Joined body

Abstract

To address the difficulty of providing a joined body ensured in joining strength by adjusting a carbon content of a mixed part formed by cast ion having a carbon content of a relatively high concentration and steel having a carbon content of a relatively low concentration in different metal joining of cast iron and steel different in carbon content.SOLUTION: A joined body 1 comprises a solid mixed part 30 formed by mixing a component of a cast iron solid part 10 and a component of a steel solid part 20 by component mixing means 80. The solid mixed part 30 includes a cut surface 40 cut in a first direction. The cut surface 40 includes a composite section 47 formed by a plurality of sections. The composite section 47 includes a first section 44 facing a first boundary line 51 in a composite boundary line 50 having a first boundary line 51 which is a boundary line with the cast iron solid part 10 and a second boundary line 52 which is a boundary line with the steel solid part 20, and a second section 45 facing the second boundary line 52 in the composite boundary line 50 and having an area larger than that of the first section 44.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a joined body in which a three-dimensional cast iron part and a three-dimensional steel part are joined together. [Background technology]

[0002] Paragraph 0001 of Patent Document 1 describes that the document relates to a laser welding method, and in particular to a laser joining method for cast iron. Paragraph 0002 of the same document describes that it is extremely difficult to reliably weld cast iron and steel, and that when cast iron and steel are arc-welded using a welding wire for mild steel that is normally used, carbon in the cast iron diffuses into the weld metal at the boundary between the weld metal and the cast iron, resulting in a very hard martensite structure. Paragraph 0003 of the same document describes that when the weld metal becomes a very hard martensite structure, the frequency of weld cracks increases, and the structure becomes poor in toughness, resulting in low reliability of the weld. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP2001-334378A Summary of the Invention [Problem to be solved by the invention]

[0004] In dissimilar metal joining between cast iron and steel, which have different carbon contents, it is not easy to adjust the carbon content of the mixture formed by the cast iron, which has a relatively high carbon concentration, and the steel, which has a relatively low carbon concentration, and provide a joined body that ensures joining strength. [Means for solving the problem]

[0005] One aspect of the present invention is a joined body in which a cast iron three-dimensional part and a steel three-dimensional part are joined. The joined body includes a three-dimensional mixed part in which components of the cast iron three-dimensional part and components of the steel three-dimensional part are mixed by a component mixing means. The three-dimensional mixed part includes a cut surface cut in a first direction. The cut surface includes a composite cross section formed by a plurality of cross sections. The composite cross section includes a first cross section facing the first boundary line of a composite boundary line having a first boundary line with the cast iron three-dimensional part and a second boundary line with the steel three-dimensional part, and includes a second cross section facing the second boundary line of the composite boundary line, the second cross section having an area of ​​5.0 to 40.0 times the area of ​​the first cross section.

[0006] This joint includes a three-dimensional mixed portion in which the components of the cast iron three-dimensional portion and the steel three-dimensional portion are mixed. The three-dimensional mixed portion includes a composite cross-section in which a first cross-section facing the boundary line with the cast iron three-dimensional portion and a second cross-section facing the boundary line with the steel three-dimensional portion have an area ratio of 1:5.0 to 40.0. That is, an area ratio of 1:5.0 to 40.0 is set between the first cross-section in which a high concentration of carbon components is likely to be mixed and the second cross-section in which a low concentration of carbon components is likely to be mixed. By setting the lower limit of the area ratio to 5.0 times, it is easy to remove the influence of carbon components that may cause a decrease in joint strength from the three-dimensional mixed portion. Furthermore, by setting the upper limit of the area ratio to 40.0 times, it is easy to suppress the occurrence of a discrepancy in the carbon amount between the three-dimensional mixed portion and the cast iron three-dimensional portion that may cause a decrease in joint strength. Therefore, it is easy to provide a joint that ensures joint strength in dissimilar metal joints between a cast iron three-dimensional portion and a steel three-dimensional portion.

[0007] The composite cross section includes a connecting cross section in which the first cross section and the second cross section are connected, and the connecting cross section preferably has a carbon content of 0.15% by mass or more and 0.70% by mass or less. By setting the area ratio of the first cross section to the second cross section within the range of 1:5.0 to 40.0 and setting the upper limit of the carbon content of the connecting cross section to 0.70% by mass, it is easier to remove the influence of carbon components that may cause a decrease in joint strength from the three-dimensional mixed section. Furthermore, by setting the area ratio of the first cross section to the second cross section within the range of 1:5.0 to 40.0 and setting the lower limit of the carbon content of the connecting cross section to 0.15% by mass, it is easier to prevent the occurrence of a discrepancy in the carbon content that may cause a decrease in joint strength between the three-dimensional mixed section and the cast iron three-dimensional section. Therefore, it is easier to ensure the joint strength in the dissimilar metal joint between the cast iron three-dimensional section and the steel three-dimensional section.

[0008] The connecting cross section preferably has a carbon content of 0.20% by mass or more and 0.40% by mass or less, which makes it easier to remove the influence of carbon components that may cause a decrease in joint strength from the three-dimensional mixed part, and makes it easier to prevent a discrepancy in the carbon content that may cause a decrease in joint strength between the three-dimensional mixed part and the cast iron three-dimensional part.

[0009] The second cross section preferably has an area 10.0 to 20.0 times that of the first cross section. By making the area ratio of the first cross section to the second cross section fall within the range of 1:10.0 to 20.0, it is possible to more reliably remove the influence of carbon components that may cause a decrease in joint strength from the three-dimensional mixed portion, and more reliably suppress the occurrence of a discrepancy in the amount of carbon between the three-dimensional mixed portion and the cast iron three-dimensional portion, which may cause a decrease in joint strength.

