With microalloying composition design

intermediate test： 2 t medium frequency furnace-680 kg ingot forging and rolling-φ94 mm x5. 2 mm shell-cold drawn to φ89 mm x 5 mm tube-normalizing at 880°C

and commercial production: 50 t EBT EAF-LF-VD-210 mm x280 mm billet casting- rolled to φ 75 mm tube stock- piercing to φ 75 mm x 5. 5 mm shell- cold drawing to φ70. 2 mm x 5. 05 mm- tube-normalizing at 880 〜890 ℃.

the XGZT850 high strength toughness non-quenched-tempered drill steel tube (/% : 0. 35 ~0. 41C

0.20 - 0.40Si

1.40 ~ 1.70Mn

≤O. 010P

≤ 0.010S

0.40 ~0. 60Mo

0. 04 ~0. 10V

0.03 ~0.05Ti) is successfully developed. Examination results show that of steel tube the tensile strength is 1 029 MPa

yield strength is 931 MPa and the elongation is 13.5% ; the structure of steel tube is fine and uniform granular bainite ； and the tensile fracture has the characteristic of ductile fracture

and the impact fracture is quasi-cleavage + ductile fracture. The properties of high strength-toughness non-quenched-tempered drill steel tube meet the requirement of user.