Forging hammer head and manufacturing method of blade using the same

Abstract

To provide: a hammer head for forging for manufacturing a wrought cutting tool having a hard, sharp and easy-to-sharpen cutting edge with high strength and excellent toughness, in particular, a hammered cutting tool with an excellent appearance; and a method for manufacturing a cutting tool using the same.SOLUTION: A method for manufacturing a cutting tool includes at least: a hammering step of pressing a material at different locations a plurality of times using a hammer head having a plurality of striking parts on a striking surface; a pressing step of punching out the material into a workpiece in a form of the cutting tool after the hammering step; a heat-treatment step of heating the workpiece after the pressing step and then cooling the workpiece; a cutting-edge forging-heat-treatment step of forging, using the hammer head for forging, a portion to be made into a cutting edge, during cooling the workpiece in the heat-treatment step; and a cutting-edge forming step of forming the cutting edge after the cutting-edge forging-heat-treatment step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a forging hammer head used in the manufacture of cutting tools and a method of manufacturing cutting tools using the same. [Background technology]

[0002] Blades are made by forging steel. The manufacturing method has developed since ancient times along with the manufacturing techniques for Japanese swords and other items, and in modern times it is used not only in the field of traditional crafts but also in the manufacturing of industrially produced blades.

[0003] Steel materials that are tempered by forging have their grain size refined by the energy of plastic deformation. In other words, the grain boundaries between crystals of different orientations become denser. These grain boundaries have the effect of stopping the movement of dislocations in the crystals. Here, a dislocation is an atomic defect in a crystal, and refers to a region in which the arrangement of atoms in a crystal is linearly disrupted due to a defect in a portion of the atomic arrangement. When an external force is applied to the defective portion of the atomic arrangement, the nearby atoms are displaced and rearranged. At this time, the atoms near the portion where the dislocation exists move with a force smaller than the force derived from the theoretical interatomic force. The deformation caused by this movement of dislocations is called slip deformation, and the entire material is plastically deformed as the dislocation moves sequentially into the arrangement of adjacent atoms. Therefore, the tensile strength, yield point, or proof stress (hereinafter referred to as "strength, etc.") of the material is lower in the portion where the dislocation exists compared to the portion where the dislocation does not exist.

[0004] As mentioned above, when the grain size is refined and the proportion of grain boundaries is increased, the presence of the grain boundaries suppresses the movement of dislocations. In other words, when the grain size is refined by forging, the strength of the material is improved.

[0005] Incidentally, there are knives (hereafter referred to as "hammered knives") that have a hammered pattern, in which the pattern of the hammer used in forging is transferred to the belly of the blade. Knives that have been forged multiple times with a hammer have a unique hammered pattern that is different for each item. This hammered pattern is not only aesthetically pleasing, but also has a practical effect, especially in kitchen knives, in that the unevenness of the hammered pattern makes it easier to cut and separate objects.

[0006] Previously, techniques relating to hammered blades and their manufacturing methods aimed at achieving these effects have been disclosed. For example, Patent Document 1 is a publication of a utility model registration application relating to a hammered blade previously filed by the applicant of the present invention, and is the idea that became the starting point for various manufacturing techniques for hammered blades. In addition, a technique has been disclosed that relates to a method for manufacturing a hammered blade using a clad material in which steel materials of different hardness are laminated together. For example, Patent Document 2 was invented by the inventor of the present invention by developing the technique of Patent Document 1.

[0007] To give an overview of the technology in Patent Document 2, the manufacturing method of this blade uses a clad material 900, in which soft stainless steel 92·92 are laminated onto the front and back of a high-hardness blade steel 91, as shown in FIG. 9. In the manufacturing process, first, this clad material 900 is hammered to form hammered patterns 93·93... all over. Next, an external force is applied with a flat hammer to a portion 94 that will become the cutting edge, causing it to stretch and deform. After that, the blade is punched out by pressing, and then quenched and tempered. Finally, the cutting edge is ground to make the blade.

[0008] This invention is characterized by the fact that in addition to the hammering, the cutting edge portion 94 is forged with a flat hammer. This keeps the overall balance of the internal stresses and causes residual compressive stress. This has the effect of reducing cracks due to quenching and aging.

[0009] Furthermore, a technique for manufacturing a clad material that improves the hardness of the cutting edge of a blade is also disclosed. Patent Document 3 is a publication of a patent application relating to a manufacturing method of a composite steel material for blades (so-called clad material) that was previously invented by the inventor of the present invention.

