Conjugate and joining method

Abstract

To provide a conjugate in which joined parts are bonded with high strength, and to provide a joining method.SOLUTION: A conjugate is obtained by bonding lamination parts of a plurality of members. The plurality of members is made of a material of a composition comprising 0.12 wt.% or less of carbon (C), 0.10 to 0.50 wt.% of silicon (Si), 0.80 to 1.20 wt.% of manganese (Mn), 0.04 wt.% or less of phosphorus (P), 0.03 wt.% or less of sulfur (S), 14.50 to 18.50 wt.% of chromium (Cr), 4.30 to 4.70 wt.% of nickel (Ni), 2.40 to 3.20 wt.% of molybdenum (Mo), 0.01 to 0.20 wt.% of nitrogen (N), and the balance iron with inevitable impurities. A weld zone includes a melting solidified part, and a heat affected zone. At least one of the widths of the heat affected zone is 0.10 mm or less. A ratio of the hardness of the melting solidified part relative to the hardness of a base material part is 75% or higher.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bonded body and a bonding method. [Background technology]

[0002] There is known a compression spring that is placed between a first pressed body and a second pressed body and applies pressure to one or both of them (see, for example, Patent Document 1). This compression spring is a joined body made by, for example, stacking a plurality of leaf springs and joining some of them together. For example, the compression spring is made by joining a plurality of leaf springs together by welding both ends of the leaf springs in the longitudinal direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7345699 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the hardness of the welded portion is lower than that of the portion (base material) that is not affected by the heat of welding. This decrease in hardness causes a problem of reduced strength of the joined body.

[0005] The present invention has been made in view of the above, and has an object to provide a joined body in which the joined portions are joined with high strength, and a joining method. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, a joined body according to the present invention is a joined body formed by joining stacked portions of a plurality of members, and has a welded portion formed by welding the plurality of members and joining the members together, wherein the plurality of members contain 0.12 wt% or less of carbon (C), 0.10 to 0.50 wt% of silicon (Si), 0.80 to 1.20 wt% of manganese (Mn), 0.04 wt% or less of phosphorus (P), 0.03 wt% or less of sulfur (S), 14.50 to 18.50 wt% of chromium (Cr), 4.30 to 4.70 wt% of nickel (Ni), 2.40 to 3.50 wt% of chromium (Cr), and 0.12 wt% or less of silicon (Si). The weld is made of a material having a composition consisting of molybdenum (Mo) of 0.20 wt% or less, nitrogen (N) of 0.01 to 0.20 wt% or less, and the remainder being iron and unavoidable impurities, and the weld has a molten solidified portion formed by melting and solidifying the material, and a heat-affected portion formed around the molten solidified portion, and the width of the heat-affected portion, which is the width in a direction perpendicular to the stacking direction, has a maximum value of the width of at least one of the heat-affected portions located on opposite sides of the molten solidified portion, is 0.10 mm or less, and the ratio of the hardness of the molten solidified portion to the hardness of the base material portion where the weld is not formed is 75% or more.

[0007] Moreover, in the joined body according to the present invention, a ratio of a lower limit hardness of the heat-affected zone to a hardness of the base material portion is 65% or more.

