CARBIDE TRANSFORMATIONS IN LOW-ALLOY STEELS DURING LONG-TERM AGING AND SERVICE

TTT-diagrams have been obtained for several commercial low-alloy Cr-Mo -V steels over temperatures ranging from 450 to 700 degrees C. Carbide compositions and structures have been investigated and precipitation kinetics of alloying elements during long-term ageing of a metal with the original martensite structure found. The formal theory of transfor mation kinetics is shown to be useful and values of the 'n' coefficien t in Johnson-Mehl equation are determined. Cooling rate from the auste nite region has a significant effect on the character of a carbide pha se diagram. Data relating to the molybdenum content in the carbide pha ses have been obtained after long-term service of the metal for 150-20 0 thousand years.