Abstract
The use of thermal analysis as a tool for the real-time chemistry control of carbon and silicon in ductile base iron is very important for seamless melt productivity by avoiding delays in waiting for laboratory analyses of those elements by the direct but time-consuming methods via spectrometer or combustion. With the standard market availability of four (4) different thermal analysis cup types encompassing the two binary choices of ‘round versus square’ and ‘plain versus tellurium’ in amounting to the four choices, thorough comparative testing of each cup type was conducted for gage repeatability and reproducibility (GR & R) analyses and other correlativity analyses. Major results of this testing and data analysis are presented herein along with discussion and conclusions regarding the relative merits of each of the four available cup types. Based on comparative GR&R analyses and subsequent regression analysis of the data, it is concluded that, among the four (4) thermal analysis cup types to choose from for real-time control of the carbon equivalent, carbon and silicon contents of ductile base iron, the ‘RD–PL’ (round and plain) and ‘SQ–TE’ (square and tellurium) cups perform superiorly to the ‘RD–TE’ (round and tellurium) and ‘SQ–PL’ (square and plain) cups.
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Acknowledgements
The authors give special thanks to the Grede – New Castle Melt Department along with Laboratory Technicians Gary Bray, Herbert McGhee and Michael McClain for their assistance with samples and data acquisition.
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Appendices
Appendix 1: Definitions of Thermal Analysis Temperature Events
Since there is no industry-wide standardized terminology for defining the thermal events detected on cooling curves of cast iron solidification, the thermal events considered this paper are defined as follows9:
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TP; molten iron ‘T’emperature ‘P’eak detected seconds after filling thermal analysis cup.
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TL; ‘T’emperature of austenite ‘L’iquidus arrest detected at the point on the pro-eutectic portion of the cooling curve where the 1st derivative peaks out at some value less than zero and where the 2nd derivative equals zero.
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TEmin; ‘T’emperature of ‘E’utectic ‘min’imum arrest temperature on the eutectic portion of the cooling curve where the 1st derivative equals zero prior to recalescence by graphitization for base iron cast in ‘plain’ thermal analysis cup and solidified with mottled graphitic and carbidic structure.
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TEmax; ‘T’emperature of ‘E’utectic ‘max’imum arrest temperature on the eutectic portion of the cooling curve where the 1st derivative equals zero at the peak of recalescence by graphitization for base iron cast in ‘plain’ thermal analysis cup and solidified with mottled graphitic and carbidic structure.
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TS; ‘T’emperature of eutectic ‘S’olidification arrest temperature for base iron cast in ‘tellurium’ thermal analysis cup and solidified with nearly fully carbidic structure. There is no temperature recalescence by graphitization associated with the ‘TS’ arrest temperature, so the ‘TS’ arrest is detected at the point on eutectic portion of the cooling curve where the 1st derivative peaks out at some value equal to or less than zero and where the 2nd derivative equals zero.
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t(s); elapsed ‘t’ime in ‘s’econds from initial sensing of molten iron in thermal analysis cup until any of the foregoing thermal events.
Appendix 2: LECO Combustion Analysis Parameters
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Cree, J., Grybush, I., Robles, M. et al. Statistical Comparisons of Four (4) Different Thermal Analysis Sample Cup Types for Chemistry Control of Ductile Base Iron. Inter Metalcast 15, 729–746 (2021). https://doi.org/10.1007/s40962-020-00498-z
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DOI: https://doi.org/10.1007/s40962-020-00498-z