In the preceding study, we investigated the effects of torsoional working temperature on the short time torsional creep strength for a plain 18-8 stainless steel bars twisted in the range of temperatures -60°-800°C. As a comparative work, the effect of torsional working temperature on the surface hardness, torsional strength of -60°C and room temperatnre, and magnetism for the plain 18-8 stainless steel have been observed in this study. And also, the effect of solution-treatment temperature on these hardness, torsional strength, and magnetism have been measured. The results obtained are summarized as follows: (1) With the decrease of torsional working temperature, the torsional strength at -60°C and room temperature and hardness for a plain 18-8 stainless steel increase, (2) Although a considerable magnetism are found even in the specimens which were twisted to only 0.128π/cm at -60°C, so much magnetism was not generated by twisting less than about 0.7π/cm at room temperature. (3) The hardness of the as-solution treated or thereafter twitsted specimens increases with decreasing solution treatment temperature, but the torsional strength were not affected so much as the hardness. (4) The magnetism produced by torsional working slightly reduces at first and then increases with temperature, and takes a maximum at 400∼500°C, but diminishes rapidly beyond a temperature of 500°C. The inclination of the change of hardness due to heating is same as the magnetism.
The authors have previously reported on the mirror extensometer which magnified the longitudinal elongation and the contraction of the specimen under axial fatigue load as much as 2000 times, and on some of the experimental results obtained of two kinds of steel. In this paper, similar experiments were made on five kinds of carbon steel. The strain occurred on each specimen under completely reversed axial load was measured through the test. The plastic strain, by which we mean half the width of a hysteresis loop on the stress-strain diagram, was obtained from a simple calculation. There was ovserved a difference between the behaviour of plastic strain of the low carbon steels and that of the high carbon steels. Howevever, the variation of the plastic strain was moderate and converged to some final value. One exception was the case of 0.25% carbon steel. This steel showed a quite different and complicated behaviour of the plastic strain that offered us a subject of more detailed investigation in future. For the other steels, there exists a linear relationship between the plastic strain and the number of stress cycles to failure when plotted on a log-log paper. A similar relationship was found when the hysteresis energy was plotted instead of the plastic strain. Some discussions were also made on the stress-strain curves under fatigue load.
From a review of previous reports concerning the notch effect on the fatigue strength of metals, it is understood that the damaging effect of notch is reduced at elevated temperatures in many cases. However, metallic materials are activated metallurgically at high temperature, so that many factors such as loading frequency, state of stress, grain size and atomosphere surrounding a specimen have remarkable effects on the strength of notched specimen, and, as easily understood, their influences vary according to the kind of material. Moreover, when a material is tested under a repeating load superimposed on a static load, some properties are observed characteristic to notched specimens, which are considered to be related with the well-known strengthening effect of notches under creep load. This investigation aims to study those properties of the notched specimen of Cr-Mo-V steel, a kind of heat resistant steel, under pulsating load at 490°C. An emphasis is put on the clarification of the effect of loading frequency. The results have been discussed in comparison with those obtained from the previous experiment on the plain specimen of the same steel under similar conditions. It is concluded that, in the stress range where the repeating load is moderately small, the frequency has effects to increase the strength both for deformation and for fracture, and that the strength itself is largely increased in the notched specimen than that of the plain specimen in the same stress range. This result concides in its tendency with those of previous reports worked by several authors.
The authors previously carried out repeated tension impact tests on carbon steels and aluminum alloys by using the universal repeated impact testing machine and Charpy impact testing machine, and clarified the discontinuity of their impact fatigue curves. We have studied, as shown in this paper, about copper and brass under the same tests. Results obtained were as follows: (1) In the diagram of the relation between repeated impact energy and the number of repetition of impacts to failure, two curves come out as shown in Fig. 2, which are found to be discontinuous. As already reported in the previous paper, the specimens fractured, on upper curves, with large scale plastic deformation, whereas on lower curves with true fatigue fracture. (2) Unlike the curves in the previous paper, the curves at N=106 about copper and brass do not show a tendency to lie horizontally. (3) We have found the discontinuous changes of α, β and ψ with impact energy on non-heat treated brass. But every change is not discontinuous on annealed copper and brass. (4) By observating true fatigue fracture of specimens, we have perceived the relation between the radius of arcs of shell patterns and impact energy. When impact energy was near energy of discontinuous point, arcs of shell patterns formed similar concentric circle.
Though it is well known that the valency state of cations in Mn-Fe ferrites has much effects on their electric and magnetic properties, we have never had a method suited to analyze the valency state. In this paper, the method is shown by which the valency state of cations in those ferrites may be analyzed chemically. And then, appropriateness of the method is discussed in comparison with the results of electric resistivity and disaccomodation of those ferrites and we may conclude that the method gives reasonable results. From the results analysed chemically by the method, it is also shown that actual Mn-Fe ferrite has a chemical composion Mn2+1-x-yMn3+yFe2+x+y-zFe3+2-y+z_??_3/8zO4+z/2 and the amount of y and z depending on firing conditions of the ferrite gives much effects on electric resistivity and disaccomodation of those ferrites.