2018 年 104 巻 2 号 p. 98-106
In our previous report (Tetsu-to-Hagané, 103(2017), 194), we investigated the microstructure of induction-heated SUJ2 steel. The austenitization was carried out at much higher temperatures (900-1000°C) than those typically being used at present in furnace heat treatment. It is worth noting that the fraction of retained austenite tended to be relatively high in induction-heated steels, which seem to be disadvantageous for the components of rolling bearing. In this study, the mechanical properties, in particular static and dynamic load capacities, were evaluated for the induction-heated steels containing 4 to 12 vol% undissolved carbide and austenitized at from 900 to 1000°C in order to establish the conditions for which the mechanical properties of SUJ2 steel are equal to or better than those of furnace heated SUJ2 steels.
Dimensional change over time, static load capacity and torsion fatigue life were evaluated. From the results, the conditions 900°C with 8 vol%, 900°C with 10 vol%, 950°C with 8 vol% and 950 with 12 vol% were found to be promising. Using these conditions, deep groove ball bearings were further fabricated, and rolling contact fatigue tests were conducted. Data obtained from these tests were statistically processed and the fatigue life of these bearings was found to be more than three times the predicted fatigue life. The performance can be closely related to the amount of each constituent such as tempered martensite, retained austenite and undissolved carbide.
