The effects of low-temperature-quenching (LTQ) and spheroidizing treatments on the fatigue and the impact strengths of steels were investigated. The specimens were of plain carbon steels containing carbon, from 0.04% to 0.8%, and the heat treatments were carried out as follows;
(a) LTQ; The annealed steels were heated at 700°C for 100min., quenched into ice water and kept for about 2hr. at 0°C.
(b) Spheroidizing treatment; The annealed steels were austenitized for 15min. at 50°C above their appropriate A₃ temperature, quenched into water, and subsequently reheated at 700°C for 100min., quenched into ice water and kept for about 2hr.
After the heat treatment, the specimens were turned down, and the rotating beam fatigue test and the notched bending impact test were carried out at room temperature.
The results obtained were as follows:
(1) The fatigue and the impact strengths of steels are markedly influenced by both the strength of ferrite and the morphology of the carbide phase, to be greatly improved by spheroidizing the carbide and by low temperature quenching.
(2) The LTQ strengthens the ferrite matrix by supersaturating the carbon and the nitrogen in it. Accordingly, the more the ferrite in steels, in other words, the less the carbon content of steel is, the more effective the improvement of the fatigue and the impact strengths by LTQ are.
(3) The spheroidizing treatment relieves the internal notch effect and it may be plausible to assume that the ratio of the endurance limit of spheroidite to that of lamellar pearlite is a measure of the fatigue notch factor of the carbide lamella in pearlite. The mean value of this ratio is approximately 1.25.
(4) Fatigue strength is more improved by LTQ and spheroidizing than static strength is. It may be due to both the relieving of internal notch effect and the strain-aging which takes place during repeated loading.
(5) The endurance limits of spheroidized steels are of almost the same value in most cases (about 30kg/mm²) regardless to their carbon content, while the less the carbon content of steels is, the higher the impact value is. Therefore, for many machine parts which require higher fatigue resistance and toughness such as absorption spring or shaft, low carbon steels which are low-temperature-quenched or spheroidized will be more advantageous by used than to use high carbon steels.

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The method of galvanic anode is used for preventing damages owing to the corrosion fatigue in the hull or machine parts.
We carried out an experiment in order to ascertain the effect of the corrosion protection by this method on the strength of corrosion fatigue of cast iron.
The experiment was made as to two kinds of cast iron in 3% saline solution.
As the result of this experiment, it was found out that the perfect corrosion protection could be brought about by keeping the anticorrosive potential of cast iron in 3% saline solution at about-0.95V (S.C.P.) and that the strength of corrosion fatigue could be reduced by this protection method to be about equal to that of corrosion fatigue in the air.

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Fatigue test results on the large size roller chains for power transmission (Tsubakimoto RS 0206) was reported in this paper. The test results were discussed on the fatigue strength of large size roller chains and compared with those obtained on the small size roller chains reported in the provious issue.
For fatigue testing two kinds of Losenhausen oil pressure type fatigue testing machines were used, that is, UHS type (capacity, static load 35ton, dynamic load 20ton) and UHP type (capacity, static load 20ton, dynamic load 10ton). The former was used for repeated load over 10ton, and the latter for under 9ton. Also fatigue tests on steel plates for chain links were carried out by Haighs fatigue testing machine (capacity 1.5ton) for comparison's sake. The driving speed of the testing machines was 800cycle/min at Losenhausen machine and 1800cycle/min at Haigh machine.
The results obtained are as follows:
1. The critical part of the chains applied to tests was the cross section of roller links perpendicular to longitudinal direction, where bushes were press-fitted.
2. The endurance ratio of the large size roller chains is about 1/4. This value is larger than that for small size roller chains which was about 1/7, as previously reported. The reason is considered to be due to the fact that the endurance ratio of roller link plate materials for large size roller chains was larger than that for smaller ones.
3. The effective stress concentration factor for the large size roller chain was 3.4 at 10⁷, and 2.2 at 10⁵.
4. Eliminating the effect of fitting pressure, the value of the effective stress concentration factor was calculated to be 4.8 at 10⁷, which is nearly equal to the value of the stress concentration factor for the eye end plate loaded by a pin with clearance.

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