[0010] To summarize the technology of Patent Document 3, this technology is a manufacturing method in which an alloy plate of a specified thickness made of a specified ratio of copper and nickel is inserted between high carbon steel and low carbon steel, and the peripheral edges of the overlapping part are sealed by means of welding or the like, and then hot rolled. Because copper and nickel, which have a low tendency to form carbides, are present between the high carbon steel and the low carbon steel, the phenomenon of carbon migrating from the high carbon steel to the low carbon steel during heat treatment is prevented, and the hardness of the high carbon steel that becomes the cutting edge can be maintained at a high level. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Jpn. Jpn. 43-020827 Publication [Patent Document 2] Japanese Patent Publication No. 56-146633 [Patent Document 3] Special Publication No. 47-043425 Summary of the Invention [Problem to be solved by the invention]

[0012] As described in Patent Document 2, tempering is generally performed after quenching. Quenching utilizes the fact that a structure called austenite at high temperatures is rapidly cooled, and hard carbides are incorporated between iron crystals to transform into a structure called martensite, and the structure after quenching becomes very hard. However, steel material that has been quenched as is is not practical because the entire material becomes brittle due to the effects of grain boundary brittle fracture caused by crystals that have become coarse due to the high temperature and the effects of hard and brittle carbides incorporated into the iron crystals, and it breaks easily. Therefore, tempering is generally performed by reheating the steel to appropriately release the carbon incorporated between the iron crystals, improving toughness and removing residual stress. For these reasons, steel is tempered after quenching, which improves toughness by forming fine precipitates of hard carbides. However, the hardness achieved by quenching is reduced. Generally, the tempering temperature is set as a compromise between the reduction in hardness and the increase in toughness, but it is desirable to avoid a reduction in hardness as much as possible for blades. In particular, when sharpening cutting edges, a low hardness makes the cutting edge more likely to curl or cause fine defects, so a high hardness makes it possible to sharpen the blade thin and sharp. For this reason, it is desirable to form cutting edges from as hard a steel as possible.

[0013] As mentioned above, there are material technologies such as those in Patent Document 3 that can increase the hardness of the cutting edge, but even if such material technologies are applied, the hardness obtained by quenching cannot be maintained if a heat treatment that increases the temperature again, such as tempering, is performed. Therefore, conventionally, there is a technique of thermomechanical treatment, represented by ausforming, in the cooling process of quenching. Thermomechanical treatment is a processing method in which plastic deformation processing is performed in a specific temperature range where the time until the transformation from austenite to martensite starts due to cooling can be secured long, and processing is terminated before isothermal transformation occurs. Here, isothermal transformation is a phenomenon in which austenite transforms into bainite or sorbite by holding a steel material at a constant temperature for a predetermined time during cooling. When the thermomechanical treatment is performed, metastable austenite, which has become in a state where it is easy to transform, is forced to undergo martensitic transformation by the energy of plastic deformation processing. In addition, the crystal grain size is extremely fined by plastic deformation processing, improving strength, while the dense crystal grain boundaries suppress grain boundary brittle fracture and maintain toughness. Steel material that has been subjected to such thermomechanical processing is excellent in hardness and toughness even when heated to a temperature equivalent to tempering.

[0014] However, in thermomechanical treatment, it is difficult to control the temperature during plastic deformation, and in forging in particular, the heat of the steel material is likely to escape through the hammer head every time the hammer head comes into contact with the surface to be forged. Therefore, it is necessary to frequently place the material in a heating furnace during processing to raise the temperature. As a result, sufficient plastic deformation cannot be performed before martensite resulting from plastic deformation (hereinafter referred to as "deformation-induced martensite") is obtained, and isothermal transformation occurs during that time to form bainite or sorbite, which is made of α-iron and iron carbide. Such a structure has lower strength and toughness than a structure in which martensite due to quenching formed by thermomechanical treatment and deformation-induced martensite coexist. Thus, even if a thermomechanical treatment is adopted in the manufacturing method of a blade, there is a problem in that it is practically impossible to perform processing at a constant temperature.

[0015] The present invention has been made in consideration of the above-mentioned problems, and has as its object to provide a forging hammer head for producing a forging knife which is hard, easy to sharpen, has a cutting edge with high strength and other properties, and which has excellent toughness, and which, in the case of a hammered knife in particular, has an excellent aesthetic appearance, and a method for manufacturing a knife using the same. [Means for solving the problem]

[0016] The means adopted by the present inventors to solve the above problems will be described below. The forging hammer head of the present invention (hereinafter simply referred to as "hammer head") has a structure having a plurality of striking portions on a striking surface that strikes a surface of a material to be forged during forging. The multiple impact parts are the parts that come into contact with the forged surface of the material first when the hammer head descends during forging, and are formed in multiple numbers on the entire impact surface. This does not mean that all of the multiple impact parts come into contact with the forged surface of the material first at the same time. For example, it may be that one of the multiple impact parts comes into contact first and the other impact parts come into contact sequentially, or that some of the multiple impact parts come into contact first at the same time.

