JPH11236619A - Crawler track bush and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a crawler belt bush and a method for manufacturing the same, which can improve productivity and cost more than carburizing treatment and induction hardening treatment. SOLUTION: The crawler belt bush material made of steel is heated from the outer peripheral surface side by a high-frequency coil 2 to at least the inner peripheral surface temperature of the crawler belt bush material to a temperature that can be quenched, and then cooling from the inner peripheral surface is performed first. Quenching from the outer peripheral surface and the inner peripheral surface to the center of the wall thickness by a series of one quenching operation of cooling from the outer peripheral surface and cooling from the outer peripheral surface. A hardened layer is formed to form a soft unquenched layer between the two hardened hardened layers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crawler bush used for construction machines such as bulldozers and a method for manufacturing the same, and more particularly to a crawler bush excellent in wear resistance and impact fatigue resistance. And a production method for producing the crawler bush in a simpler manner at a lower cost.

[0002]

2. Description of the Related Art As shown in FIG. 11, a crawler belt 51 of a construction machine or the like is composed of a group of parts. In particular, a crawler belt bush 52 meshes with a sprocket tooth for transmitting a rotational motion from a final reduction gear. Since the bush has a function of rotating the crawler belt 51 and travels on and in debris, wear resistance is required on the inner and outer peripheral surfaces. Severe strength and toughness are required. In order to satisfy these required characteristics, the following method has been conventionally used in manufacturing this crawler belt bush. Case hardening steel is carburized to form high-hardness martensite on the inner and outer surface layers to ensure abrasion resistance and strength (see, for example, Japanese Patent Publication No. 52-34806). Using medium-carbon steel, the inner and outer diameters of the bush material that has been tempered are induction-hardened to form high-hardness martensite on the inner and outer surface layers to ensure wear resistance and strength. (See Japanese Patent Publication No. 63-16314). Using medium-carbon steel with very fine control of hardenability while finely adjusting the chemical composition of the steel material, rapidly cool the bush heated at 800 ° C or more to adjust the hardening depth of the inner and outer diameter surface parts. , Designed to ensure wear resistance and strength. FIGS. 12A and 12B are schematic diagrams of typical cured patterns of bushes produced by these conventional methods.
(C) and the hardness distribution (d) of the cross section are shown respectively.

[0003]

However, in the carburizing method, the carburizing time is long,
From the viewpoint of cost, such as mass use of carburizing gas, the problem is large.For example, in the case of a large crawler bush in which the thickness of the bush is large, the required hardened layer depth becomes deeper from the viewpoint of strength and wear resistance. The problem is that the performance is low and the cost is high. Furthermore, since the carburizing heating time is long on the inner and outer peripheral surfaces, a grain boundary oxide layer and an incompletely quenched layer are formed with a thickness of several tens of μm, and the fatigue strength and impact resistance are likely to deteriorate. There is.

On the other hand, the induction hardening method has been improved in cost as compared with the carburizing method. However, the material tempering treatment and the inner diameter,
There is a problem that the heat treatment is still expensive, for example, the quenching process is required twice for the outer diameter. In addition, when induction hardening the inner peripheral surface of a small-diameter cylindrical part, it becomes more difficult to produce an inner peripheral surface heating coil.
As means for hardening the inner and outer peripheral surfaces of these cylindrical parts, the above-mentioned carburizing treatment is performed in many cases, resulting in high cost.

Further, the outer peripheral surface of the bush is exposed to severe earth and sand wear conditions during use, and it is desirable to deepen the hardened hardened layer on the outer peripheral surface of the bush in order to prolong the wear life of the bush. Kosho 63-163
In the method disclosed in Japanese Patent Publication No. 14, after once hardening deeply from the outer peripheral portion by induction hardening from the outer peripheral surface,
The inner peripheral surface is shallowly quenched by induction hardening from the inner peripheral surface, and a softened layer that has been subjected to high-temperature tempering is provided between the two quenched layers.In any case, it is necessary to perform these two induction hardenings. This makes productivity worse and is economically disadvantageous. According to the technique disclosed in this publication, the hardness of the inner peripheral surface is adjusted so that the hardness of the inner peripheral surface does not become HRC40 or more by the induction hardening from the outer peripheral portion, thereby preventing quenching cracks during the subsequent inner peripheral surface induction hardening. In order to apply this method to, for example, a relatively thin cylindrical component (crawler bush), it is necessary to control the temperature control of the inner peripheral surface very accurately during high-frequency heating from the outer peripheral surface and / or Alternatively, it is necessary to accurately control the hardenability (DI value) of the steel used, and as a result, there is a problem that the technical difficulty of increasing the outer peripheral surface hardening depth and an increase in the cost of the steel material are unavoidable. There is.

