Spot Welded Tensile Properties in Automobile Ultrahigh Strength TRIP-aided Martensitic Steel Sheet

Akihiko Nagasaka, Tomohiko Hojo, Katsuya Aoki, Hirofumi Koyama, Akihiro Shimizu
2020 Tetsu to hagane  
Effect of heat-affected zone (HAZ) softening on tensile strength (TS) and total elongation (TEl) of spot welded ultrahigh strength TRIP-aided martensitic (TM) steel sheet was investigated for automobile applications. Tensile test was performed on an Instron type tensile testing machine at a crosshead speed of 3 mm/min (strain rate of 8.3×10 -4 s -1 ), using spot welded specimen. The results are as follows. (1) The spot welded specimen at the current value (I) of 6.5 kA for the TM steel with the
more » ... e TM steel with the maximum stress (TS*) of 1450 MPa and the fracture elongation (TEl*) of 7.0% was superior to that of hot stamping steel (the HS1 steel), and it was found that the TS* and the TEl* for the TM steel possessed those of base metal specimen for the HS1 steel with the tensile strength (TS) of 1469 MPa and the total elongation (TEl) of 7.7%. (2) The TRIP effect for the TM steel with an excellent strength-ductility balance (TS×TEl) of 14.4 GPa% (i.e. the tensile strength (TS) of 1532 MPa and the total elongation (TEl) of 9.4%) suppressed HAZ softening and was able to express a high maximum stress (TS*) of 1450 MPa for the TM steel of the spot welded specimen.
doi:10.2355/tetsutohagane.tetsu-2019-112 fatcat:mnk543zpsjcbncb4jiwapxibfu