Seam welding

A process for seam welding steel sheets together, comprising:

• placing respective end portions of first and second steel sheets in overlapping contact with one another to provide overlapping end portions with opposite first and second sides;
• subjecting the overlapping end portions to a first weld pass of a seam welder comprising weld electrodes operating at a first-pass applied current and a first-pass pressure and being moved relative to the overlapping end portions from the first side to the second side of the overlapping end portions at a first-pass carriage speed to pass electric current through the overlapping end portions and establish a weld seam;
• and
• subsequent to the first weld pass, starting at either the first side or the second side of the overlapping end portions and subjecting the weld seam to a second weld pass of the seam welder in which the weld electrodes operate at a second-pass applied current that is lower than the first-pass applied current and a second-pass pressure that is equal to or higher than the first-pass pressure and in which the weld electrodes move relative to the weld seam at a second-pass carriage speed that is greater than the first-pass weld carriage speed to pass electric current through the overlapping end portions and form a weld joint.

A method of continuously processing joined advanced high strength steel sheets, comprising:

• placing respective end portions of first and second advanced high strength steel sheets in overlapping contact with one another to provide overlapping end portions with opposite first and second sides;
• subjecting the overlapping end portions to a first weld pass of a seam welder comprising weld electrodes operating at a first-pass applied current and a first-pass pressure and being moved relative to the overlapping end portions from the first side to the second side of the overlapping end portions at a first-pass carriage speed to pass electric current through the overlapping end portions and establish a weld seam comprising a weld nugget comprising a martensite phase;
• subsequent to the first weld pass, starting at either the first side or the second side of the overlapping end portions and subjecting the weld seam to a second weld pass of the seam welder in which the weld electrodes operate at a second-pass applied current that is lower than the first-pass applied current and at a second-pass pressure and move relative to the weld seam at a second-pass carriage speed to pass electric current through the overlapping end portions and form a weld joint by fusing microcracks, lap openings, and porosity in the weld seam, relieve the residual stress in the weld joint, and temper the martensite phase of the weld nugget;
• and
• applying a continuous processing step to the joined advanced high strength steel sheets.