In order to study the effect of the oxygen pressure on the decarburization reaction, Fe-C alloys containining about 1-4% carbon were melted and decarburized with the oxygen gas stream, which had previously been prepared to show a partial pressure between 20 and 760mm Hg by mixing pure oxygen gas (or pure nitrogen) into air, the rate of the carbon removal being measured by flow method. In this case the equation of the rection rate was simplified as follows:
The carbon contents measured at every time interval into this equation being introduced, the values of the specific constant, k0, were estimated for various oxygen pressures with the result of which the relation between k0 and po2 was found as
Besides this, in case of lower carbon contents up to 1%, each value was found to be constant at higher oxygen pressures above 300mm Hg, where the oxygen contents on the surface of molten iron, could be presumed as predominant over those of carbon. In order to determine where the reaction occurred, the reaction rate was measured by varying the area of interface between gaseous and liquid phases. In consequence, it was found linearly proportional to that area, the reaction being shown to take place on the interface. The oxygen contents, dissoved in molten iron during the process of this reaction, were analysed in the samples killed with aluminum and were found to have no proportionality to the partial pressure of oxygen in gaseous phase, and to show the characteristic values corresponding to carbon contents. According to the results stated above, the reaction mechanism of this sort was presumed as follows:
(1) The oxygen molecule dissociated on being adsorbed at the gas-metal interface, and then its atom was dissolved into the surface layer to participate in the reaction.(2) The oxygen which participated in this reaction must be in equilibrium with that in the gaseous phase at a given pressure.
When the pressure of carbon monoxide produced in the reaction became considerable as compared with the oxygen pressure, this reaction was found to be retarded by the former gas.

抄録全体を表示

Two different shapes of test casting were used for determining hot-tearing tendency of cast steels. The first one comprised a 40mm diameter vertical cylinder and four horizontal, radial branches, each joined to the cylinder by a special design. The hot-tearing tendency of a steel was determined by fracturing these joints at room temperature. The test casting of the second type was a kind of plate casting, the thickness of its main part being 20mm. Length of hot-tear in this plate was taken as an index to hot-tearing tendency of the cast steel.
Several spoonfuls of molten steel sample were taken from each heat of ordinary cast steel manufactured in a 5-ton basic arc furnace, and then each spoonful was tested after addition of various elements into the spoon. Again, the correlations between the analysis of each element and the resistance of steel to hot-tearing was studied by use of many heats of steel without any addition in the spoon.
From results of studying on the influences of C, Si, Mn, P and S followng conclusions were obtained:
(1) Hot-tearing tendency increased with increase in the carbon content within the range of 0.16-0.6%C.
(2) Silicon did not seem to affect the hot-tearing tendency in a simple way, but a study on the correlation showed that steels containing 0.4-0.5% silicon had the maximum resistance to hottearing.
(3) Hot-tearing tendency decreased as the manganese content increased until the latter reached at least 0.75%, but it seemed to have a minimum point before the manganese content reaches 1%.
(4) Even small additions of phosphorus were so detrimental that increase of the phosphorus from 0.02% to 0.04% had nearly the same effect as increase of the sulphur from 0.01% to 0.02%.
(5) The wellknown fact that sulphur was the most deleterious element was accertained here again.

抄録全体を表示

(1) In a Tamman furnace cast iron was melted under the most suitable conditions found in the previous investigation for production of the cast iron having eutectic graphite structure. Then the cast iron melt was kept at liquid state in the furnace for various durations of time, after the cover of the liquid slag had been removed. And then, the cast iron melt was cast in a dry sand mould and the graphite structure of the cast metal was esamined.
It was confirmed that the eutectic graphite structure appeared even in the cast iron which had been kept at naked, liquid state for 60 minutes before the melt was cast.
(2) Two kinds of cast iron-cast iron A and cast iron B were prepared, both having the same composition except Ti and the eutectic graphite structure. The former was produced by the new process the authors discovered and the latter by casting liquid cast iron into a metal mould.
They had been remelted and then kept in the furnace without the cover of liquid slag for various durations of time before the cast iron melt was cast into a dry sand mould. It was found that, in the case when cast iron A was used in the esperiments, the eutectic graphite atructure appeared even in the cast metal which had been kept for 60 minutes in the furnace at liquid state before tbe melt was cast. In the case when cast iron B was used in the experiments, however, the eutectic graphite structure was not observed even in the cast metal which had been kept for such a short time as 15 minutes at liquid state before tho melt was cast.
(3) Al content of the cast iron melt should be kept as low as possible for production of the cast iron with the eutectic graphite structure by the new process the authors discovered.
(4) It was confirmed tbat the basicity of the slag-CaO/SiO₂ should be taken into consideration when the new process the authors discovered was applied in practice.

