Oxygen is one of the most important impurities present in iron or steel, mainly forming oxide inclusions. Therefore, it is often desirable to know the solubility of oxygen in solid iron with a reasonable accuracy, but investigations yield highly discordent results. As shown by many literatures, this is attributed to oxydizable impurities in solid iron, such as Si, Mn and Al, etc. In the present work, we carried out the experiments in lowering the crucible very slowly under purified argon gas, using the Tammann furnace, and the equiliblium between solid iron and liquid was noted. Then, chromium was added to liquid iron and the effect of it on the solubility of oxygen in δiron was also studied. These results were summarized as follows; 1. The measurement of the monotectic point in the Fe-O system showed that the concentration of oxygen was 0.16% and the temperature was 1528°C. 2. The liquidus line could be drawn by a straight line combining two points, i.e., the freezing point of purified iron (1538°C) and the monotectic point (1528°C, 0.16%0). 3. The distribution ratio of oxygen (Lo) is 0.076 in the temperature range between 1528°C and 1538°C, independent of the concentration of oxygen in liquid iron, and the solubility of oxygen is 0.012% at 1528°C. 4. The relation between the concentrations of chromium and oxygen was obtained in liquid iron at the temperature of solid-liquid interface. It has an approximately good agreement with the calculation using the values which were recommended by Japan Society of the Promotion of Science. 5. The distribution ratio of oxygen increased with increases in the concentration of chromium, and became 0.13 at 10% chromium. 6. The distribution ratio of oxygen in the Fe-O system has a good agreement with the ratio obtained in the Fe-O-Cr system by extraporation.
respectively. The results are summarized as follows. 1) The maximum extrusion punch pressure pmax changes discontinuously at the temperature of α-γ transformation, and above the temperature, it is related to the temperature T (°K) by the following equation, pmax=A'In R (B/T) Where the constant A' decreases with carbon content, while B increases. The estimated punch pressure at the melting temperature Tm, which expresses resistance of viscocity of extrusion at R=2·3, becomes 26kg/mm2, irrespective to the carbon content. 2) The constant B gives the value of the activation energy of deformation ΔH in the relationship B=ΔH/mk, where m is the parameter of stress dependence of the strain rate, and k the Boltzmann constant, respectively. The observed increases of B with the carbon content comes from the dependence of m on the carbon content. The value m changes from 10 to 5 due to the increase of the carbon content from 0.02 to 0.52%, which gives 32-37 kcal/mol as ΔH. This result shows that the activation energy of deformation in the impact extrusion is fairly small compared with the energy of self diffusion of γ-iron, and it is suggested that the deformation mechanism operative in the impact extrusion differs from that for the static deformation. 3) The following empirical relationship in M. K. S. unit for the maximum impact extrusion punch pressure pmax (kg/mm2) versus carbon content C% at different extrusion conditions are proposed, _??_ The second term in the right hand side of the equation represents the inertia resistance associated with the high rate extrusion, where g is the gravity constant and ρ the density of steel.
In order to develope the low-alloy hot-work forging-die steels with a superior thermal-crack risistivity, the effec of alloy components: C, Si, Mn, Cr, Mo, and V, and the effect of additional alloyingelements: Ni, Cu, Co, Ti, W, Zr and Nb, on the properties of.the Si-Cr-Mo-V steel have been investigated. Critical transformation temperatures, length change due to transformation, a thermal expansioncoefficient, hardenability, elevated temperature mechanical properties as well as room-temperaturetensile and impact properties of variously heat-treated structures (quenched and tempered, normalizedand tempered) were determined. Si, which was considered to be most important alloying element, wasvery effective for the elevation in transformation temperatures and reduction in length change due totransformation. On the other hand, the variation in hardenability and transformation characteristicswith increasing Si content was relatively small. The effect of increasing Si content on the mechanicalproperties of tempered martensitic structure was small, up to 2%Si. As for normalized and temperedstructures, the variation of tensile properties with Si was small, but the impact value at the lowerhardness level was decreased as Si content was increased. By the thermal-crack resistivity measurements, it was shown that these Si-Cr-Mo-V steels have very excellent resistivity in comparison with theconventional forging-die steel. Characteristics of Si-Cr-Mo-V steels in the present investigation (basic composition: 0.35%C-1.5%Si-1%Cr-0.4%Mo-0.2%V) are considered as follows: high resistivity for softening during tempering, high yield and tensile strength at elevated temperature, relatively good ductility and toughness, andsuperior thermal-crack resistivity.
The initial precipitate states in 18-8 Ti stainless steel with variable precipitate amount and shapesare made by heat treatment and their effects on the creep and creep rupture characteristics are mainlyinvestigated. Hardness at room temperature and short time tensile test at high temperature are examinedfor comparision with creep strength. The microstructures from extracted replica and thin foilare observed by electron microscopy. The creep characteristics are good represented for soluble Ti content (or soluble C content) and itis suggested that mutual action between soluble Ti and C is fairly great for creep strength. Moreover, the creep characteristics are strongly influenced by the initial precipitate states and this is discussedfrom the view points of mutual action between precipitates and dislocation. The needle type precipitate, which is assumed to be Cr3C2, is found to have the relation with the great decrease of creepstrength and its mechanism is discussed. It is observed that the effect of the initial precipitate stateson the hardness and short time tensile properties are very little.