The production flow sheet of SCM435 steel is 80 t BOF-LF-RH-280 mm x 325 mm bloom casting. LF end refining slag composition is (/% ：) 45 〜55 CaO

10 〜15SiO

2

20 〜30 Al

2

O

3

∑(FeO + MnO) ≤ 1 % . The effect of RH adding calcium (0.0013% Ca) and RH non-adding calcium (0. 0002% Ca) on D and Ds inclusion in Φ13 mm coil is analyzed. The results show that

the inclusion maximum size in steel with RH non-adding calcium treatment process is 7.65 μm

the pass rate of Ds≤0.5 is 100%

and that with the RH ading calcium treatment process is 25.68

μm

and the pass rate of Ds≤0.5 is 95%. The inclusion index of non-adding calcium treatment process decreases from original RH adding c

alcium process 0. 72 to 0. 68 and pass rate of D

≤1.0

increases from original RH adding calcium process 30% to 75% . With non-ackling calcium treatment process the inclusions are mainly MgO·Al

2

O

3

? and a small amount of Calcium aluminate

and with RH adding calsium process the inclusions are magnesium-alumina spinel

calcium aluminate and CaS heterogeneous inclusions. Therefore

in terms of size

quantity and type control of inclusions of brittle D and Ds

the improvement of RH non-adding Calcium treatment is obvious.