a frosted portion having a surface roughness greater than that of the glossy portion. Since the area of the glossy portion is larger than the area of the frosted portion, the glossy feeling of the plated member can be ensured in addition to the effects of any one of the first to third aspects.

According to the plated member of the fifth aspect, the plated member is a chain formed by connecting a plurality of endless links. The link has a pair of curved portions facing each other, linear portions adjacent to the curved portions, and weld portions joining the facing linear portions. Since the ground portion is present at the boundary between the welded portion and the straight portion, it is possible to make it more difficult to cause a sense of incongruity due to the ground portion in addition to the effect of the fourth aspect.

Drawings

Fig. 1 is a front view of a plated member in an embodiment.

FIG. 2 is a cross-sectional view of the plated member at line II-II of FIG. 1.

FIG. 3A is a schematic view of crystal grains at the initial stage of the electrogalvanizing step, FIG. 3B is a schematic view of crystal grains at the middle stage of the plating step, and FIG. 3C is a schematic view of crystal grains after the completion of the plating step.

Fig. 4A is a schematic view of an observation surface of a plated member, and fig. 4B is a schematic view of crystal grains.

Fig. 5 is a partial front view of a plated member.

FIG. 6 is a graph showing the relationship between the ratio of crystal grains having a diameter of 20 to 60 μm and the ultimate stress/yield stress.

Fig. 7 shows the measurement results of the amount of diffusible hydrogen.

Description of the reference numerals

10 plated component

11 plated member

12 part of curve

14 second straight line part (straight line part)

15 welding part

16 surface of plated member

17 zinc plating

20 crystal grains

21 observation surface

22 circumscribed circle

23 gloss part

24 frosted part

Distance D

S diameter

Detailed Description

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. First, the structure of the plated member 10 according to an embodiment of the present invention will be described with reference to fig. 1. Fig. 1 is a front view of a plated member 10 according to an embodiment, and fig. 2 is a cross-sectional view of the plated member 10 taken along line 11-11 of fig. 1.

In the present embodiment, the plated member 10 will be described by taking a chain as an example. Examples of the chain include a load-bearing chain used for a chain block, a chain type lever block, an electric chain block, and the like, and a chain hoist used for a hoist, and the like. Note that, in fig. 1, a part of the middle portion in the longitudinal direction of the plated member 10 is omitted from illustration, and in fig. 2, a part of the cross section is enlarged and illustrated.

As shown in fig. 1, the plating member 10 is formed by connecting a plurality of annular members to be plated 11 (links) formed in an O-shape. The plated member 11 is formed of a steel bar material such as carbon steel, alloy steel, special steel, or stainless steel. The steel is preferably a case hardened steel, a heat treated steel, a non heat treated steel, or the like, which is subjected to surface hardening such as carburizing, quenching, tempering, or the like.

The plated member 11 (link) has a pair of curved portions 12 facing each other, first straight portions 13 adjacent to one ends of the curved portions 12, respectively, and connecting the curved portions 12 to each other, a pair of second straight portions 14 adjacent to the other ends of the curved portions 12 and spaced apart from the first straight portions 13, and a welded portion 15 joining the second straight portions 14 facing each other to each other. The welded portion 15 is formed in the second linear portion 14 by resistance welding or the like, and the second linear portion 14 is a portion facing each other by bending the bar material forming the curved portion 12.

As shown in fig. 2, in the plated member 10, a zinc plating layer 17 is formed on the surface 16 of the plated member 11. In the zinc plating layer 17, in order to prevent the plated member 11 from rusting, the distance (thickness) T between the surface 16 of the plated member 11 and the surface 18 of the zinc plating layer 17 is set to 5 μm or more. The thickness T of the zinc plating layer 17 was measured in accordance with JIS H8501: 1999, any of the microscope cross-section test method, the magnetic force test method, the electrolytic test method, and the X-ray fluorescence test method.

The zinc plating layer 17 may contain components other than Zn, such as Zn-Ni plating, Zn-Fe plating, Zn-Al plating, etc., or may not contain components other than Zn. The composition of the zinc plating layer 17 generally contains 0 mass% to 20 mass% of Fe and 0 mass% to 1 mass% of Al, and further contains 0 mass% to 20 mass% of a total of 1 or 2 or more metals selected from Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Be, Bi and rare earth metals, with the balance being Zn and unavoidable impurities.