[0008] Furthermore, the joining method according to the present invention is characterized in that a plurality of members made of a material having a composition of 0.12 wt% or less carbon (C), 0.10 to 0.50 wt% silicon (Si), 0.80 to 1.20 wt% manganese (Mn), 0.04 wt% or less phosphorus (P), 0.03 wt% or less sulfur (S), 14.50 to 18.50 wt% chromium (Cr), 4.30 to 4.70 wt% nickel (Ni), 2.40 to 3.20 wt% molybdenum (Mo), 0.01 to 0.20 wt% nitrogen (N), the remainder being iron and unavoidable impurities, are partially overlapped, and a laser beam is irradiated to the overlapping portion of the plurality of members by nanosecond pulse laser welding, in which the pulse width per pulse is in nanosecond units, to form a weld that joins the plurality of members together. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain a joined body in which the joined portions are joined with high strength. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a plan view showing the configuration of a bonded body according to one embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating the formation of a weld surface bead formed by pulse laser welding. [Figure 3] FIG. 3 is a diagram illustrating seam welding. [Figure 4] FIG. 4 is a diagram showing an optical microscope image showing a cross section of a bonded portion of a bonded body according to Example 1 of the present invention. [Figure 5] FIG. 5 is a diagram showing the hardness of the broken line portion in the optical microscope image shown in FIG. [Figure 6] FIG. 6 is a diagram showing an optical microscope image showing a cross section of a bonded portion of a bonded body according to Example 2 of the present invention. [Figure 7] FIG. 7 is a diagram showing the hardness of the broken line portion in the optical microscope image shown in FIG. [Figure 8]FIG. 8 is a diagram showing an optical microscope image showing a cross section of a bonded portion of a bonded body according to Comparative Example 1 of the present invention. [Figure 9] FIG. 9 is a diagram showing the hardness of the dashed line portion in the optical microscope image shown in FIG. [Figure 10] FIG. 10 is a diagram showing an optical microscope image showing a cross section of a bonded portion of a bonded body according to Comparative Example 2 of the present invention. [Figure 11] FIG. 11 is a diagram showing the hardness of the broken line portion in the optical microscope image shown in FIG. [Figure 12] FIG. 12 is a diagram showing an optical microscope image showing a cross section of a bonded portion of a bonded body according to Comparative Example 4 of the present invention. [Figure 13] FIG. 13 is a diagram showing the hardness of the dashed line portion in the optical microscope image shown in FIG. [Figure 14] FIG. 14 is a diagram showing an optical microscope image showing a cross section of a bonded portion of a bonded body according to Comparative Example 5 of the present invention. [Figure 15] FIG. 15 is a diagram showing the hardness of the dashed line portion in the optical microscope image shown in FIG. [Figure 16] FIG. 16 is a diagram showing an optical microscope image showing a cross section of a bonded portion of a bonded body according to Comparative Example 6 of the present invention. [Figure 17] FIG. 17 is a diagram showing the hardness of the broken line portion in the optical microscope image shown in FIG. [Figure 18] FIG. 18 is a diagram showing an optical microscope image showing a cross section of a bonded portion of a bonded body according to Comparative Example 7 of the present invention. [Figure 19] FIG. 19 is a diagram showing the hardness of the broken line portion in the optical microscope image shown in FIG. [Figure 20] FIG. 20 is a diagram illustrating the test pieces according to Examples 1 and 2 used in the tensile test. [Figure 21] FIG. 21 is a diagram illustrating the test piece of the base material used in the tensile test. [Figure 22] FIG. 22 is a diagram illustrating a test piece according to Comparative Example 2 used in the tensile test. [Figure 23]FIG. 23 is a diagram illustrating a test piece according to Comparative Example 3 used in the tensile test. [Figure 24] FIG. 24 is a diagram showing the results of tensile tests on Examples 1 and 2 and the base material. [Figure 25] FIG. 25 is a diagram showing the results of tensile tests on Comparative Examples 2 and 3 and the base material. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the following description, a bonded assembly will be described as a form for carrying out the present invention (hereinafter referred to as "embodiment"). However, the present invention is not limited to this embodiment. Furthermore, in the drawings, the same parts are given the same reference numerals. Furthermore, it should be noted that the drawings are schematic, and the relationship between the thickness and width of each member, the ratio of each member, etc., may differ from reality. Furthermore, the drawings may include parts with different dimensions and ratios.

[0012] (Embodiment) Fig. 1 is a plan view showing the configuration of a bonded body according to one embodiment of the present invention, in which Fig. 1(a) is a plan view seen from a direction perpendicular to the stacking direction of the members and the longitudinal direction of the members, and Fig. 1(b) is a plan view seen from the direction of arrow A shown in Fig. 1(a), in the stacking direction of the members.

[0013] The joined body 1 according to this embodiment is, for example, a leaf spring that is provided between a first pressed body and a second pressed body by elastic force and applies pressure to both pressed bodies. For example, in the example shown in Fig. 1(a), the two pressed bodies are arranged so as to sandwich the joined body 1 in the vertical direction of the paper.

[0014] The joined body 1 includes a first member 10, a second member 11, and a third member 12.

[0015] The first member 10 and the second member 11 are formed by bending the center portion in the longitudinal direction of a strip-shaped member. The third member 13 has a flat plate shape.

[0016] The bonded body 1 is configured by sandwiching a third member 12 between a first member 10 and a second member 11. In this case, the protruding directions of the bent portions of the first member 10 and the second member 11 are opposite each other via the third member 12. In other words, the bonded body 1 is configured such that the central portions in the longitudinal direction of the first member 10 and the second member 11 protrude in opposite directions relative to the stacking direction.

