Takashi Yasunaka1, Tôru Araki2 and Satoshi Watanabe1
1National Research Institute for Metals, Tokyo
Ausforming was applied to 18Ni-Co-Mo steels containing 0.002∼0.1%C. Effects of ausforming on the aging behavior, mechanical properties and microstructure with thin foil and extruction replica electron microscopy have been studied.
Disk-shaped precipitates in overaged low carbon alloys were found to have a structure close to that of Ni3Mo.
Ausforming accelerated age hardening and precipitation of Mo2C, but diminished the strength increment due to aging. In fully aged alloys, increase in 0.2% yield strength by ausforming was increased with carbon content but the trend gradually saturated beyond 0.05%C. The increasing rate of yield strength of the aged 0.1%C alloy was 0.39 kg/mm2 per % reduction above 17% reduction in thickness.
The strength of the present alloys ausformed and fully aged can be explained by the combination of ordinary strengthening and the decreased age hardening by ausforming, the primary cause of the former being the increase of dislocation density in martensite.
Please do not copy without permission.