JP4676993B2 - Bush making - Google Patents

Description

  The present invention relates to a method of manufacturing a bush used for, for example, a bulldozer.

  As shown in FIG. 1, the bush used for a bulldozer or the like requires wear resistance on its outer surface 2 and inner surface 3, and also requires strength and toughness to withstand the load applied to the bush 1. In order to satisfy such requirements, conventionally, the following bush manufacturing method has been proposed.

  In Patent Document 1, in mass%, C: 0.05 to 0.40%, Si: 0.1 to 0.8%, Mn: 0.5 to 2.0%, Cr: 0.1 to 2 0.0%, Ti: 0.005-0.5%, B: 0.0005-0.005%, Al: 0.005-0.10%, N: 0.005% or less, the balance being substantially Fe And a wear resistant steel consisting of inevitable impurities. Then, after the hot-rolled steel slab is heated, hot rolling is performed. 950 to 1250 ° C. is preferable). Further, in hot rolling, rolling is performed at a cumulative reduction ratio of 50% or more in an austenite non-recrystallized region of 900 ° C. or lower, and the degree of elongation of the prior austenite grains is set to 2 or more, and the austenite non-recrystallized region is 900 ° C. or lower. Rolling at a low temperature side, preferably 850 ° C. to Ar 3, with a cumulative rolling reduction of 50% or more. After the heat treatment hot rolling, quenching is performed immediately after the rolling so that the effect of the cumulative reduction in the non-recrystallized region tempered at 300 ° C. to Ac1 is not lost. After quenching, tempering is performed at 300 ° C to Ac1, preferably 300 to 650 ° C. According to the method of Patent Document 1, Brinell hardness is 335 to 435 (Hrc 36 to Hrc 46.1), and toughness is 71 to 141 J with an absorption energy of −40 ° C. However, in order to obtain high strength and high toughness, there is a problem that the rolling process is necessary, and that the process is complicated, such as quenching immediately after the rolling process.

  Patent Document 2 proposes a method in which case-hardened steel (for example, JIS: SCM415), which is a low carbon steel, is used as a material, carburized on the surface of the material, and then quenched and tempered. It is disclosed that wear resistance is obtained on the surface by the carburizing process, and strength and toughness are obtained in the core by quenching and tempering of the case hardening steel, but the carburizing process usually takes 40 to 50 hours, This is a batch process, and there is a problem that the required amount of the bush cannot be manufactured continuously in a short time, and the manufacturing cost is increased.

  On the other hand, in Patent Document 3, based on a high carbon steel containing 0.5 to 1.0% by weight of C, at least one element of Mn, Cr, and Mo and B are added. In the process, the bush material is induction-hardened from the outer surface, and in the second process, the inner material is quenched while liquid-cooling the outer surface. In the third process, the bush material is subjected to low-temperature tempering, and the inner and outer surfaces The nearby structure is tempered from tempered martensite. And according to the manufacturing method of patent document 3, it is supposed that the total thickness is carbon amount: 0.5% or more, and it can be considered that the total thickness is a carburized layer. According to the manufacturing method of Patent Document 3, the depth of the layer having hardness up to HRC 52.3 is 3.2 mm on the inner side and 4.4 mm on the outer side, and the hardness of the outer surface is about HRC60. Further, according to the manufacturing method of Patent Document 2, although it is expected to have toughness equal to or higher than that according to the conventional method, it is not described how much toughness is specifically obtained. In the manufacturing method of Patent Document 3, a material having a carbon content of 0.5 to 1.0% is used to manufacture a bush having high hardness and high toughness. However, in the manufacturing method of Patent Document 3, the core intermediate layer is martensite. It is a layer that has been tempered when it is induction hardened from the inner diameter, and the martensite structure and the ferrite and pearlite structure are mixed, or the sorbite structure and the fine pearlite structure are mixed. The toughness falls to 70 to 80% compared to the bush whose core intermediate layer is a sorbite structure, the toughness is not sufficient, and there is a high possibility that the bush suddenly breaks during operation. There's a problem.

JP 2002-20837 A Japanese Patent Publication No. 52-34806 JP-A-5-78745

  As described above, Patent Document 1 requires a complicated and costly process of quenching immediately after the rolling process using a base material having a low carbon content of 0.05 to 0.40% by weight. Yes. Patent Document 3 describes the toughness of the intermediate layer generated in the process of quenching the inside while liquid cooling the outside in the quenching process using a base material having a high carbon content of 0.5 to 1.0% by weight. Sex is not enough.

