1. See machined surface
Gray iron: gray, very dark gloss, rough surface. Ductile iron: gray, the gloss is brighter than that of gray iron, and the surface roughness is similar to that of gray iron.
2. Filing test
Gray iron: The filing resistance is low, there is a "swoosh" sound when filing, very little stickiness, the swarf is gray-black, with a few silver-white bright spots. Grind with your fingers, it is easy to blacken your fingers. Ductile iron: When filing, the resistance is slightly larger than that of gray iron, and there is also a more obvious "swoosh" sound, rarely sticking to the file, the dust is gray-black, with fine bright spots, and the particle size varies, but large particles are the most common. Lord, grinding the dust with your fingers can make the fingers black, but the degree of blackening is lighter than that of gray iron.
3. Listen to the percussion
Gray Iron: Low voice, very short duration. Ductile Iron: The sound is crisp, with reverberation and short duration.