The Partitioning of Impurity Elements in Iron-Carbon Alloys
ARMY MATERIALS AND MECHANICS RESEARCH CENTER WATERTOWN MA
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The partitioning at 600 C of the elements tin, phosphorus, silicon, antimony, and arsenic between the ferrite and carbide phases was investigated in Fe-C-X alloys, where X is one of the the above elements. These elements are all known to increase the susceptibility for temper brittleness in steels and are suspected of playing a similar role in the phenomenon of tempered martensite embrittlement or 500 F embrittlement. The procedures of metallographic examination, electron microprobe analysis, ferrite lattice parameter measurement, and chemical analysis and crystal structure determination of extracted carbides were employed in the study. It was determined that of the above elements only tin and phosphorus appear to partition to the carbide phase, tin apparently forming a ternary carbide. The remaining elements silicon, antimony, and arsenic partition to ferrite, thus providing a condition conducive to the accumulation of these impurities on the ferrite side of ferritecarbide interfaces during tempering. By virtue of its more potent solid solution strengthening effect in ferrite, one might, therefore, anticipate a greater embrittling tendency from the impurity element antimony, a prediction borne out by experiment. Solubility limits, distribution coefficients, and other phase relations were determined during the course of this study.
- Properties of Metals and Alloys