  Therefore, the present invention uses a base material having a medium carbon content, has a simple process and a low manufacturing cost, and is superior to the conventional bush in both hardness and toughness as compared with the conventional bush manufacturing method. The aim is to provide a bush that is not inferior.

The manufacturing method of the bush of the present invention is
A method for producing a bush, comprising 0.32 to 0.60% by weight of carbon (C), heat-treating a bush base material made of a cylindrical steel material having an outer diameter of 65 to 130 mm and an inner diameter of 43 to 80 mm,
(A) The bushing base material is heated with a high frequency of 0.5 to 3 kHz under the conditions of electric power of 0.5 to 3 kW / cm ² and time of 20 to 200 seconds, and baked from the outer surface to the inner surface of the bushing base material. A step of heating to 800 to 920 ° C. which is an entrance transformation temperature;
(B) quenching and cooling the bush base material heated in the step (a) to 30 to 130 ° C;
(C) The bush base material quenched and cooled in the step (b) is heated with high frequency of 0.5 to 3 kHz under conditions of electric power of 0.5 to 3 kW / cm ² and time of 20 to 200 seconds. Or the process of moving and heating at a feed rate of 2 to 10 mm / sec and tempering,
(D) The outer surface and the inner surface of the bush base material are subjected to transfer quenching under the conditions of a power of 0.5 to 5 kW / cm ² and a feed rate of 0.5 to 10 mm / sec with a high frequency of 5 to 30 kHz. It is characterized by comprising a step of leaving the intermediate layer and (e) a step of low-temperature tempering with a furnace.

Moreover, the manufacturing method of the bush of this invention is
A method for producing a bush, comprising 0.32 to 0.60% by weight of carbon (C), heat-treating a bush base material made of a cylindrical steel material having an outer diameter of 65 to 130 mm and an inner diameter of 43 to 80 mm,
(F) The bush base material is moved and heated at a power of 0.5 to 3 kW / cm ² and a feed rate of ² to 10 mm / second with a high frequency of 0.5 to 3 kHz. Heating to 800-920 ° C., which is the quenching transformation temperature, to the surface;
(G) quenching and cooling the bush base material heated in the step (f) to 30 to 130 ° C .;
(H) The bush base material quenched and cooled in the step (g) is heated with a high frequency of 0.5 to 3 kHz under conditions of electric power of 0.5 to 3 kW / cm ² and time of 20 to 200 seconds. Or the process of moving and heating at a feed rate of 2 to 10 mm / sec and tempering,
(I) The outer surface and the inner surface of the bush base material are subjected to transfer quenching with a high frequency of 5 to 30 kHz under conditions of electric power of 0.5 to 5 kW / cm ² and a feed rate of 0.5 to 10 mm / sec. It is characterized by comprising a step of leaving the intermediate layer and (j) a step of low-temperature tempering in a furnace.

  Further, in the step (b) or (g), it is preferable to carry out with a liquid having a cooling concentration such that maximum martensite is obtained in the entire inner and outer diameters.

  Moreover, it is preferable that the said process (c) or (h) is high temperature tempering of 570-650 degreeC.

  Moreover, it is preferable that the hardness of the core part of the said intermediate | middle layer is Hv272-354.

  Moreover, it is preferable that the hardened layer depth more than Hrc45 of the said bush exists in the range of 20-45% of thickness from an outer surface, and 15-35% from an inner surface.

  Further, the bush base material preferably contains 0.40 to 0.50% by weight of carbon (C).

The second aspect of the present invention heat-treats a bush base material made of a cylindrical steel material containing 0.50 to 0.60% by weight of carbon (C) and having an outer diameter of 65 to 130 mm and an inner diameter of 43 to 80 mm. A method of manufacturing a bush, comprising:
(A) The bushing base material is heated with a high frequency of 0.5 to 3 kHz under the conditions of electric power of 0.5 to 3 kW / cm ² and time of 20 to 200 seconds, and baked from the outer surface to the inner surface of the bushing base material. A step of heating to 800 to 920 ° C. which is an entrance transformation temperature;
(B) quenching and cooling the bush base material heated in the step (a) to 30 to 130 ° C;
(C) a step of low-temperature tempering the bush base material quenched and cooled in the step (b) in a furnace;
(D) A step of moving and quenching the inner surface of the bushing base material with a high frequency of 5 to 30 kHz and cooling the outer surface under a feed rate of 0.5 to 10 mm / second to form an intermediate layer. It is characterized by comprising.