[0017] In this way, by first contacting the surface of the material to be forged with multiple striking parts, the force of the hammer of the forging equipment is concentrated on a small area compared to when forging is performed with the entire striking surface, and the forging pressure increases. Therefore, even with small-scale forging equipment with small hammer force, forging is possible, and plastic deformation by forging occurs deep into the material. In particular, in the case of hammered blades made of clad material, the recesses of the hammered pattern tend to reach the relatively hard intermediate steel layer that becomes the cutting edge through the relatively soft front and back steel. In addition, the amount of heat transfer is generally proportional to the contact area. Since the hammer head of the present invention has multiple striking parts on the striking surface, the area that initially comes into contact with the forged surface of the material is smaller than when forging is performed with the entire striking surface. Therefore, when performing thermal processing, the amount of heat that escapes through the hammer head is extremely small.

[0018] A method for manufacturing a blade using the hammer head (hereinafter simply referred to as the "manufacturing method") will be described below. The manufacturing method of the present invention includes at least a press processing step of punching a material into the shape of a blade, a heat treatment step of heating and then cooling after the press processing step, and a cutting blade forming step of forming a cutting blade after the heat treatment step, but may further include the following steps depending on the type of blade to be manufactured.

[0019] When the cutting tool to be manufactured is a hammered cutting tool, a hammering process is provided before the press working process in which the material is pressed multiple times at different positions with the hammer head. In addition, in the case of producing a blade that does not have a hammered pattern, a thermo-mechanical treatment step is provided in which at least a part of the punched material is forged with the forging hammer head during the cooling in the heat treatment step. The above-mentioned hammering process and heat treatment process may both be included. In this case, the heat treatment process is a cutting edge heat treatment process in which the part that will become the cutting edge is forged with the forging hammer head.

[0020] In the case of a hammering process, the hammer head of the present invention has the aforementioned effect of making it easier for the recesses of the hammered pattern to reach deep into the material. In addition, by pressing multiple times in multiple places, the hammered pattern created by the multiple striking parts is randomly transferred to the entire material. Furthermore, in the case where a thermo-mechanical treatment step or a cutting edge thermo-mechanical treatment step is provided, the use of the hammer head of the present invention provides the aforementioned effect that the amount of heat escaping through the hammer head is extremely reduced.

[0021] Among the means for solving the problems according to the present invention, those based on the basic configuration are as described above, but in the present invention, it is also possible to use the following means. As one example, the plurality of striking portions may be formed by dividing the striking surface into a plurality of seating surfaces, each of which may further have a convex portion. With this configuration, the convex portions provided on the multiple seating surfaces are the first to come into contact with the forged surface of the material during forging, but as the forged surface plastically deforms and sinks, the seating surfaces, which are the bases of the convex portions, may then come into contact with the forged surface of the material. When manufacturing hammered blades, the gradual contact between the convex portions and the seating surfaces in this way forms a complex hammered pattern, and the grain flows, which are crystal structures that are aligned in a fibrous form due to forging, become more complex, causing the material to be locally elongated and further refined in crystal grain size.

[0022] Here, it is also possible to form the plurality of striking parts in such a way that when the hammer head descends during forging, the striking parts come into contact with the surface to be forged from one side to the other. Examples of this shape include a shape in which the striking parts closer to the center are made higher in height and the surrounding striking parts are made lower in height. However, this is not necessarily limited to a shape in which the striking parts closer to the center are made higher, and it is also possible for the striking parts at one end of the striking surface to be the highest and the striking parts at the opposite other end to be the lowest. In this configuration, when multiple impact parts contact and press the forged surface, the first part of the forged surface is expanded in the surface direction by the successive impact parts. This causes the material to be locally elongated and the grain size to be further refined. In addition, by pressing multiple times at different locations, not only is the grain size refined, but the refined grain boundaries tend to be uniformly distributed throughout the material.

[0023] One example of the shape of the multiple hitting parts is that the height of each of the multiple hitting parts is set to a height that follows a convex imaginary curved surface that covers the entire hitting surface. In this configuration, when the tips of the multiple striking parts are connected, they can be regarded as a smoothly curved convex surface as a whole. Therefore, the forged surface is smoothly elongated by the pressure of the hammer head, and the grain size is easily refined.

