某船用柴油机曲轴在最终精加工后表面局部出现黑色麻点导致产品失效。通过宏观分析、低倍检验、化学成分分析、扫描电镜微观分析、金相分析以及能谱分析等方法，对曲轴表面黑色麻点产生的原因进行了分析。结果表明：曲轴表面的黑色麻点为点腐蚀坑，是曲轴在机械加工过程中接触到了腐蚀性介质发生了腐蚀，最终的精加工余量较小，未能完全被去除腐蚀影响层，从而在曲轴表面形成了黑色麻点。

Black pits appeared on the surface of a marine diesel engine crankshaft after final finishing, which resulted in the failure of the product. By means of macroscopic analysis, macro examination, chemical composition analysis, SEM microscopic analysis, metallographic analysis, energy spectrum analysis and so on, the causes of the black pits on the crankshaft surface were analyzed. The results show that the black pits on the crankshaft surface were pitting corrosion pits which resulted from the corrosion of the crankshaft because it was exposed to the corrosive medium during the machining process. The final finishing allowance was small and the corrosion affected layer could not be completely removed, so black pits formed on the crankshaft surface.