JP2007254895A - Crawler bush and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a more inexpensive production method for a crawler bush where the securance of oil sealing properties as an oil-sealed crawler bush, the securance of excellent toughness to an impact, severe load, and the improvement of wear resistance and a wear life are attained. <P>SOLUTION: For example, a means where, after preferential cooling from the outer circumferential face or inner circumferential face for a crawler bush 5 whose whole body is heated, the whole circumferential face is cooled, or a means where, during the preferential cooling, high frequency heating is performed from the opposite face thereof is performed, so as to be a constitution in which an outer circumferential hardened layer 2, an edge face hardened layer 4 and an inner circumferential tempered martensite hardened layer 6 are formed, and a soft layer 1 formed between the outer circumferential hardened layer 2 and the inner circumferential tempered martensite hardened layer 6 is composed of one or more selected from a pearlite structure, a bainite structure, a martensite and a tempered martensite structure, and the soft layer is connected to the inner circumferential face of the edge face part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a crawler belt bush used for construction machinery and the like, and a manufacturing method thereof. More specifically, the present invention relates to an oil-filled crawler bush having excellent wear resistance and impact fatigue resistance, and to produce it at a lower cost. It relates to a manufacturing method.

  Conventionally, the crawler belt 51 of a construction machine is composed of a group of parts as shown in FIG. 26. In particular, the crawler belt bush 52 engages with sprocket teeth that transmit the rotational motion from the final reduction gear, and rotates the crawler belt 51. Therefore, wear resistance is required on the outer peripheral surface, and strength and toughness are required on the inner peripheral surface in order to withstand the load applied thereto.

  Also, in a crawler track that runs at a high speed like a bulldozer, an oil-filled crawler belt in which lubricating oil is interposed in these gaps is used in order to prevent seizure between the crawler belt pin 53 and the crawler belt bush 52. In addition to the wear resistance of the outer peripheral surface that is in direct contact with the sprocket, it is necessary to seal the lubricating oil with the flat surfaces (seal flat portion) 61 and the dust seal 62 on both ends of the crawler belt bush as shown in FIG. In addition, it is necessary that at least the range of the contact position with the dust seal 62 in the seal flat portion 61 on the bush end surface (the contact position after wear from the outer peripheral surface to about 1/2 of the wall thickness) is sufficiently hardened by quenching. .

In order to satisfy these required characteristics, conventionally, the following method has been carried out in manufacturing the crawler belt bush.
(I) Carburizing treatment for case-hardened steel to form high-hardness martensite on the inner and outer peripheral surfaces and both end surfaces thereof to ensure wear resistance, strength and oil sealability (for example, patent documents) 1).
(Ii) After forming and processing the carbon steel containing the hardenability improving element into the crawler belt bush and quenching the whole, only the inner peripheral surface of the crawler belt bush is quenched by induction heating so that the outer peripheral surface, end surface and inner A crawler belt bushing in which a hardened hardened layer is formed on the peripheral surface, a toughened tempered softened layer is formed between the hardened hardened layers, and the softened layer is connected to the inner peripheral surface in the vicinity of both ends of the crawler belt bushing. The manufacturing method is disclosed in Patent Document 2. Also, in Patent Document 3, the entire thickness of the crawler belt bush is quenched and hardened, induction hardening is performed only from the inner peripheral surface, and the quenched and tempered softened layer formed at the center of the thickness is within the vicinity of both end surfaces. A method of manufacturing a crawler belt bush formed by connecting to a peripheral surface is disclosed.
(Ii) In addition, using a quenching device that can separate the cooling medium for the inner peripheral surface of the crawler bush and the cooling medium for the outer peripheral surface with a partitioning jig, the high frequency is higher than the temperature at which the intermediate carbon steel bushing material can be temporarily quenched. Start the cooling from the outer peripheral surface after a predetermined time after heating and precooling the inner peripheral surface, or cool the inner peripheral surface while heating the outer peripheral surface by high frequency heating, stop the outer peripheral surface heating after a predetermined time, and By a series of quenching operations of surface cooling, a hardened hardened layer is formed from the outer peripheral surface and inner peripheral surface of the crawler belt bush toward the center of the thickness, leaving a soft unquenched layer between the two hardened hardened layers. It has a U-shaped smooth hardness distribution, and further, the hardened layer depth from the outer peripheral surface portion is formed deeper than the hardened layer depth from the inner peripheral surface, and the end face is devised by devising the partitioning jig Part width 1/2 or more oil-filled type crawler bush having excellent cured wear resistance and its low-cost production method are disclosed in Patent Documents 4 and 5.

  However, the crawler belt bush made by the carburizing method of (i) is also carburized and hardened uniformly at the end surface portion, so the wear resistance of both end surface portions as an oil-filled bush is good, but the wear resistance at the outer cylindrical surface Since it is necessary to deepen the carburized hardened layer in order to improve the properties, it takes a long time for carburizing and there is a problem in terms of cost due to a large amount of carburizing gas used. For example, in the case of a large crawler belt bush that increases the thickness of the bush, the required hardened layer depth becomes deeper from the viewpoint of strength and wear resistance, which causes problems of a decrease in productivity and an increase in cost. Furthermore, since the carburizing heating time takes a long time on the inner and outer peripheral surfaces, a grain boundary oxide layer and an incompletely hardened layer are formed with a thickness of several tens of μm, and fatigue strength and impact resistance characteristics are likely to deteriorate. There is a problem.

  On the other hand, the induction hardening method of (ii) is improved in cost compared with the carburizing method of (i), but it is necessary to re-harden the inner peripheral surface of the track bush once hardened completely. In addition, there are problems with sufficient quality control, such as the occurrence of burning cracks, the difficulty of induction tempering the inner surface of the small-diameter track bush, low productivity such as moving induction hardening, and more Since a heat treatment process is required, there is a problem that the cost cannot be reduced.

  In addition, in the induction hardening method of (ii), as disclosed in Patent Document 6 and Patent Document 7, the outer peripheral surface hardened layer is tempered near the center by induction heating from the inner peripheral surface, There is a problem that the hardness of the hardened hardened layer on the outer peripheral surface tends to soften toward the center, and the wear resistance of the outer peripheral surface cannot be sufficiently improved.

  Further, in Patent Document 8 and Patent Document 9, mobile induction hardening for moving the crawler bush is simultaneously performed from both the outer peripheral surface and the inner peripheral surface of the crawler belt bush, and at least the portion that meshes with the sprocket is applied to the inner peripheral surface. A crawler belt bushing with increased strength of the crawler belt bushing without induction hardening and a method for manufacturing the same are disclosed, but as described above, it is difficult to heat-treat the inner diameter of the crawler belt bush with difficulty, and movement with low productivity. It is induction-hardened, requires two power sources for high-frequency heating, has high capital investment, and the inner peripheral surface unquenched layer is ferrite and pearlite structure less than HRC35, so that the toughness is not sufficient. In order to avoid this, it is easy to make it through-hard because the thin crawler belt bushing is cooled simultaneously from the inner and outer peripheral surfaces. To the outer circumferential surface hardened layer depth becomes shallower, there are problems such as the wear life of the crawler bush is not sufficient.

  In addition, in the induction hardening method of (ii), the unevenness of the hardened portion and the omission of the hardened layer at the end surface portion of the thin oil-filled crawler belt bush are inevitable and a final inspection process is required. There is a problem.

Japanese Patent Publication No. 52-34806 Japanese Examined Patent Publication No. 3-69969 JP 2001-98326 A JP 11-61264 A JP-A-11-236619 Japanese Patent Publication No. 63-16314 JP-A-5-78745 JP-A-6-247351 Japanese Patent Laid-Open No. 10-68023

  The present invention has been made in view of such problems, and based on inexpensive induction hardening technology, ensuring oil sealing performance as an oil-filled crawler track, ensuring excellent toughness against shocking severe loads The main object is to improve wear resistance and wear life, and to provide a more inexpensive manufacturing method than the methods (i) to (ii).

  The present invention also improves the seizure resistance between the crawler belt bushing and the crawler belt pin that rotates and swings and becomes a problem with the increase in the size and load of the construction machine and the method for preventing the crawler belt link from coming off from the crawler belt link. It is intended to do.

