Abstract
The various basic roles of micro-alloying additions are examined within a framework which emphasizes their modes of distribution in alloys. On the one hand, the effects of solute atoms when segregated to vacancies, dislocations and grain boundaries are briefly reviewed, and on the other, the formation of precipitates involving micro-additions are shown to influence markedly the behaviour of many alloys. Examples are given of the effects of solute atoms in the nucleation and growth of phases in both ferrous and non-ferrous alloys. Another important field is illustrated by the control of grain growth and recrystallization by micro-alloying additions to achieve ultra-fine grain sizes, for example in aluminium alloys to obtain superplastic behaviour, and in HSLA steels to obtain high strength and toughness. Some examples are also given of the effects of micro-alloying in phase transformations, particularly nucleation of precipitates at inter-phase boundaries. Finally, some beneficial effects of minor additions made to creep-resistant nickel-base and Cr–Ni austenitic alloys are discussed.
