Relationship betwen artificial aging of technically pure iron and the preliminary period of aging at room temperature

Abstract

1. As well as depending on the aging conditions, variation in properties during artificial aging depends on the time elapsing between quenching and the start of heating for aging. The results of many previous research projects, in which this circumstance was not taken into account, cannot be considered reliable. 2. The effectiveness of artificial aging also depends on the period of storage after quenching. In the case of technically pure iron, artificial aging at 100\dgC is most effective after the metal has been stored for one day. Industrial instructions for artificial aging must indicate for every alloy the ideal period of storage after quenching. 3. The artificial aging curves for technically pure iron have two hardness peaks, and accordingly two ductility minima. This shows that two different hardening processes take place during aging. When working out artificial aging conditions, the aging time must be so selected as to ensure that the second hardness peak is reached. 4. The processes taking place during room temperature and artificial aging are evidently different. During natural aging, processes of segregation of the dissolved substance take place in the lattice of the solvent; the coherent growth of an excess phase probably also begins. In artificial aging, particles of a new phase are precipitated.