抄録全体を表示

In indicating austenite grain size, the hitherto-used method is sufficient in case all the grains are of almost uniform size, but if there are different sizes of grains mixed up, the old method is of no effect at all, and when the author try to use it forcibly, the following faults will come out: -
(1) Even if it is of uniform grains, there is no way of ascertaining it.
(2) When grains of large size and of small size are mixed up closely as well as uniformly in the microscopic field, it is to be represented as of uniform grains (microscopic mixed grains), though it seems to be of mixed-up grains.
(3) As the sample is looked in its section, small-size grains will naturally be seen more than those that actually are, while large size grains are less.
(4) There is no way of estimating the volume fractions of large-size and small-size grains contained in a sample.
(5) Discrepancy in the number of grain sizes obtained by the hitherto-used method denotes only the differences of average grain sizes in different visual fields, and does not exactly represent the grade of the mixed-up grains. (macroscopic mixed grains.)
In order to make up these shortcomings and to represent mixed-up grains exactly, the author accordingly tried to work out distribution function i.e. g(r) of radii of grains contained in a sample following method: -
Drawing a random line on the top of each microscopic photo of a sample, at the same time-making the ensemble of length of intercepts {Li} where L is lineal traverse of length limited by grain boundaries, the distribution function of Li, i.e. f(L) is to be finally found out.
When applying the theory actually, the intercepts are first classified into three groups (large length of intercept which is denoted by Λ₀): small intercepts (below Λ0/4), medium intercepts (from Λ₀/4 to Λ₀/2) and large intercepts (over Λ₀/2) and the author count fractions of these intercepts α', β' and γ'. And by use of the values of theseα', β' and γ', the following quantities are obtained.
(1) Volume fraction of small grains (its diameters extend from V₀/8 to Λ₀/4) α, medium grains (from Λ₀/4 to Λ₀/2) β, and large grains (above Λ₀/2) γ.
(2) The radius of such sphere as gives the average value of total grains volumes.
(3) The degree of mixed grains.
(4) The surfacial area of grains boundaries in the unit volume.
(5) The average value of lengths of intercepts calculated out theoretically from the g(r) which is obtained by f (L).
In this study, equations and figures or tables giving the above mentioned values are proposed.
Further, if there is the greater discrepancy between (5) and the actual average length of intercept over 5%, the classification into three groups will be at fault, and therefore it should be classified into more groups, and the equation thereof are also here proposed.

抄録全体を表示

To investigate the influence of silicon on the properties of shock-resisting steel containing 0.5% carbon. 1.5% chromium, 2.2% tungsten and 0.2% vanadium, the authors measured the critical point, the Jominy hardenability, the as-quenched and the as-tempered hardenss, the length-change during tempering, the specific gravity, and the mechanical properties.
The results obtained are as follows:
(1) Critical point is raised with the silicon content, and a full hardness 57 to 61 Rockwell C is obtained by oil-quenching from 900-960°C.
(2) Hardenability is increased by addition of the silicon up to 0.78%, then decreased with more silicon addition. Steels containing 0.4% molybdenum posssess higher hardenability.
(3) The rate of softening with tempering temperature decreases in the steels between 200 and 350°C, and the magnitude of this decreases in softening rate is related to the silicon contents of the steels. In fact, the rate of softening becomes nil at about 300°C in the steels which contain 1% or more silicon.
(4) The quantity of the retained austenite measured by saturation permeameter increases slightly with the silicon content and quenching temperature. And the transformation of the retained austenite is retarded as the silicon content increases.
(5) From the results of dilatometer test, it was found that the temperature at which the third stage contraction can be detected is raised with the silicon content, and the temperature range over which the contraction occured is greater in lower silicon steel.
(6) The specific gravity of the 1% or more silicon steel does not decrease appreciably with 1-hour tempers at increasing tempering temperatures, between 200 and 350°C.
(7) Yield strength measured by tensil test and bend test is incresed. with the silicon, up to 0.8% and then slightly decreased with more silicon content. Hot hardness and tensile strength at 400°C increase with the silicon content.

抄録全体を表示

In the heat resisting steel, the W and Mo were often used for the purpose of elevation of the creep strength in high temperature. The authors studied the effect of W, Mo and (W+Mo) contents on the aging of Ni-Cr-Co austenitic heat-resisting steel containing 15% Ni, 20% Cr and 15% Co.
The authors first examined the change of their hafdness due to various heat treatments of each sample: i, e. tbe solid-solution treatment and aging, and then observed the microstructure.
As results of these experiments, the most moderate composition and heat treatment for Ni-Cr-Co austenitic heat-resisting steel were found. The optimum conditions were as follows: (1) The most suitable composition, W 3.0-5.0%, Mo 3.0-5.0%, W+Mo (3+5-(5+3)%; (2) the treatment at 1200-1250°C, for the solution treatment, and 700-750°C, for the aging temperature, and the aging time for 6-12 hours.

抄録全体を表示

The charateristic structure of white-heart malleable castings in their distinctive outer layer was described. It was compared with the microstructure of the peeled one on which was studied by J.C.W. Humfrey and others in England. By microscopic examinsation, sulphur print and chemical analysis, it was recognized that such a sulphide penetration as in the case of the peeled layer did not exist in this layer but on the contrary desulphurization occurred.
Under various conditions, white castings were decarburized with mill-scales and tested by a microscope, and it was manifest that the time or the temperature of decarburizing process did not give any influence on the depth of the distinctive layer, but the pearlite band which existed in this layer/metal interface changed considerably. In consideration of the furnace atmosphere the mechanism of formation of this layer was described.

抄録全体を表示