JPWO2009041665A1 - Method for refining the structure of steel material, steel material having fine structure and blade - Google Patents

Abstract

The present invention provides a method for refining a structure in a surface layer portion of a steel material, and provides a steel material having a fine structure capable of realizing high performance and long life of a cutting tool and a blade. The present invention provides a cutting tool in which a fine structure region is processed into a cutting edge. Structure refinement means refinement of base crystal grains and refinement of carbides. The structure refinement method of a steel material according to the present invention includes a first step for forming a carbide refined region and a second step for forming a refined region. As a first step, the surface layer portion of the steel material is rapidly heated locally by a laser to form a molten pool, and then the molten pool is rapidly solidified to form a carbide refined region. As a second step, a friction stir process is applied to the carbide refined region formed in the first step to form a microstructure refined region. [Selection] Figure 1

Description

  The present invention relates to a method for surface modification by refining a structure in a surface layer portion of a steel material and a steel material having a fine structure, and particularly to a tool steel and a cutting tool having a fine structure and an advantageous manufacturing method thereof. “Structural refinement” means refinement of crystal grains of a metal matrix and refinement of carbides present in the metal matrix.

  In various industrial and medical industries, there is an increasing demand for higher performance and longer life for cutting tools and blades. From the standpoint of sharpness, it is desired to increase the hardness of the material constituting the cutting tool, the blade, etc., and in order to produce a sharp cutting edge, it is indispensable to refine the structure of the material.

It is known that the mechanical properties (hardness, strength, etc.) of a metal material are greatly influenced by the grain size of the crystal grains constituting the metal material. In general, the smaller the crystal grain size, the more the mechanical properties of the metal material. The characteristics are improved. Various techniques such as ECAP (Equal Channel Angular Pressing) and ARB (Accumulative Roll Bonding) have been developed as methods for refining crystal grains of metal materials (JP 2003-096551, JP 2000-073152). It is extremely difficult to refine the crystal grains of steel materials, particularly tool steel, used for tools and blades. The technology to obtain tool steel with fine structure by solidifying and molding metal powder with strong strain has been released (New Energy and Industrial Technology Development Organization “Nanometal Technology Project” “Ultra High Strength by Nanostructure Control” In this method, it is not easy to obtain a material having a size necessary for manufacturing a cutting tool and a cutting tool.

In addition, when high hardness, high strength, high wear resistance, etc. are required for various tools, knives, dies, etc., Cr, Mo, W, V can be used as the base material of the steel material constituting the tool. A carbide-forming element such as is added to disperse and precipitate the carbide in the base material. Coarse carbides reduce the sharpness of cutting tools and cutting tools and shorten the life, and therefore, miniaturization of carbides is important for improving the performance and life of cutting tools and cutting tools.

  From the above viewpoint, the inventor has developed a method for refining a metal material using local melting of a material surface by a laser beam (Japanese Patent Laid-Open No. 2005-146378). This technique has made it possible to refine carbides in the surface layer of the metal material. However, the refined carbide precipitates alongside the grain boundaries of the metal matrix crystal grains, and the strength of the grain boundaries is significantly reduced, so that it is possible to achieve significant improvements in performance and life of cutting tools and blades. Has not reached.

JP2003-0965551 JP 2000-073152 JP-A-2005-146378 New Energy and Industrial Technology Development Organization “Nanometal Technology Project” “Research and Development of Ultra-High Strength and Corrosion Resistant Tool Steel by Nanostructure Control” report

  In the prior art, it is difficult to simultaneously achieve grain refinement of the steel material and refinement of the carbide. Although the refinement of the carbide is possible by the technique developed by the inventor, the uniform dispersion of the carbide and the refinement of the crystal grain of the steel material are not sufficient.

  The present invention has been made in view of the above problems, and provides a method for refining the structure in the surface layer portion of a steel material, and has a fine structure that can realize high performance and long life of cutting tools and cutting tools. The steel material which has is provided and the cutter which processed the structure | tissue micro area | region into the blade edge | tip is provided.

FIG. 1 shows a conceptual diagram of the structure refinement method of a steel material of the present invention. The structure refinement method of a steel material according to the present invention includes a first step (S01) for forming a carbide refined region and a second step (S02) for forming a refined region. As a first step, the surface layer portion of the steel material is rapidly heated locally by a laser to form a molten pool, and then the molten pool is rapidly solidified to form a carbide refined region. As a second step, a friction stir process is applied to the carbide refined region formed in the first step to form a microstructure refined region.

