How to distinguish between ductile iron castings and gray iron castings?

Castings made from ductile iron are called ductile iron castings (QT), which are widely used due to their excellent strength, toughness, and other properties. And we often hear a type of casting called gray iron casting (HT) in our daily life. Some people who are not very proficient in casting can easily confuse the two and cannot distinguish which one is. Below, we will briefly analyze the identification methods of QT ductile iron castings and HT gray iron castings.

Generally speaking, there are five methods for identifying from the aspects of appearance and parameter detection:

1. From the appearance of the striking fracture surface (not a mechanically processed surface), it can be observed with the naked eye that the grain size of ductile iron castings is small and black gray; The HT grains of gray iron castings are relatively coarse, gray white, and the crystal surface has a metallic luster.

2. From the perspective of machining surface, the QT of ductile iron castings is brighter than that of gray iron castings, and the microstructure is finer than that of gray iron castings.

3. Using tapping sound discrimination, the QT sound of ductile iron castings is clear and crisp, with a long echo, and the tapping sound is similar to that of carbon steel; The gray cast iron part HT has no echo and the sound is muffled.

4. From the spark generated by the grinding wheel, it can be seen that the spark beam of gray iron castings is thin and short, appearing orange red or dark red, with feather shaped tail flowers at the tail.

5. From tensile strength δ Looking at it, ductile iron castings δ The value of b is between 400 and 900 MPa, for gray iron castings δ The value of b is between 80 and 340MPa, δ B can be measured using a portable internal hardness tester.