JP2007270345A - Method for producing member for transport equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently produce a member for transport equipment represented by the outer ring member of a constant velocity joint by subjecting a steel material to plastic deformation working. <P>SOLUTION: A workpiece made of a steel material is heated to a suitable temperature which is equal to or higher or lower than an Ac1 point, and is subjected to plastic deformation working, for obtaining an outer ring member. The outer ring member is cooled in the temperature range of an Ar1 point or below to 500°C or above at a cooling rate of 50 to 150°C/min, and is thereafter heated up to the temperature between an Ac1 point and an Ac3 point, so as to be held. For holding, it takes only ≤60 min, and, preferably, about 10 min. Finally, the outer ring member is cooled until the temperature ranges between less than an Ar1 point and 600°C or above at a cooling rate of 50 to 150°C/min. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a member for transportation equipment in which heat treatment is performed after plastic deformation.

  An outer ring member of a constant velocity joint constituting a traveling engine of an automobile is generally formed by sequentially performing forward extrusion molding, upsetting molding, and backward extrusion molding on a carbon steel workpiece made of a cylindrical body. Is produced by plastic deformation into the shape of the outer ring member (see, for example, Patent Document 1). In addition, before performing the above forging process, a carbon steel workpiece may be heated to a predetermined temperature. That is, when manufacturing an outer ring member, warm forging or hot forging may be performed.

  The outer ring member thus molded is cooled to room temperature and then conveyed to a heat treatment facility. Then, various heat treatments such as low temperature annealing, spheroidizing annealing, or normalizing are performed in this heat treatment equipment in order to soften the outer ring member and improve the deformability or to make the hardness uniform.

  Next, a shot blasting process for removing oxide scales and the like generated during the heat treatment is performed, and a lubricating chemical conversion film made of zinc phosphate or the like is formed on the outer surface of the outer ring member. Thereafter, ironing (sizing molding) is performed on the outer ring member, whereby the outer ring member is finished to a final dimension. This ironing process is usually cold forging.

JP 11-182568 A

  By the way, when going through the manufacturing process described above, a large space for storing the outer ring member before heat treatment is necessary, but it is economically disadvantageous to secure the space only for the purpose of storage. . Further, since it takes time to cool the outer ring member to room temperature, there is an inconvenience that the outer ring member finished to the final dimensions cannot be obtained efficiently.

  Furthermore, any heat treatment equipment for performing low-temperature annealing, spheroidizing annealing, or normalization requires a large-scale equipment, and therefore, equipment investment increases.

  Therefore, it is considered effective to immediately perform ironing on the outer ring member that has undergone warm forging or hot forging. However, the outer ring member immediately after being subjected to warm forging or hot forging may have a temperature distribution depending on the size and thickness. In this case, a different metal structure is formed depending on the part. Variations in hardness occur. Further, due to this variation, there is a concern that the outer ring member may be cracked in the ironing forming of the next process. That is, when a large-sized outer ring member that is likely to generate a temperature distribution is provided by warm forging or hot forging, a problem that cracks are likely to occur in the next ironing process has become apparent. In addition, for example, when the tooth portion is provided on the shaft portion of the outer ring member, the dimensional accuracy of the tooth portion may be lowered.

  The present invention has been made to solve the above-described problems, and does not require a storage space, can be carried out in a short time with simple equipment, and further achieves a uniform metal structure. It is an object of the present invention to provide a method for manufacturing a member for a transportation device that is easy to handle.

In order to achieve the above object, the present invention is a method for manufacturing a member for transport equipment constituting a transport equipment,
A first step of producing the member for transport equipment by performing plastic deformation in a warm region or a hot region on a workpiece made of steel; and
A second step of cooling the member for transport equipment at a cooling rate of 50 to 150 ° C./min until the temperature range of not more than Ar 1 point and 500 ° C. or higher;
A third step of heating the transport device member whose temperature has been lowered by the second step and maintaining the temperature between Ac1 to Ac3 before the temperature falls below 500 ° C .;
A fourth step of cooling the member for transportation equipment heated and held in the third step at a cooling rate of 50 to 150 ° C./min until a temperature range of 600 ° C. or higher below the Ar1 point;
It is characterized by having.

