Recrystallization-Precipitation Interaction Study of Two Medium Carbon Niobium Microalloyed Steels

抄録

Recrystallization-precipitation-time-temperature (RPTT) diagrams for strains of 0.20 and 0.35 have been determined for two microalloyed steels with niobium percentages of 0.024 and 0.058, respectively, and equal percentages of carbon and nitrogen. The method known as "back extrapolation" has been used for the determination of static recrystallization kinetics and also for the plotting of the diagrams. While a single plateau was observed on the recrystallized fraction against time curves for the first steel, as a consequence of strain induced precipitation, these curves for the second steel showed the formation of a double plateau, whose interpretation, confirmed by calorimetric analysis, supposes the formation of two types of precipitates. The work uses transmission microscopy to show the precipitates which are formed in both steels, as well as the size most probably capable of inhibiting recrystallization. Finally, an analysis is made of the RPTT diagrams and of the large amount of information which they offer for designing a more appropriate rolling schedule in order to obtain finer precipitates and a better austenitic microstructure before the austenite→ferrite transformation.