How to inspect the ductile iron castings?

Nowadays, iron foundries supply varies of ductile iron products, ranging from low quality to high quality. How to detect the ductile iron to control the quality? This is the experience from Dandong Foundry in China for your reference.

1. Metallographic inspection

Take samples of ductile iron material, observe under the microscope and analyze the graphite morphology.
In ductile iron tissue, graphite is spherical which can improve the phenomena of stress concentration. The presence of spherical graphite in ductile iron can reduce the isolation of the matrix and bring out the potential of the matrix fully.

Grey Iron Microstructure                                  Ductile Iron Mictrostructure

We can draw the conclusion from the pictures above, the graphite in ductile iron is spherical but it is slender and flaky in grey cast iron. The key purpose of metallographic inspection is to get the nodularity. Nodularity is just a reflection of the final form of graphite. In general, the nodularity is higher, the performance is relatively favorable. But it is not judged by nodularity completely.

2. Chemical Analysis

Iron foundries often use ductile iron chemical analysis instruments to analyze the Content of chemicals. For example, DF100 direct reading spectrometer is a good choice. Of course, the content is based on standard, taking your own need into consideration.

Spectrometer

3. Mechanical properties

There are two main methods of inspecting the mechanical properties of ductile iron. One is the tensile test; the other is the hardness test. The standard is below:

Because the tensile test requires complex technology and precise equipment, so we often use hardness test instead of tensile test. Brinell hardness tester is applied to inspect hardness. Usually, the 3000kg force, the diameter of pressure ball is 10mm, which are the best experimental conditions. Just one condition cannot meet the needs of different material. There are two rules we should remember, the first one is that the ratio of test force and the square of the diameter is a constant; the second is that after experiment, the indentation diameter should range from 0.24D to 0.26D.

Brinell hardness tester

4. Surface inspection

4.1 Take cuttings

A qualified cast iron product, during the machining cutting process, the chip was sheet or strip. While the chip of gray cast iron is significantly powder.

4.2 Percussion method

Lift the body, with the instruments hitting. The sound is pleasant and the sound waves present simple harmonic motion.

4.3 Visual inspection

Inspect if there is casting defects such as trachoma, stomas, and cracks in ductile iron.

In order to get ductile iron of high quality, besides the inspecting methods mentioned, we should concentrate on the manufacturing process, improve producing technology, and control the process parameters strictly. Only in this way, the iron foundries can produce satisfying ductile iron parts.

 Home | More Articles