Abstract: In the current study, steel samples were taken at each step of steelmaking, LF refining and casting for the production of 200-series stainless steels. The content of total oxygen (T.O), the morphology, amount, composition, and size distribution of inclusions in steel samples were analyzed, which was in favor of the solution of the product defects and improvement of steel cleanliness. The total oxygen in steel samples during LF refining gradually deceased and it was 41×10-6 at the end of ladle refining, 16×10-6 lower than that at LF start. There was an increase in the T.O during transfer operations from the end of ladle refining to the start of casting due to the air entrainment, which was avoided through shortening the transport and transformation of the ladle. Inclusions in steel samples were mainly MnO-SiO2 and its average composition deviated from the low melting temperature region. Inclusion plasticization could be achieved by adjusting the basicity and strictly controlling the sources of Al in raw materials. From the end of LF refining to the slab, the total number density of inclusions increased to a maximum value of 473.6/mm2 in the steel sample at 30 min of casting in tundish inlet and then gradually decreased and it was 74.7/mm2 in the slab. For oxide inclusions, the variation of its maximum size was the same as the total number density of inclusions. The maximum value was 73.5 μm and it was 22 μm in the slab. Through three measures of lowering the slag basicity from 2.2 to 1.5~1.8 during LF refining, increasing the tundish capacity to 45 t and strictly controlling the air absorption during continuous casting, the sliver defects was decreased from 20% to 3.0%.

Key words: 200 series stainless steel, sliver defects, inclusions, slag basicity, tundish capacity