注塑机用38CrMoAl钢料筒，在机械加工过程中，其表面出现大量黑色斑点。采用宏观观察、扫描电镜分析、金相检验等方法，分析料筒表面产生黑斑的原因。结果表明：注塑机用38CrMoAl钢料筒表面渗氮不均匀，在机械加工过程中，料筒表面白亮层较厚区域发生沿晶开裂及氮化层剥落，形成点状凹坑，这是料筒表面出现黑斑的主要原因。

The 38CrMoAl steel barrel used for injection molding machine had a large number of black spots on its surface after the machining process, Use methods such as macroscopic observation, scanning electron microscope analysis, and metallographic inspection to analyze the causes of black spots on the surface of the barrel. The results showed that the surface of 38CrMoAl steel barrel for injection molding machine was not uniformly nitrided. During machining process, intergranular cracking and peeling of the nitride layer occurred in the thicker area of nitride layer on the surface of barrel. This was the main reason for the black spots on the surface of the barrel.