JP6780932B2 - Chain manufacturing equipment and chain manufacturing method - Google Patents

Description

The present invention relates to a chain manufacturing apparatus and a method for manufacturing a chain.

Link chains used for electric chain blocks, conveyor chains, etc. are required to have high wear resistance and fatigue resistance because a large tensile force is applied to them. Since an impact load also acts, the link chain is required to have strength (tensile strength) and toughness. For this reason, a surface treatment chain that has been carburized and hardened and tempered is used (Patent Document 1).

Japanese Patent No. 3311949

However, there is a demand for further strength improvement with respect to the above-mentioned conventional technique.

The present invention has been made in order to meet the above-mentioned requirements, and an object of the present invention is to provide a chain manufacturing apparatus and a chain manufacturing method capable of improving the strength and toughness of a surface-hardened chain.

Means for Solving Problems and Effects of Invention

In order to achieve this object, according to the chain manufacturing apparatus according to claim 1, the thickness of the carburized layer covering the core portion of the work in which the links formed by the steel wire rods are connected to each other is increased by the carburizing furnace. Carburizing is performed by heating to 850 to 950 ° C. for a time of 2% or more of the wire diameter of the link, and the carburized work is slowly cooled to 200 ° C. at 15 to 30 ° C./min by a slow cooling furnace. Subsequent to induction hardening apparatus, the workpiece is quenched after the workpiece has been heated for 5-10 seconds frequency as slowly cooled workpiece is heated to 850 to 1000 ° C.. A surface hardening chain is formed by heating the work with a high frequency for 5 to 10 seconds so that the hardened work is heated to 200 to 400 ° C. by a high frequency tempering device . Since the structure can be made into a fine martensite structure by induction hardening, there is an effect that the strength and toughness of the surface-hardened chain can be improved.
The steel constituting the link before carburizing in the carburizing furnace is C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass. %, P: 0.03% by mass or less, S: 0.03% by mass or less, B: 0.0005 to 0.0030% by mass, and when the balance is composed of Fe and unavoidable impurities, the hardenability is improved. Moreover, it has the effect of ensuring strength and toughness.
Further, the steel constituting the link before being carburized in the carburizing furnace is C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1. It contains 65% by mass, P: 0.03% by mass or less, S: 0.03% by mass or less, Ni: 0.70 to 1.2% by mass, and Cr: 0.40 to 0.60% by mass. Mo: When it contains at least one of 0.15 to 0.25% by mass and the balance is Fe and unavoidable impurities, it has the effect of improving hardenability and improving toughness and corrosion resistance.

According to the method for manufacturing a chain according to claim 2, a work in which carburized steel links are connected to each other is prepared by the preparation step. Specifically, in the preparatory step, the carburized layer is heated to 850 to 950 ° C. so that the thickness of the carburized layer covering the core is 2% or more of the wire diameter of the link, and then carburized to 200 ° C. Prepare the work formed by slowly cooling at / min. The induction hardening process, the work is quenched the workpiece after the workpiece has been heated for 5-10 seconds frequency to be heated to 850 to 1000 ° C.. In the tempering step, a surface hardening chain is formed by heating the work at high frequency for 5 to 10 seconds so that the work hardened at high frequency is heated to 200 to 400 ° C. and tempering . Since the structure can be made into a fine martensite structure by induction hardening, there is an effect that the strength and toughness of the surface-hardened chain can be improved.
The steel constituting the link before the carburizing treatment is C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass, P. : 0.03% by mass or less, S: 0.03% by mass or less, B: 0.0005 to 0.0030% by mass, and when the balance is composed of Fe and unavoidable impurities, the hardenability is improved and the hardenability is improved. It has the effect of ensuring strength and toughness.
Further, the steel constituting the link before the carburizing treatment is C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass. , P: 0.03% by mass or less, S: 0.03% by mass or less, Ni: 0.70 to 1.2% by mass, Cr: 0.40 to 0.60% by mass, Mo: 0 When it contains at least one of .15 to 0.25% by mass and the balance is composed of Fe and unavoidable impurities, it has the effect of improving hardenability and improving toughness and corrosion resistance.

