To provide an automobile undercarriage component having excellent low cycle fatigue properties, and to provide a method for producing the same.
In the automobile undercarriage component, ≥80% of the microstructure of a steel member composing the component is formed from bainite, and also, the value of R/t, i.e., the ratio between the sheet thickness t at a part to form into the starting point of the low cycle fatigue crack of the component after forming and the curvature radius R of the outer surface is ≤5, thus microvoids promoting the generation and propagation of a fatigue crack in the component after forming are reduced, and the value of the X-ray half-value width in the (211) face is ≤5(deg), further, since its structure consists essentially of bainite and is uniform, its fatigue damage is not localized, and its fatigue properties are excellent. Further, since its structure consists essentially of bainite and is uniform, to a high stress amplitude in a low cycle fatigue region, its yield stress is higher than that in a structure consisting essentially of ferrite such as a DP steel on the same strength level, the skid resistance of dislocation to repeated stress is high, and the generation of a fatigue crack can be suppressed.
NAKAMURA HIDEYUKI
ANAI ISAO
Fumio Yamamoto