Moreover, the 2nd aspect of this invention contains the bush base material which consists of cylindrical steel materials containing 0.50-0.60 weight% carbon (C), outer diameter 65-130mm, and inner diameter 43-80mm. A method of manufacturing a bush to be heat treated,
(F) The bush base material is moved and heated at a power of 0.5 to 3 kW / cm ² and a feed rate of ² to 10 mm / second with a high frequency of 0.5 to 3 kHz. Heating to 800-920 ° C., which is the quenching transformation temperature, to the surface;
(G) quenching and cooling the bush base material heated in the step (f) to 30 to 130 ° C .;
(H) a step of low-temperature tempering the bush base material quenched and cooled in the step (g) in a furnace;
(I) a step of moving and quenching the inner surface of the bushing base material while cooling the outer peripheral surface at a feed rate of 0.5 to 10 mm / second with a high frequency of 5 to 30 kHz and forming an intermediate layer; and (j) a furnace And a step of low-temperature tempering.

  According to the present invention, the manufacturing process is not complicated, the number of processes is small, the heat treatment cost is low, and the intermediate layer of the bush has toughness, and the inner surface and the outer surface have high wear resistance. Bush can be provided.

  Hereinafter, a method for manufacturing a bush according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a longitudinal sectional view of the bush of the present invention, FIG. 2 is an enlarged view of region X in FIG. 1, and FIG. 3 is a diagram showing the relationship between hardness and Charpy impact value, hardness and tensile strength. 4 is a graph showing the cross-sectional hardness of the bush manufactured by the method of the present invention, and FIG. 5 is a graph showing the cross-sectional hardness of the bush manufactured by the second embodiment of the method of the present invention.

The bush base material 1 in the present invention is a medium carbon low alloy steel in which any of Mn, Cr and B are added to a medium carbon steel containing 0.32 to 0.60% C by weight. Further, it is more preferable to contain 0.40 to 0.50% C by weight. The reason is that a bush with high hardness can be manufactured. The purpose and amount of addition of these alloy elements are as follows.
(1) The addition of Mn is for ensuring hardenability, and the addition amount is 0.55 to 0.90%.
(2) The addition of Cr is for ensuring hardenability and wear resistance, and the addition amount is 0.45 to 1.20%.
(3) The addition of B is for securing toughness, and the addition amount is 0.0005 to 0.0035%.

  Hereinafter, the 1st aspect of the manufacturing method of the bush of this invention is shown.

(A) Step of heating bush base material In the step of heating the bush base material 1 in the present invention, a high frequency current having a frequency of 0.5 to 3 kHz is applied to the high frequency heating coil, and 0.32 to 0.60 by weight%. % Of carbon (C), bush base material 1 having an outer diameter of 65 to 130 mm and an inner diameter of 43 to 80 mm is placed in a high-frequency heating coil, and has an electric power of 0.5 to 3 kW / cm ² and a time of 20 to 200 seconds Heating is performed under conditions, or moving heating at a feed rate of 2 to 10 mm / sec, and heating is performed from the outer surface 2 to the inner surface 3 of the bush base material 1 at a quenching transformation point temperature of 800 to 920 ° C. In particular, the outer surface 2 is set to 920 ° C. or lower, and the inner surface 3 is heated to 800 ° C. or higher. By heating in this way, the bush base material 1 is austenitized. This is because if the outer surface 2 exceeds 920 ° C., the crystal grains become coarse and sufficient strength cannot be obtained. It is because there exists a possibility that it may not become austenite in it being 800 degrees C or less. As a heating method, specifically, the bush base material 1 to be processed is fixed or moved by a uniform dummy material that is heated up and down, and a high-frequency current having an appropriate frequency is applied to the heating coil while rotating around the center line. The product is fixed or moved with respect to the heating coil and energized for an appropriate time until the inner and outer surfaces of the bush base material 1 reach the austenitizing temperature (outer surface 850 to 920 ° C., inner surface 800 to 850 ° C.). The reason for rotating the bush base material 1 is to perform uniform induction hardening over the entire outer surface 2. At this time, the frequency of the outer surface 2 is selected so that the crystal grains are not coarsened.

(B) Cooling step After the step (A), the heated bush base material 1 is quenched and cooled to 30 to 130 ° C. Specifically, after the heat treatment of the bush base material 1, a liquid having a cooling concentration that prevents cracking and that the inner and outer surfaces become maximum martensite is sprayed from the cooling jacket, and from the outer surface 2 or the inner and outer surfaces. To cool and quench rapidly. Water or a soluble quench is used as the cooling liquid, and it is cooled to 30 to 130 ° C.

