Abstract
The investigation on the transformation of austenite to martensite based on the statistical thermodynamics was carried out using the iron-nitrogen binary alloys containing about 1.8 to 2.8 weight per cent nitrogen. The result of this treatment was compared with that of the iron-carbon binary alloys. The Ms point which was determined microscopically by the Greninger and Troiano method descends with the increase of the nitrogen content and attains room temperature at about 2.2 weight per cent nitrogen showing a complete austenitic structure. Ms points of the iron-nitrogen and iron-carbon alloys containing the same atomic percentage agreed with each other. The T0γ−α′ temperature (ΔFγ→α′=0) of the iron-nitrogen alloy fell nearly parallel to the change in the Ms point with increase of the nitrogen content. On the other hand, the driving force necessary for initiating the martensite transformation increased with increase of the nitrogen content. The effect of carbon on the thermodynamic properties of martensite transformation agreed with the effect of nitrogen. Stabilities of martensites and supersaturated ferrites of the nitrogen- and the carbon-iron alloys were also discussed.