The crystal grains 20 of the zinc plating layer 17 will be described with reference to fig. 3A to 3C. Fig. 3A is a schematic view of the plated member 11 at the initial stage of the electrogalvanizing step, fig. 3B is a schematic view of the plated member 11 at the middle stage of the plating step, and fig. 3C is a schematic view of the plated member 11 after the plating step is completed. In the electrogalvanizing step, the member to be plated 11 and a zinc electrode (not shown) are immersed in a plating solution containing a metal salt of zinc or a zinc alloy, and electrolytic plating is performed with the member to be plated 11 as a cathode and the zinc electrode as an anode. The concentration of zinc in the plating solution is about 20-70 g/L, and the plating solution does not contain additives or has the minimum content even if the plating solution contains the additives.

As shown in fig. 3A, at the initial stage of the plating step, metal atoms 19 including zinc are deposited on the plated member 11. Since the melting point of zinc is relatively low, as shown in fig. 3B, the metal atoms 19 grow and become crystal grains 20 in the middle stage of the plating process. The crystal grains 20 continue to grow and develop into columnar shapes extending in the thickness direction of the zinc plating layer 17 (the vertical direction in fig. 3B). The crystal grains 20 become larger as the zinc plating layer 17 becomes thicker.

As shown in FIG. 3C, the zinc plating layer 17 has crystal grains 20 on an observation surface 21 separated in the thickness direction (vertical direction in FIG. 3C) of the zinc plating layer 17 at a distance D of 5 to 20 μm from the surface 16 of the member 11 to be plated. In the present embodiment, the observation surface 21 is a polished surface of the surface 18 of the zinc plating layer 17. However, it is needless to say that the surface 18 of the zinc plating layer 17 can be an observation surface when the thickness T (see fig. 2) of the zinc plating layer 17 is 20 μm or less.

Further, since the crystal grains 20 become larger as the zinc plating layer 17 becomes thicker, the distance D between the surface 16 of the member 11 to be plated and the observation surface 21 is set to 5 to 20 μm in order to keep the measurement conditions constant. The thickness T of the zinc plating layer 17 varies depending on the application, size, etc. of the plated member 11, and therefore the distance D is set to a range of 5 to 20 μm without being set to a constant value in order to select the distance D between the surface 16 of the plated member 11 and the observation surface 21 within a 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 set out in JISG 0553: 2008, the plating member 10 is immersed in a corrosive liquid such as nital (nital) and the observation surface 21 is corroded, and then the observation surface 21 is observed with a microscope such as a metallographic microscope or SEM. The diameter S of the circumscribed circle 22 of the crystal grain 20 can be measured by performing arithmetic processing on the microscope image of the observation surface 21. In the plated member 10, crystal grains 20 having a diameter S of 20 to 60 μm circumscribed with a circle 22 appear on an observation surface 21.

On the other hand, when the zinc concentration of the plating solution is about 15g/L and the plating solution contains a sufficient amount of the additive, the additive is adsorbed on the member to be plated 11 and the metal atoms 19, and the subsequent precipitation of a part of the metal is suppressed to make the crystal grains fine. The additive reduces the roughness of the surface 18 of the zinc plating layer 17, and gives the zinc plating layer 17 a luster. In this case, the grain size of the crystal grains appearing on the observation surface 21 is generally 1 μm or less.

When the additive of the plating solution or the like suppresses the deposition of the metal atoms 19, the current efficiency becomes low, and the amount of electricity not used for the deposition of the metal among the amount of electricity applied to the plating solution is used for the generation of hydrogen atoms. As a result, the amount of hydrogen atoms generated increases, and the possibility that more hydrogen atoms will penetrate into the member to be plated 11 increases. In contrast, in the present embodiment, the concentrations of zinc and additives in the plating solution are adjusted to increase the current efficiency in the zinc electroplating.

The appearance of the crystal grains 20 having a diameter S of 20 to 60 μm circumscribing the circle 22 on the observation surface 21 indicates the height of the current efficiency in the electrogalvanizing. By improving the current efficiency in the electrogalvanizing, the amount of electricity used in addition to the precipitated metal can be reduced in the electrogalvanizing. This can suppress the generation of hydrogen atoms during the electrogalvanizing, thereby reducing the amount of hydrogen atoms absorbed into the plated member 11 during the electrogalvanizing. Thereby, the delayed fracture of the plated member 10 can be suppressed.

