Steel plate joined body, steel plate joined body manufacturing method and spot welding method

摘要

Provided is a joined body capable of maintaining the required strength of the welded part during the manufacturing process and use of the joined body. The joined body of steel plates according to the present invention is C: 0.4% or less, Si: 3.0% or less, Al: 3.0% or less, Mn: 0.2% to 6.0% by mass%, P: 0.1% or less, S: 0.07% or less, with the balance having a component composition of Fe and inevitable impurities, tensile strength of 1470 MPa or less, plate thickness of 0.3 mm or more and 5.0 mm It is a joined body of steel plates formed by superposing a plurality of the following steel plates, and is formed by applying an adhesive and a carbon supply agent in advance to at least one interface among the superposed surfaces, and then performing welding. In the welded portion of the joined body, the nugget diameter is 2.8√t (mm) or more, and the C content is increased by 0.02% by mass or more as compared with the steel plate before applying the adhesive and the carbon supply agent.