Suppression of Coarse Columnar Grain Formation in As-cast Austenite Structure of a Hyperperitectic Carbon Steel by Nb Addition

Effects of Nb addition on as-cast γ-austenite grain structure in 0.2 mass% carbon steel are investigated by means of furnace cooling and permanent mold casting experiments. In the furnace-cooled samples with Nb addition, Nb(C,N) particles crystallize from the last-solidifying liquid in non-equilibrium solidification condition and they act as pinning particles for γ grain growth just after the solidification completion. The Nb addition produces a strong pinning effect on the as-cast γ grain structure. In the permanent mold casting experiment, Coarse Columnar Grains (CCG) structure develops from the mold wall in the sample without Nb. The increase in Nb concentration gradually decreases the fraction of CCG region and increases the fraction of Fine Columnar Grains (FCG), thus leading to the grain refinement. This refinement could be ascribed to the pinning effect of Nb(C,N) particles

Suppression of Coarse Columnar Grain Formation in As-cast Austenite Structure of a Hyperperitectic Carbon Steel by Nb Addition

Effects of Nb addition on as-cast γ-austenite grain structure in 0.2 mass% carbon steel are investigated by means of furnace cooling and permanent mold casting experiments. In the furnace-cooled samples with Nb addition, Nb(C,N) particles crystallize from the last-solidifying liquid in non-equilibrium solidification condition and they act as pinning particles for γ grain growth just after the solidification completion. The Nb addition produces a strong pinning effect on the as-cast γ grain structure. In the permanent mold casting experiment, Coarse Columnar Grains (CCG) structure develops from the mold wall in the sample without Nb. The increase in Nb concentration gradually decreases the fraction of CCG region and increases the fraction of Fine Columnar Grains (FCG), thus leading to the grain refinement. This refinement could be ascribed to the pinning effect of Nb(C,N) particles

Geothermal Survey of the Volcanoes Kirishima

In and around the volcanoes Kirishima, there were many seismic swarms since September 1975, especially frequent under the craters Ohachi and Shinmoe-dake. For the prediction of steam explosion which is most probable at the volcanoes Kirishima, it is important to notice the variation in their thermal activities. However, the thermal states of these craters have not been investigated thoroughly. Therefore, the authors carried out geothermal surveys of Ohachi and Shinmoe-dake which are present active craters, and of Iwo-yama, the most thermally active area in Kirishima, during November, 1978. The results of the surveys are summarized as follows. 1) Surface temperature distributions are made clear by the measurements with an infra-red thermometer (Fig. 2 b, 3 c, 4 b). 2) Statistics of these surface temperature distributions give the surface temperature of the "normal" area, T0 as 6.2℃, 6.9℃ and 2.9℃, at Ohachi, Shinmoe-dake and Iwoyama, respectively (Table 8). Through these analyses, high thermal anomalies (higher than T0+SσT) are recognized at each site. 3) The fumarolic temperature of Ohachi is 96℃, the same as in 1972, which is the boiling temperature of water at that altitude. The fumarolic temperatures of Iwoyama range from 93.5℃ to 174.0℃ (Table 5). 4) Heat discharge and H2O emission rates from these areas are estimated by successive photographs of fumarolic plumes and by surface temperature distributions of steaming grounds. The heat discharge rates of Ohachi, Shinmoe-dake and Iwo-yama are 2.1×106 watt, 2.2×107 watt and 6.1×107 watt, respectively. The H2O emission rate of Ohachi is less than 7.8×102 g/sec, from Shinmoe-dake, between 7.2×103 and 7.9×1O3 g/sec and from Iwo-yama, 2.2×104 g/sec (Table 9)