TechnologyExchange
CUI Hong, WANG Hao, SHI Chao, LÜ Dan, LIU Yubao, WANG Rui
Taking a domestically produced HSLA steel as the research object, this study applied a dual-process approach combining narrow-window refining process control with constant casting speed and accurate rare-earth wire feeding into the mold. The recovery rate, content, and distribution of rare earth in the slab were systematically investigated. Through comprehensive sampling and comparative testing, the effects of rare earth addition on the internal cleanliness, segregation behavior, and solidification structure of the slab were evaluated. The results show that the refining-continuous casting dual process enables a rare earth recovery rate exceeding 80%, with the residual rare earth content in the steel maintained above 200×10-6, uniformly distributed across different slab locations. This method significantly reduced both the average total oxygen content and its fluctuation in the slab, indicating improved steel cleanliness. After adding a high concentration of rare earth, conventional inclusions such as Al2O3, MgO and MnS were modified into rare earth-containing inclusions (e.g., RE-O, RE-S, RE-Al-O, RE-S-O). The dominant inclusion size range shifted from above 10 μm to below 5 μm, and the morphology changed from elongated or chain-like to spherical or spindle-like. Compared with the rare earth-free slab, the number density of inclusions increased in the rare earth-treated slab, while the area density decreased, indicating that rare earth modifies, refines, and disperses inclusions, effectively reducing large heterogeneous inclusions in the steel matrix and enhancing microstructural continuity. The uniform distribution of rare earth also notably suppressed the development of columnar crystals, increased the equiaxed crystal ratio, and refined the dendrite arm spacing. This refined and homogeneous solidification structure alleviated solute element enrichment toward the slab center, reducing segregation and cracking tendency. These improvements help minimize banded structure formation during rolling and enhance the strength, toughness, and fatigue resistance of the steel through grain refinement.