2008 Volume 94 Issue 11 Pages 553-561
Cu precipitation hardening behavior and mechanical properties were investigated in Cu added martensitic ultra-high strength steels. In this work, hardness measurement, TEM observation, lattice parameter measurement and tensile testing were conducted for 0.19%C–1.5%Mn steels with addition of up to 4% Cu those were water-quenched followed by aging at 250 through 550°C for 20 s through 360 min. Cu added steels exhibited higher hardness than a Cu free steel in each aging condition. Precipitated Cu content estimated by lattice parameter well corresponded to hardness increment in 4% Cu steels compared with Cu free steels aged at the same aging condition. Regarding the tensile properties of the aged Cu free and 4% Cu steels, 4% Cu steel exhibited superior balance of tensile strength and elongation with tensile strength level of 1300 MPa. Lower activation energy estimated by peak hardness increment than that of Cu diffusion in bcc-Fe matrix suggested that high dislocation density introduced by martensitic transformation accelerated the growth of Cu precipitates. And smaller Cu precipitation hardening in martensite matrix compared with that in ferrite matrix was also discussed taking into consideration nonlinear summation of dislocation hardening and precipitation hardening.
