Abstract
1. Increasing the cooling rate in liquid nitrogen from 3–5 to 50–70 deg/min changes the transformation of retained austenite in quenched steel R6M5 from martensitic to bainitic-martensitic. 2. The bainitic transformation during rapid cooling shifts the martensitic transformation proper to lower temperatures (−100 to −150°) and thus changes the morphology of martensite crystals. 3. After partial stabilization at +20° for 24 h the austenite is transformed by the bainitic-martensitic mechanism during slow cooling and by the bainitic mechanism with rapid cooling to the temperature of liquid nitrogen, which reduces the amount of austenite transformed. 4. Rapid cooling in liquid nitrogen has a stronger shrinkage effect during subsequent heating in the temperature range of −60 to +120°, i.e., increases the density of martensite lattice defects. 5. The characteristics of the transformation of retained austenite (not stabilized or partially stabilized) must be taken into consideration in selecting the cold treatment for tools made of high-speed teel.
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