Abstract: The metallurgical flow sheet of tested pipeline steel X52 (/% : 0.070~0.0790, 0.22Si, 1.29~1.32Mn, 0.008~0.009P, 0.002S, 0.028Al, 0.0016~0.0017T[O], 0.0053〜0.0065N) is hot-metal pretreatment- 220t BOF-LF-VD-230 mm slab CC. The main steelmaking processes are adding aluminium shot in tapping of BOF； main ingredient of LF refining slag- (/%) : 54.41~58.54CaO, 7.66~8.42SiO₂, 22.57~24.69A1₂O₃, 4.15〜4.58MgO, 0.78~2.89FeO ； and feeding calcium wire treatment after VD. The evolution of inclusions in steel during steelmaking process is studied by auto scanning electron microscope with ASPEX ( Application Specific Products employing Electron Beam and X-ray technology). Results show that before LF refining the inclusions in liquid are AI2O3 cluster and granule, after LF refining the Al₂O₃ is modified to globular CaO-MgO-Al₂O₃, inclusion, then modified to globular CaO-Al₂O₃-CaS inclusion after calcium treatment; by VD treatment the number of inclusions in liquid decreases from 30〜35/mm² to 7~15/ mm² and the T[O] and [N] markedly decrease to 12 x 10^-6~13 x 10^-6 and 41 x 10^-6~48 X 10^-6. from end soft stirring to tundish the number of inclusions in liquid dramatically increases to 33/mm² ； at end VD the average size of inclusions is up to maximum i. e. 2.6~3.6 μm, but in tundish that decreases to 1.9~2.1 μm: during feeding wire and soft blowing process the T[O] and [N] increase to some extent, it shows that the secondary oxidation of liquid occurs； with LF refining, VD and calcium treatment the S content in steel decreases lo 16 x 10 ; and the high (SiO₂) and ( FeO + MnO) content in tundish shielding flux lead to resulfurization of liquid in tundish.

Key words: X52 Pipeline Steel, Al₂O₃, CaO-MgO- Al₂O₃, CaO- Al₂O₃-CaS, ASPEX, Cleanliness

摘要： 试验X52管线钢（/%:0.070~0.079C，0.22Si，1.29~1.32Mn，0.008~0.009P，0.002S，0.028A1，0.0016~0.0017T[O]，0.0053~0.0065N）的冶金流程为铁水预处理-220t BOF-LF-VD-230 mm板坯连铸。主要工艺为BOF出钢加铝粒，LF精炼渣主要组成为（/%）:54.41~58.54CaO，7.66~8.42SiO₂，22.57~24.69Al₂O₃，4.15~4.58MgO，0.78~2.89FeO；VD后喂钙线处理。利用电子束和X-射线技术的ASPEX自动扫描电镜研究了该钢冶炼过程夹杂物的变化。结果表明，LF进站时钢中夹杂物为簇群状或颗粒状Al₂O₃，LF终点Al₂O₃转变为球状CaO-MgO-Al₂O₃系夹杂物，钙处理后转变为球状CaO-Al₂O₃-CaS系。VD真空处理过程夹杂物数量从30~35个/mm²降至7~15个/mm²、T[O]和[N]大幅降低至12×10^-6~13×10^-6和41×10^-6~48×10^-6。软吹搅拌到中间包,钢中夹杂物数量剧增至33个/mm²。夹杂物平均尺寸在VD破空后达到最大,为2.6~3.6μm,中间包则减小到1.9~2.1μm。喂线及软吹搅拌过程钢中T[O]和[N]都有增加,说明发生了二次氧化。LF精炼、VD及钙处理后钢中S含量降至16×10^-6。中间包覆盖剂中（SiO₂）和（FeO+MnO）太高会导致中间包钢水回硫。

关键词: X52 管线钢, Al₂O₃, CaO-MgO-Al₂O₃, CaO-Al₂O₃-CaS, ASPEX, 洁净度