针对某批次S355NL钢冲击韧度不合格的现象，从钢板的化学成分、力学性能、显微组织、夹杂物及断口等方面进行了分析，并重点对冶炼、连铸、轧制工序的主要参数进行了探讨。结果表明：晶粒尺寸不均匀、杂质颗粒粗大是导致S355NL钢冲击韧度低的主要原因。通过优化冶炼工艺制度以控制化学成分和夹杂物，优化轧制工艺参数以保证钢板的晶粒度，有效地提高了S355NL钢冲击韧度的合格率。

For the phenomenon of low-temperature impact toughness disqualification of S355NL steel, the steel plates were analyzed from the aspects of chemical composition, mechanical property, microstructure, inclusions, fracture and so on. The main parameters of the smelting, continuous casting, the rolling process were discussed with an emphasis. The results show that:the non-uniform grain size and coarse impurity particles were the main reasons leading to the low impact toughness of S355NL steel. By optimizing the smelting process to control the chemical compositions and inclusions, and optimizing the rolling process parameters to ensure the grain size of the steel plates, the qualified rate of the impact toughness of the S355NL steel was effectively improved.