  The Ar1 point is defined as the temperature at which eutectoid transformation from austenite to ferrite and cementite starts when the steel material is cooled. Therefore, the metal structure of the steel material lowered to the Ar1 point or less in the second step becomes a substantially uniform structure including ferrite and pearlite. For this reason, the final metal structure of the steel material which passed through the 2nd process is made substantially uniform, and the member for transportation equipment in which various properties are almost uniform can be obtained.

  In addition, in the member for transportation equipment in which the temperature has dropped after the plastic deformation process, the metal structure may be slightly uneven. However, in the present invention, the transport equipment member is maintained at a temperature between Ac1 to Ac3 in the third step, thereby forming a metal structure in which austenite and ferrite coexist substantially uniformly on the transport equipment member. I am doing so. For this reason, it becomes possible to make the metal structure of the member for transport equipment more uniform.

  In addition, since the cooling rate in the second step is 50 ° C./min or more, it is avoided that pearlite grows and phase separates from ferrite. Moreover, by setting it as 150 degrees C / min or less, it is avoided that the bainite which causes the crack at the time of ironing shaping | molding produces | generates.

  Moreover, the member for transport equipment obtained by the 1st process (plastic deformation process) softens by passing through the 2nd process-the 4th process. Along with this, the hardness of the member for transportation equipment becomes substantially equal regardless of the distance from the part or the surface. In other words, all parts can be deformed with substantially the same degree in post-processing such as ironing. Therefore, it becomes difficult to generate | occur | produce a crack in the member for transport equipment, and the dimensional accuracy of the member for transport equipment becomes favorable.

  Moreover, in the present invention, since the heat treatment is performed when the processing heat remains in the product and the temperature of the product does not fall below 500 ° C., it is not necessary to store the product. Accordingly, it is not necessary to prepare a space for storage, and the space can be effectively used for other purposes.

  In the present invention, the “plastic deformation process” includes a process of applying pressure to a steel material to cause plastic deformation. Specifically, forging, forging, rolling, etc. are exemplified.

  The holding time in the third step is preferably within 60 minutes. In this case, the scale of the heat treatment equipment can be made smaller than that of conventional heat treatment equipment such as spheroidizing annealing equipment. For this reason, it is avoided that capital investment soars. In addition, since the heat treatment efficiency is improved, the energy required for the heat treatment is reduced and the production efficiency is improved. After all, it becomes advantageous in cost. The “holding” in the third step includes not only the case where the constant temperature is maintained for a predetermined time, but also the case where the temperature rises and falls within the temperature range of Ac1 to Ac3 within the predetermined time. That is, for example, after the temperature is raised to the Ac3 point, it may be gradually lowered to the Ac1 point within a predetermined time.

  The holding time can be within 10 minutes. In this case, the above effect becomes more remarkable.

  On the other hand, in the third step, the rate of temperature increase until the steel material reaches the temperature between Ac1 to Ac3 is preferably 15 to 50 ° C./min. If it is less than 15 degreeC / min, the heat processing efficiency of steel materials will fall. Moreover, when it exceeds 50 degreeC / min, a defect may generate | occur | produce in the metal structure of steel materials.

  In addition, as a suitable example of the steel material which is the material of a workpiece | work, 0.35-0.55 mass% C, 1.0 mass% or less Si, 0.2-1.5 mass% Mn, 0. 03 mass% or less P, 0.15 mass% or less S, 0.5 mass% or less Cu, 0.5 mass% or less Ni, 0.05-3.2 mass% Cr, 1.3 mass % Or less of Mo and 0.002 to 0.1% of Al. In this case, the workpiece is excellent in toughness and can be machined at a large machining rate, so that cracks and the like are less likely to occur.

  The workpiece may contain 0.1% by mass or less of Ti and 0.01% by mass or less of B.

  And as a suitable example of the member for transport equipment, the outer ring member which comprises a constant velocity joint can be mentioned.

