Method for dividing metal material

Abstract

This method for dividing a metal material includes: a first step for forming a molten pool in a metal material by selectively heating a principal surface of the metal material and forming a solidified portion of the molten pool; and a second step for dividing the metal material within the solidified portion, and / or from the outer edge of the solidified portion in a plan view as a starting point.

Description

How to divide metal materials

[0001] The present disclosure relates to a method for dividing a metal material.

[0002] Conventionally, cutting methods such as gas cutting and laser cutting have been used to divide metal materials such as steel. For example, Patent Document 1 below discloses a gas cutting method in which a target object is cut using a flammable gas containing hydrogen. In the cutting method described above, the metal material is melted using a high-temperature heat source such as a flame or a laser. The molten portion of the metal material is then blown away and removed from the metal material by a jet of supply gas, assist gas, or the like.

[0003] JP 2024-8321 A

[0004] In the above-described fusing method, it is necessary to completely melt the portion of the metal material to be removed and then blow away the portion as spatter (waste). Therefore, the melted region, which is the portion of the metal material to be removed, needs to extend from the front surface to the back surface of the metal material. Therefore, when fusing metal material, the amount of energy required to melt the metal material tends to be large. In addition, when fusing metal material, the spatter is scattered around. Therefore, when fusing metal material, consideration and maintenance of the surrounding environment are required.

[0005] An object of one aspect of the present disclosure is to provide a method for dividing a metal material that can suppress both the amount of energy consumed for melting the metal material and the generation of spatter.

[0006] A method for dividing a metal material according to one aspect of the present disclosure includes a first step of forming a molten pool in the metal material by selectively heating a main surface of the metal material and forming a solidified portion of the molten pool, and a second step of dividing the metal material starting from within the solidified portion and / or the outer edge of the solidified portion in a planar view.

[0007] According to one aspect of the present disclosure, it is possible to provide a method for dividing a metal material that can suppress both the amount of energy consumed for melting the metal material and the generation of spatter.

[0008] Each of (a) to (c) in Figure 1 is a schematic diagram for explaining a method for dividing a metal material according to an embodiment. (a) in Figure 2 is a diagram showing the temperature-hydrogen solubility curve of a pure iron material, and (b) in Figure 2 is a diagram showing the temperature-hydrogen solubility curve of an aluminum material. (c) in Figure 3 is a schematic perspective view showing a metal material according to a modified example. (d) in Figure 4 is a schematic diagram showing a method for preparing an experimental sample. (a) and (b) in Figure 5 are diagrams showing the results of a thermal desorption test. (e) in Figure 6 is a diagram showing the relationship between laser output and hardness of the solidified portion. (a) in Figure 7 is a photograph showing a main portion of the front side of a medium-carbon steel plate after standing, and (b) in Figure 7 is a photograph showing a main portion of the back side of the medium-carbon steel plate after standing. FIG. 8(a) is a photograph showing a main portion of the front side of the joined body of Experimental Example 2, FIG. 8(b) is a photograph showing a main portion of the back side of the joined body of Experimental Example 2, FIG. 8(c) is a photograph showing a main portion of the front side of the joined body of Experimental Example 3 after standing, FIG. 8(d) is a photograph showing a main portion of the back side of the joined body of Experimental Example 3 after standing, FIG. 8(e) is a photograph showing a main portion of the front side of the joined body of Experimental Example 4 after standing, and FIG. 8(f) is a photograph showing a main portion of the back side of the joined body of Experimental Example 4 after standing. FIG. 9 is a photograph showing the parting surface of the joined body of Experimental Example 4. FIG. 10 is a diagram showing the fracture test results of Experimental Example 5. FIGS. 11(a) and 11(b) are enlarged photographs showing the fracture surface of the fifth sample after the fracture test, and FIGS. 11(c) and 11(d) are enlarged photographs showing the fracture surface of the fourth sample after the fracture test. FIG. 12 is a diagram showing the change in fracture properties of a metal material depending on whether or not a solidified portion is present in Experimental Example 6. FIG. 13(a) is an enlarged photograph showing the fracture surface of Sample 6 after a fracture test, and FIG. 13(b) is an enlarged photograph showing the fracture surface of Sample 7 after a fracture test. FIG. 14 is a diagram showing the change in fracture properties of a metal material depending on whether or not a solidified portion is present in Experimental Example 8. FIG. 15(a) is an enlarged photograph showing the fracture surface of Sample 8 after a fracture test, and FIG. 15(b) is an enlarged photograph showing the fracture surface of Sample 9 after a fracture test. FIG. 16(a) is a cross-sectional perspective view of Sample 11, and FIG. 16(b) is a cross-sectional perspective view of Sample 12. FIG. 17 is a schematic diagram showing the measurement area of ​​residual stress. FIG. 18(a) is a diagram showing the measurement results of residual stress of Sample 13, and FIG. 18(b) is a diagram showing the measurement results of residual stress of Sample 14.19(a) and 19(b) are enlarged photographs showing the cross section of Sample 13 after the residual stress measurement, and Fig. 20(a) and 20(b) are enlarged photographs showing the cross section of Sample 14 after the residual stress measurement.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, identical elements or elements having the same functions will be designated by the same reference numerals, and redundant explanations will be omitted. In this specification, the term "same" and similar words are not limited to "completely identical." Furthermore, since the drawings are intended to conceptually explain the embodiments, the dimensions and ratios of the depicted components may differ from the actual dimensions.

[0010] (1) Overview of the method for dividing a metal material The method for dividing a metal material according to this embodiment melts the metal material while suppressing spattering of the metal material. The dividing method includes a first step of selectively heating a main surface of the metal material to form a molten pool in the metal material and forming a solidified portion of the molten pool, and a second step of dividing the metal material starting from within the solidified portion and / or the outer edge of the solidified portion in a plan view.

[0011] (2) Details of the method for dividing a metal material Next, details of the method for dividing a metal material according to this embodiment will be described with reference to (a) to (c) of Figure 1. (a) to (c) of Figure 1 are each a schematic diagram for explaining the method for dividing a metal material according to this embodiment.

[0012] First, we will explain the metal material to be divided. FIGS. 1A to 1C show the metal material 1 to be divided. In FIGS. 1A to 1C, the metal material 1 is a single member having a plate shape, but this is not limited thereto. For example, the metal material 1 may have a cylindrical, square, H-shaped, I-shaped, or T-shaped configuration. Furthermore, the metal material 1 may be a butt-welded or fillet-welded assembly of different metal materials (e.g., a plate-shaped first metal material and a plate-shaped second metal material). The metal material 1 is a member made of a metal plate or an alloy plate. The metal material 1 includes, for example, aluminum, iron, magnesium, copper, titanium, nickel, zinc, cobalt, niobium, zirconium, silver, etc. Therefore, the metal material 1 includes, for example, aluminum materials such as aluminum alloys, steel materials such as stainless steel, nickel-chromium steel, invar (alloy steel), and carbon steel, magnesium materials such as magnesium alloys, titanium alloys, copper alloys, etc. In one example, the thickness of the metal material 1 is 1 mm or more and 100 mm or less. In this case, the metal material 1 can be satisfactorily divided by the dividing method according to this embodiment. The thickness of the metal material 1 corresponds to the dimension of the metal material 1 along a direction (thickness direction) perpendicular to the direction in which the main surface 1a of the metal material 1 extends. Hereinafter, viewing the metal material 1 from the thickness direction may be referred to as a planar view.