In the quenching method described above,
Can solve the cost problem, but accurately grasp the relationship between the thickness of the bush to be used and the cooling rate, and control the hardenability (DI value) of the steel to be used accurately and narrowly. Therefore, there is a problem in the availability of steel materials as a production method. In addition, as the bush thickness becomes thinner, the entire thickness becomes hardened, and a large tensile residual stress is generated on the inner and outer surfaces, thereby causing quenching cracks during quenching and remarkable deterioration of fatigue strength. . For this reason, the DI value is inevitably reduced, and practical availability in the market is lost. Further, when the DI value is reduced in this manner, there is a problem that uneven grilling is likely to occur in various places of the crawler bush.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a main object of heating a cylindrical steel crawler belt bushing material from an outer peripheral surface at a high frequency to quench at least the inner peripheral surface. Temperature, and cooling from the inner peripheral surface is started in advance, while cooling from the inner peripheral portion of the outer peripheral portion is suppressed by high frequency heating from the outer peripheral surface, and subsequent outer diameter cooling is performed. In order to prevent quenching at the thick core portion from occurring sufficiently, cooling from the outer peripheral surface with a time delay until cooling is performed in one step of the quenching operation, so that the inner and outer peripheral surfaces are cooled. It is an object of the present invention to provide a crawler belt bush and a method of manufacturing the same, in which a quenched hardened layer is formed on the surface, whereby productivity and cost can be improved as compared with the above-described carburizing and induction hardening.

Further, in the present invention, the formation of a quenched and hardened layer from the inner peripheral surface is ensured, and as described above, the pre-cooling from the inner peripheral surface and the high-frequency heating from the outer peripheral surface, followed by the time delay By performing cooling from the outer peripheral surface with the above, it is a method of forming a soft layer on the thick core portion closer to the inner peripheral surface of the bush thick section, so if the cooling from the inner peripheral surface Even if steel with a large DI value, which is hardened only by itself, is used as a crawler bush material, a softened layer is formed on the thick core, thereby preventing quenching during quenching and hardening the hardened layer from the outer peripheral surface. It is an object of the present invention to provide a crawler belt bush which is deeper than a quenched hardened layer depth from the inner peripheral surface to improve the abrasion resistance of the bush and has excellent fatigue strength, and a method of manufacturing the same at low cost.

The high-frequency heating and quenching method of the present invention can be easily applied to a cylindrical part similar to a crawler bush, but in particular, the present invention does not require heat quenching from the inner peripheral surface. Another object of the present invention is to provide a small-diameter cylindrical component (small crawler bush) or a thin cylindrical component (crawler bush) in which it is more difficult to produce a coil for high-frequency heating of the inner peripheral surface, and a method of manufacturing the same at low cost.

Further, according to the present invention, a softened layer can be formed inside the thick part of the crawler bush and the quenching crack can be prevented even for steel having high hardenability as described above. Crawler belt bush which is a steel material with good quench hardening properties, has a high carbon content up to about 2.0% by weight, and has a more excellent outer surface wear resistance by quenching as described above from an austenitic state in which cementite grains are dispersed. Provide an inexpensive manufacturing method. It is desirable that the crawler belt bushing material before the quenching operation be made to substantially uniformly disperse cementite grains in advance by material refining or the like.

Further, by utilizing the above-described quenching principle, the hardened layer on the inner peripheral surface is deepened by a quenching method in which the inner peripheral surface is cooled after the outer peripheral surface has been pre-cooled, and the inner peripheral surface has abrasion resistance. And to provide an inexpensive method for producing the same.

