At low strains (e < 0.25), the precipitation of Ti, Nb, V carbides in austenitic Fe -Mn -C steels which exhibit twinning induced plasticity has no significant effect on work hardening. Strengthening follows the Orowan mechanism and can be described by a simple yield stress offset. However, at higher strains (e > 0.3) the work hardening rate decreased slightly. Synchrotron X-ray diffraction analysis suggested that this was due to a reduction in the kinetics of twin formation. The highest strengthening coefficient in cold strips was obtained with Ti additions £ 0.1 wt.% (+1 380 MPa/ wt.% Ti) but the effect quickly saturated after an increase of *+150 MPa. With Nb additions only modest hardening (+187 MPa/wt.%) could be achieved. The strengthening due to V was > 530 MPa/wt.% for V additions £ 0.4 wt.% Saturation effects are less critical with V additions and yield stress increases of +375 MPa were demonstrated.

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In recent years several studies have shown the importance of thermal fracturing of rocks due to temperature variations, on Earth and Mars. Rock thermal cracking might also be a process at play on the lunar surface. These temperature variations as well as change rates can reach important amplitude on bodies without an atmosphere, in particular on those that reach small perihelion distances such as near-Earth asteroids. On the other hand, the formation, geometry and extension of cracks on these bodies have not been fully investigated yet. Here we show results of thermal cracking laboratory experiments on chondrite meteorites, which develop networks of cracks when subjected to rapid temperature cycles with amplitudes similar to those experienced by asteroids with low perihelion distances. The depth of the cracks can reach a few hundred of microns in some hundreds of temperature cycles, in agreement with theoretical studies. We find that dehydration of hydrous minerals enhances the cracking process. The formation of crack networks increases the porosity both at the surface and in the sub-surface of our specimens. We propose that this process could help explaining the recent finding of the very highly porous surfaces of most of the boulders on the asteroids Ryugu and Bennu.