[0010] It is preferable that the cast iron three-dimensional part includes a first surface, the steel three-dimensional part includes a second surface, and the three-dimensional mixed part includes an exposed surface exposed on the first surface and / or the second surface. In this embodiment, the exposed surface is formed by applying a component mixing means directly from the outside to the surface of the cast iron three-dimensional part and / or the surface of the steel three-dimensional part. That is, it is easy to adjust the carbon component in the three-dimensional mixed part to a desired state directly through the surface that is easily accessible from the outside. Therefore, it is easy to increase the probability that the carbon component is uniformly dispersed in the composite cross section. Therefore, it is easy to suppress the bias of the strength characteristics in the three-dimensional mixed part.

[0011] It is preferable that the cast iron three-dimensional part includes a first flat plate part, the steel three-dimensional part includes a second flat plate part, and the exposed surface includes a first exposed surface exposed in the plate thickness direction of the first flat plate part and / or the second flat plate part. In this embodiment, a composite cross section extending in the plate thickness direction is easily formed by applying a component mixing means directly from the outside (typically along the plate thickness direction) to the first flat plate part and / or the second flat plate part. Therefore, the shape of the composite cross section is easily uniformed along the plate thickness direction. Therefore, it is easier to increase the probability that the carbon component is uniformly dispersed in the composite cross section. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view that typically shows a bonded body according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view of the bonded body shown in FIG. [Diagram 3] FIG. 3 is a cross-sectional view of the bonded body shown in FIG. 2 (cross-section taken along line III-III in FIG. 2). [Figure 4] FIG. 4 is a cross-sectional view of a bonded body according to a second embodiment of the present invention. [Diagram 5] FIG. 5 is a cross-sectional view of a bonded body according to a third embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional view of a bonded body according to a fourth embodiment of the present invention. [Figure 7]7A and 7B are diagrams showing a bonded body according to a fifth embodiment of the present invention, in which FIG. 7A is a cross-sectional view showing the bonded body in a state before bonding, and FIG. 7B is a cross-sectional view showing the bonded body in a state after bonding. [Figure 8] FIG. 8 is a diagram showing the area ratio, carbon content, and tensile strength in the examples and comparative examples of the joined body according to the first embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] First Embodiment Fig. 1 is a perspective view that typically shows a joined body 1 according to a first embodiment of the present invention. As shown in Fig. 1, the joined body 1 of this embodiment includes a three-dimensional cast iron portion 10, a three-dimensional steel portion 20, and a three-dimensional mixed portion 30 in which the components of the three-dimensional cast iron portion 10 and the three-dimensional steel portion 20 are mixed by a component mixing means 80. The joined body 1 is formed by joining the three-dimensional cast iron portion 10 and the three-dimensional steel portion 20 via the three-dimensional mixed portion 30.

[0014] The cast iron three-dimensional portion 10 is formed, for example, by using spheroidal graphite cast iron or flake graphite cast iron. The steel three-dimensional portion 20 is formed, for example, by using rolled steel for general construction. One example of the component mixing means 80 is laser welding, which irradiates a laser beam onto the metals to be joined, melts and solidifies the metals, and joins them together. The same applies to the following embodiments.

[0015] The cast iron three-dimensional part 10 includes a rectangular parallelepiped cast iron flat plate part 11 and a first surface 12 constituting the surface of the cast iron flat plate part 11. The first surface 12 includes an upper surface 12a and a bottom surface 12b arranged opposite each other in a direction along the plate thickness direction (Z direction) of the cast iron flat plate part 11, a side surface 12c and a side surface 12d arranged opposite each other in a direction (X direction, length direction) perpendicular to the Z direction of the cast iron flat plate part 11, and a side surface 12e and a side surface 12f arranged opposite each other in a direction (Y direction, width direction) perpendicular to the X direction and Z direction of the cast iron flat plate part 11. The upper surface 12a of this embodiment includes a contact surface 121 in contact with the steel three-dimensional part 20.

[0016] The three-dimensional steel portion 20 includes a rectangular parallelepiped steel flat portion 21 disposed adjacent to the cast iron flat portion 11 in the Z direction, and a second surface 22 constituting the surface of the steel flat portion 21. The second surface 22 includes an upper surface 22a and a bottom surface 22b disposed opposite the steel flat portion 21 in the Z direction, a side surface 22c and a side surface 22d disposed opposite the steel flat portion 21 in the X direction, and a side surface 22e and a side surface 22f disposed opposite the steel flat portion 21 in the Y direction. The bottom surface 22b in this embodiment includes a contact surface 221 that contacts the cast iron three-dimensional portion 10 (contact surface 121).

[0017] As shown in FIG. 1, the three-dimensional mixing section 30 is semi-ellipsoidal in shape as a whole, and is formed so as to span both the interior 11i of the cast iron flat plate portion 11 and the interior 21i of the steel flat plate portion 21. The three-dimensional mixing section 30 includes an elliptical exposed surface (first exposed surface) 31 exposed from the upper surface 22a of the steel flat plate portion 21 toward one side Z1 in the Z direction, an elliptical truncated cone-shaped mixing section 32 formed so as to connect from the exposed surface 31 to the other side Z2 in the Z direction, and a semi-ellipsoidal mixing section 33 formed so as to connect from the elliptical truncated cone-shaped mixing section 32 to the other side Z2. The elliptical truncated cone-shaped mixing section 32 is formed in the interior 21i of the steel flat plate portion 21. The semi-ellipsoidal mixing section 33 is formed in the interior 11i of the cast iron flat plate portion 11.