[0012]

Means for Solving the Problems and Actions / Effects To achieve the above-mentioned object, a crawler belt bush according to the present invention has a carbon content of 0.35 to 2.0% by weight, Mn,
The outer peripheral surface of the crawler belt bushing material is made of a hardenable steel which contains one or more alloying elements such as Si, Cr, Mo, Ni and the like, and is hardened by simultaneous cooling from the inner and outer peripheral surfaces of the crawler belt bushing material. After heating at least the inner peripheral surface temperature of the crawler belt bush material to a temperature at which quenching can be performed by high-frequency induction heating from the side, (1) cooling from the inner peripheral surface is performed in advance, (2) and While performing cooling from the inner peripheral surface, perform heating from the outer peripheral surface,
(3) Next, by a series of one quenching operation for cooling from the outer peripheral surface, a quench-hardened layer is formed from the outer peripheral surface and the inner peripheral surface toward the center of the thickness, and a soft quenched layer is formed between the two quench-hardened layers. An unquenched layer is left, and the soft structure between the two hardened layers hardens and precipitates during the cooling process from the quenching temperature. One or more structures of ferrite, pearlite, bainite, and martensite, or a granular structure in the structure. It is characterized by comprising a structure in which cementite is dispersed.

Further, in the method of manufacturing a crawler belt bush according to the present invention, at least the inner peripheral surface temperature of the crawler belt bush material is heated to a temperature at which quenching treatment can be performed by high-frequency induction heating from the outer peripheral surface side. After that, (1) cooling from the inner peripheral surface is performed in advance, and (2)
In addition, while performing cooling from the inner peripheral surface, heating is performed from the outer peripheral surface. (3) Next, by performing a series of one quenching operation for cooling from the outer peripheral surface, the outer peripheral surface and the inner peripheral surface are cooled. A quenched and hardened layer is formed toward the center of the thickness, and a soft unquenched layer is formed between the two hardened and hardened layers.

Further, the method for manufacturing the crawler bush includes a method in which the crawler bush material made of steel is moved and induction-heated from the outer peripheral surface side by using at least two stages of induction coils, and at a certain position of the crawler bush, While heating the temperature of the peripheral surface to a temperature of A1, A3 and / or Acm or higher that can be hardened, (2) cooling from the inner peripheral surface is performed in advance,
(3) The inner peripheral surface layer and the outer peripheral surface layer are substantially martensitic phases by each step of heating from the outer peripheral surface with an induction coil and (3) cooling from the outer peripheral surface, and quenching and hardening. Is what you do.

After the inner circumference of the crawler belt bushing material is heated to a temperature at which quenching can be performed by the high-frequency induction heating method from the outer circumference, a cooling medium such as water, a water-soluble quenching liquid, or oil is used as described above. While starting cooling from the inner peripheral surface in advance, partially high-frequency heating from the outer peripheral surface,
It is necessary to suppress the cooling from the inner surface of the outer peripheral part, and to perform cooling from the outer peripheral surface with a time delay until quenching inside the thickness does not sufficiently occur even after the outer diameter cooling. In one step of the quenching operation, a soft incomplete quenched structure is formed in the thick core, and sufficient outer peripheral surface hardened layer depth is obtained by cooling from the outer peripheral surface which starts with a time delay. Thus, a crawler belt bush having a hardened hardened layer on the inner and outer peripheral surfaces can be manufactured at low cost.

[0016] Further, as described above, even when the steel having an alloy composition that becomes a sulhard is used by simultaneous cooling from the inner and outer peripheral surfaces or only from the inner peripheral surface, as described above, the preceding cooling from the inner peripheral surface is performed. Since the high frequency heating from the outside diameter is used together, a soft layer can be formed on the thick core near the inner peripheral surface of the bush thick section, so in many cases the quenching of the steel used This eliminates the need to substantially control the properties, makes it possible to use inexpensive steel materials that can be easily obtained in the market, and to reduce track bushing costs.

