Aging phenomenon in low lattice-misfit cobalt-free maraging steel: Microstructural evolution and strengthening behavior

We elucidate here the impact of aging temperature on microstructural evolution and strengthening behavior on low lattice misfit cobalt-free maraging steel. The best combination of high-strength (1850 MPa) and high-toughness (125.4 MJ m(-3)) was obtained at the optimal aging temperature of 520 degrees C, without sacrificing ductility. Electron back scattered diffraction studies suggested that preferred orientations of {101}, fraction of high angle grain boundary (HAGB) and total length of grain boundary per unit area (mu m/mu m(2)) were increased with increase of aging temperature, which was beneficial to both strengthening and toughening of maraging steel. The strengthening contribution from the precipitates was transformed from shearing mechanism to bypass mechanism when the aging temperature is greater than 520 degrees C. The aging tempered steel of 520 degrees C provided maximum strengthening increment of 1463 MPa through shearing mechanism, while granular reverted austenite at this temperature contributed to high toughness.