The acid-resistant pipe line steel API X65 (/% : ≤0. 045C

0. 15 ~0. 35Si

1. 50 ~ 1. 65Mn

≤ 0. 008P

≤0. 001 2S

0.02 ~ 0.06Alt

0.45 ~ 0.65Nb

0.01 ~ 0. 025Ti) is melt by desulphurized metal-100 t top and bottom combined blowing Converter-LF-RH-slab CC flow sheet. The effect of process parameters including drainage sand quality ( graphite content 0. 22% ~0. 86% )

residence time of molten steel in ladle ( < 180 ~ > 270 min)

LF refining temperature ( < 1620 ~ 1690 ℃)，tap hole perpendicularity and ladle upper nozzle service life (2 ~ 28 times) on ladle free-opening rate has been analyzed. Results show that with lower graphite content in drainage sand

longer residence time of molten steel in ladle

higher LF refining temperature

tap nozzle and stream shifting

less service times of ladle upper nozzle

the ladle free-opening rate is lower. By stabilizing relative technology factors

controlling the process parameters including graphite content in drainage sand ^0. 8%

residence time of molten steel in ladle 180 ~ 240 min and LF end liquid temperature ≤1 640 °C

the free-opening rate of ladle with acid resistant steel increases from 84. 52% to 97. 47% .