[0013] In the method for dividing a metallic material 1 according to this embodiment, first, as shown in Figures 1(a) and 1(b), a main surface 1a of the metallic material 1 is selectively heated to form a molten pool MP in the metallic material 1, and a solidified portion 2 of the molten pool MP is formed (Step 1). For the sake of explanation, the step of selectively heating the main surface 1a of the metallic material 1 to form a molten pool MP in the metallic material 1 will be referred to as Step 1A, and the step of forming the solidified portion 2 of the molten pool MP will be referred to as Step 1B. Figure 1(a) shows Step 1A, and Figure 1(b) shows Step 1B. Steps 1A and 1B may be performed simultaneously or successively.

[0014] In the first step, a fragile portion VP including a solidified portion 2 may be formed in the metal material 1. The fragile portion VP is a portion of the metal material 1 that has become fragile during and / or after the first step. When the fragile portion VP is formed in the metal material 1, the fragile portion VP may be formed simultaneously with the formation of the molten pool MP, or the fragile portion VP may be formed after the formation of the molten pool MP. The fragile portion VP corresponds to, for example, the solidified portion 2, but is not limited to this. The solidified portion 2 may be a part of the fragile portion VP. For example, the fragile portion VP may correspond to the solidified portion 2 and its surrounding area in the metal material 1. Note that, depending on the type of metal material 1, the fragile portion VP may not be formed in the first step.

[0015] As shown in FIG. 1A, in step 1A, a laser beam L is irradiated onto a main surface 1a of a metal material 1 using a laser irradiation device LA. This melts a portion of the metal material 1, forming a molten pool MP. In one example, the depth of the molten pool MP is 10% to 100% of the thickness of the metal material 1. From the viewpoint of energy consumption associated with dividing the metal material 1, the depth of the molten pool MP may be 10% to 50%, 20% to 40%, or 25% to 30% of the thickness of the metal material 1. From the viewpoint of ease of dividing the metal material 1 (described later), the depth of the molten pool MP may be 50% to 95%, 75% to 92%, or 80% to 90% of the thickness of the metal material 1. In step 1A, a laser beam L is irradiated onto a portion of the metal material 1 to be divided. When the metallic material 1 is the above-described welded body, the planned division portion may be formed at a joint between a first metallic material and a second metallic material in the welded body. In this case, a molten pool MP is formed at the joint that is the planned division portion. Note that the welded portion is a solid-state welded body formed by solid-state welding such as friction stir welding, linear friction welding, or pressure-controlled current welding.

[0016] In this embodiment, the metal material 1 is placed on a stage (not shown) or the like when the above-described step 1A is performed. That is, the laser L is irradiated onto the main surface 1 a of the metal material 1 with the main surface 1 a aligned in the horizontal direction. However, the laser L may also be irradiated onto the main surface 1 a of the metal material 1 with the main surface 1 a aligned in the vertical direction or intersecting with the horizontal direction.

[0017] The laser irradiation device LA moves in one direction (movement direction D of the laser irradiation device LA) in the direction in which the main surface 1a extends. As a result, a molten pool MP is formed along the movement direction D. In this embodiment, the movement direction D corresponds to the long side direction of the main surface 1a of the metal material 1, but is not limited thereto. In one example, the movement speed of the laser irradiation device LA (the rate of change of the irradiation position of the laser L) is 300 mm / min (5 mm / s) or more and 1500 mm / min (25 mm / s) or less. The output of the laser L from the laser irradiation device LA depends on the material of the metal material 1, but is, for example, 0.5 kW or more and 50 kW or less. Note that in Step 1A, arc discharge or the like may be used instead of the laser irradiation device LA. That is, in Step 1A, a molten pool MP may be selectively formed in the metal material 1 by a method other than laser irradiation. In one example, when the metallic material 1 is a steel material, the output of the laser L is set to 1.4 kW or more and 2.0 kW or less, and the change rate is set to 400 mm / min or more and 700 mm / min or less. In this case, an appropriate heat input to the metallic material 1 can be applied so that pearlite does not precipitate in the molten pool MP. In addition, uniform martensitic transformation can occur in the molten pool MP. Note that pearlite precipitates when the heat input to the metallic material 1 is excessive. The precipitation of pearlite makes it less likely that cracks B, which will be described later, will occur.

[0018] In step 1A, atmospheric gas AG (shielding gas) is sprayed onto the main surface 1a of the metal material 1. In one example, the atmospheric gas AG is sprayed onto the main surface 1a by a gas holder H that is located near the main surface 1a of the metal material 1 and is movable along the movement direction D. The gas holder H moves in conjunction with the movement of the laser irradiation device LA. This allows the spraying of the atmospheric gas AG to effectively exhibit its anti-oxidation function. The spray amount (flow rate) of the atmospheric gas AG is, for example, 3.3 × 10 －４ m ３ / sec or more 4.2 x 10 －４ m ３ In the first A step, instead of spraying the atmospheric gas AG, the molten pool MP may be formed in an oxygen-reduced environment.

[0019] In step 1A, atmospheric gas AG is sprayed onto the main surface 1a of the metal material 1, while dissolving gas in the molten pool MP. The gas is contained in the atmospheric gas AG. The atmospheric gas AG contains at least one of nitrogen gas, hydrogen gas, and an inert gas. Therefore, the gas dissolved in the molten pool MP is at least one of nitrogen gas, hydrogen gas, and an inert gas. In one example, the atmospheric gas AG may be only an inert gas, may be only nitrogen gas, or may contain an inert gas and at least one of nitrogen gas and hydrogen gas. The proportion of at least one of nitrogen gas and hydrogen gas in the atmospheric gas AG is 0.1 vol% or more and 5 vol% or less. In other words, the proportion of the inert gas in the atmospheric gas AG is 95 vol% or more and 99.9 vol% or less. The proportion of at least one of nitrogen gas and hydrogen gas in the atmospheric gas AG is, for example, 0.3 vol% or more, 0.5 vol% or more, 1 vol% or more, and 4 vol% or less, 3 vol% or less, 2.5 vol% or less. When the metal material 1 is a steel material, aluminum material, magnesium material, or the like, the gas dissolved in the molten pool MP may contain hydrogen. This prevents embrittlement caused by hydrogen (hydrogen embrittlement), making it easier to divide the metal material 1. When the metal material is a copper material, from the standpoints of cost, gas solubility, and the like, the gas dissolved in the molten pool MP may contain nitrogen. The inert gas is, for example, a rare gas.

