JOINED BODY OF HIGH TENSILE STRENGTH STEEL SHEET AND RESISTANCE WELDING METHOD FOR HIGH TENSILE STRENGTH STEEL SHEET

摘要

PROBLEM TO BE SOLVED: To provide a joined body of high tensile strength steel sheets and a resistance welding method for the high tensile strength steel sheet, which attains the improvement of rupture strength by suppressing the development of cracks to the inside of a nugget.SOLUTION: The joined body of high tensile strength steel is made by joining parts to be joined containing at least high tensile strength steel sheets overlapped mutually by resistance welding. In this joined body of the high tensile strength steel sheets, the diameter of crystal particles of a nugget 13 is a fine grain diameter in which the large tilt angle grain boundary of tilt angle 15 degrees or more has a fine grain diameter of smaller than 30 μm, preferably, has a fine grain diameter of smaller than 20 μm.