Spot welded joint and spot welding method

Abstract

A spot welded joint in which a high CTS is obtained even if including one or more high strength steel sheets and a method of welding of the same, that is, a spot welded jointincluding a plurality of steel sheets, wherein one or more steel sheets is a tensile strength 750 to 2500 MPa high strength steel sheet and, at a cross-section in the sheet thickness direction of the steel sheets, when defining superposed surfaces of a high strength steel sheet Sarranged at an outermost side and another steel sheetB as the 'plane A' and defining a plane passing through a point of one-half of a distance between a nugget end position E of a high strength steel sheet Sside on the line Lin the sheet thickness direction and a crossing point O of the plane A and the line Land parallel to the plane A as the 'plane B', at a square area SA of sides of 30 μm centered about a crossing point X of a line L, which is separated by 250 μm to the heat affected zone side from a tangent at any position on a nugget end line NEL sandwiched between the plane A and plane B and parallel to that tangent, and a line Lvertical to Lincluded in a heat affected zonehaving a high strength steel sheet Sas a base material, an average value of widths of the blocks formed from lath martensite is 0.5 to 7.0 μm.