Nsk Corporation

Yuuji Miyamoto

Shigeru Okita

Hideyuki Uyama

Tomoyuki Nakamoto

A method for carburizing a steel member of the present invention includes: bringing a carburizing agent into contact with at least a part of a surface of a steel member; and heating the steel member and the carburizing agent to allow carbon to penetrate into at least a part of the surface, in which the carburizing agent contains a Fe-C alloy powder, a graphite powder in an amount of 20% by volume or more and 70% by volume or less relative to a total volume of the carburizing agent, and a binder that binds the Fe-C alloy powder and the graphite powder to each other, and in the heating, a heating temperature is held for a certain period of time within a temperature range of an austenite region of a eutectic point of the steel member or higher and lower than the peritectic point of the steel member.

Method for carburizing steel member, steel component, and carburizing agent

In a wheel-support rolling bearing unit, in order to made a flangethinner and thus lighten the bearing unit without impairing fatigue strength, machinability, and workability after forging, the composition of the alloy steel constituting the flange attached member (hub ring), the surface hardness of the root portionon the axial outside surface side of the flange, and the surface roughness, are stipulated to thereby improve the durability ratio (fatigue limit strength/tensile strength) of the flange. In one aspect, the member is made from an alloy steel containing C: 0.5 to 0.65 weight %, Mn: 0.3 to 1.5 weight %, Si: 0.1 to 1.0 weight %, Cr: 0.01 to 0.5 weight %, S: 0.35 weight % or less, and any one type or more selected from 0.01 to 0.2 weight % of V, 0.01 to 0.15 weight % of Nb, and 0.01 to 0.15 weight % of Ti, with the rest being Fe and inevitable impurities, and the oxygen contents is 15 ppm or less. Moreover, the surface hardness of the inner racewayformed with the hardened layer, is between Hv 650 and 780, and the surface hardness of a portion not formed with the hardened layer is between Hv 230 and 300.

Growing community of inventors

Fujisawa, Japan

Yuuji Miyamoto