Joint unit, magnetic rotating arc joining method, and method of manufacturing joint unit

A joint unit comprising:

• a first metal pipe;
• a second metal pipe;
• and
• a joint portion at which end faces of the first and second metal pipes are joined to each other,
• wherein at a joint interface between the first metal pipe and the second metal pipe in the joint portion, a dendrite layer does not exist in a region inside outer circumferential surfaces of the first and second metal pipes and outside inner circumferential surfaces of the first and second metal pipes.

A magnetic rotating arc joining method comprising the steps of:

• preparing first and second metal pipes;
• performing preheating until temperature at a position 2 mm away from end faces of the first and second metal pipes reaches a preheating temperature, by producing an arc discharge between the end faces of the first and second metal pipes in a state in which the end faces are disposed to be opposed to each other and applying a magnetic field between the end faces to move a position of the arc discharge in between the end faces;
• performing main heating until temperature at the position 2 mm away from the end faces of the first and second metal pipes reaches a joining temperature, by producing an arc discharge between the end faces of the first and second metal pipes and applying a magnetic field between the end faces to move a position of the arc discharge in between the end faces;
• and
• a step of joining the end faces by butting the end faces to each other after the step of main heating.

A magnetic rotating arc joining method comprising the steps of:

• preparing first and second metal pipes;
• performing main heating until temperature at a position 2 mm away from the end faces of the first and second metal pipes reaches a joining temperature, by producing an arc discharge between the end faces of the first and second metal pipes and applying a magnetic field between the end faces to move a position of the arc discharge in between the end faces;
• and
• joining the end faces by butting the end faces each other, after the step of main heating,
• wherein in the step of joining, a relative pressure welding speed of the first metal pipe to the second metal pipe in butting the end faces to each other is 20 mm/s or more.