The process flowsheet for high strength steel 82B (/% : 0. 79 ~0. 83C

0. 15 〜0. 25Si

0. 72 -0. 80Mn

≤0.020P

≤0. 015S

≤0. 15Cu

0. 18 ~0. 30Cr) is BOF-LF-165 mm x 165 mm billet casting-hot rolling to Φ 12. 5 mm coil-cold drawing to Φ5. 05 mm products. It is obtained by analysis on cold-drawn fracture of wire rod that the factors including obvious martensite at center of wire rod and network of cementite produced by segregation

large size MgO-CaO-Al

2

0

3

- SiO

2

compound inclusions and surface defects lead to cold drawn fracture of wire rod. With the process measures including decreasing the overheating extent of liquid from original 25 ~35 °C to 15 ~25 °C

decreasing the billet

casting speed from 1. 80 m/min to 1. 65 m/min

decreasing the amount of secondary cooling water from 0. 80 L/kg to 0. 65 L/kg

increasing the soft argon blowing time from 10 min to 12 min and insuring aging for 3 h at 250 ℃ after rolling

the rating of center porosity

center segregation and shrinkage cavity of casting billet decreases respectively from 1. 5

1. 0 and 0. 5 ~ 2. 5 to 0. 5

0. 5 and 0 ~ 0. 5

and the total content of inclusions in steel decreases from 0.0035% 〜0.0043% to 0.0017% ~ 0.0021% to basically avoid the occurrence of cold drawn fracture of wire rod.