JP2015212559A - Screw shaft and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw shaft which can achieve both improvement in accuracy and reduction in cost at high levels, and a production method thereof.SOLUTION: A screw shaft 1 has a spiral screw groove 10 on its outer peripheral face, the screw shaft having a cured layer 30 comprising nitrogen martensite in the vicinity of the surface.

Description

  The present invention relates to a screw shaft used in a screw transmission device that converts rotational motion into linear motion or converts linear motion into rotational motion, and a manufacturing method thereof.

  Conventionally, screw conduction devices are used in various machines such as various machine tools and conveying devices. The screw transmission device mainly includes a screw shaft in which a spiral thread groove (thread) is formed on the outer peripheral surface, and a substantially cylindrical nut in which a spiral thread groove (thread) is formed on the inner peripheral surface. The ball screw transmission device using a ball screw in which the ball rolls between the screw groove of the screw shaft and the screw groove of the nut, and a slide screw in which the screw shaft and the nut are directly screwed are used. It is roughly divided into two types: a sliding screw transmission device.

Of these, the ball screws are further divided into JIS B1192 into highly accurate positioning ball screws and relatively low accuracy conveying ball screws. Then, in JIS B1192, C0, C1, C3 and C5, and the _{C p 0, C p 1,} C p 3 and _{C p} 5 defined as accuracy class of the positioning ball screws, as accuracy class of the conveying ball screw C _t 0, C _t 1, C _t 3, C _t 5, C _t 7 and C _t 10 are defined.

  In the manufacture of screw shafts and nuts, in order to improve fatigue strength and wear resistance, induction hardening or carburizing hardening is generally performed after forming a thread groove. However, since such a heat treatment rapidly cools the material after it is heated to a relatively high temperature, the material is likely to be distorted, and deformation accompanying the strain causes a decrease in the accuracy of the ball screw. In particular, a decrease in lead accuracy due to deformation of the screw shaft is a serious problem because it causes vibration and noise in addition to deterioration in positioning accuracy.

  Therefore, in manufacturing a screw shaft of a positioning ball screw that requires high accuracy, generally, a screw groove is formed in a material by cutting, and then heat treatment such as induction hardening is performed, and then bending correction, outer diameter, shaft end, etc. are performed. After grinding, the lead groove is finished by grinding to improve the lead accuracy. For this reason, the screw shaft of the positioning ball screw is inferior in productivity and high in cost instead of realizing high accuracy.

  On the other hand, in the manufacture of ball screws for conveyance that do not require high accuracy, it is common to increase the productivity and reduce the cost by forming thread grooves in the material at one time by rolling before heat treatment. It is. In such a manufacturing method, a method for improving the lead accuracy has been proposed (for example, see Patent Document 1 or 2).

JP 2003-119518 A Japanese Patent Laying-Open No. 2005-066608

  However, since the methods of Patent Document 1 or 2 are all based on the premise of conventional heat treatment with a large strain, it is difficult to eliminate the decrease in accuracy caused by the heat treatment strain, and the improvement in accuracy and the reduction in cost are high. It wasn't something that was compatible at the level.

  In view of such circumstances, the present invention is intended to provide a screw shaft capable of achieving both high accuracy and low cost at a high level, and a manufacturing method thereof.

  (1) The present invention is a screw shaft provided with a helical thread groove on an outer peripheral surface, and having a hardened layer containing nitrogen martensite in the vicinity of the surface.

  (2) The present invention is also the screw shaft according to (1), wherein the hardened layer is formed by performing nitrogen quenching after forming the thread groove in a material. .

  (3) In the present invention, the nitriding quenching is performed after the material having the thread groove formed is held at a predetermined temperature within a range of 590 ° C. or higher and 850 ° C. or lower for a predetermined time in an atmosphere containing ammonia gas. The screw shaft according to (2) above, which is performed by quenching.

  (4) The present invention is also the screw shaft according to the above (2) or (3), wherein the material is a carbon steel material for mechanical structure or a rolled steel material for general structure.