[0018] FIG. 2 is a plan view of the joint 1 shown in FIG. 1. FIG. 3 is a cross-sectional view (III-III cross section in FIG. 2) of the joint 1 shown in FIG. 2. As shown in FIG. 2 and FIG. 3, the joint 1 includes a cut surface 40 cut in a first direction. In this embodiment, the first direction is a cutting direction in which the III-III cross section in FIG. 2 is formed. As shown in FIG. 3, the cut surface 40 includes a cut surface 41 of the cast iron flat plate portion 11, a cut surface 42 of the steel flat plate portion 21, and a cut surface 43 of the three-dimensional mixed portion 30. The cut surface 43 of the three-dimensional mixed portion 30 has a semi-elliptical shape as a whole, and is connected to the cut surfaces 41 and 42 via a composite boundary line 50 that forms a boundary between the cut surfaces 41 and 42. The composite boundary 50 includes a first boundary 51 which is a boundary between the cut surface 41 and the cut surface 43, a pair of second boundary lines 52 which are boundary lines between the cut surfaces 42 and 43 and face each other in the Y direction, a first connecting point 53 which connects the first boundary line 51 to one of the second boundary lines 52a, and a second connecting point 54 which connects the first boundary line 51 to the other of the second boundary lines 52b. In this embodiment, the first connecting point 53 and the second connecting point 54 face each other in the Y direction.

[0019] The cut surface 43 of the three-dimensional mixing section 30 includes a first cross section 44 facing the first boundary line 51, a second cross section 45 facing the second boundary line 52, and a virtual boundary line 46 that virtually forms a boundary between the first cross section 44 and the second cross section 45. In this embodiment, the virtual boundary line 46 is a straight virtual line connecting the first connecting point 53 and the second connecting point 54. In this manner, the cut surface 43 includes a composite cross section 47 in which a plurality of cross sections (the first cross section 44 and the second cross section 45) are combined with the virtual boundary line 46 as a virtual boundary. The composite cross section 47 in this embodiment includes a connected cross section 48 in which the first cross section 44 and the second cross section 45 are connected via the virtual boundary line 46.

[0020] In this embodiment, the area S2 of the second cross section 45 is 5.0 times or more and 40.0 times or less than the area S1 of the first cross section 44. That is, an area ratio R (S2 / S1) of 1:5.0 to 40.0 is set between the first cross section 44, which is likely to be mixed with a high concentration of carbon components, and the second cross section 45, which is likely to be mixed with a low concentration of carbon components. By setting the lower limit of the area ratio R to 5.0 times, it is easy to remove the influence of carbon components that may cause a decrease in the joining strength from the three-dimensional mixed portion 30. Furthermore, by setting the upper limit of the area ratio R to 40.0 times, it is easy to suppress the occurrence of a discrepancy in the carbon amount between the three-dimensional mixed portion and the cast iron three-dimensional portion, which may cause a decrease in the joining strength. Therefore, it is easy to provide a joined body 1 that ensures the joining strength in the dissimilar metal joining between the cast iron three-dimensional portion 10 and the steel three-dimensional portion 20.

[0021] In this embodiment, the lower limit of the area ratio R(S2 / S1) is preferably 5.5, more preferably 6.0, more preferably 6.5, more preferably 7.0, more preferably 7.5, more preferably 8.0, more preferably 8.5, more preferably 9.0, more preferably 9.5, and even more preferably 10.0. Furthermore, the upper limit of the area ratio R(S2 / S1) is preferably 39.0, more preferably 38.0, more preferably 37.0, more preferably 36.0, more preferably 35.0, more preferably 34.0, more preferably 33.0, more preferably 32.0, more preferably 31.0, more preferably 30.0, more preferably 29.0, more preferably 28.0, more preferably 27.0, more preferably 26.0, more preferably 25.0, more preferably 24.0, more preferably 23.0, more preferably 22.0, more preferably 21.0, and even more preferably 20.0.

[0022] In this embodiment, the connecting section 48 has a carbon content of 0.15% by mass or more and 0.70% by mass or less. By setting the upper limit of the carbon content of the connecting section 48 to 0.70% by mass, it is easier to remove the influence of carbon components that may cause a decrease in joint strength from the three-dimensional mixed section 30. Furthermore, by setting the lower limit of the carbon content of the connecting section 48 to 0.15% by mass, it is easier to prevent a discrepancy in the carbon content that may cause a decrease in joint strength between the three-dimensional mixed section and the cast iron three-dimensional section. Therefore, it is easier to ensure the joint strength in the dissimilar metal joint between the cast iron three-dimensional section 10 and the steel three-dimensional section 20.

[0023] In this embodiment, the upper limit of the carbon content of the connecting cross section 48 is preferably 0.65 mass%, more preferably 0.60 mass%, more preferably 0.55 mass%, more preferably 0.50 mass%, more preferably 0.45 mass%, and even more preferably 0.40 mass%. The lower limit of the carbon content of the connecting cross section 48 is preferably 0.16 mass%, more preferably 0.17 mass%, more preferably 0.18 mass%, more preferably 0.19 mass%, and even more preferably 0.20 mass%.

[0024] In this embodiment, a component mixing means (such as a laser welding device) 80 is applied directly from the outside to the upper surface 22a of the steel plate-like portion 21, forming an exposed surface 31 exposed from the upper surface 22a toward one side Z1 in the Z direction. That is, the carbon components in the three-dimensional mixed portion 30 can be easily adjusted to a desired state directly via the upper surface 22a, which is easily accessible from the outside. This makes it easier to increase the probability that the carbon components are uniformly dispersed in the composite cross section 47. This makes it easier to suppress bias in the strength characteristics in the three-dimensional mixed portion 30.

[0025] A component mixing means (such as a laser welding device) 80 is applied directly to the upper surface 22a from the outside (typically from the Z direction), thereby forming a composite cross section 47 extending in the Z direction. This makes it easier to make the shape of the composite cross section 47 uniform along the Z direction. This makes it easier to increase the probability that the carbon component is uniformly dispersed within the composite cross section 47.

