In the former reports it was found that segregated lines of ingot showed a remarkable segregation and that some of them moreover contained sands in segregated line and cavities. On the other hand, large steel forgings forged from large carbon steel ingots revealed often defects in segregated zones, which were classified roughly into ghosts and segregation-flaws. Hitherto, while the former have been well known as the representative defect of large steel fargings, the latter have been scarecely found out, and so the former should resign the name "ghosts" to the latter. Investigatng the Λ segregated zone of ingot, the author got the idea that segregationflaw of forgings might originate in defects appearing in segregated lines of ingots. In order to confirm this idea, he investigated at first the characteristics of segregation-flaws, the time of its formation and the refation between its formation and manufacturing conditions.
It is important to eliminate blowholes or pinholes in iron and steel, but the mechanism of growth of them has not been suffciently studied yet. As a first step to study this mechanism, it is necessary to analyse the gases existing in blowholes or pinholes. For this purpose, a vacuum cutting apparatus was designed and set up instead ot drilling the sample in water or oil. As already stated, a vacuum cutting apparatus was a lathe which worked in hjgh vacuum, and was composed of three parts, that is, high-vacuum part, 1ow-vacuum part, and atmospheric part. During the cutting with this apparatus, there were two kinds of gases extracted, one was discharged from blowholes or pinholes, the other was evolved from chips because of their high temperature. To prevent the mixing, the apparatus was designed so that its cutting velocity to be as slow as possible. Furthermore, to eliminate gases which evaporated from oil in vacuum, 1ow-pressure oil was used. Blowhole samlples were cast from molten steel which absorbed oxygen or hydrogen and then cut in a vacuum-cutting apparatus. The gases discharged from blowholes were collected by a mercury diffusion pump and a jet mercury pump, then analysed by an orsat microanalysis apparatus. Chemical compositions of gases in blowholes were as fo1lows.<Br>1) Gases in blowholes were for the most part hydrogen and nitrogen, while CO, CO2, CH4 were of very small quantities. 2) Free oxygen gas existed for the small amount in the blowho1es. 3) Gases in blowholes which grew in non-deoxidizing steel were for the most part nitrogen, while hydrogen was of very small amount. On the other hand, gases in blowholes which grew indeoxidizing steel were for the most part hydrogen while nitrogen was very small in amount. From this composition of gases, it was presumed that the CO gas existed in blowholes (which evolved from molten steel) decomposed in cooling; and the pressure in blowholes reduced; and then hydrogen and nitrogen diffused in to blowholes from the steel around.
Following the previous report of some studies on residual stress measurements, the author studied in this report the sinking and plug drawing of wall thickness, outside diameter ratio, about 10% steel tubings, and investigated on the relations between residual stress and two drawing conditions, namely die contour and reduction. The results clarified were summarized as follows. a) In case of sinking (Fig. 6 & Fig. 7) a. 1) Residual stress increased with the increase of outside diameter reduction. a. 2) The larger the die angle, within limit of about 10% reduction of olltside diameter, the residual stress of sunk steel tubings were greater. a. 3) On the other hand, when in excess of 15% reduction of outside diameter, the residual stress of suhk steel tubings with smaller die angle became greater. a. 4) Within 10-15% reduction of outside diameter, almost no influence of die angle could be observed. b) In case of plug drawing (Fig. 8 & Fig. 9) b. 1) By reduction of the wall thickness the residual stress decreased remarkably with the increase of reduction of wall thickness. b. 2) In case of about 10% reduction of the wall thickness, the residual stress generally increased with. the increase of the outside diameter reduction and the die angle. b. 3) In case of about 20% reduction of wall thickness, when reduction of the outside diameter and die apgle were smaller, considerable negative stress remained on outer surface, but they decreased with the increase of the die angle. In case of larger reduction of the outside diameter, this phenomenon could not be observed and a comparatively smaller positive residual stress occurred regardless of the die angle. b. 4) In conclusion, wheh cold-working steel tubing, a moderate reduction of outside diameter and a sufficient reduction of wall thickness are required for the manufacture of cold-drawn steel tubing with smaller residual stress.