[0024] Incidentally, in the manufacturing method of the present invention, the hammering step may use a hammer head having a plurality of striking parts shaped so that the order of contact with the forged surface when the hammer head descends is from one side to the other, and the cutting edge heat treatment step may use a hammer head having a striking surface with a substantially flat shape. The hammer heads used in the hammering step and the cutting edge heat treatment step both have a plurality of striking parts on their striking surfaces, but as long as the hammer head used in the cutting edge heat treatment step has a plurality of striking parts whose tips are uniform in height and whose striking surface is flat as a whole, the tips of the plurality of striking parts do not have to be flat. In the case of such a configuration, the part that will become the cutting edge of the material having the hammered pattern formed all over it can be flattened and hammered to leave a compressive stress.

[0025] Here, if the material is finished into a blade with residual tensile stress, defects such as cracks occurring over time will occur due to the action of the residual tensile stress. In the above configuration, the hammered pattern is formed by multiple striking parts that are shaped so that the contact order with the forged surface is from one side to the other, and the forged surface and its interior are stretched, making it easy for tensile stress to remain. In this state, when the blade is pushed and pulled as a blade or pressed with the tip tilted, the root part of the microscopic saw blade shape at the blade tip is subjected to a tensile load as an external force in the thickness direction and the length direction. When an external force is applied to the root part of the microscopic saw blade shape, the residual tensile stress is added to the tensile stress due to the external force, causing the microscopic saw blade shape to partially break, and this occurs and expands in multiple places, causing the tip of the blade tip to wear out. In addition, cracks may occur at the blade tip over time even if no external force is applied. To prevent these problems, the cutting edge is forged using a hammer head with a generally flat striking surface, which removes the residual tensile stress caused by the hammering process. Also, because the striking surface of the hammer head is generally flat, the material is not stretched in the surface direction in the thermo-mechanical treatment process, but is compressed in the thickness direction. As a result, the residual tensile stress caused by the hammering process is removed, and compressive stress remains.

[0026] In general, metal materials break when the tensile stress generated inside them exceeds the tensile strength. In terms of material mechanics, the same is true for compression, where the material breaks when the compressive stress generated inside them exceeds the compressive strength. However, unlike brittle materials, ductile materials rarely break when compressed. Therefore, even if compressive stress is left in a blade, cracks or other defects rarely occur. Rather, by intentionally leaving compressive stress remaining and applying compressive stress in advance, the tensile stress generated by the external force applied to the cutting edge when the blade is in use is offset, reducing the possibility of cracks occurring during use and improving wear resistance.

[0027] The manufacturing method of the present invention can also use a clad material in which an intermediate layer made of a steel material and front and back layers made of a steel material having a lower hardness than the intermediate layer are laminated together. In the case of a manufacturing method using such a clad material, the front and back layers are made of steel material with a lower hardness than the intermediate layer, which makes it easier to form a hammered pattern in the hammering process. Even in this case, the hammer head can be used to easily reach the intermediate layer steel material through the front and back layers, as described above. Effect of the Invention

[0028] In the present invention, by providing multiple striking parts on the striking surface of the hammer head, the forging pressure increases and plastic deformation easily reaches the inside of the material, which leads to finer grain size and allows the formation of an aesthetically pleasing hammered pattern in hammered blades. In addition, in the thermomechanical treatment process of the manufacturing method, the hammer head has multiple striking parts, which reduces the heat escaping from the hammer head and facilitates isothermal plastic deformation processing. As a result, a dual-phase structure in which quenched martensite and processing-induced martensite coexist can be obtained, which has excellent hardness, toughness, strength, etc. As a result, the hammer head and manufacturing method of the present invention have the effect of making it possible to manufacture a striking blade that is hard and easy to sharpen, has a cutting edge that has high strength, etc., and has excellent toughness. [Brief description of the drawings]

[0029] [Figure 1] 1A and 1B are front and cross-sectional views of a hammer head for use in a hammering process of the present invention; [Diagram 2] 1A and 1B are a front view, a cross-sectional view, and a perspective view showing a hammer head for use in a cutting edge heat treatment process according to the present invention. [Diagram 3] FIG. 2 is an explanatory diagram showing the order of steps in the manufacturing method of the present invention. [Figure 4] 3A to 3C are explanatory diagrams showing the state of a blade at each step of the manufacturing method of the present invention. [Diagram 5]1A and 1B are a front view and a cross-sectional view showing a first modified example of a hammer head according to the present invention. [Figure 6] 11A and 11B are a front view and a cross-sectional view showing a second modified example of a hammer head according to the present invention. [Figure 7] FIG. 11 is an explanatory diagram showing a modified example 3 of the manufacturing method of the present invention. [Figure 8] FIG. 11 is an explanatory diagram showing a fourth modified example of the manufacturing method of the present invention. [Figure 9] 1A and 1B are a front view and a cross-sectional view showing a conventional example of Patent Document 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. It should be noted that the hammered patterns and structure diagram in Figure 4 are shown diagrammatically for the purpose of explanation and differ from the actual product.