[0017] The first member 10 to the third member 12 are formed using a material having a composition of 0.12 wt% or less carbon (C), 0.10 to 0.50 wt% silicon (Si), 0.80 to 1.20 wt% manganese (Mn), 0.04 wt% or less phosphorus (P), 0.03 wt% or less sulfur (S), 14.50 to 18.50 wt% chromium (Cr), 4.30 to 4.70 wt% nickel (Ni), 2.40 to 3.20 wt% molybdenum (Mo), 0.01 to 0.20 wt% nitrogen (N), and the remainder being iron and unavoidable impurities. The first member 10 to the third member 12 may be made of materials having the same composition, or may be made of materials having different compositions within the above range.

[0018] The first member 10 to the third member 12 are joined by laser welding in a stacked state. In this embodiment, the members of the joined body 1 are joined by nanosecond pulse laser welding.

[0019] The joined body 1 has joints 13 and 14 that join the first member 10 to the third member 12, respectively. The joints 13 and 14 are welded portions formed when the members are melted, mixed, and solidified by nanosecond pulse laser welding. The joint 13 is formed on one end side of the joined body 1 in the longitudinal direction (the left side in FIG. 1(a)). The weld 14 is formed on the other end side of the joined body 1 in the longitudinal direction (the right side in FIG. 1(a)).

[0020] Fig. 2 is a diagram illustrating the formation of a weld surface bead formed by pulsed laser welding. In Fig. 2, an example will be described in which the overlap ratio of the surface weld bead formed by welding is 97%, and the weld 13 is formed by the weld surface bead. As shown in Fig. 2, by overlapping the weld surface beads 131, even when the laser is emitted intermittently, parts of the overlapping nuggets 131 melt and mix together, forming a welded portion in which the weld surface beads 131 are continuously connected.

[0021] Furthermore, the weld surface bead (weld) formed by nanosecond pulse laser welding has a molten solidified portion where the material melts and solidifies during welding, and a heat-affected portion formed around the molten solidified portion (outer edge) where the material does not melt during welding but where the properties change due to heat. In this heat-affected portion, for example, the properties such as microstructure and hardness change compared to the portion not affected by heat. Note that when parts of the nugget overlap as shown in Figure 2, the molten solidified portions are connected and a heat-affected portion is formed around them.

[0022] In the joined body 1, the width of the heat-affected zone in the direction perpendicular to the lamination direction, at least one of the widths of the heat-affected zones located on opposite sides of the molten solidified zone, is 0.10 mm or less, and the ratio of the hardness of the molten solidified zone to the hardness of the base material portion where no weld (weld bead) is formed is 75% or more. In this way, the region where the heat-affected zone is formed is narrow, and the hardness of the molten solidified zone is maintained at the hardness of the base material portion, resulting in a joined body with high joint strength. It is more preferable that the sum of the widths of the heat-affected zones located on opposite sides of the molten solidified zone is 0.10 mm or less.

[0023] Furthermore, the joined body 1 preferably has a ratio of the lower limit hardness of the heat-affected zone to the hardness of the base material of 65% or more. The heat-affected zone caused by welding has a lower hardness than the molten solidified zone. In contrast, by setting the ratio of the hardness of the heat-affected zone to the hardness of the base material to 65% or more, a joined body with even higher strength can be obtained.

[0024] In the above-described embodiment, members made of a material having a composition of 0.12 wt% or less carbon (C), 0.10 to 0.50 wt% silicon (Si), 0.80 to 1.20 wt% manganese (Mn), 0.04 wt% or less phosphorus (P), 0.03 wt% or less sulfur (S), 14.50 to 18.50 wt% chromium (Cr), 4.30 to 4.70 wt% nickel (Ni), 2.40 to 3.20 wt% molybdenum (Mo), 0.01 to 0.20 wt% nitrogen (N), and the remainder being iron and unavoidable impurities, are joined together by, for example, nanosecond pulse laser welding. Therefore, the use of a material with a low softening rate and nanosecond pulse laser welding with a low heat input results in a weld with a small difference in hardness between the base material and the molten portion, and a small heat-affected zone. According to this embodiment, a weld is formed in which there is no difference in hardness from the base material and the heat-affected zone where this difference occurs is small, so that a joint in which the joint parts are joined with high strength can be obtained. [Example]

[0025] Examples of the bonded structure according to the present invention will be described below, but the present invention is not limited to these examples.