It is preferable that the proportion of crystal grains 20 having a diameter S of 20 to 60 μm circumscribed about a circle 22 among the crystal grains 20 appearing on the observation surface 21 in a rectangular visual field having a size of 300X 400. mu.m is 60% or more. Thus, it is considered that the current efficiency at the time of the zinc electroplating has been made higher, and the delayed fracture of the plated member 10 can be further suppressed.

Fig. 5 is a partial front view of the plated member 10. As shown in fig. 3C, since the surface 18 of the zinc plating layer 17 is uneven and has little gloss, the roughness of the surface 18 of the zinc plating layer 17 is reduced by, for example, rubbing the plated members 10 against each other, rubbing the plated members 10 against an abrasive (not shown), or performing a blasting treatment or the like as required.

As shown in fig. 5, the zinc plating layer 17 of the plated member 10 having the surface 18 with reduced roughness has a glossy portion 23 and a frosted portion 24 having a surface roughness greater than that of the glossy portion 23. The glossy portion 23 is a portion where the surface 18 of the zinc plating layer 17 is sufficiently rubbed, and the frosted portion 24 is a portion where the rubbing is less or no rubbing than the glossy portion 23. In the plated member 10, the area of the glossy portion 23 is larger than the area of the frosted portion 24, so that the glossy feeling of the plated member 10 can be ensured.

The ground portion 24 is present at the boundary between the welded portion 15 and the second straight portion 14 of the plated member 10. Since the welded portion 15 and the second straight portion 14 have different textures, a sense of incongruity due to the ground portion 24 is less likely to be caused. In the present embodiment, since the welded portion 15 is thicker than the second straight portion 14, the ground portion 24 is formed at the corner between the second straight portion 14 and the welded portion 15. By forming the polishing portion 24 at the corner, it is possible to make it more difficult to cause a sense of incongruity due to the polishing portion 24.

[ examples ]

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(preparation of sample)

Various samples (plated members) plated with zinc having a target thickness of 20 μm were prepared by immersing a chain (plated member) comprising 5 steel endless links in a plating solution. The zinc concentration of the plating solution, the concentration of the additive, and the current density during plating were varied for each sample, and the grain size of crystal grains appearing on the surface of the zinc plating layer was varied. The material and size of the chain links (steel) of each sample and the temperature of the plating solution were constant. The samples were not subjected to so-called baking.

After the surface of the zinc plating layer of each sample was polished and the structure of the observation surface (polished surface) was developed by nitroethanol (nital) etching, the ratio (%) of crystal grains having a circumscribed circle diameter of 20 to 60 μm among crystal grains developed in a rectangular visual field of 300 × 400 μm was measured by image processing using a metallographic microscope. Further, the following is measured by JIS H8501: 1999, it was confirmed that the distance between the surface of the plated member and the observation surface was in the range of 5 to 20 μm.

(hysteresis fracture resistance characteristics)

The tensile test was conducted by holding both ends of each sample (chain) in the longitudinal direction and applying a tensile force at a speed of 10 mm/min to each sample. The loading time for applying the pulling force is 168 hours at the maximum. The hysteresis fracture resistance was evaluated by the ratio of the ultimate stress to the yield stress, using the maximum stress at which fracture did not occur during 168 hours of applying a tensile force as the ultimate stress. When the ultimate stress/yield stress is 1.00 or more, the hysteresis fracture resistance is considered to be excellent, and when less than 1.00, the hysteresis fracture resistance is considered to be poor.

FIG. 6 is a graph showing the relationship between the ratio of crystal grains having a circumscribed circle with a diameter of 20 to 60 μm (hereinafter simply referred to as "ratio") among crystal grains appearing in a visual field of 300X 400. mu.m, and the ultimate stress/yield stress. As shown in fig. 6, the ultimate stress/yield stress was 0.86 (less than 1.00) for the sample with the ratio of 0%. In the sample with a ratio of 0%, the grain size of the crystal grains appearing on the observation surface was 1 μm or less.

On the other hand, in a sample in which crystal grains having a diameter of 20 to 60 μm and circumscribing a circle exist in a visual field (ratio > 0%), the ultimate stress/yield stress is 1.00 or more. As a result, it is found that crystal grains having a diameter of 20 to 60 μm of the circumscribed circle appear in the visual field, and the hysteresis breakdown can be suppressed.