[0031] First, of the hammer heads of the present invention, a hammer head 100 used in the hammering process (hereinafter simply referred to as a "hammering head") will be described. This hammering head 100 applies impact force to the workpiece by the force of the up and down movement of a drive part called a ram of a forging machine, and is made by quenching a machined alloy tool steel for dies or the like.

[0032] As shown in Fig. 1, the hammering head 100 of the present invention has a striking surface 1 formed at the tip of a cylindrical main body measuring approximately φ12 mm to φ15 mm. This striking surface 1 is made up of a number of striking portions 2·2.... In the embodiment shown in Fig. 1, the multiple striking portions 2·2... are formed as seating surfaces 21·21... formed by dividing a square base into a 5 x 5 grid by grooves 22·22..., and each seating surface 21·21... has small cylindrical convex portions 23·23... protruding therefrom.

[0033] Here, the height of each striking portion 2·2... is the height that follows the imaginary curved convex surface 3 that covers the entire striking surface 1. More specifically, the imaginary curved surface 3 is a surface that forms part of a sphere, and the top surfaces of the convex portions 23·23... follow this imaginary curved surface 3, so that they form an imaginary spherical surface as a whole. Note that the seating surfaces 21·21... also follow a surface that is a similar, smaller version of the imaginary curved surface 3, but the seating surfaces 21·21... may also be flat surfaces. As a result of the height of each impact portion 2·2... being set to the same height as the imaginary curved surface 3, when the hammering head 100 is lowered during forging, the contact order of each impact portion 2·2... is from the center to the outer periphery as the forged surface undergoes plastic deformation and becomes concave.

[0034] Next, of the hammer heads of the present invention, a hammer head 101 used in the heat treatment process or cutting edge heat treatment process (hereinafter simply referred to as the "heat treatment head") will be described. As shown in Fig. 2, the heat treatment head 101 has the same basic structure as the hammering head 100, but differs in that the top surfaces of the convex portions 23 of each striking portion 2 have a substantially flat shape. Since each of the striking portions 2·2... making up the striking surface 1 has a substantially flat shape, each of the striking portions 2·2... comes into even contact with the surface to be forged when the thermo-mechanical treatment head 101 descends during forging.

[0035] Next, a method for manufacturing a blade using the hammering head 100 and the thermomechanical treatment head 101 will be described with reference to FIGS. Fig. 3 is a diagram showing the manufacturing steps in order, and Fig. 4 is a diagram explaining the state of the material or blade at each step in Fig. 3. The following explanation will be given with occasional reference to Figs. 3 and 4.

[0036] First, in the manufacturing method of the present invention, as shown in A of FIG. 4, a clad material 4 is used, which is made by laminating a plurality of metal materials and rolling them together. The layer structure of the clad material 4 is such that an alloy tool steel is used for the intermediate layer 42, and a steel material having a lower hardness than the intermediate layer 42 is used for the front and back layers 41·41. Specifically, SKD12 (JIS G4404) or the like, which has a high carbon content and good hardenability, is preferably used for the intermediate layer 42. Also, it is preferable to use stainless steel for the front and back layers 41·41 from the viewpoint of corrosion resistance. As an example, various ferritic stainless steels (JIS G4304) can be used, but martensitic stainless steel (JIS G4304) or the like can also be used as long as it has a lower hardness than the intermediate layer 42.

[0037] In this clad material 4, an alloy layer of copper and nickel (not shown) is interposed between the intermediate layer 42 and the front and back layers 41, 41. This alloy has a composition ratio of 25 to 70 wt% copper and 30 to 75 wt% nickel, and has a thickness of 0.2 mm or more. With such an alloy layer interposed, the layers are rolled at a temperature 150°C lower than the melting point of the alloy to laminate and integrate them. At this time, it is preferable to weld the outer circumferential surface of the clad material 4 in order to obtain a non-oxidized state. The clad material 4 having the above-mentioned layer structure prevents the phenomenon in which carbon atoms move from the high-carbon intermediate layer 42 to the low-carbon front and back layers 41, 41 during the heat treatment process described below due to the action of copper and nickel, which have a low carbon tendency. As a result, the carbon content of the intermediate layer 42, which becomes the cutting edge, can be maintained, and high hardness can be maintained.

