JP4368849B2 - Carbonitriding method, machine part manufacturing method and machine part - Google Patents

Description

  The present invention relates to a carbonitriding method, a method for manufacturing a machine part, and a machine part, and more specifically, a carbonitriding method capable of stable carbonitriding, and a machine capable of manufacturing a machine part having stable quality. The present invention relates to a part manufacturing method and a machine part having stable quality.

In general, in carbon carbonitriding treatment, particularly gas carbonitriding treatment performed on an object made of steel, a heat treatment furnace is supplied with RX gas and ammonia (NH ₃ ) gas at a constant flow rate (amount supplied per unit time). And the atmosphere in the heat treatment furnace is controlled by controlling the carbon potential (C _P ) value in the heat treatment furnace based on the partial pressure of carbon dioxide (CO ₂ ) in the heat treatment furnace. . Here, it is difficult to directly measure the amount of nitrogen entering the surface layer portion of the workpiece during carbonitriding. Therefore, for each heat treatment furnace, the relationship between the flow rate of ammonia gas and the amount of nitrogen entering the surface layer of the workpiece can be determined empirically based on past production results and directly measured during carbonitriding In many cases, the amount of nitrogen entering the surface layer of the workpiece is controlled by adjusting the flow rate of the ammonia gas.

  And the flow rate of this ammonia gas is determined empirically based on the past production results of each heat treatment furnace, taking into account the amount and shape of the object to be processed, but there is no past production record When it becomes necessary to perform carbonitriding on an object to be processed in an amount or shape, trial and error for determining the optimum flow rate of ammonia gas in the carbonitriding process is required. As a result, not only is it difficult to stabilize the quality of the object to be processed until the optimum ammonia gas flow rate is determined, but it is necessary to carry out the above trial and error in the mass production line, so the required quality is not met. An object to be processed may be generated, which may cause an increase in production cost.

On the other hand, the undecomposed ammonia concentration (residual ammonia gas), which is the concentration of gaseous ammonia remaining in the heat treatment furnace, not the flow rate of ammonia gas that changes with the shape of the heat treatment furnace, the amount or shape of the object to be treated There has been proposed a method for controlling the amount of nitrogen that enters a workpiece by adjusting (concentration) (see, for example, Non-Patent Document 1 and Patent Document 1). That is, the undecomposed ammonia concentration that can be measured during carbonitriding is measured, and the undecomposed ammonia concentration that can be determined regardless of the shape of the heat treatment furnace, the amount and shape of the object to be treated, and the nitrogen that enters the object to be treated The flow rate of ammonia gas is adjusted based on the relationship with the amount. This makes it possible to control the amount of nitrogen entering the object to be processed without determining the optimum ammonia gas flow rate by trial and error, and to stabilize the quality of the object to be processed.
Tsunekawa Yoshiki and two others, “Void Generation and Nitrogen Diffusion Behavior in Gas Carbonitriding”, Heat Treatment, 1985, 25, 5, p.242-247 JP-A-8-13125

  However, when the supply amount of ammonia supplied into the heat treatment furnace during the carbonitriding process changes as in the carbonitriding method using the undecomposed ammonia concentration as a parameter, the surface layer of the object to be processed is excessive. Defective structures such as over-carburized structures with carbon intrusion, decarburized structures with reduced carbon content, and disappearance of precipitates (carbides, carbonitrides, etc.) may occur, preventing stability of the quality of the workpiece. There was a problem.

  Therefore, the object of the present invention is to control the amount of nitrogen entering the workpiece by adjusting the supply amount of ammonia during the carbonitriding process, and to detect defects such as the loss of overcarburized structure, decarburized structure and precipitates. An object of the present invention is to provide a carbonitriding method capable of performing a stable carbonitriding process by suppressing generation of a structure. Another object of the present invention is to provide a method of manufacturing a machine part capable of manufacturing a machine part having stable quality by performing a stable carbonitriding process. Still another object of the present invention is to provide a mechanical component having a stable quality by performing a stable carbonitriding process.

The carbonitriding method according to the present invention includes an atmosphere control step in which the atmosphere in the heat treatment furnace is controlled, and a heating pattern control step in which the temperature history applied to the workpiece in the heat treatment furnace is controlled. . The atmosphere control process includes an undecomposed ammonia concentration control process for controlling the undecomposed ammonia concentration in the heat treatment furnace by adjusting the supply amount of ammonia supplied into the heat treatment furnace, and carbon monoxide and carbon dioxide in the heat treatment furnace. And a partial pressure control step for controlling at least one of the partial pressures. In the partial pressure control step, the ammonia supply amount is changed in the undecomposed ammonia concentration control step, and the partial pressure ratio, which is the ratio between the partial pressure of carbon monoxide and the partial pressure of carbon dioxide, is changed. In such a case, the partial pressure of at least one of carbon monoxide and carbon dioxide is changed so as to cancel the change from the partial pressure ratio before the change of the ammonia supply amount to the partial pressure ratio after the change of the ammonia supply amount. Is done. Further, in the undecomposed ammonia concentration control step, the carburizing gas supplied to the heat treatment furnace at 20 ° C. and 1.05 atm after the change of the previous ammonia supply amount performed immediately before in the undecomposed ammonia concentration control step . It is determined whether or not the volume is equal to or greater than the volume of the heat treatment furnace, and when it is determined that the volume is equal to or greater than the volume of the heat treatment furnace, the supply amount of ammonia is changed.

  The present inventor has studied in detail the relationship between the controlled state of the atmosphere in the heat treatment furnace and the occurrence of defective structures in the surface layer portion of the workpiece. As a result, when the supply amount (flow rate) of ammonia supplied into the heat treatment furnace is changed, the partial pressure ratio between carbon monoxide and carbon dioxide, which affects the carburizing behavior, changes accordingly. It was found that if the atmosphere control was not fully taken into account, the intrusion behavior of carbon into the surface layer of the workpiece was not controlled as intended and a defective structure was generated. In the carbonitriding process, if the supply amount of ammonia is changed, the change in the partial pressure ratio between carbon monoxide and carbon dioxide is immediately canceled, so that at least one of carbon monoxide and carbon dioxide is removed. The inventors have found that the generation of defective tissues can be suppressed by changing the pressure, and have arrived at the present invention.

