Abstract: In order to understand the cleanliness of MRT-2.5 tin plate steel by a BOF-LF-CC route, the system sampling was performed to analysis the content of nitrogen and total oxygen in liquid steel during LF refining, and variation of the types of inclusions, number and size of inclusions were studied during LF process. Transformation mechanism of inclusions was also studied at different stages. The experimental results show that, w（T.O）=34.8×10^-6 and w（N）=21.1×10^-6 at the end of LF refining. The main types of oxide inclusions are MgO-Al2O3 after slag forming, Al2O3 after aluminum addition, and CaS-CaO-Al2O3 at the end of calcium treatment. The number density of inclusions which decreases during LF refining is 3.9/mm2 at the end of LF refining and the diameter of inclusion particle size is gradually concentrated in the range of 0-5μm. Under the conditions in a company, w（Ca） content in liquid steel should be controlled in （2—20）×10^-6, and w（Mg） content in liquid steel should be controlled in （0.45—8）×10-6, and a（O） should be controlled in （2—6）×10^-6 in order to contr^ol inclusions in low melting point and w（S） content in liquid steel should be controlled in less than 0.0042% in order to avoid CaS inclusions with precipitation.

Key words: tinplate, LF refining, Inclusion, cleanliness