[0020] 1B, a solidified portion 2 is formed in the metal material 1. In the first step, the molten pool MP formed in the metal material 1 is cooled to form the solidified portion 2 extending along the moving direction D. The cooling of the molten pool MP is not particularly limited, but may be, for example, natural cooling.

[0021] In Step 1B, the solidified portion 2 may be formed so that the metal structure within the solidified portion 2 differs from the metal structure of a portion of the metallic material 1 other than the solidified portion 2. This may result in differences in hardness, etc., between the solidified portion 2 and the portion other than the solidified portion 2 in the metallic material 1. Furthermore, solidification of the molten pool MP may cause a portion of the metallic material 1 to deform. Based on the above phenomenon, tensile stress (residual stress) may occur within the solidified portion 2 or at the boundary between the solidified portion 2 and the portion of the metallic material 1 other than the solidified portion 2 (e.g., the outer edge 2a of the solidified portion 2 in a plan view). Note that, when the metallic material 1 is a steel material, quenching may be performed during the formation of the solidified portion 2. For example, when the metallic material 1 is a steel material, martensitic transformation may occur during the formation of the solidified portion 2. At this time, when hydrogen is dissolved in the molten pool MP in Step 1A, the hydrogen may diffuse to the prior austenite grain boundaries of the martensitic structure. This may result in the formation of a brittle portion VP. The above-mentioned changes in hardness, deformation, etc. can occur not only in the solidified portion 2 but also in the vicinity of the solidified portion 2 in the metal material 1. The degree of the above-mentioned changes in hardness, deformation, etc. can be adjusted by the conditions for forming the molten pool MP in step 1A (i.e., the heating conditions for the metal material 1).

[0022] In step 1B, blowholes (not shown) caused by the gas are formed in the solidified portion 2. These blowholes can be formed when the gas dissolved in the molten pool MP in step 1A escapes as the molten pool MP cools. The blowholes are formed by utilizing the difference in solubility between the solid and liquid metal materials 1. For example, as shown in FIG. 2A, when the metal material 1 is pure iron, the gas solubility in the solid metal material 1 is approximately 10 ppm, whereas the gas solubility in the liquid metal material 1 is approximately 30 ppm. For another example, as shown in FIG. 2B, when the metal material 1 is aluminum, the gas solubility in the solid metal material 1 (e.g., at 600°C or lower) is 1 ml / 100 g or less, whereas the gas solubility in the liquid metal material 1 (e.g., at 1000°C or higher) is 4 ml / 100 g or more. In addition, in the first step, from the viewpoint of promoting the formation of blowholes by suppressing the release of gas, the laser L may be irradiated onto the main surface 1a of the metal material 1 in a state where the main surface 1a is aligned along the vertical direction or intersects with the horizontal direction.

[0023] Next, as shown in FIG. 1C, the metal material 1 is split within the solidified portion 2 and / or at the outer edge 2a of the solidified portion 2 as a starting point (second step). In the second step, a crack B is generated within the solidified portion 2 and / or at the outer edge 2a of the solidified portion 2 due to, for example, the generation of the tensile stress described above. Next, the metal material 1 is split using the crack B. In this manner, the splitting of the metal material 1 is carried out. Note that the force required to generate the crack B and split the metal material 1 corresponds to the sum of the residual stress of the metal material 1 and the external force applied to the metal material 1. The force required to generate the crack B and the force required to split the metal material 1 may be the same or different. Here, the external force may be zero. For example, the crack B may be generated while the metal material 1 is left stationary, or may be generated by applying an external force to the metal material 1. In the latter case, for example, cracks B may occur by pulling the metal material 1 in a direction perpendicular to the thickness direction and the moving direction D. When blowholes are formed in the first step B, hydrogen embrittlement occurs, or the like, cracks B may occur even when the metal material 1 is left stationary.

[0024] According to the method for dividing a metallic material 1 according to the present embodiment, a molten pool MP is formed in the metallic material 1 in step 1A, and then a solidified portion 2 of the molten pool MP is formed in step 1B. In this case, a difference in hardness between the solidified portion 2 and a portion other than the solidified portion 2 in the metallic material 1, partial deformation of the metallic material 1, and other problems may occur. This may result in residual stress within the metallic material 1. Therefore, tensile stress may be generated within the solidified portion 2 and / or at the outer edge 2a of the solidified portion 2. This tensile stress can then be used to divide the metallic material 1 starting from the solidified portion 2 and / or the outer edge 2a of the solidified portion 2 in step 2. By performing the first and second steps described above, fusion cutting is not required when dividing the metallic material 1. In other words, the metallic material 1 is divided without any molten portion present. Therefore, by performing the method for dividing a metallic material 1 according to the present embodiment, it is possible to reduce both the energy consumption for melting the metallic material 1 and the generation of spatter.

[0025] In one example, in the first step, a gas may be dissolved in the molten pool MP, thereby forming blowholes due to the gas in the solidified portion 2. In this case, cracks B are likely to occur in the solidified portion 2 and / or on the outer edge 2a of the solidified portion 2, making it easier to split the metal material 1.

[0026] In one example, in the first step, gas may be dissolved in the molten pool MP by spraying atmospheric gas onto the main surface 1a of the metal material 1. The atmospheric gas may also contain at least one of nitrogen gas and hydrogen gas, and an inert gas. The proportion of at least one of nitrogen gas and hydrogen gas in the atmospheric gas may be 0.1% by volume or more and 5% by volume or less. In these cases, blowholes are more likely to form in the solidified portion 2.

[0027] In one example, the metal material 1 is a steel material, an aluminum material, or a magnesium material, and the gas may contain hydrogen. In this case, hydrogen embrittlement occurs in the metal material 1, and cracks B are likely to occur in the solidified portion 2 and / or on the outer edge 2 a of the solidified portion 2, making the metal material 1 easily splittable.

[0028] In one example, the metal material may be a copper material and the gas may contain nitrogen. In this case, blowholes are likely to be formed in the solidified portion 2 at low cost.

[0029] In one example, in the second step, the metal material 1 may be left to stand until cracks B occur in the solidified portion 2 and / or on the outer edge 2 a of the solidified portion 2, and then the metal material 1 may be divided. In this case, the metal material 1 can be divided at low cost.

[0030] In one example, the laser L may be irradiated onto the main surface 1 a of the metal material 1 in a state where the main surface 1 a is aligned vertically or intersects with the horizontal direction. In this case, the strength of the solidified portion 2 can be effectively reduced.

