Austenite formation in low carbon-manganese steels upon intercritical annealing proceeds by nucleation and growth of the manganese-enriched phase accompanied by concurrent dissolution of the manganese-lean high-carbon austenite transformed from pearlite. When the annealing temperature is below the A 1 for the nominal Mn content, the austenite forms in the same way while pearlitic carbide dissolves. The rate controlling mechanism is the diffusion of manganese in ferrite, and it is likely that volume, grain-boundary as well as phase-boundary diffusion contribute to growth. The manganese content of the isothermally formed austenite is temperature dependent in an inverse way, rendering a high hardenability to steels treated at and below 725 degree C
Godkänd; 1984; 20080307 (cira)