Abstract: Niobium-containing phase precipitating in liquid steel during solidification in (220 mm×260 mm) continuous casting bloom of Nb microalloying F40MnVS steel (adding 0.029% Nb) is studied in the paper. The results show that there are many micro-sized large particles of NbC(/%:80-94Nb,1.2-7. 1V,1.6- 17. 1Ti) in bloom. The large NbC is distributed between the dendrites its morphologies can be block shape, long strip shape, or eutectic shape with steel matrix, part attached to sulfide. NbC at the edge position in bloom is mostly less than 5 μm,the morphology is mostly dotted while that at middle and center position is large and mostly long with size even up to tens of microns. The large NbC still exists in hot- rolled bar. According to calculated results by Thermo-Calc software, the NbC precipitates in liquid steel during solidification process when solid fraction reaches 0.961, and the existence of element Ti may be the mutual dissolution result of NbC and TiN. By increased the heating temperature of bloom before rolling to1200 ℃, the size of large NbC could be obviously decreased.

Key words: Micron-Sized Large NbC Particles, Nb-Microalloyed, F40MnVS Steel, Continuous Casting Bloom, Thermo-Calc

摘要： 针对铌微合金化(加0.029%Nb) F40MnVS非调质钢(220 mm×260 mm)连铸坯中含铌相进行研究，结果表明：F40MnVS钢连铸坯中可见较多微米级大颗粒NbC相(/%:80～94Nb, 1.2～7.1V,1.6～17.1Ti) 。大颗粒NbC分布在枝晶间，其形貌可呈块状、长条状或与钢基体的共晶形态，部分依附于硫化物存在。在连铸坯边部NbC多在5μm以下，形貌以点状居多；连铸坯中间及心部NbC可达数十微米，多为细长条。这些大颗粒NbC相在热轧材中仍然存在。依据Thermo-Calc计算结果，钢液凝固末期，当固相率达到0.961时，NbC可在元素富集的钢液中析出，其成分存在Ti可能是与先析出的TiN成分互溶的结果；通过将轧前铸坯加热温度提高至1200℃,可明显降低大颗粒NbC的尺寸。

关键词: 微米级大颗粒NbC, 铌微合金化； F40MnVS, 连铸坯； Thermo-Calc