Effects of Rolling Process on Low Temperature Toughness of High Strength Bridge Heavy Steel Plate

The effect of different rolling processes on the low temperature impact toughness of 56 mm thick Q500qE bridge steel with different widths was studied by optical microscope, scanning electron microscope, transmission electron microscope（TEM）, EBSD energy spectrum analyzer and tensile and impact tester. The results show that when the width of steel plate is big, the number of rolling passes and the compression ratio of passes is small, the effective grain size is bigger and the proportion of high angle grain boundary is small, which results in the impact toughness at low temperature lower than that of steel plate with smaller width; the transverse and longitudinal strength difference of the steel plate is less, and the anisotropy is relatively small. When the rolling temperature and cooling rate are the same, reducing the passes and increasing the pass compression ratio promote the precipitates to be uniform, fine and dispersed, which is conducive to improving the low-temperature impact toughness of the steel.