Non-Homogenous Precipitation Annealing of Maraging Steels
Nickel maraging steels in the as-delivered state show a microstructure consisting primarily of oversaturated lath martensite. The final mechanical properties are achieved with precipitation annealing, during which the dissolved alloying elements start to precipitate. The newly-formed precipitated phases efficiently hinder shifts of dislocations, which results in considerable changes of the mechanical properties. Strength and hardness thus essentially increase whereas the material shows a relatively high fracture toughness. The precipitated phases formed during precipitation annealing also cause some distortion of a workpiece and transformational residual stresses on the micro and macro scales. Linear strains after precipitation annealing range from -0.05% to -0.1% and depend primarily on temperature/time conditions during the precipitation process. The non-homogenous annealing such as laser annealing produces temperature-induced residual stresses which are combined with transformational stresses. These stresses are expected to be lower and much more different than the stresses occuring in comparable classical heat-treated steels, however they cannot be neglected due to the exceptional performance of maraging steels and also their employment with high-demanding products. The results of the residual stress measurements after laser-induced and classical heat treatments of Ni-Co-Mo maraging steel with 12% nickel are presented.
Sabine Denis, Takao Hanabusa, Bob Baoping He, Eric Mittemeijer, JunMa Nan, Ismail Cevdet Noyan, Berthold Scholtes, Keisuke Tanaka, KeWei Xu
J. Grum and M. Zupančič, "Non-Homogenous Precipitation Annealing of Maraging Steels ", Materials Science Forum, Vols. 490-491, pp. 469-474, 2005