| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a cold-rolled steel sheet for resistance welding, including a high tensile strength of ≥590 MPa, and an excellent weld zone strength when being projection-welded, and suitable for a material for an automobile component to which projection welding is used. <P>SOLUTION: The cold-rolled steel sheet for resistance welding has a chemical composition including 0.05-0.20% C, 0.4-1.6% Si+Al, 0.1-3.0% Mn, ≤0.02% P, ≤0.01% S, ≤0.01% N, and a remainder composed of Fe and impurities, and has mechanical properties in which the total of a solid solution Si concentration and a solid solution Al concentration of a steel sheet surface layer part specified by formula (1): solid solution Si concentration=T<SB POS="POST">Si</SB>-O<SB POS="POST">Si</SB>and formula (2): solid solution Al concentration=T<SB POS="POST">Al</SB>-O<SB POS="POST">Al</SB>is ≥0.20 mass%, the largest depth of a crack of the steel sheet surface is ≤5 μm, the number density of cracks having the width of ≤6 μm and the depth of ≥2 μm is ≤10/50 μm, and a tensile strength is ≥590 MPa, wherein T<SB POS="POST">Si</SB>and T<SB POS="POST">Al</SB>are each concentration (unit: mass%) of the total of Si and Al in the steel sheet surface layer part from the steel sheet surface to a position of the depth of 30 nm, and O<SB POS="POST">Si</SB>and O<SB POS="POST">Al</SB>are each concentration (unit: mass%) of Si and Al forming oxides in the steel sheet surface layer part. <P>COPYRIGHT: (C)2012,JPO&INPIT |