  According to the present invention, a heat treatment member (steel material) whose processing heat remains and is 500 ° C. or higher is subjected to heat treatment under predetermined conditions. This heat treatment softens the transport equipment member and makes the transport equipment hardness substantially constant. For this reason, it becomes difficult to generate | occur | produce a crack at the time of ironing shaping | molding, and the dimensional accuracy of the site | part shape | molded in this ironing shaping | molding becomes favorable.

  Further, since the heat treatment is performed when the processing heat remains, it is not necessary to prepare a space for storage.

  Furthermore, since the holding time is within 60 minutes, the structure of the heat treatment equipment is simplified. Moreover, since the holding time is relatively short, the heat treatment efficiency is improved, and in addition, the energy required for the heat treatment is reduced and the production efficiency is improved.

  Furthermore, since the cooling rate of the outer ring member after warm forging or hot forging is in the range of 50 to 150 ° C./min, pearlite grows excessively and phase separates from ferrite, or cracks during ironing molding It is avoided that bainite that causes the generation of bainite is generated.

  Hereinafter, with respect to the method for manufacturing a member for a transportation device according to the present invention, a preferred embodiment will be given by way of example in which a steel workpiece is forged and plastically deformed into an outer ring member, with reference to the accompanying drawings. Will be described in detail.

  The manufacturing method of the outer ring member (transport equipment member) according to the present embodiment is shown in FIG. 1 as a flowchart. This heat treatment method includes a first step S1 for obtaining an outer ring member from a workpiece made of steel, a second step S2 for cooling the obtained outer ring member, and heating the outer ring member whose temperature has decreased between Ac1 to Ac3 points. It has the 3rd process S3 holding at temperature, and the 4th process S4 which recools the outer ring member which temperature maintenance ended.

  FIG. 2A to FIG. 2F are flowcharts showing a process until the outer ring member 28 is manufactured by subjecting the cylindrical workpiece 10 made of steel to forging (plastic deformation) in the first step S1.

  First, the steel material that is the material of the workpiece 10 will be described. In this embodiment, this steel material contains C, Si, Mn, P, S, Cu, Ni, Cr, Mo, Al, Ti, and B, and the balance is Fe and inevitable impurities.

  C plays a role of improving the hardenability of the workpiece 10 and thus the outer ring member 28. That is, when the outer ring member 28 is quenched, the hardness is significantly increased as compared with that before quenching. C also has a function of increasing tensile strength and bending strength.

  The composition ratio of C is preferably set to 0.35 to 0.55% (numbers are mass%, the same applies hereinafter). If it is less than 0.35%, it is difficult to ensure sufficient strength. On the other hand, if it is more than 0.55%, the hardness after hot working becomes excessively high, so that machinability is lowered and impact resistance is lowered.

  Si is an element that functions as a deoxidizing agent that reduces oxygen in the outer ring member 28. However, when the ratio exceeds 1.0%, the hardness of the outer ring member 28 after hot working increases excessively, The machinability is reduced. For this reason, the composition ratio of Si is preferably set to 1.0% or less.

  Mn improves the hardenability and strength of the outer ring member 28. In order to reliably obtain this effect, it is preferable to set the composition ratio of Mn to 0.2% or more. If the composition ratio of Mn exceeds 1.5%, the hardness of the outer ring member 28 may increase excessively and the machinability may decrease. After all, the preferable range of the composition ratio of Mn is 0.2 to 1.5%.

  P segregates at the grain boundary to lower the grain boundary strength and excessively increases the hardness of the workpiece 10. In order to avoid this, the composition ratio of P is set to 0.03% or less.

  S is a component that improves the machinability of the workpiece 10 by forming MnS and TiS together with Mn and Ti in the metal structure of the workpiece 10. However, since the processing rate of the workpiece 10 is reduced if it is excessive, it is preferable to set the S composition ratio to 0.15% or less in order to avoid this.

  Cu is a component that improves the hardenability and toughness of the workpiece 10. However, if it exceeds 0.5%, this effect is saturated, which is disadvantageous in terms of cost. Therefore, the composition ratio of Cu is preferably 0.5% or less.