The pre-cooling of the inner peripheral surface of the present invention means that the heat capacity of the thick core of the crawler bush is reduced, and the outer peripheral surface is cooled by cooling from the outer peripheral surface. The principle is that by increasing the speed, the quenched hardened layer depth on the outer peripheral surface can be made deeper than the quenched hardened layer depth on the inner peripheral surface. This manufacturing method is suitable for manufacturing a crawler belt bush having excellent outer peripheral surface wear life.

In the case where the hardened hardened layer on the outer peripheral surface is further remarkably deepened, for example, the hardenability obtained by hardening only from the outer circumferential surface is equal to or more than the hardenability (DI value) at which the hardened hardening depth is １ ／ of the wall thickness. The use of steel of high hardness, while hardening almost to the wear life allowance (1/2 depth of the thickness) of the crawler bush, and forming the above-mentioned quenched softening layer on the thick core from the inner peripheral surface Thus, a crawler bush having excellent toughness and excellent abrasion life can be manufactured.

As a high-frequency heating system from the outer peripheral surface of the crawler belt bush, a whole heating system and a moving heating system can be adopted. In the overall heating method, as shown in FIG. 1, when the outer peripheral surface is heated by the high-frequency coil 2 during the inner peripheral surface cooling by the inner peripheral surface cooling nozzle 4, the high-frequency coil 2 By adjusting the electric power, the depth of the hardened hardened layer from the inner and outer peripheral surfaces can be adjusted. The cooling from the outer peripheral surface is performed, for example, by using the high-frequency coil 2.
Is moved upward, the outer peripheral surface cooling nozzle 5 is moved from below, and cooling is performed by a separate cooling jet from the gap between the inductors of the high-frequency coil 2.

In the moving heating method, as shown in FIG. 2, the induction coil is made to be a wide coil, or preferably, the induction coils (high-frequency coils) 8, 9 are replaced by two.
The induction heating coils are arranged so that the outer peripheral surface side is prevented from being cooled by the cooling from the inner peripheral surface by high frequency heating as described above. In this way, control is performed so that quenching and hardening in the inside of the wall thickness do not sufficiently occur.

In particular, the quench hardening depth from the inner and outer peripheral surfaces is
In consideration of the relative moving speed between the induction coil and the crawler bush, the second-stage high-frequency coil 9 mainly has a role of outer surface induction heating during inner-peripheral surface cooling. Can be easily controlled by controlling the high-frequency heating time from the outer peripheral surface from the start of the inner peripheral surface cooling to the start of the outer peripheral surface cooling by adjusting the distance from the outer peripheral surface.
In the high-frequency heating and quenching method of the present invention described above,
In particular, since there is no need for heating and quenching from the inner peripheral surface, it is more difficult to produce a coil for high-frequency heating on the inner peripheral surface. A small-diameter cylindrical component (small crawler bush) or a very thin cylindrical component (crawler bush) ) Can be manufactured at low cost.

The steel of the crawler belt bushing material used in the present invention has a quench hardness of HR from the viewpoint of wear resistance and strength.
It is preferable to use steel containing 0.35 to 2.0% by weight of carbon so that the hardness of the outer peripheral surface quench hardened layer is increased so as to be C50 or more. It is well known that increasing the carbon content of the steel material used is effective for inexpensively producing crawler belt bushes having better wear resistance and wear life. According to the conventional induction hardening method, 0.55
The steel is not carried out because the risk of quenching cracks is high in steels of not less than% by weight. However, since the present invention employs the above-mentioned heating and cooling principle, quenching cracks can be prevented, and therefore steel materials having relatively hardenability are used. By performing quenching as described above from an austenitic state in which the carbon content is high up to about 2.0% by weight and cementite grains are dispersed, a crawler belt bush having more excellent outer surface wear resistance can be manufactured at low cost. Can be. It is desirable that the crawler belt bushing material before the quenching operation be made to substantially uniformly disperse cementite grains in advance by material refining or the like.

In particular, in order to improve the wear resistance of the outer peripheral surface of the crawler bush, the bush material is heated to a temperature capable of being quenched and then quenched by the above-described method of pre-cooling the inner peripheral surface and the outer peripheral surface. Superior in wear resistance and impact resistance over carburized hardened layer by applying high frequency tempering from the inner circumferential surface and increasing the toughness of the inner hardened surface layer in particular, while increasing the hardness of the hardened hardened layer on the side Crawler track bush is manufactured at low cost.

