The hardness distribution of carburized case, tensile strength and compressive strength were measured, after sub-zero treatment was applied to some Ni-Cr, Ni-Cr-Mo and Cr-Mo carburized steels. The results were as follows. 1) The carburized case of Cr-Mo (containing high % of Mo) and Ni-Cr-Mo steels were not so hard as we expected owing to the appearance of a large amount of retained austenite. But sub-zero treatment improved such a poor condition of carburized case, that is, the hardness became very high. 2) Generally speaking, the tensile strength of carburized specimens decreased after they were sub-zero treated, because the internal stress increased. But these specimens recovered their strength after tempering, because the internal stress was eliminated. 3) In general, the compressive strength of carburized specimens increased after they were sub-zero treated. This phenomenon can be explained by the same reason. But in Cr-Mo steels (containing high % of Mo), it was reverse. This phenomenon can be explained by the brittle carburized case with complex carbides in Cr-Mo steels.
The dimensional stability of ball bearing steel was disscussed from the different points of view by M. Cohen. (Trans. A.S.M., 1945, vol. 34, p. 216). Apart from his studies, the authors studied on the influence of the ordinary industrial oil quenching and tempering, including no sub-zero treatment, on the dimensional stability of ball bearing steel. Specially, they investigated the effects of the difference of cooling method, the temperature of quenching oil, the time of tempering, the secondary tempering (after the grinding) and the repeated quench. The effects, afforded by these treatments to dimensional changes which occurred in aging at room temperature, were mentioned on the basis of austenite-martensite reaction and dislocation theory. (a) If the specimen is arrested at the higher temperature, the greater dimensional changes will occur in aging at room temperature. (b) The most parts of dimensional changes which may occur in aging at room temperature, reveal in the period of one and a half days after the quench. (c) Rapid cooling in the cold water to the room temperature directly after the arrested quench gives less dimensional changes. (d) The tempering directly after the arrested quench, which is prevailed in the industrial heat treatments of steel in order to avoid the cracks and distortions, gives the greatest dimensional changes in aging at room temperature. (e) High temperature of the quenching oil will afford no good effect to the dimensional stability, but in the case of arrested quench, it will not be influenced by the temperature of quenching oil. (f) The increase of tempering time and the secondary tempering will affect favourably the dimensional stability. (g) Repeated quench, involving the increase of the content of dissolved carbide in austenitic matrix during the repeated heating, increases the retained austenite. Nevertheless, the result that the dimensional changes have occurred unexpectedly less in aging at room temperature is noteworthy in respect of the behavior of retained austenite.
Mechanical properties of low alloy steel castings, that containedO.6-1.8%Mn, 0.1-3.O% Cr, and up to O.5% Mo, were investigated. Heattreatments used were homogenization (1000°C and 1100°C), normalizing (870°C) and tempering (650°C). Without tempering, heat trgatments were carried on by air cooling. Tempetings were carried on by air cooling and furnace cooling. The results obtained were as follows; O.35% C, 1.7% Mn, O.3% Mo steel casting had shore hardness mumber 33-38, as normalized and tempered. Elongation of Cr-Moseries and elongation and impact value of Mn-Mo series treated by homogenization were better than that which were not homogenized. There was no difference in the other mechanical properties, between homogenized and not homogenized.
Results of an investigation into the effect of shot hardness on residual stress induced in the sub-surface layer of specimen are reported in this paper. Analyses of residual stress were made by the dissection method. Some of the conclusion reached are; (1) Residual stress distributions show the tendency to take max. value on the surface when the soft specimen is peened with hard shots, while the rest of combination cause max. point at the inner part of specimen. (2) The magnitude of max. residual stress is concerned to the hardness of specimen, and the min. shot hardness to take the full gain of this value is equal to that of specimen. (3) Size or velocity of shot has minor effect on the magnitude of residual stress in specimen. (4) Depth of cold-worked layer increase as the hardness of specimen decrease or using harder shot. (5) In the industrial viewpoint, hardness of shot is desirable to be same with that of work. (6) Almen test strip is useful to measure the residual stress as it is or tempering at low temperature to the same hardness of the work.
Authors studied the effect of reduction of the hot-cold working on creep rupture properties at 650°C, 31·5kg/mm2. The results are as follows: 11.1t was observed by macroetching the transverse section of the specimen that hot-cold-worked specimen was not worked uniformly in its section. When it is finished in square section by hot-cold working, severely stressed portion disperses in diagonal line. When it is finished in round section, severely stressed portion concentrates in the center. The reduction of working of the specimen differs fairly with the location in the square section from which specimen is taken. So, a round bar is used to study the effects of the reduction of hot-cold working. 2. Creep resistance increases by the reduction of working to the critical value, but exceeding this limit it decreases. This critical value of the reduction of working is dependent on the working temperature and the pre-treatment of hot-cold woking. 3. Three specimens were picked from the diferent locations in a section of 40mm square bar which was hot-cold worked. Creep characteristics of the specimens differs owing to their location where they are taken.
Application of oxygen to iron and steel making is discussed on the basis of its, general trends in Europe and America as well as experiments carried out in Yawata Iron & Steel Works, concerning a low shaft experimental furnace, open hearth furnaces and an experimental converter. In the low shaft furnace were examined effects of raw material size, oxygen percentage in the blast, etc. on the furnace conditions. It was found possible, as one of the results, that under an adequate condition pig iron for steel, that for foundry, ferro-manganese, etc. could be produced even with a weak coke. As is universally known, in the open hearth furnace, application of oxygen resulted in cutting melting hour and fuel rate. A 5-ton top-blown converter was operated, for production of various sorts of steel. Among its fruitful results it was found that by blowing-in highly pure oxygen the nitrogen in steel was dimished to as low as 0.003 per cent, and this stoods comparison with that of open hearth steel. The property examination conducted in various aspects of the steel thus produced showed that it cauld compete with the open hearth steel satisfactorily and that P as well as N content had a remarkable effect on the properties of the converter steel. The further improvement of quality of the converter steel should be expected through the betterment of practice.
The Osaka Steel Manufacturing Company was reorganized in 1937 from the former Takaishi Rolling Mill established in 1921. After the war, improvement of the ro1ling mill was undertaken, and a small size semi-continuous type of ro11ing mill was completed in 1947 at the present Amagasaki plant.This impfoved rolling mill is able to produce small section round bars as we1l as deformed bars with a capacity of 7, 500 tons permonth. In 1951, a new rolling mill that produces small section bars and wire-ods was completed at the Kyobashi plant.The time required for the resetting of this mill from bars to wirerods and vice versa is only a couple of hours.Thus it is featured for its high maneuverbility in meeting the demands to produce various types of products with a capability of 12, 000 tons per month both for bars and wire-rods. The pos-war rationalization trend in the iron products in Japan as well as in other countries had little attention in the field of medium size products, and therefore an attempt to construct an all-continuous medium size mill had bee planned, which resulted in the completion of the first of its kind in Japan after one year of endeavor in 1955 at the Kyobashi plant.With this mi11, it is possible to roll angles and shapes of various medium sizes from 3"up to 8"with a monthly capacity of 15, 000 tons. We are proud toanounce the new born continuous mi11, highly efficient in its rolling operation and superior in its labor productivity.
Some improved methods have been established recently in Japan with reference to manufacturing of cast alloy steel rolls, built-up and back-up rolls, main steam pipes for, high temperature and high pressure boilers and heat resistant high alloys for gas turbines. The purpose of the present paper is to describe the engineering technique for manufacture of these products of alloy steels covering importnt processes from melting to inspection.