That is, according to the carbonitriding method of the present invention, the ammonia supply amount is adjusted using the undecomposed ammonia concentration in the heat treatment furnace as a parameter, and the nitrogen amount entering the workpiece is adjusted. When the ammonia supply amount is changed by adjusting the ammonia supply amount, the partial pressure ratio between carbon monoxide and carbon dioxide, which changes with the ammonia supply amount, can be quickly returned to the state before the change. As a result, the partial pressure ratio is a parameter, which directly affects the carburizing behavior of the workpiece (see Equation (1) and Equation (2)) and the carbon potential (C _P ) value in the heat treatment furnace and the workpiece It becomes possible to control the carbon activity (a _C ) and the like in the medium with high accuracy, and to suppress the occurrence of defective structures and stabilize the quality of the workpiece.
In addition, the present inventor has intensively studied a measure for suppressing the influence of the change in the ammonia supply amount on the accuracy of controlling the partial pressure ratio between carbon monoxide and carbon dioxide. As a result, if there is a change in the amount of ammonia supply that is normally required to control the undecomposed ammonia concentration, the partial pressure ratio of carbon monoxide and carbon dioxide that has changed is the state before the change in the ammonia supply amount. In order to return to the above condition, it has been found that it is necessary to supply a carburizing gas that exceeds the volume of the heat treatment furnace at 20 ° C. and 1.05 atm.
Therefore, after confirming that the above-mentioned conditions are satisfied, the ammonia supply amount is changed, so that after the partial pressure ratio is restored to the state before the previous ammonia supply amount change, a new ammonia supply amount is obtained. Changes will be made. As a result, in the carbonitriding method of the present invention, control of C _P , a _C, etc. is further facilitated, and generation of defective structures is further suppressed.

Here, C _P and a _C are defined by the following formulas (1) and (2).

In formulas (1) and (2), _{A S} is the physical property values that depend on the temperature, _{a c} is the activity of the carbon in the _steel, the partial pressure of _{P CO} is carbon monoxide _{(CO), P CO2} is carbon dioxide (CO ₂ ) partial pressure, K is <C> + CO ₂ ⇔2CO
Is the equilibrium constant.

  The undecomposed ammonia concentration refers to the concentration in the atmosphere in the heat treatment furnace of the ammonia supplied in the heat treatment furnace and remaining in the gaseous ammonia state without being decomposed.

  Preferably, in the carbonitriding method, in the undecomposed ammonia concentration control step, the undecomposed ammonia concentration in the heat treatment furnace is measured, and the heat treatment is performed based on the relationship between the undecomposed ammonia concentration and the nitrogen concentration in the surface layer portion of the workpiece. By adjusting the flow rate of ammonia supplied into the furnace, the nitrogen concentration in the surface layer portion of the workpiece is controlled.

  Thereby, the undecomposed ammonia concentration in the atmosphere in the heat treatment furnace can be accurately controlled, and the amount of nitrogen entering the object to be processed can be accurately controlled.

Here, as the carburizing gas used in the carbonitriding method of the present invention, for example, a mixed gas of RX gas and enriched gas can be used. In addition, the control of the partial pressure ratio of carbon monoxide and carbon dioxide is controlled by adjusting the supply amount (flow rate) of propane (C ₃ H ₈ ) gas, butane gas (C ₄ H ₁₀ ) or the like as an enriched gas. Can be implemented.

The method for manufacturing a machine part according to the present invention includes a steel member preparation step for preparing a steel member formed into a schematic shape of a machine part, and a steel member prepared in the steel member preparation step. after performing carbonitriding treatment by cooling from a temperature of more than a ₁ point to the M _S point below the temperature, and a quench-hardening step of quench-hardening the steel member. And the carbonitriding process in a quench hardening process is implemented using the above-mentioned carbonitriding method of this invention.

Here, the point A ₁ in the case of heating the steel refers to a point that the structure of the steel corresponds to the temperature to start the transformation from ferrite to austenite. Further, the M _s point means a point corresponding to a temperature at which martensite formation starts when the austenitized steel is cooled.

  According to the method for manufacturing a mechanical component of the present invention, the above-described carbonitriding method of the present invention capable of stable carbonitriding is employed in the quench hardening process, thereby manufacturing a mechanical component having stable quality. Is possible.

  The mechanical component of the present invention may be used as a component constituting a bearing. The mechanical component of the present invention, whose surface layer is strengthened by carbonitriding and whose quality is stable, is suitable as a component constituting a bearing that is a mechanical component that requires fatigue strength, wear resistance, and the like. .

  In addition, you may comprise the rolling bearing provided with the above-mentioned machine component and the rolling element which contacts a bearing ring and contacts a bearing ring, and is arrange | positioned on an annular | circular shaped raceway. That is, at least one of the raceway and the rolling element is the above-described machine part. By carrying out the carbonitriding, the surface layer is strengthened and the mechanical parts of the present invention with stable quality are provided, so that according to the rolling bearing, the quality is stable and the rolling life is long. A bearing can be provided.

  As is apparent from the above description, according to the carbonitriding method of the present invention, the amount of nitrogen entering the workpiece is controlled by adjusting the supply amount of ammonia during the carbonitriding process, It is possible to provide a carbonitriding method capable of stable carbonitriding by suppressing the occurrence of defective structures such as decarburized structure and disappearance of precipitates. Moreover, according to the manufacturing method of the mechanical component of this invention, the manufacturing method of the mechanical component which can manufacture the mechanical component with the stable quality can be provided by performing the stable carbonitriding process. Moreover, according to the machine component of the present invention, a stable carbonitriding process is performed, so that a machine component with stable quality can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

  FIG. 1 is a schematic cross-sectional view showing a configuration of a deep groove ball bearing as a rolling bearing provided with a mechanical component according to an embodiment of the present invention. With reference to FIG. 1, the deep groove ball bearing as a rolling bearing in one embodiment of this invention is demonstrated.

