Production process and quality control of nodular cast iron sector test block for spent nuclear fuel vessel

Using high-purity pig iron as the main raw material, the high-temperature pure and high-quality molten iron meeting the composition requirements can be obtained by electric furnace melting, so as to control the chemical composition and trace elements. Trace elements interfere with the spheroidization of large low temperature high toughness low temperature ductile iron castings, and affect the graphite morphology and matrix structure, especially the graphite morphology in the center of large cross section. In order to ensure that the fracture toughness and – 40 ° C impact toughness meet the requirements, the content of trace elements and the control range of trace elements are strictly controlled, and the sum of 11 trace elements is less than 0.06%.

The superheating temperature of molten iron is 1490 ° c-1500 ° C, the tapping temperature is 1440 ° c-1460 ° C, the spheroidizing process is adopted, and the amount of spheroidizing agent is about 1.3%. 0.6% 75sife was added for one inoculation. After the spheroidizing reaction, skim the slag, add 0.4% high calcium barium inoculant (particle size 3-8mm) into the ladle for floating silicon inoculation, measure the temperature after skimming, and pour when the temperature drops to 1350 ° c-1360 ° C, then use 0.1% sulfur oxygen inoculant for flow inoculation, pouring and flow inoculation.

The temperature measurement device is turned on during pouring, and the temperature measurement curve of 45 ° sector test block and mold is shown in the figure. In addition, it is necessary to adopt on-line detection and quality control system of molten iron quality in front of furnace, formulate extremely strict production control process to ensure the stability and reliability of molten iron quality in front of furnace, and obtain qualified castings with high stability and consistency.