Design and development of treatment alloys for ductile cast iron

Abstract

The possibilities of using directionally cooled ductile cast iron specimens, made under controlled conditions, in design and development of ferro-silicon based liquid metal treatment alloys have been investigated. Several heats of experimental ductile cast iron were produced using both commercially available and experimental melt treatment alloys to demonstrate the versatility of the casting method. In addition, heats containing either lead or lanthanum were produced to provoke the formation of degenerated graphite nodules in the iron. Evaluation of the directionally solidified specimens, both by time-temperature recordings and by microstructure examination, showed that the reproducibility of the casting method is good. The decrease in the cooling rate with increasing distance from the cooled bar end resulted in a systematic change in the iron carbide content as well as the size, shape and graphite nodule count. Since the extension of the carbide zone is an indirect measure of the nucleating conditions for graphite in the iron, this parameter can be used to rank the effectiveness of the melt treatment alloys during casting. Such information may be reported in the form of a critical cooling rate for carbide formation.