  By executing the first step a plurality of times so that the carbide refined regions at least partially overlap, a wider carbide refined region can be formed. Further, by executing the second step a plurality of times inside the carbide refined region, a wider texture refined region can be formed.

  By using a semiconductor laser as the laser used in the first step, a good carbide refined region can be formed without causing cracks or defects. Moreover, it is preferable to use a steel material having a relatively high carbon content (for example, 0.3% by weight or more), and most preferably a tool steel.

The steel material having a microstructure of the present invention is a tool steel having a base crystal grain size of 5 μm to 50 μm, and a tool steel having a modified region in which the base crystal grain size is refined to 10 nm to 1 μm. . The modified region and the non-modified region are inseparable from each other, and are not joined or bonded after the fact. Moreover, it is preferable that the particle size of the carbide | carbonized_material in a modification | reformation area | region is 10 nm-1 micrometer.

  The cutting tool of the present invention is processed using the refined region of the structure as a cutting edge portion. The structure refinement region is formed by rapidly heating the surface layer of the steel material processed into the blade locally by a laser to form a molten pool, and then rapidly solidifying the molten pool to form a carbide refined region, It is formed by subjecting the carbide refined region to a friction stirring process. The base material crystal grain size in the microstructured region is preferably 10 nm to 1 μm, and the particle size of the carbide dispersed in the texture refined region is preferably 10 nm to 1 μm. In some cases, the base material crystal grain size and the carbide grain size in the microstructure refinement region may be increased by the heat treatment.

In the structure refinement method of a steel material according to the present invention, the structure refinement region is utilized by utilizing local rapid heating and cooling of the steel material by laser and local stirring effect and crystal grain refining effect by friction stirring process. Therefore, it is possible to easily refine the structure of an arbitrary region in the vicinity of the steel material surface layer. By refining only the portion of the cutting edge, such as a cutting tool or cutting tool, which is processed, it is possible to realize high performance and long life of the cutting tool and cutting tool at a low cost. Further, it can be widely used when high hardness, high strength, high wear resistance and the like are required for steel materials.
Since the tool steel having a microstructure of the present invention has a modified region in which crystal grains and carbides of the base material are refined, cutting is performed by using the modified region for a cutting edge of a cutting tool or a cutting tool. High performance and long life of tools and blades can be realized at low cost. In addition, the tool steel can be widely used when high hardness, high strength, high wear resistance, etc. are required.
Since the cutting tool of the present invention processes the modified region in which the crystal grains and carbides of the base material are refined into the cutting edge, high performance and long life are realized at low cost. The cutting edge having high hardness and high toughness exhibits excellent cutting ability and can maintain the cutting ability for a long time. Further, since the carbides present at the cutting edge are fine, the influence of dropping of the carbides on the life of the blade is extremely small.

It is a conceptual diagram of the structure refinement | miniaturization method of the steel material of this invention. It is a conceptual diagram of the 1st process of the structure refinement | miniaturization method of the steel materials of this invention. It is the schematic diagram which showed the cross section of the steel material after 1st process implementation of the structure refinement | miniaturization method of the steel material of this invention. It is the schematic diagram which showed the cross section of the steel material after implementing the 1st process of the structure refinement | miniaturization method of the steel material of this invention in multiple times. It is a conceptual diagram of the 2nd process of the structure refinement | miniaturization method of the steel materials of this invention. It is the schematic diagram which showed the cross section of the steel material after 2nd process implementation of the structure refinement | miniaturization method of the steel material of this invention. It is a schematic diagram of the cross section of the tool steel which has the microstructure of this invention. It is a schematic diagram of the cross section of the cutter of this invention. 2 is an overall photograph of the sample obtained in Example 1. It is an optical microscope photograph of an unprocessed DC53 board | plate material. It is an optical micrograph of a region melted and rapidly solidified by laser irradiation. It is an enlarged photograph of FIG. 2 is an overall photograph of a sample obtained in Example 2. 3 is an optical micrograph of a cross section of a sample obtained in Example 2. It is a Vickers hardness measurement result of the sample obtained in Example 2. It is a scanning electron micrograph of a structure | tissue refinement | miniaturization area | region. It is an EDX qualitative analysis result of unprocessed DC53 board | plate material. It is an EDX qualitative analysis result of a structure refinement | miniaturization area | region. 4 is an overall photograph of the sample obtained in Example 3. 4 is an optical micrograph of a cross section of a sample obtained in Example 3. It is a Vickers hardness measurement result of the sample obtained in Example 3. It is the photograph of the wrinkles processed using the structure refinement | miniaturization area | region as the blade edge | tip. It is a structure | tissue photograph of the blade edge | tip of the scissors processed using the structure | tissue refinement | miniaturization area | region as a blade edge | tip. It is the photograph after the cutting test of the wrinkle which processed the structure refinement | miniaturization area | region into the blade edge | tip. It is the photograph after the cutting test of the wrinkle which processed the carbide | carbonized_material refinement | miniaturization area | region into the blade edge | tip. It is a photograph of a veneer slicer. It is an organization photograph of the cutting edge of a veneer slicer. It is a photograph of the cutting edge of a veneer slicer after a cutting test. It is the photograph of the blade edge | tip of the produced knife after a cutting test. It is the photograph of the blade edge | tip of the commercially available scalpel after a cutting test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Laser light source 12 ... Laser beam 14 ... Steel material 16 ... Molten pool 18 ... Tool steel 20 ... Carbide refinement | miniaturization area | region 22 ... Structure refinement | miniaturization area | region 30 ... Tool