  By quenching in the above (A) and (B), the outer surface 2 to the inner surface 3 are martensitic, and the bush base material 1 is once fully cured. In the present invention, the total hardening means that the total thickness of the bush is made martensite by quenching the total thickness of the bush. The entire thickness of the bush is fully cured, and the total thickness is martensitic, so that the tensile strength and impact value after high-temperature tempering are 15-30 compared with the case of incomplete quenching that is not fully cured. % Improvement. In this induction hardening, it is necessary to set the outer surface 2 of the bush base material 1 to Hrc 58 to 65 and the inner surface 3 to Hrc 56 to 65. As described above, induction hardening can prevent the occurrence of a decarburized layer by combining heating for a short time and a water-soluble coolant, and the martensite conversion rate is increased as compared with quenching by a furnace. Hardening hardness is about 2 to 5 higher in Hrc than quenching by a furnace.

(C) Tempering step After the steps (A) and (B), the bush base material 1 that has been completely hardened by quenching is energized with a high-frequency current of a frequency of 0.5 to 3 kHz through a high-frequency heating coil, and a power of 0.5 to Tempering is performed by heating under conditions of 3 kW / cm ² and a time of 20 to 200 seconds, or moving and heating at a feed rate of 2 to 10 mm / second. Specifically, the bush base material 1 is fixed or moved with a vertically heated uniform dummy material, and a high frequency current with a frequency of 0.5 to 3 kHz is applied to the heating coil for 20 to 200 seconds while rotating around the center line, or Heating is performed at a feed rate of 2 to 10 mm / sec until the inner and outer surfaces of the bush base material 1 reach a tempering temperature of 570 to 650 ° C. By this high-temperature tempering, the entire thickness that is fully cured and martensified becomes a sorbite structure. Here, the sorbite structure is a structure obtained when martensite is tempered, and is a structure that is not as hard or brittle as martensite, is harder and stronger than pearlite, and has a high impact resistance. By induction hardening and induction high temperature tempering, if the hardness is the same, tempering at a high temperature increases toughness, and a bush having high toughness can be manufactured. Referring to FIG. 3, the relationship between tensile strength and hardness when quenched and tempered in a furnace is indicated by A in FIG. 3, and the relationship between Charpy impact value and hardness when quenched and tempered in a furnace is indicated by B. The relationship between tensile strength and hardness when quenched and tempered at high frequency is indicated by C, and the relationship between Charpy impact value and hardness when quenched and tempered at high frequency is indicated by D. As for the tensile strength and Charpy impact value of the bush, the points E and F, which are the intersections in Fig. 3, are ideal. It can be seen that is superior in tensile strength and Charpy impact value. At this time, the frequency is selected so that the temperature difference between the inner and outer surfaces is as small as possible. By reducing the temperature difference, a bush having uniform strength can be manufactured.

  Moreover, when quenching and tempering in a conventional furnace, the energy efficiency is about 10%, but by quenching and tempering at a high frequency, the energy efficiency is improved to 40 to 50%. Furthermore, in the quenching and tempering by high frequency, the bush can be continuously produced as compared with the quenching and tempering by the furnace, and can be operated and stopped in a few minutes when necessary, thereby saving energy and labor costs.

(D) Quenching step After the step (C), the outer surface 2 and the inner surface 3 of the bush are energized with a high-frequency current having a frequency of 5 to 30 kHz through a high-frequency heating coil, and moved and fired at a feed rate of 0.5 to 10 mm / sec As shown in FIG. 2, the outer hardened layer 4, the inner hardened layer 6, and the intermediate layer 5 sandwiched between the outer hardened layer 4 and the inner hardened layer 6 are left. By this quenching process, the outer quenching layer 4 and the inner quenching layer 6 have a martensite structure, and the intermediate layer 5 has a sorbite structure. The bush base material 1 is fixed at the upper and lower centers, and a high frequency current having a frequency of 5 to 30 kHz is energized at a power of 0.5 to 5 kW / cm ² while rotating at the center line, and heated under conditions of a time of 20 to 300 seconds. Alternatively, the hardened layer depth at which the outer surface 2 of the bush base material 1 exceeds Hrc45 is 20 to 45% of the thickness of the bush base material 1 by moving quenching at a feed rate of 0.5 to 10 mm / second. Quench. Moreover, it hardens so that the hardened layer depth over which the inner surface 3 exceeds Hrc45 may be 15 to 35% of the thickness of the bush base material 1. By this quenching, the intermediate layer 5 remains and the hardness is lower than that of the outer quenching layer 4 and the inner quenching layer 6, but the same hardness as that of the conventional bushing and excellent in toughness. Can be provided. The intermediate layer left by the quenching step (D) becomes a sorbite structure which is a tempered layer of a layer having a high martensite conversion rate, and a layer having high toughness is formed. The mid layer 5 has a Vickers hardness of Hv 272 to 354. Further, the Charpy impact value of the intermediate layer 5 is 90 to 140 J / cm ² . Moreover, the surface hardness of the outer periphery side hardening layer 4 and the inner periphery side hardening layer 6 becomes Hrc60 or more, and becomes Hrc52-61 by subsequent furnace tempering.

