In the present report, we have studied on the effect of low temperature annealing at 200 and 400°C upon the fatigue processes of cold drawn steel, mentioned in the 3rd report. The results obtained are as follows:
(1) The fatigue process in case of the repeated stress below the fatigue limit.
In low temperature annealed steel with high carbon content, the progress of fatigue does not occur with the increase of number of stress cycles.
In low temperature annealed steel with low carbon content, when the repeated stress is small, it does not occur, either. But when the repeated stress is near the fatigue limit, the fatigue progresses up to the stage of formation of submicroscopic cracks.
In this case, as the fatigue failure does not occur, it is considered that this process of formation of submicroscopic cracks stops within a certain extent.
These results described above have the same tendency with the case of cold drawn steel, mentioned in the 3rd report.
(2) The fatigue process in case of the repeated stress above the fatigue limit.
In the low temperature annealed steel with either high or low carbon content, the fatigue process is almost the same as in the case of cold drawn steel, mentioned in the 3rd report. But according to the annealed temperatures, the relative duration of fatigue stages differs respectively.
(3) The cycle ratio at the time of formation of submicroscopic cracks.
(a) In high carbon steel, it has a value of about 85% for cold drawn state, about 60% for annealed state at 200°C and about 70% for annealed state at 400°C. But in either case, it has no relation to the magnitude of repeated stress and shows a nearly constant value.
(b) The low temperature annealing after cold drawing makes it small for high carbon steel, but large for low carbon steel.

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The creep rupture behavior of 18-8 austenitic stainless steel was tested at 600-700°C, using notched and plain specimens, and the changes of microstructure during the creep test were also investigated.
The results obtained are as follows:
1) Creep rupture strength at 600°C of 18-8 stainless steel is little affected either by the presence of notch or by the type of notch. Notched specimens grow in strength more and more than plain ones with elevation of temperature between 600-700°C, and the strengthening rate is increased by notch.
2) The observation of microstructure after the creep rupture test shows that the slip bands are hardly visible. This proves there are some striking differences between the creep and the fatigue behavior at high temperatures.
3) An investigation of crack initiation and propagation at 650°C in notched specimen shows that the crack during creeping appears at the grainboundary below the notchroot and is propagated toward the notchroot and the center of specimen. The crack behavior and the changes of notchwidth show the same tendency in their developments.
4) The creep rupture elongation of plain specimen of 18-8 stainless steel differed greatly in character according to testing temperature and rupture time. Therefore the creep rupture elongation and the change of microstructure may have a close affinity with each other.

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Effects of pre-heattreatment on the anisothermal relaxation of S30C, S45C, SUP3 and quasi-SUP6 during annealing were studied.
In order to investigate the relaxation behavior, the changes of load of variously heat-treated steels, which were made to keep the constant deflection in the 4-points-support bending tests, were measured continuously during heating and cooling. In annealed steel, the load remained, to some extent, upto temperature Ac₁, but in quenched or quenched and tempered steel, a sharp decrease of the load was recognized with progress of tempering process. These phenomena can be explained by considering the high-deformability of steel during its structural change. It is necessary to consider these facts in the discussion of the mechanism of stress-relief-annealing.

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We investigated on the forming pressure effects on the fatigue strength and on the other mechanical properties. Test pieces of the forming pressures 160, 80, and 50kg/cm² were prepared. Fatigue characteristics were tested on the rotating bending fatigue test machine, whose number of revolution per minute were either 1900 or 1000. The thermo-paint was coated on the surface of the piece for fatigue test so that its temperature might be known, and the colour changing might show the aspect of internal heat producing.
Main test results obtained were as follows:
1) The forming pressure has a remarkable effect on the mechanical properties in the case of loading parallel to the laminates, but the effect in the case of loading perpendicular to the laminates was not clearly detected. In the case of loading parallel to the laminates, fatigue strength, bending stiffness, tensile strength and tensile stiffness decrease, and impact strength increases as the forming pressure is lowered, but compressive strength has maximum values at a forming pressure of 80kg/cm².
2) The apparent S-N diagram of cotton cloth laminates consist of three curves for the higher, middle and lower stresses. The true fatigue strength at a curve of higher stress must be larger than that given by the curve, because points on the curve show the numbers of revolution at which certain deflections are given by the stresses. The points on the curve of middle stress show the numbers of revolution at which the test pieces are fractured mainly due to the effect of internal heat producing. In this case the temperatures of the surface of the test pieces are about 110-150°C. The points on the curve of lower stress show the numbers of revolution at which the test pieces are fractured mainly by the effect of stress. In this case the temperatures of the surface of the test pieces are about 70-110°C. At a fatigue limit (N=10⁷), the temperatures of the test pieces are below 50°C.
3) As the number of revolution per minute decreases, the fatigue strength slightly increases. As the effect of the number of revolution per minute are not extinguished in curves of middle and lower stresses, the effect of internal heat producing has to be taken into consideration at lower stress at which test pieces are fractured mainly through the effect of stress.

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In our previous paper, the relationship between the thermal expansion and the packing of the particles of refractory bodies were investigated.
The conclusions were as follows:
(1) In the case of the powder composed of single component, the volume changes of the void spaces produced by the thermal expansion were proportional to the volume changes of the bodies.
(2) In the case of the two or more components systems, however, these volume changes were not proportional to those of the bodies.
In this paper, many observation about such none-similar changes of void spaces of packed bodies were attempted, using model experiments, and the following formula was decided to relate the actual thermal expansion (ε_x) and the calculated one (ε_mx)
ε_x-ε_mx=S/3v=|ε₁-ε₂|(f₁·f₂)ⁿ
here, n is the experimental constant.
The n values decided by many observations are 0.55-1.25.

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Nowadays, various types of hermetic seals made by glass-to-iron sealing technique are widely used in electronic industry. Though some theoretical and experimental studies on stresses in seals have been reported by several researchers, we have as yet very little informations as to practical sealing procedures, such as condition of preoxidation of iron or sealing atmosphere. This study was planned for finding the optimum sealing procedure and for disclosing the mechanisms of glass-to-iron bonding. The results obtained may be summerized as follows;
(1) The excellent glass-to-iron bonding may be obtained by preoxidizing iron to a predetermined and controlled amount of oxidation.
(2) In such seals, iron oxide is completely dissolved into glass, and glass is directly contacted with rough surface of metallic iron without showing gradual structure transition from glass to iron.
(3) In seals which are made with oxide free iron, glass is contacted with smooth surface of metallic iron, and glass-to-iron bonding is not so strong as that of oxide seals.
(4) In spite of these facts, oxidation of iron seems not always necessary for practical application.
(5) Effects of carbon contents in iron on sealability are not clear.

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