The structure refinement method of a steel material according to the present invention forms a carbide refined region by rapidly solidifying the surface of the steel material with a laser to form a molten pool and then rapidly solidifying the molten pool. A first step and a second step of forming a microstructure refined region by applying a friction stir process to the carbide refined region. In addition, microplasma welding etc. can also be used for the local rapid heating and rapid solidification of the steel material surface layer part in a 1st process.

  FIG. 2 shows an example of the first step. The laser beam 12 emitted from the laser light source 10 is condensed near the surface of the steel material 14. By irradiating the steel material 14 with the laser beam 12 in this way, the surface layer portion of the steel material 14 is rapidly heated locally, and a molten pool 16 is formed in the surface layer portion. The laser beam 12 is scanned at a predetermined speed in the scanning direction, and when the laser beam 12 moves from the melt pool 16, the melt pool 16 rapidly solidifies due to thermal diffusion to the peripheral region. Therefore, the region scanned with the laser beam 12 in the surface layer portion of the steel material 14 is subjected to rapid heating and rapid solidification by the laser beam 12. The laser light source 10 may be any laser light source that can generate a laser capable of forming the molten pool 16 by locally rapidly heating the surface layer portion of the steel material 14, but a semiconductor laser is preferably used.

  FIG. 3 is a schematic view showing a cross section of the steel material after the first step. The molten pool 16 is rapidly solidified, and a carbide refined region 20 is formed in the surface layer portion of the steel material 14. When a wider carbide refined region 20 is required, the laser scan is performed a plurality of times so that the carbide refined region 20 formed by one laser scan at least partially overlaps, as shown in FIG. Such a wide carbide refined region 20 can be obtained.

The second step is a step of subjecting the carbide refined region formed in the first step to a friction stirring process. The friction stir process was established in 1991 by British TWI (The
The friction stir welding method, which is a joining technique devised by Welding Institute), is applied as a surface modification method for metal materials. Friction stir welding is performed by press-fitting into a region where a cylindrical tool rotating at a high speed is to be joined (having a protrusion called a probe on the bottom of the tool, and the probe is press-fitted), and softened by frictional heat This technique achieves joining by scanning in the direction of joining while stirring. The region agitated by the rotating tool is generally called an agitator, and depending on the joining conditions, the material is homogenized and the mechanical properties are improved with the reduction of the crystal grain size. A technique that uses as a surface modification a material homogenization by friction stirrer and an improvement in mechanical properties accompanying a decrease in crystal grain size is a friction stir process, and has been widely studied in recent years.

FIG. 5 shows an example of the second step. A columnar tool 30 that rotates into the carbide refined region 20 is press-fitted and scanned along the carbide refined region 20 to form the tissue refined region 22. The rotation speed of the tool 30 is 100 to 2000
The rpm, the moving speed is preferably 10 to 1000 mm / min, and the compressive load is preferably 4903 to 98066 N (500 to 10000 kgf), but this is not limited as long as frictional stirring can be achieved. Moreover, since the coarse carbide | carbonized_material will be involved when the press-fitted tool 30 comes out of the carbide | carbonized_material refinement | miniaturization area | region 20, it is preferable to press-fit the tool 30 inside the carbide | carbonized_material refinement | miniaturization area | region 20. The shape of the tool 30 may be any shape as long as it can achieve a friction stir process for the carbide refined region 20, and is not limited by the presence or absence of the probe on the bottom surface of the tool 30 or the shape thereof.