  Ni, like Cu, functions to improve the hardenability and toughness of the workpiece 10. The composition ratio of Ni is preferably 0.5% or less. This is because even if the composition ratio exceeds 0.5%, this effect is saturated, which is disadvantageous in terms of cost.

  Cr, like Mn, improves the hardenability and strength of the outer ring member 28. A suitable composition ratio of Cr is 0.05 to 3.2%. If it is less than 0.05%, it will be difficult to ensure the strength required for the outer ring member 28. On the other hand, if it exceeds 3.2%, the hardness after hot forging increases excessively, so the machinability decreases.

  Mo also improves the hardenability and strength of the outer ring member 28. However, if the composition ratio exceeds 1.3%, a bainite structure is generated after hot working, so the hardness of the outer ring member 28 is excessively increased. The processing rate may be reduced. In order to avoid this, it is preferable to set the Mo composition ratio to 1.3% or less.

Al is a component that contributes to deoxidation in the same manner as Si. When the Al composition ratio is less than 0.002%, the deoxidation effect is poor. Further, when Al is present in excess, increased oxide impurities such as Al ₂ O _3, as a result, fatigue properties, deformability during plastic deformation decreases. For this reason, it is preferable that Al is 0.1% or less.

  Ti has a function of capturing free N in the workpiece 10. When free N is trapped in this way, the effect of adding B described later becomes more remarkable. Moreover, it combines with C and forms a carbide | carbonized_material, It contributes to refinement | miniaturization of a crystal grain.

  The composition ratio of Ti is preferably set to 0.1% or less. If it exceeds 0.1%, the effect of miniaturization is saturated, which is disadvantageous in terms of cost, and the hardness after hot forging increases excessively, so that machinability decreases.

  B is a component that improves the grain boundary strength. In addition, the presence of B improves the hardenability of the workpiece 10. However, if it exceeds 0.001%, the hardenability may be lowered, so the B composition ratio is preferably set to 0.001% or less.

  The workpiece 10 is heated to a predetermined temperature in a warm region or a hot region, for example, 600 to 1250 ° C. However, since there is a transformation point of carbon steel at a temperature exceeding 720 to less than 800 ° C., it is preferable to avoid this temperature range. That is, the temperature of the workpiece 10 is preferably 600 to 720 ° C or 800 to 1250 ° C.

  Thereafter, the workpiece 10 is subjected to forward extrusion molding. That is, the workpiece 10 is pressed from the other end surface side while the one end surface of the workpiece 10 is supported. As a result, the other end surface is crushed. As a result, as shown in FIG. 2B, the primary molded product 18 in which the large diameter portion 12, the reduced diameter portion 14 reduced in a taper shape, and the shaft portion 16 are formed. can get. Thereafter, the forward extrusion molding is performed again, and the secondary molded product 20 is provided as shown in FIG. 2C.

  Next, upset molding is performed on the secondary molded product 20. Specifically, as shown in FIG. 2D, the third molded product 24 having a cup portion 22 is obtained by expanding only the large diameter portion 12 of the secondary molded product 20 to compress the large diameter portion 12. And

  Next, backward extrusion molding is performed on the third molded product 24 to extend the cup portion 22 and to form six ball grooves 26 a to 26 f in the cup portion 22. That is, a punch having a projecting portion for forming the ball grooves 26a to 26f is brought into contact with the central portion of one end face of the cup portion 22, and then the tip portion of the shaft portion 16 is pressed to form a third molded product. 24 is displaced toward the punch. Thereby, the outer ring member 28 shown in FIG. 2E is obtained.

  Each forging process is performed by a separate forging device, and the workpiece 10, the first molded product 18, the second molded product 20, and the third molded product 24 are transported between the forging devices such as transfer. Transported by the device.

  The outer ring member 28 subjected to the above forging process is preheated to a predetermined temperature (warm range or hot range) before the forging process is performed, and also has a processing heat accompanying the plastic deformation process. Therefore, it is hot. The outer ring member 28 is transferred from the forging station 30 to the heat treatment furnace 32 through the cooling tank 31 as shown in FIG. During the transfer to the cooling tank 31, the shaft portion 16 is aligned on the transfer 36 so as to face upward by the operation of the robot 34.

