|About this Abstract
||Materials Science & Technology 2012
||Recent Developments in Steel Processing
||Fracture Toughness of a 1.5 GPa Grade C-Si-Mn-Cr-Nb TRIP-Aided Martensitic Steel
||Junya Kobayashi, Daiki Ina, Koh-ichi Sugimoto
|On-Site Speaker (Planned)
Fracture toughness of ultrahigh-strength TRIP-aided steels with lath-martensite structure matrix or “TRIP-aided martensitic steel” was investigated for some applications to automobile, construction machine, ship etc. When a 0.2%C-1.5%Si-1.5%Mn-1.0%Cr-0.05%Nb, in mass%, steel was subjected to heat treatment of isothermal transformation process at temperatures below Mf after austenitizing, it exhibited a tensile strength of 1.5 GPa and a total elongation of 15 pct. In addition, the steel achieved much higher fracture toughness (120-170 MPa.m1/2) than conventional structural SCM420 steel (50-80 MPa.m1/2). The fracture toughness was the same as that of 18%Ni maraging steel. It was considered that the superior fracture toughness is essentially caused by (i) refined dual-martenite structure matrix consisting of soft and hard martensites and (ii) plastic relaxation on the strain-induced martensite transformation of retained austenite of 3-5 pct volume fraction, which disturb a crack initiation and propagation.
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