Milwaukee Paper - Experiments on the Heat Treatment of Alpha-Beta Brass (with Discussion)

Certain alloys1 that, as a result of quenching, are retained in the form of homoaeneous solid solution are known to increase in hardness and strength on standing at room temperature or on heating at slightly elevated temperatures. Other alloys2 that, on rapid cooling, are held in the form of homogeneous solid solution, as, for example, certain steels, behave in like manner on heating to somewhat higher temperatures. The observed increase in the hardness and strength of these alloys, referred to as " aging"' or as "secondary hardness," is widely accepted as being occasioned, either in whole or in part, by the precipitation in submicroscopic form of such constituents as were held in supersaturated solid solution as a result of cooling in excess of a certain critical rate. In earlier discussions of the cause of age hardening or secondary hardness, the question of the hardness of the precipitated particles does not appear to have been raised. At present, however, the general opinion appears to be that age hardening and secondary hardness are occasioned by the precipitation of hard particles within the supersaturated solid substance.3 The authors may be wrong in their belief that the last is a prevailing opinion. Nevertheless, it is thought that the following experiments,