关键词: 胀断连杆用非调质钢, C70S6 BY, 探伤, 心部裂纹, 工艺改进

Abstract: The production flow sheet of ϕ60 mm bar products of non-quenching and non-tempering steel C70S6 BY is 60 t UHP EAF-LF-VD-240 mm x240 mm bloom casting-continuous rolling. The parts of defects of continuous-rolled products are sampled by ultrasonic detection, defined defect position and sampling, and analyzed by macrostructure and microstructure examination. It is obtained tliat the defects are center cracks； its forming cause is casting bloom non-uniform heating and producing larger cooling stress after rolling. With using the measures including improving casting bloom heating process, increasing heating temperature at second zone from 1 239°C to 1 248°C , total heating time ≥2.0 h, temperature of bloom at soaking zone being I 232 °C for 20 ~40 min, modified the cooling process after rolling from stacking cooling for 24 h to pit cooling for 38 h, the off-qualified rate of products by ultrasonic detection decreases from original 36. 80% to 0.78%.