Resistance spot welded joint and related resistance spot welding method

A resistance spot welded joint having a resistance spot weld in which two or more steel sheets including at least one high-strength steel sheet are resistance spot welded, wherein

• the high-strength steel sheet has a chemical composition comprising, in mass %:
• C:
• 0.05 to 0.6%,
• Si:
• 0.1 to 2.0%,
• Mn:
• 1.5 to 4.0%,
• P:
• 0.10% or less,
• S:
• 0.005% or less,
• N:
• 0.001 to 0.010%,
• O:
• 0.03% or less, and
• the balance being Fe and incidental impurities;
• and
• the resistance spot weld is such that:
• a heat-affected zone has a first region that is a square region having an end of sheet separation as a central point of the square and having a segment with a length L, in millimeters, the length of the segment satisfying expression (1) in relation to a thickness t, in millimeters, of the high-strength steel sheet or the thinnest one of the high-strength steel sheets,
• an average hardness Hv of the first region satisfies expression (2) in relation to a hardness Hvm of a nugget central portion, and
• an average number density of carbide particles having a size of 100 nm or more is 10 particles or more per 5 μm2 of a steel sheet cross section in the first region,
• 0.5
• ×
• t
• ≥
• L
• (
• 1
• )
• 0.85
• ×
• Hvm
• >
• Hv
• .
• (
• 2
• )