Molten steel is always oxidized and nitrided by air during pit process. Oxidation of molten steel has a considerable effect upon corrosion of pit-refractories as mentioned in a previous paper in J. Jap. Inst. Metals, 2 (1954) 57, and oxides themselves also have a danger of becoming inclusions in steel.
Thereby the non-metallic inclusion in steel is greatly influenced with oxidation of molten steel by air during pit process.
The authors studied on the oxidation and non-metallic inclusion with experiments in the laboratory.
The result obtained were as follows:
(1) Silicon, manganese, iron, aluminium and carbon were oxidized by oxygen in air and total oxygen in the molten steel increased with pouring to the mould from the ladle. Consequently they remained in the ingot in the form of SiO₂, MnO, Al₂O₃ and FeO. These oxides had a cause of becoming microscopic non-metallic inclusions, and inclusions were extracted by a modifled Dickenson's method and the total oxygen in the ingot obtained by the vacuum fusion method increased.
(2) Silicon, manganese and iron in the high-carbon molten steel were not oxidized strongly in comparison with the other kind of molten steel.
(3) The oxidation of molten steel by air were influenced with the condition of its stream. The molten steel of turbulent stream were more oxidized heavily than the case of a smooth stream.
It was imaginable that the oxidation were also influenced with the chemical composition of molten steel (for instance carbon and aluminium).

抄録全体を表示

The flowing properties of various molten irons were measured by the weight which flowed out through the capillary (2.3mm diameter, 15mm length). The flowabilities of these capillaries were determined by the mercury at room temperature. The flowing properties of the molten irons consisting of the almost same composition (C, Si, Mn, P, S) were different by its molten state, especially by the oxygen content or excess deoxidizer.
Now the authors measured the flowing properties of mercury, molten tin and bismuth by the same capillary which was used for molten iron, and obtained the relation between kinematic viscosity (ν=η/ρ) and the time (τ) required to let flow constant volume of the metal.
By the theory of hydrodynamics, τ is the function of ν, so that from the above relation for mercury, tin and bismuth the value of ν corresponding to τ which was experimentally measured about the molten iron could be obtained. The viscosity of molten iron was calculated from the value of ν.
The viscosity of molten pig generally used was 0.0156-0.0120 at 1250-1400°C, while that of steel (0.3% carbon) was 0.0195 at 1535°C. The viscosity of steel at 1620°C was estimated as 0.0169 by exterpolation, when the rate of viscosity-change of the molten steel against the temperature was assumed to be the same as that of molten pig.

抄録全体を表示

By the use of the high-temperature and high-speed tensile testing machine montioned in report No. 1 (Tetsu-to-Hagane vol. 41 (1955) No. 5, p. 506-515), the author performed tensile tests of the following combinations in regard to 15 kinds of steels (refer to Table 1) to be used for seamless tubes.
For all of these, the author obtained both the nominal stress-strain curve and the true stress-natural strain curve. The values of deforming stress (at 20% strain) were listed in Table 2. These data conformed to those of other authors already developed.
Among such factors as deforming stress σ, deformation (strain) ε, deforming speed ε and temperature (absolute) Tk, the author obtained the following equation. In this report the above relation was fully discussed.

抄録全体を表示

Effects of B on the transformation, hardenability, quenched and tempered hardness, and mechanical properties etc. of Cr and Cr-Mo case-hardening steels and high-tensile steels were investigated. The results obtained were. as follows.
The Ac₁ points were not ffected by addition of 0.001 to 0.011% B, but the Ac3 points were raised, while the Ar points were lowered. In this range of B contents, about 0.003% B is most effective to increase the hardenability.
The quenched and tempered hardness of both Cr and Cr-Mo case-hardening steels containing B was higher than that of those steels contains no B at tempering temperature of 200-300°C, but the hardness of the formers decreased remarkably when tempered at about 400°C at which there was no difference between them. High-tensile steels had the same inclination.
The yielding point and tensile strength increased, while the elongation and reduction and reduction of area decreased by adding B, but the impact value of case-hardening steels. decreased and that of high-tensile steels increased a little. The effect of B on carburizing property of case-hardening steels was not so remarkable and the carburized depth increased a little by adding B.

