Carburized component and method of manufacturing the same

Abstract

This invention aims to provide a carburized component realizing a larger strength for power transmission components such as gears, and a method of manufacturing the same. The carburized component of this invention, aimed at realizing the object, consists essentially of, in % by mass and both ends inclusive, C: 0.1-0.30%, Si: 0.80-1.50%, Mn: 0.30-1.20%, Cr: 2.0-5.5%, and the balance of Fe and inevitable impurities; has a mean C concentration over the range from the surface of the steel to a depth of 0.2 mm after vacuum carburization of 1.2% or more and 3.0% or less, and has a ratio of a carbide area over the range from the surface to a depth of 50 μm of 15% or more and 60% or less, has the carbide precipitated in a finely dispersed manner so that the carbide having a grain size of 10 μm or less accounts for 90% or more of the entire portion, and has a depth of a grain boundary oxide layer below the surface of 1 μm or less.

Description

FIELD OF THE INVENTION [0001] This invention relates to a carburized component and a method of manufacturing the same. BACKGROUND ART [0002] Gears used as power transmission components for automobiles and so forth are components suffering from dedendum fractures which occur at the dedendum where bending stress happens, and from slip-induced fracture (pitting) which occurs in the vicinity of the pitch point. A technique of carburizing the surface of the component has, therefore, widely been used for the purpose of fulfilling characteristics enough for withstanding harsh conditions, and further improvement has been made by combining various materials and heat treatments. [0003] Particularly in recent years, a successful development has been made on a material capable of suppressing growth of grain boundary oxide layer and abnormally carburized layer during carburization, which are understood as being harmful to dedendum fracture. Another achievement has been made on improvement in the...

AI Technical Summary

Benefits of technology

[0026] The carburized component of this invention is subjected to vacuum carburization. The vacuum carburization makes it possible to decrease the growth of the grain boundary oxide layer, and is therefore successful in raising the strength of the carburized component.

[0027] As described in the above, Si is added as an essential ingredient. Si is an element promoting the grain boundary oxidation in the process of the general gas carburization, and such grain boundary oxidation is causative of reducing the impact strength and fatigue strength of the dedendum. It is, therefore, extremely difficult for the general gas carburization to achieve a large Si content. Whereas the vacuum carburization can, however, suppress formation of the grain boundary oxide layer, and can readily realize a high Si content.

Problems solved by technology

Gears cause slippage on the tooth surface thereof, and the repetitive contact generates heat at the portion just under the tooth surface.

Temperature in this state is known to fall in the range of about 200 to 300° C., and the heat generated herein supposedly softens the material and consequently results in pitting fracture.

The gear has, however, has been demanded to have a larger hardness with the recent increases in the output of automobiles and so forth, but the present situation is that the above-described material is insufficient for fulfilling the requirements.

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