Abstract: Morphology, size and number density of MnS inclusions of F45MnVS non-quenched and tempered steel produced by 120 t LD-LF-RH-240 mm x 240 mm CC process before improvement are analyzed. By adopting improvement measures including ： (1) the aluminum ingots for deoxidation are intermittently added into the molten steel in batches surrounding the impact zone during LD tapping； (2) low carbon and low sulfur ferromanganese without MnS inclusions being employed as alloy materials； and (3) added sulfur wire into the furnace ladle in batches during LF refining. Tlie experimental results show that based on the optimized production processes, the MnS inclusion sizes in steel during the production of LF, RH, Tundish, continuous casting bloom and the rolled products are all effectively reduced. Compared with the routine production processes before improvement, the number density of large scale inclusions (＞5μm) in the position of edge, 1/4 and center of the casting bloom decreases from original 35 , 83 and 51 per mm² to 24, 57 and 39 per mm² after the optimization, respectively. The decrease amplitude reaches 31.43% ,31.33% and 23.53% , respectively. The ratings for the thin and thick inclusions in the steel products after rolling have been improved. The ratio of the inclusions with the length-width ratio in the range of 0-3 to the total inclusions increases from 63.07% before improvement to 71.23% after improvement.

Key words: F45MnVS Non-Quenched and Tempered Steel, MnS Inclusion, Process Improvement, Cleanliness

摘要： 分析了改进前120 t LD-LF-RH-240 mm×240 mm CC工艺生产F45MnVS非调质钢中硫化物夹杂形貌、尺寸、数量密度等特性。通过采取以下改进措施：(1)转炉出钢过程脱氧铝锭加入用环绕钢液冲击区域分时段、分批次方式；(2)使用不含有MnS夹杂物的低碳低硫锰铁等合金辅料；(3)LF精炼过程S线喂入分批次加入等。试验结果表明：改进工艺后，LF、RH、中间包、铸坯以及轧材所有钢中硫化物夹杂的尺寸均有所降低，铸坯边缘、铸坯1/4处以及铸坯中心的大尺寸(＞5μm)夹杂物数量密度分别由改进前的35、83、51个/mm²下降至改进后的24、57、39个/mm²,降幅分别达到31.43%、31.33%、23.53%。改进后轧材中细系和粗系夹杂物评级均有所改善，夹杂物长宽比为0～3的比例由改进前的63.07%增加至改进后71.23%。

关键词: 非调质钢F45MnVS, MnS夹杂, 工艺改进, 洁净度