[0026] <Material composition used> The compositions of the materials used in the examples (Example Material 1, Comparative Material 1, and Comparative Material 2) are shown in Table 1. The mechanical properties of each material are shown in Table 2. Representative examples of Example Material 1 include ASL350, a precipitation hardening stainless steel, Comparative Material 1 includes SUS632J1, a precipitation hardening stainless steel, and Comparative Material 2 includes maraging steel. [Table 1] [Table 2]

[0027] <Bonding process> The bonding process used in the example is as follows. Implementation process 1: Nanosecond pulsed laser welding Comparison Process 1: Seam welding (see Figure 3) Comparison Process 2: Continuous wave (CW) laser welding

[0028] 3 is a diagram illustrating seam welding. In seam welding, members 101 and 102 to be joined are overlapped, and disk-shaped roller electrodes 201 and 202 are rotated on opposite sides of the members 101 and 102 while an electric current is applied, joining the members 101 and 102 together by heating due to electrical resistance. During this process, by controlling the current flow, for example, a plurality of nuggets 103, as shown in FIG. 3, are continuously formed at the boundary between the members 101 and 102.

[0029] Example 1 In Example 1, two plates having the composition of Example Material 1 shown in Table 1 were used to prepare a joint by joining the plates using Example Process 1. In this case, the laser welding was performed at a processing speed of 0.46 m / s, a pulse width of 1020 nanoseconds, a peak power of 10 kW, a frequency of 141 Hz, a nugget overlap ratio of 97%, and three welds.

[0030] <Hardness measurement> The Vickers hardness was measured in accordance with the Vickers hardness test method specified in JIS Z 2244. In the hardness measurement, the hardness was measured continuously along a path passing through the hardness of the base material part and the hardness of the molten and solidified part melted and solidified by welding in the cross section of the joint.

[0031] The welding conditions and properties in Example 1 are shown in Table 3. [Table 3]

[0032] Fig. 4 is a diagram showing an optical microscope image of a cross section of a joint portion of a joint body according to Example 1 of the present invention. Fig. 5 is a diagram showing the hardness of the broken line portion in the optical microscope image shown in Fig. 4. The welded portion can be confirmed from the optical microscope image (see Fig. 4). Also, in Fig. 5, the hardness B of the base material portion E11 , hardness of the molten and solidified part B E12 , upper limit hardness B of the heat-affected zone E13 , the lower limit hardness of the heat-affected zone B E14 The width of the heat-affected zone is the area R E11 , R E12 The lower limit hardness of the heat-affected zone is the minimum value of the measured results, and the upper limit is the hardness of the base material multiplied by 0.9. The width of the heat-affected zone is the upper limit hardness B of the heat-affected zone. E13 It is set based on the hardness B E11 is the average of 10 points of the base material, hardness B E12 is the average hardness of the molten and solidified part, B E13 is the hardness of the base material x 0.9, hardness B E14 was the minimum value of the entire measurement range. The measurement pitch was 0.01 mm. The range of the heat-affected zone was the range where the hardness was equal to or less than the upper limit of the heat-affected zone.

[0033] Example 2 Example 2 was the same as Example 1 except that the welding speed was 0.141 m / sec, the peak power was 4 kW, and the overlap ratio was 90%. The welding conditions and properties in Example 2 are shown in Table 3.

[0034] Fig. 6 is a diagram showing an SEM image of a cross section of a joint portion of a joint body according to Example 2 of the present invention. Fig. 7 is a diagram showing the hardness of the broken line portion in the SEM image shown in Fig. 6. The welded portion can be confirmed from the SEM image (see Fig. 7). Also, in Fig. 7, the hardness B of the base material portion E21 , hardness of the molten and solidified part B E22 , upper limit hardness B of the heat-affected zone E23 , hardness of heat-affected zone B E24 The width of the heat-affected zone is the area R E21 , R E22 It is equivalent to the sum of

[0035] (Comparative Example 1) In Comparative Example 1, two plates having the composition of Example Material 1 shown in Table 1 were used to produce a joint by joining the plates using Comparative Process 1. In this case, seam welding was performed at a welding speed of 0.03 m / s, a current of 2 kA, a pressure of 0.75 kN, a heating time of 5 ms, a cooling time of 10 ms, an electrode end face diameter of 100 mm, and one weld. In Comparative Example 1, the nuggets did not overlap, resulting in an overlap ratio of -200%. The welding conditions and characteristics in Comparative Example 1 are shown in Table 3.