It is a front view of the surface hardening chain in one Embodiment of this invention. It is sectional drawing of the surface hardening chain in line II-II of FIG. (A) is a schematic view of a chain manufacturing apparatus according to an embodiment of the present invention, (b) is a sectional view of a carburizing furnace in line IIIb-IIIb of FIG. 3 (a), and (c) is a modified example. It is sectional drawing of the carburizing furnace in.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The configuration of the surface hardening chain 10 according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a front view of the surface hardening chain 10 according to the embodiment of the present invention, and FIG. 2 is a cross-sectional view of the surface hardening chain 10 along the arrows II-II of FIG. It should be noted that in FIG. 1, the illustration of the intermediate portion in the longitudinal direction of the surface hardening chain 10 is partially omitted, and in FIG. 2, a part of the cross section is enlarged.

As shown in FIG. 1, the surface hardening chain 10 is a link chain in which a plurality of annular links 11 formed in an O shape are connected. The link 11 is formed of a steel wire rod (round bar) in which the content of alloying elements is suppressed. The welded portion 12 is a portion where the end faces of the wire rods butted by bending are joined by electric resistance welding or the like.

As shown in FIG. 2, the link 11 is formed with a carburized layer 14 covering the core portion 13 on the outer peripheral side of the core portion 13. The carburized layer 14 is a layer in which carbon is diffused in the link 11 by gas carburizing, plasma carburizing, or the like. The link 11 is slowly cooled after carburizing (after the carburizing layer 14 is formed), and then induction hardening is performed. The wear resistance of the surface hardening chain 10 can be ensured by forming the charcoal layer 14 and hardening the surface 15. The chemical composition of the steel constituting the link 11 is as follows.

C is an element for ensuring the strength of the link 11, particularly the strength of the core portion 13, and the content is 0.25 to 0.30% by mass. The lower limit of C is 0.20% by mass in order to secure the strength of the link 11. If C exceeds 0.30% by mass, the toughness decreases, so the upper limit is 0.30% by mass.

Si is an element necessary for ensuring the strength of the link 11, and the content is 0.15 to 0.30% by mass. The lower limit of Si is 0.15% by mass in order to secure the strength of the link 11. Since the toughness of Si decreases when it exceeds 0.30% by mass, the upper limit is 0.30% by mass.

Mn is used as a deoxidizing element and reacts with S in steel to form MnS, which is an element useful for detoxifying S. The Mn content is 0.60 to 1.65% by mass. If Mn is excessively contained, hardenability increases and toughness decreases, so the upper limit is 1.65% by mass.

Since P reduces the ductility of steel, it is desirable that it be as small as possible. Further, since P is easily segregated at the grain boundaries and the grain boundaries are easily broken, the content is 0.03% by mass or less (not including 0%).

Since S reduces the ductility of steel like P, it is desirable that S is as small as possible. Further, since S is easily segregated at the grain boundaries and the grain boundaries are easily broken, the content is 0.03% by mass or less (not including 0%).

B is an element that improves hardenability, has the effect of strengthening the grain boundaries of the former austenite, and contributes to the suppression of fracture. However, since this effect is saturated even if B is excessively contained, the content of B is set to 0.0005 to 0.0030% by mass.

Ni is an element effective in suppressing surface decarburization and improving corrosion resistance. It has the function of making steel tough and preventing low-temperature brittleness and coarsening of crystal grains at high temperatures. Cr and Mo are optional additive elements. Cr and Mo improve hardenability and are effective in improving heat resistance and creep resistance.

A chain manufacturing apparatus 20 for manufacturing the surface hardening chain 10 will be described with reference to FIG. 3, and a method for manufacturing the surface hardening chain 10 will also be described. FIG. 3A is a schematic view of the chain manufacturing apparatus 20 according to the embodiment of the present invention, and FIG. 3B is a cross-sectional view of the carburizing furnace 44 in line IIIb-IIIb of FIG. 3A. FIG. 3C is a cross-sectional view of the carburizing furnace 44 in the modified example. In FIGS. 3 (b) and 3 (c), a part of the work W in the longitudinal direction is not shown.

