Study and test of an active thermosiphon experimental set-up to validate Super-FRS dipoles cooling system

International audienceIn the framework of the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, CEA is in charge of the design studies for superferric dipole magnets of the Superconducting Fragment Separator (Super-FRS). Each of these dipoles has 2 coils with a trapezoidal shape, each coil being cooled by a horizontal 20 × 10 mm2 liquid helium channel (below or above the coil). The static heat load to extract is 5 W and, to generate a mass flow, the principle of a thermosiphon is implemented with a heater on the return pipe to force the flow direction of the thermosiphon. To validate this cooling system, an experimental set-up was designed and built at CEA Paris-Saclay. This paper presents the experimental set-up and the results of the tests. The effect of the horizontal heat load and the influence of the heater are reported

Numerical investigations of the effects of substitutional elements on the interface conditions during partitioning in quenching and partitioning steels

International audienceIn quenched and partitioned steels, carbon partitioning is considered to be driven by a constraint para-equilibrium at the martensite/austenite interface. Using Thermo-Calc calculations, we investigated the effect of non-partitioned elements on the resulting interface condition. Among all tested elements, only aluminum and chromium have significant effects. From this numerical study, a practical composition- and temperature-dependent relationship describing interface tie lines was derived and calibrated for Fe-C-2.5Mn-1.5Si-X wt pct alloys (X = Cr or Al)

Chemistry and Properties of Medium-Mn Two-Stage TRIP Steels

Eight medium manganese steels ranging from 10 to 15 wt pct Mn have been produced with varying levels of aluminum, silicon, and carbon to create steels with varying TRIP (transformation-induced plasticity) character. Alloy chemistries were formulated to produce a range of intrinsic stacking fault energies (ISFE) from − 2.2 to 13.3 mJ/m2 when calculated at room temperature for an austenitic microstructure having the nominal alloy composition. Two-stage TRIP behavior was documented when the ISFE of the γ-austenite phase was 10.5 mJ/m2 or less, whereas an ISFE of 11.9 mJ/m2 or greater exhibited TWIP (twin-induced plasticity) with single-stage TRIP to form α-martensite. Properties were measured in both hot band (hot rolled) and batch annealed (hot rolled, cold rolled, and annealed) conditions. Hot band properties were influenced by the Si/Al ratio and this dependence was related to incomplete recovery during hot working for alloys with Si/Al ratios greater than one. Batch annealing was conducted at 873 K (600 °C) for 20 hours to produce ultrafine-grained microstructures with mean free slip distances less than 1 µm. Batch-annealed materials were found to exhibit a Hall—Petch dependence of the yield strength upon the mean free slip distance measured in the polyphase microstructure. Ultimate tensile strengths ranged from 1450 to 1060 MPa with total elongations of 27 to 43 pct. Tensile ductility was shown to be proportional to the sum of the products of volume fraction transformed times the volume change associated for each martensitic transformation. An empirical relationship based upon the nominal chemistry was derived for the ultimate tensile strength and elongation to failure for these batch-annealed steels. Two additional alloys were produced based upon the developed understanding of these two-stage TRIP steels and tensile strengths of 1150 MPa with 58 pct total elongation and 1400 MPa and 32 pct ductility were achieved