Influence of Solution Treatment on Impact Toughness and Microstructure of Cobalt-free Maraging Steel

The influence of different solution temperature on microstructure and impact toughness of cobalt-free maraging steel 00Ni14Cr3Mo3Ti was investigated by SEM and X-Ray diffractometer. The experimental results showed that with the solution temperature variation, the martensite morphology has not changed, is still lath martensite. Undissolved Laves phase hindered the dislocation movement after 750 degrees C solution heat treatment, which result in a very low impact absorbed energy, the impact fracture has no obvious plastic deformation, with bad toughness. With the solution temperature increased, the undissolved phase gradually dissolved, the impact absorbed energy increased gradually. All the Laves phase dissolved when reach to 900 degrees C, the impact absorbed energy reaches the maximum, is 61 J. Fracture morphology change from brittle fracture into toughness transgranular fracture with deep dimple. When solution temperature is above 900 degrees C, with the solution temperature further increase, austenite grain size increases significantly. Average grain diameter of austenite is about 70 mu m after 1050 degrees C solution treatment, the density of precipitates on the grain boundary of maraging steel is increase substantially, deformation compatibility deteriorate, which result in the impact absorbed energy decreased significantly. Fracture type becomes transgranular and quasi-cleavage mixed fracture with the characteristics of the river patterns from ductile transgranular fracture.