DILATOMETRIC TECHNIQUE FOR EVALUATION OF THE KINETICS OF SOLID-STATE TRANSFORMATION OF MARAGING-STEEL

Solid-state transformation kinetics of a 350 grade commercial maraging steel were investigated using a nonisothermal dilatometric technique. Two solid-state reactions-namely, precipitation of intermetallic phas es from supersaturated martensite and reversion of martensite to auste nite-were identified. Determination was made of the temperatures at wh ich the rates of these reactions reached a maximum at different heatin g rates. The kinetics of the individual reactions in terms of activati on energy were analyzed by simplified procedures based on the Kissinge r equation. An estimated activation energy of 145 +/- 4 kJ/mol for the precipitation of intermetallic phases was in good agreement with repo rted results based on the isothermal hardness measurement technique. M artensite to austenite reversion was associated with an activation ene rgy of 224 +/- 4 kJ/mol, which is very close to the activation energy for diffusion of substitutional elements in ferrite. Results were supp lemented with microstructural analysis.