Method of manufacture of spot welded joint, steel sheet for spot welding use, and steel sheet member for spot welding use

A method of producing a spot welded joint of overlaid steel sheets, at least one of the steel sheets having tensile strength of 500 MPa or more, facing surfaces of the steel sheets being coated with oil, the method comprising:

• at one or both of the surfaces of the steel sheets becoming the facing surfaces of said steel sheets, working in advance a location where the steel sheets contact each other to form a contact part at the time of initial squeezing of spot welding to form lines of a plurality of line-shaped grooves running through the contact part and connected to the outside of the contact part;
• and
• performing the spot welding at the location of the contact part while discharging the oil to the outside of the contact part through the lines,
• wherein the lines are formed by abrasive paper, abrasive cloth, a die, or a scriber,
• the number of the lines is respectively four or more at least at one of the surfaces of the steel sheets becoming the facing surfaces of the steel sheets and,
• regarding the widths of the lines and the surface roughness Sa of the steel sheet surfaces of the contact part,
• the surface of the at least one steel sheet becoming the facing surface is worked to form the lines so that,
• when the number of lines N is 4≤N<20, the width of the lines is 0.4/N (mm) or more and the surface roughness Sa is −0.07×N+1.9 (μm) or more and when the number of lines N is 20≤N, the surface roughness Sa is 0.5 μm or more.