JP2016079458A - Wear-resistant steel and surface modification method of steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wear-resistant steel capable of exhibiting high wear resistance and having small distortion under a condition free from a lubricant such as a lubricating oil.SOLUTION: A wear-resistant steel of the present invention has, on a surface of a round shaft TS, a structure where a hard powder is bonded to components of the round shaft TS. The structure is formed by embedding treatment of a hard powder into the surface of the round shaft TS, performed by rotating the round shaft TS made of a steel, contacting a tip of a tool 4 with an outer peripheral surface of the round shaft TS, relatively moving the round shaft TS and the tool 4 in the axial direction of the round shaft TS while rotating the tool 4, and supplying the hard powder harder than the round shaft TS to a contact part between the round shaft TS and the tool 4, and then subjecting the round shaft TS, in which the hard powder has been embedded, to surface heat treatment.SELECTED DRAWING: Figure 1

Description

  The present invention provides high wear resistance under conditions where there is no lubricant such as lubricating oil, and imparts wear resistance by surface-modifying the wear-resistant steel with less distortion and the steel. The present invention relates to a method for surface modification of a steel material.

  Conventionally, as one method for strengthening only the steel surface layer by heat treatment, surface heat treatment such as carburizing treatment has been applied to sliding members of various machines. The surface heat treatment can provide a relatively thick hardened layer easily and has excellent wear resistance compared to the untreated material, but may not exhibit sufficient wear resistance depending on the sliding conditions and environment. In particular, the wear resistance of sliding parts where the lubricating oil has run out or to which the lubricating oil cannot be applied is not sufficient, and its improvement is an urgent issue.

  In view of such a situation, it is a common practice to increase the wear resistance by forming a hard thin film on the surface of a substrate. As a method of forming a hard thin film on the surface of the base material, a method of forming a thin film on the surface of the base material by heating and softening the material by frictional heat generation (Patent Document 1), or forming a thin film by an arc ion plating method Methods (Patent Documents 2 and 3) have been known.

  However, the method of forming a thin film by heating and softening a material with high frictional heat has a problem that the base material itself may be deformed by the influence of heat. In addition, the method of forming a thin film by the arc type ion plating method has a problem that a large-scale apparatus having a vacuum generator and a plurality of processing chambers is required and the cost is high.

  In view of this, the inventors of the present invention disclosed in Patent Document 4 that a flat or conical tip surface of a tool in which a round shaft is rotated and a spiral groove is formed on the outer peripheral surface is connected to a line or a point on the outer peripheral surface of the round shaft. The hard powder is embedded in the surface of the round shaft by bringing it into contact with the round shaft and the tool by feeding fine hard powder harder than the round shaft with the rotation of the tool. A method of modifying the surface of the round shaft was proposed.

JP 2006-102803 A Japanese Patent Laid-Open No. 7-118832 JP 2004-138128 A Japanese Patent No. 5289990

  According to the modification method proposed by the present inventors in Patent Document 4, the hard powder is embedded on the surface of the round shaft and a non-directional hard film is created in an island shape, so that the wear resistance is improved. In addition, since the tool and the round shaft rotate relative to each other in the axial direction of the round shaft and rotate in line contact or point contact, high heat is not generated, and therefore, distortion and deformation of the round shaft are suppressed. The effect of being done etc. was acquired. However, there is a problem that the wear resistance cannot be exhibited under the sliding condition where there is no lubricant such as lubricating oil and the friction coefficient is high.

  Recently, steel materials that exhibit high wear resistance even under non-lubricated conditions where lubrication cannot be performed have been demanded. As a technique for further improving the wear resistance, there is a method of firing the surface of a steel material. According to this method, by firing the surface of the steel material in which the hard powder is embedded, the adhesion of the hard powder to the steel material is improved, and further improvement in wear resistance is expected. However, if the steel material is simply fired, the steel material is distorted.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a wear-resistant steel material that can exhibit high wear resistance under conditions where there is no lubricant such as lubricating oil and that has little distortion. And It is another object of the present invention to provide a method for modifying the surface of a steel material that can be made into a wear-resistant steel material having excellent wear resistance and little distortion by subjecting the steel material to surface modification.

  In order to achieve the above-mentioned object, the wear-resistant steel material of the present invention rotates a round shaft made of a steel material, makes the tip of a tool contact the outer peripheral surface of the round shaft, and rotates the tool while rotating the tool. The tool is relatively moved in the axial direction of the round shaft, and hard powder harder than the round shaft is supplied to the contact portion between the round shaft and the tool, thereby embedding the hard powder on the surface of the round shaft. And a structure formed by subjecting the round shaft embedded with the hard powder to a surface heat treatment, the hard powder having a structure combined with a component of the round shaft on the surface of the round shaft. It is characterized by that.

According to a preferred aspect of the present invention, the surface heat treatment is carburizing and quenching.
According to a preferred aspect of the present invention, the round shaft is made of chromium molybdenum steel or low carbon steel.
In a preferred aspect of the present invention, the hard powder is any one of molybdenum powder, chromium powder, silicon powder, and tungsten carbide powder.

