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The influence of martensitic microstructure and prior austenite grain (PAG) size on the mechanical properties of novel maraging steel was studied. This was achieved by looking at two different martensitic structures with PAG sizes of approximately 40 µm and 80 µm, produced by hot rolling to different reductions. Two ageing heat-treatments were considered: both heat-treatments consisted of austenisation at 960 °C, then aging at 560 °C for 5 h, but while one was rapidly cooled the other was slow cooled and then extended aged at 480 °C for 64 h. It is shown that for the shorter ageing treatment the smaller PAG size resulted in significant improvements in strength (increase of more than 150 MPa), ductility (four times increase), creep life (almost four times increase in creep life) and fatigue life (almost doubled). Whereas, the extended aged sample showed similar changes in the fatigue life, elongation and hardness it displayed yet showed no difference in tensile strength and creep. These results display the complexity of microstructural contributions to mechanical properties in maraging steels.

In the present study, monotonic and cyclical torsional deformations of an X-70 microalloyed steel were conducted at austenite temperatures below the recrystallisation-stop temperature (T5%). The austenite deformation is followed by accelerated continuous cooling to allow the investigation of the strain reversal effect on the subsequent phase transformation mechanisms. The transformation behaviours were studied by a dilatometry method, and the microstructures of the transformed products have been analysed using electron back scatter diffraction (EBSD). The results of this study shows that although subjected to the same total cumulative strain and the same cooling rate, strain path reversal by cyclical torsion produces lower temperature transformation products involving mainly a displacive mechanism, comparing to simple strain path deformation which leads to higher temperature transformation by a reconstructive mechanism.

Atom Probe Tomography (APT) is becoming increasingly applied to understand the relationship between structure and composition of new alloys at the micro-and nano-scale and their physical properties. Here, we use APT datasets from two modern aerospace alloys to highlight the detailed information available from APT analysis, along with potential pitfalls that can affect data interpretation. The interface between two phases in a Ti-6Al-4V alloy is used to illustrate the importance of parameter choice when using proximity histograms or concentration profiles to characterise interfacial chemistry. The higher number density of precipitates and large number of constituent elements in a maraging steel (F1E) present additional challenges such as peak overlaps that vary across the dataset, along with inhomogenous interface chemistries.