Abstract: Because of high content of vanadium and nitrogen in high-strength weathering steel, as well as carbon content in peritectic reaction zone, subcutaneous net cracks on slab were easy to generate in continuous casting process. The reasons of cracks defects were analyzed, and on this basis, mold powder, which could meet the needs of continuous casting process for this kind of steel grade, were studied and developed. Industrial tests showed that, when the casting speed was increased from 0.70~0.75 m/min to 0.90~0.95 m/min, the thickness and consumption of liquid powder in mold could be controlled in 9~11mm and 0.45～0.65 kg/t respectively. The acceptable ratio of slab surface quality for Q450NQR1 steel is as high as 90.14 %, and furthermore, the peeling defect ratio on hot rolled coil was reduced from 41.29 % to 4.24 %.

Key words: high strength weathering steel, continuous casting, mold powder, net cracks