  In the cooling bath 31, a second step S <b> 2 for cooling the outer ring member 28 transferred by the transfer 36 is performed. That is, the cooling tank 31 is configured so that compressed gas (cooling air) can be ejected from below and the compressed gas can be exhausted from an upper exhaust port. As the outer ring member 28 comes into contact with the cooling air flowing from below to above in the cooling tank 31, the temperature of the outer ring member 28 decreases.

  The flow rate of the cooling air and the length of the cooling tank 31 at this time are the temperature drop rate of the outer ring member 28, in other words, the cooling rate is 50 to 150 ° C./min, and the temperature of the outer ring member 28 is the Ar1 point. The temperature is set within a range of 500 ° C. or higher. In short, in the second step S2, the outer ring member 28 is cooled to a temperature range not higher than the Ar1 point and not lower than 500 ° C at a cooling rate of 50 to 150 ° C / min. By controlling the cooling rate within this range, austenite disappears from the metal structure of the outer ring member 28, and a substantially uniform structure in which fine ferrite and pearlite coexist is obtained.

  Here, when the cooling rate is lower than 50 ° C./min, it gradually cools, and pearlite grows excessively to cause phase separation with ferrite, and accordingly, a tendency to form a banded structure that induces cracking is recognized. . On the other hand, when it is higher than 150 ° C./min, it rapidly cools and bainite tends to be generated. In this case, if further machining such as ironing is performed after finishing the fourth step S4, cracking may occur or accuracy may be deteriorated.

  Next, the third step S3 is performed. That is, the outer ring member 28 led out from the cooling bath 31 is quickly introduced into the heat treatment furnace 32 and subjected to a reheating process in which the outer ring member 28 is heated and held up to a temperature range of Ac1 to Ac3.

  As can be understood from this, the third step S3 is performed immediately following the second step S2. As described above, the outer ring member 28 is in the temperature range of not more than Ar1 and not less than 500 ° C. when the second step S2 is completed. Therefore, in the third step S3, the temperature of the outer ring member 28 does not fall below 500 ° C. Start at the point. Of course, the distance from the cooling bath 31 to the heat treatment furnace 32 is set as short as possible so that the outer ring member 28 whose temperature has dropped can be quickly introduced into the heat treatment furnace 32 (see FIG. 3). Further, the conveyance speed by the transfer 36 is set according to the number of production of the outer ring member 28 per unit time.

  Thus, according to the present embodiment, the outer ring member 28 heated by plastic deformation is only slightly cooled, and thereafter, the outer ring member 28 is introduced into the heat treatment furnace 32 as quickly as possible. For this reason, a space for storing the outer ring member 28 becomes unnecessary, and therefore the space can be effectively used for other purposes.

  In addition, when the outer ring member 28 whose temperature has dropped to below 500 ° C. is introduced into the heat treatment furnace 32, it is necessary to increase the temperature increase rate in the heat treatment furnace 32 in order to increase the temperature to Ac1 to Ac3 in a short time. However, in this case, a defect may occur in the metal structure due to the coarsening of the crystal grains, and the strength of the outer ring member 28 may be insufficient.

  In order to avoid this, in order to raise the temperature of the outer ring member 28 that has fallen to a temperature lower than 500 ° C. at a slow rate of temperature increase, it is necessary to provide the heat treatment furnace 32 as a large-scale one, and so the capital investment increases. Invite.

  Here, FIGS. 4 and 5 show general temperature patterns when the forging process in the first step S1 is performed at a temperature lower than the Ac1 point or a temperature higher than the Ac1 point, respectively. FIG. 4 shows a case where forging is performed at a relatively high temperature of less than Ac1 point. In this case, since the workpiece 10 is at a temperature lower than the Ac1 point, the outer ring member 28 immediately after the rear extrusion is finished has a shape in which ferrite and pearlite are stretched in the crystal grains.

