Transformation from continuous-to-isothermal aging applied on a maraging steel

The advantage of continuous Differential Scanning Calorimetry (DSC) experiments is the possibility of the precise determination of a reaction's enthalpy, the corresponding transition temperatures as well as a material's heat capacity. Additionally, continuous experiments are usually less time-consuming than isothermal procedures. On the contrary, in industry steels are subjected to isothermal aging treatments in order to obtain the desired mechanical properties by the precipitation of nanometer-sized particles. The application of continuous-to-isothermal transformation schemes, which have been developed mostly for precipitation hardened aluminium alloys, combines the benefits of continuous DSC experiments with industrial interests. The premise for the application of such transformation schemes on steels is an appropriate baseline construction strategy for the evaluation of the DSC experiments. In the present investigation, the applicability of a transformation scheme based on a Johnson-Mehl-Avrami-Kolmogorov-approach is tested successfully on a maraging steel hardened by copper precipitates. The results are verified by hardness tests on continuously and isothermally aged samples. Three-dimensional atom probe tomography is carried out in order to interpret the differences in the precipitation behavior between these two types of aging treatments. (C) 2010 Elsevier B.V. All rights reserved.