[0036] Fig. 8 is a diagram showing an SEM image of a cross section of a joint portion of a joint body according to Comparative Example 1 of the present invention. Fig. 9 is a diagram showing the hardness of the broken line portion in the SEM image shown in Fig. 8. The welded portion can be confirmed from the SEM image (see Fig. 8). Also, in Fig. 9, the hardness B of the base material portion C11 , hardness of the molten solidified part B C12 , upper limit hardness B of the heat-affected zone C13 , hardness of heat-affected zone B C14 The width of the heat-affected zone is the area R C11 is equivalent to

[0037] (Comparative Example 2) In Comparative Example 2, two plates having the composition of Comparative Material 1 shown in Table 1 were used and joined using Implementation Process 1 to produce a joint. Laser welding was performed at a processing speed of 0.141 m / s, a pulse width of 0.001020 milliseconds (1020 nanoseconds), a peak power of 4 kW, a frequency of 141 Hz, a nugget lap ratio of 97%, and one weld. The welding conditions and characteristics for Comparative Example 3 are shown in Table 3.

[0038] Fig. 10 is a diagram showing an SEM image of a cross section of a joint portion of a joint body according to Comparative Example 2 of the present invention. Fig. 11 is a diagram showing the hardness of the broken line portion in the SEM image shown in Fig. 10. The welded portion can be confirmed from the SEM image (see Fig. 10). Also, in Fig. 11, the hardness B of the base material portion C21 , hardness of the molten solidified part B C22 , upper limit hardness B of the heat-affected zone C23 , hardness of heat-affected zone B C24The width of the heat-affected zone is the area R C21 is equivalent to

[0039] (Comparative Example 3) In Comparative Example 3, two plates having the composition of Comparative Material 1 shown in Table 1 were used and joined using Implementation Process 1 to produce a joint. Laser welding was performed at a processing speed of 0.141 m / s, a pulse width of 0.001020 milliseconds (1020 nanoseconds), a peak power of 4 kW, a frequency of 141 Hz, a nugget lap ratio of 97%, and three welds. The welding conditions and properties for Comparative Example 3 are shown in Table 3. Note that the hardness of Comparative Example 3 is assumed to be the same as that of Comparative Example 2, since the welding conditions, etc. were the same.

[0040] Comparative Example 4 Comparative Example 4 is the same as Comparative Example 1 except that the plate material is Comparative Material 1. The welding conditions and properties in Comparative Example 4 are shown in Table 3.

[0041] Fig. 12 is a diagram showing an SEM image of a cross section of a joint portion of a joint body according to Comparative Example 4 of the present invention. Fig. 13 is a diagram showing the hardness of the broken line portion in the SEM image shown in Fig. 12. The welded portion can be confirmed from the SEM image (see Fig. 12). Also, in Fig. 13, the hardness B of the base material portion C41 , hardness of the molten and solidified part B C42 , upper limit hardness B of the heat-affected zone C43 , hardness of heat-affected zone B C44 The width of the heat-affected zone is the area R C41 is equivalent to

[0042] (Comparative Example 5) Comparative Example 5 is the same as Comparative Example 2 except that the plate material is Comparative Material 1. The welding conditions and properties of Comparative Example 6 are shown in Table 3.

[0043] Fig. 14 is a diagram showing an SEM image of a cross section of a joint portion of a joint body according to Comparative Example 5 of the present invention. Fig. 15 is a diagram showing the hardness of the broken line portion in the SEM image shown in Fig. 14. The welded portion can be confirmed from the SEM image (see Fig. 14). Also, in Fig. 15, the hardness B of the base material portion C51, hardness of the molten and solidified part B C52 , upper limit hardness B of the heat-affected zone C53 , hardness of heat-affected zone B C54 The width of the heat-affected zone is the area R C51 is equivalent to

[0044] (Comparative Example 6) Comparative Example 6 was the same as Example 1 except that the plate material was Comparative Material 2. The welding conditions and properties in Comparative Example 6 are shown in Table 3.

