Effect of continuous annealing temperature on microstructure and properties of ferritic rolled interstitial-free steel

In this report, the microstructure, mechanical properties, and textures of warm rolled interstitial-free steel annealed at four different temperatures (730, 760, 790, and 820 degrees C) were studied. The overall structural features of specimens were investigated by optical microscopy, and the textures were measured by X-ray diffraction (XRD). Nano-sized precipitates were then observed by a transmission electron microscope (TEM) on carbon extraction replicas. According to the results, with increased annealing temperatures, the ferrite grains grew; in addition, the sizes of Ti4C2S2 and TiC precipitates also increased. Additionally, the sizes of TiN and TiS precipitates slightly changed. When the annealing temperature increased from 730 to 820 degrees C, the yield strength (YS) and the ultimate tensile strength (UTS) showed a decreasing trend. Meanwhile, elongation and the strain harden exponent (n value) increased to 49.6% and 0.34, respectively. By comparing textures annealed at different temperatures, the intensity of {111} texture annealed at 820 degrees C was the largest, while the difference between the intensity of {111}< 110 > and {111}< 112 > was the smallest when the annealing temperature was 820 degrees C. Therefore, the plastic strain ratio (r value) annealed at 820 degrees C was the highest.