  (5) The present invention is also the screw shaft according to any one of (1) to (4), wherein the thread groove is formed by rolling.

  (6) The present invention is also any one of the above (1) to (5), wherein the hardened layer has a hardness of Hv500 or more in a range from the surface to a depth of 0.1 mm. The screw shaft.

  (7) The present invention also includes a first step of forming a screw groove in the material, and a second step of performing nitriding quenching on the material in which the screw groove is formed. A method for manufacturing a screw shaft.

  (8) In the present invention, in the second step, after the material having the thread groove formed therein is held for a predetermined time at a predetermined temperature within a range of 590 ° C. or higher and 850 ° C. or lower in an atmosphere containing ammonia gas. The method of manufacturing a screw shaft according to (7) above, wherein the method is rapidly cooled.

  (9) The present invention also provides the screw shaft manufacturing method according to (7) or (8) above, wherein in the first step, the thread groove is formed by rolling.

  According to the screw shaft and the manufacturing method thereof according to the present invention, it is possible to achieve an excellent effect that it is possible to achieve both improvement in accuracy and reduction in cost at a high level.

(A) It is the schematic which showed the screw shaft which concerns on embodiment of this invention. (B) It is the schematic sectional drawing to which the A section of Drawing 1 (a) was expanded. It is the flowchart which showed the manufacture procedure of the screw shaft. It is the figure which showed an example of the time chart of nitrogen quenching. (A) It is the schematic which showed the measuring method of the shake of the radial direction of the test piece which concerns on the Example of this invention. (B) It is the table | surface which showed the measurement result of the change of the deflection | deviation of radial direction, and the measurement result of the elongation of an axial direction. (C) It is the graph which showed the measurement result of the hardness of test piece TP1. (D) It is the graph which showed the measurement result of the hardness of test piece TP2. (A) It is the graph which showed the measurement result of the hardness of test piece TP3. (B) It is the graph which showed the measurement result of the hardness of test piece TP4. (C) It is the graph which showed the measurement result of the hardness of test piece TP5.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  Fig.1 (a) is the schematic which showed the screw shaft 1 which concerns on this embodiment, FIG.1 (b) is the schematic sectional drawing which expanded the A section of Fig.1 (a). The screw shaft 1 of the present embodiment is used for a ball screw transmission device. As shown in FIG. 1A, a spiral screw groove 10 and a screw thread 20 are formed on the outer peripheral surface of the screw shaft 1. Is formed. The material of the screw shaft 1 is carbon steel for machine structure such as S45C or S55C.

  As shown in FIG. 1B, a hardened layer 30 having a hardness higher than that of the base material is formed in the vicinity of the surface of the screw shaft 1 in order to increase wear resistance and fatigue strength. The hardened layer 30 is formed by nitrogen quenching and is a layer containing nitrogen martensite. That is, in this embodiment, nitrogen martensite is introduced into the nitrogenous layer (layer in which nitrogen is diffused in the steel) by allowing nitrogen to enter and dissolve in the steel in the austenite region in the Fe-N phase diagram and then quenching. The cured layer 30 is formed by generating

  The hardness of the hardened layer 30 is not particularly limited, but in order to obtain appropriate wear resistance and fatigue strength as the screw shaft of the screw transmission device, the hardness within a range from the surface to a depth of 0.1 mm is required. It is preferably HV500 or more, more preferably HV600 or more, and most preferably HV700 or more. In order to further improve the wear resistance and fatigue strength, the hardness of the hardened layer 30 is such that the hardness within the range from the surface to a depth of 0.1 mm is HV500 or more, and the depth from the surface to 0.3 mm. The hardness within the range is preferably HV400 or more, the hardness within the range from the surface to a depth of 0.1 mm is HV600 or more, and the hardness within the range from the surface to a depth of 0.3 mm is HV450 or more. More preferably, the hardness in the range from the surface to a depth of 0.1 mm is HV700 or more, and the hardness in the range from the surface to a depth of 0.3 mm is most preferably HV500 or more.