  In order to achieve the above-described object, the surface modification method for a steel material according to the present invention comprises rotating a round shaft made of steel material, bringing a tip of a tool into contact with an outer peripheral surface of the round shaft, and rotating the tool while rotating the tool. The hard powder is embedded in the surface of the round shaft by relatively moving the shaft and the tool in the axial direction of the round shaft and supplying hard powder harder than the round shaft to the contact portion between the round shaft and the tool. It is characterized in that the round shaft embedded with the hard powder is subjected to surface heat treatment.

According to a preferred aspect of the present invention, the surface heat treatment is carburizing and quenching.
According to a preferred aspect of the present invention, the round shaft is made of chromium molybdenum steel or low carbon steel.
According to a preferred aspect of the present invention, the hard powder is made of any one of molybdenum powder, chromium powder, silicon powder, and tungsten carbide powder.

According to a preferred aspect of the present invention, after the surface heat treatment, the round shaft is rotated, the tip of the finishing tool is brought into contact with the outer peripheral surface of the round shaft, and the round shaft is rotated while the finishing tool is rotated. A finishing tool is relatively moved in the axial direction of the round shaft to perform a finishing process.
According to a preferred aspect of the present invention, after the embedding process and before the surface heat treatment, the round shaft is rotated, the tip of a finishing tool is brought into contact with the outer peripheral surface of the round shaft, and the finishing While the tool is rotated, the round shaft and the finishing tool are relatively moved in the axial direction of the round shaft to perform a finishing process.
According to a preferred aspect of the present invention, the round shaft is used under a condition without a lubricant.

  According to the present invention, the hard powder is embedded in the surface of the steel material, and further the surface heat treatment is performed on the steel material in which the hard powder is embedded, thereby obtaining a wear-resistant steel material having excellent wear resistance and low distortion. be able to. This wear-resistant steel material can exhibit high wear resistance under conditions where there is no lubricant such as lubricating oil.

FIG. 1 is a schematic cross-sectional view showing an embedding process in a steel surface modification method according to an embodiment of the present invention. FIG. 2 is a schematic perspective view showing the relationship between the test piece and the tool in the embedding process. FIG. 3 is a flowchart of carburizing and quenching processing according to an embodiment of the present invention. FIG. 4A is a front view showing the relationship between the test piece and the conical tool in the finishing process. FIG. 4B is a side view showing the relationship between the test piece and the conical tool in the finishing process. FIG. 5 is an optical microscope observation photograph of the surface structure of the modified carburized steel. FIG. 6 is a graph showing the measurement results of micro Vickers hardness of carburized steel and modified carburized steel. It is the optical microscope observation photograph of the low magnification of the surface structure | tissue of the chromium molybdenum steel which performed the finishing process after the embedding process of Mo powder. It is the optical microscope observation photograph of the high magnification of the surface structure | tissue of the chromium molybdenum steel which performed the finishing process after the embedding process of Mo powder. It is the optical microscope observation photograph of the low magnification of the surface structure | tissue of the chromium molybdenum steel which gave the finishing process after performing the embedding process and surface heat treatment of Mo powder. It is the optical microscope observation photograph of the high magnification of the surface structure | tissue of the chromium molybdenum steel which gave the finishing process after performing the embedding process and surface heat treatment of Mo powder. FIG. 9 is a diagram showing a form of a reciprocating test. FIG. 10 is a table showing conditions for a reciprocating test and a fretting wear test. FIG. 11A is a diagram showing wear marks of carburized steel produced by a reciprocating test. FIG. 11B is a diagram showing wear marks of the modified carburized steel generated by the reciprocating test. FIG. 12A is a diagram showing wear marks of carburized steel produced by a fretting wear test. FIG. 12B is a diagram showing wear marks of the modified carburized steel produced by the fretting wear test. FIG. 13 is a table showing specific wear amounts of the modified carburized steel and carburized steel in the reciprocating test and the fretting wear test. FIG. 14 is a bar graph for comparing the specific wear amounts shown in FIG. FIG. 15A is an optical microscope observation photograph of the surface of the test piece after performing a reciprocating motion test on chromium molybdenum steel subjected only to the Mo powder embedding process. FIG. 15B is an optical microscopic observation photograph of the surface after the adhesive tape has been applied to the surface of the test piece after the reciprocating motion test was performed on chromium molybdenum steel subjected only to the Mo powder embedding process and peeled off. FIG. 16A is an optical microscope observation photograph of the surface after performing a reciprocation test on chromium molybdenum steel subjected to Mo powder embedding treatment and surface heat treatment. FIG. 16B is an optical microscopic observation photograph of the surface after the adhesive tape is attached to the surface of the test piece after the reciprocation test was performed on the chromium molybdenum steel subjected to the Mo powder embedding treatment and the surface heat treatment, and then peeled off. is there. FIG. 17 shows the specific wear amount when the surface heat treatment is applied to the test piece of chromium molybdenum steel not subjected to the embedding treatment, and the surface of the test piece of chromium molybdenum steel embedded with Mo powder. Specific wear amount when heat treatment is performed and when surface heat treatment is not performed, and specific wear amount when the surface heat treatment is applied to the specimen of chromium molybdenum steel embedded with Cr powder and when surface heat treatment is not performed It is a table | surface which shows. FIG. 18 is a bar graph for comparing the specific wear amounts shown in FIG. FIG. 19 shows a specific wear amount when a surface heat treatment is applied to a chromium molybdenum steel specimen embedded with Si powder and a specific wear amount when a surface heat treatment is applied to a chromium molybdenum steel specimen embedded with WC powder. It is a table | surface which shows.

