Description:
<jats:p>In case of the low carbon chromium steel that have widely been used for the carburized
gears or rolling bearings, the austenite grain coarsening may be occasionally occurred during
carburizing. To restrain this phenomenon, most of hot forged parts have been given to an isothermal
heat treatment or normalizing immediately after hot forging and/or prior to carburizing. Therefore,
their production cost includes unexpected additional expenses caused by such a non-value added
process. To confirm the possibility of an energy saving, as well as attaining a superior fatigue life,
in the production of automotive parts to be carburized, the austenite grain coarsening with the
manufacturing process of the microalloyed steel, containing Nb and B as a grain refining elements,
was investigated. The heat treatment characteristics and rolling contact fatigue behavior of the
carburized specimens with the isothermal heat treatment were also investigated. In spite of omitting
the isothermal heat treatment after hot forging, the abnormally coarse austenite grains were not
found out in the carburized specimens. However, the rolling contact fatigue life of the carburized
specimens, in which the isothermal heat treatment was omitted, was shorter than that of
isothermally heat-treated specimens.</jats:p>