0.6% C・Ni-Cr-Mo鋼の連続冷却変態挙動におよぼす成分範囲内における化学成分変動の影響

抄録

Continuous cooling transformation diagrams were determined for five steels selected from the same grade, 0.6% C.ENi-Cr-Mo steel. It was revealed that small variations in chemical composition within the specified range of the steel resulted in an appreciable difference in transformation behaviors. Transformation behaviors of the steels were expressed or compared quantitatively in terms of important characteristic values capable of representing CCT diagrams. Various empirical relations were presented which enabled us to predict continuous cooling transformation behaviors of the steels from their chemical composition and grain size. Critical cooling rates for various amounts of bainite formation were correlated to “the ideal critical diameter” which was calculable from chemical composition and grain size of steel. Critical cooling rates for various amounts of pearlite were shown to be evaluated from the C content of steel. Interrelationships among various critical cooling rates (corresponding to various amounts of transformation) were shown for bainite and pearlite transformations.
Hardness of as-continuously-cooled and as-cooled-and-tempered specimens was determined as a function of cooling rate on continuous cooling, and it was correlated to the constitution of microstructure. The relation of the amount of transformation product (bainite or pearlite) to the dilatometric expansion due to transformation was also investigated.