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%.

摘要： 非调质钢C70S6 BY ϕ60 mm棒材的生产流程为60 t UHP EAF-LF-VD-240 mm x 240 mm坯连铸-连轧。连轧材经现场超声波探伤并对缺陷定位取样，通过低倍、金相显微等检验方法对缺陷进行分析,得出该缺陷为心部裂纹，其产生原因主要是铸坯加热不均和轧后冷却应力较大造成。通过改善铸坯加热工艺，将加热二段温度从1 239°C提高至1 248 °C，总加热时间≥2. 0h,均热段1 232 °C ,20 - 40 min,轧后冷却由堆冷24 h改成坑冷38 h, 探伤不合格率由36.80%降至0.78%。

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