[0045] Fig. 16 is a diagram showing an SEM image of a cross section of a joint portion of a joint body according to Comparative Example 6 of the present invention. Fig. 17 is a diagram showing the hardness of the broken line portion in the SEM image shown in Fig. 16. The welded portion can be confirmed from the SEM image (see Fig. 16). Also, in Fig. 17, the hardness B of the base material portion C61 , hardness of the molten and solidified part B C62 , upper limit hardness B of the heat-affected zone C63 , hardness of heat-affected zone B C64 The width of the heat-affected zone is the area R C61 is equivalent to

[0046] (Comparative Example 7) Comparative Example 7 is the same as Comparative Example 1 except that the plate material was Comparative Material 2. In Comparative Example 7, the nuggets did not overlap each other, and the overlap ratio was -100%. The welding conditions and properties in Comparative Example 7 are shown in Table 3.

[0047] As can be seen from Table 3, Examples 1 and 2 have a small width of the heat-affected zone and a high rate of change in the weld zone, which indicates the degree to which the hardness of the weld zone is maintained relative to the hardness of the base material. In contrast, Comparative Examples 1 and 2, in which seam welding or millisecond pulse laser welding was performed using Example Material 1, and Comparative Examples 3 to 8, in which welding was performed using either Comparative Materials 1 or 2, all had a larger width of the heat-affected zone and a lower rate of change in the weld zone, which indicates the degree to which the hardness of the weld zone is maintained relative to the hardness of the base material, compared to Examples 1 and 2. This indicates that by producing a joint using Example Material 1 by nanosecond pulse laser welding, a joint can be obtained in which the hardness of the weld zone is maintained at the same level as the hardness of the base material.

[0048] Fig. 18 is a diagram showing an SEM image of a cross section of a joint portion of a joint body according to Comparative Example 8 of the present invention. Fig. 19 is a diagram showing the hardness of the broken line portion in the SEM image shown in Fig. 18. The welded portion can be confirmed from the SEM image (see Fig. 18). Also, in Fig. 19, the hardness B of the base material portion C71 , hardness of the molten and solidified part B C72 , upper limit hardness B of the heat-affected zone C73 , hardness of heat-affected zone B C74 The width of the heat-affected zone is the area R C71 is equivalent to

[0049] <Tensile test> Test pieces for tensile tests were prepared and tensile tests were carried out for Examples 1 and 2 and Comparative Examples 2 and 3. Tensile tests were carried out three times for each test piece of each example, and the results were compared with the load capacity of the base material. FIG. 20 is a diagram illustrating the test pieces according to Examples 1 and 2 used in the tensile test. (a) of FIG. 20 is a diagram illustrating the test piece as viewed from the lamination direction of the member, and (b) of FIG. 20 is a diagram illustrating the test piece as viewed from a direction perpendicular to the lamination direction and the longitudinal direction. FIG. 21 is a diagram illustrating the test piece of the base material portion used in the tensile test. FIG. 22 is a diagram illustrating the test piece according to Comparative Example 3 used in the tensile test. FIG. 23 is a diagram illustrating the test piece according to Comparative Example 4 used in the tensile test.

[0050] 20, the test piece 300 according to Examples 1 and 2 was prepared by overlapping three members 301 to 303 made of Example Material 1 with their longitudinal lengths aligned, and then performing nanosecond pulse laser welding on the overlapping portions according to the conditions of each example to form three welds 311 to 313. The test piece 300 was pulled in the longitudinal direction, and the withstand load at the time of fracture was measured.

[0051] 21, the test piece 400 used for comparison is a base material formed from the example material 1 and the comparative material 1, and is a band-shaped member with a large width at both ends. The test piece 400 was pulled in the longitudinal direction, and the load at which it broke was measured.

[0052] 22, the test piece 500 according to Comparative Example 2 was prepared by overlapping three members 501 to 503 made of Comparative Material 1 with their longitudinal lengths aligned, and then performing nanosecond pulse laser welding according to certain conditions at the overlapping portion of the three members to form and join a single weld 511. The test piece 500 was pulled in the longitudinal direction, and the withstand load at the time of fracture was measured.

[0053] 23, the test piece 600 according to Comparative Example 3 was prepared by overlapping three members 601 to 603 made of Comparative Material 1 with their longitudinal lengths aligned, and then performing nanosecond pulse laser welding on the overlapping portions of the three members according to certain conditions to form three welds 611 to 613. The test piece 600 was pulled in the longitudinal direction, and the withstand load at the time of fracture was measured.

[0054] Fig. 24 shows the results of tensile tests on Examples 1 and 2 and the base material. In Fig. 24, the base material is Example Material 1. As shown in Fig. 24 and Table 3, it can be seen that Examples 1 and 2 have load-bearing capacities that are almost equivalent to the load-bearing capacity of the base material.