  As is clear from the above description, the bushing manufacturing method of the present invention omits the carburizing step and changes the tempering step to high frequency, thereby simplifying the manufacturing step, and the resulting bushing is as follows. As shown, it has wear resistance, strength and toughness not inferior to those of the bushes manufactured by the methods of the conventional patent documents 1 to 3.

  The bushes manufactured according to the present invention have a surface hardness of Hrc 52 to 61, which is not inferior to that of carburized bushes. In addition, they have excellent wear resistance and can be continuously operated for about 3000 hours. On the other hand, the bush obtained by the invention of Patent Document 1 has a hardness of about Hb350 (about Hrc37.7) when the carbon content is smaller than 0.32%. Under the same conditions, only half the continuous operation is possible for about 1500 hours. Further, the bush obtained by the invention of Patent Document 1 has a hardness of about Hb435 (about Hrc46) when the carbon content is 0.32% or more and 0.40% or less, and is the same condition as the operation of the present invention. Below, only about 2/3 of 2000 hours of continuous operation is possible.

  As for toughness, the core of the bush manufactured according to the present invention is a sorbite structure by high-temperature tempering of the martensite structure. The bush of Patent Document 3 has a martensite structure, a ferrite and a pearlite structure. It is mixed, or a sorbite structure and a fine pearlite structure are mixed, and only toughness of about 70 to 80% is obtained at most as compared with the present invention.

  Next, a second aspect of the method for manufacturing a bush according to the present invention will be described.

(E) The process of heating a bush base material The process of heating a base material is the same as that of a 1st aspect.

(F) Cooling step The cooling step is the same as in the first embodiment.

(G) Tempering Step After the steps (E) and (F), the bush base material 1 that has been completely hardened by quenching is tempered at a low temperature in a furnace. Tempering is performed by heating at 150 to 200 ° C. for 4 to 6 hours in a furnace.

(H) Quenching step After the tempering step, a high frequency current of 5 to 30 kHz is supplied to the high frequency heating coil with a power of 0.5 to 5 kW / cm ² and the outside is cooled, while a feed rate of 0.5 to 10 mm / The inner hardened layer 4 is moved and hardened in seconds to leave the outer hardened layer 4, thereby forming the inner hardened layer 6 and the intermediate hardened layer 4 sandwiched between the outer hardened layer 4 and the inner hardened layer 6. By this quenching process, the outer hardened layer 4 and the inner hardened layer 6 have a martensite structure, and the intermediate layer 5 is tempered by heating from the inner side to have a sorbite structure. The bush base material 1 is fixed at the upper and lower centers, and a high frequency current of 3 to 30 kHz is applied at a power of 0.5 to 5 kW / cm ² while rotating at the center line, and moved at a feed rate of 0.5 to 10 mm / second. Hardened, the inner surface 3 exceeds Hrc45 so that the hardened layer depth of the outer surface 2 of the bushing base material 1 exceeds Hrc45 remains in the range of 20 to 45% of the thickness of the bushing base material 1 Quenching is performed so that the layer depth is in the range of 15 to 35% of the thickness of the bush base material 1. By quenching in this way, the intermediate layer 5 is formed, and the hardness is lower than that of the outer quenching layer 4 and the inner quenching layer 6, but a bush having excellent toughness while maintaining the same hardness as the conventional bushing. Can be provided. The intermediate layer formed by the quenching step (H) has a sorbite structure, which is a tempered layer having a high martensite conversion rate, and a layer having high toughness is formed. The intermediate layer 5 has a Vickers hardness of Hv 300 to 450. Further, after the quenching step (H), the surface hardness of the outer hardened layer 4 and the inner hardened layer 6 becomes Hrc56-61.