  Hereinafter, an embodiment of a surface modification method for a steel material according to the present invention will be described with reference to FIGS. In FIG. 1 to FIG. 19, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a schematic cross-sectional view showing an embedding process in a steel surface modification method according to an embodiment of the present invention. As shown in FIG. 1, the apparatus for performing the embedding process includes a cylindrical portion 1 having an open lower end and a funnel-shaped portion 2 connected to the upper end portion of the cylindrical portion 1. The test specimen TS is installed in the lower end opening of the cylindrical portion 1. In the present embodiment, a round bar (round shaft) of chromium molybdenum steel (SCM420) is used as the test piece TS. A tool insertion hole 3 is formed in the cylindrical portion 1, and a cylindrical tool 4 is inserted into the tool insertion hole 3. The inner diameter of the tool insertion hole 3 is set slightly larger than the outer diameter of the tool 4. Mo powder (molybdenum powder) as hard powder is continuously supplied to the funnel-shaped portion 2 from a hopper (not shown) or the like. In this embodiment, the # 3 mesh is used as the Mo powder, and in order to improve the fluidity of the Mo powder, high-speed spherical particles (high-speed steel (HSS) particles) having an average particle diameter of 50 μm are used in a bulk ratio of 1: 9 is mixed (the ratio of the high-speed particles 9 to the Mo powder 1).

  In the present embodiment, the steel material constituting the test piece (round shaft) TS is chromium molybdenum steel (SCM material), but a steel material having a carbon content (mass percent concentration) of 0.3% or less may be used. Good. Therefore, a low carbon steel having a carbon content of 0.25% or less can be used as a steel material. Examples of such low carbon steel include S20C and S25C.

  The hard powder embedded in the outer peripheral surface of the test piece TS is harder than the test piece (round shaft) TS. As such a hard powder, in addition to the Mo powder, a powder made of a material (spraying material) used for thermal spraying such as silicon (Si), tungsten carbide (WC), or chromium (Cr) may be used. As the hard powder, it is preferable to select a material having excellent tribological characteristics (particularly friction / wear characteristics). Moreover, it is preferable that the material which couple | bonds favorably with the structural component of test piece TS is selected by performing the surface heat processing mentioned later. For example, since chromium molybdenum steel already contains Cr and Mo in the chromium material, it is assumed that the Cr powder and the Mo powder are well bonded to the constituent components of the specimen TS made of chromium molybdenum steel. Therefore, when chromium molybdenum steel is used for the test piece TS, it is preferable to select Mo powder or Cr powder as the hard powder.

  The tool 4 is made of a cylindrical body made of a hard and wear-resistant material such as tungsten carbide (WC). In the tool 4, a spiral groove 4 s is formed on the outer peripheral surface of the portion inserted in the tool insertion hole 3. The tool 4 has a flat or conical tip surface 4f. The base end portion of the tool 4 is attached to a machine tool such as a drilling machine so that a load can be applied to the test piece TS made of a round bar (round shaft) through the tip surface 4f while the tool 4 is rotated. It has become.

  In order to embed Mo powder in the surface of the test piece TS made of a round bar using the apparatus configured as shown in FIG. 1, the tip surface 4f of the tool 4 is brought into line contact or point contact with the outer peripheral surface of the test piece TS. Then, Mo powder and high-speed particles are continuously supplied to the funnel-shaped portion 2. Then, the tool 4 is rotated and the test piece TS is rotated. As the tool 4 rotates, Mo powder and high-speed particles are fed into the contact portion between the tool 4 and the test piece TS by the spiral groove 4s. The tool 4 is moved in the axial direction of the test piece TS along the surface of the test piece TS while being rotated. The tool 4 may be reciprocated a plurality of times in the axial direction of the test piece TS. Instead of moving the tool 4, the test piece TS may be moved in the axial direction of the test piece TS.

  FIG. 2 is a schematic perspective view showing the relationship between the test piece TS and the tool 4 in the embedding process. As shown in FIG. 2, the test piece TS is rotated, the tool 4 is rotated, and the tool 4 is moved in the axial direction of the test piece TS along the surface of the test piece TS to perform the embedding process.

