提高20～60mm规格Q345B钢板探伤合格率的攻关实践

为找出20~60 mm规格Q345B钢板超声波探伤不合格原因,在检测缺陷部位取样,利用金相?扫描电镜和能谱等检测手段,对钢板探伤不合格部位的组织和成分进行了分析。结果表明,探伤不合格的主要原因是组织中存在着条状硫化锰和锰元素的偏析以及由异常组织粒状贝氏体引起的微裂纹。针对以上原因,探讨了一些改进措施,比如提高钢质纯净度、控制浇注温度和拉速、适当增大比水量、降低锰元素的含量、加硅钙线、实行铸坯和钢板下线迅速堆冷、延长铸坯加热时间、后4道次实行小压下量轧制等,通过这些措施可以使该规格段的Q345B超声波探伤合格率由攻关前的65.8%提高到91.7%。

Practice on Increasing Qualified Ratio of Ultrasonic Flaw Detection on Q345B Steel Plate of 20～60 mm

In order to increase the qualified ratio of ultrasonic flaw detection on Q345B steel plate of 20～60 mm,the sample from the disqualified part of the steel plate was examined and analyzed with the help of metallurgical phase,scanning electron microscope and energy spectrum.The results showed that there were banded manganese sulphide and the segregation of manganese and the tiny crack caused by abnormal structure of granular bainite in the structure of the plate and these were the main reasons of disqualification in ultrasonic inspection.The paper discussed some measures taken in the practice,such as improving the steel purity,changing the inclusion form,controlling the casting temperature and speed,increasing the quantity of cooling water,reducing the element content of manganese,making use of Ca-Si wire,cooling slow of casting and plate,extending the heating time of casting and rolling in small reduction for last four passes.By this means,the qualified rate of flaw detection can be increased from 65.8% to 91.7%.