[0026] Here, an example of a method for manufacturing the joined body 1 is shown. As shown in FIG. 1, first, the cast iron flat plate portion 11 and the steel flat plate portion 21 are overlapped so that the upper surface 12a of the cast iron flat plate portion 11 and the bottom surface 22b of the steel flat plate portion 21 are in contact with each other. Next, a laser beam is irradiated to a first position P1 on the upper surface 22a of the steel flat plate portion 21 using a laser welding device 80, and the cast iron flat plate portion 11 and the steel flat plate portion 21 are fused through their contact surfaces 121 (221). Next, the laser beam is moved from the first position P1 to a second position P2 in the X direction. As a result, a fusion portion is formed in the interior 11i of the cast iron flat plate portion 11 and the interior 21i of the steel flat plate portion 21, where the components of the cast iron three-dimensional portion 10 and the steel three-dimensional portion 20 are fused together. Then, the irradiation of the laser light is stopped and the temperature of the molten part is lowered to form a three-dimensional mixed part 30 that spans both the interior 11i of the cast iron flat plate part 11 and the interior 21i of the steel flat plate part 21. This makes it possible to manufacture a joined body 1 in which the cast iron three-dimensional part 10 and the steel three-dimensional part 20 are joined via the three-dimensional mixed part 30. An example of the laser welding device 80 is a laser oscillator (FEC6000M) manufactured by Furukawa Electric Co., Ltd.

[0027] <Second embodiment> Fig. 4 is a cross-sectional view of a joined body 2 according to a second embodiment of the present invention. As shown in Fig. 4, the joined body 2 of this embodiment includes a cast iron three-dimensional portion 61, a steel three-dimensional portion 62, and a three-dimensional mixed portion 63 in which the components of the cast iron three-dimensional portion 61 and the steel three-dimensional portion 62 are mixed by a component mixing means 80 (not shown). The joined body 2 is formed by joining the cast iron three-dimensional portion 61 and the steel three-dimensional portion 62 via the three-dimensional mixed portion 63.

[0028] The cast iron three-dimensional portion 61 includes a base 610, a cylindrical cast iron cylindrical portion 611 formed to be continuous with the base 610, and a first surface 612 constituting the surface of the cast iron cylindrical portion 611. The first surface 612 includes an inner surface 61a and an outer surface 61b arranged opposite each other in a direction (Z direction, radial direction) along the thickness direction of the cast iron cylindrical portion 611. The outer surface 61b in this embodiment includes a contact surface 61c in contact with the steel three-dimensional portion 62.

[0029] The three-dimensional steel portion 62 includes a cylindrical steel portion 621 arranged so as to surround the cast iron portion 611 from one side Z1 in the Z direction, and a second surface 622 constituting the surface of the steel portion 621. The second surface 622 includes an inner surface 62a and an outer surface 62b arranged opposite to each other in the Z direction of the steel portion 621. The inner surface 62a in this embodiment includes a contact surface 62c that contacts the cast iron portion 611 (contact surface 61c) inserted into the steel portion 621. In this embodiment, the cast iron portion 611 is inserted into the steel portion 621, so that the central axis C1 of the cast iron portion 611 and the central axis C2 of the steel portion 621 coincide with each other.

[0030] As shown in FIG. 4, the three-dimensional mixing portion 63 is formed so as to span both the inside 611i of the cast iron cylindrical portion 611 and the inside 621i of the steel cylindrical portion 621. The three-dimensional mixing portion 63 is formed along the circumferential direction of the cast iron cylindrical portion 611 and the steel cylindrical portion 621, centered on the central axis C1 of the cast iron cylindrical portion 611 and the central axis C2 of the steel cylindrical portion 621. Therefore, the three-dimensional mixing portion 63 has an annular shape centered on the central axes C1 and C2. The three-dimensional mixing portion 63 includes a band-shaped exposed surface 631 exposed from the outer surface 62b of the steel cylindrical portion 621 toward one side Z1 in the Z direction, an annular mixing portion 632 formed so as to connect from the exposed surface 631 to the other side Z2 in the Z direction, and an annular mixing portion 633 formed so as to connect from the annular mixing portion 632 to the other side Z2 in the Z direction. The annular mixing portion 632 is formed in the interior 621i of the steel cylindrical portion 621. The annular mixing portion 633 is formed in the interior 611i of the cast iron cylindrical portion 611.

[0031] The joined body 2 includes a cut surface 64 cut in a first direction. In this embodiment, the first direction is a cutting direction in which a cross section passing through the central axes C1 and C2 of the cylindrical parts 611 and 621 is formed. The cut surface 64 includes a cut surface 641 of the cast iron cylindrical part 611, a cut surface 642 of the steel cylindrical part 621, and a cut surface 643 of the three-dimensional mixed part 63. The cut surface 643 of the three-dimensional mixed part 63 has a semi-elliptical shape as a whole, and is connected to the cut surfaces 641 and 642 via a composite boundary line 65 that forms a boundary between the cut surfaces 641 and 642. The composite boundary 65 includes a first boundary 651 which is a boundary between the cut surface 641 and the cut surface 643, a pair of second boundary lines 652 which are boundary lines between the cut surfaces 642 and the cut surfaces 643 and face each other in the Y direction, a first connecting point 653 which connects the first boundary line 651 and one of the second boundary lines 652a, and a second connecting point 654 which connects the first boundary line 651 and the other of the second boundary lines 652b. In this embodiment, the first connecting point 653 and the second connecting point 654 face each other in the Y direction.

[0032] The cut surface 643 of the three-dimensional mixing portion 63 includes a first cross section 644 facing the first boundary line 651, a second cross section 645 facing the second boundary line 652, and a virtual boundary line 646 that virtually forms a boundary between the first cross section 644 and the second cross section 645. In this embodiment, the virtual boundary line 646 is a straight virtual line connecting the first connecting point 653 and the second connecting point 654. In this manner, the cut surface 643 includes a composite cross section 647 in which a plurality of cross sections (the first cross section 644 and the second cross section 645) are combined with the virtual boundary line 646 as a virtual boundary. The composite cross section 647 in this embodiment includes a connected cross section 648 in which the first cross section 644 and the second cross section 645 are connected via the virtual boundary line 646.

