The Rapid Tempering Behaviors of a Low‐Carbon Bainitic Pipeline Steel With Two Strength Grades

The strength‐plastic mechanism of a low‐carbon bainitic pipeline steel and its response to rapid tempering were investigated by microstructural characterization and tensile assessment. Notably, the rapid‐tempering effects differ markedly between high‐strength and low‐strength plates. For high‐strength plate after rapid tempering, both yield strength and tensile strength decrease, whereas the elongation improves. In contrast, regarding the low‐strength plate, rapid tempering leads to increases in both yield strength and tensile strength, but the elongation diminishes relative to the hot‐rolled plate. In addition, for hot‐rolled plate, coiling at elevated temperature promotes finer grains and a higher fraction of large‐angle grain boundaries. Conversely, hot‐rolled plate coiled at lower temperature retains portions of lath bainite, resulting in higher values of kernel average misorientation and geometry necessary dislocation. Furthermore, lath bainite demonstrates high thermal stability during the rapid tempering of high‐strength plate. Based on the experimental data, an empirical equation for predicting the hardness after rapid tempering was derived.