  When forging is performed with the temperature pattern shown in FIG. 4, the temperature of the workpiece 10 during forging is preferably set to a value obtained by subtracting 180 ° C. from the value of the Ac1 point, for example, and 150 ° C. is subtracted from the value of the Ac1 point. More preferably (approximately 580 ° C.).

  On the other hand, FIG. 5 shows a case where forging is performed at a high temperature exceeding the Ac1 point, and the outer ring member 28 is introduced into the heat treatment furnace 32 after reaching a temperature slightly below the Ar1 point. As shown in FIG. 5, when the temperature is higher than the Ac1 point, it is preferable to set the Ac3 point or higher. In this case, since the temperature of the workpiece 10 exceeds the Ac3 point at which the transformation of ferrite to austenite is completed, austenite occupies most of the metal structure of the outer ring member 28 immediately after the rear extrusion is completed. Further, recrystallization occurs in the metal structure, and dislocations are remarkably reduced. That is, by setting it to Ac3 point or more, the metal structure can be made more uniform.

  When forging is performed at a temperature of Ac1 or higher, the temperature of the outer ring member 28 immediately before being introduced into the cooling bath 31 is approximately 600 to 720 ° C., but as described above, the second step S2 is performed. Thus, the temperature falls below the Ar1 point, which is the starting temperature of eutectoid transformation from austenite to ferrite and cementite during cooling, for example, to a temperature obtained by subtracting 50 ° C from the numerical value of the Ar1 point, and in some cases down to 500 ° C. Is done.

The heat treatment furnace 32 that performs the third step S3 will be described. The heat treatment furnace 32 has three furnaces, that is, a heating furnace 38, a soaking furnace 40, and a recooling tank 42 configured in the same manner as the cooling tank 31. Among these, the heating furnace 38 and the soaking furnace 40 are maintained at the same temperature. Note that N ₂ gas may be introduced into the three furnaces so that heating, holding, and cooling are performed in an N ₂ atmosphere.

  While the outer ring member 28 is placed on the transfer 36, the outer ring member 28 is first introduced into the heating furnace 38 and heated to a temperature between the points Ac <b> 1 to Ac <b> 3.

  Here, as described above, if the rate of temperature increase is set too high, the crystal grains may become coarse and defects in the metal structure may occur. In order to avoid this, it is preferable to set the temperature of the heating furnace 38 so as to obtain a heating rate of 50 ° C./min or less. If the rate of temperature increase is less than 15 ° C./minute, the heat treatment efficiency of the outer ring member 28 is reduced. Further, in order not to decrease the heat treatment efficiency even at a temperature rising rate of less than 15 ° C./min, it is necessary to enlarge the heat treatment furnace 32, so that the capital investment increases. After all, a preferable temperature increase rate is 15 to 50 ° C./min, and more preferably 17 to 46 ° C./min.

  In the present embodiment, the temperature of the heating furnace 38 is set to 800 to 850 ° C. in order to obtain this rate of temperature increase. The outer ring member 28 that was 500 to Ar1 point (for example, 720 ° C.) before introduction of the heating furnace 38 reaches 720 to 780 ° C. before passing through the heating furnace 38.

  The outer ring member 28 that has passed through the temperature raising furnace 38 is then introduced into the soaking furnace 40. In the soaking furnace 40, the outer ring member 28 heated to about 720 to 780 ° C. in the temperature raising furnace 38 is maintained at that temperature.

  It is sufficient that the temperature rise / holding is within 60 minutes in total. When the heat treatment is performed further, the heat treatment furnace 32 and the transfer 36 become longer, so that the heat treatment equipment becomes large-scale. That is, capital investment will soar. Even if heating and holding for more than 60 minutes is performed, the degree of softening and homogenization of hardness is almost the same as that within 60 minutes, which is disadvantageous in terms of cost. It is sufficient for the temperature raising / holding time to be within 10 minutes in total, for example, 5 minutes or 3 minutes.

  In the outer ring member 28 maintained at a temperature between the points Ac1 to Ac3, a substantially uniform metal structure in which austenite and ferrite coexist is formed.

