高温焼戻脆化したNi-Cr鋼の機械的性質におよぼす変形速度および温度の影響

抄録

Temper embrittled nickel-chromium steels were subjected to the impact and static tensile tests and Charpy test in the temperature rangefrom ambient temperature down to that of liquid nitrogen, in order to investigate the effect of deformation rate on yield and tensile strengths and the variation of ductile brittle transition temperature with carbon content and austenite grain size.
The variation of yield and tensile strengths with decrease of temperature was found to be significantly different between temper embrittled and unembrittled specimens. In temper embrittled specimens, the ducile-brittle transition phenomena similar to Charpy test was observed in the impact tensile tests and the strength of the specimens intergranulally fractured in a brittle manner was constant irrespective of austenite grain size and deformation rates.
The relationship between the transition temperature and lnd^-1/2 (d: austenite grain size) was linear regardless of deformation mode and rate. The slope of these lines was estimated to be 125°C/cm^1/2, which is larger than that of mild steel. This result suggests that the ductile-brittle transition phenomena of temper embrittled steels are significantly depend on austenite grain size.