  For example, an oil-filled crawler belt bush for small and medium-sized bulldozers is thin, and the end face is subjected to end face processing for press-fitting into the crawler belt link, and the inner peripheral face is subjected to local contact by bending with the crawler belt pin. Since the chamfering process for avoiding the above is performed, the parallel surface of the end surface portion is extremely narrow. For this reason, it is necessary to reliably cure the outer peripheral surface press-fit end face processed part in order to ensure the end face seal part hardened layer and to prevent press-fitting failure due to galling when press-fitting the crawler belt bush into the crawler belt link. It is. Furthermore, in order to ensure the strength, toughness and wear resistance as the crawler belt bush, at least the outer peripheral surface is formed with a hard hardened and hardened layer having an HRC of 50 or more, and a soft layer having an HRC of 45 or less in the thickness inside. It is necessary to prevent burning cracks during heat treatment.

Therefore, in the crawler belt bush according to the present invention,
A track bushing material comprising carbon steel and / or low alloy steel containing at least carbon in the range of 0.35 to 1.2% by weight, and having a total thickness adjusted to a hardness of less than HRC 30 to 45 The outer peripheral surface hardened layer and the end surface hardened layer continuously connected to the outer surface hardened layer are formed by high-frequency heating and quenching from the outer peripheral surface (first invention).

  From the viewpoint of securing the wear life of the crawler belt bush, when quenching by high frequency heating from the outer peripheral surface, the inner peripheral surface is not heated above the A1 temperature (720 ° C.) of the steel from the beginning or during the heating. The cooling of the inner peripheral surface is started before the outer peripheral surface, and after the heating from the outer peripheral surface is finished, the outer peripheral surface is cooled to increase the depth of the hardened hardened layer on the outer peripheral surface to 30 to 80% of the wall thickness. Preferred (second invention). When the outer peripheral surface is hardened to 70% or more of the wall thickness, it is well experienced that the impact strength of the crawler bush begins to deteriorate, and the wear limit of the crawler bush is set to approximately 60%. Therefore, the depth of the outer peripheral hardened layer is more preferably 40 to 70%.

  The toughened tempered martensite structure in which fine granular cementite is dispersed with HRC 45 or less is subjected to tempering treatment (quenching and tempering treatment) of the crawler belt bush material, and then the outer peripheral surface and both end surfaces by induction hardening from the outer peripheral surface of the crawler belt bush. However, high temperature tempering brittleness does not appear remarkably in order to obtain a tougher crawler belt bush (Cr is 0.5% by weight or less and the remainder is Mn, C, Si, Al, Carbon steel or carbon boron steel (containing Ni, Mo, Ti, etc.) is preferable as the crawler belt material, and the tempering temperature of the tempering treatment is preferably 150 ° C. or higher. Further, since induction hardening from the outer peripheral surface is repeatedly performed as the post-heat treatment, it is preferable to temper to HRC 45 or less in order to avoid the cracking property and increase the productivity.

  In the crawler belt bush in which the outer peripheral surface portion and both end surface portions are induction hardened, there is no significant problem in seizure even when the inner peripheral surface of the crawler belt bush that slides under oil lubrication with the crawler belt pin is less than HRC45. When the load is large and uneven load is easily applied, or when continuous running at high speed for a long distance is repeated, the inner surface of the crawler bushing and the outer surface of the crawler pin slide at a low speed, and galling is likely to occur. At the same time, it is important to improve the fatigue strength of the crawler belt bush under high load.

Therefore, in the third aspect of the present invention, the outer peripheral surface hardened layer and the end surface hardened layer are connected to each other by induction hardening from the outer peripheral surface, and the inner peripheral surface of the crawler belt bush having an HRC45 of less is hardened on the seal flat portions on both end surfaces. Avoiding the hardened part, induction cuffing the inner peripheral surface of the crawler belt bush, the inner peripheral surface hardened hardened layer depth is 1-15% of the thickness, and the soft layer formed inside the crawler bush is thick While avoiding the flat seal portion on both end faces of the bush, it is formed to be connected to the inner peripheral face in the vicinity of both end faces, and a large compressive residual stress of 30 kg / mm ² or more is applied to the inner peripheral face.

  Further, also in the carbon steel and / or carbon boron steel, tempering after quenching is necessary for toughness recovery, and at least 150 ° C. or more, preferably 200 ° C. or more was tempered. In each invention, a tempering process of 150 ° C. or higher is performed, the hardness of the induction-hardened hardened layer surface is HRC50 or higher, and the hardening depth of both end faces is 0.5 mm or higher, and wear resistance I tried to ensure sex.

  Since the crawler belt used for a hydraulic excavator is a dry type that is not oil-filled and does not involve lubrication as described above, the inner peripheral surface of the crawler belt bush is hardened and hardened, but both end portions are not hardened. In this dry-type crawler belt bush, if both end surfaces can be additionally quenched and hardened, stable formation of the end surface portion hardened and hardened layer, common use of production equipment, and improvement of productivity can be achieved epoch-making.

  Also, in the crawler belt bush shape, when the outer peripheral chamfering position near both end faces is closer to the crawler bush central position than the inner peripheral chamfering position, the end chamfered portion is greatly bent due to the offset load or bending load applied to the crawler belt pin. Since there is a high risk of generating a load and damaging the vicinity of the end face, it is preferable that the chamfering start point on the inner peripheral surface side is located at the center position of the crawler belt bush more than the outer peripheral surface chamfering start point (fifth invention). .

  In addition, when both ends of the crawler belt bush are subjected to quench hardening, a softening layer exists between the inner peripheral surface hardened layer, the outer peripheral surface hardened layer, and the end surface hardened layer, so that overload stress acts on this portion. Therefore, it is preferable to make the inner peripheral surface side chamfered portion larger than the outer peripheral surface chamfered portion in the shape in the vicinity of both end surface portions of the crawler belt bushing, and a large bending stress is generated in the corner portion of the crawler belt bush end surface due to the uneven load It is preferable to prevent this. This result is also considered effective for galling with crawler belt pins.

  Further, when there is a softening layer between the inner peripheral surface hardened layer, outer peripheral surface hardened layer, and end face hardened layer, tensile residual stress is likely to occur. It is preferable to apply a large compressive residual stress by shot peening the end face to improve the strength (sixth invention). It is to be noted that applying shot peening to the inner peripheral surface is extremely effective as a means for improving the breakthrough strength of the crawler belt bushing and improving the seizure resistance with the crawler belt pins.

  Even in the crawler belt bush in which both end faces are additionally quenched and hardened, it is preferable that the inner peripheral surface and the outer peripheral surface thereof are subjected to chemical conversion treatment or plating treatment such as a phosphate film as described above (seventh invention).

Next, the manufacturing method of the crawler belt bush according to the eighth invention is as follows:
Using a crawler bush material with a hardness of less than HRC45, from the beginning or from the middle of heating so that the inner peripheral surface is not heated above the A1 transformation temperature of steel by moving from the outer peripheral surface or by overall high-frequency heating. While cooling before the outer peripheral surface, induction hardening is performed from the outer peripheral surface, the outer peripheral surface quenching hardening depth is deeper, and the hardened layer of the seal flat part at both end surfaces connected to the outer peripheral surface is Further, it is characterized in that it covers a width of 1/2 or more of the thickness, and further, the inner circumferential surface of the crawler belt bush is induction-hardened by avoiding the hardened hardening portion of the seal flat portion on both end faces of the crawler belt bush, The depth of the hardened hardened surface is 5 to 15% of the thickness, and a compressive residual stress of 30 kg / mm ² or more is generated (ninth invention).

  In the crawler belt bush that is induction hardened on the outer peripheral surface portion and both end surface portions, the inner peripheral surface of the crawler belt bush that slides under the oil lubrication with the crawler belt pin is also tempered even in the case of tempered martensite or pearlite structure in which granular cementite less than HRC45 is dispersed. Although there is no big problem in sticking property, especially in a large-sized bulldozer, since the load is larger, an uneven load is likely to be applied, and galling may occur when sliding at a low speed. In this case, it is preferable to increase the surface hardness of the inner peripheral surface of the crawler bushing to HRC45 or more by avoiding the hardened hardening portions of the seal flat portions at both ends of the crawler belt bushing. It was assumed that it can be used after being induction-quenched shallowly so as to be 5 to 15% of the wall thickness. Further, from the viewpoint of production cost, 1 to 3 mm is preferable, in which the inner peripheral surface hardened and hardened layer depth is stabilized.

  When performing induction hardening from the inner peripheral surface, it is preferable to cool the outer peripheral surface so that the outer peripheral surface hardened layer is not softened by thermal diffusion of the inner peripheral surface by high-frequency heating. In this case, it is preferable to use a power source of 50 kHz or more as the inner peripheral surface high-frequency heating power source.