[0033] In this embodiment, the area S2 of the second cross section 645 is 5.0 to 40.0 times larger than the area S1 of the first cross section 644. In this embodiment, the connecting cross section 648 has a carbon content of 0.15 to 0.70 mass %.

[0034] <Third embodiment> Fig. 5 is a cross-sectional view of a joined body 3 according to a third embodiment of the present invention. As shown in Fig. 5, the joined body 3 of this embodiment includes a cast iron three-dimensional portion 71, a steel three-dimensional portion 72, and a three-dimensional mixed portion 73 in which the components of the cast iron three-dimensional portion 71 and the steel three-dimensional portion 72 are mixed by a component mixing means 80 (not shown). The joined body 3 is formed by joining the cast iron three-dimensional portion 71 and the steel three-dimensional portion 72 via the three-dimensional mixed portion 73.

[0035] The cast iron three-dimensional portion 71 includes a rectangular parallelepiped cast iron flat plate portion 711 and a first surface 712 that constitutes the surface of the cast iron flat plate portion 711. The first surface 712 includes an upper surface 71a and a bottom surface 71b that are disposed opposite each other in a direction along the plate thickness direction (Z direction) of the cast iron flat plate portion 711. The upper surface 71a in this embodiment includes a contact surface 71c that contacts the steel three-dimensional portion 72.

[0036] The three-dimensional steel portion 72 has an inverted T-shape overall, and includes a rectangular parallelepiped steel flat portion 721 arranged adjacent to the cast iron flat portion 711 in the Z direction, a second surface 722 constituting the surface of the steel flat portion 721, and a steel wall portion 723 extending from the steel flat portion 721 toward one side Z1 in the Z direction. The second surface 722 includes an upper surface 72a and a bottom surface 72b arranged to face the steel flat portion 721 in the Z direction. The bottom surface 72b in this embodiment includes a contact surface 72c in contact with the cast iron flat portion 711 (contact surface 71c).

[0037] As shown in FIG. 5, the three-dimensional mixing portion 73 is formed so as to span both the inside 711i of the cast iron flat plate portion 711 and the inside 721i of the steel flat plate portion 721. In this embodiment, the three-dimensional mixing portion 73 is formed along a direction (X direction, length direction (direction penetrating the paper surface)) perpendicular to the Z direction of the cast iron flat plate portion 711 and the steel flat plate portion 721, and has a semi-ellipsoidal shape as a whole. The three-dimensional mixing portion 73 includes a first three-dimensional mixing portion 73a located on one side Y1 in a direction (Y direction, width direction) perpendicular to the X direction and Z direction of the steel flat plate portion 721 with respect to the steel wall portion 723, and a second three-dimensional mixing portion 73b located on the other side Y2 in the Y direction.

[0038] The first three-dimensional mixing section 73a includes an elliptical exposed surface (first exposed surface) 731 exposed from the upper surface 72a of the steel plate-like portion 721 toward one side Z1 in the Z direction, an elliptical truncated cone-shaped mixing section 732 formed so as to connect from the exposed surface 731 to the other side Z2 in the Z direction, and a semi-ellipsoidal mixing section 733 formed so as to connect from the elliptical truncated cone-shaped mixing section 732 to the other side Z2. The elliptical truncated cone-shaped mixing section 732 is formed in the interior 721i of the steel plate-like portion 721. The semi-ellipsoidal mixing section 733 is formed in the interior 711i of the cast iron plate-like portion 711. The same is true for the second three-dimensional mixing section 73b.

[0039] The joined body 3 includes a cut surface 74 cut in a first direction. In this embodiment, the first direction is a cutting direction in which a cross section defined by the Y direction and the Z direction is formed. The cut surface 74 includes a cut surface 741 of the cast iron flat plate portion 711, a cut surface 742 of the steel flat plate portion 721, a cut surface 743a of the first three-dimensional mixed portion 73a, and a cut surface 743b of the second three-dimensional mixed portion 73b.

[0040] The cut surface 743a of the first three-dimensional mixing portion 73a has a semi-elliptical shape as a whole, and is connected to the cut surface 741 and the cut surface 742 via a composite boundary line 75 that forms a boundary between the cut surface 741 and the cut surface 743a. The composite boundary line 75 includes a first boundary line 751 that is a boundary line between the cut surface 741 and the cut surface 743a, a pair of second boundary lines 752 that are boundary lines between the cut surface 742 and the cut surface 743a and face each other in the Y direction, a first connecting point 753 that connects the first boundary line 751 and one of the second boundary lines 752a, and a second connecting point 754 that connects the first boundary line 751 and the other of the second boundary lines 752b. In this embodiment, the first connecting point 753 and the second connecting point 754 face each other in the Y direction. The same applies to the cut surface 743b of the second three-dimensional mixing portion 73b.

[0041] The cut surface 743a of the first three-dimensional mixing portion 73a includes a first cross section 744 facing the first boundary line 751, a second cross section 745 facing the second boundary line 752, and a virtual boundary line 746 that virtually forms a boundary between the first cross section 744 and the second cross section 745. In this embodiment, the virtual boundary line 746 is a straight virtual line connecting the first connecting point 753 and the second connecting point 754. In this manner, the cut surface 743a includes a composite cross section 747 in which a plurality of cross sections (the first cross section 744 and the second cross section 745) are combined with the virtual boundary line 746 as a virtual boundary. The composite cross section 747 in this embodiment includes a connected cross section 748 in which the first cross section 744 and the second cross section 745 are connected via the virtual boundary line 746. The same applies to the cut surface 743b of the second three-dimensional mixing portion 73b.

[0042] In this embodiment, the area S2 of the second cross section 745 is 5.0 to 40.0 times larger than the area S1 of the first cross section 744. In this embodiment, the connecting cross section 748 has a carbon content of 0.15 to 0.70 mass %.

