Controlling the ferrite and pearlite banded structure of 20CrMnTi steel hot rolled bar

This paper studied the banded structure of 20CrMnTi steel bar samples at different positions in the rolling line. In the rough rolling section with small plastic deformation and high temperature, the banded structure is relatively light. In the final rolling section with large plastic deformation and low stop rolling temperature,the banded structure is relatively heavy. Based on the above results, the rolling process was controlled through experiments with final rolling temperatures of 800℃, 825℃, 865℃, 905℃, 915℃, and 945℃, and cooling speeds of 0.53℃/s and 1.50℃/s to control the banded structure of 20CrMnTi steel hot-rolled bars. The results show that when the final rolling temperature is＞915℃ and the cooling speed is controlled at 1.50℃/s, the banded structure of 20CrMnTi steel hot-rolled bars can be controlled at ≤2.0 grade. The formation mechanism of hot-rolled bar banding was analyzed, which was the result of the combined effects of metal plastic deformation during rolling and the cooling phase transformation of austenite into ferrite and pearlite. When the bar structure is in the austenite region during metal plastic deformation, it is beneficial to control the banding. When the temperature is ＜913℃, austenite undergoes phase transformation to precipitate primary ferrite, followed by plastic deformation, which is unfavorable for controlling the banding. The 20CrMnTi steel bar samples were scanned using the EPMA-1720 electronic probe device after hot rolling and annealing, and the results showed that annealing treatment can aggravate the steel banding, causing C, Mn, and Cr elements to accumulate along the metal extension direction.