Also, in the method of quenching by moving high frequency heating from the outer peripheral surface to continuously form a quench hardened layer of the outer peripheral surface and both end surface portions of the crawler belt bush,
(1) The moving relative speed of the high-frequency heating coil and the crawler belt bushing is slowed at the end face part. (2) The inner peripheral surface cooling for adjusting the inner peripheral surface temperature by heat diffusion from the outer peripheral face is weakened near the both ends of the crawler belt bushing. (3) A cylindrical or substantially cylindrical jig is disposed so as to be in contact with the inner peripheral surface in the vicinity of the end surface of the crawler belt bushing to weaken the cooling from the inner peripheral surface portion, or to improve the heat insulating property. (4) A collet chuck made of a material with good thermal conductivity is placed on the inner peripheral surface where cooling of the inner peripheral surface is required to hold the crawler belt bush. It is preferable to perform quench hardening by combining one or more methods.

  In the above-mentioned moving induction hardening method, in order to continuously produce the crawler belt bushes, it is a viewpoint of productivity to carry out the moving induction hardening by sandwiching a spacer with high heat insulation between the inner peripheral surfaces in the vicinity of the end faces between the crawler belt bushes. To preferred.

  Further, in the moving induction hardening method, in order to deeply harden the outer periphery of the crawler belt bush, the inner peripheral surface does not exceed the A1 temperature of the steel, and the inner peripheral surface is formed to form a tempered martensite layer on the inner peripheral surface. It is preferable to carry out mobile induction hardening from the outer peripheral surface side while cooling from the inner peripheral surface so that the surface temperature is not excessively raised. Further, in the vicinity of the end surface portion of the crawler belt bushing, the cooling from the inner peripheral surface is weakened or stopped to delay the cooling from the inner peripheral surface, and the moving heating rate from the outer peripheral surface is decreased to reduce the entire end surface portion. It is preferable that almost all of the end face is quenched and hardened by the subsequent cooling. In addition, as described above, it is also possible to carry out moving induction hardening by sandwiching a cylindrical or substantially cylindrical spacer with high heat insulation in the inner peripheral surface in the vicinity of the end surface, because it shows the same effect of sufficiently quenching and hardening the end surface portion. More preferable from the viewpoint of productivity.

  In addition, as a cooling method of the inner peripheral surface, it is preferable to perform cooling while arranging a cooling nozzle on the inner peripheral surface and spraying water, a water-soluble quenching liquid, air, spray, etc. It is more preferable to control the ON or OFF control.

  Furthermore, the inner peripheral surface collet chuck made of a material with good thermal conductivity (for example, copper-based or iron-based metal materials) needs to cool the inner peripheral surface while avoiding the inner peripheral surface near the end surface of the crawler belt bush. It is preferable to hold the crawler belt bushing by arranging it on the inner peripheral surface portion, and to these, heat insulating material is arranged on the inner peripheral surface in the vicinity of both end faces of the crawler belt bush, and the end face portion is hardened and hardened in a shorter time. It is preferable to be heated to a sufficient temperature. In addition, it is preferable to devise so that the cooling efficiency of the collet chuck portion made of the metal material can be further increased and adjusted. For example, it is preferable that a cooling medium such as air or water is emitted.

In the method of quenching by overall high-frequency heating from the outer peripheral surface for continuously forming the quench hardened layer on the outer peripheral surface and both end surface portions of the crawler belt bush,
(1) A saddle type, spiral coil, or cylindrical coil is used so that both end portions of the crawler belt bush can be effectively heated at high frequency. (2) Cooling of the inner peripheral surface for adjusting the inner peripheral surface temperature by thermal diffusion from the outer peripheral surface. (3) A cylindrical or substantially cylindrical jig is placed in contact with the inner peripheral surface in the vicinity of the end surface of the crawler belt bush to weaken the cooling from the inner peripheral surface portion. (4) A collet chuck made of a material with good thermal conductivity is used as an inner peripheral surface portion that requires cooling of the inner peripheral surface. One or more methods of placing and holding the track bushing can be combined and hardened by hardening.

Moreover, the quenching method of performing high-frequency heating from the outer peripheral surface is as follows:
While applying high-frequency heating from the outer peripheral surface of the crawler belt bushing and pressing the partitioning jig against both end surfaces of the crawler belt bushing so that the inner peripheral surface cooling medium and the outer peripheral surface cooling medium of the crawler belt bush do not interfere with each other, Using a quenching device that can perform surface cooling and outer peripheral surface cooling independently, the entire cylindrical cushion bushing material starts induction heating while rotating around the center of the cylindrical axis, and the inner peripheral surface exceeds the A1 transformation temperature of steel. Cooling the inner peripheral surface from the beginning or before the outer peripheral surface in the middle of heating so that the outer peripheral surface is cooled after the heating from the outer peripheral surface is finished. In addition, the surface layer of the seal flat part at both end face parts is hardened and hardened over a width of 1/2 or more of the thickness of the crawler belt bush from the position of the outer peripheral surface.

  When heat-treating a plurality of crawler belt bushes at the same time, the end surface portion is sufficiently quenched by cooling from the outer peripheral surface with a partition jig interposed between the crawler belt bushes so that the end surface portion of the crawler belt bush is not hidden. In that case, these partitioning jigs contact the inner peripheral surface or chamfered portion of the crawler belt bush and cover the inner peripheral surface in the vicinity of the end surface, and cool the inner peripheral surface in the vicinity of the end surface when cooling the inner peripheral surface. It is preferably a cylindrical shape or a substantially cylindrical shape that delays the rotation. Moreover, water, a water-soluble quenching liquid, air, fog, etc. can be utilized as an inner peripheral surface cooling medium.

  In the crawler belt bush manufactured according to the invention, the depth of the hardened hardened layer on the outer surface is increased to 30 to 80% of the wall thickness to improve the wear life of the crawler belt bush. Since the lifetime is designed as the time when the outer peripheral surface wear amount reaches 50 to 60% of the wall thickness, it is more preferable to set the outer peripheral surface hardened and hardened layer depth to 40 to 70% of the wall thickness ( 10th invention).

  Further, in the crawler belt bush, a tempering process of 150 ° C. or higher is performed, the surface hardness of the inner and outer peripheral surface portions and both end surface portions is HRC50 or more, and the quench hardening depth of both end surface portions is 0.5 mm or more, In order to ensure long-term oil sealability, it is preferably 2.0 mm or more (11th invention).

  Also, in the crawler belt bush in which both end surfaces are additionally quenched and hardened, it is preferable that the inner peripheral surface and the outer peripheral surface thereof are subjected to a chemical conversion treatment or a plating treatment such as a phosphate coating as described above (Twelfth Invention).

  Next, specific embodiments of the crawler belt bush and the manufacturing method thereof according to the present invention will be described with reference to the drawings.

FIG. 1 shows an outer peripheral surface (position A) when a crawler belt bush having an outer diameter of 60 mm, an inner diameter of 40 mm, and a wall thickness of 10 mm is heated to 850 ° C. and simultaneously strongly cooled from the inner peripheral surface and the outer peripheral surface, and 2 mm deep from the outer peripheral surface. It shows the relationship between the temperature at the vertical position (B position) and the thickness center (C position) and the cooling time.
In addition, the thick broken line in the figure shows the range of the pearlite precipitation start line (C curve) in the continuous cooling transformation diagram of the S45C equivalent material with α and β C curves. Estimated based on the depth of the hardened hardened layer on the outer peripheral surface when the 10.4 mm thick crawler bushing was simultaneously quenched from 850 ° C., the αC curve is a steel with a low hardenability (DI = 0.515 in). , 0.47C-0.34Mn), the outer peripheral surface hardened layer depth is about 2.2 mm, and the thickness center hardness is Hv = 310. Furthermore, the βC curve is obtained when DI = 0.72 in and 0.53 C-0.48 Mn carbon steel is used, and the hardness of the outer peripheral surface hardened layer is Hv = 760. Thick center hardness is Hv = 510 and through-ha Since it was de reduction, but is described to intersect the cooling line at approximately position C, forming a thick inside unhardened layer it can be seen that determined by the slight difference in the DI.