  In this embodiment, as described above, by providing the hardened layer 30 containing nitrogen martensite near the surface of the screw shaft 1 by nitriding quenching, the manufacturing process of the screw shaft 1 is simplified and the accuracy of the screw shaft 1 is improved. It is possible to achieve both. In other words, in nitrocarburizing, it is only necessary to hold the material at a relatively lower temperature than in the conventional induction hardening and carburizing quenching, and because the holding time is short, it is possible to keep heat treatment strain small. It has become. Therefore, since the process of correcting the bend after the heat treatment can be omitted, the manufacturing process can be simplified. Furthermore, in addition to improving lead accuracy due to small heat treatment strain, bending correction can be omitted, and lead errors newly generated by bending correction can be eliminated. Therefore, thread grooves are formed by grinding after heat treatment. Even if it does not do it, it is possible to obtain the screw shaft 1 with sufficiently high accuracy.

  Nitrogen quenching does not perform local heating / quenching unlike induction quenching, so heat treatment strain is relatively uniform in the axial direction, and bending correction can be omitted. Thus, there is no change in the amount of distortion caused by the bending correction. That is, in the screw shaft 1 of the present embodiment, the lead fluctuation due to the heat treatment is less likely to occur. Therefore, it is possible to further improve the lead accuracy of the screw shaft 1 by forming the screw groove 10 and the thread 20 in advance of heat treatment strain and reducing the accumulated representative lead error.

  Thus, in the screw shaft 1 of the present embodiment, it is possible to improve the lead accuracy more than before while simplifying the manufacturing process and improving the productivity. That is, in the screw shaft 1 of the present embodiment, it is possible to improve the accuracy more than before at a lower cost than before.

  In the present embodiment, the surface treatment layer 40 for rust prevention is provided on the outermost surface of the screw shaft 1 by, for example, blackening processing or phosphate coating treatment. For example, the surface treatment layer 40 may be omitted. That is, according to the nitriding and quenching, the corrosion resistance of the screw shaft 1 is improved by the nitride present in the outermost portion of the hardened layer 30, so that the rust prevention treatment can be omitted. Further, as the surface treatment layer 40, for example, a solid lubricating film such as molybdenum disulfide, fluorine, or graphite may be provided.

  Next, the detail of the manufacturing method of the screw shaft 1 is demonstrated. FIG. 2 is a flowchart showing a manufacturing procedure of the screw shaft 1. In the manufacture of the screw shaft 1, a material such as a round bar is first cut into a predetermined length (cutting step S1). The material is preferably a carbon steel material for mechanical structure from the viewpoint of strength and quality, but may be a general structural rolled steel material depending on the application. In other words, nitrous quenching increases the hardness in the vicinity of the surface by nitrogen martensite, so there is no need to use alloy steels such as alloy steels for machine structures in order to improve hardenability. Even a steel material can obtain desired wear resistance and fatigue strength easily and stably.

  After cutting the material, outer diameter grinding is performed (outer diameter grinding step S2). Here, the material is processed into a predetermined outer dimension by centerless grinding, and the outer dimension of the material is set within a predetermined tolerance. Once the material has been finished to a predetermined outer dimension, screw rolling is performed to form the screw groove 10 and the thread 20 on the outer peripheral surface of the material (screw rolling step S3). Here, the screw groove 10 and the screw thread 20 are formed by pressing the pair of roll dies against the material while rotating them, and transferring the screw shape of the roll dies to the outer peripheral surface of the material.

  In this embodiment, since the heat treatment strain can be suppressed small by adopting nitriding quenching, the highly accurate screw shaft 1 is manufactured while adopting the thread rolling before heat treatment with high productivity. Is possible. Furthermore, sufficient rolling resistance and fatigue strength can be obtained after heat treatment even when a relatively low-workability steel material is used as a raw material as described above, so that thread rolling is also performed with high accuracy and high quality. It is possible.

After the thread groove 10 and the thread 20 have been formed, a heat treatment by nitriding quenching is performed (nitrogen quenching step S4). FIG. 3 is a diagram showing an example of a time chart of nitrous quenching. In nitriding quenching, the raw materials are housed in a sealed heat treatment furnace, and the furnace is heated to a predetermined nitriding temperature T by heating the inside of the furnace while introducing nitrogen (N ₂ ) gas at a predetermined flow rate. Raise the temperature.