A feature of the present invention is that a heat treatment operation in which the outer peripheral surface is cooled and the quenching operation is completed during a one-step quenching operation after the inner peripheral surface pre-cooling is started while high-frequency moving heating of the bush as described above. Unlike the conventional induction hardening method, there is no need to adjust the hardening depth twice on the inner peripheral surface side and the outer peripheral surface side, and there is no need to separately heat and quench the inner and outer diameters. This is preferable in that productivity can be realized, capital investment is suppressed, and energy efficiency is improved.

Further, according to the quenching method of the present invention, the output of the outer peripheral surface heating while the preceding inner peripheral surface cooling is adjusted, and the subsequent outer peripheral surface cooling is performed, so that the quenching depth from the inner peripheral surface is reduced. Since the depth can be made deeper than the quenching depth from the outer peripheral surface, it can also be used as a method for producing a high-strength steel pipe that requires abrasion resistance at the inner diameter portion of, for example, slurry.

As a cooling method for the cylindrical inner peripheral surface side, a jet cooling system such as a water spray or an oil spray is preferable because cooling unevenness is easily generated. In order to prevent the medium from interfering with the outer peripheral portion during the pre-cooling, the spray angle may be set in consideration of the flow of the cooling medium as shown in FIGS.
It is preferable to provide a partition structure like the shielding plate 1 described above.
Further, it is also possible to arrange a plurality of crawler belt bushes such that the end faces thereof abut each other as described above, and to perform quenching by controlling by the above-described quenching method.

[0027] While a part of the crawler bush is moved and heated by using the induction coil, the above-described inner peripheral surface is cooled first, and the cooling of the outer peripheral surface due to cooling from the inner peripheral surface is suppressed. The time difference quenching method of heating by the high-frequency coil and subsequently cooling the outer peripheral surface is a method that does not require a large-scale quenching facility and has high production flexibility. Also in this case, for example, as shown in FIG. 1, the shielding plate 1 and the shielding cap 6 are arranged on the upper and lower end surfaces of the crawler belt bush, and the inner peripheral surface cooling nozzle 4 pre-cools the induction heating zone, While cooling the outer peripheral surface with a time delay and rotating the crawler bush 3,
It is desirable that the induction heating coil 2 and the inner and outer peripheral surface cooling nozzles 4 and 5 are relatively moved in the axial direction of the bush to be quenched.

According to the present invention, the crawler belt bush is continuously quenched with high frequency moving heating, inner diameter cooling, and outer diameter cooling, each having a time difference, thereby forming a hardened hardened layer on the outer peripheral surface and the inner peripheral surface. In addition, a crawler belt bush having a softened layer formed on a thick core portion and a crawler bush having a hardened hard layer depth from the outer peripheral surface deeper than a hardened hard layer depth from the inner peripheral surface are manufactured by a single hardening operation. By this, it is possible to prevent quenching cracks during quenching even for steel that is originally hard due to simultaneous cooling from the inner and outer peripheral surfaces, and to increase the carbon content in the steel as described above, It is possible to provide an improved abrasion life of the bush and an inexpensive manufacturing method thereof, thereby obtaining a great economic advantage.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, specific embodiments of the crawler belt bush and the method of manufacturing the same according to the present invention will be described with reference to the drawings.