  FIG. 2 is an experimental determination of the relationship between the DI value of various carbon steels containing 0.4 to 0.6 wt% carbon and the thickness of the crawler belt bushing to be through-hardened. It was found that (inch) ≦ 1.75 × thickness (inch) (linear relationship in FIG. 2). Furthermore, the DI value variation range of the readily available S45C equivalent material is indicated by a broken line in FIG. 2. For example, 0.56 inch for PC60 (wall thickness 8.25 mm) and 0.71 inch for PC200 (10.4 mm). It is necessary to manage the steel material range strictly and narrowly so that it has the following hardenability, the availability of the steel material is extremely difficult, and the wall thickness of the small and medium crawler belt bushes by the simple inner and outer surface simultaneous quenching method It turns out that the manufacturing method which forms a soft unquenched layer inside is very difficult.

  Moreover, when manufacturing a large crawler belt bush with a wall thickness of 17 mm or more that does not necessarily become through-hard using the steel shown by the broken line in FIG. 2, the average DI value (0.96 inch) is low, so the outer peripheral surface It is clear that the quench hardened layer depth becomes as shallow as about 3.4 mm (about 20% of the wall thickness), and there is a problem that the wear life of the crawler belt bush cannot be improved sufficiently.

  In view of the above, in the present invention, various heat treatment methods are used to slow down the cooling rate inside the crawler bush thickness, thereby promoting pearlite transformation even inside the crawler bush thickness using a steel material with a higher DI value. I will try to let you.

  FIG. 3 shows the positions A, B, and C when the same crawler belt bushing as in FIG. 1 is stopped for 2 seconds after simultaneous cooling of the inner and outer peripheral surfaces from 850 ° C. for 2 seconds, and then the inner and outer peripheral surfaces are simultaneously recooled. The temperature at the A and B positions is reheated while the simultaneous cooling of the inner and outer peripheral surfaces is temporarily stopped (2 seconds), and at the C position at the center, the temperature is 550 to 500 ° C. It can be seen that the cooling behavior is such that it is isothermally treated for 2 seconds.

  It is well known that the temperature (nose) at which pearlite transformation occurs in the shortest time in the CCT diagram is around 550 ° C., and that the nose position of the steel moves to the longer side as the DI value increases. For example, the relationship between the linear relationship in FIG. 2 and the cooling time for the wall thickness at various thicknesses to be 550 ° C. is obtained, and the delay of 2 seconds becomes through-hard at DI = 0.7 inch. It can be seen that it is shown that it is possible not to make the through-hardening until DI = 1.05.

  In addition, when the cooling curve at the center of the wall thickness shown in FIG. 3 is in a state close to a constant temperature state, it is considered more appropriate to discuss with a TTT diagram (a constant temperature transformation diagram) rather than a study with a CCT diagram. 3 shows a TTT diagram (bold broken line; 50% pearlite transformation line, thick solid line; 100% pearlite transformation line) and martensite start temperature (Ms) of 0.5 wt% C-0.91 wt% Mn carbon steel. However, since the TTT diagram that normally occurs when the driving force for pearlite transformation is large is on the shorter side than the CCT diagram, pearlite transformation is likely to occur at the center of the wall thickness. Is clear.

  Further, from the relationship with each cooling line, in the vicinity of the outer peripheral surface layer, tempering by thermal diffusion from the inner peripheral portion occurs once it is martensite, and at the B position, the temperature is reheated, but the soft tissue is in that period. Although it is not formed and it hardens | cures by recooling, it turns out that pearlite transformation advances and a soft structure | tissue is formed in C position of a thickness center.

  FIG. 4 is a comparison of the cooling curves at the center of the wall thickness (C position) when the cooling stop time is 4 seconds. The fact that the stop time during the cooling can be made considerably long is a fairly wide range of quenching. It is clear that a soft unquenched layer can be formed inside the wall thickness of the crawler belt bush made of high carbon steel.

  Although the above method is found to be an extremely effective method for delaying the cooling rate inside the crawler belt bush thickness, for example, not only the simultaneous cooling of the inner and outer peripheral surfaces is stopped simultaneously, but also, for example, the inner peripheral surface It is clear that the cooling rate inside the wall thickness can be delayed by temporarily stopping the cooling or completely stopping the cooling without recooling.

  5 (a) and 5 (b) are partial cross-sectional views of the crawler belt bush according to the present embodiment in accordance with the concept of temporarily stopping the cooling after the start of the simultaneous cooling of the inner and outer peripheral surfaces. The bush also has a martensite structure whose entire peripheral surface is quenched and hardened, and an unquenched hardened layer containing a pearlite structure is formed inside the wall thickness. Further, FIG. After the surface simultaneous cooling, only the inner peripheral surface cooling is stopped, and the martensite on the inner surface side is made into a tempered martensite structure less than HRC45 by thermal diffusion from the inside.

  Furthermore, as a method of delaying the cooling rate inside the wall thickness of the crawler belt bush, after the entire heating, one of the outer peripheral surface or the inner peripheral surface is precooled for a predetermined time, and the pearlite transformation is performed by cooling the central portion of the wall thickness slowly. It is obvious that a method of raising both the inner and outer peripheral surfaces after a predetermined time is effective.

  FIG. 6 shows each temperature distribution in the thickness section in each step when the crawler belt bush having the same thickness as above is heated to 850 ° C., then precooled from the inner peripheral surface for 4 seconds, and then the outer peripheral surface is cooled. Compared to the temperature distribution during simultaneous cooling of the inner and outer peripheral surfaces in the figure, the cooling rate at the center of the wall thickness is clearly delayed. Refer to the C curve shown in FIG. Thus, it is clear that this is an effective means for forming a soft unquenched layer inside the thickness of the crawler belt bush.

  Also, contrary to the case of FIG. 6, even with the method of cooling the inner peripheral surface after the outer peripheral surface precedent cooling, it is possible to effectively delay the cooling rate of the thickness center portion substantially the same as FIG. it is obvious.

  More specifically, in the crawler belt bush of PC200 with a wall thickness of 10.4 mm, it has been described above that the DI value of steel that is through-hardened by simultaneous cooling of the inner and outer peripheral surfaces is 0.72 inch, but only the inner peripheral surface is cooled. The DI value of through-hardening is approximately doubled to 1.45 inches, so it is easy to use steel with a wide hardenability by following the method of precooling one of the outer peripheral surface or inner peripheral surface for a predetermined time. It can be seen that a pearlite transformation layer can be formed inside the wall thickness.

  7 (a), 7 (b) and 7 (c) are partial cross-sections of the crawler belt bushing of the present embodiment in accordance with the concept of pre-cooling one of the outer peripheral surface or the inner peripheral surface and cooling the entire periphery after a predetermined time. FIG. 7 (a) shows a diagram in which a jig for partitioning the cooling medium between the inner peripheral surface and the outer peripheral surface is pressed against the inner peripheral surface side of the end surface, and the outer peripheral surface and the end surface are simultaneously cooled by the outer peripheral surface cooling medium. The outer peripheral surface and the end surface portion are pre-cooled or the inner peripheral surface is pre-cooled, and the entire peripheral surface is cooled after a predetermined time, thereby including a pearlite structure inside the wall thickness. The soft layer is manufactured so as to be connected to the inner peripheral surface of the end face portion. Further, FIG. 7B controls the cooling of the inner peripheral surface during the heat treatment, and the hardened hardening layer formed on the inner peripheral surface is formed. It is tempered to a hardness of less than HRC45 by thermal diffusion at the thickness center. In addition, FIG. 7 (c) presses a jig that partitions the cooling medium between the inner peripheral surface and the outer peripheral surface against the outer peripheral surface side of the end surface, so that the inner peripheral surface and the end surface are simultaneously cooled by the outer peripheral surface cooling medium, The outer peripheral surface and the end surface portion are precooled or the inner peripheral surface is precooled, and the entire peripheral surface is cooled after a predetermined time so that the soft layer containing the pearlite structure inside the wall is formed on the outer peripheral surface. It is manufactured to be connected.

  Furthermore, after the entire crawler belt bushing is heated, when it is pre-cooled from one of the inner peripheral surface or the outer peripheral surface, an extremely large temperature gradient is formed in the wall thickness by applying induction heating from the opposite surface of the cooling surface, And it is clear that the cooling rate of the thick core part can be most delayed, and this method of stopping the induction heating after a predetermined time after the pearlite transformation layer is formed inside the thickness and cooling the heated surface, By appropriately selecting the induction heating depth, the input power, and the preceding cooling time by induction heating, the restriction on the hardenability of the steel used is greatly relaxed, and the pearlite transformation layer formation position and its width inside the wall thickness are reduced. It can be seen that it has features that can be arbitrarily adjusted.

