The degassing mechanism in the R-H degassing equipment was investigated by analyzing the degassing action by single bubble as a model, and these results were utilized to estimate the rate of the circulation flow and the decarburizatipn curve. Of the total volume of CO reaction, one-third occurs within the up-leg and two-thirds within the vacuum chamber. This ratio, however, varies depending on the concentrations of carbon and oxygen in the liquid metal. If the concentrations are rather high, more reaction occurs within the up-leg, while higher ratio of the reaction is noted within the vacuum chamber at lower concentrations. In deoxidizing low carbon steel, it is necessary to inject a substantial amount of argon in order to attain a below 100ppm level without using any deoxidizing agent. Although the inner pressure fo the vacuum chamber generally has much effect upon the degassing, significant effect is no longer shown at a pressure as low as minus 1 torr. In removing the hydrogen from killed steel, care should be taken to obtain much splash in the vacuum chamber. The rate of the circulation flow is proportional to the 1·5th power of the inner diameter of the circulation legs and to the 0·33rd power of the argon injection rate. The rate of circulation flow in the treatment of undeoxidized steel attains its maximum when a certain rate of argon injection, which depends upon the leg size, is applied.
Relationship between the strength and the change of grain size and precipitation behavior of NbC by various heat treatments was examined with pure 0.2% carbon steels containing 0.02-0.09% Nb. The results were summarized as follows: 1. Though NbC particles precipitated in Nb treated steels tend to coalesce with increase of austenitizing temperature, they remain in steel and prevent the grain coarsening of austenite because of its small solubility and dissolving rate in austenite. 2. The highest strength was obtained when the cooling rate from austenitizing temperature to room temperature was 25°C/min. When Nb treated steel is continuously cooled after full solution treatment for long time at sufficiently high temperature such as 1250°C, NbC seems to precipitate not only at lower temperatures than A3 point but also at the temperature range of austenite, and the precipitation from austenite will cause less strengthening effect than that from ferrite. 3. Strengthening effect by Nb treatment may be explicable on the assumption that both effects of grain refinement and dispersion of fine particles of NbC are additive; that is, an increase of strength in Nb treated steels austenitized at lower temperatures than about 1050°C is due mainly to refining of ferrite grain size and that at higher temperatures is due mainly to fine precipitation of NbC.
Effect of metallographical factors on the rolling fatigue life of 1%C-1.5%Cr bearing steel was investigated, and the most profitable component for the bearing life was discussed. The results obtained are as follows: (1) Metallographical factors affected on the rolling fatigue life of bearing steel were not amount and size of residual cementite but the chemical compositions soluted in fhe matrix. (2) The most effective factor affected on the rolling fatigue life was carbon content soluted in the matrix and the most desirable carbon content in the matrix was about 0.5 percent. (3) It was recognized that the mechanism of flaking was related to the third stage of the tempering of martensite. This was deduced from the observation of the micro-structure of cyclic stressed area by the transmission electron microscopy and the result of bearing life test of a new type steel with higher silicon of which the starting temperature of the third stage was rised by silicon.