(Example 1) The steel components used in this example are shown in Table 1, and the bush shape used in this example is shown in FIG.
Is shown in As the quenching device, a high-frequency moving quenching device as shown in FIG. 2 was used. The quenching apparatus has a two-stage high-frequency coil 8 for heating from the outer periphery,
9. An inner peripheral surface cooling nozzle 10 for cooling the inner peripheral surface of the bush, and an outer peripheral surface cooling nozzle 11 for cooling the outer peripheral surface. Done to be done. Also, the inner peripheral surface cooling nozzle 10 is configured to have an appropriate injection angle with respect to the inner peripheral surface normal direction in consideration of the fact that water in the inner diameter portion of the bush flows in the lower portion of the bush without stagnation. At the lower end of the bush, there is a shielding plate for separating the flow of cooling water for cooling the inner peripheral surface and the flow of cooling water for outer peripheral surface, and at the upper end of the bush, the cooling water for cooling the inner peripheral surface. Caps are provided for partitioning the flow and the flow of cooling water for cooling the outer peripheral surface. The used high frequency power supply is 6
Khz 50KW output, almost 27-32KW
A quenching experiment was performed with power. After the quenching operation, basically, a low-temperature tempering treatment was performed at 140 ° C. for 3 hours. Further, partly, the high-frequency heating power supply is the same, and the heating method is the entire high-frequency heating from the outer peripheral surface side. Was started, and after 6 seconds, heating was terminated to cool the outer peripheral surface.

[0031]

[Table 1]

FIGS. 4 to 6 show a case where the inner and outer peripheral surfaces are simultaneously cooled by the moving quenching method using the steel track bushing materials shown in Table 1 and a case where the outer peripheral cooling nozzle position is shifted downward. After pre-cooling the inner peripheral surface by shifting to
10 shows a hardness distribution in a thick section when the outer peripheral surface is cooled and quenched after 10 seconds. The crawler belt bush material shown in FIG. 6 is a material which has been subjected to oil tempering after heating at 1020 ° C. for 30 minutes and then tempering at 600 ° C. for 1 hour.

From these results, as described above, (1) when the inner and outer peripheral surfaces were originally cooled at the same time, the outer peripheral surface of both the thick core portion of the bush and the hardened steel was cooled during the precedent cooling of the inner peripheral surface. By performing high-frequency heating from the surface, it is possible to give a U-shaped hardness distribution in which a soft layer is formed on a thick core portion closer to the inner peripheral surface of the bush thick section, and (2) further baking In relation to the cracking frequency, quenching cracks in the bush, which is originally sulhardened by simultaneous quenching of the inner and outer surfaces, can be completely prevented by the quenching method of the present invention,
It has been found that a very high carbon content steel can be used for the track bush. (3) Further, even in a bush which is not originally hardened, the heat capacity at the thick core portion of the crawler belt bush is reduced by the pre-cooling from the inner peripheral surface, and the outer peripheral surface is cooled by the outer peripheral surface having a time delay. It has been found that the effect of increasing the cooling rate on the surface side can further increase the depth of the hardened layer. (4) Further, in the present embodiment, since high-carbon steel is used as the crawler bush material, the hardness of the hardened hardened layer is hardened substantially equal to or more than the hardness of the carburized crawler bush, and Since the carburized bush is deeper than the hardened layer depth, the wear life of the crawler bush can be remarkably improved (the normal crawler bush wear life is evaluated as the wear life when about 1/2 of the wall thickness is worn). I understand.

FIG. 7 shows the hardness distribution of the thick section when the entire crawler belt bush is heated by high-frequency heating as described above, then the inner circumferential surface is pre-cooled, and after 10 seconds, the outer circumferential surface is cooled. . This result is almost the same as the data confirmed in FIG. 5, and it can be seen that the quenched and hardened layer is formed by the same heating and cooling mechanism as in the preceding moving quenching.

Further, FIG. 8 shows that the outer peripheral surface cooling power was reduced to about 1/3 (13 KW) together with the inner peripheral surface preliminary cooling, and the outer peripheral surface was cooled after 10 seconds using the entire high frequency heating crawler track bush. The hardness distribution of the thick cross section at the time is shown, but the depth of the hardened hardened layer on the inner peripheral surface can be made deeper, contrary to the result of FIG. It was found to be suitable for applications such as wear resistant and strong pipe products.