When the inside of the furnace reaches the nitriding temperature T, the furnace temperature is controlled so as to maintain the nitriding temperature T. Then, introduction of ammonia (NH 3) gas into the furnace is started after a predetermined soaking time t ₁ while maintaining the nitriding temperature T. Ammonia gas is introduced into the furnace together with the nitrogen gas at a predetermined flow rate, so that the atmosphere in the furnace becomes a nitrogen gas atmosphere containing ammonia gas. Will be. After the beginning of the introduction of ammonia gas, if窒時between t ₂ predetermined immersion has elapsed, then immersed in an oil bath removed material from the furnace, quenched. Thereby, the hardened layer 30 is formed, and the nitriding quenching is completed.

  The nitrous layer in which nitrogen diffuses in the steel substantially follows the Fe—N phase diagram, and the A1 transformation point is lowered to about 590 ° C. Therefore, by setting the nitriding temperature T to 590 ° C. or higher, it is possible to quench and quench the raw material as it is after nitriding. That is, in the nitrous layer, nitrogen austenite is generated as nitrogen enters and diffuses, so that the hardened layer 30 having the required hardness is formed by rapidly cooling this to generate nitrogen martensite. be able to.

  Nitrogen penetration / diffusion into the material is promoted as the nitriding temperature T increases. However, when the nitriding temperature T exceeds 850 ° C., ammonia gas is excessively decomposed in the furnace, and the surface of the material As a result, the amount of ammonia gas reaching the temperature decreases, and the nitriding rate decreases. Further, the heat treatment strain increases as the nitriding temperature T increases. Therefore, from the point of balance between nitriding speed and accuracy, the nitriding temperature T is preferably set to a temperature in the range of 590 ° C. to 850 ° C., and set to a temperature in the range of 700 ° C. to 800 ° C. More preferably.

The soaking time t ₁ may be appropriately set according to the volume of the furnace, the dimensions of the material, etc., and the nitriding time t ₂ is appropriately set according to the required thickness, hardness, etc. of the hardened layer 30. do it. Further, the flow rate of nitrogen gas and the flow rate of ammonia gas introduced into the furnace may be appropriately set according to the volume of the furnace, the dimensions of the material, the nitriding temperature T, and the like. Further, an inert gas such as argon gas may be used instead of nitrogen gas.

  Returning to FIG. 2, tempering is performed as necessary after the nitriding quenching (tempering step S <b> 5). As described above, in the present embodiment, the hardened layer 30 having sufficient hardness can be obtained without using alloy steel, so that the temper softening resistance is high and tempering can be effectively performed. . After tempering, the material is washed (cleaning step S6), and surface treatment such as black dyeing is performed (surface treatment step S7). Nitrogen quenching makes it difficult to oxidize the surface of the material and adhere to scales, so that surface finishing such as polishing can be omitted. Finally, a predetermined completion inspection is performed (completion inspection step S8), and the screw shaft 1 is completed by passing this.

  As described above, the screw shaft 1 according to the present embodiment is a screw shaft including the helical thread groove 10 on the outer peripheral surface, and has the hardened layer 30 including nitrogen martensite in the vicinity of the surface. By adopting such a configuration, it is possible to achieve both improvement in accuracy and cost reduction at a high level. That is, the hardened layer 30 can be formed by quenching from a temperature lower than that of conventional induction hardening or carburizing and quenching according to the Fe—N phase diagram, and heat treatment strain can be reduced. A highly accurate screw shaft 1 can be obtained while reducing the cost by omitting the subsequent bending correction and grinding of the thread groove.

  In addition, because it does not require alloy components to enhance hardenability, it is possible not only to use relatively low-priced and low-priced steel, but also to effectively temper by improving temper softening resistance. Therefore, the screw shaft 1 with higher accuracy can be manufactured at a lower cost than before. Moreover, since it becomes possible to improve corrosion resistance with the nitride which exists in the surface, a rust prevention process can be simplified.

