Cu precipitation kinetics during martensite tempering in a medium C steel

The Cu precipitation kinetics during martensite tempering of an Fe-0.44C-0.60Mn-0.21Si-0.11Cr-1.53Cu (wt.%) steel was quantitatively investigated by separating the Cu precipitation from the cementite precipitation through electrical resistivity, small-angle neutron scattering (SANS), dilatometry, and thermodynamic calculations. The cementite precipitation was already finished during continuous heating to 450 degrees C, and then Cu precipitation occurred above 450 degrees C. The Cu precipitation kinetics was accelerated with increasing tempering temperature. The fcc epsilon-Cu particles were precipitated mainly at cementite interfaces, while bcc Cu-rich particles were formed in the tempered martensite matrix, and transformed to 9R, 3R, and fcc epsilon-Cu during further tempering, resulting in higher hardness of a medium C steel. The activation energy for isothermal Cu precipitation (64.9 +/- 13.3 kJ/mol) during martensite tempering of the present medium C steel was even lower than that of a low C steel due to the greater cementite fraction. (C) 2012 Elsevier B.V. All rights reserved.