  Referring to FIG. 1, a deep groove ball bearing 1 is arranged between an annular outer ring 11, an annular inner ring 12 arranged inside the outer ring 11, and between the outer ring 11 and the inner ring 12. 14 and a plurality of balls 13 as rolling elements held by 14. An outer ring rolling surface 11 </ b> A is formed on the inner circumferential surface of the outer ring 11, and an inner ring rolling surface 12 </ b> A is formed on the outer circumferential surface of the inner ring 12. And the outer ring | wheel 11 and the inner ring | wheel 12 are arrange | positioned so that 12A of inner ring | wheel rolling surfaces and 11A of outer ring | wheels may mutually oppose. Further, the plurality of balls 13 are in contact with the inner ring rolling surface 12A and the outer ring rolling surface 11A, and are arranged at a predetermined pitch in the circumferential direction by the cage 14, so that they can roll on an annular track. Is retained. With the above configuration, the outer ring 11 and the inner ring 12 of the deep groove ball bearing 1 are rotatable relative to each other.

  Here, among the outer ring 11, the inner ring 12, the ball 13, and the cage 14 that are mechanical parts, the outer ring 11, the inner ring 12, and the ball 13 are particularly required to have rolling fatigue strength and wear resistance. Therefore, at least one of these is the machine part of the present invention, so that the quality of the deep groove ball bearing 1 can be stabilized and the life can be extended.

  FIG. 2 is a schematic cross-sectional view showing a configuration of a thrust needle roller bearing as a rolling bearing provided with mechanical parts according to an embodiment of the present invention. With reference to FIG. 2, the thrust needle roller bearing as a rolling bearing in one embodiment of the present invention will be described.

  Referring to FIG. 2, thrust needle roller bearing 2 has a disk-like shape, and a pair of races 21 as a rolling member arranged so that one main surface faces each other, and a rolling member As a plurality of needle rollers 23 and an annular retainer 24. The plurality of needle rollers 23 are in contact with the raceway rolling surfaces 21A formed on the mutually opposing main surfaces of the pair of raceways 21 and are arranged at a predetermined pitch in the circumferential direction by the cage 24, thereby forming an annular shape. It is held so that it can roll on the track. With the above configuration, the pair of race rings 21 of the thrust needle roller bearing 2 can rotate relative to each other.

  Here, among the bearing ring 21, the needle roller 23, and the cage 24, which are mechanical parts, in particular, the rolling ring 21 and the needle roller 23 are required to have rolling fatigue strength and wear resistance. Therefore, at least one of these is the mechanical part of the present invention, so that the quality of the thrust needle roller bearing 2 can be stabilized and the life can be extended.

  FIG. 3 is a schematic partial cross-sectional view showing a configuration of a constant velocity joint including mechanical parts according to an embodiment of the present invention. FIG. 4 is a schematic sectional view taken along line IV-IV in FIG. FIG. 5 is a schematic partial sectional view showing a state in which the constant velocity joint of FIG. 3 forms an angle. FIG. 3 corresponds to a schematic cross-sectional view taken along line III-III in FIG. With reference to FIGS. 3-5, the constant velocity joint in one embodiment of this invention is demonstrated.

  3 to 5, the constant velocity joint 3 includes an inner race 31 connected to the shaft 35, an outer race 32 arranged so as to surround the outer peripheral side of the inner race 31, and connected to the shaft 36. A torque transmitting ball 33 disposed between the inner race 31 and the outer race 32 and a cage 34 for holding the ball 33 are provided. The ball 33 is disposed in contact with the inner race ball groove 31A formed on the outer peripheral surface of the inner race 31 and the outer race ball groove 32A formed on the inner peripheral surface of the outer race 32 so that the ball 33 is not dropped. 34.

  As shown in FIG. 3, the inner race ball groove 31A and the outer race ball groove 32A formed on the outer peripheral surface of the inner race 31 and the inner peripheral surface of the outer race 32 pass through the centers of the shaft 35 and the shaft 36, respectively. In a state where the axes are in a straight line, each of them is formed in a curve (arc) shape having a curvature center at points A and B that are equidistant from the joint center O on the axis to the left and right on the axis. That is, the trajectory of the center P of the ball 33 that rolls in contact with the inner race ball groove 31A and the outer race ball groove 32A is centered on the point A (inner race center A) and point B (outer race center B). Each of the inner race ball groove 31A and the outer race ball groove 32A is formed so as to have a curved line (arc). As a result, even when the constant velocity joint makes an angle (when the constant velocity joint operates so that the axes passing through the centers of the shaft 35 and the shaft 36 intersect), the ball 33 always has the shaft 35 and the shaft 36. Located on the bisector of the angle (∠AOB) formed by the axis passing through the center.

  Next, the operation of the constant velocity joint 3 will be described. 3 and 4, in constant velocity joint 3, when rotation around the shaft is transmitted to one of shafts 35 and 36, the ball fitted in inner race ball groove 31A and outer race ball groove 32A. The rotation is transmitted to the other of the shafts 35 and 36 via 33.

  Here, when the shafts 35 and 36 form an angle θ as shown in FIG. 5, the ball 33 includes the inner race ball groove 31 </ b> A and the outer race ball having the centers of curvature at the inner race center A and the outer race center B described above. Guided by the groove 32A, the center P is held at a position on the bisector of ∠AOB. Further, the inner race ball groove 31A and the outer race ball groove 32A are formed so that the distance from the joint center O to the inner race center A and the distance from the outer race center B are equal. The distances from the center P to the inner race center A and the outer race center B are equal, and ΔOAP and ΔOBP are congruent. As a result, the distances L from the center P of the ball 33 to the shafts 35 and 36 are equal to each other, and when one of the shafts 35 and 36 rotates around the axis, the other also rotates at a constant speed. Thus, the constant velocity joint 3 can ensure constant velocity even when the shafts 35 and 36 form an angle. The cage 34, together with the inner race ball groove 31A and the outer race ball groove 32A, prevents the balls 33 from jumping out from the inner race ball groove 31A and the outer race ball groove 32A when the shafts 35 and 36 rotate. It performs the function of determining the joint center O of the constant velocity joint 3.

  Here, among the inner race 31, the outer race 32, the ball 33, and the cage 34 that are mechanical parts, the inner race 31, the outer race 32, and the ball 33 are particularly required to have fatigue strength and wear resistance. Therefore, at least one of these is the machine part of the present invention, so that the quality of the constant velocity joint 3 can be stabilized and the life can be extended.