  Further, the hardened layer 30 is formed by performing nitriding quenching after forming the screw groove 10 in the material. By doing in this way, since it becomes possible to quench by quenching from a temperature lower than induction quenching or carburizing quenching, heat treatment strain can be reduced. Moreover, since oxidation of the surface of the material and adhesion of scales are unlikely to occur, a good finished skin can be obtained and surface finishing after heat treatment can be omitted. Also, compared with gas soft nitriding, heat treatment can be efficiently performed in a shorter time and with less gas usage. In addition, since oxidation of the material surface, adhesion of scale, and the like are unlikely to occur, a good finish skin can be obtained as compared with conventional heat treatment, and surface finish after heat treatment can be omitted.

  Nitrogen quenching is performed by holding the material in which the thread groove 10 is formed in an atmosphere containing ammonia gas at a predetermined temperature within a range of 590 ° C. or higher and 850 ° C. or lower for a predetermined time and then rapidly cooling. By doing in this way, the hardened layer 30 of desired hardness can be obtained efficiently in a short time.

  The material is a carbon steel material for mechanical structure or a rolled steel material for general structure. By doing in this way, while reducing material cost and rolling can be performed with high precision and easily, the screw shaft 1 can be manufactured at low cost. Moreover, the quality of the screw shaft 1 can be improved by improving the temper softening resistance.

  The thread groove 10 is formed by rolling. By doing in this way, a manufacturing process can be simplified and the screw shaft 1 can be manufactured at low cost.

  Further, the hardened layer 30 has a hardness of Hv500 or more in a range from the surface to a depth of 0.1 mm. By doing in this way, the abrasion resistance and fatigue strength which are requested | required as a screw axis | shaft for screw transmission apparatuses can be obtained.

  Moreover, the manufacturing method of the screw shaft 1 according to the present embodiment includes a first step (screw rolling step S3) for forming the screw groove 10 in the material, and nitrous quenching on the material in which the screw groove 10 is formed. And a second step (nitrogen quenching step S4) to be performed. By adopting such a configuration, it is possible to form the hardened layer 30 containing nitrogen martensite by rapid cooling from a lower temperature than conventional induction hardening or carburizing and quenching according to the Fe-N phase diagram. Since the heat treatment strain can be reduced, the highly accurate screw shaft 1 can be obtained while reducing the cost by omitting the bending correction and the thread groove grinding after the heat treatment.

  In the second step (nitrogen quenching step S4), after the material in which the thread groove 10 is formed is held at a predetermined temperature within a range of 590 ° C. to 850 ° C. for a predetermined time in an atmosphere containing ammonia gas. Cool quickly. By doing in this way, the hardened layer 30 of desired hardness can be obtained efficiently in a short time.

  In the first step (screw rolling step S3), the thread groove 10 is formed by rolling. By doing in this way, a manufacturing process can be simplified and the screw shaft 1 can be manufactured at low cost.

  As mentioned above, although embodiment of this invention was described, the screw shaft of this invention and its manufacturing method are not limited to above-described embodiment, In the range which does not deviate from the summary of this invention, various changes are carried out. Of course, it can be added. For example, in the said embodiment, although the example in case the screw shaft 1 was for ball screws was shown, this invention is not limited to this, The screw shaft 1 may be for slide screws.

  Moreover, in the said embodiment, although the example in the case of forming the thread groove 10 and the thread 20 by rolling was shown, the thread groove 10 and the thread 20 are formed by machining, such as cutting and grinding. There may be. In this case, similar to the manufacture of the conventional positioning ball screw, the thread groove 10 and the thread 20 formed by cutting before the nitriding and quenching are ground after the nitriding and quenching so as to be finished to a desired accuracy. Alternatively, the thread groove 10 and the thread 20 may be formed at one time by cutting or cutting and grinding before the nitriding quenching. Further, the thread groove 10 and the thread 20 formed by rolling before the nitriding and quenching may be ground and finished after the nitriding and quenching.