  FIG. 8 illustrates the above-described relationship. In the state where the inner peripheral surface is precooled after the crawler belt bush is entirely heated, a temperature gradient as shown by the line in the figure is formed. When induction heating is performed from the outer peripheral surface, a further steep temperature gradient as shown by the arrow in the figure is formed, and the above-mentioned TTT transformation diagram and CCT transformation diagram at the internal thickness position near 550 ° C. The pearlite transformation described in (1) takes precedence, and further, by heating from the outer peripheral surface to a temperature that can be quenched to the vicinity of the center of the wall thickness, by stopping the induction heating and cooling the outer peripheral surface, It is clear that a surface-quenched hardened layer can be formed, which proves to be a preferred method for manufacturing a crawler belt bushing suitable for improving wear life.

  Furthermore, the heat diffusion from the outer peripheral surface side or the outer peripheral surface can be performed by temporarily stopping the preceding cooling of the inner peripheral surface during induction heating from the outer peripheral surface or by stopping induction heating and cooling the outer peripheral surface as it is. It is clear that the martensitic structure of the inner peripheral surface is tempered by thermal diffusion due to induction heating from.

  Even when the induction heating method from the inner peripheral surface opposite to the induction heating method from the outer peripheral surface is taken, the inner peripheral surface induction heating during the outer peripheral surface preceding cooling is concentrated on the inner peripheral surface side. Thus, it is also clear that the outer peripheral surface hardened layer can be made deeper and the inner peripheral surface hardened layer can be made shallower.

  9 (a) and 9 (b) show partial cross-sectional views of the crawler belt bushing of the present embodiment in accordance with the concept of performing prior heating from the opposite surface while performing induction heating from the outer peripheral surface or inner peripheral surface described above. In order to improve the wear life of the crawler belt bush, the outer peripheral surface side hardened layer is made deeper, and in FIG. 9B, the inner peripheral surface hardened layer is made tough tempered martensite structure. Is. In addition, as shown in FIG. 7, the soft layer including the pearlite structure inside the wall has either a position where the jig for partitioning the cooling medium between the inner peripheral surface and the outer peripheral surface is pressed, the inner peripheral surface, or the outer peripheral surface. It is obvious that the adjustment is made so as to be connected to the outer peripheral surface, the inner peripheral surface or the end surface portion depending on whether induction heating is performed.

  FIG. 10 shows an outer peripheral surface when a crawler belt bush having an outer diameter of 70 mm, an inner diameter of 45.2 mm, and a wall thickness of 12.4 mm is heated to 960 ° C. while adjusting power in multiple steps using a power source of 3 kHz and 200 kW. The induction heating state in the wall thickness center part and the inner peripheral surface is shown.

  As apparent from FIG. 10, the inner peripheral surface temperature reaches about A1 temperature (720 ° C.) in about 12 seconds from the start of heating, but at the center of the thickness at that time, it is substantially the same as the outer peripheral surface temperature of 930 to 940 ° C. It is clear that the crawler belt bushing quenched in this state can obtain a thickness of ½ or more of the thickness as a hardened outer peripheral surface. In addition, referring to the inner peripheral surface temperature rise curve, it is possible to cool the inner peripheral surface at a timing at which the inner peripheral surface hardness does not become too soft, and the inner peripheral surface is previously quenched and hardened, or oil By performing high-frequency heating from the outer peripheral surface using a crawler belt bush that has been hardened as a whole by quenching or the like, a soft layer is formed at the center of the thickness while leaving a hardened layer tempered on the inner peripheral surface, In addition, it is obvious that the end face hardened layer can be formed with a thickness of 1/2 or more, and the softened layer at the center of the thickness can be connected to the inner peripheral surface near the end face. This manufacturing method is extremely effective as a manufacturing method for a small-diameter crawler belt bushing with a small inner diameter surface and high-frequency quenching of the inner peripheral surface. The inner peripheral surface also serves as a tempering process at a high temperature for a short time, and is tempered in a separate process. This is a low-cost manufacturing method that does not require processing.

  11 (a) to 11 (c) are partial cross-sectional views of the crawler belt bushing of the present embodiment in accordance with the above-mentioned idea, and FIG. 12 shows the hardness distribution in the crawler belt bush thickness cross section at that time. It is a thing. Here, FIGS. 11 (a) and 11 (b) show the outer circumference after the crawler belt bush material is once quenched and the entire thickness is quenched and hardened (lines (a) and (b) in FIG. 12 (a)). By induction hardening from the surface, the soft core 1 (line (a) in FIG. 12 (b)) having a soft tempered martensite structure of less than HRC45 in the thick core portion, or the soft layer 1 and the outer peripheral surface is quenched. A soft layer 3 containing pearlite (line (b) in FIG. 12B) is formed in the vicinity of the boundary with the hardened layer 2, and the soft layers 1 and 3 avoid the end face hardened hardened layer 4 and 2 is a partial cross-sectional view of an oil-filled crawler belt bush 5 formed to be connected to an inner peripheral surface in the vicinity of a portion. FIG. 11 (c) and 11 (b), at least the inner peripheral surface of the crawler belt bush material is quenched, and a hardened hardened layer is formed on the inner peripheral surface toward the thick core portion including the pearlite structure (FIG. 12). After (b) and (c) lines in (a), it is a partial sectional view of the oil-filled crawler belt bush 5 subjected to induction hardening from the outer peripheral surface in the same manner as described above ((b) in FIG. 12 (b)) ), (C) line). In addition, in FIG. 11, the code | symbol 6 is a tempered martensite hardened layer of an internal peripheral surface part, and the code | symbol 7 is a ferrite + pearlite unhardened hardened layer below HRC45.

  The steel material for quenching and hardening the entire thickness uses an expensive material with higher hardenability, whereas at least the steel material whose inner peripheral surface is hardened and hardened can keep the hardenability low. Therefore, a cheaper steel material (for example, 0.3 to 1.5% by weight C, ~ 1.5% by weight Mn, ~ 0.5% by weight Cr, medium carbon containing two or more kinds of alloy elements, high carbon Steel) is available.

  Further, in the present embodiment, the hardened hardened layer on the inner peripheral surface is tempered by thermal diffusion from the outer peripheral surface during high-frequency heating from the outer peripheral surface, so that a tempering step that has been conventionally performed to recover the toughness of the crawler belt bushing. Further, it is extremely effective that the hardened hardened layer on the outer peripheral surface and the end surface portion that require more wear resistance can be used in a higher hardness state as a result.

  Further, since the crawler belt bushing is usually replaced as the life of the crawler belt bush when the wear depth from the outer peripheral surface reaches 1/2 of the wall thickness, the hardened outer peripheral surface of the crawler belt bush is made thicker. It is more effective as a measure for extending the wear life to deepen up to 40 to 70% of the material. In this embodiment, the inner peripheral surface is started by various methods from the start of high-frequency heating from the outer peripheral surface or from the middle. By cooling, the hardened hardened layer on the inner peripheral surface was not tempered too softly, and deep induction hardening from the outer peripheral surface was made possible.

  As a high-frequency heating method from the outer peripheral surface, a method of induction hardening using a saddle coil 8 in which the end surface portion and the outer peripheral surface are efficiently heated as shown in FIG. 13A is also effective. As shown in FIG. 13 (c), the method using the spiral coil-shaped dielectric 9 in which the end face is efficiently heated is effective from the viewpoint of supplying large heating power. Here, FIG.13 (b) is an A arrow view of Fig.13 (a).

  The frequency for high-frequency heating to be used is optimized by the thickness of the crawler belt bush. However, when considering the sharing of equipment, it is preferable to use a high frequency power source of about 1 to 20 kHz. The high-frequency heating from the outer peripheral surface is made uniform while rotating, the high-frequency heating from the outer periphery is stopped after a predetermined time, and the quenching operation is performed by cooling from the outer peripheral surface with water spray or the like. good. Further, in order to obtain a deeper outer peripheral surface hardened layer while securing the hardness of the inner peripheral hardened layer at HRC 45 or more, it is necessary to perform cooling from the inner peripheral surface as described above. It is necessary to control the peripheral surface temperature so as not to be overheated to 500 ° C. or higher.

