在线淬火Q690D钢板探伤不合原因分析及控制措施

Analysis and control measures of unqualified detection of direct quenched Q690D plate

针对采用在线淬火工艺生产Q690D钢板时易出现探伤不合的问题,对缺陷形貌,铸坯、钢板的显微组织、硬度分布、元素偏析等情况进行了分析,结合其化学成分设计及轧线实际生产工艺参数,研究了在线淬火工艺生产Q690D钢板探伤不合原因,并提出了控制措施。结果表明:低合金高强钢Q690D铸坯中心偏析严重及不合理的轧制工艺加剧了中心偏析程度,造成钢板在线淬火后产生细小裂纹而导致其探伤不合。通过适当降低C、Mn含量,炼钢工序提高钢水纯净度和连铸坯质量,轧钢工序强化加热、轧制及缩短钢板轧制完成到超快冷开冷的时间等措施,有效控制了在线淬火Q690D钢板探伤不合缺陷,探伤合格率达到99%以上。

In response to the problem of unqualified defects encountered during the production of low alloy high strength steel Q690D using direct quenching process,the defect morphology,microstructure,hardness distribution,and element segregation of the casting billet and plates were analyzed.By considering the chemical composition design and actual rolling production process parameters,the causes of unqualified defects in law detection for Q690D steel produced through direct quenching process were investigated and the control measures were proposed.The results indicate that severe center segregation in the casting billet of low alloy high strength steel Q690D and the inappropriate rolling process exacerbates the degree of center segregation in the plates,leading to the occurrence of fine cracks after the DQ process,which is a critical factor contributing to the unqualified defects in law detection.Effective control of unqualified defects in direct quenched low alloy high strength steel Q690D during law detection can be achieved by appropriately reducing the content of C and Mn,improving the steel cleanliness and continuous casting billet quality in the steelmaking process,and implementing measures such as enhanced heating and rolling processes,as well as shortening the time from the completion of rolling to the start of ultrafast cooling.With the implementation of these optimization measures,the qualification rate during law detection for direct quenched low alloy high strength steel Q690D exceeded 99%.