  FIG. 6 is a schematic view showing a cross-section of the steel material after the second step. By subjecting the carbide refined region 20 to a friction stirring process, a microstructure refined region 22 is formed in the surface layer portion of the steel material 14. When a wider structure refinement region 22 is required, a wider carbide refinement is performed by performing laser scanning a plurality of times so that the carbide refinement region 20 formed by one laser scan at least partially overlaps. After obtaining the region 20, the second step may be performed a plurality of times on the carbide refined region 20.

  The tool steel having a microstructure of the present invention has a cross section as shown in FIG. The base crystal grain size of the tool steel 18 is 5 μm to 50 μm, and the base crystal grain size in the structure refinement region 22 is 10 nm to 1 μm. Moreover, the particle size of the carbide | carbonized_material in the structure | tissue refinement | miniaturization area | region 22 is 10 nm-1 micrometer. The tool steel 18 and the structure refinement region 22 are continuously present via the carbide refinement region 20, and the tool steel 18 and the structure refinement region 22 are not joined or bonded.

  The cutting tool of the present invention has a cross section as shown in FIG. 8, for example, and the texture refined region 22 is processed into a cutting edge. The base material crystal grain size of the steel material 14 is preferably 5 μm to 50 μm, and the base crystal grain size in the structure refinement region 22 is preferably 10 nm to 1 μm. Moreover, it is preferable that the particle size of the carbide | carbonized_material in the structure | tissue refinement | miniaturization area | region 22 is 10 nm-1 micrometer. Here, in the manufacture of the blade, a heat treatment such as quenching and tempering may be appropriately performed, and the base material crystal grain size and the carbide grain size in the structure refinement region 22 may be increased by the heat treatment. The steel material 14 and the structure refinement region 22 exist continuously through the carbide refinement region 20, and the steel material 14 and the structure refinement region 22 are not joined, bonded, or the like.

EXAMPLES Examples and comparative examples of the present invention will be described below with reference to the drawings, but the present invention is not limited to these examples. In addition, DC53 used as a to-be-processed material in an Example is general purpose cold die steel, and is tool steel which has the outstanding toughness etc.
Example 1
A carbide refined region was formed on the DC53 plate using a semiconductor laser (output: 1 kW). The laser was just focused on the surface of the DC53 plate (the laser diameter on the surface of the DC53 plate was about 1 mm), and the laser scanning speed was 1000 mm / min. The laser irradiation position is moved by 0.7 mm perpendicularly to the laser scanning direction at the end of each laser scan so that the carbide refined regions formed by one laser scan at least partially overlap each other. A total of 5 laser scans were performed. A photograph of the obtained sample is shown in FIG. It can be confirmed that there is a region formed by laser irradiation on the surface of the DC53 plate material.

  FIG. 10 shows an optical micrograph of an untreated DC53 plate, and FIG. 11 shows an optical micrograph of a region melted and rapidly solidified by laser irradiation. In the observation with an optical microscope, each sample is etched with a 3% nital solution in order to facilitate the observation of the structure. Coarse carbides exceeding 10 μm are confirmed in the untreated region, but the carbides in the region subjected to the laser treatment are refined to 1 μm or less. FIG. 12 shows the result of observing the region shown in FIG. 11 at a higher magnification, and it is confirmed that the refined carbides exist side by side at the crystal grain boundaries of the base material.

Table 1 shows the Vickers hardness in the depth direction from the surface of the region melted and rapidly solidified by laser irradiation. The Vickers hardness was measured under the conditions of a load of 2.94 N (300 gf) and a holding time of 15 seconds. Vickers hardness of untreated area is 200-300
Although it is about Hv, the Vickers hardness of the region subjected to the treatment with the laser has increased to around 500 Hv.

