Volume 4, Issue 5 (May 2007)
Observation of Austenitic Grain Growth in Some Alloy Structural Steels
In order to satisfy the demands coming from the thermal and thermo-chemical treatments, higher treatment temperature values are required to shorten the soaking time or to increase the structurally modified thickness, or both. Toughness and mechanical strength of a steel are strictly related to the presence of small grain dimension microstructure, which can be obtained through the presence of precipitates at the grain boundaries. The refinement of the microstructure is connected to the chemical composition and dimension of the precipitates, which dissolve partially or totally above a critical temperature. In this paper, two steels for mechanical application have been studied. In the supply conditions these steels are characterized by a precipitation condition due to the thermal treatment carried out in the steelmaker plant. By metallographic techniques, the grain growth has been studied, varying temperature and soaking time during thermal treatments. The dilatometric tests have been useful to follow the transformations able to contain the increase of the austenitic grain size and TEM analysis has contributed to confirm the nature of these transformations.