[0031] In one example, the thickness of the metal material 1 is 1 mm or more and 100 mm or less. In this case, the metal material 1 can be suitably divided by the method for dividing the metal material 1 according to this embodiment.

[0032] In one example, in the first step, the depth of the molten pool MP may be 10% or more and 100% or less of the thickness of the metallic material 1. In this case, the strength of the solidified portion 2 can be reduced satisfactorily.

[0033] In one example, the metallic material 1 is a joined body of a first metallic material and a second metallic material, and in the first step, a molten pool MP is formed at the joint between the first metallic material and the second metallic material in the joined body. The joined body may be a solid-state joined body. In these cases, residual stress may be generated inside the metallic material 1 (particularly at the joint and its periphery) due to strain generated during the formation of the joint. The presence of this residual stress makes it easy to separate the metallic material 1. Here, the residual stress may vary depending on the joining conditions. Therefore, by adjusting the manufacturing conditions of the joined body, it becomes easier to separate the metallic material 1.

[0034] The methods for dividing a metallic material according to the present disclosure are as described in [1] to

[14] below, and have been described in detail based on the above-mentioned embodiments. [1] A method for dividing a metallic material, comprising: a first step of selectively heating a main surface of the metallic material to form a molten pool in the metallic material and form a solidified portion of the molten pool; and a second step of dividing the metallic material starting from within the solidified portion and / or the outer edge of the solidified portion in a plan view. [2] The method for dividing a metallic material according to [1], wherein the first step involves dissolving a gas in the molten pool to form blowholes in the solidified portion due to the gas. [3] The method for dividing a metallic material according to [2], wherein the first step involves spraying an atmospheric gas against the main surface of the metallic material to dissolve the gas in the molten pool. [4] The method for dividing a metallic material according to [3], wherein the atmospheric gas includes at least one of nitrogen gas and hydrogen gas, and an inert gas. [5] The method for dividing a metallic material according to [4], wherein the proportion of at least one of the nitrogen gas and the hydrogen gas in the atmospheric gas is 0.1% by volume or more and 5% by volume or less. [6] The method for dividing a metallic material according to any one of [2] to [5], wherein the metallic material is a steel material, an aluminum material, or a magnesium material, and the gas contains hydrogen. [7] The method for dividing a metallic material according to any one of [2] to [5], wherein the metallic material is a copper material, and the gas contains nitrogen. [8] The method for dividing a metallic material according to any one of [1] to [7], wherein in the third step, the metallic material is left to stand and cracks occur in the solidified portion and / or on the outer edge of the solidified portion, and then the metallic material is divided. [9] The method for dividing a metallic material according to any one of [1] to [8], wherein in the first step, the depth of the molten pool is 10% by volume or more and 100% by volume or less of the thickness of the metallic material.

[10] The method for dividing a metal material according to any one of [1] to [9], wherein in the first step, the laser is irradiated onto the main surface of the metal material in a state where the main surface is aligned along the vertical direction or intersects with the horizontal direction.

[11] The method for dividing a metallic material according to

[10] , wherein, when the metallic material is a steel material and hydrogen is dissolved in the molten pool in the first step, the output of the laser is 1.4 kW or more and 2.0 kW or less, and the rate of change of the laser irradiation position is 400 mm / min or more and 700 mm / min or less.

[12] The method for dividing a metallic material according to any one of [1] to

[11] , wherein, when the direction perpendicular to the direction in which the main surface of the metallic material extends is the thickness direction of the metallic material, the thickness of the metallic material is 1 mm or more and 100 mm or less.

[13] The method for dividing a metallic material according to any one of [1] to

[12] , wherein the metallic material is a joined body of a first metallic material and a second metallic material, and in the first step, the molten pool is formed at the joint between the first metallic material and the second metallic material in the joined body.

[14] The method for dividing a metallic material according to

[13] , wherein the metallic material is a solid-state joined body of the first metallic material and the second metallic material.

[0035] However, one aspect of the present disclosure is not limited to the above embodiment and the above [1] to

[14] . One aspect of the present disclosure can be further modified within the scope of the gist thereof.

[0036] In the above embodiment, in the second step, an external force is applied to the metal material along a direction perpendicular to the thickness direction and the moving direction, but this is not limited to this. The method of applying an external force to the metal material can be appropriately changed depending on the shape of the metal material, etc. FIG. 3 is a schematic perspective view showing a metal material according to a modified example. As shown in FIG. 3, the metal material 5 according to the modified example is a fillet-welded joint of a first metal material 6 and a second metal material 7, and has a T-shape. In the metal material 5, the center of the main surface 6 a of the first metal material 6 and the second metal material 7 are integrated with each other via fillet welds 8 and 9. The fillet weld 8 is formed on a part of the main surface 6 a of the first metal material 6 and a part of the back surface 7 b of the second metal material 7, and is part of the main surface of the metal material 5. The fillet weld 9 is formed on another part of the main surface 6 a of the first metal material 6 and another part of the main surface 7 a of the second metal material 7, and is part of the main surface of the metal material 5. In this modification, the first metallic material 6 and the second metallic material 7 can be separated using a method similar to that of the above embodiment. For example, in the first step, the fillet weld 8 is selectively heated to form a molten pool in the metallic material 5, and a solidified portion of the molten pool is formed. At this time, for example, the main surface 6 a of the first metallic material 6 or the main surface 7 a of the second metallic material 7 may be selectively heated. Furthermore, not only the fillet weld 8 but also the fillet weld 9 may be selectively heated. Subsequently, in the second step, the first metallic material 6 and the second metallic material 7 are separated from each other starting from within the solidified portion and / or the outer edge of the solidified portion in a plan view. For example, when applying an external force to the metallic material 5 in the second step, the first metallic material 6 and the second metallic material 7 can be efficiently and easily separated by fixing the first metallic material 6 and applying an external force OP along the thickness direction of the second metallic material 7 to the free end 7 c of the second metallic material 7.

[0037] The present disclosure will be explained in more detail by the following experimental examples, but the present disclosure is not limited to these examples.