(Embodiment 2) FIG. 9 shows an impact fatigue test method. The crawler belt bush subjected to the same moving induction hardening treatment as in the first embodiment and subjected to the tempering treatment at 180 ° C. for 3 hours is pressed into the crawler belt link, and the striking hammer is dropped. , 3,4
The impact fatigue properties of the bushes were compared by applying an impact load under conditions equivalent to twice the number of times and examining the number of impacts before breaking. In this example, after using SCrB440H boron steel, a tempering treatment of oil quenching and tempering (850 ° C. quenching, 500 ° C. for 3 hours) was performed, and then the hardening depth from the inner and outer peripheral surfaces was reduced to about 3 by induction hardening. Bush (base hardness Vickers Hv = about 280) adjusted to 0.5 mm and S
After carburizing and quenching Cr420H at 930 ° C, 180
A crawler bush whose tempering was performed at 3 ° C. for 3 hours and the hardened layer depth was adjusted to 2.5 was used for comparison.

The measurement results are shown in FIG. 10, and it is apparent that the product of the present invention has a higher impact strength than the conventional carburized bush. This is because the grain boundary oxidation or the incompletely quenched layer is present on the inner peripheral surface of the conventional carburized bush and the surface carbon concentration of the carburized product is high (about 0.
8% by weight carbon), which is thought to be due to the higher surface hardness. In this sense, it is possible to increase the impact fatigue strength of the product of the present invention by adjusting the inner peripheral surface hardness and increasing the toughness. In a conventional experiment, the optimum strength is known when the inner surface has a surface hardness of Hv = 500 to 600. For example, even when Hv = 400, the strength is higher than that of the conventional carburized bush, but the inner diameter deformation after the test is small. Hv = 450 or more, which has no problem, is preferable because it becomes too large to cause interference with the crawler belt pin. Also,
Although the upper limit of the maximum hardness is not particularly specified in comparison with the conventional carburized bush product, it is considered that this is almost the same as the carburized surface hardness (〜Hv = 750) and causes no problem. However, from the viewpoint of optimizing the impact performance, it is considered preferable to keep the inner peripheral surface hardness at about Hv = 650. In particular, No. 1 in which granular cementite is dispersed. In the bush of the invention No. 3, it is important that cementite does not precipitate at the old austenite grain boundary, and most of the soft layer formed on the thick core portion has dispersed particulate cementite in the bainite structure. It would be desirable to be composed of an organization that does

[Brief description of the drawings]

FIG. 1 is a schematic view of an entire heating induction hardening apparatus.

FIG. 2 is a schematic diagram of a moving induction hardening apparatus.

FIG. 3 is a cross-sectional view of a crawler bush material for a test.

FIG. 4 shows composition Nos. 1 is a graph showing the result of moving induction hardening of No. 1.

FIG. 5 shows composition No. 2 is a graph showing a result of the moving induction hardening of No. 2;

FIG. 6 shows composition Nos. 3 is a graph showing the result of moving induction hardening of No. 3;

FIG. 7 shows composition Nos. 2 is a graph (1) showing the result of induction hardening of the entirety.

FIG. 8 shows composition No. 2 is a graph (2) showing a result of the whole induction hardening of No. 2;

FIG. 9 is a diagram showing an impact fatigue test method.

FIG. 10 is a graph showing the results of an impact fatigue test.

FIG. 11 is an exploded perspective view of a crawler belt bush.

FIGS. 12 (a), (b) and (c) are schematic diagrams of typical hardening patterns of bushes produced by a conventional method ((a) carburized quenching bush, (b) induction hardened bush A). (QT + outer peripheral surface IQ + inner peripheral surface IQ), (c) Induction hardened bush B (outer peripheral surface IQ + inner peripheral surface IQ), FIG.
(D) is a graph showing the hardness distribution of the cross section.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 shield plate 2 high-frequency coil for overall heating 3 crawler belt bush 4 inner peripheral surface cooling nozzle 5 outer peripheral surface cooling nozzle 6 shielding cap 7 water tank 8 high frequency coil (first stage) 9 high frequency coil (second stage) 10 inner peripheral surface cooling nozzle 11 Outer surface cooling nozzle

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C22C 38/00 301 C22C 38/00 301H 38/22 38/22

Claims (11)

