Effect of heat-affected zone (HAZ) softening on tensile strength (TS) and total elongation (TEl) of spotwelded automobile 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 8.310? 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 maximum tensile stress (TS*) of 1 450 MPa and the fracture elongation (TEl*) of 7.0% was superior to that of hot stampted (HS1) steel sheet and it was found that the TS*and the TEl*for the TM steel possessed same level as those of base metal specimen for the HS1 steel with the tensile strength (TS) of 1 469 MPa and the total elongation (TEl) of 7.7%. (2) The TRIP effect for the TM steel with an excellent strength-ductility balance (TSTEl) of 14.4 GPa% (i.e. the tensile strength (TS) of 1 532 MPa and the total elongation (TEl) of 9.4%) suppressed the HAZ softening and was able to express a high maximum stress (TS*) of 1 450 MPa of the spot-welded specimen for the TM steel.
|出版ステータス||Published - 2021 2月 15|
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