  During the embedding process, the tip surface 4f of the tool 4 and the outer peripheral surface of the test piece TS rotate and slide in line contact or point contact, so that they were fed into the contact portion without applying a large load. A high surface pressure acts between the Mo powder and the test piece TS to cause cold welding, that is, welding at a low temperature due to high contact pressure or shear force. As a result, Mo powder is embedded in the outer peripheral surface of the test piece TS, and an island-like film having no directionality is formed on the surface of the test piece TS. Thus, in the state where Mo powder exists between the front end surface 4f of the tool 4 and the outer peripheral surface of the test piece TS, the test piece TS and the tool 4 are brought into contact with each other while being rotated, whereby the test piece TS Mo can be embedded in the outer peripheral surface.

  The surface of the specimen TS wears under high surface pressure and shearing force, but most of the wear powder mixes with the Mo powder and retransfer occurs, resulting in very little wear on the specimen TS. And since high temperature does not generate | occur | produce, distortion and deformation | transformation of the test piece TS can be suppressed.

  Next, surface heat treatment is performed on the test piece TS in which the hard powder is embedded. In this surface heat treatment, by heating the surface of the test piece TS, the hard powder embedded in the surface of the test piece TS is firmly bonded to the constituent components of the test piece TS, that is, the hard powder and the test piece TS are bonded. It is a process executed to realize alloying and solid phase bonding by permeation diffusion at an atomic level between constituent components.

  In the present embodiment, the surface heat treatment is a carburizing and quenching process including a carbon infiltration process and a quenching process performed after the carbon infiltration process. The carbon infiltration treatment is a treatment for infiltrating carbon into the surface of the steel material by heating the steel material in the carburizing agent. The quenching process is a process of rapidly cooling a steel material heated to a predetermined high temperature state. By performing the quenching process, the structure of the steel material is transformed into a martensite structure. A nitriding treatment or a carbonitriding quenching treatment may be performed instead of the carburizing quenching treatment. The nitriding treatment is a treatment for permeating nitrogen into the surface of the steel material by heating the steel material in an atmosphere containing nitrogen such as ammonia. Carbonitriding and quenching treatment is a treatment that heats steel in an atmosphere containing carbon and nitrogen to infiltrate the surface of the steel with carbon and nitrogen, and then performs a quenching treatment, thereby hardening the surface of the steel. .

  FIG. 3 shows a flowchart of the carburizing and quenching process according to the present embodiment. In the carburizing and quenching process shown in FIG. 3, the specimen TS is maintained at a temperature of 930 ° C. for about 7 hours in a carburizing agent (for example, in a gas atmosphere containing carbon dioxide, hydrogen, methane, water vapor, and the like). (Carbon permeation treatment). The holding temperature and holding time of the test piece TS in the carbon infiltration treatment are appropriately determined according to the material of the test piece TS, the material of the hard powder, and the like. The holding temperature is determined from, for example, a range from 900 ° C. to 950 ° C. By performing the carbon infiltration treatment, carbon penetrates and diffuses on the surface of the test piece TS.

  Next, the test piece TS is held for about 1.5 hours in a state where the temperature of the test piece TS is lowered to 830 ° C., and immediately after that, it is immersed in oil and rapidly cooled (quenching treatment). The temperature of the cooled specimen TS is 20 ° C. Instead of cooling in oil, the test piece TS may be cooled by immersing it in water. In the carburizing and quenching process shown in FIG. 3, after the quenching process is completed, the test piece TS is tempered. In the tempering process shown in FIG. 3, the test specimen TS is held at a temperature of 180 ° C. for about 1.5 hours. The carburizing and quenching process is a process including at least a carbon infiltration process and a quenching process. Therefore, the carburizing and quenching process may or may not include a tempering process.

  The carbon infiltration treatment creates a carbon-rich layer on the surface of the steel material and makes the steel material ready for quenching. By quenching the steel material subjected to the carbon infiltration treatment, the surface structure of the steel material in which the Mo powder is embedded is transformed into martensite, and a hard needle-like structure is formed. By performing such surface heat treatment (carburizing and quenching treatment), a hard powder embedded in the surface of the steel material is formed on the surface of the specimen TS because the structure in which the hard powder is firmly bonded to the structural components of the steel material is formed. High wear resistance can be imparted. Moreover, since the surface of steel material itself hardens | cures by performing a carburizing quenching process, still higher abrasion resistance can be provided to the surface of steel material. Furthermore, since the distortion generated in the steel material during the carburizing and quenching process is extremely small, no large distortion occurs in the steel material.

  Next, for the purpose of improving the surface roughness of the modified surface of the test piece TS, a finishing process (burnishing in a lubricating oil) is performed using a conical tool. 4A and 4B are views showing the relationship between the test piece TS and the conical tool 6 in the finishing process. The conical tool 6 is a cemented carbide tool with a DLC film. 4A and 4B, the test piece TS is rotated while the conical surface 6c of the conical tool 6 is pressed against the outer peripheral surface of the test piece TS under lubrication, and the conical tool 6 is rotated and tested. The burnishing process is performed by moving the specimen TS in the axial direction along the surface of the specimen TS. Thereby, the surface roughness of the test piece TS is improved and smoothed.