  As is apparent from the above description, the bush manufacturing method of the present invention omits carburization and changes the tempering process to a high frequency, so that the manufacturing process is simplified and the resulting bush is also shown below. As described above, it has wear resistance, strength and toughness equivalent to or higher than those of the bushes manufactured by the methods of the conventional patent documents 1 to 3.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the examples.

Example 1
Bush material SCrB440KH having a length L = 225 mm, an outer diameter D1 = 98 mm, an inner diameter D2 = 60.5 mm, and a carbon (C) content of 0.41 wt% was used as the bush base material 1.

(1) First, the bush base material 1 is fixed with a uniform dummy material heated up and down, and rotated by 100 rpm around the axis of the bush base material 1 by means of a device that gives the bush base material 1 rotation. The bush base material 1 was heated by an oscillator PTG-350 manufactured under the conditions of a frequency of 2.4 kHz, a power of 85.8 to 141.1 kW, and a heating time of 60 seconds. As a result, when the surface temperature was measured by attaching a thermocouple, the temperature of the outer surface rose to 892 ° C., and the inner surface rose to 836 ° C.

(2) Next, the bush base material 1 heated in the step (1) was quenched and cooled from the outside. As a coolant, Solvable NT-3 manufactured by Daido Chemical Industry Co., Ltd. was used, and quenching cooling was performed under conditions of a concentration of 2%, a flow rate of 250 L / min, and a time of 30 seconds. As a result, the temperature of the outer surface decreased to 30 ° C., and the temperature of the inner surface decreased to 30 ° C.

  As a result of this quenching, the hardness of the outer surface was Hrc60, and the hardness of the inner surface was Hrc56.

(3) Next, the fully cured bush base material 1 was tempered by quenching. For tempering, the same oscillator as in (1) was heated at a frequency of 2.4 kHz and a power of 77.4 kW for 70 seconds. As a result, when the surface temperature was measured by attaching a thermocouple, the temperature of the outer surface rose to 600 ° C., and the inner surface rose to 580 ° C. As a result, the hardness of the outer surface was Hrc 32.5, the hardness of the inner surface was Hrc 30, and the bush base material had a sorbite structure.

(4) Next, a high frequency current having a frequency of 5.0 kHz was applied to the heating coil on the outer surface, and transfer quenching was performed under the condition of a feed rate of 4.0 mm / second. As a result, the surface temperature was measured with a pyroscope. However, the outer surface temperature increased to 850 ° C., and the inner surface temperature increased to 350 ° C. At the same time, it was cooled and quenched by the moving cooling method, and the hardness of the outer surface was Hrc64. Next, a high frequency current having a frequency of 15.8 kHz was applied to the heating coil on the inner surface, and the outer surface was moved and quenched while cooling at a feed rate of 2.5 mm / sec. The hardness of the inner surface was Hrc64. The cross-sectional hardness distribution after tempering at 180 ° C. in a furnace is shown in FIG. The cross-sectional hardness refers to the hardness of the fracture surface when the bush is cut at a certain position. Referring to FIG. 4, out of the total thickness of the bush of 22 mm, the hardened layer depth of Hrc45 or more was 7.1 mm from the outer peripheral surface and 5.2 mm from the inner peripheral surface. And the hardness of the intermediate | middle layer which is a layer smaller than Hrc45 has shown Hrc28-32.5, and as shown in FIG. 4, the intermediate | middle layer has shown the substantially same hardness and is hard to be destroyed.

Comparative Example 1
A bush material SCrB440KH having a length L = 225 mm, an outer diameter D1 = 98 mm, an inner diameter D2 = 60.5 mm, and a carbon (C) content of 0.41% by weight was used as a comparative example.

(1) First, the bush base material 1 was heated to 850 ° C. in a non-oxidation quenching furnace and held for 1 hour.

(2) Next, the bush base material 1 heated in the step (1) was quenched and cooled. For quenching and cooling, the bush base material 1 was added to quenching oil (cold) at 60 ° C. and cooled for 10 minutes.

(3) Next, it was heated to 570 ° C. in the air in the tempering furnace, held for 3.5 hours, and then air cooled.

