Toyota Jidosha Kabushiki Kaisha

Nippon Steel & Sumitomo Metal Corporation

Satoru Shimazu

Yasushi Yamamoto

Hideyuki Nakamura

Masaaki Kondo

Takaaki Fukushi

Izuru Yamamoto

Isao Anai

The present invention provides a steel material for automobile chassis parts which has high fatigue characteristics, does not require much cost for heat treatment, and further is superior in shapeability and a method of production of automobile chassis parts using this steel material, that is, one being a steel material to which Nb and Mo have been compositely added and having a difference 50 to 150 points between a Vicker's hardness of the center of plate thickness and a maximum value of Vicker's hardness within 0.5 mm from the surface after bending by a bending R of the plate outer surface of 2 to 5 times the plate thickness. The surface is high in hardness and the center part is low in hardness, so the fatigue characteristics and shapeability are superior. Note that if annealing under conditions giving a tempering parameter &#x3bb; defined by &#x3bb;=T(20+log(t)) of 14000 to 19000 (where T is the absolute temperature, t is the time (h), and the temperature rise is 660&#xb0; C.), it is possible to relieve the internal stress and further improve the fatigue characteristics.

Steel material for automobile chassis parts superior in fatigue characteristics and method of production of automobile chassis parts using the same

The present invention provides a steel material for automobile chassis parts, having high fatigue characteristics, without a heat treatment, and superior shapeability, and a method of production of such automobile chassis parts. The surface of the steel has a high hardness and the center has a low hardness, providing the superior characteristics. With an annealing step of the invention, it is possible to relieve internal stress and further improve fatigue characteristics.

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Nisshin, Japan

Satoru Shimazu