  In this embodiment, the embedding process, the surface heat treatment, and the finishing process are performed in this order, but the surface modification method of the present invention is not limited to this order. The embedding process, the finishing process, and the surface heat treatment may be performed in this order.

  FIG. 5 is an optical microscope observation photograph of the surface structure of the modified carburized steel. The modified carburized steel refers to a test piece TS (chromium molybdenum steel) in which embedding treatment, finishing treatment, and surface heat treatment (carburizing treatment and quenching) are performed in this order in accordance with the above-described embodiment. The order of finishing treatment and surface heat treatment may be reversed.

  As shown in FIG. 5, depressions were observed on the surface of the modified carburized steel. This depression is formed during the embedding process, and the presence of this depression is considered to allow carbon to penetrate into the test piece TS during the carburizing process. In order to confirm this point, the micro Vickers hardness (indentation load) of the steel material subjected only to the surface heat treatment (carburizing and quenching treatment) and the above modified carburized steel subjected to the embedding treatment, finishing treatment, and surface heat treatment. : 0.49 N). In the following description, a steel material that has undergone only surface heat treatment (carburizing and quenching treatment) is referred to as carburized steel.

  FIG. 6 is a graph showing the measurement results of the micro Vickers hardness of the modified carburized steel and the carburized steel. In FIG. 6, the horizontal axis represents the Vickers hardness [HV] of the test piece, and the vertical axis represents the distance [μm] from the surface of the test piece toward the inside. In FIG. 6, white circles show the measurement results of the modified carburized steel, and black circles show the measurement results of the carburized steel. As described above, the Mo powder is not embedded in the carburized steel.

  As is apparent from the measurement results shown in FIG. 6, the outermost surface of the modified carburized steel is about 90 harder in micro Vickers hardness than the outermost surface of the carburized steel. This is presumably because the outermost surface of the modified carburized steel in which the Mo powder was embedded was hardened by surface heat treatment (carburizing and quenching treatment). The micro Vickers hardness other than the outermost surface showed no clear difference between the modified carburized steel and the carburized steel. As can be seen from this measurement result, by performing the carburizing and quenching process after the Mo powder embedding process, the carbon penetrates the outermost surface where the Mo powder is embedded, and the outermost surface of the steel material can be cured. .

  In order to confirm that the outermost surface of the steel material is hardened by carburizing and quenching treatment, chromium molybdenum steel that has been subjected to finishing treatment after the Mo powder embedding treatment, Mo powder embedding treatment and surface heat treatment (carburizing and quenching treatment) A chromium-molybdenum steel was prepared after finishing. FIG. 7A and FIG. 7B are optical microscopic observation photographs of the surface structure of chromium molybdenum steel that has been subjected to a finishing process after the Mo powder embedding process. FIG. 7A is a low-magnification optical microscope observation photograph, and FIG. 7B is a high-magnification optical microscope observation photograph. FIG. 8A and FIG. 8B are optical microscope observation photographs of the surface structure of chromium molybdenum steel that has been subjected to the finishing treatment after the Mo powder embedding treatment and the surface heat treatment. FIG. 8A is a low magnification optical microscope observation photograph, and FIG. 8B is a high magnification optical microscope observation photograph.

  7A and FIG. 8A are black spots that are formed during the embedding process. Comparing FIG. 7A and FIG. 8A, it can be seen that the chromium molybdenum steel that has not been subjected to the carburizing and quenching treatment shown in FIG. 7A has a smaller dent area than the chromium molybdenum steel that has been subjected to the carburizing and quenching treatment shown in FIG. 8A. Moreover, the fine black spot in the photograph of FIG. 8B is Mo powder. In FIG. 8B, many Mo powders can be observed, whereas in FIG. 7B, almost no Mo powder can be observed. This is because the outermost surface of the chrome molybdenum steel that has been carburized and hardened is hardened, so that the outermost surface is not scraped by the conical tool 6 (see FIGS. 4A and 4B) during the finishing process, and is formed during the embedding process. This is because the hollows and the embedded Mo powder remain almost intact. On the other hand, in chromium molybdenum steel that has not been carburized and quenched, the outermost surface is scraped by the conical tool 6 during the finishing process, so the area of the dent is reduced, and the Mo powder together with the outermost steel material It will be scraped off. From these comparisons, it can be seen that when the carburizing and quenching process is performed after the embedding process, the outermost surface of the steel material is hardened.

  Next, in order to investigate the effect of improving the wear resistance by the surface modification treatment, a reciprocating test and a fretting wear test were performed on the modified carburized steel and the carburized steel as a wear test. Carburized steel was used as a comparative material to study the wear resistance of the modified carburized steel.

  FIG. 9 is a diagram showing a form of a reciprocating test. In the reciprocating test, as shown in FIG. 9, the hard material is reciprocated in a state where the test piece (steel material whose wear resistance is to be investigated, that is, modified carburized steel or carburized steel) and the hard material are in point contact. I moved it. In the fretting wear test, the hard material was reciprocated with a small stroke while the test piece and the hard material were in point contact.