[0055] Fig. 25 shows the results of tensile tests on Comparative Examples 2 and 3 and the base material. In Fig. 25, the base material is Comparative Material 1. As shown in Fig. 25 and Table 3, it can be seen that the load-bearing capacity of Comparative Examples 2 and 3 is lower than that of the base material.

[0056] From the test results shown in Figures 24 and 25, it can be said that when nanosecond pulse laser welding is performed under the same conditions, by using Example Material 1, a joint having a load capacity almost the same as that of the base material can be obtained.

[0057] Here, since precipitation hardening materials gradually soften as the heat input increases, the joined body after welding is less likely to soften when using a nano-pulse laser with a small heat input. The material according to this embodiment is less likely to soften with the same heat input than precipitation hardening stainless steel such as SUS632, so softening due to welding is less. The hardness improvement mechanism of precipitation-hardening stainless steels is a two-stage process: quench hardening, which depends on the carbon content, and precipitation hardening, which causes the formation of fine precipitates. Metallic precipitates are easily dissolved in the molten matrix, while carbide precipitates tend to coarsen at high temperatures and are relatively easily dissolved in the molten matrix, making it difficult to maintain the precipitation hardening mechanism. Meanwhile, nitride precipitates are the most thermally stable and are difficult to dissolve in the molten matrix. Example Material 1 has a high carbon content and intentionally added nitrogen, resulting in the dominance of nitride precipitates. In contrast, Comparative Material 1 has a low carbon content, resulting in the precipitation of metallic compounds. Comparative Material 2 also has a relatively high carbon content, but contains added titanium, which easily reacts with metals and carbon, resulting in the precipitation of carbides such as titanium carbide. Therefore, it is desirable to use Example Material 1, which has adjusted carbon and nitrogen contents in the material.

[0058] In this way, the present invention can include various embodiments not described here, and various design changes can be made within the scope that does not deviate from the technical idea specified by the claims.

[0059] As described above, the joined body and joining method according to the present invention are suitable for obtaining a joined body in which the joined portions are joined with high strength even when the weight is reduced. [Explanation of symbols]

[0060] 1 zygote 10 First member 11 Second member 12 Third member 13, 14 Welded parts 131 Weld surface bead

Claims

1. A bonded body formed by bonding laminated portions of a plurality of members, a welded portion formed by welding the plurality of members and joining the members together; and the plurality of components are made of a material having a composition consisting of 0.12 wt% or less carbon (C), 0.10 to 0.50 wt% silicon (Si), 0.80 to 1.20 wt% manganese (Mn), 0.04 wt% or less phosphorus (P), 0.03 wt% or less sulfur (S), 14.50 to 18.50 wt% chromium (Cr), 4.30 to 4.70 wt% nickel (Ni), 2.40 to 3.20 wt% molybdenum (Mo), 0.01 to 0.20 wt% nitrogen (N), and the remainder being iron and unavoidable impurities; The welded portion is A molten and solidified portion formed by melting and solidifying the material; A heat-affected zone formed around the molten solidified portion; and The width of the heat-affected zone is a width in a direction perpendicular to the stacking direction, and the maximum value of the width of at least one of the heat-affected zones located on opposite sides of the molten solidified portion is 0.10 mm or less, The ratio of the hardness of the molten solidified portion to the hardness of the base material portion where the weld is not formed is 75% or more. A conjugate characterized by:

2. The ratio of the lower limit hardness of the heat-affected zone to the hardness of the base material is 65% or more.

2. The bonded body according to claim 1 .

3. a plurality of members each made of a material having a composition of 0.12 wt% or less carbon (C), 0.10 to 0.50 wt% silicon (Si), 0.80 to 1.20 wt% manganese (Mn), 0.04 wt% or less phosphorus (P), 0.03 wt% or less sulfur (S), 14.50 to 18.50 wt% chromium (Cr), 4.30 to 4.70 wt% nickel (Ni), 2.40 to 3.20 wt% molybdenum (Mo), 0.01 to 0.20 wt% nitrogen (N), the remainder being iron and unavoidable impurities, a nanosecond pulse laser welding method in which a pulse width per pulse is in nanosecond units is used to irradiate a laser beam onto an overlapping portion of the plurality of members, thereby forming a weld that joins the plurality of members together; A joining method characterized by:

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