Jfe Steel Corporation

Reiko Endo

Hiroshi Matsuda

Koichi Taniguchi

Rinsei Ikeda

Muneo Matsushita

Katsutoshi Takashima

A resistance spot weld, a resistance spot welding method, a resistance spot welded joint, and a method for manufacturing the resistance spot welded joint. In the resistance spot weld, at least one of steel sheets is a high-strength steel sheet having a prescribed chemical composition. In at least one of a nugget edge region corresponding to a faying interface, the nugget edge region has a metal microstructure including tempered martensite as a main phase. The hardness Hv of the nugget edge region and the hardness Hmw of martensite in the nugget as a whole satisfy formula (4). In at least one of a strong HAZ region corresponding to the faying interface, the hardness Hh of the strong HAZ region and the hardness Hmh of martensite in a prescribed steel sheet satisfy formula (8).

Resistance spot weld, resistance spot welding method, resistance spot welded joint, and method for manufacturing resistance spot welded joint

The present invention provides a resistance spot welding method. A resistance spot welding method according to the present invention in which a sheet combination of two or more overlapping steel sheets is sandwiched between a pair of electrodes and joined together by applying current while applying pressure, the method including a main current application step in which current application is performed with a current I(kA), and subsequently, a post-tempering heat treatment step in which after cooling is performed for a cooling time t(ms) shown in formula (1) below, current application is performed with a current I(kA) shown in formula (2) below for a current application time t(ms) shown in formula (3) below: 800≤t. . . formula (1), 0.5×I≤I≤I. . . formula (2), and 500≤t. . . formula (3).

Resistance spot welding method and method for producing resistance spot welded joint

Main current passage and subsequent current passage are performed, with a cooling time of 0.01 s or more being provided between the main current passage and the subsequent current passage. Ip/I which is a ratio of a current value of the subsequent current passage to a current value of the main current passage is controlled to satisfy a predetermined relationship depending on a constant A defined by Mn content and P content of a steel sheet as a part to be welded, in relation to a welding time Tp of the subsequent current passage, a cooling time T, and the constant A.

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Tokyo, Japan

Reiko Endo