[0043] <Fourth embodiment> Fig. 6 is a cross-sectional view of a joined body 4 according to a fourth embodiment of the present invention. As shown in Fig. 6, the joined body 4 of this embodiment includes a three-dimensional cast iron portion 81, a three-dimensional steel portion 82, and a three-dimensional mixed portion 83 in which the components of the three-dimensional cast iron portion 81 and the three-dimensional steel portion 82 are mixed by a component mixing means 80 (not shown). The joined body 4 is formed by joining the three-dimensional cast iron portion 81 and the three-dimensional steel portion 82 via the three-dimensional mixed portion 83.

[0044] The cast iron three-dimensional portion 81 includes a rectangular parallelepiped cast iron flat plate portion 811 and a first surface 812 constituting the surface of the cast iron flat plate portion 811. The first surface 812 includes an upper surface 81a and a bottom surface 81b arranged opposite each other in a direction along the plate thickness direction (Z direction) of the cast iron flat plate portion 811. The upper surface 81a in this embodiment includes a contact surface 81c in contact with the steel three-dimensional portion 82.

[0045] The three-dimensional steel portion 82 includes a rectangular parallelepiped flat steel portion 821 arranged adjacent to the cast iron flat portion 811 in the Z direction, and a second surface 822 constituting the surface of the flat steel portion 821. The second surface 822 includes an upper surface 82a and a bottom surface 82b arranged opposite to the flat steel portion 821 in the Z direction, and a side surface 82c arranged on one side Y1 in a direction perpendicular to the Z direction (Y direction, width direction) of the flat steel portion 821. The bottom surface 82b in this embodiment includes a contact surface 82d that contacts the three-dimensional cast iron portion 81 (contact surface 81c). The side surface 82c in this embodiment includes an inclined surface 82e that is inclined downward so as to protrude to one side Y1 in the Y direction as it moves from the upper surface 82a to the bottom surface 82b.

[0046] As shown in FIG. 6, the three-dimensional mixing section 83 includes a first mixing section 831 formed along the inclined surface 82e of the steel plate-shaped section 821, and a semi-ellipsoidal second mixing section 832 formed in the interior 811i of the cast iron plate-shaped section 811 so as to be continuous with the first mixing section 831 to the other side Z2 in the Z direction. In this embodiment, the first mixing section 831 is formed along a direction perpendicular to the Y direction and Z direction of the steel plate-shaped section 821 (X direction, length direction (direction penetrating the paper surface)). In addition, the second mixing section 832 is formed along the X direction of the cast iron plate-shaped section 811. The first mixing section 831 includes an exposed surface 833 exposed to the outside. The exposed surface 833 is formed on one side Y1 in the Y direction with respect to the inclined surface 82e so as to sandwich the first mixing section 831 between the inclined surface 82e and the exposed surface 833.

[0047] The joint 4 includes a cut surface 84 cut in a first direction. In this embodiment, the first direction is a cut direction in which a cross section defined by the Y direction and the Z direction is formed. The cut surface 84 includes a cut surface 841 of the cast iron flat plate portion 811, a cut surface 842 of the steel flat plate portion 821, and a cut surface 843 of the three-dimensional mixed portion 83. The cut surface 843 of the three-dimensional mixed portion 83 is connected to the cut surfaces 841 and 842 via a composite boundary line 85 that forms a boundary between the cut surfaces 841 and 842. The composite boundary 85 includes a first boundary 851 which is a boundary between the cut surface 841 and the cut surface 843, a second boundary 852 which is a boundary between the cut surface 842 and the cut surface 843, a first connecting point 854 which connects the first boundary 851 and the second boundary 852, and a second connecting point 855 which connects the first boundary 851 and the exposed surface 833. In this embodiment, the first connecting point 854 and the second connecting point 855 face each other in the Y direction.

[0048] The cut surface 843 of the three-dimensional mixer 83 includes a first cross section 844 facing the first boundary line 851, a second cross section 845 facing the second boundary line 852, and a virtual boundary line 846 that virtually forms a boundary between the first cross section 844 and the second cross section 845. In this embodiment, the virtual boundary line 846 is a straight virtual line connecting the first connecting point 854 and the second connecting point 855. In this manner, the cut surface 843 includes a composite cross section 847 in which a plurality of cross sections (the first cross section 844 and the second cross section 845) are combined with the virtual boundary line 846 as a virtual boundary. The composite cross section 847 in this embodiment includes a connected cross section 848 in which the first cross section 844 and the second cross section 845 are connected via the virtual boundary line 846.

[0049] In this embodiment, the area S2 of the second cross section 845 is 5.0 times or more and 40.0 times or less than the area S1 of the first cross section 844. In this embodiment, the connecting cross section 848 has a carbon content of 0.15% by mass or more and 0.70% by mass or less.

[0050] <Fifth embodiment> 7 shows a joined body 5 according to a fifth embodiment of the present invention, in which Fig. 7(a) is a cross-sectional view showing the joined body 5 before joining, and Fig. 7(b) is a cross-sectional view showing the joined body 5 after joining. The joined body 5 of this embodiment includes a cast iron three-dimensional portion 91, a steel three-dimensional portion 92, and a three-dimensional mixed portion 93 in which the components of the cast iron three-dimensional portion 91 and the steel three-dimensional portion 92 are mixed by a component mixing means 80. The joined body 5 is formed by joining the cast iron three-dimensional portion 91 and the steel three-dimensional portion 92 via the three-dimensional mixed portion 93.

[0051] 7(a), in a state before joining, the cast iron three-dimensional portion 91 includes a rectangular parallelepiped cast iron flat plate portion 911 and a first surface 912 constituting the surface of the cast iron flat plate portion 911. The first surface 912 includes a top surface 91a and a bottom surface 91b arranged opposite each other in a direction along the plate thickness direction (Z direction) of the cast iron flat plate portion 911, and an end surface 91c arranged on the other side Y2 in a direction (Y direction, width direction) perpendicular to the Z direction of the cast iron flat plate portion 911. The end surface 91c of this embodiment includes a contact surface 91d in contact with the steel three-dimensional portion 92.