  FIG. 10 is a table showing conditions for a reciprocating test and a fretting wear test. As shown in FIG. 10, high-carbon chromium bearing steel (SUJ2, HV770) was used as the hard material. The reciprocating test and the fretting wear test were performed in the atmosphere and under non-lubricated conditions. In this test, the relative humidity was adjusted so that the conditions were as much as possible in consideration of the influence of the relative humidity. Specifically, the relative humidity (RH) was adjusted to 29 ± 7%. The stroke of the reciprocating motion was 20 mm, the number of repetitions of the reciprocating motion was 21600 times (repetition speed 1.0 Hz, 6 hours), and the contact load was 4.9 N. The stroke of the reciprocating motion in the fretting wear test was 0.1 mm, the number of reciprocating motions was 216000 times (repetition speed 3.0 Hz, 20 hours), and the contact load was 9.8 N.

  FIG. 11A is a diagram showing wear marks of carburized steel produced by a reciprocating test, and FIG. 11B is a diagram showing wear marks of modified carburized steel produced by a reciprocating test. FIG. 12A is a diagram showing the wear marks of the carburized steel produced by the fretting wear test, and FIG. 12B is a diagram showing the wear marks of the modified carburized steel produced by the fretting wear test.

  As shown in FIG. 11A, the wear scar diameter of the carburized steel produced by the reciprocating test was 1.88 mm. On the other hand, as shown in FIG. 11B, the diameter of the wear scar of the modified carburized steel produced by the reciprocating test was 1.63 mm. This test result shows that the wear scar diameter of the modified carburized steel is about 13% smaller than the wear scar diameter of the carburized steel. Furthermore, as shown to FIG. 11A, the maximum depth of the wear trace of the carburized steel produced by the reciprocation test was 73.6 micrometers. On the other hand, as shown in FIG. 11B, the maximum depth of the wear scar of the modified carburized steel produced by the reciprocating test was 43.8 μm. From this test result, it can be seen that the depth of the wear mark of the modified carburized steel is about 40% smaller than the depth of the wear mark of the carburized steel.

  As shown in FIG. 12A, the wear scar diameter of the carburized steel produced by the fretting wear test was 1.15 mm. On the other hand, as shown in FIG. 12B, the diameter of the wear scar of the modified carburized steel produced by the fretting wear test was 0.87 mm. This test result shows that the diameter of the wear marks of the modified carburized steel is about 24% smaller than the diameter of the wear marks of the carburized steel. Furthermore, as shown to FIG. 12A, the maximum depth of the wear trace of the carburized steel produced by the fretting wear test was 15.1 μm. On the other hand, as shown in FIG. 12B, the maximum depth of the wear scar of the modified carburized steel produced by the fretting wear test was 6.4 μm. From this test result, it can be seen that the depth of the wear mark of the modified carburized steel is about 60% smaller than the depth of the wear mark of the carburized steel.

The specific wear amount of the modified carburized steel and carburized steel in the reciprocating motion test was calculated from the shape of the wear marks shown in FIGS. 11A and 11B. Similarly, the specific wear amount of the modified carburized steel and carburized steel in the fretting wear test was calculated from the shape of the wear marks shown in FIGS. 12A and 12B. FIG. 13 is a table showing specific wear amounts [mm ² / N] of the modified carburized steel and carburized steel in the reciprocating test and the fretting wear test. FIG. 14 is a bar graph for comparing the specific wear amounts shown in FIG.

As shown in FIGS. 13 and 14, the specific wear amount of the carburized steel in the reciprocating test is 2.2 × 10 ⁻⁸ mm ² / N, and the specific wear amount of the modified carburized steel in the reciprocating test is 0. It was 9 × 10 ⁻⁸ mm ² / N. From this result, it can be seen that the specific wear amount of the modified carburized steel is reduced to about 41% of the specific wear amount of the carburized steel in the atmosphere and under non-lubricated conditions. The specific wear amount of the carburized steel in the fretting wear test is 2.2 × 10 ⁻⁸ mm ² / N, and the specific wear amount of the modified carburized steel in the fretting wear test is 0.5 × 10 ⁻⁸ mm ² / N. N. From this result, it is understood that the specific wear amount of the modified carburized steel is reduced to about 23% of the specific wear amount of the carburized steel under the atmosphere and in the non-lubricated condition.

  The reason why the wear resistance is improved is that the Mo powder embedded in the surface of the test piece TS is firmly bonded to the constituent components of the test piece TS, and the surface of the test piece TS by the carburizing and quenching process is cured. Conceivable. In addition to these reasons, the generation of compressive residual stress due to the surface modification treatment and the increase in surface hardness associated with the generation of this compressive residual stress can be considered. Moreover, since a structure rich in Mo is created on the outermost surface of the steel material, a decrease in wear (decrease in friction coefficient) associated with the formation of Mo carbides and Mo oxides during carburizing and quenching can be considered. The test results shown in FIGS. 13 and 14 show that the wear resistance of the modified carburized steel is significantly improved in the air and without lubrication. The wear resistance of the modified carburized steel is also significantly improved in a vacuum or in an inert gas atmosphere.