  Next, a description will be given of a method of manufacturing machine elements such as the above-described machine component, a rolling bearing equipped with the machine component, and a constant velocity joint, which is an embodiment of the method of manufacturing a machine component of the present invention. FIG. 6 is a diagram showing an outline of a machine part and a method of manufacturing a machine element provided with the machine part in one embodiment of the present invention. With reference to FIG. 6, first, a steel member preparation step of preparing a steel member formed into a schematic shape of a machine part is performed. Specifically, for example, a steel bar is used as a raw material, and machining such as cutting, forging, and turning is performed on the steel bar, thereby mechanical parts such as an outer ring 11, a race ring 21, and an inner race 31 as mechanical parts. The steel member shape | molded by the following general shape is prepared.

Next, after the carbonitriding process is performed on the above-described steel member prepared in the steel member preparation step, the steel member is cooled to a temperature equal to or lower than the _MS point from a temperature of A ₁ point or higher. A quench hardening process for quench hardening the member is performed. Details of this quench hardening process will be described later.

Next, a tempering step for improving the toughness and the like of the hardened and hardened steel member is performed by heating the steel member subjected to the hardening and hardening step to a temperature of A ₁ point or less. The Specifically, the hardened and hardened steel member is heated to a temperature of 150 ° C. or higher and 350 ° C. or lower, which is a temperature of A ₁ or less, for example, 180 ° C., and a time of 30 minutes or longer and 240 minutes or shorter, for example, 120 minutes. Held and then cooled in air at room temperature (air cooling).

  Furthermore, the finishing process in which a finishing process etc. are given with respect to the steel member in which the tempering process was implemented is implemented. Specifically, for example, grinding is performed on the inner ring rolling surface 12A, the raceway rolling surface 21A, the outer race ball groove 32A, and the like of the steel member on which the tempering process has been performed. Thereby, the machine part in one embodiment of the present invention is completed, and the method for manufacturing the machine part in one embodiment of the present invention is completed. Further, an assembly process is performed in which the machine elements are assembled by combining the completed machine parts. Specifically, the deep groove ball bearing 1 is assembled by combining, for example, the outer ring 11, the inner ring 12, the ball 13 and the cage 14, which are the machine parts of the present invention manufactured by the above-described process. Thereby, the machine element provided with the machine part of the present invention is manufactured.

  Next, the detail of the above-mentioned quench hardening process is demonstrated. FIG. 7 is a diagram for explaining the details of the quench hardening process included in the method of manufacturing a mechanical component in one embodiment of the present invention. FIG. 8 is a diagram showing an example of a method for controlling the ratio of partial pressures of carbon monoxide and carbon dioxide included in the partial pressure control step included in the carbonitriding step of FIG. Moreover, FIG. 9 is a figure which shows an example of the heating pattern (temperature history given to a to-be-processed object) in the heating pattern control process included in the carbonitriding process of FIG. In FIG. 9, the horizontal direction indicates time, and the time elapses toward the right. In FIG. 9, the vertical direction indicates the temperature, and the higher the temperature, the higher the temperature. With reference to FIGS. 7-9, the detail of the hardening process included in the manufacturing method of the machine component in this Embodiment is demonstrated.

Referring to FIG. 7, in the quench hardening process of the method for manufacturing a machine component in one embodiment of the present invention, the carbonitriding process is performed using the carbonitriding method in one embodiment of the present invention. . In the carbonitriding method according to one embodiment of the present invention, first, a carbonitriding process is performed in which a steel member as a workpiece is carbonitrided. Thereafter, a cooling step is performed in which the steel member is cooled from a temperature of A ₁ point or higher to a temperature of M _S point or lower.

  The carbonitriding process includes an atmosphere control process in which the atmosphere in the heat treatment furnace is controlled, and a heating pattern control process in which the temperature history applied to the workpiece in the heat treatment furnace is controlled. The atmosphere control step and the heating pattern control step can be performed independently and in parallel. The atmosphere control step includes an undecomposed ammonia concentration control step for controlling the undecomposed ammonia concentration in the heat treatment furnace, and a partial pressure control for controlling a partial pressure of at least one of carbon monoxide and carbon dioxide in the heat treatment furnace. Process.

  Specifically, in the undecomposed ammonia concentration control step, first, an undecomposed ammonia concentration measurement step for measuring the undecomposed ammonia concentration in the heat treatment furnace is performed. The measurement of the undecomposed ammonia concentration can be performed using, for example, a gas chromatograph. Then, an undecomposed ammonia concentration determination step for determining whether or not an ammonia supply amount adjustment step for increasing or decreasing the supply amount of ammonia gas to the heat treatment furnace based on the undecomposed ammonia concentration measured in the undecomposed ammonia concentration measurement step is performed. Is implemented. This determination is performed based on, for example, the relationship between the undecomposed ammonia concentration experimentally obtained in advance and the nitrogen concentration in the surface layer portion of the workpiece.

  Here, the surface layer portion of the object to be processed refers to a region near the surface of the object to be processed. For example, the distance from the surface in a state where the object to be processed is a finished product is 0.1 mm or less. An area that should be an area. That is, the surface layer portion of the object to be processed is an area where the nitrogen concentration should be controlled in a state where the object to be processed is a product in view of the required characteristics for the product manufactured by processing the object to be processed. It can be determined appropriately for each product.

FIG. 11 shows the amount of undecomposed ammonia in the heat treatment furnace and the amount of nitrogen intrusion into the object to be treated (carbonized amount) when carbonitriding was performed under the conditions of carbonitriding time of 9000 seconds and a _C value of 1.0. It is a figure which shows the relationship with the mass of the nitrogen which penetrate | invaded into the to-be-processed object from the unit surface area of a to-be-processed object. With reference to FIG. 11, one embodiment of the undecomposed ammonia concentration determination step will be described.