  In addition, the functions and effects shown in the above embodiment are merely a list of the most preferable functions and effects resulting from the present invention, and the functions and effects of the present invention are not limited to these.

  Examples of the present invention will be described below. Note that the present invention is not limited to these examples.

<Example 1>
In this example, nitriding and quenching were performed on the two test pieces according to the time chart shown in FIG. 3, and the change in radial run-out before and after nitriding and quenching and the axial direction after nitriding and quenching were performed. Elongation was measured. Moreover, the test piece was cut | disconnected after these measurements, and the hardness of the surface vicinity was measured. Each of the two test pieces was obtained by cutting a screw shaft for a slide screw having an outer diameter of 16 mm formed by rolling a material of S45C into a length of 300 mm before heat treatment. The test piece TP1 was formed, and the test piece TP2 was formed with a thread groove of 7 mm lead.

Nitrogen quenching was performed by setting the nitriding temperature T to 750 ° C., the soaking time t ₁ to 30 minutes, and the nitriding time t ₂ to 60 minutes. Further, the supply amount of gas introduced into the furnace was set to a nitrogen gas supply flow rate of 1.0 Nm ³ / Hr with the aim that the ammonia concentration in the furnace atmosphere would be 0.5 vol%. The supply flow rate was set to 0.8 Nm ³ / Hr. The temperature of the oil tank was set to 65 ° C. As shown in FIG. 4A, the radial deflection was measured by rotating the test pieces TP1 and TP2 supported by two V blocks and measuring the amount of deflection at the center. The hardness was measured using a micro Vickers hardness meter, and the hardness from the surface to a depth of 0.5 mm was measured.

  FIG. 4B is a table showing the measurement result of the change in radial deflection and the measurement result of the elongation in the axial direction. The runout after the nitriding and quenching was 0.09 mm for the test piece TP1 and 0.07 mm for the test piece TP2 as opposed to 0.01 mm before the nitriding and quenching. Further, the elongation in the axial direction after the nitriding and quenching was 0.012 mm for the test piece TP1 and 0.020 mm for the test piece TP2.

  The increase in radial runout after nitriding and quenching is a small value of less than 0.1 mm for both test pieces TP1 and TP2, and by applying nitriding and quenching to heat treatment after thread rolling, It was confirmed that the straightening of the bend can be omitted. In addition, in the accuracy grade C5 of the positioning ball screw in JIS B1192, when the allowable value of the accumulated representative lead error (representative movement amount error) when the effective length of the screw portion is 315 mm or less is 0.023 mm, the nitriding quenching The subsequent elongation in the axial direction is lower than both of the test pieces TP1 and TP2, and even when the thread groove is formed by rolling, nitriding quenching is applied to the subsequent heat treatment to dramatically improve the lead accuracy. It was confirmed that the improvement was possible.

  FIG. 4 (c) is a graph showing the measurement result of the hardness of the test piece TP1, and FIG. 4 (d) is a graph showing the measurement result of the hardness of the test piece TP2. In the test piece TP1, the hardness at a distance (depth) 0.1 mm from the surface was HV600 or more, and the hardness at a distance 0.3 mm from the surface was HV400 or more. Further, in the test piece TP2, the hardness at a distance of 0.1 mm from the surface was HV800 or more, and the hardness at a distance of 0.3 mm from the surface was HV500 or more. The deep part hardness (hardness of the base material) was HV350 for the test piece TP1 and HV299 for the test piece TP2. As a result, it was confirmed that a hardened layer having a hardness required for the screw shaft can be formed even when nitrogen quenching is applied to the heat treatment after the thread rolling.

<Example 2>
In this example, the three test pieces were subjected to nitriding and quenching according to the time chart shown in FIG. 3, and the hardness in the vicinity of the surface after the nitriding and quenching was measured with a micro Vickers hardness meter. In addition, the metal structure near the surface after nitriding and quenching was observed with an optical microscope. All three test pieces are pre-heat-treated ball screw screw shafts with thread grooves formed on a S45C material by rolling. The test piece TP3 has a deep thread groove and has a large thread. Was a test piece TP4, and a test piece TP5 was one having a small thread.