  In order to confirm that the Mo powder embedded in the surface of the test specimen TS is firmly bonded to the constituent components of the test specimen TS by performing a carburizing and quenching process, a chromium molybdenum steel subjected only to the Mo powder embedding process and A chromium molybdenum steel subjected to Mo powder embedding treatment and surface heat treatment (carburizing and quenching treatment) was prepared. The prepared chromium-molybdenum steel was brought into point contact with the hard material (see FIG. 9), and a single reciprocation test was performed in which the hard material was moved by one reciprocation in this state. The contact load was 24.5N. The surface structure of the chromium molybdenum steel immediately after the reciprocation test was performed was observed with an optical microscope. Further, after observation with an optical microscope, an adhesive tape was attached to the surface of the chromium molybdenum steel and peeled off, and then the surface structure of the chromium molybdenum steel was again observed with an optical microscope.

  FIG. 15A is an optical microscope observation photograph of the surface of the test piece TS after performing a reciprocation test on chromium molybdenum steel subjected only to the Mo powder embedding process. FIG. 15B is an optical microscopic observation photograph of the surface after the adhesive tape is applied to the surface of the test piece TS after the reciprocating motion test is performed on the chromium molybdenum steel subjected only to the Mo powder embedding process and peeled off. . As can be seen from the comparison between FIG. 15A and FIG. 15B, it was observed that the surface texture at the center of the photograph was removed by the adhesive tape. Therefore, if only the Mo powder embedding process is performed, the embedded Mo powder is easily detached as wear powder.

  FIG. 16A is an optical microscope observation photograph of the surface of the test piece TS after performing a reciprocation test on chromium molybdenum steel subjected to Mo powder embedding treatment and surface heat treatment. FIG. 16B is an optical microscope observation photograph of the surface after the adhesive tape is attached to the surface of the test piece TS after the reciprocation test was performed on the chromium molybdenum steel subjected to the Mo powder embedding treatment and the surface heat treatment, and then peeled off. It is. As can be seen from the comparison between FIG. 16A and FIG. 16B, no difference was observed in the surface structure of the chromium molybdenum steel. Therefore, when surface heat treatment is performed after the Mo powder embedding process, the Mo powder is firmly bonded to the constituent components of the steel material and is not easily detached.

FIG. 17 shows the specific wear amount when Mo is applied to a test piece of chromium molybdenum steel that has not been subjected to embedding treatment of hard powder, and Mo when Mo is not subjected to such surface heat treatment. The specific wear amount when the surface heat treatment is applied to the chrome molybdenum steel specimen embedded with powder and when the surface heat treatment is not applied, and the surface heat treatment is applied to the chrome molybdenum steel specimen embedded with Cr powder (chromium powder) It is a table | surface which shows the amount of specific abrasion when not giving surface heat processing with the case where it gave. FIG. 18 is a bar graph for comparing the specific wear amounts shown in FIG. The vertical axis in FIG. 18 represents the specific wear amount [mm ² / N]. Cr powder was embedded in the surface of chromium molybdenum steel in the same manner as Mo powder using the apparatus shown in FIG. The specific wear amount shown in FIGS. 17 and 18 was measured after a reciprocating test (see FIG. 9) was performed under the experimental conditions shown in FIG.

When the surface heat treatment was not performed, the specific wear amount of the test piece not subjected to the embedding treatment was 2.8 × 10 ⁻⁸ mm ² / N, and the specific wear amount of the test piece embedded with the Mo powder was 2 .8 × a ¹⁰ -8 ^mm 2 / N, the specific wear rate of embedded specimens Cr powder was ^{3.4 × 10 -8 mm 2 / N} . Therefore, there is no great difference between these specific wear amounts, and it is understood that the wear resistance is not improved so much by simply embedding Mo powder or Cr powder in chromium molybdenum steel.

The specific wear amount when the surface heat treatment was performed on the test piece not subjected to the embedding treatment and the specific wear amount when the surface heat treatment was not performed were 2.2 × 10 ⁻⁸ mm ² / N, respectively. It is 2.8 × 10 ⁻⁸ mm ² / N, and it can be seen that the wear resistance is improved to some extent by performing the surface heat treatment. On the other hand, the specific wear amount when the surface heat treatment is performed on the specimen TS embedded with Mo powder and the specific wear amount when the surface heat treatment is not performed are 0.9 × 10 ⁻⁸ mm ² / N and 2.8 × 10 ⁻⁸ mm ² / N. Moreover, the specific wear amount when the surface heat treatment is performed on the specimen TS embedded with the Cr powder and the specific wear amount when the surface heat treatment is not performed are 0.6 × 10 ⁻⁸ mm ² / N, respectively. It was 3.4 × 10 ⁻⁸ mm ² / N. From these results, the wear resistance is significantly improved by applying surface heat treatment (carburizing quenching treatment, nitriding treatment, or carbonitriding quenching treatment) to steel materials embedded with hard powder such as Mo powder or Cr powder by embedding treatment. I understand that