As shown in FIG. 3A, the chain manufacturing apparatus 20 includes a molding apparatus 30 for connecting links 11 (see FIG. 1) to form a work W, a carburizing apparatus 40 for carburizing the formed work W, and a carburizing treatment. The work W is provided with a slow cooling device 50 for slowly cooling the work W, a high frequency quenching device 60 for quenching the slowly cooled work W, and a high frequency tempering device 70 for tempering.

The forming apparatus 30 is an apparatus for forming a work W to which a link 11 (see FIG. 1) is connected by cutting a wire rod M, heating it, bending it, welding it, and the like. In the molding device 30, the steel wire rod M is supplied to the molding machine 32 by the supply device 31, and the work W formed by the molding machine 32 is stored in the storage device 33.

The carburizing device 40 is a device for carburizing the work W. In the present embodiment, the work W conveyed by the belt 43 rotating in a certain direction is continuously gas carburized in the carburizing furnace 44. .. In the carburizing device 40, the work W is supplied to the dispersion device 42 by the supply device 41. The disperser 42 reciprocates the work W in a direction orthogonal to the transport direction of the work W by the belt 43, thereby causing the work W to meander (bend left and right many times) as shown in FIG. 3 (b). It is a device to be placed on the belt 43 (in a state of being folded).

Since the carburizing device 40 transports the work W in a meandering state in the carburizing furnace 44 for carburizing, the length of the carburizing furnace 44 can be shortened and per unit time as compared with the case where the work W is not meandered. The amount of carburized work W can be increased. By adjusting the degree of meandering of the work W, the processing amount per unit time by the carburizing device 40 and the slow cooling device 50 can be made substantially the same as the processing amount per unit time by the induction hardening device 60. As a result, the retention of the work W between the steps can be suppressed.

The disperser 42 is omitted, and the work W is linearly formed on the belt 43 so as to be parallel to the longitudinal direction of the belt 43 (horizontal direction in FIG. 3C) as shown in FIG. 3C. It is possible to carry out the carbon dioxide treatment by arranging a plurality of work Ws (for example, 6 to 8) in the width direction (short direction) of the belt 43. The amount of carbonation of the work W per unit time can be increased according to the number of the work W arranged.

The carburizing furnace 44 heats the work W to 850 to 950 ° C., and the belt 43 has a carburized layer 14 (see FIG. 2) having a thickness (total carburizing depth) of 2% or more of the wire diameter of the work W (link 11). Work W is conveyed at a speed that becomes. The staying time of the work W in the carburizing furnace 44 is about 40 to 80 minutes. The total carburizing depth is the depth at which the C concentration distribution formed by the carburizing treatment converges on the C concentration of the base metal. The portion beyond this depth is the core portion 13 (see FIG. 2).

The slow cooling device 50 is a device for slowly cooling the work W that has been carburized by the carburizing device 40. In the present embodiment, the slow cooling furnace 51 is continuously provided in the carburizing furnace 44. The work W is conveyed in the slow cooling furnace 51 following the carburizing furnace 44 by the belt 43. It is desirable that the inside of the slow cooling furnace 51 has a reducing atmosphere. This is to prevent the oxidation of steel. The slowly cooled work W is collected from above the belt 43 by the collection device 52 and stored in the storage device 53. The cooling rate of the work W by the slow cooling furnace 51 is preferably 15 to 30 ° C./min. This is because the heat treatment strain is suppressed while ensuring the production efficiency, and the martensite structure is less likely to be formed in the work W.

The induction hardening device 60 is a device that austenites the work W by high frequency heating and then transforms it by quenching. In the induction hardening device 60, the work W is supplied to the induction furnace 62 (high frequency induction furnace) by the supply device 61, and the work W heated in the induction furnace 62 is charged into the liquid tank 63 and quenched, and then the liquid tank. It is pulled up from 63 and stored in the storage device 64. By induction hardening, the old austenite crystal grains of the work W are refined, and the strength and toughness of the work W are improved.

The induction furnace 62 heats the work W to 850 to 1000 ° C., and the work W is heated in the induction furnace 62 while moving, so that the work W passes through the temperature range within 5 to 10 seconds. This is to dissolve the carbide in a solid solution to form austenite and to prevent coarsening of crystal grains.

