在机械制造过程中，有些零件经淬火、回火后，尚需进行发黑处理。这些零件经淬火回火后，由于各种因素的影响，往往会使有的零件产生目测难以发现的裂纹。如把这些零件装入主机，会带来极大的危害。 　　在生产实践中，在无探伤检测设备的情况下，我们用目测亦可将这些有裂纹的 In the mechanical manufacturing process, some parts after quenching, tempering, the need for blackening. After quenching and tempering these parts, due to various factors, often make some parts of the visual hard to find cracks. If these parts into the host, will bring great harm. In production practice, in the absence of testing equipment, we can visually detect these cracked