Referring to FIG. 11, when it is desired to set the nitrogen intrusion amount to the object to be processed under a condition where the a _C value is 1.0 and the carbonitriding process is performed for 9000 seconds, the target from the relationship of FIG. The undecomposed ammonia concentration of can be determined. Therefore, in the undecomposed ammonia concentration determination step, it is determined whether or not the ammonia supply amount adjustment step is necessary depending on whether or not the ammonia concentration measured in the undecomposed ammonia concentration measurement step is the target undecomposed ammonia concentration. can do. The relationship for determining the target undecomposed ammonia concentration is not limited to the relationship between the undecomposed ammonia concentration and the nitrogen intrusion amount as described above. For example, the relationship between the undecomposed ammonia concentration and the surface of the object to be treated is a predetermined depth. It may be a relationship with the nitrogen concentration at this position.

  If the undecomposed ammonia concentration is not the target undecomposed ammonia concentration, an ammonia supply amount adjusting step for increasing or decreasing the undecomposed ammonia concentration in the heat treatment furnace is performed, and then the undecomposed ammonia concentration measuring step is performed. Will be implemented again. The ammonia supply amount adjusting step includes, for example, a mass flow controller attached to the pipe for the amount of ammonia flowing into the heat treatment furnace per unit time from an ammonia gas cylinder connected to the heat treatment furnace via the pipe. It can implement by adjusting with the flow control apparatus with which it was equipped. That is, when the measured undecomposed ammonia concentration is higher than the target undecomposed ammonia concentration, the ammonia supply amount adjusting step can be performed by decreasing the flow rate, and increasing the flow rate when the concentration is low. In this ammonia supply amount adjustment step, when there is a predetermined difference between the measured undecomposed ammonia concentration and the target undecomposed ammonia concentration, the degree of increase or decrease in flow rate is determined experimentally in advance. It can be determined based on the relationship between increase / decrease in gas flow rate and increase / decrease in undecomposed ammonia concentration.

  On the other hand, when the undecomposed ammonia concentration is the target undecomposed ammonia concentration, the undecomposed ammonia concentration measuring step is performed again without performing the ammonia supply amount adjusting step.

In the partial pressure control step, by adjusting the supply amount of propane (C ₃ H ₈ ) gas, butane gas (C ₄ H ₁₀ ), etc. as an enriched gas, at least one of the partial pressures of CO and CO ₂ The partial pressure is controlled to adjust the a _C value, the _CP value, and the like. Specifically, for example, the partial pressure P _CO2 partial pressure P _CO and carbon monoxide to carbon dioxide in the atmosphere by using an infrared gas concentration measurement device are measured. Then, based on the measured values, as such _{a C} value and _{C P} value is the value of the target, propane _(C 3 _{H 8)} as enriched gas Gas supply rate of such butane gas _{(C 4 H 10)} Is adjusted.

  Here, in the partial pressure control step, when the supply amount of ammonia is changed in the undecomposed ammonia concentration control step, the partial pressure ratio that is the ratio of the partial pressure of carbon monoxide and the partial pressure of carbon dioxide changes. In this case, the partial pressure of at least one of carbon monoxide and carbon dioxide is set so as to cancel the change from the partial pressure ratio before the change of the ammonia supply amount to the partial pressure ratio after the change of the ammonia supply amount. Be changed.

  Specifically, as shown in FIG. 8, first, a supply amount change determination step is performed in which it is determined whether or not the supply amount of ammonia has been changed within a predetermined time. As described above, when the supply amount of ammonia is changed, for example, the partial pressure of carbon monoxide changes accordingly. The predetermined time is determined in advance in consideration of the time from the change in the supply amount of ammonia based on the capacity of the heat treatment furnace until the partial pressure of carbon monoxide is affected. Whether or not the measurement of the partial pressure of carbon monoxide and carbon dioxide, which will be described later, is determined is determined depending on whether or not the supply amount is changed.

When the supply amount of ammonia is not changed within a predetermined time, a normal partial pressure control step, which is a normal partial pressure control step, for example, a partial pressure P _CO of carbon monoxide in the atmosphere at regular intervals and / or is measured partial pressure P _CO2 of carbon dioxide, as such a _C value and C _P value is a value of the target, step feed amount of enriched gas is adjusted, it is performed. Alternatively, a process similar to the process from the process of measuring the partial pressure of CO and CO ₂ in FIG. 8 described later to the process of controlling the partial pressure of CO and CO ₂ so that the determination variable becomes a reference value is constant. You may carry out every hour. Then, the supply amount change determination step is performed again.

On the other hand, if the supply amount of ammonia was changed within a predetermined time, the partial pressure measurement step of partial pressure P _CO2 partial pressure P _CO and / or carbon monoxide to carbon dioxide is measured is performed, the partial pressure ratio P _CO A decision variable calculation step is performed in which decision variables such as / P _CO2 , a _C value, and _CP value are calculated. Then, a determination variable determination step is performed for determining whether the determination variable is a predetermined reference value. When the judgment variable is the reference value, for example, when the _CP value as the judgment variable is the reference value of 1.0, or within a predetermined allowable range (for example, 0.95 to 1.05) If this is the case, the present process corresponding to the change in the supply amount of ammonia is terminated as it is. When the determination variable is not the reference value, a step of controlling the partial pressure of CO and CO ₂ is performed so that the determination variable becomes the reference value. For example reduces the _{P CO,} if the partial pressure ratio _P CO _{/ P CO2} as determined variable is smaller than the reference value, as determined variable as a reference value, for example pressure ratio decreases the _{P CO2} partial _{P CO} The flow rate of the rich gas is changed so that / P _CO2 is returned to the reference value.

On the other hand, in the heating pattern control step, the heating history applied to the steel member as the object to be processed is controlled. Specifically, as shown in FIG. 9, in an atmosphere in which the steel member is controlled by the above-described atmosphere control step, a temperature of 800 ° C. or higher and 1000 ° C. or lower, which is a temperature of _one point or higher, for example, 850 ° C. It is heated and held for 60 minutes to 300 minutes, for example 150 minutes. As the holding time elapses, the heating pattern control process ends, and at the same time, the atmosphere control process ends.

Thereafter, the steel member by being dipped (oil cooling) in oil, a cooling step is cooled from a temperature of more than ₁ point A to M _S point below the temperature is carried out. Through the above steps, the steel member is carbonitrided and hardened and hardened at the surface. Thereby, the quench hardening process of this Embodiment is completed.