[0038] The first step in the manufacturing method is a hammering process in which the above-mentioned clad material 4 is hammered, as shown in Figure 3 and Figure 4A. That is, using the hammering head 100, hammered patterns 43, 43... are forged into the front and back layers 41, 41 of the clad material 4, respectively, with a forging machine (not shown). This hammering process is cold forging carried out at room temperature. Various forging machines can be used, but it is preferable to use one that can sustain a constant load near the bottom dead center of the up and down movement of the ram. Suitable forging machines include belt hammers and spring hammers, but knuckle joint presses using flywheels can also be used. When using these forging machines, the descent is gradually decelerated to a low speed near the bottom dead center, and the ascent is rapid. This lengthens the time at the bottom dead center, and the kinetic energy of the ram is sufficiently imparted to the surface to be forged. Therefore, a sufficient amount of plastic deformation can be obtained with one stroke.

[0039] In the hammering process, the hammering head 100 is pressed multiple times against different locations on the front and back layers 41·41.... At this time, it is possible to press again at locations that have already been pressed once. The striking surface 1 of the hammering head 100 is neatly divided into a checkerboard pattern as shown in Figure 1, but by pressing different locations multiple times in this way, a random hammered pattern 43·43... is created.

[0040] As described above, the hammering head 100 has a plurality of striking portions 2·2... on the striking surface 1, and therefore the area in contact with the surface to be forged during forging is relatively small. As a result, a greater pressure is generated during the hammering process, causing plastic deformation in the intermediate layer 42 beyond the low-hardness front and back layers 41·41.... Furthermore, because the striking surface 1 has a height that follows the imaginary curved surface 3, the intermediate layer 42 is deformed so as to be pushed outward from the center of the hammering head 100 toward its outer periphery. In this way, by deforming the intermediate layer 42 multiple times in such a way that the intermediate layer 42 is pushed outward, the crystal grain size of the intermediate layer 42 becomes finer, the intermediate layer 42 elongates, and dense crystal grain boundaries are evenly distributed throughout the intermediate layer 42.

[0041] The next step is a press working step, as shown in Figures 3 and B of Figure 4. The clad material 4 that has been through the hammering step is punched out by a press machine (not shown) to obtain a blank material 5 in the shape of a blade. This punched shape will be approximately the outer shape of the blade that will be the final product, but since some elongation occurs due to forging in the cutting edge processing heat treatment step described below, it is preferable to take this amount of elongation into consideration when forming the shape.

[0042] The next step is a heat treatment step by quenching, as shown in Fig. 3 and C and D of Fig. 4. When the blank material 5 is placed in a heating furnace and heated to a temperature equal to or higher than the austenite transformation point, the pearlite (structure of ferrite 61 and cementite 62) of the alloy tool steel in the intermediate layer 42 transforms into austenite 63, as shown in Fig. 4C. Next, when the blank material 5 is quenched, the austenite 63 of the alloy tool steel in the intermediate layer 42 transforms into martensite 64, as shown in Fig. 4D.

[0043] Generally, if a high temperature is used during quenching, the crystal grain size will become coarse and the strength will decrease depending on the temperature and holding time. However, as described above, the blank 5 that has been hammered in advance with the hammering head 100 has extremely fine crystal grains, so that the decrease in strength can be suppressed even after quenching. Here, oil cooling or water cooling can be used for quenching, but air cooling is preferable when air cooling is sufficient to induce martensitic transformation, because the next thermo-mechanical treatment step is carried out in air.

[0044] The next step is a thermo-mechanical treatment step, as shown in Fig. 3 and E in Fig. 4. When the step is performed on the part that will become the cutting edge, it is distinguished as a cutting edge thermo-mechanical treatment step, but in any case, it is preferable to perform ausforming. Ausforming is a thermomechanical treatment that utilizes the aforementioned isothermal transformation. Ausforming is a processing method in which the material is held at a temperature higher than the martensite transformation point during cooling during quenching, and plastic deformation processing is performed before the isothermal transformation occurs. As a result, metastable austenite, which is in an unstable state that is prone to transformation, undergoes martensite transformation due to the energy of the plastic deformation processing. In addition, by completing processing and rapidly cooling before the isothermal transformation occurs, martensite transformation also occurs due to quenching.

[0045] Generally, martensite that has only been quenched is hard but brittle, so it is tempered, but while tempering imparts toughness, it also reduces hardness. However, ausformed structures are two-phase structures consisting of processing-induced martensite and martensite caused by quenching. This processing-induced martensite has extremely dense crystal grains, is hard, and exhibits little loss of toughness. In addition, most of the austenite remaining from ausforming is transformed into martensite by quenching, so there is little retained austenite and physical properties such as strength are stable over time.