[0038] <Confirmation of Gas Dissolved in Metal Material As a Weld Pool Forms> Using the sample shown in Figure 4, the presence of gas dissolved in metal material as a weld pool forms was confirmed. Figure 4 is a schematic diagram showing the preparation method of the experimental samples. First, multiple medium-carbon steel plates P1 (model number: S45C) with long sides of 15 mm, short sides of 10 mm, and thickness of 2 mm were prepared, and multiple medium-carbon steel plates P2 (model number: S45C) with sides of 10 mm and thickness of 2 mm were prepared. All samples were degassed in advance by leaving them in a vacuum furnace at 70°C for at least 24 hours. Next, as shown in Figure 4, the medium-carbon steel plate P1 was sandwiched between a pair of medium-carbon steel plates P2, and the medium-carbon steel plates P1 and P2 were fixed together. Next, the main surfaces (surfaces) of the medium-carbon steel plates P1 and P2 were irradiated with a laser while atmospheric gas was sprayed onto them. Solidified portions 2A were formed on the medium-carbon steel plates P1 and P2 by solidification of the molten pool generated by laser irradiation. Within 30 seconds after the formation of the solidified portions 2A, the medium-carbon steel plates P1 and P2 were immersed in ice water. Within 60 seconds after the formation of the solidified portions 2A, the medium-carbon steel plates P1 and P2 were immersed in liquid nitrogen. The medium-carbon steel plates P1 and P2 were stored in liquid nitrogen until immediately before the thermal desorption test described below. The boundaries between the medium-carbon steel plates P1 and P2 were then cut, and the medium-carbon steel plate P1 with the solidified portion 2A was removed and used as a sample. The atmospheric gas used was either a mixture of argon gas (97% by volume) and hydrogen gas (3% by volume), or argon gas (100% by volume). Specifically, a first sample using the above-mentioned mixed gas and a second sample using only argon gas were prepared. The laser was irradiated at a 45° angle relative to the main surfaces. The laser output was 1.0 kW, and the laser irradiation position change speed was 10 mm / s. A medium-carbon steel plate P1 without a solidified portion 2A was used as a third sample. After the degassing treatment, the third sample was immersed in ice water within 30 seconds and then in liquid nitrogen within 60 seconds.

[0039] Next, a thermal desorption test was performed on each of the first and second samples described above, and a medium-carbon steel plate P1 (third sample) on which the solidified portion 2A was not formed. The thermal desorption tests on the first and second samples were performed within 24 hours after the first and second samples were formed. In the thermal desorption test, the samples were heated in a vacuum using infrared rays from 40°C to 340°C at a heating rate of 100°C / hr, and the change over time in the amount of hydrogen gas desorbed from the samples was measured using a quadrupole mass spectrometer.

[0040] 5A and 5B show the results of a thermal desorption test. In FIG. 5A, the horizontal axis represents test time, and the vertical axis represents the intensity or temperature of the desorbed gas. Also, in FIG. 5A, graph 11 shows the test results for the first sample, graph 12 shows the test results for the second sample, graph 13 shows the test results for the third sample, and graph 14 shows the temperature change. In FIG. 5B, the horizontal axis represents temperature, and the vertical axis represents the intensity of the desorbed gas. Also, in FIG. 5B, graph 21 shows the test results for the first sample, graph 22 shows the test results for the second sample, and graph 23 shows the test results for the third sample. As shown in FIGS. 5A and 5B, unlike the third sample, hydrogen gas desorption was observed at low temperatures in the first and second samples. This indicates that the first and second samples contain diffusible hydrogen, which can cause hydrogen embrittlement. Furthermore, the amount of desorption from Sample 1 was significantly greater than that from Sample 2. This confirmed that the use of hydrogen gas, rather than simply an inert gas, as the atmospheric gas can effectively contain gas in the molten pool.

[0041] <Relationship between Heating Conditions and Hardness of Solidified Portion> A medium-carbon steel plate (model number: S45C) with a long side of 150 mm, a short side of 100 mm, and a thickness of 2 mm was prepared as the metal material. Next, the medium-carbon steel plate was clamped and then irradiated with a laser while spraying atmospheric gas onto the main surface (surface) of the medium-carbon steel plate. The molten pool generated by the laser irradiation solidified, forming a solidified portion on the medium-carbon steel plate. The atmospheric gas was a mixture of argon gas (97% by volume) and hydrogen gas (3% by volume). The laser was irradiated at a 45° angle relative to the main surface. The hardness of the solidified portion was measured by varying at least one of the laser power and the laser irradiation position change rate. The laser power was 0.5 kW to 2.0 kW, and the laser irradiation position change rate was 300 mm / min (5 mm / s) to 1300 mm / min. The dimension of the molten pool MP along the movement direction of the laser irradiation device was 40 mm. The hardness of the solidified portion was measured by carrying out a micro-Vickers test on the surface of a cross section cut out from a medium carbon steel plate, with a test load of 300 gf and a holding time of 15 seconds.

[0042] FIG. 6 shows the relationship between laser output and hardness of the solidified portion. In FIG. 6, the horizontal axis represents laser output, and the vertical axis represents hardness of the solidified portion. Graph 31 shows the relationship between laser output and hardness of the solidified portion when the laser irradiation position change rate is 300 mm / min (5 mm / s). Graph 32 shows the relationship between laser output and hardness of the solidified portion when the laser irradiation position change rate is 600 mm / min (10 mm / s). Graph 33 shows the relationship between laser output and hardness of the solidified portion when the laser irradiation position change rate is 900 mm / min (15 mm / s). As shown in FIG. 6, when the laser irradiation position change rate is low, the hardness of the solidified portion tends to decrease as the laser output increases. On the other hand, when the laser irradiation position change rate is 10 mm / s or more and 15 mm / s or less, almost no change was observed in the relationship between laser output and hardness of the solidified portion. From the above results, it was found that cracks tend to occur more easily in the solidified portion when the energy supply to the metal material is relatively high. In one example, setting the laser output to 1.4 kW or more and 2.0 kW or less and setting the change rate to 400 mm / min or more and 700 mm / min or less tends to make it easier to generate cracks in the solidified portion.

[0043] Experimental Example 1: A medium-carbon steel plate (model number: S45C) with a long side of 150 mm, a short side of 100 mm, and a thickness of 2 mm was prepared as a metal material. Next, the medium-carbon steel plate was clamped, and then a laser was irradiated onto the main surface (surface) of the medium-carbon steel plate while spraying atmospheric gas. A molten pool generated by the laser irradiation solidified, forming a solidified portion on the medium-carbon steel plate. The medium-carbon steel plate was then left stationary for 900 seconds. The atmospheric gas was a mixture of argon gas (97% by volume) and hydrogen gas (3% by volume). The laser was irradiated at a 45° angle relative to the main surface. The laser output was 1.0 kW, and the laser irradiation position change speed was 10 mm / s. The dimension of the molten pool MP along the movement direction of the laser irradiation device was 50 mm.

[0044] 7(a) is a photograph showing a main portion of the front side of the medium-carbon steel plate after standing, and FIG. 7(b) is a photograph showing a main portion of the back side of the medium-carbon steel plate after standing. As shown in FIGS. 7(a) and 7(b), after the medium-carbon steel plate was stood, cracks were confirmed that reached from the front side to the back side of the medium-carbon steel plate. Therefore, it is presumed that it is easy to split the medium-carbon steel plate using these cracks as starting points.