[0052] As shown in FIG. 7(a), before joining, the steel three-dimensional part 92 includes a rectangular parallelepiped steel flat plate part 921 arranged adjacent to the cast iron flat plate part 911 in the Y direction, and a second surface 922 constituting the surface of the steel flat plate part 921. The second surface 922 includes an upper surface 92a and a bottom surface 92b arranged opposite to the steel flat plate part 921 in the Z direction, and an end surface 92c arranged on one side Y1 in the Y direction of the steel flat plate part 921. The end surface 92c of this embodiment includes a contact surface 92d that contacts the cast iron three-dimensional part 91 (contact surface 91d). In this way, the cast iron flat plate part 911 and the steel flat plate part 921 are butted against each other from both sides in the Y direction, with the positions of the contact surfaces 91d, 92d that are in contact with each other before joining being set as contact position P3.

[0053] As shown in Fig. 7(a), first, in a state where the cast iron flat plate portion 911 and the steel flat plate portion 921 are butted together, a laser beam is irradiated to the contact position P3 or its vicinity using a laser welding device 80, thereby forming a molten portion in which both contact surfaces 91d, 92d are melted. Next, the irradiation of the laser beam is stopped and the temperature of the molten portion is lowered, thereby forming a three-dimensional mixed portion 93 that joins the cast iron flat plate portion 911 and the steel flat plate portion 921, as shown in Fig. 7(b).

[0054] As shown in FIG. 7(b), in the state after joining, the three-dimensional mixture portion 93 includes a first exposed surface 931 exposed to the outside toward one side Z1 in the Z direction, a second exposed surface 932 exposed to the outside toward the other side Z2 in the Z direction, and a mixture portion 933 formed along the Z direction so as to be connected to the first exposed surface 931 and the second exposed surface 932. The mixture portion 933 includes a first mixture portion 934 formed so as to be connected to the cast iron flat plate portion 911, and a second mixture portion 935 formed so as to be connected to the first mixture portion 934 and the steel flat plate portion 921. In this embodiment, the first mixture portion 934 is formed along a direction (X direction, length direction (direction penetrating the paper)) perpendicular to the Y direction and Z direction of the cast iron flat plate portion 911. In addition, the second mixture portion 935 is formed along the X direction of the steel flat plate portion 921.

[0055] As shown in FIG. 7(b), the joint 5 includes a cut surface 94 cut in a first direction. In this embodiment, the first direction is a cut direction in which a cross section defined by the Y direction and the Z direction is formed. The cut surface 94 includes a cut surface 941 of the cast iron three-dimensional part 91, a cut surface 942 of the steel three-dimensional part 92, and a cut surface 943 of the three-dimensional mixed part 93. The cut surface 943 of the three-dimensional mixed part 93 is connected to the cut surfaces 941 and 942 via a composite boundary line 95 that forms a boundary between the cut surfaces 941 and 942. The composite boundary line 95 includes a first boundary line 951 that is a boundary line between the cut surfaces 941 and 943, and a second boundary line 952 that is a boundary line between the cut surfaces 942 and 943. In this embodiment, the first boundary line 951 and the second boundary line 952 face each other in the Y direction.

[0056] As shown in FIG. 7(b), in the state after joining, the cut surface 943 of the three-dimensional mixed portion 93 includes a first cross section 944 facing the first boundary line 951, a second cross section 945 facing the second boundary line 952, and a virtual boundary line 946 that virtually forms a boundary between the first cross section 944 and the second cross section 945. In this embodiment, the virtual boundary line 946 is a straight virtual line (a boundary line between the cast iron three-dimensional portion 91 and the steel three-dimensional portion 92 before joining) that extends in the Z direction so as to pass through the contact position P3 before joining. In this manner, the cut surface 943 includes a composite cross section 947 in which a plurality of cross sections (the first cross section 944 and the second cross section 945) are combined with the virtual boundary line 946 as a virtual boundary. The composite cross section 947 in this embodiment includes a connected cross section 948 in which the first cross section 944 and the second cross section 945 are connected via the virtual boundary line 946.

[0057] In this embodiment, the area S2 of the second cross section 945 is 5.0 times or more and 40.0 times or less than the area S1 of the first cross section 944. In this embodiment, the connecting cross section 948 has a carbon content of 0.15% by mass or more and 0.70% by mass or less.

[0058] <Examples and Comparative Examples> 8 is a diagram showing the area ratio R (S2 / S1) of the second cross section 45 to the first cross section 44, the carbon content X [mass%] of the connecting cross section 48, and the tensile strength T [MPa] of the joined body 1 in examples and comparative examples of the joined body 1 according to the first embodiment of the present invention. Among the examples and comparative examples shown in FIG. 8, Example 1 is the joined body 1 joined using a cast iron 3D part 10 having a carbon content of 3.33 mass% and a steel 3D part 20 having a carbon content of 0.18 mass%, and Examples 2 to 5, Comparative Examples 1 and 2 are the joined body 1 joined using a cast iron 3D part 10 having a carbon content of 3.33 mass% and a steel 3D part 20 having a carbon content of 0.06 mass%. In FIG. 8, the area S1 of the first cross section 44 and the area S2 of the second cross section 45 (see FIG. 3) used to calculate the area ratio R(S2 / S1) were measured by setting a measurement target area along the first boundary line 51, the second boundary line 52, and the imaginary boundary line 46 in the connected cross section 48 observed using a microscope (Keyence Corporation / VHX-7000) with an area measurement function. The carbon amount X of the connected cross section 48 was measured using a carbon-sulfur analyzer (LECO Japan LLC / CS844 type). The carbon amount X shown in parentheses is a value calculated using the carbon amount of each of the cast iron three-dimensional part 10 and the steel three-dimensional part 20 and the area ratio R(S2 / S1). The tensile strength T is the maximum tensile load at the time of fracture of the joint 1 outputted from a fracture testing machine (Shimadzu Corporation / 300kN universal testing machine) divided by the fracture cross-sectional area of ​​the fractured portion. The fracture cross-sectional area was calculated based on the dimensions of the fractured portion obtained by measuring with a dimensional measuring tool such as a caliper. The fracture test was carried out based on the conditions of the cross tension test specified in JIS Z3137 (test piece dimensions and test method for cross tension test of resistance spot and projection welded joints).