抄録全体を表示

The precipitation phenomena of Timken 16-25-6 alloy, the heat resisting steel for gas turbine, have already been reported in this journal. The effect of solution-treatment was studied and reported in relation to aging in (I) and (VI) of this series. In this report, the solution phenomena of precipitated particles were researched. There were nine kinds of samples, each having different amounts of C, Mo, and N contents, including the standard 16-25-6 alloy. For the purpose of studying the influence of varied contents of added elements on solution-treatment, eight groups were made by various combination of the nine samples. (see Table 1)
Before solution-treatment, which is the purpose of this reports, all samples were treated to finish or almost finish the precipitation in two ways (A) and (B). In (A), samples were heated at a rather high temperature (ex. 950°C, 900°C, and 850°C etc.) for more than several hours respectively after usual solution-treatment (1150°C×1h), and then kept at 700°C more than 100 hours. This meant the coagulating of precipitated particles, besides finishing the usual precipitation. In (B), samples were aged at 800°C for from 100 hours to 150 hours after usual solution-treatment. (B) meant the samples got stable high hardness and general precipitation more or less by aging. Samples, treated in (A) way, were heated at three grades of temperature 1000°C, 1150°C, and 1230°C for 2 honrs respectively for solution-treatment. Samples, treated in (B) way, were heated at three, grades of temperature, 1000°C, 1100°C, and 1200°C for from 10 minutes to 7.5 hours. All samples, which were solutiontreated in each temperature and time, were tested by Vickers hardness tester and observed through microscope to study the disolving phenomena of precipitated particles.
In (A), the precipitated particles were not yet disolved by heating at 1000°C for 2 hours, but disolved at 1150°C and annealing twins were observed. When the samples were heated at 1230°C annealing twins were easily seen and grain coarsening was also observed.
In (B), the softening of hardness by heating was almost parallel with the disolvening phenomena of precipitated particles. Some samples showed that the heating temperature 1000°C was not enough for solution-treatment of precipitated particles. The process of disolving of precipitated particles was clearly observed during heating at. 1100°C. The temperature 1200°C was too high to watch the process, because solution-treatment finished and annealing twins appeared after 10 minutes heating. The effect of C, Mo, and N content in 16-25-6 alloy on solution-treatment was also discussed The samples of low carbon showed rather low. hardness at both aged condition and solution-treated condition. More Mo samples meant more difficulties than with the low Mo samples. N showed similar influence with Mo, except the samples denitrolized by the addition of Ti. In this report, the articles which were precipitated artificially were disolved for the purpose of test, so that the conclusion from this data can not always be applied to the, case of practical solution-treatment under factory conditions.

抄録全体を表示

To investigate the influence of vanadium and molybdenum on the properties of air-hardening die steel containing 1.5%carbon and 12%chromium, the authors measured the critical point, hardenability, quenched and tempered hardness, retained austenite, dimensional change and toughness.
The results obtained were as follows:
(1) The critical point was raised with the vanadium and the molybdenum conten, respectively. The hardenability increased by the addition of molybdenum and ipcreased slightly by vanadium by its addition up to O.8%.
(2) Vanadium addition refined the grain size, and the molybdenum had little effect on the grain size. Full hardness was obtained by quenching from-1000°C to 1O50°C, and as the vanadium contenlt increased, a slightly higher austenitizing temperature was necessary for obtaining the full hardness.
(3) The quantity of retained anstenite measured by the magnetic method decreased with vanadium addition, and themolybdenumhad little effect on the retention of austenite. The authors found more retained austenite in air-hardening than in oil-quenching from the same temperature, and the.amgunt of retaihed atistenite increased as the austenitjzing temperature was raised.
(4) Sub-zero treatment fdllowing.the.original hardehing operationcaused the transformation of large amount of.retained austenite and this breakdown of austenite at-680°C decreased with vanadium addition.
(5) The volume increment. resu1tipg from the air-hardening was less, than oil-quenching from the ordinary temperature. This increment decreased by the addition of vanadium up to O.4%, then increhsed with more vlahadium content. A steel containing 0.45% vanadium showed a dimensionlal change of +0.109% in the direction of hot-working and -0.03% in the transverse direction by air-hardening from 1050°C.
(6) Some of retained austenite in hardened steel decomposed during aging at room temperature and about half of that during the first 24 hts after the uenching. Small amount of reained austenite decomposed on tempering up to 500°C, and all of the retained austenite decomposed at a temperature between 550°C to 600°C the secondary hardness was exhibited at 500°C after quenching from lO50°C and was very marked at 550°C after quenching from 1100°C.
(7) The toughness measured by static bending test.increased with addition of vanadium up to 1%and then decreased with more vanadium content and also O.8-1.0% molybdenunm increased the toughness.

抄録全体を表示

In order to determine rapidly the small amounts(under O.05%) of the carbon in iron and steel without usjng any complicated apparatus, the authors studied the titration method.
(1) For the purpose of increasing the absorption efficiency of the carbon dioxide, the helical-type absorption tube(1ength about 1.6m, inside diameter of tube 4mm, diameter of turn 8cm, number cf turn 6) was used instead of the ordinary vertical type.
(2) The results of comparison of the absorption solutions(N/100 KOH, N/100 NaOH, N/100 Ba(OH)₂) indicated that potassium hydroxide and sodium hydroxide solutions were most suitable.
(3) The best rate of the oxyge flow at the carbon dioxide detection bulb was 40ml per minute.
(4) By the above method, 0.01 to 0.05% carbbn in iron and steel could be determined with the accuracy of ±0.001% within 17 to 23 minutes.
(5) The authers'method was recommendable for the control analysis in the plant.

抄録全体を表示

When a 1adle sample of an open-hearth charge was taken, from the angle of its chemical analysis value, the probability that the chemical representation value of the charge was above the lower limit of a given standard value or lay between the lower and uppe limits was sought for under various assumptions and the following points were clarified.
A.Relation between the probability of coming withil the standard value and the chemical representation value of the charge.
B. Relation between the probability and standard deviations of chemical compositions value in or between the charges.

抄録全体を表示