In the first report, the effect of austenitizing temperature on retained austenite in high-carbon high-chromium steel and its decomposition were studied. In this report, the effects of subzero chilling and holding time at isothermal transformation temperatures on retained austenite in the same steel have been investigated by means of hardness and electrical resistance measurement and by magnetic analysis. The results are summarized as follows: (1) The retained austenite is greatly stabilized against transformation by subzero chilling with increase of the holding time at room temperature. (2) The retained austenite transforms into martensite by subzero chilling, but during subsequent heating the martensite begins to decompose at a lower temperature than the decomposition-commencing temperature of martensite in ordinary quenching. (4) The amount of retained austenite increases remarkably with increase of the holding time at the bainite transformation temperature. (4) Complete transformation of the retained austenite is not attained by subzero chilling in liquid oxygen.
It was described in previous reports that the stepped-quenching method may be adapted to such high-alloy steels to prevent quenching deformation and quenching crack. In this report the effects of stepped-quenching on the hardness, the quantity of retained austenite and the mechanical properties were investigated in comparison with ordinary quenching method by means of hardness measurement, magnetic analysis, repeated impact test and bending test. The results are summarized as follows: (1) The amount of retained austenite in stepped-quenched steel is more than that in ordinarily-quenched steel. (2) The hardness and the amount of retained autsenite decrease with increase of the holding time in the hot bath (500°) in stepped quenching. (3) The amount of retained austenite also increases remarkably with decrease of the cooling rate from the hot-bath temperature (500°). (4) The stepped-quenching method improves the mechanical properties.
Carbon steel tape of 0.13 mm thickness was quenched on a watercooled iron plate under varying drawing speed, quenching temperature and tempering temperature. Razor blades were made of these samples, and the relationship between the sharpness and the bending test results was studied. The finishability of cutlery had much to do with the brittlenes of the material. Concerning the finishability, the material must not be too brittle or too tenacious as well; it must break in a certain range in bending tests. Bending tests revealed sharply the remarkable difference among the samples which showed almost equal values in hardness tests. The optimum condition was strictly determined by bending tests.
Rough-honed blade edges were finished by electrolytic polishing in which H3PO4-CrO3 solution was used. The current density and the time were varied and the optimum condition was searched. Since the finishing of the blade edge by electrolytic polishing is free from the restrictions which are inevitable to mechanical polishing, better sharpness can be expected by electrolytic polishing.
Hydrogen atmosphere containing a small quantity of hydrogen chloride vapor is useful for bright heating of stainless steels. The weight changes and appearances of 18-8 stainless steel, 19% chromium steel and carbon steel heated in such atmosphere were observed. The higher the concentration of water vapor in hydrogen gas, the more hydrogen chloride was necessary to obtain a bright surface. High temperature corrosion was severe in an atmosphere of high concentration of hydrogen chloride, and showed quite different appearance for each kind of steels.
The effect of inoculants in Mg-treated iron was clarified by means of microstructure-test on the boundary zone between inoculants and molten iron. The action of inoculants only or that of inoculants plus Mg alloy, each of them being set at the bottom of shell-mould, was also investigated in both conditions of bottom-pour and lip-pour. The results obtained were as follows: (1) The local concentration gradient of Si is set up due to the incomplete solution and diffusion in process of the reaction of Si with molten iron, thereby producing nuclei of graphite and SiC from super-saturated molten iron. The nuclei of SiC decompose easily as the decrease of the concentration gradient of Si in iron proceeds. (2) The effect of inoculants or inoculants plus Mg alloy in lip-pour of molten iron is superior to that in bottom-pour. The effect of the size is found to be best in moderate size of both the inoculants and the Mg alloy. (3) The inoculating effect of Si in Mg alloy containing Si is inferior to that of Si mechanically placed together with Mg-alloy. In the former case of the addition of Mg alloy containing Si, the rate of local concentration gradient of Si in molten iron decreases, and the inoculation becomes less effective.
Continuing the former report, the changes of viscosity of molten metals in air were measured by flowing-dow method under different melting conditions. The results obtained were as follows: (1) The difference of max. heating temperature was one of the most effective factors on the viscosity and its effect was indicated as an indented curve of viscosity by increase of max. heating temperature. (2) The effects of holding time at max.heating temperature were very different according to the temperature at which the specimen was held and a close relation was recognized with the heating velocity as the same factor of time. (3) Fast heating for melting showed good results for viscosity in general but under low max.heating temp, fast heating was not always profitable for viscosity. (4) As the total melting time, the best condition of viscosity was found at about 100 min under any combination of holding time and heating velocity. In the range above 100 min, the second best condition was found at about 200 min and the midway temperatures resulted in the worst condition for viscosity. Above 200 min, the viscosity increased.
