Method of manufacturing japanese sword

Abstract

To provide a method of manufacturing a Japanese sword that can forge a sword with minimum reduction of steel.SOLUTION: A method of manufacturing a Japanese sword includes: a first step S1 of heating and beating out steel; a second step S2 of crushing the beaten steel; a third step S3 of selecting steel of good quality from the crushed steel; a fourth step S4 of stacking the selected steel; a fifth step S5 of heating and integrating the stacked steel; and a sixth step S6 of heating and beating out the integrated steel, and then folding it in two layers. In the first step S1, the steel is heated to a temperature of 800°C or lower and rolled to a thickness of 0.3 mm or less, and the sixth step S6 is repeated three times or four times.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a Japanese sword that allows forging while minimizing the loss of steel. [Background technology]

[0002] As a conventional method for manufacturing Japanese swords, for example, the method described in Patent Document 1 is known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7050373 Summary of the Invention [Problem to be solved by the invention]

[0004] In the traditional manufacturing process of Japanese swords, the steel is flattened, then folded and stacked in two, a process that is repeated about 15 times. 15 =32,768 layers of steel are formed, which is said to result in a strong Japanese sword.

[0005] However, it is said that after repeated forging, only about 10 to 20 percent of the steel's weight remains. The reason for this is thought to be that an oxide film is likely to form on the surface of hot steel during forging, and this oxide film peels off during forging. Incidentally, even if the loss per each repeated forging is 10%, the steel remaining after 15 forgings is only 0.9% of the original weight. 15 =0.21, which means only about 20% remains.

[0006] Therefore, an object of the present invention is to provide a method for manufacturing a Japanese sword that allows for forging while minimizing the loss of steel. [Means for solving the problem]

[0007] The manufacturing method of the Japanese sword of the present invention comprises a first step of heating and beating steel, a second step of crushing the beaten steel, a third step of selecting high-quality steel from the crushed steel, a fourth step of stacking the selected steel, a fifth step of heating the stacked steel to combine it into one piece, and a sixth step of heating and beating the combined piece of steel and then folding it back to make two pieces. In the first step, the steel is heated to a temperature of 800°C or less and beaten into a thickness of 0.3 mm or less, and the sixth step is repeated three or four times. Effect of the Invention

[0008] According to the method for manufacturing Japanese swords of the present invention, the heating temperature of the steel in the first step is set to 800°C or less, which is lower than the conventional temperature, thereby minimizing the oxidation of the steel. Also, in the first step, the steel is hammered out to a thickness of 0.3 mm or less, which is thinner than the conventional method, thereby effectively removing impurities. Furthermore, by reducing the number of times of the sixth step to three or four times, which is less than the conventional number of times, the amount of steel that oxidizes can be suppressed. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is an explanatory diagram showing the steps of the method for manufacturing a Japanese sword of the present invention. [Diagram 2] FIG. 13 is an explanatory diagram showing the folding forging process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The method for manufacturing a Japanese sword of the present invention will be described in detail based on the following examples. Note that the present invention is not limited to the following examples, and various modifications are possible without departing from the spirit of the present invention.

[0011] Explaining with reference to Figure 1, first, steel that will be the raw material for the Japanese sword is prepared (S0). For this steel, steel called tamahagane, which has an appropriate carbon content and is of excellent quality, is preferably used.

[0012] In the first step, the steel is heated and hammered (S1). This process is called Mizuheshi.

[0013] In conventional methods, steel is heated to 1000°C or higher in this process. However, when heated to 1000°C or higher, steel is easily oxidized, resulting in the loss of some of the valuable raw materials. Therefore, in the method of the present invention, the heating temperature of steel is set to 800°C or lower to minimize the oxidation of steel. The heating temperature of steel is preferably 700 to 800°C, which is the quenching temperature of steel, and more preferably 750 to 800°C. This is because a low heating temperature reduces the ductility of steel, making it difficult to process, and a high heating temperature causes the oxidation of steel to proceed rapidly.

[0014] In addition, in conventional methods, the steel is rolled to a thickness of about 5 to 10 mm in this step. In contrast, in the method of the present invention, the steel is rolled to a thickness of 0.3 mm or less, and lumps of hard and brittle impurities such as silicon oxide contained in the steel are crushed and removed from the steel. It is preferable that the thickness of the steel after rolling is as thin as possible in order to remove the impurities, but in consideration of workability, it is preferable that the thickness be 0.1 to 0.3 mm, and more preferably 0.1 to 0.2 mm.

[0015] Finally, the burnt black skin on the surface is removed by hitting it with a hot steel foil on a damp anvil.

[0016] Next, in the second process, the steel that was rolled out in the first process is crushed (S2). This process is called "shredding." As a result, thin strips of steel are obtained.