[0046] Although ausforming has the above-mentioned characteristics, in practice, temperature control is extremely difficult. For example, when forging is performed as a plastic deformation process, a large amount of heat is removed from the steel when the hammer head comes into contact with the steel, causing the temperature to drop immediately. If the temperature of the steel falls below the martensite transformation point, transformation to processing-induced martensite does not occur, and the effect of ausforming cannot be obtained. There is also a method of maintaining the temperature by placing the steel in a heating furnace after each forging blow, but this requires frequent placement in the heating furnace during forging, and isothermal transformation occurs during which the austenite transforms into bainite or sorbite, preventing sufficient forging. Thus, although ausforming is a conventionally known technique, it is practically impossible to adopt it in forging, particularly in the manufacturing method of cutting tools.

[0047] In this regard, the heat treatment head 101 used in the cutting edge heat treatment process of the present invention has a striking surface 1 having a plurality of striking portions 2, 2..., and therefore the area of ​​contact with the forged surface during forging is small. Therefore, less heat escapes from the blank 5 through the heat treatment head 101. This allows the blank 5 to be sufficiently forged before its temperature drops below the martensite transformation point. Even if the temperature drops, the blank 5 can be placed in the heating furnace less frequently and for less time, allowing the blank 5 to be sufficiently forged and rapidly cooled before isothermal transformation occurs.

[0048] Furthermore, in the cutting edge heat treatment process, the heat treatment head 101 having a flat striking surface 1 is used, so that residual tensile stress in the portion that will become the cutting edge can be removed and compressive stress can be accumulated. This removes the tensile stress remaining from the hammering process, preventing the problem of cracks occurring over time when used as a blade. In addition, the remaining compressive stress offsets the tensile stress caused by external forces applied during use, preventing chipping and wear of the cutting edge.

[0049] The final step is a cutting blade formation step, as shown in Fig. 3 and Fig. 4F. In particular, by grinding the cutting blade using an automatic grinding machine, the cutting edge can be sharpened to form a blade 7 as shown in Fig. 4F. The blade 7 manufactured in this manner has beautiful hammered patterns 43, 43... formed by the hammering process on the belly 72. Also, the boundary between the part forged with the thermo-mechanical treatment head 101 and the part forged with the hammering head 100 appears as a wavy ridge 73 that resembles ripples. Furthermore, the cutting edge 71 is not only hard but also has excellent strength and toughness because the intermediate layer 42 is made of dual-phase steel of processing-induced martensite and martensite obtained by quenching. Therefore, it can be sharpened by grinding and has excellent wear resistance.

[0050] 『Variation 1』 Next, a modified example of a hammer head (hereinafter, also referred to as a "hammering head") used in the hammering process of the present invention will be described with reference to Fig. 5. In the following description, the same parts will be designated by the same reference numerals, and duplicated explanations will be omitted. The hammering head 102 of this modified example has the same basic structure as the hammering head 100 shown in FIG. 1, but is different in that the bearing surfaces 21 are not provided with the cylindrical convex portions 23.

[0051] In this way, when the cylindrical convex portions 23·23... are not provided, the hammered pattern 43·43... formed in the hammering process has an overall large wavy pattern, which gives a different impression from the hammered pattern 43·43... in the form shown in Figure 1. Even in this case, the bearing surfaces 21, 21... of the plurality of striking portions 2, 2... increase the forging pressure, and the crystal grain size can be made fine and dispersed uniformly.

[0052] In this modified example, when the top surface of each of the seating surfaces 21 is formed flat, it can be used in a thermo-mechanical treatment process.

[0053] 『Variation 2』 Next, another modified example of the hammering head of the present invention will be described with reference to FIG. The hammering head 103 of this modified example has a basic structure similar to that of the hammering head 100 shown in Fig. 1, but differs in that it has cylindrical convex portions 23 formed directly without having bearing surfaces 21. Another difference is that the top surfaces of the convex portions 23 are flat, with the height of each portion varying in stages.

[0054] When bearing surfaces 21·21... are provided as the striking portions 2·2..., the forged surface may be plastically deformed by forging, and part of the forged surface may come into contact with the bearing surfaces 21·21.... In this case, the grain flow lines produced by forging become more complex and contribute to refinement of the grain size, but the pattern of the bearing surfaces 21·21... may remain in the hammered patterns 43·43... that are formed. However, when the bearing surfaces 21... are not provided as in this modified example, the forging pressure in the hammering process is concentrated entirely on the cylindrical convex portions 23.... This allows plastic deformation to occur deeper into the intermediate layer 42, and the hammered patterns 43... that are formed are patterns of only circular shapes arranged randomly.

[0055] 『Variation 3』 Next, a modified example of the manufacturing method of the present invention will be described with reference to FIG. The manufacturing method of this modification is a method for manufacturing a blade without a hammered pattern using the hammer head of the present invention. The manufacturing method of this modification differs from the manufacturing method shown in Figures 3 and 4 in that it does not include a hammering process.

