CHEMICAL DRIVING-FORCE, SHEAR MODULI OF FERRITE AND METASTABLE AUSTENITE, AND STRAIN-ENERGY FOR GAMMA-]ALPHA A TRANSFORMATION IN PURE IRON

The chemical driving force/unit volume Delta G(nu) for they gamma-->al pha transformation in pure iron is computed as a function of undercool ing. Similarly, the strain delta accompanying the transformation at di fferent temperatures is also calculated from lattice parameter measure ments. Shear moduli mu(alpha) of ferrite and metastable austenite mu(g amma) are derived from various sources. At temperatures down to the Cu rie temperature (768 degrees C), mu(alpha) and mu(gamma) are very simi lar, and enable the strain energy/unit volume W to be calculated from the expression W = 2 (mu(alpha) + mu(gamma))delta(2). The data give th e metastable equilibrium temperature T-o for the massive ferrite trans formation as 1156 K. The distinction between equiaxed ferrite, massive ferrite, and Widmastatten ferrite is discussed. (C) 1995 The Institut e of Materials.