  When the final temperature of the outer ring member 28 is less than the Ac1 point, it is difficult to soften the outer ring member 28 and to make the hardness uniform. Further, when the temperature is raised and maintained to a temperature exceeding the Ac3 point, austenite coarsening (abnormal grain growth) occurs. For this reason, as shown in FIG. 6, the hardness is varied depending on the distance between different parts or the surface. As shown in FIG. 7, A to D in FIG. 6 represent the measured values in the parts A to D at a position 50 mm from the tip of the shaft portion 16, and each measured value is within the horizontal cross section from the surface. The same applies to the following.

  The outer ring member 28 thus heated and held is then introduced into the recooling tank 42, whereby the fourth step S4 is started.

  In the recooling tank 42, the cooling rate of the outer ring member 28 is set within a predetermined range, specifically, 50 to 150 ° C./min. By setting the cooling rate in such a range, a substantially uniform structure is obtained from the surface to the inside, and as shown in FIG. 8, there is almost no variation in hardness.

  The cooling rate is more preferably 5 to 10 ° C./min. In this case, a spheroidized structure is formed, and as shown in FIG. 9, the hardness from the surface to the inside becomes even more uniform, and the elongation and squeezing of the outer ring member 28 are improved.

  Here, the hardness in the outer ring member 28 that has not been subjected to heat treatment after forging is shown in FIG. 8 and FIG. 9 and FIG. 10 are compared, the heat treatment according to the present embodiment causes the outer ring member 28 to be softened and the hardness variation of the outer ring member 28 is suppressed. Obviously you can.

  Cooling may be performed to a temperature below the Ar1 point and at which the precipitation of pearlite is completed. This precipitation end temperature varies depending on the temperature drop rate and the type of steel material, but is generally between 680 and 600 ° C. Accordingly, the cooling is preferably continued until the temperature is between 680 and 600 ° C., for example, may be performed until the temperature falls to 650 ° C. Along with this temperature drop, a metal structure in which ferrite and pearlite coexist is formed on the outer ring member 28.

  Thus, in the present embodiment, the outer ring member 28 passes through the heating furnace 38, the soaking furnace 40, and the recooling tank 42 in a short time. For this reason, the heat treatment equipment from the heating furnace 38 to the recooling tank 42 can be configured simply.

  After the fourth step S4 is finished, the outer ring member 28 is unloaded from the re-cooling tank 42 by the transfer 36, cooled to room temperature, and then subjected to shot blasting and lubrication conversion film forming, and forging in which ironing is performed. It is transferred to the processing station.

  In the ironing molding, the outer ring member 28 is easily deformed because the elongation and drawing of the outer ring member 28 are improved. Further, the hardness of the outer ring member 28 is substantially the same regardless of the portion, and is substantially constant from the surface to the inside. For this reason, the deformability is substantially the same over all parts, and therefore the degree of deformation is also substantially the same. For this reason, the outer ring member 28 excellent in dimensional accuracy can be manufactured up to a relatively small portion such as a tooth portion.

  Moreover, the molding load at this time may be about 70 to 80% as compared with the case where ironing is performed on the outer ring member that is not subjected to heat treatment after warm forging. That is, since the load on the ironing apparatus is reduced, it contributes to the extension of the life of the ironing apparatus.

  Furthermore, since the rolling accuracy is stable, there is also an advantage that, for example, the life of the blade for providing the tooth portion on the shaft portion is improved by about 50%.

  As described above, the occurrence of cracks can be remarkably suppressed when various components are in a predetermined ratio.

  11, 12, and 13 are respectively cooled to a predetermined temperature within the range of 500 ° C. or lower in the second step S 2 at 135 ° C./min. The surface of the outer ring member 28 that has undergone S4, a scanning electron microscope (SEM) photograph at a magnification of 1000 times at 0.5 mm from the surface and 1 mm from the surface. Is ferrite. From FIG. 11, FIG. 12, and FIG. 13, it is clear that the outer ring member 28 in which fine pearlite is uniformly present from the surface to the inside is obtained through the first step S1 to the fourth step S4. It is.