Example 2
After the DC53 plate material was treated with a laser to form a carbide refined region, a friction stirring process was applied to the carbide refined region. A semiconductor laser (output: 1 kW) was used to form the carbide refined region, and the laser was just focused on the surface of the DC53 plate (the laser diameter on the surface of the DC53 plate was about 1 mm). The laser scanning speed was 1200 mm / min. The laser irradiation position is moved by 0.7 mm perpendicularly to the laser scanning direction at the end of each laser scan so that the carbide refined regions formed by one laser scan at least partially overlap each other. A total of 15 laser scans were performed. For the friction stirring process, a cemented carbide tool having a cylindrical shape with a diameter of 10 mm was used, and the tool rotating at a speed of 400 rpm was press-fitted into the carbide refined region with a load of 2600 kg. The moving speed of the tool was set to 400 mm / min, and oxidation of the tool and the sample was prevented by flowing argon gas. The insertion position of the tool was set at the center of the carbide refined region, and sufficient care was taken so that the tool did not stir the untreated DC53 plate material.

  FIG. 13 shows a photograph of the surface of the obtained sample. A friction stir process is applied to the area treated by the laser. The friction stir process is performed in the region treated by the laser treatment, and it can be confirmed that the untreated DC 53 plate material is not friction stir.

  FIG. 14 shows an optical micrograph of a cross section of the obtained sample. In the observation with an optical microscope, an etching process is performed with a 3% nital solution in order to facilitate the observation of the structure. There is a carbide refined region formed by laser processing from the surface of the DC53 plate material to a depth of about 1 mm, and a microstructure refined region exists from the surface to a depth of about 200 μm in the carbide refined region. In this embodiment, since a cylindrical tool having no probe is used in the friction stir process, the amount of press-fitting of the tool into the carbide refined region is small, and the influence of the friction stir does not reach the entire region of the carbide refined region.

  FIG. 15 shows the measurement results of Vickers hardness for the obtained sample. The Vickers hardness was measured under the conditions of a load of 2.94 N (300 gf) and a holding time of 15 seconds. The Vickers hardness of the microstructure refined region formed by the friction stir process is significantly higher than the hardness of the carbide refined region formed only by the laser treatment.

  FIG. 16 shows a scanning electron micrograph of the microstructured region. In the observation with a scanning electron microscope, an etching process is performed with a 3% nital solution in order to facilitate the observation of the structure. The crystal grain size of the base material is clearly less than 1 μm, and it is considered that the carbide is finer than the crystal grain size of the base material.

  FIG. 17 shows the EDX qualitative analysis result of the unprocessed DC53 plate material, and FIG. 18 shows the EDX qualitative analysis result of the structure refinement region formed by the laser processing and the friction stir process. The constituent elements of the unprocessed DC53 plate material and the structure refinement region are the same, and it is clear that the structure refinement method of the steel material of the present invention is not due to the addition of other elements.

Example 3
After the DC53 plate material was treated with a laser to form a carbide refined region, a friction stirring process was applied to the carbide refined region. A semiconductor laser (output: 1 kW) was used to form the carbide refined region, and the laser was just focused on the surface of the DC53 plate (the laser diameter on the surface of the DC53 plate was about 1 mm). The laser scanning speed was 1200 mm / min. The laser irradiation position is moved by 0.7 mm perpendicularly to the laser scanning direction at the end of each laser scan so that the carbide refined regions formed by one laser scan at least partially overlap each other. A total of 15 laser scans were performed. For the friction stirring process, a cemented carbide tool having a cylindrical shape with a diameter of 10 mm was used, and the tool rotating at a speed of 400 rpm was press-fitted into the carbide refined region with a load of 2600 kg. The moving speed of the tool was set to 400 mm / min, and oxidation of the tool and the sample was prevented by flowing argon gas. The insertion position of the tool was adjusted so that about half of the tool was applied to the unprocessed DC53 plate material from the carbide refined region, and the tool stirred the unprocessed DC53 plate material and the carbide refined region simultaneously.

  FIG. 19 shows a photograph of the surface of the obtained sample. A friction stir process is simultaneously applied to the region treated by the laser and the untreated region. It can be confirmed that almost the center of the tool used in the friction stir process passes near the boundary between the region treated by the laser and the untreated region.

