車軸圧入部に発生する疲れき裂の諸特性に及ぼす低温焼入れの影響
1978 年 64 巻 9 号 p. 1404-1413
詳細
1978 年 64 巻 9 号 p. 1404-1413
This study has been made to improve fatigue strength of press-fitted parts of car axles by sub-critical quenching; water quenching from the temperature just below Ac1.
The effect of sub-critical quenching on behaviours of fatigue crack propagation, the relation between σw2 (fatigue limit for failure) and sub-critical quenching temperature as well as the relation between hardness of ferrite structure and residual compressive stress at surface were investigated using notched specimens of 15mm in diameter (0.35%C steel) and are press-fitted specimens of 50 mm in diameter (0.4%C steel).
Results obtained are as follows.
(1) In sub-critical quenched specimens, both notched and press-fitted, fatigue cracks initiated and propagated to some extent and stopped, when the stress was applied above σw1 (fatigue limit for crack initiation) and below σw2. The crack length depended probably on the applied stress.
(2) Maximum value of σw2 was obtained in the specimens, both notched and press-fitted, sub-critical quenched from about 650-750°C.
(3) In the surface of sub-critical quenched specimens, hardness of ferrite structure was considerably increased. It was presumed that about 60% of total hardness increase was provided by age hardening after quenching, and about 40% of it by residual compressive stress generated on the surface by the quenching.