  In the above-described embodiment, the outer ring member 28 of the constant velocity joint is exemplified and described as the transport equipment member. However, the present invention is not particularly limited thereto, and any member may be used as long as it constitutes the transport equipment. It may be.

  Further, the plastic deformation process is not limited to the forging process, and may be any process that applies a pressure to the work and deforms the work. For example, it may be a rolling process.

  Furthermore, a steel material that does not contain Ti and B may be used as the workpiece.

It is a flowchart of the manufacturing method of the outer ring member concerning this embodiment. FIG. 2A to FIG. 2E are process explanatory views showing the plastic deformation from the workpiece to the outer ring member. It is a schematic diagram explaining the work place until an outer ring member is transferred from a forging process station to a heat treatment furnace. It is a graph which shows the general temperature pattern in the case of forging at the temperature below Ac1 point. It is a graph which shows the general temperature pattern in the case of forging at the temperature more than Ac1 point. It is a graph explaining the variation in the hardness of the axial part at the time of heating up and holding to the temperature exceeding Ac3. It is a horizontal sectional view of the position of 50 mm from the tip part of the shaft part for explaining the parts A to D in FIG. It is a graph which shows the hardness which goes to the inside from the surface of the axial part of the outer ring member which passed through the 2nd process. It is a graph which shows the hardness which goes to the inside from the surface of the axial part of an outer ring member at the time of setting the cooling rate in a 2nd process to 5-10 degreeC / min. It is a graph which shows the hardness which goes to the inside from the surface of the axial part of the outer ring | wheel member which did not heat-process after a forge process. It is a SEM photograph (1000 times) of the surface of the outer ring member obtained by setting the cooling rate in the second step to 135 ° C./min. It is a SEM photograph (1000 times) of the site | part of the depth 0.5mm from the surface in the outer ring member of FIG. It is a SEM photograph (1000 times) of the site | part of the depth of 1 mm from the surface in the outer ring member of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Work 18, 20, 24 ... Molded product 22 ... Cup part 28 ... Outer ring member 30 ... Forging process station 31 ... Cooling tank 32 ... Heat treatment furnace 38 ... Temperature rising furnace 40 ... Soaking furnace 42 ... Recooling tank

Claims (6)

A method for manufacturing a member for transportation equipment constituting a transportation equipment,
A first step of producing the member for transport equipment by performing plastic deformation in a warm region or a hot region on a workpiece made of steel; and
A second step of cooling the member for transport equipment at a cooling rate of 50 to 150 ° C./min until the temperature range of not more than Ar 1 point and 500 ° C. or higher;
A third step of heating the transport device member whose temperature has been lowered by the second step and maintaining the temperature between Ac1 to Ac3 before the temperature falls below 500 ° C .;
A fourth step of cooling the member for transportation equipment heated and held in the third step at a cooling rate of 50 to 150 ° C./min until a temperature range of 600 ° C. or higher below the Ar1 point;
The manufacturing method of the member for transport equipment characterized by having.   The manufacturing method according to claim 1, wherein the holding time in the third step is 60 minutes or less.   The manufacturing method according to claim 2, wherein the holding time in the third step is within 10 minutes.   In the manufacturing method of any one of Claims 1-3, as said workpiece | work, 0.35-0.55 mass% C, 1.0 mass% or less Si, 0.2-1.5 mass % Mn, 0.03% by mass or less P, 0.15% by mass or less S, 0.5% by mass or less Cu, 0.5% by mass or less Ni, 0.05 to 3.2% by mass The manufacturing method of the member for transport equipment characterized by using the thing made from the steel material which contains Cr, 1.3 mass% or less Mo, and 0.002-0.1% Al at least.   5. The manufacturing method according to claim 4, wherein the work further contains 0.1% by mass or less of Ti and 0.01% by mass or less of B. .   The manufacturing method of any one of Claims 1-5 WHEREIN: The outer ring member which comprises a constant velocity joint is provided as the said member for transportation apparatuses, The manufacturing method of the member for transportation apparatuses characterized by the above-mentioned.

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