Study on cleanliness of SPHC steel by CSP process

By the methods of metallographic observation,EPMA,and sample-electrolyzing,the morphologies and composition of nonmetallic inclusions in SPHC steel are investigated.The results show that w(T.O) and w(N) in slab are(28~33)×10-6 and(30~43)×10-6 separately.The average number of inclusions decreases form 8.979 3 mm-2 to 7.344 2 mm-2,the proportion of less than 10 μm inclusions is 93 %.Under the normal conditions the macro-inclusion content of 10 kg liquid steel in tundish is 6.8 and 5.9 mg in slab.However as soon as slag entrapment occurs large inclusions will increase rapidly and they may reach as high as 12.3 mg and the 100~280 μm inclusions come up to 26.32 %.The inclusions in the tundish are mainly composed of deoxidized products and deoxidized compound inclusions;the inclusions in the slab mainly consist of compound inclusions;inclusions in the tundish and slab are mainly silicon aluminate compound inclusions and silicate inclusions and magnesium and potassium are also found in the inclusions.It shows that the lining of the tundish is already eroded and slag entrapment occurs in the mold as well.