Abstract: Due to the high inclusion content and low elongation after cold rolling,the DL350 low carbon titanium microalloy cold-rolled structural steel produced by a certain plant cannot meet the customer′s requirements.In order to reduce the production cost and improve the elongation after fracture of cold rolled products,a reasonable slag washing process was developed, and the influence of slag washing process on the cleanliness and performance of steel was analyzed.The results show that the inclusions in steel are mainly MnS, TiN, MnS-TiN and a small amount of Al₂O₃ inclusions, and the content of oxygen and nitrogen in molten steel decreased significantly with slag washing.After slag washing, the average content of micro-inclusions in the billet decreased from 21.3 to 15.7 per mm².At the same time, the grade of Class A inclusion was reduced from 2.0-2.5 to 1.0-1.5, and Class B inclusion was reduced from 1.5-2.0 to 0.5-1.0, indicating that the slag washing process significantly improved the cleanliness of the billet. Through the performance test of hot-rolled and cold-rolled products, it can be found that the elongation after hot-rolled fracture of slag-washing process samples has been increased from 26 %-28 % to 29 %-31 %, and the elongation after cold-rolled fracture has been increased from 15 %-16 % to 18 %-20 %, the overall strength changes little, which meets the customer′s requirements.

Key words: slag washing, micro inclusions, cleanliness, mechanical property, microalloyed steel