Effects of austenitizing temperature on the kinetics of bainite reaction at constant austenite grain size in FeC and FeNiC alloys

The influence of austenitizing temperature on a subsequent diffusional transformation has been investigated. The overall bainite transformation rate in a slightly hypo-eutectoid Fe-7.6Ni-0.48C alloy is increased by a double austenitizing treatment. Optical microscope observations have revealed that this acceleration of bainite transformation is caused mostly by the acceleration of nucleation rate at austenite grain boundaries. Intergranular fracture surface observations have shown that a second austenitizing treatment enhances cementite precipitation on grain boundaries. It is considered that the enrichment of sulfur at grain boundaries by a second austenitizing treatment enhances the precipitation of cementite during the subsequent cooling to the transformation temperature. When the second austenitizing temperature is 750°C or below, disc shaped Fe-rich FeS precipitates are formed together with the cementites. The initial stage of bainite transformation has shown that the cementites and Fe-rich FeS precipitates act as preferential nucleation sites for bainite. The precipitation of cementite and Fe-rich FeS by a double austenitizing treatment is also observed in a Ni free Fe-0.61C alloy.     

Plastic properties of CU2O,mechanical tests and transmission electron microscopy—I. low temperature

Cu₂O single crystals have been compressed along 〈001〉 and 〈011〉 below 600°C. A temperature of 250°C must be reached to induce plastic deformation. Various slip systems have been activated: {110} 〈1̄10〉, {110} 〈001〉 and {010} 〈001〉. The critical resolved shear stresses of these systems have been measured for various temperatures and partial pressures of oxygen. These observations together with those made by optical and transmission electron microscopy allowed to conclude on the nature of obstacles to dislocation glide and also on the work hardening mechanism.