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.