Abstract:  The production flow sheet of 4>60 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-c-ontinuous 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 that 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, in¬creasing heating temperature at second zone from 1 239 X to 1 248 °C , total heating time m2.0 h, temperature of bloom at soaking zone being 1 232 龙 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% .

Key words: Material Index Non-Quenching and Non-Tempering Steel C70S6 BY for Fracture Splitting Connecting Rod, Ultra?sonic Detection, Center Cracks, Process Improvement 

摘要： 非调质钢C70S6 BYΦ60 mm棒材的生产流程为60 t UHP EAF-LF-VD-240 mm×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℃提高至1 248℃,总加热时间≥2.0 h,均热段1 232℃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