[0045] Experimental Example 2 Two 2 mm thick medium-carbon steel plates (model number: S45C) were prepared as metal materials. Next, the two medium-carbon steel plates were butted together, and the butted portions were joined by friction stir welding. This resulted in a joint of two medium-carbon steel plates. The friction stir welding was performed using a joining tool (made of cemented carbide, shoulder diameter: 12 mm, probe diameter: 4 mm, probe length: 1.8 mm) under conditions of a rotation speed of 250 rpm, a travel speed of 250 mm / sec, and a load of 20 kN. Figure 8(a) is a photograph showing a key portion of the front side of the joint of Experimental Example 2, and Figure 8(b) is a photograph showing a key portion of the back side of the joint of Experimental Example 2. In Figures 8(a) and 8(b), the weld formed by friction stir welding was observed from both the front and back sides of the joint. Unlike Experimental Example 1, no cracks or other defects occurred in the joint, even after the joint was left stationary for several days.

[0046] (Experimental Example 3) After the bonded body prepared in Experimental Example 2 was fixed with a clamp, a laser was irradiated onto the main surface (surface) of the bonded body while atmospheric gas was sprayed onto it. Here, the laser was irradiated onto the bonded portion of the bonded body. A molten pool generated by the laser irradiation solidified, forming a solidified portion at the bonded portion. Next, the bonded body was left to stand for 900 seconds. The atmospheric gas was argon gas. The laser was irradiated while tilted 45° relative to the main surface. The laser output was 1.0 kW, and the speed of change of the laser irradiation position (movement speed of the laser irradiation device) was 10 mm / s.

[0047] Fig. 8(c) is a photograph showing a main portion of the front side of the joined body of Experimental Example 3 after standing, and Fig. 8(d) is a photograph showing a main portion of the back side of the joined body of Experimental Example 3 after standing. As shown in Fig. 8(c) and (d), unlike Experimental Example 1, no cracks or the like occurred in the joint or the like even after the medium carbon steel plates were stood still.

[0048] (Experimental Example 4) A solidified portion was formed in the joint of a bonded body in the same manner as in Experimental Example 3, except that the atmospheric gas was a mixture of argon gas (97% by volume) and hydrogen gas (3% by volume). The bonded body was then allowed to stand for 900 seconds. (e) of FIG. 8 is a photograph showing a main portion of the front side of the bonded body of Experimental Example 4 after standing, and (f) of FIG. 8 is a photograph showing a main portion of the back side of the bonded body of Experimental Example 4 after standing. As shown in (e) and (f) of FIG. 8, after standing, cracks were observed extending from the front side of the bonded body to the back side of the medium carbon steel plate. After standing for several tens of minutes, the solidified portion and its surroundings fractured. That is, the bonded body of Experimental Example 4 spontaneously split. (c) of FIG. 9 is a photograph showing the split surface of the bonded body of Experimental Example 4. As shown in FIG. 9, numerous blowholes (BH) were observed on the split surface of the bonded body. From this, it is presumed that in Experimental Example 4, the fracture described above occurred due to blowholes BH caused by gases mainly consisting of dissolved hydrogen gas and hydrogen embrittlement.

[0049] Experimental Example 5: A medium-carbon steel plate (model number: S45C) with a long side of 120 mm, a short side of 120 mm, and a thickness of 5 mm was prepared as the metal material. Next, the medium-carbon steel plate was clamped, and then a laser was irradiated onto the main surface (surface) of the medium-carbon steel plate while atmospheric gas was sprayed onto it. A fourth sample was prepared in which a solidified portion was formed on the medium-carbon steel plate by solidification of the molten pool generated by the laser irradiation. The atmospheric gas was nitrogen gas (100% by volume). The laser was irradiated at a 45° angle relative to the main surface. The laser output was 2.0 kW, and the laser irradiation position change speed was 5 mm / s. The dimension of the molten pool MP along the movement direction of the laser irradiation device was 60 mm. A medium-carbon steel plate without a solidified portion was also prepared as a fifth sample.

[0050] The fourth and fifth samples were subjected to the following fracture test. In this fracture test, tensile test specimens with a parallel portion length of 40 mm and a parallel portion width of 6 mm were cut out from the fourth and fifth samples. Subsequently, the tensile test specimens were subjected to a tensile displacement at a displacement rate of 2 mm / min until fracture.

[0051] FIG. 10 shows the fracture test results of Experimental Example 5. In FIG. 10, the horizontal axis represents displacement, and the vertical axis represents normal stress. Also in FIG. 10, graph 41 shows the change in normal stress and displacement applied to the fourth sample, and graph 42 shows the change in normal stress and displacement applied to the fifth sample. As shown in FIG. 10, the fourth sample fractured from the center of the solidified portion when a normal stress of 704.7 MPa was applied in the fracture test. On the other hand, the fifth sample fractured after a maximum of 763.2 MPa was applied in the fracture test, and then the displacement exceeded 10 mm. From these results, it is inferred that a certain effect is achieved even when the dissolved gas is nitrogen.

[0052] 11(a) and 11(b) are enlarged photographs showing the fracture surface of the fifth sample after the fracture test, and 11(c) and 11(d) are enlarged photographs showing the fracture surface of the fourth sample after the fracture test. 11(a) is a 100x magnified photograph of the fracture surface of the fifth sample, and 11(b) is a 2000x magnified photograph of the fracture surface of the fifth sample. 11(c) is a 40x magnified photograph of the fracture surface of the fourth sample, and 11(d) is a 1000x magnified photograph of the fracture surface of the fourth sample. As shown in 11(a) and 11(b), numerous dimples due to ductile fracture were observed on the fracture surface of the fifth sample. On the other hand, as shown in 11(c) and 11(d), cleavage planes due to brittle fracture were observed on the fracture surface of the fourth sample. In addition, as shown in FIG. 11(c), blowholes were also confirmed on the fracture surface of the fourth sample.

[0053] (Experimental Example 6) A magnesium-containing aluminum alloy plate (model number: A5083, hereinafter simply referred to as "Al alloy plate") with a long side of 300 mm, a short side of 50 mm, and a thickness of 5 mm was prepared as a metal material. Next, the Al alloy plate was fixed with a clamp, and then a laser was irradiated onto the main surface (surface) of the Al alloy plate while atmospheric gas was sprayed onto it. A molten pool generated by laser irradiation solidified, resulting in a solidified portion formed on the Al alloy plate, producing a sixth sample. The atmospheric gas was argon gas. The laser was irradiated at a 45° angle relative to the main surface. The laser output was 2.0 kW, and the laser irradiation position change speed was 5 mm / s. The dimension of the molten pool MP along the movement direction of the laser irradiation device was 70 mm.