Table 1 shows the values of the tensile strength and Charpy impact value of the bushes manufactured according to the examples and comparative examples. For the measurement of Charpy impact value, a Charpy impact test was performed at room temperature using a 2 mm U notch standard size test piece based on the JISKU2. The tensile strength was measured using a JIS 14A test piece. As shown in Table 1, Charpy impact value of the bushing produced in this example, in Examples 1-1 is a high frequency hardening and tempering articles, Charpy impact ^{value, 122J / cm 2, 129J /} cm 2, 128J / Cm ² . In Example 1-2, the Charpy impact value indicated ^{120J / cm 2, 130J / cm} 2, 122J / cm 2. In Comparative Example 1 a furnace quenching and tempering articles, Charpy impact value indicates ^{100J / cm 2, 87J / cm} 2, 104J / cm 2, in Comparative Example -2 Charpy impact value, 99j / cm ^2, 101 J / cm ² and 108 J / cm ² were shown. From this data, the bush manufactured in Example 1 that is quenched and tempered at high frequency has an average Charpy impact value that is 1.25 times that of Comparative Example 1 compared to the bush that was quenched and tempered in the furnace. Thus, it was found that toughness is high by quenching and tempering at high frequency. Moreover, the tensile strength of Example 1-1 was 980 N / m ² , and the tensile strength of Example 1-2 was 983 N / m ² . The tensile strength of Comparative Example 1 is 936 N / m ² , the tensile strength of Comparative Example 2 is 941 N / m ² , and the average tensile strength is high-frequency quenching and tempering in this example. It was found to be 1.046 times that of the comparative example, and the tensile strength was comparable.

Example 2
Bush material SCrB440KH, size L = 154 mm, outer diameter D1 = 73 mm, inner diameter D2 = 44.6 mm, C content of 0.41% by weight was used as the base material of the bush.

(1) First, an oscillator PTG manufactured by Denki Kogyo Co., Ltd. is rotated while rotating at 100 rpm around the axis of the base material by a device that fixes the base material with a uniform dummy material that is heated up and down and rotates the base material. The base material was heated by −350 at a frequency of 2.4 kHz, a power of 95 to 136 kW, and a heating time of 25 seconds. As a result, when the surface temperature was measured by attaching a thermocouple, the temperature of the outer surface rose to 910 ° C., and the inner surface rose to 850 ° C.

(2) Next, the base material heated in the step (1) was quenched and cooled. As a coolant, Solvable NT-3 manufactured by Daido Chemical Industry Co., Ltd. was used, and quenching cooling was performed under conditions of a concentration of 2%, a flow rate of 250 L / min, and a time of 25 seconds. As a result, the temperature of the outer surface decreased to 30 ° C., and the temperature of the inner surface decreased to 30 ° C.

  As a result of this quenching, the hardness of the outer surface was Hrc60, and the hardness of the inner surface was Hrc56.7.

(3) Next, the hardened base material was tempered by quenching to obtain a bush. For tempering, the furnace was tempered in an oven at 160 ° C. for 5 hours. As a result, the hardness of the outer surface was Hrc57 and the hardness of the inner surface was Hrc54.

(4) Next, in order to harden the inner surface of the bush, a high-frequency current having a frequency of 15.6 kHz was applied to the heating coil, and moving quenching was performed under the condition of a feed rate of 7 mm / sec while cooling the outer surface. As a result, the inner surface temperature rose to 810 ° C. At the same time, quenching and cooling were performed by the moving cooling method, and the hardness of the outer surface became Hrc57 and the hardness of the inner surface became Hrc63. FIG. 5 shows the hardness distribution after tempering at 180 ° C. in the furnace after this quenching step. Referring to FIG. 5, out of the total thickness of 22 mm of the bush, the depth of the hardened layer of Hrc45 or more was 6 mm from the outer surface and 2.5 mm from the inner surface. And the hardness of the core part of the intermediate | middle layer which is a layer smaller than Hrc45 became Hv300-450.

  Below, the table | surface which compared Example 1 and 2 and patent document 1 and 3 about the characteristic, hardness, structure | tissue, and the possibility of crack destruction is shown. Tables 2 and 3 are a comparison between Example 1 and Comparative Example 2, and are comparisons for the surface of the bush and the core. Comparative Example 2 is manufactured at a quenching temperature of 730 ° C. and a tempering temperature of 450 ° C. using the method described in Patent Document 1, particularly a base material containing 0.29 wt% carbon. Tables 4 and 5 are a comparison between Example 1 and Comparative Example 3. In Comparative Example 3, the method described in Patent Document 1, in particular, a base material containing 0.33% by weight of carbon was used. It is manufactured at an input temperature of 720 ° C and a tempering temperature of 700 ° C. Table 6 is a comparison between Examples 1 and 2 and Comparative Example 4, and Comparative Example 4 is a method described in Patent Document 3.