As described above, according to the carbonitriding method of the present embodiment, usually, for example, the partial pressure P _CO of carbon monoxide and / or the partial pressure P _{CO2 of} carbon dioxide in the atmosphere is measured at regular intervals. as such a _C value and C _P value is the value of target, while the step of supplying the amount of enriched gas is adjusted is performed, if the supply amount of ammonia is changed, accordingly Therefore, the necessity of adjusting the partial pressure ratio P _CO / P _CO2 is determined, and the partial pressure of at least one of P _CO and P _CO2 is changed so that the a _C value, the _CP value, etc. become the target values. The That is, when the partial pressure of one of _PCO and _PCO2 increases, the partial pressure is decreased by the increased amount, or when the partial pressure decreases, the partial pressure is increased by the decreased amount. The change in P _CO / P _CO2 can be canceled out. When one partial pressure increases by x% of the partial pressure before changing the ammonia supply amount, the other partial pressure is also increased by x% of the partial pressure before changing the ammonia supply amount. When the pressure decreases by x% of the partial pressure before the change of the ammonia supply amount, the other partial pressure is also decreased by x% of the partial pressure before the change of the ammonia supply amount, so that the partial pressure ratio P _CO / P You may cancel the change of _CO2 . As a result, it is possible to accurately control the _CP value and a _C value in the heat treatment furnace, which directly affects the carburizing behavior of the workpiece, and suppress the occurrence of defective structures and stabilize the quality of the workpiece. Can be made.

  Further, according to the carbonitriding method of the present embodiment, the undecomposed ammonia concentration is controlled based on the measured value of the undecomposed ammonia concentration in the heat treatment furnace so that the undecomposed ammonia concentration becomes the target concentration. Yes. For this reason, it is easy to accurately control the concentration of undecomposed ammonia in the atmosphere in the heat treatment furnace and to accurately control the amount of nitrogen entering the object to be processed.

  Furthermore, in the carbonitriding method of the present embodiment, the change in the ammonia supply amount in the undecomposed ammonia concentration control step is a heat treatment after the previous change in the ammonia supply amount performed immediately before the change in the ammonia supply amount. It is preferable to carry out after the volume of the carburized gas supplied to the furnace at 20 ° C. and 1.05 atm is equal to or greater than the volume of the heat treatment furnace.

  Specifically, for example, the following control is preferably performed in the ammonia supply amount adjustment step of the undecomposed ammonia concentration control step. FIG. 10 is a diagram showing an example of a method for controlling the supply amount of ammonia included in the ammonia supply amount adjustment step of the undecomposed ammonia concentration control step provided in the carbonitriding step of FIG. Referring to FIGS. 7 and 10, in the ammonia supply amount adjusting step of FIG. 7, as shown in FIG. 10, first, after the change of the ammonia supply amount previously performed, a predetermined volume, for example, a heat treatment furnace A carburizing gas supply amount determining step for determining whether or not the carburizing gas exceeding the volume is supplied is performed.

  If, for example, a carburizing gas larger than the volume of the heat treatment furnace is supplied from the change in the supply amount of ammonia previously performed, the ammonia supply amount adjustment step is completed by changing the ammonia supply amount. On the other hand, when the carburizing gas exceeding the capacity of the heat treatment furnace has not been supplied yet, the supply amount of ammonia is not changed and the carburizing gas supply amount determining step is executed again. Whether the carburizing gas of a predetermined volume or more has been supplied can be determined based on the time required for introducing the carburizing gas of a predetermined volume when the flow rate of the carburizing gas is constant. Further, when the flow rate of the carburizing gas changes, it can be determined by integrating the volume of the carburizing gas that has flowed.

As described above, when there is a change in the ammonia supply amount that is normally required to control the undecomposed ammonia concentration, the partial pressure ratio of carbon monoxide and carbon dioxide that has changed is changed before the change in the ammonia supply amount. In order to return to this state, it is necessary to supply a carburizing gas exceeding the capacity of the heat treatment furnace at 20 ° C. and 1.05 atm. Therefore, after the ammonia supply amount adjustment step is performed as described above, after the partial pressure ratio P _CO / P _CO2 returns to the state before the previous change in the ammonia supply amount, a new ammonia supply amount is changed. since the be, C _P value, control such as a _C value becomes easier, defective tissue is further suppressed.

Incidentally, C _P value, from the viewpoint of further facilitating control of such a _C value, it is preferable to change the ammonia supply amount after 2 times or more the carburizing gas volume of the heat treatment furnace has been supplied is performed, In order to further stabilize, it is preferable that the ammonia supply amount is changed after three times or more of the carburizing gas is supplied. On the other hand, in order to sufficiently control the residual ammonia concentration, it is preferable to change the ammonia supply amount after supplying a carburizing gas that is 4 times or less, preferably 3 times or less the volume of the heat treatment furnace. .

  Moreover, according to the manufacturing method of the machine component in this Embodiment mentioned above, the machine component which has the stable quality can be manufactured by performing the stable carbonitriding process. In addition, the mechanical component of the present embodiment is a mechanical component with stable quality by performing a stable carbonitriding process.

  In the present embodiment, a deep groove ball bearing, a thrust needle roller bearing, and a constant velocity joint have been described as examples of the mechanical component of the present invention. However, the mechanical component of the present invention is not limited to this, and fatigue of the surface layer portion is also described. It may be a machine part that requires strength and wear resistance, such as a hub, a gear, and a shaft.

Examples of the present invention will be described below. The impact of changes frequency stability on the ammonia supply amount of C _P value An experiment was conducted to investigate. The experimental procedure is as follows.