Nitrogen quenching involves setting the nitriding temperature T to 750 ° C., the soaking time t ₁ to 30 minutes, and the nitriding time t ₂ to 180 minutes for the test piece TP3 and 60 minutes for the test pieces TP4 and TP5. Set and went. Moreover, the supply amount of the gas introduced into the furnace is set such that the supply flow rate of nitrogen gas is 1.0 Nm ³ / Hr, and the ammonia gas is set so that the ammonia concentration in the furnace atmosphere becomes 0.6 to 1.0 vol%. Was set to 1.5 Nm ³ / Hr. The temperature of the oil tank was set to 65 ° C. The hardness was measured from the surface to a depth of 0.6 mm for the test piece TP3, and the hardness from the surface to a depth of 0.4 mm was measured for the test pieces TP4 and TP5.

  FIG. 5A is a graph showing the measurement results of the hardness of the test piece TP3. In the test piece TP3, the hardness at a distance (depth) of 0.1 mm from the surface is HV700 or more, the hardness at a distance of 0.3 mm from the surface is HV400 or more, and the hardness required for the screw shaft even when the thread groove is deep. It was confirmed that a cured layer of can be formed. The deep hardness (base material hardness) of the test piece TP3 was HV301.

FIG. 5B is a graph showing the measurement result of the hardness of the test piece TP4, and FIG. 5C is a graph showing the measurement result of the hardness of the test piece TP5. Despite a shortened immersion窒時between _{t 2} to 60 minutes, close to HV600 in hardness test piece TP4 at a distance 0.1mm from the surface was a value exceeding HV600 the test piece TP5. As a result, nitriding and quenching originally had a shorter processing time than conventional heat treatment, but it was confirmed that the processing time could be further reduced depending on the required screw shaft specifications. . The depth hardness of the test piece TP4 was HV264, and the depth hardness of the test piece TP5 was HV265.

  Although not shown, observation with an optical microscope confirmed that a good nitrogen martensite structure was formed in the vicinity of the surface in any of the test pieces TP3, TP4, and TP5.

  From the above results, it was confirmed that according to the screw shaft of the above embodiment and the manufacturing method thereof, it is possible to achieve both improvement in accuracy and reduction in cost at a high level.

  The screw shaft and the manufacturing method thereof according to the present invention can be used not only in the field of screw transmission devices but also in the field of various screws.

1 Screw shaft 10 Screw groove 30 Hardened layer S3 Thread rolling process S4 Nitrogen quenching process

Claims (9)

A screw shaft provided with a helical thread groove on the outer peripheral surface,
It has a hardened layer containing nitrogen martensite in the vicinity of the surface,
Screw shaft. The hardened layer is formed by performing nitriding quenching after forming the thread groove in a material,
The screw shaft according to claim 1. The nitriding quenching is performed by rapidly cooling the raw material in which the thread groove is formed at a predetermined temperature within a range of 590 ° C. or higher and 850 ° C. or lower in an atmosphere containing ammonia gas and then rapidly cooling the raw material. Features
The screw shaft according to claim 2. The material is a carbon steel material for mechanical structure or a rolled steel material for general structure,
The screw shaft according to claim 2 or 3. The thread groove is formed by rolling,
The screw shaft according to any one of claims 1 to 4. The hardened layer has a hardness in a range from the surface to a depth of 0.1 mm of Hv500 or more,
The screw shaft according to any one of claims 1 to 5. A first step of forming thread grooves in the material;
A second step of performing nitriding quenching on the material in which the thread groove is formed,
Manufacturing method of screw shaft. In the second step, the material in which the thread groove is formed is rapidly cooled after being held for a predetermined time at a predetermined temperature within a range of 590 ° C. or higher and 850 ° C. or lower in an atmosphere containing ammonia gas,
The manufacturing method of the screw shaft of Claim 7. In the first step, the thread groove is formed by rolling,
The manufacturing method of the screw shaft of Claim 7 or 8.

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