The present invention relates to a welding method. Particularly, the present invention relates to a cast iron welding method when a product having a weld structure between a part formed of a cast iron and a part formed of a steel is manufactured, for example, a weld structural part of a plurality of members represented by a differential ring gear, a differential case, or the like in a differential gear of an automobile as a functional part or a case is manufactured.
A drive system part of an automobile requires high strength, and thus, a strong steel, a cast iron, or the like is used, and a method is adopted in which a part made by plastic working or casting is assembled by a bolt fastening structure.
If this mechanical fastening structure can be replaced by a fastening structure by welding, it is possible to reduce weight. However, in welding between a cast iron and a steel, cracks easily occur due to fragile textures generated by phase transformation occurring molten and solidified portions and the vicinities thereof or stress generated by thermal expansion or shrinkage.
Accordingly, in welding of the cast iron in the related art, a method of performing welding while supplying an austenitic welding wire such as a Ni wire.
[PTL 1] Japanese Patent No. 5293840
However, in the above-described method, even when cracks are prevented during the welding, hardening of a heat affected zone by welding cannot be avoided, and in this welded state, a hardened fragile region (a phase configured of ledeburite and martensite) becomes a fracture starting point, reliability of a weld zone decreases, and thus, it is necessary to perform heat treatment after the welding.
In addition, PTL 1 discloses a technology of forming a cavity in a joint portion in advance.
The present invention is made in consideration of the above-described technical problem, and an object thereof is to provide a welding method capable of improving strength characteristics.
In order to achieve the above-described object, according to a first invention, there is provided a welding method for welding a first member and a second member having a hardness lower than that of the first member, comprising: a first step of inserting a third member having a hardness lower than that of the second member into a portion between the first member and the second member; a second step of welding a boundary portion between the first member and the third member; and a third step of welding a boundary portion between the second member and the third member.
In order to achieve the above-described object, according to a second invention, in the welding method according to the first invention, the welding method further includes a fourth step of welding a center of the third member. In addition, in order to achieve the above-described object, according to a third invention, in the welding method according to the first or second invention, the welding is performed using a high energy beam in the steps other than the first step.
According to the welding method of the present invention, it is possible to improve strength characteristics.
Hereinafter, Embodiments of a welding method according to the present invention will be described with reference to the drawings.
In the welding method according to the present embodiment, when a part formed of a cast iron and a part formed of a steel are welded to each other, first, as shown in
Next, as first pass welding, a boundary portion between the cast iron 11 and the insert material 13 is welded by a high energy beam such as a laser beam or an electron beam from an upper side of a paper surface of
In addition, as second pass welding, a boundary portion between the steel 12 and the insert material 13 is welded by a high energy beam from an upper side of a paper surface of
In the present embodiment, according to the above-described method, it is possible to decrease hardness of the heat affected zone 11B on the cast iron 11 side having very high hardness, and thus, it is possible to prevent cracks and improve strength characteristics.
Moreover, in the second pass welding, the heat affected zone is formed on the steel 12 side by the weld zone 12A. However, this heat affected zone is not hard (not brittle) compared to the heat affected zone 11B on the cast iron side, and thus, this is not mentioned in the present embodiment.
In addition to operational effects of Embodiment 1, in the present embodiment, the hardness of the heat affected zone on the steel 12 side formed by the second pass welding decreases. Hereinafter, a procedure up to the second pass welding in this embodiment is the same as that of the first embodiment, and thus, descriptions thereof will be omitted, and descriptions after the second pass welding will be made.
As shown in
In the present embodiment, as third pass welding, the center of the insert material 13, that is, a position equidistant from the weld zone 11A and the weld zone 12A is welded by a high energy beam from an upper side of a paper surface of
Accordingly, the heat affected zone 11B on the cast iron 11 side formed by the first pass welding and the heat affected zone 12B on the steel 12 side formed by the second pass welding are tempered by heat conduction of the third pass welding. Therefore, it is possible to decrease the hardness of the heat affected zones 11B and 12B.
In the present embodiment, it is possible to decrease the hardness of the heat affected zone 12B on the steel 12 side as well as the hardness of the heat affected zone 11B on the cast iron 11 side having very high hardness, and thus, it is possible to prevent cracks and maintain the strength characteristics.
The present embodiment describes a method which is used in a case where a V-shaped groove is formed between a plate-shaped cast iron and a plate-shaped steel and welding is performed.
In the welding method according to the present embodiment, as shown in
Accordingly, as shown in
Therefore, as shown by a broken line arrow of
As shown in
In the present embodiment, in a case where the V-shaped groove is formed between the plate-shaped cast iron and the plate-shaped steel and the welding is performed, it is possible to decrease the hardness of the heat affected zones 21B and 21B′ on the cast iron 21 side and the hardness of the heat affected zone 22B′ of the steel 22 side, and thus, it is possible to prevent cracks and to maintain the strength characteristics.
The present invention is suitable for a welding method.
Number | Date | Country | Kind |
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2016-109936 | Jun 2016 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2017/017329 | 5/8/2017 | WO | 00 |