[0056] First, a clad material 4, which is a raw material, is pressed to obtain a blank material 5. This blank material 5 is quenched, and during the cooling process, ausforming is performed using a thermomechanical treatment head. Here, in the manufacturing method of Figs. 3 and 4, ausforming is performed on the portion that becomes the cutting edge, but this modified example is different in that ausforming is performed on the entire blank piece 5 in a thermo-mechanical treatment step.

[0057] In this way, by using the thermo-mechanical treatment head of the present invention, ausforming can be performed on the entire blank material 5 without suddenly lowering the temperature of the blank material 5. In addition, since the thermo-mechanical treatment head has a plurality of striking portions 2, plastic deformation by forging can be caused in the entire blank material 5 up to the intermediate layer 42. As a result, the intermediate layer 42 can be made into a dual-phase steel of deformation-induced martensite and quenched martensite in the entire blank material 5.

[0058] 『Variation 4』 Next, another modified example of the manufacturing method of the present invention will be described with reference to FIG. The manufacturing method of this modification is a manufacturing method for a hammered blade using the hammer head of the present invention. The manufacturing method of this modification differs from the manufacturing method shown in Figures 3 and 4 in that it does not include a thermo-mechanical treatment step.

[0059] In this modification, the cutting edge is not ausformed, but is tempered at a low temperature, and then the portion that will become the cutting edge with hammered pattern 43 is polished by an automatic polishing machine to form the cutting edge. Therefore, no processing-induced martensite is formed in intermediate layer 42 in the portion that will become the cutting edge, and the hardness is slightly reduced by tempering.

[0060] However, by using the hammering head of the present invention for forging in the hammering process, the grain size is already extremely fine, and even if tempered, the decrease in strength, etc. can be suppressed compared to blades that have been subjected to general heat treatment. In addition, by adjusting the tempering temperature and time, it is possible to adjust the balance between toughness and hardness while maintaining high strength, etc. [Explanation of symbols]

[0061] 100,102,103 Hammer heads for hammering processes 101 Hammerheads for thermomechanical processing 1. Striking surface 2. Striking section 21 Seat 22 Groove 23 Convex part 3 Virtual curved surface 4. Clad Materials 41 Front and back layers 42 Middle Class 43 Hammered pattern 5 Blank material 6. Organization Chart 61 Ferrite 62 Cementite 63 Austenite 64 Martensite 7. Knives 71 Cutting Edge 72 Belly 73 Ridge

Claims

1. In forging hammer heads used in the forging of cutting tools, The striking surface has a plurality of striking portions, A forging hammer head, characterized in that the multiple impact portions are shaped so that they contact the forged surface from one side to the other when the hammer head is lowered during forging.

2. The hitting portions are formed by dividing the hitting surface into a plurality of bearing surfaces, 2. The forging hammer head according to claim 1, characterized in that each bearing surface further comprises a convex portion.

3. 3. The forging hammer head according to claim 2, wherein the height of each of the plurality of striking portions is a height along a convex imaginary curved surface that covers the entire striking surface.

4. In a method for manufacturing a blade using the forging hammer head according to claim 1 or 2, a hammering process in which the forging hammer head is pressed against the material at different positions multiple times; A press working process for punching out the shape of a blade after the hammering process; A heat treatment step of heating and then cooling after the press working step; and forming a cutting edge after the heat treatment step.

5. In a method for manufacturing a blade using the forging hammer head according to claim 1 or 2, The press processing process cuts the material into the shape of a blade. A heat treatment step of heating and then cooling after the press working step; a thermomechanical treatment step of forging at least a part of the punched material with the forging hammer head during the cooling in the heat treatment step; and forming a cutting edge after the thermomechanical treatment step.

6. In a method for manufacturing a blade using the forging hammer head according to claim 1 or 2, a hammering process in which the forging hammer head is used to press the material at different positions multiple times; A press working process for punching out the shape of a blade after the hammering process; A heat treatment step of heating and then cooling after the press working step; a cutting edge processing heat treatment process in which a portion that becomes a cutting edge is forged with the forging hammer head during cooling in the heat treatment process; and forming a cutting edge after the cutting edge heat treatment step.

7. In the hammering process, a hammer head having a plurality of striking portions is used, the striking portions being shaped so that the order of contact with the forged surface when the hammer head descends is from one side to the other, 7. The method for manufacturing a blade according to claim 6, wherein a hammer head having a striking surface of a substantially flat shape is used in the cutting edge heat treatment step.

8. The method for manufacturing a blade according to any one of claims 4 to 7, characterized in that the material is a clad material having an intermediate layer made of steel and front and back layers made of steel having a lower hardness than the intermediate layer and laminated integrally on the front and back of the intermediate layer.

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