چكيده به لاتين
Rapid heating is associated with energy and cost savings, increased productivity, and maintained or improved quality compared to heating at a conventional rate. In this study, the cold rolling was performed on StW 22 steel (hot rolled) with different thickness reduction values. Then, the effect of temperature changes on the recrystallization fraction was examined and the temperature 650℃ was selected as the constant temperature. The samples were subjected to conventional annealing with constant temperature (650℃) and varied time. Its microstructure, mechanical properties, recrystallization fraction, and kinetics were examined. Then, the samples with moderate and high thickness reduction percentages were undergone the induction annealing process with a rapid heating rate and their microstructural and mechanical properties were compared with the conventional annealing samples. According to the results, the increased rolling percentage increases the hardness (up to 59%) and yield strength (up to 45%) and reduces formability. The annealing time at a constant temperature decreases by increasing the rolling percentage. Also, the average grain diameter after annealing is generally lower than the average diameter of the prototype. However, the lower the rolling percentage, the higher the average grain diameter after annealing would be. Recrystallization annealing reduces the strength and increases the ductility and formability. Induction annealing reduces the recrystallization time to a few seconds; however, it is a highly difficult task to control the temperature and create similar conditions for all the samples. In sample with 45% cold reduction, the recrystallization time reduces to less than 9 s, while the grain diameter is not different from the conventional annealing of this steel, it shows a higher yield strength (34%). The grain growth occurs by holding this sample for more than 30 s. In the case of sample 75%, it is almost impossible to create the same conditions at all holding times of this sample due to very small thickness, the presence of electromagnetic field of induction annealing, and high penetration depth. However, this sample is fully recrystallized even at holding time 0 s and its yield strength is higher than the conventional annealing by 66%. At 27 s, this sample shows the same properties as a conventional annealing sample, except that its mean grain diameter is 3 μm more. The 27 s sample has the lowest mechanical properties and the highest grain size among the induction annealing samples. Therefore, one can conclude that a sample with the lowest mechanical properties and the maximum grain size in the rapid annealing method is similar to the best conventional annealing sample. Even if the comparison is done in a similar length increase, in 243 s, which is the longest holding time, the yield strength is higher than the conventional annealing as 27%. In any case, all the induction annealing samples showed better properties than the conventional annealing and had a more uniform microstructure.