  FIG. 20 shows an optical micrograph of a cross section of the obtained sample. In the observation with an optical microscope, an etching process is performed with a 3% nital solution in order to facilitate the observation of the structure. There is a carbide refined region formed by laser processing from the surface of the DC53 plate material to a depth of about 1 mm, and a microstructure refined region exists from the surface to a depth of about 200 μm in the carbide refined region. In addition, since the friction stir process is simultaneously performed on the carbide refined region and the unprocessed DC53 plate material, the microstructure refined region exists outside the carbide refined region, and the structure in the vicinity of the surface A relatively coarse carbide exists in the miniaturized region. It is considered that coarse carbides present in the untreated DC 53 plate material are mixed into the refined region of the structure due to plastic flow by the friction stir process. In this embodiment, since a cylindrical tool having no probe is used in the friction stir process, the amount of press-fitting of the tool into the carbide refined region is small, and the influence of the friction stir does not reach the entire region of the carbide refined region.

  FIG. 21 shows the measurement results of Vickers hardness for the obtained sample. The Vickers hardness was measured under the conditions of a load of 2.94 N (300 gf) and a holding time of 15 seconds. The Vickers hardness of the microstructure refined region formed by the friction stir process is significantly higher than the hardness of the carbide refined region formed only by the laser treatment.

Example 4
After the DC53 plate material was treated with a laser to form a carbide refined region, a friction stirring process was applied to the carbide refined region. A semiconductor laser (output: 1 kW) was used to form the carbide refined region, and the laser was just focused on the surface of the DC53 plate (the laser diameter on the surface of the DC53 plate was about 1 mm). The laser scanning speed was 1200 mm / min. The laser irradiation position is moved by 0.7 mm perpendicularly to the laser scanning direction at the end of each laser scan so that the carbide refined regions formed by one laser scan at least partially overlap each other. A total of 15 laser scans were performed. A cemented carbide tool having a cylindrical shape with a diameter of 10 mm was used for the friction stirring process, and the tool rotating at a speed of 400 rpm was press-fitted into the carbide refined region with a load of 2600 kg. The moving speed of the tool was set to 400 mm / min, and oxidation of the tool and the sample was prevented by flowing argon gas. Thereafter, the region subjected to the friction stir process (structure refinement region) was processed as a cutting edge to produce a scissors. For comparison, a scissor was also fabricated using a carbide refined region that had not been subjected to the friction stir process as a cutting edge.

  FIGS. 22 and 23 show a photograph of a wrinkle processed with the structure refinement region as a blade edge and a structure photograph of the blade edge, respectively. It can be confirmed that the structure of the cutting edge portion is very fine, and the particle size of the carbide dispersed in the region is smaller than 1 μm.

  The veneer board called LVL was cut with the produced scissors, and the characteristics of the scissors were evaluated. Cutting conditions were as follows: cutting speed: 96 mm / min, cutting depth: 0.15 mm, tool post angle: 35 °, blade edge angle: 31 °, and after cutting 5 LVL plates with a length of 1.8 m, the shape of the blade edge was Observed with an optical microscope. FIG. 24 shows a photograph of a wrinkle processed with a texture refined region with a cutting edge, and FIG. 25 shows a photograph of a wrinkle processed with a carbide refined region with a cutting edge. The cutting edge of the scissors processed using the carbide refined region as the cutting edge is greatly deformed, whereas the cutting edge of the scissors processed using the microstructure refined region as the cutting edge is hardly deformed.

Example 5
After the DC53 plate material was treated with a laser to form a carbide refined region, a friction stirring process was applied to the carbide refined region. A semiconductor laser (output: 1 kW) was used to form the carbide refined region, and the laser was just focused on the surface of the DC53 plate (the laser diameter on the surface of the DC53 plate was about 1 mm). The laser scanning speed was 1200 mm / min. The laser irradiation position is moved by 0.7 mm perpendicularly to the laser scanning direction at the end of each laser scan so that the carbide refined regions formed by one laser scan at least partially overlap each other. A total of 15 laser scans were performed. For the friction stirring process, a cemented carbide tool having a cylindrical shape with a diameter of 10 mm was used, and the tool rotating at a speed of 400 rpm was press-fitted into the carbide refined region with a load of 2600 kg. The moving speed of the tool was set to 400 mm / min, and oxidation of the tool and the sample was prevented by flowing argon gas. Then, the area | region (structure refinement | miniaturization area | region) which gave the friction stirring process was processed as a blade edge | tip, and the woodworking cutter (Veneer slicer) was produced.

A photograph of a veneer slicer processed using the microstructured region as a cutting edge and a structure photograph of the cutting edge are shown in FIGS. 26 and 27, respectively. It can be confirmed that the structure of the cutting edge portion is very fine, and the particle size of the carbide dispersed in the region is smaller than 1 μm.