[Claims] 1. A carbon content of 0.35 to 2.0% by weight
And alloy elements such as Mn, Si, Cr, Mo, Ni
Using hardening steel that is hardened by simultaneous cooling from the inner and outer peripheral surfaces of the crawler bush material, and by high-frequency induction heating from the outer peripheral surface side of the crawler bush material, After heating the inner peripheral surface temperature of the
(1) Cooling from the inner peripheral surface is performed in advance, and (2) heating is performed from the outer peripheral surface while performing cooling from the inner peripheral surface. (3) Next, cooling from the outer peripheral surface is performed. By a series of one quenching operation for cooling, a quench hardened layer is formed from the outer peripheral surface and the inner peripheral surface toward the center of the thickness, and a soft unquenched layer is left between the two quench hardened layers, The soft structure between the two quench-hardened layers consists of at least one of ferrite, pearlite, bainite and martensite precipitated during the cooling process from the quenching temperature or a structure in which granular cementite is dispersed in these structures. A crawler bush characterized by the following. 2. The crawler belt according to claim 1, wherein the depth of the hardened hard layer on the outer peripheral surface side is formed to be 1.1 times or more the depth of the hardened hard layer on the inner peripheral surface side. bush. 3. The quenched crawler bush is kept at 140 ° C. or higher.
3. The crawler belt bush according to claim 1, wherein the bush is tempered at a low temperature of 50 ° C. or lower. 4. The crawler belt bushing material made of steel is heated to a temperature at which the inner peripheral surface temperature of the crawler belt bushing material can be quenched by high frequency induction heating from the outer peripheral surface side. (2) And, while cooling from the inner peripheral surface, heating from the outer peripheral surface is performed, and (3) Next, a series of one-time cooling is performed from the outer peripheral surface. Forming a quenched hardened layer from the outer peripheral surface and the inner peripheral surface toward the center of the thickness by the quenching operation, and forming a soft unquenched layer between the two quenched hardened layers. . 5. The temperature of the inner peripheral surface portion can be quenched at a certain position of the crawler belt bush while moving and inductively heating the crawler belt bush material made of steel from the outer peripheral surface side using at least two stages of induction coils. (A) A3, A3 and / or Acm temperature or higher. (2) Cooling from the outer peripheral surface, partially heating the outer peripheral surface with an induction coil, while performing cooling from the inner peripheral surface in advance. A method for manufacturing a crawler belt bush, wherein the inner peripheral surface layer and the outer peripheral surface layer are substantially martensitic by each of the steps described above, and are quenched and hardened. 6. An inner peripheral portion cooling medium and an outer peripheral portion cooling medium in consideration of the flow of the cooling medium so that the cooling medium when precooling the inner peripheral surface side does not interfere with the outer peripheral surface side during the precooling. The method for manufacturing a crawler belt bush according to claim 4, wherein a quenching device having a partition structure is used between the crawler bush and the bush. 7. During moving quenching by the induction heating,
7. The method for manufacturing a crawler bush according to claim 6, wherein the crawler bush, the induction heating coil, and the inner and outer circumference cooling nozzles are relatively moved in the axial direction of the crawler bush, and the crawler bush is rotated around its axis. . 8. The cooling medium is any one of quenching oil, water, a water-soluble quenching liquid, and spray cooling, and the cooling on the inner peripheral surface is performed by spraying or the like that cools the inner peripheral surface almost uniformly. The method for manufacturing a crawler belt bush according to any one of claims 4 to 7, wherein the method is jet cooling. 9. The crawler belt bush quenched at 140 ° C. in the manufacturing method according to claim 4,
A method for producing a crawler belt bush, wherein low-temperature tempering is performed at a temperature of at least 350 ° C. 10. The steel used for said crawler bush is 0.1 mm.
A steel having a carbon concentration in the range of 35 to 2.0% by weight. The soft structure between the hardened layers on the inner and outer peripheral surfaces is formed of one or more of ferrite, pearlite, bainite, and martensite precipitated in a cooling process from the quenching temperature. The method for manufacturing a crawler belt bush according to any one of claims 4 to 9, wherein the structure is a structure or a structure in which granular cementite is dispersed in the structure. 11. The manufacturing of a crawler belt bush according to claim 10, wherein the depth of the hardened hard layer on the outer peripheral surface side is set to be 1.1 times or more the depth of the hardened hard layer on the inner circumferential surface side. Method.