Experimental study on nodular cast iron sector test block for nuclear spent fuel container

1) The self-developed 16 channel temperature measuring device was used to successfully collect the temperature curves of 45 ° fan-shaped test block and mold. By comparing the simulated solidification time with the measured solidification time and the simulated solidification sequence with the actual solidification sequence, it is proved that the simulation results are consistent with the actual situation, and the simulation software can be used to optimize the casting process of large-scale ductile iron spent fuel container;

2) Compared with the cold iron, the temperature rise of the metal mold is later, the temperature fluctuation range is smaller, the temperature difference between the two sides of the metal mold is larger, and the temperature of the metal mold does not reach the same temperature as that of the cold iron, which proves that the heat dissipation capacity of the metal mold is stronger than that of the cold iron under the same heat source conditions, and the temperature difference between the two sides of the metal mold is larger than that of the cold iron, and it remains at about 200 ° C for a long time Good heat storage capacity and thermal conductivity make the cooling condition of 45 ° fan-shaped block outside better than inside;

3) The cooling conditions of each part of the 45 ° fan-shaped test block are different, so the solidification time of each part of the 45 ° fan-shaped test block is different; the cooling conditions of both sides are good, the solidification speed is fast, the cooling conditions of the central part are poor, the solidification speed is slow, and the thermal conductivity of both sides of the 45 ° fan-shaped test block is unbalanced, resulting in that the solidification time of the inner side is longer than that of the outer side at the same distance from the center, and the solidification time is the shortest The solidification sequence of 45 ° fan-shaped block is as follows: outer L / 8 (57 min), inner L / 8 (85 min), outer L / 4 (136 min), Center (181 min), inner L / 8 (85 min);

4) The results show that the microstructure of 45 ° fan-shaped block is ferrite matrix, graphite spheroidization grade 2-3, number of graphite balls 250 / mm2, spheroidization rate ≥ 86.1%; there is no abnormal graphite, graphite does not decline, all the indexes of 45 ° fan-shaped block meet the requirements of foreign ductile iron nuclear spent fuel container; it shows that under the existing domestic conditions, it can meet the requirements Performance index of foreign spent ductile iron fuel container;

5) The number of graphite balls has little effect on the tensile strength, yield strength, elongation and other conventional mechanical properties, but has great effect on the impact property, especially on the impact property at – 40 ° C. with the decrease of the number of graphite balls, the impact value at – 40 ° C decreases from 8.0j/cm2 on the outside to 5.4j/cm2 on the center; considering the error caused by sampling, the inner 1 / 4 position is smaller The weak part of the impact performance at – 40 ° C is near the impact point;

6) In addition to reasonable selection of raw materials, strict control of trace element content, selection of suitable spheroidizing agent and spheroidizing treatment process, inoculant and inoculation treatment process, it is also necessary to ensure that the mold has sufficient cooling capacity, so that the 45 ° fan-shaped test block can solidify in 3.5H, and the number of graphite balls is 2:50 / mm2, so as to ensure the microstructure and ductility of the 45 ° fan-shaped test block All the energy indexes can meet the requirements of nuclear spent fuel container.