In the present paper, the authors studied the effect of thickness, cold working and preheating of base metal. Two different methods were used to coat the steel sheet of 0.2∼1.2 mm thickness namely; the single bath method and double bath method. The results obtained were as follows: (1) The formation of the alloy layer is affected by thickness of the sheet. It is due particularly to the local temperature drop adjacent to the base metal. (2) Cold working of the base metal has no effect on the alloy formation. The internal strain is removed during the dipping process and an annealed structure is obtained. (3) The alloy layer can be formed thicker by the preheating effect of double bath method but its effect is practically the same if the duration of the preheating treatment varies. The authors have tried to study the experimental results statistically and also the mechanism of alloy layer formation are considered.
The effect in the hot-dipped aluminizing process of the alloying elements found in steel on the mechanism of interfacial alloy layer formation was investigated. The results obtained were as follows: (1) Silicon, chromium or manganese in steel act as inhibitor in the same way as when these elements are added to the aluminium bath. (2) A more effective inhibitive action is obtained by addition of silicon to the aluminium bath than by its addition to the base metal. (3) The softening effect of silicon in steel on the hard alloy layer is more efficient with the increase of silicon content. (4) The mean chemical composition of the alloy layer produced with pure iron and pure aluminium is somewhat higher in Fe-content than FeAl3. The rate of silicon content in the alloy layer was found to be correlated with the silicon content in the steel.
As the tin content in the enriched layer of steel was expected to vary within a wide range of 0.02 to 30 per cent, the range was devided into three parts and the analytical conditions were studied for each of them. Because of the large gradient of the concentration of tin in the layer, care was taken to make the depth of the crater of the discharge as small as possible. An intermittent arc was used to analyze the range of 0.02 to 0.4 per cent tin. It was found that the arc discharge employed consisted of a train of discharges of short duration, flushing once per cycle of line voltage, and at the beginning of the discharge each short discharge was liable to go to the different parts of surface of the sample leaving an equal number of tiny and shallow craters, but after 20 cycles or more the crater began to overlap one another, so after 20 cycles each the sample was moved a bit laterally, and the depth of crater was thus kept within 0.011 and 0.018 mm. A Feussner spark was applied to analyze the tin over 0.3 per cent. Both the prespark and exposure times were reduced as much as possible, so that the depth of the crater was 0.009 mm for medium (up to 2 per cent) concentration, and 0.002 mm for high concentration. The sparking curves were found different in form according to the concentration of tin.
“Schiebung” transformation exhibits peculiar behaviour at the free surface of crystal, the twin boundary and the interface between austenite and martensite previously formed by “Umklapp” transformation. The transformation temperature, Ms, at the free surface and the twin boundary is usually higher by about 20° than in the interior. The interface between austenite and martensite is also a preferred site for nucleation of “Schiebung” transformation. These situations may be accounted for in terms of less surface energy and less strin energy of new martensite nucleus in those regions than in the interior of the crystal. The microstructure in the surface zone about 0.1 mm thick differs considerably from that in the interior of the crystal. The martensite in the surface zone does not belong to a family of the definite habit planes.
In dependence of Ni concentration, the temperature range of the Schiebung and Umklapp transformation was determined by means of microscopic and acoustic methods. The results obtained were as follows: (1) The two types of transformation can take place in specimens of the same Ni concentration by supercooling to low temperature. (2) The highest temperature in which the Umklapp transformation can take place is always lower than that of the Schiebung, and is about −10° independent of nickel content.
Using plastically deformed aluminium crystals, changes in distribution of the strain during heating were investigated with X-ray diffraction microscopy (Berg-Barrett method), in order to clarify the polygonization and recrystallization process. The X-ray micrographs locally showed recovery aspects and sub-grain formation. In the crystal which showed deformation bands the sub-grains formed with recovery are parallel to the bands. In case the deformation bands did not appear the subgrains are nearly parallel to slip bands.
Recrystallization phenomena have been studied with 4 kinds of specimens (99%, 99.9%, 99.99%, 99.99%Zn). The results were as follows: (1) The higher the purity, the larger the grain size of primary recrystallization. (2) In 99.999%Zn, primary recrystallization is partially observed immediately after 10% cold-rolling, and is completed after 30% cold-rolling. (3) Secondary recrystallization occurs at a low temperature with increasing cold-rolling reduction. (4) At the same cold-rolling reduction rate, it was found that there exists a minimum point of secondary recrystallization temperature at 99.99% purity. (5) In recrystallization diagram of zinc specimens of higher purity than 99.9%, it was found that the grain size has the maximum value at a certain temperature.
Recrystallization phenomena have been observed on variously cold-rolled high purity zinc, and the following results were obtained: Abnormal growth is observed in every grades of zinc heated at temperatures higher than 200∼300°. Secondary recrystallization occurs at lower temperature with increasing cold rolling reduction and this phenomenon is also recognised in specimens already completing the primary recrystallization under the same conditions. The sizes of the secondary recrystallized grains are strongly influenced by the heating rate. By rapidly heating to above 300°, secondary recrystallization produced a relatively fine-grained structure, and slow heating produced a large-grained structure. It is also considered that the nucleation of secondary recrystallization would be influenced by the heating rate And secondary recrystallizaiton seems to be occasioned by nucleation and growth, because its character closely resembles that of primary recrystallization.