The effect of Mn, Si or Cr on the M_s-temperature and the martensite structure of Fe-0.3%C alloywere examined under hydrostatic pressure up to 41kbar using a “girdle” type high pressure apparatus.
The results obtained are as follows;
(1) The M_s-temperature was lowered approximately 40°C/10kbar in all alloys and its tendency wasnot significantly affected by alloying elements.
(2) The measured M_s-temperatures at 1 atm (≈0.001 kbar), 29 and 38.5kbar are in reasonable agreementwith those calculated by the Predmore's equation concerning the free energy change for γ-α transformation.
(3) The plate-like structure was observed as a result of the martensite transformation above 38.5kbar.The reason for the appearance of this structure can be explained qualitatively by P-T diagram of iron.
(4) The hardness of martensitic structures increases with an increase of pressure. This tendency can beinterpreted by the fact that the M_s-temperature is lowered by pressure, accompanying with the change of martensite structure.