  According to Table 2 and Table 3, the bush manufactured by the method of Example 1 has a core part with higher toughness than Comparative Example 2, a surface part is harder than Comparative Example 2, and has higher wear resistance than Comparative Example 2. It can be seen that the bushing is less prone to breakage.

  According to Table 4 and Table 5, the bush manufactured by the method of Example 1 has the same core toughness as Comparative Example 3, but the surface part is harder than Comparative Example 3, and the bush of Comparative Example 3 is Under the same operating conditions as the bushing of Example 1, only continuous operation for about 2000 hours can be performed, whereas the bushing of Example 1 is capable of continuous operation for about 3000 hours and has excellent cost performance. A bush can be provided.

  According to Table 6, although the toughness of the core part of Comparative Example 4 is unknown, the structure of the core part of Comparative Example 4 is a structure in which a ferrite structure, a pearlite structure, a martensite structure, and a sorbite structure are mixed. , Low toughness and easy to break. On the other hand, Example 1 has a sorbite single-phase structure in the core, and has high toughness and is less likely to break.

It is a longitudinal cross-sectional view of the bush of this invention. It is the elements on larger scale of X in FIG. It is a figure which shows the relationship between hardness and Charpy impact value, hardness, and tensile strength. It is a graph which shows the cross-sectional hardness of the bush manufactured by the method of this invention. It is a graph which shows the cross-sectional hardness of the bush manufactured by the 2nd aspect of the method of this invention.

Explanation of symbols

1 Bush Base Material 2 Outer Surface 3 Inner Surface 4 Outer Hardened Layer 5 Intermediate Layer 6 Inner Hardened Layer

Claims (5)

A method for producing a bush, comprising 0.40 to 0.50% by mass of carbon (C), heat-treating a bush base material made of a cylindrical steel material having an outer diameter of 65 to 130 mm and an inner diameter of 43 to 80 mm,
(A) The bushing base material is heated with a high frequency of 0.5 to 3 kHz under conditions of power 85.8 to 141.1 kW and time 20 to 200 seconds, and quenched from the outer surface to the inner surface of the bushing base material. Heating to a transformation point temperature of 800-920 ° C .;
(B) quenching and cooling the bush base material heated in the step (a) from the inner and outer surfaces to 30 to 130 ° C., and converting the total thickness to martensite;
(C) The bush base material quenched and cooled in the step (b) is heated with high frequency of 0.5 to 3 kHz under conditions of electric power of 0.5 to 3 kW / cm ² and time of 20 to 200 seconds. Or the process of moving and heating at a feed rate of 2 to 10 mm / sec and tempering,
(D) The outer surface and the inner surface of the bush base material are subjected to transfer quenching under the conditions of a power of 0.5 to 5 kW / cm ² and a feed rate of 0.5 to 10 mm / sec with a high frequency of 5 to 30 kHz. Leaving the intermediate layer,
(E) A method of manufacturing a bush including a step of low-temperature tempering in a furnace. 2. The method for manufacturing a bush according to claim 1, wherein in the step (b), the bushing is cooled with a liquid having a concentration of a water-soluble cooling liquid such that the total thickness of the inner and outer diameters becomes martensite. The method for manufacturing a bush according to claim 1 or 2, wherein the step (c) is high-temperature tempering at 570 to 650 ° C. The method for manufacturing a bush according to any one of claims 1 to 3, wherein a hardness of a core portion of the intermediate layer is Hv 272 to 354. A method of manufacturing a bushing that includes 0.50 to 0.60% by mass of carbon (C) and heat-treats a bushing base material made of a cylindrical steel material having an outer diameter of 65 to 130 mm and an inner diameter of 43 to 80 mm,
(A) The bushing base material is heated with a high frequency of 0.5 to 3 kHz under the conditions of electric power of 95 to 136 kW and time of 20 to 200 seconds, and the quenching transformation point temperature from the outer surface to the inner surface of the bushing base material. Heating to 800-920 ° C.,
(B) quenching and cooling the bush base material heated in the step (a) from the inner and outer surfaces to 30 to 130 ° C., and converting the total thickness to martensite;
(C) a step of low-temperature tempering the bush base material quenched and cooled in the step (b) in a furnace;
(D) A step of moving and quenching the inner surface of the bush base material with a high frequency of 5 to 30 kHz and cooling the outer surface under a feed rate of 0.5 to 10 mm / second to form an intermediate layer ( e) A method for producing a bush comprising a step of low-temperature tempering in a furnace.

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