Abstract
Messrs. Finniston, Jones and Madsen discuss in a recent communication1 the variation of ultimate hardness number Pu with the Meyer index n, in the ball indentation test. There are several good reasons for associating a decrease in the n value with a decrease in the work-hardening capacity of a metal, especially since n and Pu have hitherto shown a negative correlation coefficient. Finniston et al., however, suggest that this generalization should be reconsidered, and they give results showing a positive correlation coefficient between Pu and n for metals of non-cubic structure and of increasing anisotropy as judged by results for thermal expansion. Their proposal is interesting because certain anomalies exist regarding the n value. Thus, during the progressive cold rolling of copper it may drop from 2.34 to 2.0 at an early stage and then remain more or less constant, while the Pu value will continue to increase and thus indicate further work-hardening2. This peculiarity has not been explained, and it should be remarked that the progressively rolled copper increasingly develops anisotropic properties (preferred orientation) as shown by X-ray diffraction and etching tests. This effect does not appear to be inconsistent with their proposal.
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References
Nature, 164, 1128 (1949).
O'Neill and Cuthbertson, J. Inst. Metals, No. 2 (1931).
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O'NEILL, H. Meyer Analysis of Metals. Nature 165, 362 (1950). https://doi.org/10.1038/165362a0
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DOI: https://doi.org/10.1038/165362a0
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