[0054] (Experimental Example 7) A seventh sample in which a solidified portion was formed on an Al alloy plate was prepared in the same manner as in Experimental Example 6, except that the atmospheric gas was a mixed gas of argon gas (97% by volume) and hydrogen gas (3% by volume). In addition, an Al alloy plate in which a solidified portion was not formed was used as a comparative sample.

[0055] The sixth, seventh, and comparative samples were subjected to the following fracture test. Tensile test specimens with a parallel portion length of 20 mm and a parallel portion width of 5 mm were cut out from the seventh and comparative samples. Tensile tests were then performed at a rate of 2 mm / min until fracture.

[0056] Figure 12 is a diagram showing the change in fracture characteristics of metal materials depending on whether or not a solidified portion is present in Experimental Example 6. In Figure 12, the bar graph shows fracture strength, and the line graph shows fracture length. For each of Samples 6 and 7, the left side shows the fracture strength and fracture length before the formation of the solidified portion, and the right side shows the fracture strength and fracture length after the formation of the solidified portion. As shown in Figure 12, it is confirmed that the formation of the solidified portion reduces the fracture strength and fracture length. In addition, it is confirmed that the use of hydrogen gas effectively reduces the fracture strength and fracture length in the Al alloy plate.

[0057] Figure 13(a) is an enlarged photograph showing the fracture surface of Sample 6 after the fracture test, and Figure 13(b) is an enlarged photograph showing the fracture surface of Sample 7 after the fracture test. Figure 13(a) is a 100x enlarged photograph of the fracture surface of Sample 6, and Figure 13(b) is a 100x enlarged photograph of the fracture surface of Sample 7. As shown in Figures 13(a) and 13(b), blowholes were observed on the fracture surface of the Al alloy plate. In addition, as shown in Figure 13(b), a large number of blowholes with larger diameters were observed in Sample 7 compared to Sample 6. From this, it can be understood that the use of hydrogen gas effectively reduced the fracture strength and fracture length of the Al alloy plate.

[0058] Experimental Example 8: Multiple medium-carbon steel plates (model number: S45C) with long sides of 150 mm, short sides of 50 mm, and a thickness of 2 mm were prepared as metal materials. Next, a laser was irradiated onto the main surfaces (surfaces) of the medium-carbon steel plates while atmospheric gas was sprayed onto them. A molten pool generated by the laser irradiation solidified, forming a solidified portion on the medium-carbon steel plates. The atmospheric gas was a mixed gas of argon gas (99.9 vol%) and hydrogen gas (0.1 vol%) or argon gas (100 vol%). Specifically, Sample 8, which used the mixed gas as the atmospheric gas, and Sample 9, which used only argon gas as the atmospheric gas, were prepared. The laser was irradiated at a 45° angle relative to the main surfaces. The laser output was 1.0 kW, and the laser irradiation position change speed was 10 mm / s. The dimension of the molten pool MP along the movement direction of the laser irradiation device was 60 mm. Furthermore, a medium carbon steel plate in which no solidified portion was formed was also prepared as a tenth sample.

[0059] The following fracture test was carried out on each of the eighth, ninth, and tenth samples. In this fracture test, a rectangular test piece measuring 50 mm in length and 4 mm in width was cut from each sample so that the long axis direction was perpendicular to the laser movement direction. The test piece was then attached to a tensile tester with a 20 mm gap between the clamping jigs. A tensile displacement was applied at a displacement rate of 0.12 mm / min until the test piece fractured. The fracture test was carried out within one hour after laser irradiation.

[0060] FIG. 14 is a diagram showing the change in fracture characteristics of the metal material depending on whether or not the solidified portion is present in Experimental Example 8. In FIG. 14, the bar graph shows fracture strength, and the line graph shows fracture length. For each of Samples 8, 9, and 10, the left side shows fracture strength, and the right side shows fracture length. As shown in FIG. 14, it is confirmed that the formation of the solidified portion reduces fracture strength and fracture length. In addition, it is confirmed that the addition of a small amount of hydrogen gas to the mixed gas effectively reduces fracture strength and fracture length.

[0061] Fig. 15(a) is an enlarged photograph showing the fracture surface of Sample 8 after the fracture test, and Fig. 15(b) is an enlarged photograph showing the fracture surface of Sample 9 after the fracture test. Fig. 15(a) is an enlarged photograph of the fracture surface of Sample 8, and Fig. 15(b) is an enlarged photograph of the fracture surface of Sample 9. As shown in Fig. 15(a) and (b), blowholes were confirmed in the fracture surface of the medium carbon steel plate.

[0062] Experimental Example 9: A magnesium-containing aluminum alloy plate (model number: A5083, hereinafter simply referred to as "Al alloy plate") with a long side of 160 mm, a short side of 50 mm, and a thickness of 3 mm was prepared as a metal material. The Al alloy plate was then fixed so that its long side was aligned vertically. Next, melting was performed by arc discharge while spraying atmospheric gas onto the main surface (front surface) of the Al alloy plate. The molten pool generated by the arc discharge solidified, resulting in the creation of an eleventh sample, in which a solidified portion was formed on the Al alloy plate. The atmospheric gas was a mixture of argon gas (99% by volume) and hydrogen gas (1% by volume). During the arc discharge, the current was 81 V, the voltage was 12 V, and the discharge position change rate was 3.6 mm / s. The discharge position changed in the direction along the short side of the Al alloy plate.

[0063] (Experimental Example 10) Gravity is 1 x 10 －５ A twelfth sample was prepared in the same manner as in Experimental Example 9, except that the aluminum alloy plate was G, and the solidified portion was formed on the aluminum alloy plate.

[0064] FIG. 16(a) is a cross-sectional view of the 11th sample, and FIG. 16(b) is a cross-sectional view of the 12th sample. As shown in FIG. 16(a), a portion of the molten portion of the Al alloy plate accumulates due to the influence of gravity. As a result, a thin portion is formed in a portion of the 11th sample. In addition, it was confirmed that a large number of large-diameter blowholes are concentrated in the thin portion. Therefore, it is inferred that the 11th sample can be easily divided by the thin portion, which can be interpreted as a weak portion. On the other hand, as shown in FIG. 16(b), it was confirmed that the 12th sample has blowholes scattered throughout the molten portion of the Al alloy plate. From this, it is inferred that the weak portion, which will be the portion to be divided, can be effectively formed by tilting the metal material or placing it vertically.

[0065] (Experimental Example 11) Multiple high-carbon steel plates (model number: SK85) with long sides of 120 mm, short sides of 50 mm, and a thickness of 2 mm were prepared as metal materials. Next, a laser was irradiated onto the main surfaces (surfaces) of the high-carbon steel plates while atmospheric gas was sprayed onto them. A molten pool generated by the laser irradiation solidified, forming a solidified portion on the high-carbon steel plates. The atmospheric gas was a mixed gas of argon gas (97% by volume) and hydrogen gas (3% by volume) or argon gas (100% by volume). Specifically, Sample 13, which used the mixed gas as the atmospheric gas, and Sample 14, which used only argon gas as the atmospheric gas, were prepared. The laser was irradiated at a 45° angle relative to the main surfaces. The laser output was 1.0 kW, and the laser irradiation position change speed was 10 mm / s. The dimension of the molten pool MP along the movement direction of the laser irradiation device was 60 mm. Generally, high carbon steel sheets tend to be more embrittled by laser irradiation than medium carbon steel sheets.