The high-frequency tempering device 70 is a device for improving the toughness of the link 11 without significantly reducing the hardness of the carburized layer 14 (see FIG. 2). In the high-frequency tempering device 70, the work W is supplied to the induction furnace 72 (high-frequency induction furnace) by the supply device 71, and the work W heated in the induction furnace 72 is charged into the liquid tank 73 to be cooled, and then the liquid tank is cooled. It is pulled up from 73 and stored in the storage device 74.

The induction furnace 72 heats the work W to 200 to 400 ° C., and the work W is heated in the induction furnace 72 while moving, so that the work W passes through the temperature range within 5 to 10 seconds. This is to make it difficult for the hardness variation in the cross section of the link 11 in the circumferential direction to occur, and to prevent the carbide from becoming coarse.

According to the chain manufacturing apparatus 20, since the vicinity of the surface of the link 11 can be formed into a fine martensite structure by induction hardening, the strength and toughness of the surface-hardened chain 10 can be improved. In the surface hardening chain 10, the former austenite crystal grains of the core portion 13 and the carburized layer 14 are refined. The carburized layer 14 has an old austenite crystal grain size number of 10 or more, preferably 11 or more, and more preferably 13 or more. The core portion 13 has an old austenite crystal grain size number of 8 or more, preferably 13 or more. The old austenite crystal grain size is measured according to JIS G0551 (2013 edition). Strength and toughness can be improved by setting the old austenite crystal grain size number of not only the charcoal layer 14 but also the core portion 13 to 8 or more. Further, the low temperature brittleness of the surface hardening chain 10 can be improved.

The surface hardening chain 10 is set so that the Vickers hardness of the charcoal layer 14 is larger than the Vickers hardness of the core portion 13 in the micro Vickers hardness test having a test force of 0.9807N. Specifically, the carburized layer 14 has a Vickers hardness of 550 to 650 on the surface 15, and the core portion 13 has a Vickers hardness of 400 to 500. The Vickers hardness is measured in accordance with JIS Z2244 (2009 version). The Vickers hardness of the core portion 13 is the hardness of the cross section of the polished core portion 13.

The present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. Table 1 shows the chemical composition of the wire rod (round bar, wire diameter 10 mm) used in this example.

これらの線材について、以下の２つの処理条件で鋼種毎に浸炭および焼入れを行い、試料１から試料４のチェーンを得た。各試料につきサンプル数は１０である。得られたチェーンについて、旧オーステナイト結晶粒度、ビッカース硬さ、静的強さ、衝撃値を測定し、サンプルの平均値を算出した。

These wire rods were carburized and hardened for each steel type under the following two treatment conditions to obtain chains of Sample 1 to Sample 4. The number of samples for each sample is 10. For the obtained chain, the old austenite crystal grain size, Vickers hardness, static strength, and impact value were measured, and the average value of the sample was calculated.

(Processing condition 1)
The wire was cut, heated, bent and welded to form a workpiece with links. Then, the work was subjected to gas carburizing treatment (carburizing temperature 850 ° C.) by a usual method. After that, the work was cooled at a rate of 20 ° C./min and taken out of the furnace when the temperature reached 200 ° C. Next, induction hardening (heating temperature 930 ° C.) was performed on the work, and then tempering was performed at 200 ° C. This processing condition is an embodiment of the present invention.

(Processing condition 2)
The wire was cut, heated, bent and welded to form a workpiece with links. Then, the work was subjected to gas carburizing treatment (carburizing temperature 870 ° C.) by a usual method. After that, the work was quenched in a salt (NaNO ₂ : KNO ₃ = 1: 1, melting point 140 ° C.) tank, and then tempered at 200 ° C. This processing condition is a comparative example (conventional processing condition).

(Former austenite grain size)
The particle size of the old austenite crystal in the carburized layer and the core was measured according to JIS G0551 (2013 edition).

(Vickers hardness)
The Vickers hardness of the surface of the carburized layer and the Vickers hardness of the center of the cross section (polished surface) of the core were measured by a micro Vickers hardness test having a test force of 0.9807 N according to JIS Z2244 (2009 version).

(Static strength test)
According to JIS B8812 (2004 version), a static tensile load was applied with a tensile tester to break the chain, and the breaking load was measured.