  Cedar logs were cut with the prepared veneer slicer, and the characteristics of the veneer slicer were evaluated. Cutting conditions were a cutting speed: 23 mm / min, a cutting amount: 0.3 mm, a blade edge angle: 20 °, and the cutting edge shape was observed with an optical microscope after cutting about 17 m. A photograph of the cutting edge after the cutting test is shown in FIG. It can be confirmed that no noticeable chipping or the like is observed on the blade edge and the good shape is maintained. Further, the thin plate of a single plate (cut thin plate) cut with a conventional veneer slicer is limited to about 150 μm, but the veneer slicer produced this time has obtained a single plate of about 75 μm.

Example 6
After the DC53 plate material was treated with a laser to form a carbide refined region, a friction stirring process was applied to the carbide refined region. A semiconductor laser (output: 1 kW) was used to form the carbide refined region, and the laser was just focused on the surface of the DC53 plate (the laser diameter on the surface of the DC53 plate was about 1 mm). The laser scanning speed was 1200 mm / min. The laser irradiation position is moved by 0.7 mm perpendicularly to the laser scanning direction at the end of each laser scan so that the carbide refined regions formed by one laser scan at least partially overlap each other. A total of 15 laser scans were performed. For the friction stirring process, a cemented carbide tool having a cylindrical shape with a diameter of 10 mm was used, and the tool rotating at a speed of 400 rpm was press-fitted into the carbide refined region with a load of 2600 kg. The moving speed of the tool was set to 400 mm / min, and oxidation of the tool and the sample was prevented by flowing argon gas. Then, the area | region (structure refinement | miniaturization area | region) which gave the friction stirring process was processed as a blade edge | tip, and the knife was produced.

  A general copy paper (high quality paper) was cut with the produced knife and a commercially available knife, and the characteristics of the knife were evaluated by observing changes in the number of cut sheets and the shape of the blade edge. Place a bundle of 210 sheets of 950g copy paper on a fixed knife (the angle between the blade surface and the copy paper is 15 °), move the bundle at 3000 mm / min, and measure how many copy sheets are cut. did. One knife was subjected to continuous 20 cutting tests, and the change in the number of cuts was observed. In addition, about 20 types of cutting | disconnection tests, it carried out 6 times about one type of knife.

  Tables 2 and 3 show the number of cuts of the produced knife and the commercially available knife, respectively. In all the cutting tests, the number of sheets cut with the produced knife is larger than the number of sheets cut with a commercially available knife. Further, as the number of cutting tests increases, the number of cuts with a commercially available scalpel decreases, whereas the number of cuts with a produced scalpel hardly decreases. This result shows that the produced knife has excellent sharpness and long life.

  The cutting edge shape after the cutting test of the produced knife is shown in FIG. 29, and the cutting edge shape after the cutting test of a commercially available knife is shown in FIG. While the blade edge of a commercially available knife is greatly crushed, the blade edge shape of the knife produced is hardly changed. Compared with a commercially available knife, it can be confirmed that the knife produced maintains the sharpness of the cutting edge even after the cutting test.

Claims (9)

A first step of forming a carbide refined region by rapidly solidifying the molten pool after rapidly heating a surface layer portion of the steel material locally by a laser to form a molten pool;
A second step of forming a microstructure refined region by applying a friction stirring process to the carbide refined region;
A method for refining the structure of a steel material having So that the carbide refined region at least partially overlaps,
The structure refinement method for a steel material according to claim 1, wherein the first step is executed a plurality of times. 3. The structure refinement method for a steel material according to claim 1, wherein the second step is performed a plurality of times inside the carbide refined region. The method for refining a structure of a steel material according to any one of claims 1 to 3, wherein a semiconductor laser is used as the laser. Tool steel is used as said steel material, The structure refinement | miniaturization method of the steel material of any one of Claims 1-4 characterized by the above-mentioned. A tool steel having a base crystal grain size of 5 μm to 50 μm,
A tool steel having a modified region in which the base material crystal grain size is refined to 10 nm to 1 μm.   The tool steel according to claim 6, wherein the grain size of carbide in the modified region is 10 nm to 1 μm.   A blade in which the structure of the cutting edge portion is refined by the structure refinement method of the steel material according to any one of claims 1 to 5. Having a carbide refined region and a texture refined region;
A cutting tool machined with the microstructured region as a cutting edge.