As repeated pre-stressing in air during the first stage, either overstressing at stress level 0.5 or 1kg/mm² over the endurance limit with the cyclic repetition of 3.4×10³ to 1.02×10⁶, or understressing at stress level 1kg/mm² below the endurance limit cycling from 1×10⁶ to 7×10⁷ was chosen, and followingly the specimen was exposed to air-saturated 5%H₂SO₄ at 25°C to which the repeated stress equivalent to prior endurance limit was applied during the second stage, until it was led to failure.
In order to give prior corrosion, rotating specimen under stress-free condition was exposed to air-saturated 5% H₂SO₄ at 25°C for 1h to 100h as the first stage. After having drained out the acid after prior corrosion, the specimen was cleaned and dried, then was subjected to repeated stress in air as the second stage, and was led to failure.
Secondary corrosion fatigue life in the second stage was slightly increased by primary overstressing in the first stage, but hardly any influence was given on secondary corrosion endurance by primary understressing in air. It was derived that, in view of these facts, endurance property conjoined with corrosion action was essentialy controlled by corrosion resisting property of metal within a given environment.
Exposure to the aqueous acid solution as the first stage, gave no practical deterioration to the specimen in the following test in the second stage if repeated stress applied in this stage did not exceed prior endurance limit. However, if the repeated stress applied in this stage was beyond prior endurance limit, serious decrease of the fatigue strength at N cycles was exhibited by short time of prior corrosion, for some austenitic stainless steel, and the reverse was exhibited for some other austenitic stainless steel.
It has been understood that this different tendency was presumably controlled by retained ductility of austenitic stainless steels, though corrosion resistance might be primary cause.

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The first factor investigated was concerned with cathodic protection in which a controlled direct current was passed through a cell whose cathode was an austenitic stainless steel specimen under cyclic loading and whose anode was a fixed carbon ring, both having been immersed in aqueous acid electrolyte. The second factor investigated was the effect of Cu⁺⁺ ion added to aqueous acid solution as a representative of oxidizing cations.
The following conclusions were obtained from this investigation:
(1) Large cathodic currents whose densities ranged from 10A/m² to 100A/m² showed the possibility of shortening corrosion fatigue life of type 316 Ti stainless steel exposed to air-saturated 5% H₂SO₄ at 25°C when smaller repeated stress than endurance limit in air was applied.
(2) From a statistical point of view, it was anticipated that applied cathodic current of around 10A/m² might perphaps not be effective, but also might not be harmful to corrosion endurance of type 316 stainless steel immersed in air-saturated 5% H₂SO₄, and cathodic current of some 2.5A/m² level, however, was expected to be promising to prolong its corrosion fatigue life, when applied repeated stress did not exceed the endurance limit in air.
(3) Under repeated stress beyond the endurance limit in air, austenitic stainless steels did not recieve any influence on their endurance neither from cathodic current nor from electrolytically charged hydrogen, and in all cases, hydrogen embrittlement was not observed.
(4) In case of mild steel, some improvement of endurance was made by imposing cathodic current, and no sign of hydrogen embrittlement was shown when applied repeated stress was below the endurance limit in air, whilst some aggravation of endurance and hydrogen embrittlement was recognized repeated overloading was beyond the endurance limit.
(5) It was found that Cu⁺⁺, an oxidizing cation, was probably effective as an inhibitor of corrosion fatigue of austenitic stainless steel exposed to air-saturated 5% H₂SO₄ at 25°C and 50°C. The same effect, generally speaking, might be expected from Fe³⁺, Cr⁶⁺ ion etc., but further detailed investigation would be needed for their practical application.

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Changes of deflection of high carbon steel plates which had been variously heattreated and bending-worked were measured continuously during re-heating. The results are as follows:
(1) In cold-bent steel which had been annealed or normalized, change of deflection in the reverse direction of bending appeared mainly during heating from 360°C to 670°C.
(2) In cold-bent steel which had been quenched and tempered, change of deflection in the reverse direction of bending occurred during heating upto temperature c.a. 220°C, and in the same direction of bending above the temperature. As the results, the total distortion was much smaller than that in annealed or normalized one. In cold-bent steel which had been quenched and tempered and cold-stretched, change of deflection only in the same direction of bending was recognized.
(3) In quenched and tempered steel which had been bent during tempering, change of deflection in the reverse direction of bending appeared above temperature at which bending had been done. So-called “Hot Setting” which was applied to high-temperature-use springs was considered to base on such phenomenon.
(4) The behavior of cold-bent steel could be explained by considering macro-residual stress after bending and high-deformability during heating of cold-worked or quenched steel.
(5) The phenomena recognized in quenched and tempered steel which had been bent during tempering could not be explained only by macro-residual stress. Micro-residual stress due to the stress-balanced structure of lattice defects such as subgrain boundaries should be taken into consideration.
(6) Cold-twisted steel showed the same behavior as that of cold-bent one as for distortion due to heating after cold-working.

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In the previous paper, we reported on our experiments about carbon steels under the repeated tension impact and the discontinuity of their E-N curves.
This paper describes about the results of studies on aluminum alloys (17S and 56S) under the repeated tension impact.
The followings are the results obtained;
(1) The repeated tension impact test discontinuously changes from impact test to fatigue test. In the diagram of the relation between repeated tension impact energy and number of impacts to failure, two curves come out as shown in Fig. 2 and they are discontinuous. The upper curve is associated with large scale plastic deformation, whereas the lower curve stands more truly for a fatigue failure.
(2) By measuring the deformation of specimens, we have found the descontinuous change of α, β and ψ with impact energy as shown Figs. 3, 4 and 5.
(3) There exists a liner relation between the impact energy and the ratio of A_f/A₀, where A_f is the area of fatigue fracture on the lower curve and A₀ is original area of specimens.

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Since Mn-Zn ferrite is to be oxydized in air atmosphere at a temperature range between 500°C and 1100°C, αFe₂O₃ and Mn₂O₃ are easily precipitated in the manufacturing process and magnetic properties of Mn-Zn ferrite are usually detoriorated. In order to remedy such a fault in the manufacturing process of Mn-Zn ferrite, rapid cooling method in air or slow cooling method in N₂ is used. In former case, however, many cracks may occur in ferrite body and even in latter case the technical problems about oxygen partial pressure are remained. In this report, the authors tried to fire Mn-Zn ferrite in N₂+CO₂ gas atmosphere converted from air and town gas or commercial propane gas. The magnetic properties of Mn-Zn ferrites fired in converted gas atmosphere are shown in the relations among B_m (maximum flux density in core subject to alternating magnetizing force), H_m (maximum magnetizing force in core subject to alternating magnetizing force), μ_AC (amplitude permeability) and W (hysteresis loss). The results show that the magnetic properties of Mn-Zn ferrite fired in the converted gas atmosphere are equal to the magnetic properties of Mn-Zn ferrite fired in N₂+0.5%O₂ atmosphere which is most suitable for the firing of Mn-Zn ferrite. So that, even if CO₂ gas in converted gas had the effect of oxidizing ferrite body, the effect might be only exerted on the oxidation of metal ions in spinel ferrite because the effect is not so strong. This has a good advantage in making Mn-Zn ferrite in commercial production which is connected with financial and O₂ partial pressure problems.

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