The rate of reduction of silica in CaO-Si02 and CaO-Al203-Si02 slags by carbon in liquid iron was measured under various experimental conditions to examine effects of slag composition, temperature, atmosphere and slag graphite interfacial area. Effect of slag composition was ascribed to the change of activity of silica. Apparent activation energies were about 100kcal/mol for binary slags and 70-85kcal/mol for ternary slags. The rate of reduction increased linearly with the ratio of slag-graphite to slag-metal interfacial area in the low ratio region. It suggests that reaction of silica reduction proceeds electrochemically, and that interfacial reaction is the rate-determining step. The rate of reduction in argon atmosphere was about twice as fast as that in CO atmosphere.
The apparent viscosity of sintered ores and pellets was measured by creep test at elevated temperature. After samples were reduced to the intended degree, atmosphere around the saple was changed from reducing gas to inert one in order to keep the degree of reduction constant during the following creep test. Apparent viscosity was calculated from the rate of deformation under various load and discussed in relation to packing state of sample particles. The effects of sample composition, reduction degree, testing temperature and packing state on viscocity were examined with the following results. 1) In general, oxidized samples showed higher viscosity than reduced ones. 2) Samples which contained only acidic components tended to have lower viscosity and activation energy of viscosity than those which contained basic components such as CaO and MgO. 3) In oxidized sample, the increase of basicity of slag components caused the decrease of viscosity. While in reduced samples, viscosity had its minimum value in the basicity of about 1.5. 4) Added silica caused increase of viscosity, but once it reacted with FeO to form fayalite (2 FeO. Si02) viscosity decreased. 5) The effect of magnesia (MgO) on viscosity was affected by coexistence of alumina (Al203)
An investigation was carried out to know the effect of alloying elements on the solubility of sulphur and to determine the interaction coefficients of sulphur in 5-iron. The solubility of sulphur was determined by using the solid-liquid equilibrium technique presented in the previous work. The crucible assembly was lowered very slowly in purified argon gas in Tamman furnace, so that equilibrium between solid and liquid iron was attained. The relation between the partition ratio of sulphur in Fe-S system (Ls′) and in Fe-S-X system (Ls) is log Ls=log Ls′+log(f(X)l/f(X)S) where ƒs(X) and ƒl(X) are the interaction coefficients in solid and liquid iron respectively. By using the relation, the interaction coefficients of various elements in solid iron obtained are as follows: log f(Mn)S=-0.58[% Mn] <0.15% Mn log f(Si)S=-0.286[% Si] <0.4% Si log f(O)S=-37.4[% O] <0.007% O log f(C)S=7.29[% C] <0.03% C
An investigation was made on the interactions induced by the simultaneous additions of interstitial solute elements such as C, N, and B, for the high temperature strength of 18 Cr-12 Ni heat resisting steel. The interactions were correlated with the age-hardening response, the softening characteristics after cold rolling and the structural change during creep. By the duplex additions of N and B, the obvious interaction that decreased the creep rupture strength lower than the sum of individual contributions was produced. This interaction was attributed in part to the strengthening of matrix more than the boundary due to precipitation hardening and in part to promoting the creep rupture by B addition in the coexistence with N. By the duplex additions of N and C, the deleterious interaction was also produced after prolonged time at 700°C. From these phenomena, the authors suggested a general condition for producing the interaction by the simultaneous additions of alloying elements for the high temperature strength.
Low and high carbon 18 Cr-12 Ni steels were solution treated at various temperatures and the creep rupture test was conducted at 600 and 700°C. These steels were employed since they were considered to give a fundamental aspect of the effects of heat treatments on creep rupture strength. The creep rupture life at the test temperature of 600°C showed a maximum at a certain solution temperature. This solution temperature, for shorter life tests (i. e., higher stress tests), was that which gave incomplete solution of carbide, and for longer life tests (i. e., lower stress tests), was that which gave just complete solution of carbide. At the test temperature of 700°C, however, appeared no maximum in the rupture life as a function of solution temperature. The above experimental facts on creep rupture life (tr) can be analysed by considering the effects of solution temperature on creep rate (ε) and rupture elongation (εr), since, apporoximately, tr is εr devided by ε. The rupture life maximum at 600°C stems from the fact that ε comes to the lowest value at a certain solution temperature and above the temperture no material change occurs ε in while εr continues to decrease as the solution temperature is raised. The result at 700°C that no maximum appeares in life can be explained by that the intergranular cracking at 700°C is of cavity type which is independent of grain size and hence εr as well as ε, does not change above the solution temperature that gives just complete solution of carbide.
A study was made on the strengthening phenomena and fracture behaviours in alminium or Ca-Si killed low carbon manganese steels with small amounts of Nb, V or Nb-V addittion. It was found that the addition of Nb, V, or in combination of these elements produced an additional strengthening due to the fine carbonitride precipitation above the strength level presumed from the refined grain size, and this was controlled by the various heat treatments. The yield strength increment in the Nb-V, -and Nb-V-steels can be divided into the two terms, i. e. grain refinement and friction stress increment, the contribution of these two depends on the kinds of the steels and heat treatment. In Al-killed steels the impact transition temperature was generally lower than that of corresponding Ca-Si killed steels. The impact transition characteristics seem to be classified into four groups by the yield strength against the strengthening mechanism, and a linear dependence of the transition temperature on the friction stress increment has been found. A good combination of strength and toughness was obtained in the steels strengthened by the balanced effect of both the grain refinement and the friction stress factor. Finally, the fracture appearance of impact specimens was examined by microfractography.