It is reported by American investigators that B-treated Cr steel TS50B60 showed very good results for leaf or coil spring material of trucks, tractors and passenger cars. But in our country there is few data about this steel, and so the authors studied the properties of TS50B60 in comparision with SUP 6 (Si-Mn steel), SAE 5160 (Mn-Cr steel) and SAE 6150 (Cr-V steel) as minutely as possible. Results of the studies were as follows: 1) Non-metallic inclusions. There was little difference between different steels and so the influence of B-addition was not found. 2) Transformation points. High temperature order was as follows: A1 point: SAE6150>SAE5160 SUP6>TS50B60 A3 point: SAE6150>SAE5160>TS50B60 SUP6 3) Hardenability. D1, calculated from the measured Jominy curves, were 115mm for SAE6150, 100mm for SAE 5160, 97mm for TS50B60 and 53mm for SUP6. The fading phenomena of B were not seen. The results of dilatometric observation at quenching were as same as above. 4) Tendency of quenching cracks. The residual stress of quenched specimen showed the transformation type for different steels and had good coincidence with the tendency of quenching cracks that is in next order, SAE6150>SAE5160>TS50B60>SUP6. 5) Grain growth characteristics. Under 1O50°C there was no marked difference and above this temperature grain growth became eminent, but TS50B60 was the most stable. 6) Decarburization, scaling and surface roughness at heating. Decarburization depth was greatest at SUP 6 and became smaller in the next order, SAE 6150>SAE5160>TS50B60, but the tendency of scaling showed the inverse order to above. Surface roughness was best at SUP 6 and worst at SAE5160.
To investigate the influence of manganese and carbon on the properties of oil-hardening non-deforming tool steel containing 1·05% carbon, 1·2% tungsten and 0·75% chromium, the authors measured the critical point, Jominy hardenability, S-curve for the transformation of austenite, quenched and tempered hardness, retained austenite, dimensional changes and toughness.
The authors studied the effects of solution treatment on Timken alloys before hot-cold. working, working temperature and reduction of working on creep rupture properties at 650°C, 31·5kg/mm2.The results were as follows. (1) Creep resistance increased by the solution treatment before hot-cold working, but ductility of creep rupture testing prominetly decreased by it as compared with the test pieces which were hot-cold worked at the comparable Working condition and not solution-treated before hot-cold working, although the hardness of the test pieces of the comparab1e working condition were not different. (2) Creep rupture time decreased, and ductility increased as working temperature increased. Creep rate of the specinens worked at 700 and 800°C were not different regardless of the reduction of working and preheat-treatment. The third stage creep strain of the epecimens which were hot-cold worked at 700°C were smaller than when it was hot-cold worked at 800°C. (3) Creep rupture life decreased while the reduction of working increasd regardless of the increasing hardness. Ductility decreased, while the reduction of working at any working temperature increased.
It has been recognized by Gakushin that non-metallic inclusions in high carbon steel or chromium steel was determined by the hot-H2SO4 method. But should quenching be not carried out on these stee1, there produced the carbide that will not be decomposed by making use of KMnO4 oxidizing agent, and no reproducible result would be obtained. The authors have made an investigation on the applicable limit of quenching and samples making on the alloying elements in this kind of stee1. The results obtained were as follows. (1) It will generally be desirable to make water quenchihg for the cutting specimens, though we trially designed the vacuum quenching apparatus for the drilling specimen. (2) It is not necessary to quench when carbon and chromium contents in Cr-steels are less than 0.7% and 1% respegtively. Quenching is generally required on 13% Cr-steel and 18-8 stainless steel, however, in case Ti is contained in them, TiC wil1 be produced which is not decomposed by KMnO4 treatment. On the other hand the authors have made an experiment on solubility of Cr2O3 by Hot-H2SO4 method, and have found that Cr2O3 content in chromium steel is determined by this method. In connection with the above, as a result of quantitative analysis of Cr2O3 contained in bearing steel or case-hardened stee1, we reached the conclusion that its content is far 1ess than silicate or aluminate inclusons.
Titanium ore is iron sand abundantly produced on the sea-coast of Japan, and refining process of iron sand to sponge titanium and consolidation process of titanium are being successfully carried out on the industrial scale in Japan. A brief description of them was published in the previous issue. In this paper, described are the processing of titanium and titanium alloys both in Japan and the United States of America, metallographical properties of titanium and various characteristics of them as a structural material. Discussions contained in the main text are as summarized below. XI Physical properties of titanium. XII Chemical compositions of unalloyed and alloyed titaniums and their mechanical properties. XIII Metallographical properties of titanium. (1) Phase diagrams (2) Comparison with Fe-C alloy and martensitic transformation (3) Structures of titanium alloys and their characteristics (4) Heat treatment of titanium alloys a. Heat treatment of 2Al-2Fe-titanium alloy b. Heat treatment of 5V-titanium alloy c. Discussion on the heat treatment of titanium alloys and on a new titauium alloy-6Al-4V-titanium alloy XIV Processing of titanium and titanium alloys (1) Forging of titanium and titanium alloys (2) Rolling (3) Extrusion (4) Tubing and wire drawing (5) Machining XV Weldability, corrosion resistance, descaling and conversion curves for hardness and strength XVI Conclusions (XIV, XV and XVI is to be printed in the next issue)