The capacity of the heat treatment furnace used in the experiment is 120 L (liter). The object to be treated was a ring made of JIS SUJ2 (carbon content 1% by mass) having an outer diameter of 38 mm, an inner diameter of 30 mm, and a width of 10 mm, and about 101 g was inserted into the heat treatment furnace. The heating pattern employed the same pattern as in FIG. 9, and the carbonitriding holding temperature was 850 ° C. Then, while the carburizing gas (mixed gas of RX gas and enriched gas) is supplied into the heat treatment furnace at a constant flow rate, changing the flow rate of ammonia gas per time t _2. Then, the partial pressure ratio P _CO / of the partial pressure P _CO2 of the carbon dioxide is changed by adjusting the flow rate of the enriched gas in accordance with the change of the partial pressure P _CO of the carbon monoxide accompanying the change in the supply flow rate of the ammonia gas. with keeping the P _CO2 constant was carried out a control to keep the _{C P} value constant. Here, the carburizing gas is supplied into a 120 L heat treatment furnace having a capacity of the heat treatment furnace at time t ₁ at 20 ° C. and 1.05 atm. Then, t ₂ is changed to 3 levels, the partial pressure P _CO of carbon _monoxide and the partial pressure P _{CO2 of} carbon dioxide in the heat treatment furnace are measured, and the _CP value is calculated by the equations (1) and (2). Thus, the stability of the _CP value was investigated.

FIG. 12 is a diagram illustrating the stability of the _CP value when t ₂ is ½ of t ₁ . FIG. 13 is a diagram showing the stability of the _CP value when t ₂ is equal to t ₁ . Further, FIG 14 is a diagram showing the stability of _{C P} value when the _{t 2} was set to 2 times the _{t 1.} 12 to 14, the horizontal axis indicates the elapsed time (processing time) of the carbonitriding process, and indicates that the processing time elapses as it goes to the right. 12 to 14, the vertical axis indicates the partial pressure of carbon monoxide (CO), the partial pressure of carbon dioxide (CO ₂ ), the ammonia gas supply flow rate, and the _CP value. The value is large. 12 to 14, the solid line indicates the partial pressure of carbon monoxide, the broken line indicates the partial pressure of carbon dioxide, the alternate long and short dash line indicates the ammonia gas supply flow rate, and the alternate long and two short dashes line indicates the _CP value. With reference to FIGS. 12-14, the experimental result of a present Example is demonstrated.

Referring to FIG. 12, if the t ₂ is the case of the outside of the carbonitriding method of the present invention was a half of t _1, C _P value that has been held at the target value, ammonia at time m0 When the gas supply flow rate is increased, the partial pressure of carbon monoxide is lowered, which is lowered. In contrast, although trying to counteract the change in the C _P value to lower the partial pressure of carbon dioxide by adjusting the flow rate of the enriched gas (change in partial pressure ratio P _{CO /} P _CO2), from time m0 time t ₂ At the time m1 when the time elapses, the ammonia gas supply flow rate further increases. As a result, C _P value without returning to the target value (the value at m0), is further reduced.

That is, in the carbonitriding method of FIG. 12, before the volume of the carburized gas supplied to the heat treatment furnace after the change in the previous ammonia supply flow rate at 20 ° C. and 1.05 atm. since the change in the supply flow rate is implemented, without C _P value is restored to the value of the target, the ammonia gas supply flow rate is further changed. Therefore, it is difficult to control the C _P value, is no longer able to hold the C _P value to the value of the target.

On the other hand, referring to FIG. 13, C _P value t ₂ is the case of the carbonitriding process even when the equal t _1, which has been held at the target value of the present invention, the ammonia gas supply at time m0 When the flow rate is increased, the partial pressure of carbon monoxide is lowered, which is lowered. The contrast, by canceling the change in the C _P value to lower the partial pressure of carbon dioxide by adjusting the flow rate of the enriched gas (change in partial pressure ratio P _{CO /} P _CO2), is from time m0 time t ₂ at time m1 to elapsed, C _P value is restored to the target value (the value at m0).

That is, in the carbonitriding method of FIG. 13, the volume of the carburized gas supplied to the heat treatment furnace after the change in the previous ammonia supply flow rate at 20 ° C. and 1.05 atm is equal to or greater than the volume of the heat treatment furnace. Since the supply flow rate is changed, the _CP value returns to the target value, and then the ammonia gas supply flow rate further changes. Therefore, improved ease of control of the C _P value, C _P value carbonitriding process in a stable state as compared with the case of FIG. 12 is performed.

Furthermore, with reference to FIG. 14, C _P value t ₂ is the case of the carbonitriding process in the case where twice the t ₁ also held in the target value of the present invention include ammonia at time m0 When the gas supply flow rate is increased, the partial pressure of carbon monoxide is lowered, which is lowered. The contrast, by canceling the change in the C _P value to lower the partial pressure of carbon dioxide by adjusting the flow rate of the enriched gas (change in partial pressure ratio P _{CO /} P _CO2), is from time m0 time t ₁ C _P value has passed since the beginning has been restored to the target value (the value at m0). Then, in approximately 50% of the time of the time t ₂ until time m1 time has passed 2 × t _1, C _P value is held at a target value.

That is, in the carbonitriding method of FIG. 14, the volume of the carburized gas supplied to the heat treatment furnace after the change in the previous ammonia supply flow rate at 20 ° C. and 1.05 atm is more than twice the volume of the heat treatment furnace. At the same time, since the change in the supply flow rate of the ammonia is carried out, after the C _P value is restored to the value of the target, it is held at the target value. Then, since the ammonia gas supply flow rate further changes, and ease further improvement in the control of the C _P value, the more C _P value is implemented carbonitriding process in a stable state.

FIG. 15 shows the time t ₂ until the ammonia gas supply flow rate is changed with respect to the time t ₁ required for supplying the carburizing gas having the same volume (20 ° C., 1.05 atm) as the capacity of the heat treatment furnace to the heat treatment furnace. the ratio T of a diagram showing the effect on the C _P value stable time ratio is the ratio of the time C _P value for the carbonitriding time is held at the target value. 15, the horizontal axis represents _{T (= t 2 / t 1} ), the vertical axis is the C _P value stable time ratio is the ratio of the time C _P value among the carbonitriding time is held at the target value . With reference to FIG. 15, the effect of T on the _CP value stabilization time ratio will be described.

