Isothermal thermo-gravimetric analysis was applied to investigate the nitridation kinetics of manganese powder with different particle sizes at 800, 900 and 1000 ℃. The apparent activation energy and nitridation kinetics equations of manganese powder with different particle sizes were obtained from unreacted shrinking core model and Arrhenius formula. It was found that the nitridation mechanism was controlied by interracial chemical reaction. The apparent activation energy and the apparent rate constant of nitridation reaction were affected by particle sizes. With the decrease of particle size, the apparent activation energy decreased whilst the apparent rate constant increased. It was suggested that the refinement of the manganese powder contributed to the increase of molar surface energy, which accounted for the lower apparent activation energy.
The liquidus and solidus temperatures of FeCrAl stainless steel were determined by differential scanning calorimetry（DSC） at different heating rates. They were also calculated by Thermo-calc software and empirical formulae separately. The accuracy of calculation results was assessed by comparison with the corresponding DSC results. The liquidus temperatures calculated by empirical formulae, which exhibited a maximum deviation of 8.6℃ were more accurate than those calculated using Thermo-calc, which exhibited a maximum deviation of 12.11℃. On the basis of Thermo-calc calculations performed under the Scheil model, the solidus temperature could be well determined from solid fraction（fS） vs. temperature（t） curves at fS = 0.99. Furthermore, a theoretical analysis to determine the solidus temperature with this method was also provided.
Zhi-biao HanJian-hua LiuYang HeKang-wei LiYi-long JiJian Liu
High manganese steels can damage the differential thermal analysis （DTA） instrument due to the manganese evaporation during high temperature experiments. After analyzing the relationship between residual oxygen and manganese evaporation, tanta- lum metal was employed to modify the crucible of DTA, and zirconium getter together with strict gas purification measures were applied to control the volatilization of manganese. By these modifications, problems of thermocouple damage and DTA instrument contamination were successfully resolved. Cobalt samples were adopted to calibrate the accuracy of DTA instruments under the same trial condition of high manganese steel samples, and the detection error was confirmed to be less than 1 ℃. Liquidus and soli- dus temperatures of high Mn steels were measured by improved DTA method. It was found that the liquidus temperatures of sam- ples tested by experiments increased linearly with the heating rates. To eliminate the effects of the heating rate, equilibrium liquidus temperature was determined by fitting the liquidus temperatures at different heating rates, and referred as real liquidus temperature. No clear relationship between solidus temperatures and heating rates was found, and the solidus temperature was finally set as the average value of several experimental data.