Further, it was observed that the ultimate stress/yield stress tended to become larger as the ratio increased. In particular, when the ratio is 60% or more and 100% or less, the ultimate stress/yield stress is 1.20 or more. When the ultimate stress/yield stress is 1.20 or more, the sample is significantly deformed (elongated) when a tensile force is applied, and thus brittle failure (delayed failure) disappears. From this, it is understood that when the ratio is 60% or more, the effect of suppressing the hysteresis breakdown is extremely high.

(analysis of Hydrogen)

The sample was immersed in a 10% aqueous solution of sodium hydroxide, and the surface plating was completely removed by an anodic dissolution reaction. Next, the sample was cut at the center in the longitudinal direction to obtain a rod-like specimen having a length of 20 mm. After the sample was obtained, hydrogen analysis was performed directly using a temperature-rising desorption analyzer. The amount of hydrogen released from the sample, i.e., the amount of hydrogen released (wt. ppm/min), was measured at each temperature with the analysis start temperature set at 25 ℃, the analysis end temperature set at 400 ℃, and the temperature increase rate set at 100 ℃/hour. Hydrogen released between ambient temperature and less than 300 c is generally referred to as diffusible hydrogen. This diffused hydrogen is believed to be the cause of the hysteresis breakdown. Fig. 7 shows the measurement results of the amount of diffusible hydrogen in the sample at a ratio of 80% (example) and the sample at a ratio of 0% (comparative example).

As shown in fig. 7, it is understood that the examples can significantly reduce the amount of hydrogen released between room temperature and 300 ℃. Since the absorption amount of hydrogen atoms is extremely small in the examples compared with the comparative examples, it is apparent that the examples can suppress the hysteresis breakdown compared with the comparative examples.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments at all, and it can be easily inferred that various modifications and changes can be made without departing from the scope of the present invention.

In the embodiment, a chain in which a plurality of annular links (plated members 11) formed in an O-shape (elliptical shape) are connected to each other is described, but the invention is not necessarily limited thereto. For example, in order to prevent the links from becoming entangled with each other, it is of course possible to use a rung link formed in a substantially θ -shaped ring shape by connecting the intermediate portions of the links by a rung in place of the link (plated member 11).

In the embodiment, the plated member 10 is described by exemplifying the example of the chain, but the invention is not limited to this. For example, it is needless to say that the plating member can be formed by zinc plating a screw, a spring, a gear, PC bar steel, or the like made of steel.

In the embodiment, the case where the zinc plating layer 17 is present on the surface of the plated member 10 is described, but the present invention is not limited to this. For example, it is needless to say that the chromate treatment is performed on the plated member 10, and a chromate film is formed on the surface of the zinc plating layer 17.

In the examples, the sample was cut and a sample having a length of 20mm for hydrogen analysis was used, but the present invention is not limited thereto. The length of the sample can be set appropriately within a range of, for example, 7 to 20mm in length, depending on the size of the sample.

Claims

1. A plated member characterized in that,

comprising a member to be plated made of steel and a zinc plating layer formed on the surface of the member to be plated,

the zinc plating layer has crystal grains with a diameter of 20-60 [ mu ] m, which circumcircle, on an observation surface separated from the surface of the plated member in a thickness direction of the zinc plating layer with a distance of 5-20 [ mu ] m.

2. The plated member according to claim 1,

on the observation surface, the ratio of crystal grains having a diameter of 20 to 60 μm with a circumscribed circle among crystal grains appearing in a visual field having a size of 300X 400 μm is 60% or more and 100% or less.

3. The plated member according to claim 1, wherein the plated member is a chain.

4. The plated member according to claim 2, wherein the plated member is a chain.

5. The plated member according to any one of claims 1 to 4,

the zinc plating layer has a glossy portion and a frosted portion having a surface roughness higher than that of the glossy portion,

the area of the gloss part is larger than that of the frosted part.

6. The plated member according to claim 5,

the plated member is a chain formed by connecting a plurality of annular chain links,

the link has a pair of curved portions facing each other, a linear portion adjacent to the curved portions, and a welding portion joining the linear portions facing each other,

the frosted portion is present at a boundary between the welding portion and the linear portion.