Annealing-Controlled Recrystallization, Grain Growth, and Tensile Properties of Cold-Rolled L-605 Cobalt-Based Alloy

This work investigated the effects of annealing temperature and holding time on recrystallization, grain growth, and tensile properties of cold-rolled biomedical Co-20Cr-15W-10Ni (L-605) alloy. The alloy was solution-treated at 1200 °C for 30 min, cold-rolled to 40% area reduction, and annealed at 800-950 °C for 15 min, 1000 °C for 5-60 min, or 1200 °C for 5-60 min. Annealing at 800-900 °C produced partially recrystallized microstructures; 950 °C yielded nearly full recrystallization with an average grain size of ~3.4 μm. At 1000 °C, the fully recrystallized microstructure retained ~5 μm fine grains even after 60 min, likely due to grain boundary migration inhibition by fine secondary-phase particles, whose composition and pinning effect remain unclarified. At 1200 °C, grains grew significantly to ~90 μm, attributed to higher grain boundary mobility and reduced particle pinning at elevated temperature. As annealing temperature rose from 800 °C to 950 °C, yield strength decreased from 1245 MPa to 800 MPa, and elongation increased from 12.6% to 45.9%. At 1200 °C, yield strength fell to 442-455 MPa and elongation reached 73.5-80.8%. The results confirm that the alloy's strength-ductility performance is directly determined by microstructure evolution from retained cold rolling deformation substructures to fine recrystallized grains, and further to coarse recrystallized grains at higher temperatures.