Effect of Micro-alloying Element Boron on the Strengthening of High-Strength Steel Q690D

The effect of boron addition on strengthening of steel Q690D was studied. The metallographic microstructures of Q690D plate samples after controlled rolling and cooling process and roughing rolling in bench-scale were observed by optical microscope and transmission electron microscope, and the mechanical properties were determined. The results showed that the microstructure of Q690D became finer distinctly with increase in the content of soluble boron in steel. The yield strength and tensile strength also increased with the increase of soluble boron. Most of boron in steel Q690D existed in solid solution state. The main precipitates in Q690D steel were the Ti(C, N) and NbC. The amount of BN was small. Among the strengthening performance of steel Q690D given by boron addition, refinement strengthening gave the greatest contribution on the strengthening effect.