The production flowsheet of 8〜10 mm plate of steel J55 for oil casing tube is hot metal pretreatment-120 t top and bottom combined blowing converter-LF refining-87 mm thin slab casting-continuous rolling process. With the process measures including based on original 0.015% ~0.025% Nb microalloying steel optimizing the composition of J55 steel for oil casing tube (/%:0.16 ~0.18C

0.5-0.7Mn

≤0.20Si

≤0.025P

≤ 0.010S

0.03 ~0.04Cr

0.01 ~ 0.03Ti

0.005 ~0.010Nb) pre-oxidizing by adding 200 ~ 400 kg aluminium magnesium calcium alloy at converter tapping

deep de-oxidizing by feeding aluminium wire and calcium treating at T[O

]

≤20 x 10

-6

during refining process

slab heating at 1 100 - 1 130 ℃ 

finishing rolling at 855 ~ 860 °C and quick cooling after rolling

and coiling at

(610 ± 10) ℃， the properties of finished steel plate are yield strength 437 ~465 MPa

tensile strength 549 〜575 MPa

elongation 30% 〜 36%

impact energy at -20 ℃ 60 ~ 96 J

180℃ cold-bending test qualified

and each properties of products are steady.