[0066] Residual stress was measured for each of the 13th and 14th samples using X-ray diffraction. A portable X-ray residual stress measurement device, model μ-X360s, manufactured by Pulstec Industrial Co., Ltd., was used to measure the residual stress distribution on the surface of the 13th sample, the residual stress distribution on the back surface of the 13th sample, the residual stress distribution on the surface of the 14th sample, and the residual stress distribution on the back surface of the 14th sample. The above-mentioned residual stresses are normal stresses in a direction perpendicular to the direction of movement of the laser irradiation device. Figure 17 is a schematic diagram showing the residual stress measurement area. In Figure 17, the arrow AR indicates the residual stress measurement position, and the dashed-dotted line CL indicates the center of the measurement position. In Figure 17, the right side of the dashed-dotted line CL on the paper is considered positive.

[0067] FIG. 18(a) shows the measurement results of the residual stress of the 13th sample, and FIG. 18(b) shows the measurement results of the residual stress of the 14th sample. In each of FIGS. 18(a) and 18(b), the vertical axis represents the residual stress, and the horizontal axis represents the distance from the center of the measurement position. On the vertical axis, positive values ​​represent tensile stress, and negative values ​​represent compressive stress. Therefore, at measurement positions where the residual stress is positive, it can be said that tensile stress occurs as residual stress within the sample. In FIG. 18(a), graph 51 shows the distribution of residual stress on the front surface, and graph 52 shows the distribution of residual stress on the back surface. In FIG. 18(b), graph 61 shows the distribution of residual stress on the front surface, and graph 62 shows the distribution of residual stress on the back surface. As shown in FIGS. 18(a) and 18(b), in both the 13th and 14th samples, large tensile stress occurs as residual stress on the front surface (main surface) irradiated with the laser. On the other hand, in both Samples 13 and 14, a relatively small compressive stress was generated as residual stress on the surface (back surface) that was not irradiated with the laser. Furthermore, no significant change in the distribution of residual stress was observed due to the difference in atmospheric gas. In other words, no significant difference was observed between the maximum value of tensile stress generated in Sample 13 and the maximum value of tensile stress generated in Sample 14.

[0068] Figures 19(a) and 19(b) are enlarged photographs showing the cross section of Sample 13 after residual stress measurement. Figures 20(a) and 20(b) are enlarged photographs showing the cross section of Sample 14 after residual stress measurement. Figures 19(a) and 20(a) are photographs showing the overall image of the solidified portion. Figures 19(b) and 20(b) are photographs showing cracks that have occurred in the samples. The magnification of the photograph shown in Figure 19(b) is the same as that of the photograph shown in Figure 20(b).

[0069] As shown in Figures 19(a) and 19(b), a crack B1 was formed in the 13th sample. Similarly, as shown in Figures 20(a) and 20(b), a crack B2 was formed in the 14th sample. As shown in Figures 19(b) and 20(b), the crack B1 was longer than the crack B2. This difference in length is presumed to be caused by the difference in the mixed gas. Specifically, it is presumed that the crack B1 became longer than the crack B2 due to the hydrogen embrittlement phenomenon caused by the addition of hydrogen to the molten pool MP of the 13th sample.

[0070] 1, 5...metal material, 1a...main surface, 2, 2A...solidified portion, 2a...outer edge, 6...first metal material, 7...second metal material, 8, 9...fillet weld portion, AG...atmospheric gas (shielding gas), B...crack, BH...blowhole, D...movement direction, H...gas holder, L...laser, LA...laser irradiation device, MP...molten pool, P1, P2...medium carbon steel plate, VP...weak portion.

Claims

1. A method for dividing a metal material, comprising: a first step of selectively heating a main surface of the metal material to form a molten pool in the metal material and forming a solidified portion of the molten pool; and a second step of dividing the metal material starting from within the solidified portion and / or the outer edge of the solidified portion in a planar view.

2. A method for dividing a metal material as described in claim 1, wherein in the first step, a gas is dissolved in the molten pool, thereby forming blowholes in the solidified portion due to the gas.

3. A method for dividing a metal material according to claim 2, wherein in the first step, an atmospheric gas is sprayed onto the main surface of the metal material, thereby dissolving the gas in the molten pool.

4. The method for dividing a metal material according to claim 3, wherein the atmospheric gas contains at least one of nitrogen gas and hydrogen gas, and an inert gas.

5. A method for dividing a metal material according to claim 4, wherein the proportion of at least one of the nitrogen gas and the hydrogen gas in the atmospheric gas is 0.1% by volume or more and 5% by volume or less.

6. A method for dividing a metal material according to any one of claims 2 to 5, wherein the metal material is a steel material, an aluminum material, or a magnesium material, and the gas contains hydrogen.

7. A method for dividing a metal material according to any one of claims 2 to 5, wherein the metal material is a copper material, and the gas contains nitrogen.

8. A method for dividing a metal material according to any one of claims 1 to 5, wherein in the second step, the metal material is left to stand until cracks occur within the solidified portion and / or on the outer edge of the solidified portion, and then the metal material is divided.

9. A method for dividing a metal material according to any one of claims 1 to 5, wherein in the first step, the depth of the molten pool is 10% or more and 100% or less of the thickness of the metal material.

10. A method for dividing a metal material according to any one of claims 1 to 5, wherein in the first step, the laser is irradiated onto the main surface of the metal material while the main surface is aligned vertically or intersecting the horizontal direction.

11. A method for dividing a metal material as set forth in claim 10, wherein, when the metal material is a steel material and hydrogen is dissolved in the molten pool in the first step, the output of the laser is 1.4 kW or more and 2.0 kW or less, and the rate of change of the laser irradiation position is 400 mm / min or more and 700 mm / min or less.

12. A method for dividing a metal material according to any one of claims 1 to 5, wherein when the direction perpendicular to the direction in which the main surface of the metal material extends is the thickness direction of the metal material, the thickness of the metal material is 1 mm or more and 100 mm or less.

13. A method for dividing a metal material according to any one of claims 1 to 5, wherein the metal material is a joint of a first metal material and a second metal material, and in the first step, the molten pool is formed at the joint between the first metal material and the second metal material in the joint.

14. The method for dividing a metal material according to claim 13, wherein the metal material is a solid-state bonded body of the first metal material and the second metal material.

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