  Also, in this case, a significant feature of the manufacturing method is that the hardness of the hardened hardened inner peripheral surface can be adjusted by high-frequency heating from the outer peripheral surface side by appropriately controlling the inner peripheral surface temperature by cooling the inner peripheral surface. For example, by controlling the inner surface hardened layer to be less than HRC45, the inner surface hardened layer can be modified to a martensite structure in which cementite grains are dispersed, and it can withstand shock loads and has high toughness. An oil-filled crawler belt bush can be manufactured.

  14A, 14B, 14C, and 14D show the inner peripheral surface cooling method described above. FIG. 14A shows partition jigs 10 and 11 that prevent the inner peripheral cooling medium from leaking to the outer peripheral surface side at both end portions of the crawler belt bush 5, and further, a cooling medium such as water or a water-soluble quenching liquid. The introduction pipe 12 is arranged on the inner peripheral surface of the crawler belt bush 5, and the direction of the cooling medium flowing in the cooling medium introduction pipe 12 is changed to constitute the outer peripheral surface of the cooling medium introduction pipe 12 and the inner peripheral surface of the crawler belt bush 5. A method of controlling the cooling of the inner peripheral surface by a laminar cooling method in which a cooling medium is flowed in the axial direction of the crawler belt bush 5 in the gap. This laminar cooling method is a preferable method because the refrigerant flow within 1 second can be turned on and off, and more accurate inner peripheral surface cooling is possible.

  FIG. 14B shows an example in which a nozzle type pipe is used as the cooling medium introduction pipe 12, and it is preferable to use a cooling medium such as air or spray in addition to water. FIG. 14 (c) shows that the inner peripheral surface avoiding the vicinity of the end surface of the crawler belt bush 5 is held by an inner diameter collet chuck 13 made of a metal material having good thermal conductivity, and the temperature of the inner peripheral surface is increased by high frequency heating from the outer peripheral surface. It is a method of suppressing. The inner diameter collet chuck 13 is preferably provided with a cooling function by blowing air from the inner diameter collet chuck 13 or squeezing water or the like.

  Further, like the partitioning jigs 10 and 11 shown in FIG. 14, the partitioning jig is shaped so as to cover the inner peripheral surface in the vicinity of the crawler belt bushing end surface, whereby the crawler belt bushing end surface by the inner peripheral surface cooling described above. Since cooling from the inner peripheral surface side of the portion is delayed and a more stable hardened and hardened layer of the end surface portion is obtained, this partition jig can be used in any of the methods of FIGS. 14 (a), (b), and (c). Is preferably applied. FIG. 14D shows a method in which a cooling glass (or water-cooled cooling glass) 14 is arranged on the inner peripheral surface, and has the least inner peripheral surface cooling effect.

  FIGS. 15A, 15B, and 15C show another example of the above-described collet chuck method. (B) shows that the heat insulating material 15 is arranged on the inner diameter collet chuck 13 so as to insulate the inner peripheral surface near the end surface of the crawler belt bush. By doing so, the hardened hardened layer at the end face portion is easily formed by heating from the outer peripheral surface for a shorter time, which is a preferable method for shortening the heat treatment cycle. (C) shows a cooling nozzle 16 at the center of the collet chuck 13 through which a cooling medium such as air or spray can be ejected.

  16 (a) and 16 (b) show a manufacturing method for forming the outer peripheral surface hardened layer and the end surface hardened layer of the crawler belt bush by the mobile induction hardening method from the outer peripheral surface. FIG. 16A shows that the above-mentioned crawler belt bush 5 is continuously pressed in the direction of arrow B and heated by the high-frequency heating coil 9 and sprayed with a cooling medium such as water or a water-soluble quenching liquid or spray from the outer peripheral surface cooling nozzle 17. Shows a method of quenching and hardening. At this time, the crawler belt bushing feed speed V1 in the vicinity of the end face is made slower than the feed speed V2 in the vicinity of the center, so that the vicinity of the end face is sufficiently heated, and the hardened hardened layer in the end face by the subsequent cooling. Is widely formed. Further, in order to form a deep hardened hardened layer while securing the inner peripheral surface hardness to be equal to or higher than HRC45, as shown in FIG. 16B, the inner peripheral surface of the crawler belt bush 5 is changed to the inner peripheral surface cooling nozzle 17A. In the above-mentioned principle, it is preferable to carry out deep high-frequency heating from the outer peripheral surface and subsequent cooling while appropriately cooling with water, water-soluble quenching liquid, air, spraying, etc. on the same principle as described above. In FIG. 16, what is indicated by reference numeral 18 is a gap jig that is inserted into the gap between the adjacent crawler belt bushings 5 and 5.

  In terms of facility convenience, the crawler belt bush 5 is not necessarily moved, and the high-frequency heating coil 9 and the cooling nozzles 17 and 17A may be moved. Further, it is not always necessary to send the crawler belt bush 5 continuously. Furthermore, it is also possible to move and quench in the vertical type instead of the horizontal type as shown in FIG. 16, for example, as shown in FIG. 17, various inner peripheral surface cooling methods as shown in FIGS. It is also possible to carry out induction hardening from the outer peripheral surface while using together.

  In this embodiment, if the crawler belt bush that has been hardened and hardened as a whole is heated too quickly from the outer peripheral surface, there is a risk of causing cracking due to so-called multiple quenching. It is preferable to make the temperature rate slightly slower, and the whole high frequency heating method capable of adjusting the heating rate is more preferable than the mobile high frequency heating method. Furthermore, the above-described inner circumferential surface hardened and hardened crawler belt bushing is more preferable because there is no risk of quenching cracks even by rapid heating from the outer peripheral surface.

  Furthermore, referring to the temperature rise curve of the crawler belt bush by overall high-frequency heating from the outer peripheral surface (FIG. 10), the inner peripheral surface temperature is heated to 800 ° C. or higher so that quench hardening can be performed. While stopping the high-frequency heating or continuing the heating, only the inner peripheral surface is strongly pre-cooled, and after quenching martensite layer is formed during the pre-cooling (after a predetermined time), the inner peripheral surface is cooled. The method of stopping the high frequency heating from the outer peripheral surface and cooling from the outer peripheral surface while tempering the hardened hardened inner peripheral surface by thermal diffusion from the outer peripheral surface to be less than HRC45, and manufacturing the tough track belt bush It turns out that it is suitable as a method.

FIGS. 18A, 18B, and 18C are partial cross-sectional views of a crawler belt bush manufactured by this manufacturing method. According to this method, it is clear that it is an extremely inexpensive manufacturing method because the entire thickness of the crawler belt bushing is quenched and hardened, and heat treatment for quenching and hardening the inner peripheral surface of the crawler belt bush is not required. . Furthermore, the tempered martensite structure layer 19 in which cementite grains less than HRC45 are dispersed is set so that the U-notch Charpy impact value is surely 5 kg-m / cm ² or more, but the tempering temperature is 400 ° C. or more. A state of being tempered for a short time at a temperature is preferable. In FIGS. 18 (a) and 18 (b), reference numeral 20 indicates a structure layer in which one or more of ferrite, pearlite, bainite, and martensite that are precipitated during cooling are tempered.

  The inventors of the present application have proposed as a prior application a technique in which the inner peripheral surface is a hardened layer of a hardened martensite structure having a hardness of HRC45 or higher by substantially the same method, but in this prior application, a harder hardened martensite is proposed. In order to continue cooling the inner peripheral surface in order to obtain a structure, the contact portion of the crawler belt bush with the partitioning jig is deformed during transformation, and the inner peripheral surface cooling medium from this part is likely to leak, and its end surface There was a problem that uneven burning was likely to occur in the part. On the other hand, in the present embodiment, the chamfered shape in the vicinity of both ends of the crawler belt bush with which the partition jig comes into contact is made larger than the chamfered shape of the outer peripheral surface, and / or the tempered martensite having a higher toughness than HRC45 is provided. In order to form, the inner peripheral surface precedent cooling is temporarily stopped halfway to prevent unevenness due to leakage of the cooling medium from the partition jig, and the heat treatment of the inner and outer peripheral surfaces is performed by a series of quenching operations. The economic effect to complete is great. Furthermore, it is clear that remarkably refinement of crystal grains (ASTM grain size number 9 to 13) is achieved by reheating and re-quenching at the center portion of the crawler belt bush thickness, which contributes to improvement of the strength of the crawler belt bush ( (See FIG. 18).