Referring to FIG. 15, the T is less than 1, the time C _P value is maintained at the target value is 0, C _P value stable time ratio is zero. Therefore, if T is less than 1, it is practically difficult to control the _CP value in the carbonitriding process. Then, C _P value stable time ratio as T increases increases, it becomes easy to control the C _P value. As shown in FIG. 15, in order to perform appropriate control of the _CP value, T is required to be at least 1 or more, and the _CP value stabilization time ratio exceeds 0.5 (that is, out of the carbonitriding time). in more than 50% of the time, it is preferable that the C _P value is maintained at the target value) 2 or more. Further, by three or more T, it exceeds the C _P value stable time ratio is 0.65, in 2/3 of the time of the entire carbonitriding time, to be able to hold the C _P value to the target value Recognize.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The carbonitriding method and the machine part manufacturing method of the present invention include a carbonitriding method for members that require rolling fatigue strength and wear resistance, and a machine part manufacturing method that requires rolling fatigue strength and wear resistance. It can be applied particularly advantageously. The mechanical component of the present invention can be particularly advantageously applied to a mechanical component that requires rolling fatigue strength and wear resistance.

It is a schematic sectional drawing which shows the structure of the deep groove ball bearing as a rolling bearing provided with the machine component which is one embodiment of this invention. It is a schematic sectional drawing which shows the structure of the thrust needle roller bearing as a rolling bearing provided with the machine component which is one embodiment of this invention. It is a general | schematic fragmentary sectional view which shows the structure of the constant velocity joint provided with the machine component which is one embodiment of this invention. It is a schematic sectional drawing in alignment with line segment IV-IV of FIG. FIG. 4 is a schematic partial sectional view showing a state in which the constant velocity joint of FIG. 3 forms an angle. It is a figure which shows the outline of the manufacturing method of the machine component and the machine element provided with the said machine component in one embodiment of this invention. It is a figure for demonstrating the detail of the quench hardening process included in the manufacturing method of the machine component in one embodiment of this invention. It is a figure which shows an example of the control method of the ratio of the partial pressure of carbon monoxide and carbon dioxide included in the partial pressure control process with which the carbonitriding process of FIG. 7 is equipped. It is a figure which shows an example of the heating pattern (temperature history given to a to-be-processed object) in the heating pattern control process included in the carbonitriding process of FIG. It is a figure which shows an example of the control method of the supply amount of ammonia contained in the ammonia supply amount adjustment process of the undecomposed ammonia concentration control process with which the carbonitriding process of FIG. 7 is equipped. The amount of undecomposed ammonia in the heat treatment furnace and the amount of nitrogen intruding into the object to be processed (unit of the object to be processed) when the carbonitriding process is performed under the condition of carbonitriding time 9000 seconds and a _C value 1.0 It is a figure which shows the relationship with the mass of the nitrogen which penetrate | invaded into the to-be-processed object from the surface area. Capacity and the same volume of the heat treatment furnace time t ₂ until the ammonia gas supply flow rate is changed (20 ° C., 1.05 atm) 1/2 time carburizing gas required to be supplied to the heat treatment furnace t ₁ of It is a figure which shows stability of _CP value at the time of setting. The t ₂ is a diagram showing the stability of C _P value when equal to t _1. The t ₂ is a diagram showing the stability of C _P value when twice the t _1. The ratio T of the time t ₂ until the ammonia gas supply flow rate is changed with respect to the time t ₁ required for the carburizing gas having the same volume (20 ° C., 1.05 atm) as the capacity of the heat treatment furnace to be supplied to the heat treatment furnace is shows the effect of C _P value for the carbonitriding time is on the C _P value stable time ratio is the ratio of time held at the target value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Deep groove ball bearing, 2 Thrust needle roller bearing, 3 Constant velocity joint, 11 Outer ring, 11A Outer ring rolling surface, 12 Inner ring, 12A Inner ring rolling surface, 13 Ball, 14 Cage, 21 Race ring, 21A Race ring rolling surface , 23 Needle roller, 24 cage, 31 inner race, 31A inner race ball groove, 32 outer race, 32A outer race ball groove, 33 balls, 34 cage, 35, 36 shafts.

Claims (5)

An atmosphere control process in which the atmosphere in the heat treatment furnace is controlled;
A heating pattern control step in which the temperature history applied to the workpiece in the heat treatment furnace is controlled,
The atmosphere control step includes
An undecomposed ammonia concentration control step of controlling the undecomposed ammonia concentration in the heat treatment furnace by adjusting the supply amount of ammonia supplied into the heat treatment furnace;
A partial pressure control step of controlling a partial pressure of at least one of carbon monoxide and carbon dioxide in the heat treatment furnace,
In the partial pressure control step, the partial pressure ratio is a ratio of the partial pressure of the carbon monoxide and the partial pressure of the carbon dioxide when the supply amount of the ammonia is changed in the undecomposed ammonia concentration control step. Is changed, the carbon monoxide and the carbon dioxide so as to cancel the change from the partial pressure ratio before the change in the ammonia supply amount to the partial pressure ratio after the ammonia supply amount is changed. At least one of the partial pressures is changed,
In the in the undecomposed ammonia concentration control step, the later change of the ammonia supply amount of the performed previously just before the undecomposed ammonia concentration control step, 20 ° C., 1.05 atm carburizing gas supplied to the heat treatment furnace volume, whether became more volume of the heat treatment furnace is determined, if the volume is determined to be equal to or more than the volume of the heat treatment furnace, changes of the supply amount of the ammonia is carried out, carbonitriding Method.   In the undecomposed ammonia concentration control step, the undecomposed ammonia concentration in the heat treatment furnace is measured, and based on the relationship between the undecomposed ammonia concentration and the nitrogen concentration in the surface layer portion of the workpiece, The carbonitriding method according to claim 1, wherein a nitrogen concentration in a surface layer portion of the workpiece is controlled by adjusting a flow rate of supplied ammonia. A steel member preparation step of preparing a steel member formed into a schematic shape of a machine part;
After the carbonitriding process is performed on the steel member prepared in the steel member preparation step, the steel member is quenched by cooling from a temperature of A1 point or higher to a temperature of MS point or lower. A quench hardening process to cure,
The said carbonitriding process in the said quench hardening process is a manufacturing method of the machine component implemented using the carbonitriding method of Claim 1 or 2 . A machine part manufactured by the method for manufacturing a machine part according to claim 3 . The machine part according to claim 4 , which is used as a part constituting a bearing.

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