فهرست مطالب ali khosravifard

Hardox-400 with an extra-high yield strength of ~1000 MPa and excellent abrasion resistance is a good candidate for several industrial applications including automotive parts, working tools, barges, loaders, etc. Due to high dimensional precision and to avoid mechanical abrasion of the work-piece, electrical discharge machining (EDM) is a proper machining technique for such steel. The influences of important process parameters, i.e. discharge current and spark pulse cycle on the electrode wear, material removal, surface roughness, and integrity of the machined material is investigated. It was observed in this work that as the discharge current increased, the electrode wear also increased but this occurred with a gradually decreasing rate. On the other hand, increasing the ratio of pulse-on to pulse-off time decreased material removal. Furthermore, it was observed that increasing both the discharge current and the pulse-on time led to a thicker solidified so-called white layer which is more susceptible to cracking and thus is detrimental to the material integrity.

In this work, dynamic mechanical properties of three high-manganese steels with TRIP/TWIP or fully TWIP characteristics are studied. High strain rate experiments in the range of true strain rates between ~500 and 1800 /s are conducted using a dynamic torsional testing setup. All the three steels show a positive strain rate sensitivity in the intermediate range of strain rates (up to 500 /s). But, they behave differently as the strain rate is further increased. The steel with the lowest carbon content shows a strain rate softening behavior, while the other two exhibit strain rate hardening. The adiabatic temperature rise of the material greatly influences its stacking fault energy during the high rate dynamic deformation. Thus, unlike the quasi-static experiments, the dominant deformation mechanism of the steel during a dynamic test changes as the deformation progresses. In this regard, the variations of the stacking fault energy during the deformation are calculated for the three steels.