  In addition, it is as above-mentioned about the outer peripheral surface induction hardening method which is connected with the hardening hardening layer of an outer peripheral surface, and an end surface part is quench-hardened. In the present embodiment, this outer peripheral surface induction hardening method is applied to obtain an oil-filled crawler belt bush including a high-toughness soft layer 21 whose portion excluding the hardening hardening layers 2 and 4 is less than HRC45. FIGS. 19A to 19E show the structure of the oil-filled crawler belt bush. In addition, as a method of forming the soft layer 21 of less than HRC45, there is a method of adjusting hardness and structure by material tempering (quenching and tempering) or the like before induction hardening on the outer peripheral surface. Adjustment is a more preferable method than the cost.

Furthermore, seizure occurs due to sliding with the crawler belt pin fitted on the inner surface of the crawler belt bush, and when the wear resistance is required or when traveling on sandy land for a long distance at a high speed, When it is necessary to increase the fatigue strength, a thin high frequency corresponding to 5 to 15% of the wall thickness is formed on the inner circumferential surface of the crawler belt bush shown in FIG. 19 as shown in FIGS. It is preferable to form the hardened hardening layer 22 and to form a compressive residual stress of 30 kg / mm ² or more on the inner peripheral surface.

  Further, since it is unavoidable that the hardness of the outer peripheral surface hardened layer decreases due to thermal diffusion by high frequency heating of the inner peripheral surface and the quench hardening depth becomes shallow, it is preferable to use a high frequency power source of 20 kHz or more and to use the outer peripheral surface. It is preferable to carry out induction hardening of the inner peripheral surface while cooling.

  21 (a) to 21 (e) show a crawler belt bush for a dry crawler belt that does not require the oil sealing property used in a hydraulic excavator or the like. As shown in the figure, in this dry crawler belt bush, a soft layer 25 at the center of the thickness formed between the outer peripheral surface hardened layer 23 and the inner peripheral hardened layer 24 is connected to both end surfaces. In FIG. 21, symbol P indicates the outer peripheral surface press-fitting start point, and symbol Q indicates the inner peripheral surface chamfering start point.

  By the way, various methods have been proposed as a method of manufacturing the crawler belt bush, but as shown in FIG. 22, the layers proposed by the present inventors in the prior application (Japanese Patent Laid-Open No. 2001-240914). A method of manufacturing a crawler belt bush in which a hardened layer is simultaneously formed on the inner and outer peripheral surfaces of a plurality of crawler belt bushes 5 by a flow quenching method and a soft layer is provided between both hardened layers can be used. In addition, in FIG. 22, in the case where an unquenched layer is formed on one or more crawler belt bushing end surfaces, the interval between the high-frequency heating coils (spiral coils) 9 is set so that the heating of the end surface is delayed when the whole is heated. It is preferable to adjust.

  FIGS. 23A to 23F show a method of manufacturing an oil-filled crawler belt bush having a hardened end surface by separately curing the end surface of the crawler belt bush.

  In FIGS. 23A to 23F, a portion indicated by reference numeral 26 in the end face portion is a hardened layer additionally induction hardened. Usually, the hardened layer 26 is required to have a higher hardness and a hardening depth of at least 0.5 mm or more in order that the oil seal slides and also functions to prevent the entry of soil from the outside system. However, when considering use for a longer time, a curing depth of 1 mm or more is required. In particular, in the crawler belt bush shown in FIGS. 23 (a), (b), and (c), the end face hardened layer 26, the outer peripheral face hardened layer 23, and the inner peripheral face hardened layer 24 are overlapped and quenched. A tempered martensite layer 27 in which soft granular cementite is dispersed is formed in the overlapping portion, and a partial ferrite and pearlite structure less than the HRC 40 is formed at the boundary with the quench hardened layer 26. When this soft part less than HRC40 exists at the press-fitting start point P of the outer peripheral portion when the crawler belt bush is press-fitted into the crawler belt link, in order to cause a press-fitting problem due to galling, the hardness of the press-fitting start point P The edge hardening quenching depth is made shallower so that the HRC is HRC 40 or more, preferably HRC 45 or more than the press-fitting start point P as shown in FIGS. 23 (b), (c) and (e). It is preferable to quench deeper. In the case where the end face quenching layer 26 is shallow or the heat affected zone is shallow, the high frequency heating power source is preferably set to 40 kHz or higher, or induction quenching is performed while cooling other than the heating quenching portion. .

  Further, in a crawler belt bush made of a low alloy steel (SMn, SCr, SCrB, SCM, SNCM steel) or a higher carbon steel (0.55% by weight or more) that is susceptible to quench cracking due to induction hardening of the end face part, In order to prevent this end face part from cracking, high-frequency heating from the end face part avoids rapid heating at the beginning of the end face part high-frequency heating. It is preferable that the crawler belt bushes whose inner peripheral surface and outer peripheral surface of the end surface portion are not quenched and hardened are hardened and hardened as shown in FIGS. 23 (d), (e), and (f).

  24 (a) (b) (c) are stacked in three stages, and both end portions of a crawler belt bush (S45C carbon steel) manufactured by inner peripheral surface preceding cooling and outer peripheral surface cooling after the entire high frequency heating are 150 kW, 40 kHz, The macrostructure of what was induction-hardened on each condition of 3,4,5 second is shown. Moreover, FIG. 25 shows the hardness measurement result of the outer peripheral surface in the arrow R direction and position shown in FIG. It can be seen that the end surface hardened layer has a seal surface hardness of HRC60 (Vickers hardness Hv = 700) and a hardness comparable to that of the carburized hardened crawler belt bush.

  Further, as is apparent from the hardness distribution diagram of FIG. 25, a softened layer by high-frequency heating spreads from the hardened hardened layer toward the center of the crawler belt bush. In order to narrow the heat-affected zone, it is preferable to cool the heat-affected zone other than the quench hardened layer, for example, a quenching method in which the crawler belt bush is immersed in the end surface portion or the end surface portion is submerged in water. It is preferable to use a quenching method or the like.

Since these crawler belt bushes are connected with the softened layer on the inner peripheral surface and the outer peripheral surface in the vicinity of the end face portion as shown in FIG. 24, there is a concern that tensile residual stress is likely to occur at the connecting portion. Residual stress at a position of 1 mm or 3 mm from the press-fitting start point of the 5-second induction-hardened product shown in FIG. As a result, a residual stress of axial stress = −53 kgf / mm ² and circumferential stress = 39 kgf / mm ² is observed at the 1 mm position, and there is a risk of circumferential cracking along the most hardened hardened layer. It became clear that there was no. Further, since the residual stress is reduced by tempering at 150 ° C. or higher by quenching, it is clear that the danger of quench cracking due to induction hardening of the end face of the crawler bush is completely avoided.

  In addition, in this embodiment, when the crawler pin is bent by receiving an offset load related to the crawler belt, even if the offset load acts near the end face of the crawler belt bush, a bending load is easily applied to the soft layer. When the end point is at least deeper than the press-fitting start point on the outer peripheral surface, the shape can reduce the bending stress, and when the tempering process of the final heat treatment step is abolished and used, For the purpose of changing the residual stress to compressive residual stress, mechanical processing such as shot peening is performed in the vicinity of the heat treatment part of the end face.

  In addition, since it is preferable that the hardening hardened layer hardness of one place or more of the inner circumference, outer circumference, and end face of the crawler belt bush is at least HRC50 or more, the carbon amount of the steel material used for the crawler belt bush is 0.30 to 1.5. It is preferable that it is weight%. In addition, the hardenability (DI value) is not particularly specified, but a large economic effect can be expected because it can be dealt with in many cases with a low hardenability of DI value = 2.0 or less and carbon boron steel.

  Furthermore, in order to further enhance the wear resistance of the end face part, it is preferable to use the hardened hardened layer obtained by additionally induction hardening the end face part in a tempered or untempered state of less than 150 ° C. It is also preferable to complete the tempering treatment in the crawler belt bush to be provided.

