某批次45圆钢出现断面收缩率一次合格率较低的情况。采用宏观观察、拉伸试验、化学成分分析、金相检验、非金属夹杂物检测、微观分析等方法对该批次45圆钢断面收缩率一次合格率较低的原因进行了分析。结果表明：该批次45圆钢中存在较多的非金属夹杂物和氢致白点缺陷，使得钢材在缺陷处出现应力集中，破坏了基体的连续性，降低了45圆钢的力学性能，造成该批次45圆钢断面收缩率一次合格率较低的情况。

A batch of 45 round steels have low primary qualified rate of percentage reduction area. The causes of the low primary qualified rate of percentage reduction area for the 45 round steels in this batch were analyzed by means of macroscopic observation, tensile test, chemical composition analysis, metallographic examination, non-metallic inclusion detection and microscopic analysis. The results show that there were many non-metallic inclusions and hydrogen induced flake defects in this batch of the 45 round steels, which make stress concentrated at the defects, destroyed the continuity of the matrix, reduced the mechanical properties of the 45 round steels, and caused the low primary qualified rate of percentage reduction area for the 45 round steels in this batch.