低温焼入による鋼の材質の変化について(第3報) : 疲労および衝撃強度の改善

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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℃ for 100 min., quenched into ice water and kept for about 2 hr. at 0℃. (b) Spheroidizing treatment ; The annealed steels were austenitized for 15 min. at 50℃ above their appropriate A_3 temperature, quenched into water, and subsequently reheated at 700℃ for 100 min., quenched into ice water and kept for about 2 hr. 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 30 kg/mm^2) 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.
社団法人日本材料学会の論文
1957-07-15

低温焼入による鋼の材質の変化について(第3報) : 疲労および衝撃強度の改善

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