A graph showing the cooling condition and continuous cooling transformation line of the crawler belt bush when the outer peripheral surface and the inner peripheral surface are rapidly cooled simultaneously after heating to 850 ° C. Experimentally obtained the relationship between the thickness of the crawler belt bushing and the DI value, which becomes through-hard when the outer peripheral surface and inner peripheral surface are quenched at the same time. A graph showing the cooling condition of the track bush and the constant temperature transformation line of the S50C carbon steel after the entire surface was heated to 850 ° C., the outer peripheral surface and the inner peripheral surface were quenched at the same time for 2 seconds, and then the cooling was temporarily stopped for 2 seconds. A graph showing the cooling condition of the track bush and the constant temperature transformation line of the S50C carbon steel after the entire heating to 850 ° C., the outer peripheral surface and the inner peripheral surface are rapidly cooled simultaneously for 2 seconds, and then the cooling is temporarily stopped for 4 seconds. It is a partial sectional view of a crawler belt bush obtained by temporarily stopping the cooling after the outer peripheral surface and the inner peripheral surface of the crawler belt bush are simultaneously cooled. (B) is a tempered martensite having high toughness due to thermal diffusion inside the wall thickness. Organizational layer The graph which shows the cooling condition of the crawler belt bush which cooled the outer peripheral surface after quenching only the inner peripheral surface for 4 seconds after the whole was heated to 850 ° C. It is a fragmentary sectional view of a crawler belt bush obtained by heat treatment performed by pre-cooling the inner peripheral surface or the outer peripheral surface, (a) pressing the cooling medium partition jig against the inner peripheral portion of the end surface, The pearlite structure layer is connected to the inner peripheral surface of the end face, and (b) shows the inner peripheral surface of the tempered martensite structure layer by thermal diffusion from the inside of the wall thickness. (C) shows a cooling medium partitioning jig pressed against the outer periphery of the end face, and a soft pearlite structure layer inside the wall is connected to the outer peripheral face of the end face. This shows the temperature distribution inside the wall thickness when the inner peripheral surface is pre-cooled while performing high frequency heating from the outer peripheral surface after heating the entire track bush. It is a fragmentary sectional view of a crawler belt bush obtained by heat treatment performed by subjecting the outer peripheral surface or the inner peripheral surface to high-frequency heating and preliminarily cooling the judgment surface, and (b) shows the inner peripheral surface by diffusion of high-frequency heating heat from the outer peripheral surface. Made into a tough tempered martensite structure layer Graph showing temperature rise of crawler belt bush by high frequency heating from outer peripheral surface It is a fragmentary sectional view of an oil enclosure type crawler belt bush, (a) and (b) which hardened and hardened the whole thickness, and induction-hardened from the outer peripheral surface, (b) and (c) are inner peripheral surfaces Induction hardening from the outer peripheral surface after quenching and hardening Hardness distribution (a) of the crawler belt bushing in which the entire thickness is quenched and hardened only in the inner peripheral surface portion, and further, the hardness distribution in the thick section of the crawler belt bush that is induction hardened from the outer peripheral surface (b) Explanation of whole high frequency heating method from outer peripheral surface Explanation of various inner surface cooling methods Diagram showing inner diameter collet chuck Illustration of mobile induction hardening method from outer peripheral surface Outer surface moving induction hardening method using collet chuck cooling for inner surface cooling Partial cross-sectional view of a crawler belt bush formed with a tempered martensite structure layer having an inner peripheral surface of less than HRC45 and high-toughness granular cementite dispersed therein Partial cross-sectional view of a crawler belt bushing having a hardened end face layer that is continuously connected to the hardened outer peripheral surface, and the remaining portion being a soft layer of less than HRC45 Partial cross-sectional view of a crawler belt bushing with a hardened hardened layer on a soft layer of less than HRC45 on the inner circumference Partial cross section of dry crawler belt bush Multi-stack whole induction heating quenching method explanatory diagram Partial cross section of crawler belt bush with induction hardening Macrostructure of end hardening of crawler belt bushing Graph showing the hardness measurement results of the outer peripheral surface of the endlessly hardened crawler belt bushing An exploded perspective view of the crawler belt The figure explaining the seal contact position in the seal flat part of a crawler belt bush end surface

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Soft layer of tempered martensite structure 2 Outer peripheral surface hardened layer 2A Inner peripheral surface hardened layer 2B, 4 End surface hardened layer 2C Tempered martensite layer of inner peripheral surface less than HRC45 3 Soft layer 5 containing pearlite 5 Crawler belt bush 6 Tempered martensite hardened layer 7 Ferrite less than HRC45 + pearlite unquenched hardened layer 8 Saddle coil 9 Spiral coiled dielectric (high frequency heating coil)
10, 11 Partition jig 12 Cooling medium introduction pipe 13 Inner diameter collet chuck 14 Cooling glass 15 Heat insulating material 16, 17, 17A Cooling nozzle 18 Gap jig 19 Tempered martensite structure layer 20 in which granular cementite is dispersed Ferrite, pearlite, Structure layer 22 in which one or more of bainite and martensite are tempered 22 Quenched and hardened layer 26 having HRC45 or more End-face induction-hardened and hardened layer 27 Tempered layer P by end-surface quenching Peripheral surface press-fitting start point Q Inner surface chamfering start point

Claims (12)

  A track bushing material comprising carbon steel and / or low alloy steel containing at least carbon in the range of 0.35 to 1.2% by weight, and having a total thickness adjusted to a hardness of less than HRC 30 to 45 A crawler belt bush, wherein an outer peripheral surface hardened layer and an end surface hardened layer continuously connected to the outer surface hardened layer are formed by induction heating and hardening from the outer peripheral surface.   By cooling the inner peripheral surface during high-frequency heating from the outer peripheral surface, the outer peripheral surface hardened and hardened layer depth is increased to 30 to 80% of the wall thickness to improve the wear life of the crawler belt bush. The crawler belt bush according to claim 1. Avoid the hardened hardening part of the seal flat part of both ends of the crawler belt bush, induction harden the inner peripheral surface of the crawler belt bush, the inner peripheral hardened hardened layer depth is 5-15% of the wall thickness, and the crawler belt bush thickness The soft layer formed inside is connected to the inner peripheral surface in the vicinity of both end surfaces, avoiding the seal flat part on both end surfaces of the crawler belt bush, and compressive residual stress of 30 kg / mm ² or more is generated on the inner peripheral surface The crawler belt bush according to claim 1, wherein the crawler belt bush is provided.   The tempering process of 150 degreeC or more is performed, the hardness of the induction hardening hardened layer surface is HRC50 or more, and the hardening hardening depth of both end surface parts is 0.5 mm or more, The crawler belt bush according to any one.   5. The crawler belt bush according to claim 1, wherein a chamfered portion on an inner peripheral surface side is made larger than a chamfered portion on an outer peripheral surface side in a shape in the vicinity of both end surface portions of the crawler belt bush. The outer peripheral surface and / or the inner peripheral surface of the crawler belt bush that is press-fitted into the crawler belt link is subjected to mechanical processing by shot peening to make the outermost surface harder and to add compressive residual stress. The crawler belt bush according to any one of claims 1 to 5. The crawler belt bush according to any one of claims 1 to 6, wherein the inner peripheral surface and the outer peripheral surface are subjected to chemical conversion treatment with a phosphate film.   After adjusting the overall thickness to a hardness of less than HRC 35 to 45 using the crawler belt material, the outer peripheral surface hardened layer and the end-hardened hardened layer continuously connected to the outer surface hardened layer are obtained by high-frequency heating and quenching from the outer peripheral surface. A method of manufacturing a crawler belt bush, characterized by being formed. In the manufacturing method of the crawler belt bush, avoiding the softened hardened portions of the seal flat portions on both ends of the crawler belt bushing, induction hardening the inner peripheral surface of the crawler belt bush, and the inner peripheral hardened layer thickness is thick. 5 to 15% of the thickness, the soft layer formed inside the crawler bushing is connected to the inner peripheral surface in the vicinity of both end surfaces while avoiding the flat seal portions on both end surfaces of the crawler bushing, and the inner peripheral surface The method for manufacturing a crawler belt bush according to claim 8, wherein a compressive residual stress of 30 kg / mm ² or more is generated in the step.   By cooling the inner peripheral surface during high-frequency heating from the outer peripheral surface, the outer peripheral surface hardened and hardened layer depth is increased to 30 to 80% of the thickness to improve the wear life of the crawler belt bush. A method for manufacturing a crawler belt bush according to claim 8 or 9.   A tempering treatment at 150 ° C. or higher is performed, the hardness of the outer peripheral surface hardened layer is HRC 50-65, and the hardened depth of both end faces is 0.5 mm or higher. The method for manufacturing a crawler belt bush according to any one of 10. The method for producing a crawler belt bush according to any one of claims 8 to 11, wherein a chemical conversion treatment with a phosphate film is performed on an inner peripheral surface and an outer peripheral surface of the crawler belt bush.