[0017] In the third process, high-quality steel is selected from the steel crushed in the second process (S3), and in the fourth process, the steel selected in the third process is stacked (S4). Here, the steel is stacked on a platform made of the same quality steel. This platform has a handle attached to it.

[0018] Next, in the fifth process, the steel stacked in the fourth process is heated and integrated (S5). This process is called "tsumi-bokashi." By heating it up to about 1300℃ over a long period of time, the steel becomes completely integrated.

[0019] Furthermore, in the sixth process, the steel that was integrated in the fourth process is heated and stretched, and then folded back to make two pieces (S6). This process is called folding forging.

[0020] This process will be described with reference to Figure 2. This process is carried out while heating to over 1000°C in order to bond the two overlapping sheets of steel together. First, the steel is hammered out (S61), chiseled horizontally to fold it back (S62), and stacked into two sheets (S63). Next, if this process is to be repeated, the two overlapping sheets of steel are hammered out again into one sheet (S64), chiseled vertically in a different direction from the previous process to fold it back (S65), and stacked into two sheets (S66). If this process is to be repeated from then on, the two overlapping sheets of steel are hammered out again into one sheet (S61), and the same process is repeated from then on.

[0021] In the conventional method, this process of folding back and stacking the steel after rolling was repeated about 15 times. However, the long heating and rolling at 1000°C or higher caused a large amount of oxidation of the steel, which resulted in the loss of 80 to 90 percent of the valuable raw material before and after the folding and forging. Therefore, in the method of the present invention, this process of folding back and stacking the steel after rolling back is repeated only three or four times to prevent the oxidation of the steel. Note that if this process is repeated twice, the surface of the resulting steel is too rough, which is not preferable, while if this process is repeated five or more times, it is not preferable because the loss due to oxidation of the steel is large.

[0022] The rest of the process is the same as before: the shin-gane and kawa-gane are produced using the methods described above, the shin-gane is wrapped in kawa-gane, the shin-gane is hammered out to the length of the sword, the hi-tsuji is forged, and the sword is then placed on the ground, quenched, sharpened, engraved, and polished, before the Japanese sword is completed.

[0023] As described above, the method for manufacturing a Japanese sword of the present invention includes a first step S1 of heating and rolling steel, a second step S2 of crushing the rolled steel, a third step S3 of selecting high-quality steel from the crushed steel, a fourth step S4 of stacking the selected steel, a fifth step S5 of heating and integrating the stacked steel, and a sixth step S6 of heating and rolling the integrated steel, then folding it back to stack it in two sheets. In the first step S1, the steel is heated to a temperature of 800°C or less and rolled to a thickness of 0.3 mm or less, and the sixth step S6 is repeated three or four times. Therefore, according to the method for manufacturing a Japanese sword of the present invention, by setting the heating temperature of the steel to 800°C or less, which is lower than the conventional temperature, in the first step S1, oxidation of the steel can be prevented. In addition, by rolling the steel to a thickness of 0.3 mm or less, which is thinner than the conventional method, in the first step S1, impurities can be effectively removed. Furthermore, by performing the sixth step S6 three or four times, which is less than the conventional number of times, the amount of steel that oxidizes can be reduced.

[0024] Silicon oxide, the main impurity, is brittle and has almost no viscosity at room temperature. Steel, on the other hand, retains sufficient viscosity even when heated. This method takes advantage of the large difference in ductility between steel and silicon oxide to remove the silicon oxide present in the steel. Specifically, a small piece less than half the size of a quail's egg or chicken egg is cut out from a block of steel, and this small piece is heated and beaten to make it thinner than 0.3 mm, during which the silicon oxide falls off and is removed. At this time, the heating temperature is kept below 800°C to minimize oxidation of the steel due to heating. At this temperature, the silicon oxide in the steel retains almost no viscosity.

[0025] The lower the temperature of the steel, the less efficient the processing becomes, so in order to thin the steel to 0.3 mm or less, the heating and rolling process is repeated several times. By this method, at least half of the original weight is retained. [Explanation of symbols]

[0026] S1 First step S2 Second process S3 Third process S4 The fourth step S5 The fifth step S6 Sixth process

Claims

[Claim 1] A method for manufacturing a Japanese sword comprising a first step of heating and beating steel, a second step of crushing the beated steel, a third step of selecting high quality steel from the crushed steel, a fourth step of stacking the selected steel, a fifth step of heating the stacked steel to combine it into one piece, and a sixth step of heating and beating the combined steel piece and then folding it back to make two pieces, wherein in the first step, the steel is heated to a temperature of 800°C or less and beaten to a thickness of 0.3 mm or less, and the sixth step is repeated three or four times.

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