Two kinds of metallurgical process for melting a

<

0.005%C-≤0.005% N ultra-low carbon and ultra-low nitrogen steel by a 90 t top and bottom combined blown converter a Wuhan Iron and Steel: single slag process KR desulphuration -LD - RH-KTB - CC and two-step steelmaking process KR desulphuration - LD desiliconisation and dephosphorization-LD combined blown decarbonation - RH-KTB- CC have been analyzed. The practice results showed that during steelmaking with single slag process the average C content in liquid steel in tundish was 25.5×10

-6

and the average N content was 18.5×10

-6

and with two-step process the average C content in liquid steel in tundish was 16×10

-6

the average N content was 19×10

-6

and the end [P

]

with two-step process(60×10

-6

)was lower that with single slag process(110×10

-6

).