(Chain link impact value)
An impact test (test temperature −10 ° C.) was performed in accordance with JIS B8812 (2004 version) and JIS B8841 (2004 version), and the impact value was calculated.

The test results (mean values) are shown in Table 2.

表２によれば鋼種１では、条件１により処理された試料１は、条件２により処理された試料２に対して、旧オーステナイト結晶粒度番号は浸炭層において３６％増加し、芯部において１００％増加した。静的強さは９％増加し、衝撃値は８８％増加した。高周波焼入れにより組織を微細化することができ、強度および靭性を向上できることが確認された。

According to Table 2, in the steel type 1, the sample 1 treated under the condition 1 has the old austenite crystal grain size number increased by 36% in the carburized layer and 100% at the core as compared with the sample 2 treated under the condition 2. Increased. The static strength increased by 9% and the impact value increased by 88%. It was confirmed that the structure can be miniaturized by induction hardening and the strength and toughness can be improved.

In the steel type 2, the sample 3 treated under the condition 1 had a 20% increase in the old austenite crystal grain size number in the carburized layer and a 29% increase in the core portion with respect to the sample 4 treated under the condition 2. The static strength increased by 4% and the impact value increased by 12%. Although the rate of increase is smaller than that of steel type 1, it was confirmed that the structure of steel type 2 can be miniaturized by induction hardening, and the strength and toughness can be improved.

Steel type 1 has C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass, P: 0.03% by mass or less. S: 0.03% by mass or less, B: 0.0005 to 0.0030% by mass, and the balance is a kind of steel composed of Fe and unavoidable impurities. It was confirmed that even steels other than steel type 1 having a chemical composition in this range exhibit the same characteristics as sample 1 by performing the treatment under the above condition 1.

Steel type 2 has C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass, P: 0.03% by mass or less, S. : 0.03% by mass or less, Ni: 0.70 to 1.2% by mass, Cr: 0.40 to 0.60% by mass, Mo: 0.15 to 0.25% by mass, and the balance is Fe It is a kind of steel composed of unavoidable impurities. It was confirmed that even steels other than steel type 2 having a chemical composition in this range exhibit the same characteristics as sample 3 by performing the treatment under the above condition 1.

Further, C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass, P: 0.03% by mass or less, S: 0 Steel containing 0.03% by mass or less, Ni: 0.70 to 1.2% by mass, Cr: 0.40 to 0.60% by mass, and the balance consisting of Fe and unavoidable impurities, and C: 0.20 ~ 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass, P: 0.03% by mass or less, S: 0.03% by mass or less, Ni Even for steel containing 0.70 to 1.2% by mass and Mo: 0.15 to 0.25% by mass and the balance of which is Fe and unavoidable impurities, the sample is subjected to the above-mentioned condition 1 treatment. It was confirmed that the characteristics as shown in 3 were exhibited.

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

In the above embodiment, the surface hardening chain 10 (link chain) in which a plurality of annular links 11 formed in an O shape (oval shape) are connected has been described, but the present invention is not necessarily limited to this. For example, in order to prevent the links from being entangled with each other, it is naturally possible to adopt an annular stud link formed in a substantially θ shape in which the intermediate portions of the links are connected by studs instead of the link 11.

In the above embodiment, the chain manufacturing apparatus 20 including the carburizing furnace 44 that performs the gas carburizing treatment has been described, but the present invention is not necessarily limited to this, and it is naturally possible to use a carburizing furnace that performs another carburizing treatment. .. Other carburizing treatments include vacuum carburizing treatment in which gas carburizing is performed under reduced pressure, carburizing and nitriding treatment, and plasma carburizing treatment.

In the above embodiment, the case where the chain manufacturing apparatus 20 includes the high frequency tempering apparatus 70 has been described, but the high frequency tempering apparatus 70 is not an essential apparatus for the chain manufacturing apparatus 20, and can be omitted. Similarly, the molding apparatus 30 is not an essential apparatus for the chain manufacturing apparatus 20, and can be omitted.

