The production process flowsheet of steel 508III for nuclear power welding (/% ：0.09~0.12C

0.30~0.40Si

1.45〜1.65Mn

≤0.008P

≤0.008S. 0.45~0.60Mo

0.60~0.75Ni) is 20t EAF-LF-VD-4t ingot-forged to 150 mm x 150 mm billet-rolled to Φ5.5 mm coil. With process measures including using quality charge

high basicity slag and high FeO content

and controlling liquid temperature 1550 ~ 1570 °C

the EAF end [P

]

is ≤0.002%

and using low phosphorus alloys

the phosphorus content in steel is ≤0.006% ； in LF refining process using silicon-calcium alloy for killing and SiC powder for diffusion deoxidation

and using CaO-Al

2

O

3

-SiO

2

slag series wi

th basicity 5.0~5.5

in VD process vacuum ≤67 Pa and Ar flow rate 30~50 L/min

and shielding casting etc measures the analysis results of 3 heats steel show that the gas content in steel is 1.3 x 10

-6

~1.5 x 10

-6

[H

]

10 x10

-6

~14 x 10

-6

[ 0

]

and 44 x 10

-6

~58 x 10

-6

[N

]

to meet the cleanliness requirement of steel 508Ⅲ for nuclear power wielding.