The present paper describes microstructure, X-ray diffraction, microhardness and reduction test of calcium ferrites existed in the Ca O-Fe O-Fe2O3 ternary system. The results obtained are as follows- 1. In the identification of calcium ferrites, four calcium ferrites can be identified by the use of the polarization by reflection microscopy and the use of some etchants. 2. On the results of X-ray diffraction, interplanar spacings are computed by use of Bragg's equation. 3. From the results of the measurement of the microhardness for each specimen, it may be used for supplemental method of the identification by microscopy. 4. In the reduction test, it was recognized that the reducibility of calcium ferrites was good comparable with binary calcium ferrites reported formerly.
The rates of absorption of nitrogen in liquid iron containing surface active elements, such as oxygen.and sulphur, were measured at 1550°C and 1600°C. The transfer of nitrogen across the gas-metal interface was remarkably disturbed by those surface.active elements, adsorbed on the surface of the metal. It was also recognized that the rates of absorption in those melts were proportional to the partial pressure of nitrogen, when the metal contained more than nearly 0.03% sulphur or oxygen. Furthermore, it was observed that the rates of absorption were inversely proportional to 2/3 power of sulphur(or oxygen) concentration in the bulk Contains higher than 0.03%S (or 0.02%O). These concentrations correspond to the coverage of the surface by sulphur or oxygen nearly as Fe S or Fe, calculated by the Gibbs' adsorption equation. It becomes (dc/dt)t=0=K·PN2/(wt%S or wt%O)2/3 Consequently, it seems reasonable to regard that in those melts the transfer of nitrogen from gas into liquid iron may be chemically controlled, namely it is mainly controlled by the rate of nitrogen adsorption. It is now accepted that oxygen or sulphur behaves as a poison on the metal surface. Behaviour of surface active elements at gas-metal interface could be explained, assuming that they were concentrated to the interface as ions, S2- or 02-. The rate of reaction was also discussed from the stand--point of the absolute rates theory There is a linear relation between apparent mass transfer coefficient of nitrogen and surface tension of liquid iron containing surface active elements, practically no different between sulphur and oxygen. The activation energy for absorption of nitrogen should decrease as the surface coverage adsorbed by oxygen decreases, and is approximately 20kcal/mol at about 0.001% oxygen. This value corresponds nearly to the order of the activation energy for diffusion of oxygen in liquid iron.
We have measured the Mossbauer effect of 57Fe in iron-carbon martensite and its change after ternpering. The resonant absorption spectrum in martensite was resolved into several components arising from iron atoms, which are the 1st, 2nd, 3, 4th neighbors to the carbon atoms and remnant iron atoms. A carbon atom causes localized changes of electronic states of the surrounding iron atoms, especially affecting the 1st nearest neighboring iron atoms. The internal magnetic field at nuclei of the 1st neighbors is 265 KOe, which is far less than 330 KOe of pure iron. Variation of the isomer shift and appearance of a large positive quadrupole effect were also observed. It is suggested from the MOssbauer measurement that the bonding between the carbon atoms and the 1st neighboring iron atoms in martensite may be accompanied, possibly, by the covalent admixture of wave functions. Internal magnetic fields and isomer shifts of the 2nd and 3, 4th neighbors also deviate slightly from those of pure iron, but the sign of the deviation is opposite to those of the 1st neighbors. Their quadrupole effects were nearly zero, which means that the positive charge of the carbon ion is almost screened out within a distance of the order of 2Å by the additional electron clouds. The localized nature of the effect of the carbon atom permits a parallel discussion between the ironcarbon martensite and the α-solid solution. From the changes of the Mössbauer spectrum after tempering of martensite, we have concluded that the bonding between the carbon atoms and the iron atoms in the coherent ε-carbide formed at the stage I is essentially the same as the bonding in the martensite or the a-solid solution. We have also evidence that the χ-carbide is formed at the stage III a of tempering, the formation of which has not been fully proved in the previous x-ray or magnetic measurements. The mean internal magnetic fields after the heat treatments change from 194 KOe due to mainly χ-carbide (at 220°C) to 208 KOe due to cementite (at 520°C). The reduction of the internal field of the 1st neighboring iron atom in various Fe-C systems, irrespective of their crystal structure such as the solid solution, the ε-phase, the χ-phase, the θ-phase (cementite), is roughly proportional to the number of their nearest neighboring carbon atoms. Decreases in the internal field of an iron atom per carbon atom are about 60 KOe. These localized and additive behaviors suggest that the bonding nature between the carbon atoms and the neighboring iron atoms in the above structures can be understood on a common ground.
The effect of alloying element such as C, B, Ti and Nb, and heat treatment on the high temperature strength and micro structure of 18Cr-12Ni-3Mo austenitic heat resisting steels containing boron were investigated. In B addition, creep rupture strength increased with increasing B content, whereas in C addition, tit reached maximum at 0.2%C. These effects were ascribed mainly to a precipitation hardening duevto M23C6 occurring during creep. The effects of Ti and Nb additions on creep rupture strength were given as a function of (Ti+Nb)/C (atomic percent ratis) irrespective of C contents, and gave a maximum effect at (Ti+Nb)/C=0.4-0.8. Therefore, these effects of Ti and Nb additions were ascribed partly to a change in morphology and growth rate of M23C6, into which Ti and Nb were dissolved. Moreover, creep rupture strength increased with increasing solution temperature, up to 1250°C. Surprisingly, the eutectic structures had no negative effect upon creep rupture strength of the steels. Also, the complex borides in these alloys were identified by X ray and chemical analyses. The relation between the sort of borides and eutectic temperature was also discussed.