In the above embodiment, the work W that has passed through the slow cooling furnace 51 is stored in the storage device 53, then stored in the supply device 61 of the high-frequency quenching device 60, and the hardened work W is stored in the storage device 64. , The case where it is housed in the supply device 71 of the high frequency tempering device 70 has been described. However, the processing amount of the work W is not necessarily limited to this, and the processing amount per unit time of the carburizing device 40, the slow cooling device 50, the induction hardening device 60 and the high frequency tempering device 70 is set to be substantially the same. Carburizing and tempering can be performed continuously. Since it is not necessary for a person or a robot to transport the work W between the carburizing device 40, the slow cooling device 50, the induction hardening device 60, and the induction tempering device 70, labor saving is possible. Further, since the storage devices 53 and 64 and the supply devices 61 and 71 can be eliminated, the configuration of the device can be simplified. In this case as well, it is possible to omit the high frequency tempering device 70.

Even if the carburizing and tempering of the work W are not continuously performed, it is naturally possible to continuously perform the induction hardening to the high frequency tempering after preparing the carburized work W.

In the above embodiment, the case where the work W to which the link 11 is connected is manufactured and then carburized and induction hardened has been described, but the present invention is not necessarily limited to this. For example, first, a steel wire rod that has been carburized and slowly cooled is prepared. Next, the work W to which the link 11 is connected is formed using the wire rod. Next, it is naturally possible to manufacture the surface hardening chain 10 by performing induction hardening and induction tempering of the work W.

10 Surface hardening chain 11 Link 13 Core part 14 Carburizing layer 15 Surface 20 Chain manufacturing equipment 44 Carburizing furnace 51 Slow cooling furnace 60 Induction hardening equipment
70 High frequency tempering device W work

Claims (2)

A work in which links formed of steel wires are connected to each other is carburized by heating to 850 to 950 ° C. for a time during which the thickness of the carburized layer covering the core becomes 2% or more of the wire diameter of the links. Carburizing furnace to process and
A slow cooling furnace that slowly cools the work carburized in the carburizing furnace to 200 ° C at 15 to 30 ° C / min.
A high-frequency hardening device you quenching the workpiece after the workpiece which has been slowly cooled in the annealing furnace has the high frequency work for 5-10 seconds heating to be heated to 850 to 1000 ° C.,
An induction hardening device that forms a surface hardening chain by heating the work at a high frequency for 5 to 10 seconds so that the work hardened by the induction hardening device is heated to 200 to 400 ° C. Prepare,
The steel constituting the link before being carburized in the carburizing furnace has C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1. It contains 65% by mass, P: 0.03% by mass or less, S: 0.03% by mass or less, B: 0.0005 to 0.0030% by mass, and the balance is composed of Fe and unavoidable impurities, or
C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass, P: 0.03% by mass or less, S: 0.03 It contains not more than mass%, Ni: 0.70 to 1.2 mass%, and at least one of Cr: 0.40 to 0.60 mass% and Mo: 0.15-0.25 mass%. A chain manufacturing apparatus characterized in that the balance is composed of Fe and unavoidable impurities. A preparatory step to prepare a workpiece with carburized steel links connected to each other,
And high-frequency quenching process induction hardening its work,
The work is provided with a tempering step of forming a surface hardening chain by heating the work with high frequency for 5 to 10 seconds so that the work hardened with high frequency is heated to 200 to 400 ° C.
In the preparatory step, the carburized layer is heated to 850 to 950 ° C. so that the thickness of the carburized layer covering the core is 2% or more of the wire diameter of the link, and the carburized treatment is performed. Prepare the work formed by slowly cooling in minutes,
In the induction hardening step, the work is quenched after heating the work at high frequency for 5 to 10 seconds so that the work is heated to 850 to 1000 ° C.
The steel constituting the link before the carburizing treatment was C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass, P: 0.03% by mass or less, S: 0.03% by mass or less, B: 0.0005 to 0.0030% by mass, and the balance is composed of Fe and unavoidable impurities, or
C: 0.25 to 0.30% by mass, Si: 0.15 to 0.30% by mass, Mn: 0.60 to 1.65% by mass, P: 0.03% by mass or less, S: 0.03 It contains not more than mass%, Ni: 0.70 to 1.2 mass%, and at least one of Cr: 0.40 to 0.60 mass% and Mo: 0.15-0.25 mass%. However, a method for manufacturing a chain, wherein the balance is composed of Fe and unavoidable impurities.

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