[0059] (Comparison between Examples 1 to 5 and Comparative Examples 1 and 2) As shown in FIG. 8, the area ratios R (S2 / S1) of Examples 1 to 5 are 5.0 times or more and 40.0 times or less, whereas the area ratios R (S2 / S1) of Comparative Example 1 are less than 5.0 times and the area ratios R (S2 / S1) of Comparative Example 2 are more than 40.0 times. The carbon content X of Examples 1 to 5 is 0.15 mass% or more and 0.70 mass% or less, whereas the carbon content X of Comparative Example 1 exceeds 0.70 mass% and the carbon content X of Comparative Example 2 is less than 0.15 mass%. As shown in FIG. 8, Examples 1 to 5 exhibit higher strength than Comparative Example 1 and Comparative Example 2. Specifically, the tensile strengths T of Comparative Example 1 and Comparative Example 2 are 29.2 MPa and 19.5 MPa, respectively, whereas the tensile strengths T of Examples 1 to 5 are 54.8 MPa or more. In this manner, in Examples 1 to 5, by setting the area ratio R (S2 / S1) to be 5.0 times or more and 40.0 times or less and the carbon content X to be 0.15 mass% or more and 0.70 mass% or less, the joining strength can be ensured in the dissimilar metal joining between the cast iron three-dimensional portion 10 and the steel three-dimensional portion 20.

[0060] (Comparison of Examples 3 and 4 with Examples 1, 2 and 5) Furthermore, as shown in FIG. 8, the area ratios R(S2 / S1) of Examples 3 and 4 are 10.0 times or more and 20.0 times or less, whereas the area ratios R(S2 / S1) of Examples 1 and 2 are less than 10.0 times, and the area ratio R(S2 / S1) of Example 5 exceeds 20.0 times. Furthermore, the carbon content X of Examples 3 and 4 is 0.20 mass% or more and 0.40 mass% or less, whereas the carbon content X of Examples 1 and 2 exceeds 0.40 mass%, and the carbon content X of Example 5 is less than 0.20 mass%. As shown in FIG. 8, Examples 3 and 4 exhibit higher strength than Examples 1, 2, and 4. Specifically, the tensile strengths T of Examples 1, 2, and 5 are 54.8 MPa, 64.1 MPa, and 108.0 MPa, respectively, whereas the tensile strengths T of Examples 3 and 4 are 126.6 MPa or more. In this manner, in Examples 3 and 4, by setting the area ratio R (S2 / S1) to 10.0 to 20.0 and the carbon content X to 0.20 mass% to 0.40 mass%, the joining strength of the dissimilar metal joining between the cast iron three-dimensional portion 10 and the steel three-dimensional portion 20 can be further improved.

[0061] The present invention is not limited to the above-mentioned embodiment and examples, and includes those defined in the claims. For example, in the joint 1 shown in Fig. 1 to Fig. 3, the three-dimensional mixed part 30 may include an exposed surface that is exposed from the bottom surface 12b of the cast iron flat plate part 11 toward the other side Z2 in the Z direction so as to penetrate the cast iron three-dimensional part 10 and the steel three-dimensional part 20 in the Z direction. [Explanation of symbols]

[0062] 1 Joint, 10 Cast iron three-dimensional part, 11 Cast iron flat part, 12 First surface, 20 Steel three-dimensional part, 21 Steel flat part, 22 Second surface, 30 Three-dimensional mixed part, 31 Exposed surface, 43 Cut surface, 44 First cross section, 45 Second cross section, 47 Composite cross section, 48 Connected cross section, 50 Composite boundary line, 51 First boundary line, 52 Second boundary line, 80 Component mixing means

Claims

1. A joined body in which a cast iron three-dimensional part and a steel three-dimensional part are joined, A three-dimensional mixed portion is provided in which the components of the cast iron three-dimensional portion and the components of the steel three-dimensional portion are mixed by a component mixing means, The three-dimensional mixing section includes a cut surface cut in a first direction, the cut surface includes a composite cross section formed by a plurality of cross sections; The composite cross-section has a first boundary line which is a boundary line with the cast iron three-dimensional portion and a second boundary line which is a boundary line with the steel three-dimensional portion, and a first cross-section facing the first boundary line; and a second cross section facing the second boundary line among the composite boundary lines, the second cross section having an area that is 5.0 times or more and 40.0 times or less compared to an area of ​​the first cross section.

2. The composite cross section includes a connected cross section in which the first cross section and the second cross section are connected to each other, The joined body according to claim 1 , wherein the joint cross section has a carbon content of 0.15 mass % or more and 0.70 mass % or less.

3. The joined body according to claim 2 , wherein the joint cross section has a carbon content of 0.20 mass % or more and 0.40 mass % or less.

4. The bonded body according to claim 1 , wherein the second cross section has an area that is 10.0 times or more and 20.0 times or less than the area of ​​the first cross section.

5. the cast iron shank includes a first surface; the steel three-dimensional portion includes a second surface; The bonded body according to claim 1 , wherein the three-dimensional mixed portion includes an exposed surface that is exposed to the first surface and / or the second surface.

6. The cast iron three-dimensional portion includes a first flat plate portion, The steel three-dimensional portion includes a second flat portion, The bonded body according to claim 5 , wherein the exposed surface includes a first exposed surface exposed in a plate thickness direction of the first flat plate portion and / or the second flat plate portion.

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