On the Precipitation of the Laves Phase Particles in a Martensitic 10% Cr-3% Co-3% W-0.2% Re Steel during Creep at 650°C

The size and distribution of the Laves phase particles in a 9.85Cr-3Co-3W-0.13Mo-0.17Re- 0.03Ni-0.23V-0.07Nb-0.1C-0.002N-0.008B steel subjected to creep rupture test at 650°C under an applied stresses of 160-200 MPa with a step of 20 MPa were studied. After heat treatment consisting of normalizing of 1050°C and tempering of 770°C, M₂₃C₆ and Fe₃W₃C carbides with the mean sizes of 67±7 and 40±5 nm, respectively, were revealed along the boundaries of prior austenite grains and martensitic laths whereas round NbX carbonitrides were found within martensitic laths. During creep metastable Fe₃W₃C carbides dissolved and the stable Laves phase particles precipitated; volume fraction of Laves phase increases with time. The Laves phase particles nucleated on the interfacial boundaries Fe₃W₃C/ferrite during first 100 h of creep and provided effective stabilization of tempered martensitic lath structure until their mean size less than 150 nm.