  FIG. 19 shows the specific wear amount and the WC powder (tungsten carbide powder) embedded when surface heat treatment (carburizing and quenching) was performed on a specimen of chromium molybdenum steel embedded with Si powder (silicon powder) as a hard powder. It is a table | surface which shows the specific wear amount at the time of giving surface heat processing (carburizing hardening process) to the test piece of chromium molybdenum steel. Si powder and WC powder were embedded on the surface of chromium molybdenum steel in the same manner as Mo powder using the apparatus shown in FIG. The specific wear amount shown in FIG. 19 was measured after a reciprocating test (see FIG. 9) was performed under the experimental conditions shown in FIG. However, the relative humidity RH is adjusted to 35 ± 1% in the reciprocating test of the specimen subjected to the Si powder embedding treatment and the surface heat treatment, and the reciprocating motion of the test specimen subjected to the WC powder embedding treatment and the surface heat treatment. In the test, it was adjusted to 29 ± 3%.

As shown in FIG. 19, the specific wear amount when the surface heat treatment is performed on the test piece TS embedded with Si powder and the specific wear amount when the surface heat treatment is performed on the test piece TS embedded with WC powder are ^They were 0.5 × 10 ⁻⁸ mm ² / N and 0.8 × 10 ⁻⁸ mm ² / N, respectively. These specific wear amounts, the specific wear amount when the surface heat treatment is applied to the test piece TS embedded with Mo powder, and the ratio when the surface heat treatment is applied to the test piece TS embedded with Cr powder shown in FIG. There is no significant difference between the amount of wear. From these results, wear resistance is significantly improved by applying surface heat treatment (carburizing quenching, nitriding, or carbonitriding quenching) to steel materials embedded with hard powder of Si powder or WC powder by embedding process. I understand that

  As described above, according to the present invention, the steel material is embedded with a mixed powder composed of hard powder such as Mo powder, Cr powder, Si powder, or WC powder and Heiss particles, and then the steel material By performing the surface heat treatment, it is possible to obtain a wear-resistant steel material having high wear resistance and no distortion. This wear-resistant steel material exhibits high wear resistance under non-lubricated conditions in a gas atmosphere.

  Although the embodiment of the present invention has been described so far, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention may be implemented in various different forms within the scope of the technical idea.

DESCRIPTION OF SYMBOLS 1 Cylindrical part 2 Funnel-shaped part 3 Tool insertion hole 4 Tool 4f Tip surface 4s Spiral groove 6 Conical tool 6c Conical surface TS Test piece

Claims (11)

  Rotate a round shaft made of steel, bring the tip of the tool into contact with the outer peripheral surface of the round shaft, and move the round shaft and the tool relative to each other in the axial direction of the round shaft while rotating the tool. By supplying hard hard powder to the contact portion between the round shaft and the tool, the hard powder is embedded in the surface of the round shaft, and the round shaft embedded with the hard powder is subjected to surface heat treatment. A wear-resistant steel material having a structure formed on the surface of the round shaft, wherein the hard powder is combined with a component of the round shaft.   The wear-resistant steel material according to claim 1, wherein the surface heat treatment is carburizing and quenching.   The wear-resistant steel material according to claim 1 or 2, wherein the round shaft is made of chromium molybdenum steel or low-carbon steel.   The wear-resistant steel material according to claim 3, wherein the hard powder is made of any one of molybdenum powder, chromium powder, silicon powder, and tungsten carbide powder. Rotate a round shaft made of steel, bring the tip of the tool into contact with the outer peripheral surface of the round shaft, and move the round shaft and the tool relative to each other in the axial direction of the round shaft while rotating the tool. By supplying the hard powder to the contact portion between the round shaft and the tool, the hard powder is embedded in the surface of the round shaft,
A method for modifying the surface of a steel material, wherein the round shaft in which the hard powder is embedded is subjected to surface heat treatment.   The steel surface modification method according to claim 5, wherein the surface heat treatment is a carburizing and quenching treatment.   The method for surface modification of a steel material according to claim 5 or 6, wherein the round shaft is made of chromium molybdenum steel or low carbon steel.   The steel material surface modification method according to claim 7, wherein the hard powder is made of any one of molybdenum powder, chromium powder, silicon powder, and tungsten carbide powder.   After the surface heat treatment, the round shaft is rotated, the tip of the finishing tool is brought into contact with the outer peripheral surface of the round shaft, and the round shaft and the finishing tool are rotated while the finishing tool is rotated. The method for surface modification of a steel material according to any one of claims 5 to 8, wherein the finishing treatment is performed by relatively moving in a direction.   After the embedding process and before the surface heat treatment, the round shaft is rotated, the tip of the finishing tool is brought into contact with the outer peripheral surface of the round shaft, and the round shaft is rotated while the finishing tool is rotated. The method for surface modification of a steel material according to any one of claims 5 to 8, wherein a finishing process is performed by relatively moving the finishing tool in the axial direction of the round shaft.   The method for surface modification of a steel material according to any one of claims 5 to 10, wherein the round shaft is used under a condition without a lubricant.