a method of quench hardening a gear having a gear rim , a hub , and two rim carrying gear disk includes carburizing the gear and quenching it subsequently in a saline bath , and is improved by releasably covering the perforated disks with perforated supplemental disks , the perforations are closed during carburization but open during quenching . the gear is turned about its vertically positioned axis during quenching ; the supplemental disks are removed subsequently so that the gear disks are not carburized .